// File: contracts/AdminUpgradeabilityProxy.sol



// // SPDX-License-Identifier: MIT

// pragma solidity ^0.6.0;

// import "./UpgradeabilityProxy.sol";

// /**
//  * @title AdminUpgradeabilityProxy
//  * @dev This contract combines an upgradeability proxy with an authorization
//  * mechanism for administrative tasks.
//  * All external functions in this contract must be guarded by the
//  * `ifAdmin` modifier. See ethereum/solidity#3864 for a Solidity
//  * feature proposal that would enable this to be done automatically.
//  */
// contract AdminUpgradeabilityProxy is UpgradeabilityProxy {
//     /**
//      * Contract constructor.
//      * @param _logic address of the initial implementation.
//      * @param _admin Address of the proxy administrator.
//      * @param _data Data to send as msg.data to the implementation to initialize the proxied contract.
//      * It should include the signature and the parameters of the function to be called, as described in
//      * https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector-and-argument-encoding.
//      * This parameter is optional, if no data is given the initialization call to proxied contract will be skipped.
//      */
//     constructor(
//         address _logic,
//         address _admin,
//         bytes memory _data
//     ) public payable UpgradeabilityProxy(_logic, _data) {
//         assert(
//             ADMIN_SLOT == bytes32(uint256(keccak256("eip1967.proxy.admin")) - 1)
//         );
//         _setAdmin(_admin);
//     }

//     /**
//      * @dev Emitted when the administration has been transferred.
//      * @param previousAdmin Address of the previous admin.
//      * @param newAdmin Address of the new admin.
//      */
//     event AdminChanged(address previousAdmin, address newAdmin);

//     /**
//      * @dev Storage slot with the admin of the contract.
//      * This is the keccak-256 hash of "eip1967.proxy.admin" subtracted by 1, and is
//      * validated in the constructor.
//      */

//     bytes32
//         internal constant ADMIN_SLOT = 0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103;

//     /**
//      * @dev Modifier to check whether the `msg.sender` is the admin.
//      * If it is, it will run the function. Otherwise, it will delegate the call
//      * to the implementation.
//      */
//     modifier ifAdmin() {
//         if (msg.sender == _admin()) {
//             _;
//         } else {
//             _fallback();
//         }
//     }

//     /**
//      * @return The address of the proxy admin.
//      */
//     function admin() external ifAdmin returns (address) {
//         return _admin();
//     }

//     /**
//      * @return The address of the implementation.
//      */
//     function implementation() external ifAdmin returns (address) {
//         return _implementation();
//     }

//     /**
//      * @dev Changes the admin of the proxy.
//      * Only the current admin can call this function.
//      * @param newAdmin Address to transfer proxy administration to.
//      */
//     function changeAdmin(address newAdmin) external ifAdmin {
//         require(
//             newAdmin != address(0),
//             "Cannot change the admin of a proxy to the zero address"
//         );
//         emit AdminChanged(_admin(), newAdmin);
//         _setAdmin(newAdmin);
//     }

//     /**
//      * @dev Upgrade the backing implementation of the proxy.
//      * Only the admin can call this function.
//      * @param newImplementation Address of the new implementation.
//      */
//     function upgradeTo(address newImplementation) external ifAdmin {
//         _upgradeTo(newImplementation);
//     }

//     /**
//      * @dev Upgrade the backing implementation of the proxy and call a function
//      * on the new implementation.
//      * This is useful to initialize the proxied contract.
//      * @param newImplementation Address of the new implementation.
//      * @param data Data to send as msg.data in the low level call.
//      * It should include the signature and the parameters of the function to be called, as described in
//      * https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector-and-argument-encoding.
//      */
//     function upgradeToAndCall(address newImplementation, bytes calldata data)
//         external
//         payable
//         ifAdmin
//     {
//         _upgradeTo(newImplementation);
//         (bool success, ) = newImplementation.delegatecall(data);
//         require(success);
//     }

//     /**
//      * @return adm The admin slot.
//      */
//     function _admin() internal view returns (address adm) {
//         bytes32 slot = ADMIN_SLOT;
//         assembly {
//             adm := sload(slot)
//         }
//     }

//     /**
//      * @dev Sets the address of the proxy admin.
//      * @param newAdmin Address of the new proxy admin.
//      */
//     function _setAdmin(address newAdmin) internal {
//         bytes32 slot = ADMIN_SLOT;

//         assembly {
//             sstore(slot, newAdmin)
//         }
//     }

//     /**
//      * @dev Only fall back when the sender is not the admin.
//      */
//     function _willFallback() internal virtual override {
//         require(
//             msg.sender != _admin(),
//             "Cannot call fallback function from the proxy admin"
//         );
//         super._willFallback();
//     }
// }

// File: contracts/ArtistFactory.sol



// This contract clones an erc1155 contract for artst to own their art and create/tokenize communities around them.

import "@openzeppelin/contracts/proxy/Clones.sol";

pragma solidity ^0.6.0;

contract ArtistFactory {
    address public logic; //address of erc1155 contract

    using Clones for address;

    constructor(address _logic) public {
        logic = _logic;
    }

    function create(string calldata _name) external payable {
        bytes memory initData =
            abi.encodeWithSignature("initialize(string)", _name);

        address instance = logic.clone();
        // instance.functionCallWithValue(initData, msg.value);
    }
}

// File: @openzeppelin/contracts/proxy/Clones.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev https://eips.ethereum.org/EIPS/eip-1167[EIP 1167] is a standard for
 * deploying minimal proxy contracts, also known as "clones".
 *
 * > To simply and cheaply clone contract functionality in an immutable way, this standard specifies
 * > a minimal bytecode implementation that delegates all calls to a known, fixed address.
 *
 * The library includes functions to deploy a proxy using either `create` (traditional deployment) or `create2`
 * (salted deterministic deployment). It also includes functions to predict the addresses of clones deployed using the
 * deterministic method.
 *
 * _Available since v3.4._
 */
library Clones {
    /**
     * @dev Deploys and returns the address of a clone that mimics the behaviour of `master`.
     *
     * This function uses the create opcode, which should never revert.
     */
    function clone(address master) internal returns (address instance) {
        // solhint-disable-next-line no-inline-assembly
        assembly {
            let ptr := mload(0x40)
            mstore(ptr, 0x3d602d80600a3d3981f3363d3d373d3d3d363d73000000000000000000000000)
            mstore(add(ptr, 0x14), shl(0x60, master))
            mstore(add(ptr, 0x28), 0x5af43d82803e903d91602b57fd5bf30000000000000000000000000000000000)
            instance := create(0, ptr, 0x37)
        }
        require(instance != address(0), "ERC1167: create failed");
    }

    /**
     * @dev Deploys and returns the address of a clone that mimics the behaviour of `master`.
     *
     * This function uses the create2 opcode and a `salt` to deterministically deploy
     * the clone. Using the same `master` and `salt` multiple time will revert, since
     * the clones cannot be deployed twice at the same address.
     */
    function cloneDeterministic(address master, bytes32 salt) internal returns (address instance) {
        // solhint-disable-next-line no-inline-assembly
        assembly {
            let ptr := mload(0x40)
            mstore(ptr, 0x3d602d80600a3d3981f3363d3d373d3d3d363d73000000000000000000000000)
            mstore(add(ptr, 0x14), shl(0x60, master))
            mstore(add(ptr, 0x28), 0x5af43d82803e903d91602b57fd5bf30000000000000000000000000000000000)
            instance := create2(0, ptr, 0x37, salt)
        }
        require(instance != address(0), "ERC1167: create2 failed");
    }

    /**
     * @dev Computes the address of a clone deployed using {Clones-cloneDeterministic}.
     */
    function predictDeterministicAddress(address master, bytes32 salt, address deployer) internal pure returns (address predicted) {
        // solhint-disable-next-line no-inline-assembly
        assembly {
            let ptr := mload(0x40)
            mstore(ptr, 0x3d602d80600a3d3981f3363d3d373d3d3d363d73000000000000000000000000)
            mstore(add(ptr, 0x14), shl(0x60, master))
            mstore(add(ptr, 0x28), 0x5af43d82803e903d91602b57fd5bf3ff00000000000000000000000000000000)
            mstore(add(ptr, 0x38), shl(0x60, deployer))
            mstore(add(ptr, 0x4c), salt)
            mstore(add(ptr, 0x6c), keccak256(ptr, 0x37))
            predicted := keccak256(add(ptr, 0x37), 0x55)
        }
    }

    /**
     * @dev Computes the address of a clone deployed using {Clones-cloneDeterministic}.
     */
    function predictDeterministicAddress(address master, bytes32 salt) internal view returns (address predicted) {
        return predictDeterministicAddress(master, salt, address(this));
    }
}

// File: contracts/DuckChef2.sol



// pragma solidity ^0.6.0;

// import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
// import "@openzeppelin/contracts/token/ERC20/SafeERC20.sol";
// import "@openzeppelin/contracts/utils/EnumerableSet.sol";
// import "@openzeppelin/contracts/math/SafeMath.sol";
// import "@openzeppelin/contracts/access/Ownable.sol";

// import "../interfaces/IERC20MintBurn.sol";
// import "../interfaces/IMuse.sol";
// import "./NFT20.sol";

// import "hardhat/console.sol";

// interface IMigratorChef {
//     // Perform LP token migration from legacy UniswapV2 to tokenSwap.
//     // Take the current LP token address and return the new LP token address.
//     // Migrator should have full access to the caller's LP token.
//     // Return the new LP token address.
//     //
//     // XXX Migrator must have allowance access to UniswapV2 LP tokens.
//     // tokenSwap must mint EXACTLY the same amount of tokenSwap LP tokens or
//     // else something bad will happen. Traditional UniswapV2 does not
//     // do that so be careful!
//     function migrate(IERC20 token) external returns (IERC20);
// }

// // MasterChef is the master of token. He can make token and he is a fair guy.
// //
// // Note that it's ownable and the owner wields tremendous power. The ownership
// // will be transferred to a governance smart contract once token is sufficiently
// // distributed and the community can show to govern itself.
// //
// // Have fun reading it. Hopefully it's bug-free. God bless.
// contract DuckChef2 is Ownable {
//     using SafeMath for uint256;
//     using SafeERC20 for IERC20;
//     // Info of each user.
//     struct NftInfo {
//         uint256 amount; // How many LP tokens the user has provided.
//         uint256 rewardDebt; // Reward debt. See explanation below.
//         //
//         // We do some fancy math here. Basically, any point in time, the amount of tokens
//         // entitled to a user but is pending to be distributed is:
//         //
//         //   pending reward = (user.amount * pool.acctokenPerShare) - user.rewardDebt
//         //
//         // Whenever a user deposits or withdraws LP tokens to a pool. Here's what happens:
//         //   1. The pool's `acctokenPerShare` (and `lastRewardBlock`) gets updated.
//         //   2. User receives the pending reward sent to his/her address.
//         //   3. User's `amount` gets updated.
//         //   4. User's `rewardDebt` gets updated.
//     }
//     // Info of each pool.
//     struct PoolInfo {
//         IERC20 lpToken; // Address of LP token contract.
//         uint256 allocPoint; // How many allocation points assigned to this pool. tokens to distribute per block.
//         uint256 lastRewardBlock; // Last block number that tokens distribution occurs.
//         uint256 accTokenPerShare; // Accumulated tokens per share, times 1e12. See below.
//     }
//     // The token TOKEN!
//     IERC20MintBurn public token;

//     // the NFT20 Contract
//     IMuse public nft20;

//     // Dev address.
//     address public devaddr;
//     // Block number when bonus token period ends.
//     uint256 public bonusEndBlock;
//     // token tokens created per block.
//     uint256 public tokenPerBlock;
//     // Bonus muliplier for early token makers.
//     uint256 public constant BONUS_MULTIPLIER = 10;
//     // The migrator contract. It has a lot of power. Can only be set through governance (owner).
//     IMigratorChef public migrator;
//     // Info of each pool.
//     PoolInfo[] public poolInfo;

//     // Info of each NFT that registered to get rewards.
//     mapping(uint256 => NftInfo) public nftInfo;
//     // Total allocation points. Must be the sum of all allocation points in all pools.
//     uint256 public totalAllocPoint = 0;
//     // The block number when token mining starts.
//     uint256 public startBlock;
//     event Deposit(address indexed user, uint256 indexed pid, uint256 amount);
//     event Withdraw(address indexed user, uint256 indexed pid, uint256 amount);
//     event EmergencyWithdraw(
//         address indexed user,
//         uint256 indexed pid,
//         uint256 amount
//     );

//     constructor(
//         IERC20MintBurn _token,
//         IMuse _nft20,
//         address _devaddr,
//         uint256 _tokenPerBlock,
//         uint256 _startBlock,
//         uint256 _bonusEndBlock
//     ) public {
//         token = _token;
//         nft20 = _nft20;
//         devaddr = _devaddr;
//         tokenPerBlock = _tokenPerBlock;
//         bonusEndBlock = _bonusEndBlock;
//         startBlock = _startBlock;
//     }

//     function poolLength() external view returns (uint256) {
//         return poolInfo.length;
//     }

//     // Add a new lp to the pool. Can only be called by the owner.
//     // XXX DO NOT add the same LP token more than once. Rewards will be messed up if you do.
//     function add(
//         uint256 _allocPoint,
//         IERC20 _lpToken,
//         bool _withUpdate
//     ) public onlyOwner {
//         if (_withUpdate) {
//             massUpdatePools();
//         }
//         uint256 lastRewardBlock =
//             block.number > startBlock ? block.number : startBlock;
//         totalAllocPoint = totalAllocPoint.add(_allocPoint);
//         poolInfo.push(
//             PoolInfo({
//                 lpToken: _lpToken,
//                 allocPoint: _allocPoint,
//                 lastRewardBlock: lastRewardBlock,
//                 accTokenPerShare: 0
//             })
//         );
//     }

//     // Update the given pool's token allocation point. Can only be called by the owner.
//     function set(
//         uint256 _pid,
//         uint256 _allocPoint,
//         bool _withUpdate
//     ) public onlyOwner {
//         if (_withUpdate) {
//             massUpdatePools();
//         }
//         totalAllocPoint = totalAllocPoint.sub(poolInfo[_pid].allocPoint).add(
//             _allocPoint
//         );
//         poolInfo[_pid].allocPoint = _allocPoint;
//     }

//     // Set the migrator contract. Can only be called by the owner.
//     function setMigrator(IMigratorChef _migrator) public onlyOwner {
//         migrator = _migrator;
//     }

//     // Migrate lp token to another lp contract. Can be called by anyone. We trust that migrator contract is good.
//     function migrate(uint256 _pid) public {
//         require(address(migrator) != address(0), "migrate: no migrator");
//         PoolInfo storage pool = poolInfo[_pid];
//         IERC20 lpToken = pool.lpToken;
//         uint256 bal = lpToken.balanceOf(address(this));
//         lpToken.safeApprove(address(migrator), bal);
//         IERC20 newLpToken = migrator.migrate(lpToken);
//         require(bal == newLpToken.balanceOf(address(this)), "migrate: bad");
//         pool.lpToken = newLpToken;
//     }

//     // Return reward multiplier over the given _from to _to block.
//     function getMultiplier(uint256 _from, uint256 _to)
//         public
//         view
//         returns (uint256)
//     {
//         if (_to <= bonusEndBlock) {
//             return _to.sub(_from).mul(BONUS_MULTIPLIER);
//         } else if (_from >= bonusEndBlock) {
//             return _to.sub(_from);
//         } else {
//             return
//                 bonusEndBlock.sub(_from).mul(BONUS_MULTIPLIER).add(
//                     _to.sub(bonusEndBlock)
//                 );
//         }
//     }

//     // View function to see pending tokens on frontend.
//     function pendingToken(uint256 _pid, uint256 _nftId)
//         external
//         view
//         returns (uint256)
//     {
//         PoolInfo storage pool = poolInfo[_pid];
//         NftInfo storage nft = nftInfo[_nftId];
//         console.log("amount", nft.amount);
//         uint256 accTokenPerShare = pool.accTokenPerShare;
//         console.log("accTokenPerShare", accTokenPerShare);

//         uint256 lpSupply = nft20.totalStaked(address(pool.lpToken));

//         console.log("lpSupply", lpSupply);

//         // uint256 lpSupply = pool.lpToken.balanceOf(address(this));
//         if (block.number > pool.lastRewardBlock && lpSupply != 0) {
//             uint256 multiplier =
//                 getMultiplier(pool.lastRewardBlock, block.number);
//             uint256 tokenReward =
//                 multiplier.mul(tokenPerBlock).mul(pool.allocPoint).div(
//                     totalAllocPoint
//                 );
//             accTokenPerShare = accTokenPerShare.add(
//                 tokenReward.mul(1e12).div(lpSupply)
//             );

//             console.log("accTokenPerShare", accTokenPerShare);
//         }

//         console.log(
//             "last",
//             nft.amount.mul(accTokenPerShare).div(1e12).sub(nft.rewardDebt)
//         );
//         console.log("nft.rewardDebt", nft.rewardDebt);

//         return nft.amount.mul(accTokenPerShare).div(1e12).sub(nft.rewardDebt);
//     }

//     // Update reward variables for all pools. Be careful of gas spending!
//     function massUpdatePools() public {
//         uint256 length = poolInfo.length;
//         for (uint256 pid = 0; pid < length; ++pid) {
//             updatePool(pid);
//         }
//     }

//     // Update reward variables of the given pool to be up-to-date.
//     function updatePool(uint256 _pid) public {
//         PoolInfo storage pool = poolInfo[_pid];
//         if (block.number <= pool.lastRewardBlock) {
//             return;
//         }

//         uint256 lpSupply = nft20.totalStaked(address(pool.lpToken));
//         // uint256 lpSupply = pool.lpToken.balanceOf(address(this));
//         if (lpSupply == 0) {
//             pool.lastRewardBlock = block.number;
//             return;
//         }
//         uint256 multiplier = getMultiplier(pool.lastRewardBlock, block.number);
//         uint256 tokenReward =
//             multiplier.mul(tokenPerBlock).mul(pool.allocPoint).div(
//                 totalAllocPoint
//             );
//         token.mint(devaddr, tokenReward.div(10));
//         token.mint(address(this), tokenReward);
//         pool.accTokenPerShare = pool.accTokenPerShare.add(
//             tokenReward.mul(1e12).div(lpSupply)
//         );
//         pool.lastRewardBlock = block.number;
//     }

//     // Register NFT20 token to DuckChef for $TOKEN allocation.
//     function register(uint256 _pid, uint256 _nftId) public {
//         PoolInfo storage pool = poolInfo[_pid];
//         (address _erc20address, uint256 _amount, ) = nft20.getNFTInfo(_nftId);
//         require(_erc20address == address(pool.lpToken), "NFT don't match pool");
//         require(nft20.ownerOf(_nftId) == msg.sender, "!owner");
//         NftInfo storage nft = nftInfo[_nftId];

//         require(nft.amount == 0, "Can't register twice");

//         updatePool(_pid);

//         nft.amount = _amount;

//         // @Maybe we can ake this out as it will be by single NFT each time and when withdraw
//         // NFT info is deleted.

//         // TODO! check this, without this was returning 0 all the time.
//         // nft.rewardDebt = nft.amount.mul(pool.accTokenPerShare).div(1e12);
//         emit Deposit(msg.sender, _pid, _nftId);
//     }

//     // Withdraw all earnings and unregister NFT.
//     function withdraw(uint256 _pid, uint256 _nftId) public {
//         PoolInfo storage pool = poolInfo[_pid];
//         // does nft token match pool?
//         (address _erc20address, , ) = nft20.getNFTInfo(_nftId);
//         require(_erc20address == address(pool.lpToken), "NFT don't match pool");
//         // make sure msg.sender is owner of nft
//         require(nft20.ownerOf(_nftId) == msg.sender, "!owner");
//         NftInfo storage nft = nftInfo[_nftId];

//         updatePool(_pid);
//         uint256 pending =
//             nft.amount.mul(pool.accTokenPerShare).div(1e12).sub(nft.rewardDebt);
//         if (pending > 0) {
//             safeTokenTransfer(msg.sender, pending);
//         }

//         // delete this NFT as it is paying off all earnings up until this point.
//         delete nftInfo[_nftId];

//         emit Withdraw(msg.sender, _pid, _nftId);
//     }

//     //if staker owned many NFTs with same lp tokens use batch withdraw
//     function withdrawBatch(uint256 _pid, uint256[] memory _nftIds) public {
//         for (uint256 i = 0; i < _nftIds.length; i++) {
//             withdraw(_pid, _nftIds[i]);
//         }
//     }

//     // Safe token transfer function, just in case if rounding error causes pool to not have enough tokens.
//     function safeTokenTransfer(address _to, uint256 _amount) internal {
//         uint256 tokenBal = token.balanceOf(address(this));
//         if (_amount > tokenBal) {
//             token.transfer(_to, tokenBal);
//         } else {
//             token.transfer(_to, _amount);
//         }
//     }

//     // Update dev address by the previous dev.
//     function dev(address _devaddr) public {
//         require(msg.sender == devaddr, "dev: wut?");
//         devaddr = _devaddr;
//     }
// }

// File: contracts/DutchAuction.sol



pragma solidity ^0.6.0;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/math/SafeMath.sol";
import "@openzeppelin/contracts/token/ERC1155/ERC1155Holder.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721Holder.sol";
import "@openzeppelin/contracts/utils/EnumerableSet.sol";

import "@openzeppelin/contracts/token/ERC721/IERC721.sol";
import "@openzeppelin/contracts/token/ERC1155/IERC1155.sol";

import "../interfaces/INFT20Pair.sol";

contract DutchAuction is Ownable, ERC1155Holder, ERC721Holder {
    using SafeMath for uint256;
    using EnumerableSet for EnumerableSet.UintSet;

    struct Auction {
        uint256 id;
        address seller;
        address nft20Pair;
        uint256 tokenId;
        uint256 startingPrice; // wei
        uint256 endingPrice; // wei
        uint256 duration; // seconds
        uint256 startedAt; // time
    }

    uint256 public daoFee;
    address public daoAddress;

    uint256 public auctionId = 1; // max is 18446744073709551615

    // to query auctiosn by each pair
    mapping(address => EnumerableSet.UintSet) private _auction;

    mapping(uint256 => Auction) internal auctionIdToAuction;

    event AuctionCreated(
        uint256 auctionId,
        address indexed seller,
        address indexed nft20Pair,
        uint256 tokenId,
        uint256 startingPrice,
        uint256 endingPrice,
        uint256 duration
    );
    event AuctionCancelled(
        uint64 auctionId,
        address indexed seller,
        address indexed nft20Pair,
        uint256 tokenId
    );

    event AuctionSuccessful(
        uint256 auctionId,
        address indexed seller,
        address indexed nft20Pair,
        uint256 tokenId,
        uint256 totalPrice,
        address winner
    );

    constructor(address _daoAddress, uint256 _daoFee) public {
        daoAddress = _daoAddress;
        daoFee = _daoFee;
    }

    function createAuction(
        address _nft20Pair,
        uint256 _tokenId,
        uint256 _startingPrice,
        uint256 _endingPrice,
        uint256 _duration
    ) external {
        require(_duration >= 1 minutes);
        require(
            _startingPrice > _endingPrice,
            "!starting price should be higher"
        ); //not sure about this, need to also check getCurrentPrice()
        INFT20Pair nft20pair = INFT20Pair(_nft20Pair);

        if (nft20pair.nftType() == 721) {
            require(
                IERC721(nft20pair.nftAddress()).ownerOf(_tokenId) == msg.sender,
                "!owner"
            );
        } else if (nft20pair.nftType() == 1155) {
            require(
                IERC1155(nft20pair.nftAddress()).balanceOf(
                    msg.sender,
                    _tokenId
                ) >= 1,
                "!owner"
            );
        }

        auctionIdToAuction[auctionId] = Auction(
            auctionId,
            msg.sender,
            _nft20Pair,
            _tokenId,
            _startingPrice,
            _endingPrice,
            _duration,
            block.timestamp
        );

        _auction[_nft20Pair].add(auctionId);

        emit AuctionCreated(
            auctionId,
            msg.sender,
            _nft20Pair,
            _tokenId,
            _startingPrice,
            _endingPrice,
            block.timestamp
        );

        auctionId++;
    }

    function getAuctionByAuctionId(uint256 _auctionId)
        public
        view
        returns (
            uint256 _id,
            address _seller,
            address _nft20Pair,
            uint256 _tokenId,
            uint256 _startingPrice,
            uint256 _endingPrice,
            uint256 _duration,
            uint256 _startedAt,
            uint256 _currentPrice
        )
    {
        Auction storage auction = auctionIdToAuction[_auctionId];
        require(auction.startedAt > 0); // Not sure why this
        _id = auction.id;
        _seller = auction.seller;
        _nft20Pair = address(auction.nft20Pair);
        _tokenId = auction.tokenId;
        _startingPrice = auction.startingPrice;
        _endingPrice = auction.endingPrice;
        _duration = auction.duration;
        _startedAt = auction.startedAt;
        _currentPrice = getCurrentPrice(auction);
    }

    function cancelAuctionByAuctionId(uint64 _auctionId) external {
        Auction storage auction = auctionIdToAuction[_auctionId];

        require(auction.startedAt > 0);
        require(msg.sender == auction.seller);

        _auction[auction.nft20Pair].remove(_auctionId);

        delete auctionIdToAuction[_auctionId];
        emit AuctionCancelled(
            _auctionId,
            auction.seller,
            address(auction.nft20Pair),
            auction.tokenId
        );
    }

    function bid(uint256 _auctionId, uint256 _bid) external {
        Auction storage auction = auctionIdToAuction[_auctionId];
        require(auction.startedAt > 0);

        uint256 price = getCurrentPrice(auction);
        require(_bid >= price);

        uint256 auctionId_temp = auction.id;
        INFT20Pair nft20Pair = INFT20Pair(auction.nft20Pair);

        address seller = auction.seller;
        uint256 tokenId = auction.tokenId;
        delete auctionIdToAuction[auctionId_temp];

        if (price > 0) {
            nft20Pair.transferFrom(
                msg.sender,
                address(this),
                price.mul(daoFee).div(100)
            );
            nft20Pair.transferFrom(
                msg.sender,
                seller,
                price.mul(uint256(100).sub(daoFee)).div(100)
            );
        }

        transferNft(
            nft20Pair.nftAddress(),
            nft20Pair.nftType(),
            seller,
            msg.sender,
            tokenId
        );

        _auction[address(nft20Pair)].remove(_auctionId);

        emit AuctionSuccessful(
            auctionId_temp,
            seller,
            address(nft20Pair),
            tokenId,
            price,
            msg.sender
        );
    }

    function getCurrentPriceByAuctionId(uint64 _auctionId)
        public
        view
        returns (uint256)
    {
        Auction storage auction = auctionIdToAuction[_auctionId];
        return getCurrentPrice(auction);
    }

    // TODO Let's check this and add safe math maybe.
    function getCurrentPrice(Auction storage _thisauction)
        internal
        view
        returns (uint256)
    {
        require(_thisauction.startedAt > 0);
        uint256 secondsPassed = 0;

        secondsPassed = now.sub(_thisauction.startedAt);

        if (secondsPassed >= _thisauction.duration) {
            return _thisauction.endingPrice;
        } else {
            uint256 totalPriceChange =
                _thisauction.startingPrice.sub(_thisauction.endingPrice);

            uint256 currentPriceChange =
                (totalPriceChange.mul(secondsPassed)).div(
                    _thisauction.duration
                );

            uint256 currentPrice =
                _thisauction.startingPrice.sub(currentPriceChange);

            return currentPrice;
        }
    }

    // maybe we can rethink this for less gas?
    function transferNft(
        address nftAddress,
        uint256 nftType,
        address _from,
        address _to,
        uint256 _tokenId
    ) internal {
        if (nftType == 721) {
            IERC721(nftAddress).safeTransferFrom(_from, _to, _tokenId);
        } else if (nftType == 1155) {
            IERC1155(nftAddress).safeTransferFrom(_from, _to, _tokenId, 1, "");
        }
    }

    function auctionsAmountByPair(address _nft20pair)
        public
        view
        returns (uint256)
    {
        require(
            _nft20pair != address(0),
            "ERC721: balance query for the zero address"
        );

        return _auction[_nft20pair].length();
    }

    function auctionOfPairByIndex(address _nft20pair, uint256 index)
        public
        view
        returns (uint256)
    {
        return _auction[_nft20pair].at(index);
    }

    function recoverERC20(
        address tokenAddress,
        address receiver,
        uint256 tokenAmount
    ) public onlyOwner {
        INFT20Pair(tokenAddress).transfer(receiver, tokenAmount);
    }
}

// File: @openzeppelin/contracts/access/Ownable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../utils/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: @openzeppelin/contracts/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) return (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) return 0;
        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a % b;
    }
}

// File: @openzeppelin/contracts/token/ERC1155/ERC1155Holder.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./ERC1155Receiver.sol";

/**
 * @dev _Available since v3.1._
 */
contract ERC1155Holder is ERC1155Receiver {
    function onERC1155Received(address, address, uint256, uint256, bytes memory) public virtual override returns (bytes4) {
        return this.onERC1155Received.selector;
    }

    function onERC1155BatchReceived(address, address, uint256[] memory, uint256[] memory, bytes memory) public virtual override returns (bytes4) {
        return this.onERC1155BatchReceived.selector;
    }
}

// File: @openzeppelin/contracts/token/ERC721/ERC721Holder.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./IERC721Receiver.sol";

  /**
   * @dev Implementation of the {IERC721Receiver} interface.
   *
   * Accepts all token transfers. 
   * Make sure the contract is able to use its token with {IERC721-safeTransferFrom}, {IERC721-approve} or {IERC721-setApprovalForAll}.
   */
contract ERC721Holder is IERC721Receiver {

    /**
     * @dev See {IERC721Receiver-onERC721Received}.
     *
     * Always returns `IERC721Receiver.onERC721Received.selector`.
     */
    function onERC721Received(address, address, uint256, bytes memory) public virtual override returns (bytes4) {
        return this.onERC721Received.selector;
    }
}

// File: @openzeppelin/contracts/utils/EnumerableSet.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Library for managing
 * https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets] of primitive
 * types.
 *
 * Sets have the following properties:
 *
 * - Elements are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Elements are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableSet for EnumerableSet.AddressSet;
 *
 *     // Declare a set state variable
 *     EnumerableSet.AddressSet private mySet;
 * }
 * ```
 *
 * As of v3.3.0, sets of type `bytes32` (`Bytes32Set`), `address` (`AddressSet`)
 * and `uint256` (`UintSet`) are supported.
 */
library EnumerableSet {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Set type with
    // bytes32 values.
    // The Set implementation uses private functions, and user-facing
    // implementations (such as AddressSet) are just wrappers around the
    // underlying Set.
    // This means that we can only create new EnumerableSets for types that fit
    // in bytes32.

    struct Set {
        // Storage of set values
        bytes32[] _values;

        // Position of the value in the `values` array, plus 1 because index 0
        // means a value is not in the set.
        mapping (bytes32 => uint256) _indexes;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function _add(Set storage set, bytes32 value) private returns (bool) {
        if (!_contains(set, value)) {
            set._values.push(value);
            // The value is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            set._indexes[value] = set._values.length;
            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function _remove(Set storage set, bytes32 value) private returns (bool) {
        // We read and store the value's index to prevent multiple reads from the same storage slot
        uint256 valueIndex = set._indexes[value];

        if (valueIndex != 0) { // Equivalent to contains(set, value)
            // To delete an element from the _values array in O(1), we swap the element to delete with the last one in
            // the array, and then remove the last element (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = valueIndex - 1;
            uint256 lastIndex = set._values.length - 1;

            // When the value to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            bytes32 lastvalue = set._values[lastIndex];

            // Move the last value to the index where the value to delete is
            set._values[toDeleteIndex] = lastvalue;
            // Update the index for the moved value
            set._indexes[lastvalue] = toDeleteIndex + 1; // All indexes are 1-based

            // Delete the slot where the moved value was stored
            set._values.pop();

            // Delete the index for the deleted slot
            delete set._indexes[value];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function _contains(Set storage set, bytes32 value) private view returns (bool) {
        return set._indexes[value] != 0;
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function _length(Set storage set) private view returns (uint256) {
        return set._values.length;
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function _at(Set storage set, uint256 index) private view returns (bytes32) {
        require(set._values.length > index, "EnumerableSet: index out of bounds");
        return set._values[index];
    }

    // Bytes32Set

    struct Bytes32Set {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _add(set._inner, value);
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _remove(set._inner, value);
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(Bytes32Set storage set, bytes32 value) internal view returns (bool) {
        return _contains(set._inner, value);
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(Bytes32Set storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(Bytes32Set storage set, uint256 index) internal view returns (bytes32) {
        return _at(set._inner, index);
    }

    // AddressSet

    struct AddressSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(AddressSet storage set, address value) internal returns (bool) {
        return _add(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(AddressSet storage set, address value) internal returns (bool) {
        return _remove(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(AddressSet storage set, address value) internal view returns (bool) {
        return _contains(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(AddressSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(AddressSet storage set, uint256 index) internal view returns (address) {
        return address(uint160(uint256(_at(set._inner, index))));
    }


    // UintSet

    struct UintSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(UintSet storage set, uint256 value) internal returns (bool) {
        return _add(set._inner, bytes32(value));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(UintSet storage set, uint256 value) internal returns (bool) {
        return _remove(set._inner, bytes32(value));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(UintSet storage set, uint256 value) internal view returns (bool) {
        return _contains(set._inner, bytes32(value));
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function length(UintSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(UintSet storage set, uint256 index) internal view returns (uint256) {
        return uint256(_at(set._inner, index));
    }
}

// File: @openzeppelin/contracts/token/ERC721/IERC721.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

import "../../introspection/IERC165.sol";

/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721 is IERC165 {
    /**
     * @dev Emitted when `tokenId` token is transferred from `from` to `to`.
     */
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables `approved` to manage the `tokenId` token.
     */
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables or disables (`approved`) `operator` to manage all of its assets.
     */
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

    /**
     * @dev Returns the number of tokens in ``owner``'s account.
     */
    function balanceOf(address owner) external view returns (uint256 balance);

    /**
     * @dev Returns the owner of the `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function ownerOf(uint256 tokenId) external view returns (address owner);

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
     * are aware of the ERC721 protocol to prevent tokens from being forever locked.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be have been allowed to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(address from, address to, uint256 tokenId) external;

    /**
     * @dev Transfers `tokenId` token from `from` to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address from, address to, uint256 tokenId) external;

    /**
     * @dev Gives permission to `to` to transfer `tokenId` token to another account.
     * The approval is cleared when the token is transferred.
     *
     * Only a single account can be approved at a time, so approving the zero address clears previous approvals.
     *
     * Requirements:
     *
     * - The caller must own the token or be an approved operator.
     * - `tokenId` must exist.
     *
     * Emits an {Approval} event.
     */
    function approve(address to, uint256 tokenId) external;

    /**
     * @dev Returns the account approved for `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function getApproved(uint256 tokenId) external view returns (address operator);

    /**
     * @dev Approve or remove `operator` as an operator for the caller.
     * Operators can call {transferFrom} or {safeTransferFrom} for any token owned by the caller.
     *
     * Requirements:
     *
     * - The `operator` cannot be the caller.
     *
     * Emits an {ApprovalForAll} event.
     */
    function setApprovalForAll(address operator, bool _approved) external;

    /**
     * @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
     *
     * See {setApprovalForAll}
     */
    function isApprovedForAll(address owner, address operator) external view returns (bool);

    /**
      * @dev Safely transfers `tokenId` token from `from` to `to`.
      *
      * Requirements:
      *
      * - `from` cannot be the zero address.
      * - `to` cannot be the zero address.
      * - `tokenId` token must exist and be owned by `from`.
      * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
      * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
      *
      * Emits a {Transfer} event.
      */
    function safeTransferFrom(address from, address to, uint256 tokenId, bytes calldata data) external;
}

// File: @openzeppelin/contracts/token/ERC1155/IERC1155.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

import "../../introspection/IERC165.sol";

/**
 * @dev Required interface of an ERC1155 compliant contract, as defined in the
 * https://eips.ethereum.org/EIPS/eip-1155[EIP].
 *
 * _Available since v3.1._
 */
interface IERC1155 is IERC165 {
    /**
     * @dev Emitted when `value` tokens of token type `id` are transferred from `from` to `to` by `operator`.
     */
    event TransferSingle(address indexed operator, address indexed from, address indexed to, uint256 id, uint256 value);

    /**
     * @dev Equivalent to multiple {TransferSingle} events, where `operator`, `from` and `to` are the same for all
     * transfers.
     */
    event TransferBatch(address indexed operator, address indexed from, address indexed to, uint256[] ids, uint256[] values);

    /**
     * @dev Emitted when `account` grants or revokes permission to `operator` to transfer their tokens, according to
     * `approved`.
     */
    event ApprovalForAll(address indexed account, address indexed operator, bool approved);

    /**
     * @dev Emitted when the URI for token type `id` changes to `value`, if it is a non-programmatic URI.
     *
     * If an {URI} event was emitted for `id`, the standard
     * https://eips.ethereum.org/EIPS/eip-1155#metadata-extensions[guarantees] that `value` will equal the value
     * returned by {IERC1155MetadataURI-uri}.
     */
    event URI(string value, uint256 indexed id);

    /**
     * @dev Returns the amount of tokens of token type `id` owned by `account`.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     */
    function balanceOf(address account, uint256 id) external view returns (uint256);

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {balanceOf}.
     *
     * Requirements:
     *
     * - `accounts` and `ids` must have the same length.
     */
    function balanceOfBatch(address[] calldata accounts, uint256[] calldata ids) external view returns (uint256[] memory);

    /**
     * @dev Grants or revokes permission to `operator` to transfer the caller's tokens, according to `approved`,
     *
     * Emits an {ApprovalForAll} event.
     *
     * Requirements:
     *
     * - `operator` cannot be the caller.
     */
    function setApprovalForAll(address operator, bool approved) external;

    /**
     * @dev Returns true if `operator` is approved to transfer ``account``'s tokens.
     *
     * See {setApprovalForAll}.
     */
    function isApprovedForAll(address account, address operator) external view returns (bool);

    /**
     * @dev Transfers `amount` tokens of token type `id` from `from` to `to`.
     *
     * Emits a {TransferSingle} event.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - If the caller is not `from`, it must be have been approved to spend ``from``'s tokens via {setApprovalForAll}.
     * - `from` must have a balance of tokens of type `id` of at least `amount`.
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155Received} and return the
     * acceptance magic value.
     */
    function safeTransferFrom(address from, address to, uint256 id, uint256 amount, bytes calldata data) external;

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {safeTransferFrom}.
     *
     * Emits a {TransferBatch} event.
     *
     * Requirements:
     *
     * - `ids` and `amounts` must have the same length.
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155BatchReceived} and return the
     * acceptance magic value.
     */
    function safeBatchTransferFrom(address from, address to, uint256[] calldata ids, uint256[] calldata amounts, bytes calldata data) external;
}

// File: interfaces/INFT20Pair.sol



pragma solidity ^0.6.0;

// Interface for our erc20 token
interface INFT20Pair {
    function totalSupply() external view returns (uint256);

    function balanceOf(address tokenOwner)
        external
        view
        returns (uint256 balance);

    function allowance(address tokenOwner, address spender)
        external
        view
        returns (uint256 remaining);

    function transfer(address to, uint256 tokens)
        external
        returns (bool success);

    function approve(address spender, uint256 tokens)
        external
        returns (bool success);

    function transferFrom(
        address from,
        address to,
        uint256 tokens
    ) external returns (bool success);

    function mint(address to, uint256 amount) external;

    function burn(uint256 amount) external;

    function burnFrom(address account, uint256 amount) external;

    function nftType() external view returns (uint256);

    function nftAddress() external view returns (address);

    function track1155(uint256 _id) external view returns (uint256);

    function setParams(
        uint256 _nftType,
        string calldata name,
        string calldata symbol,
        uint256 value
    ) external;

    function getInfos()
        external
        view
        returns (
            uint256 _type,
            string memory _name,
            string memory _symbol,
            uint256 _supply
        );

    function init(
        string calldata name,
        string calldata symbol,
        address _nftAddress,
        uint256 _nftType
    ) external;
}

// File: @openzeppelin/contracts/utils/Context.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// File: @openzeppelin/contracts/token/ERC1155/ERC1155Receiver.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./IERC1155Receiver.sol";
import "../../introspection/ERC165.sol";

/**
 * @dev _Available since v3.1._
 */
abstract contract ERC1155Receiver is ERC165, IERC1155Receiver {
    constructor() internal {
        _registerInterface(
            ERC1155Receiver(address(0)).onERC1155Received.selector ^
            ERC1155Receiver(address(0)).onERC1155BatchReceived.selector
        );
    }
}

// File: @openzeppelin/contracts/token/ERC1155/IERC1155Receiver.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../introspection/IERC165.sol";

/**
 * _Available since v3.1._
 */
interface IERC1155Receiver is IERC165 {

    /**
        @dev Handles the receipt of a single ERC1155 token type. This function is
        called at the end of a `safeTransferFrom` after the balance has been updated.
        To accept the transfer, this must return
        `bytes4(keccak256("onERC1155Received(address,address,uint256,uint256,bytes)"))`
        (i.e. 0xf23a6e61, or its own function selector).
        @param operator The address which initiated the transfer (i.e. msg.sender)
        @param from The address which previously owned the token
        @param id The ID of the token being transferred
        @param value The amount of tokens being transferred
        @param data Additional data with no specified format
        @return `bytes4(keccak256("onERC1155Received(address,address,uint256,uint256,bytes)"))` if transfer is allowed
    */
    function onERC1155Received(
        address operator,
        address from,
        uint256 id,
        uint256 value,
        bytes calldata data
    )
        external
        returns(bytes4);

    /**
        @dev Handles the receipt of a multiple ERC1155 token types. This function
        is called at the end of a `safeBatchTransferFrom` after the balances have
        been updated. To accept the transfer(s), this must return
        `bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))`
        (i.e. 0xbc197c81, or its own function selector).
        @param operator The address which initiated the batch transfer (i.e. msg.sender)
        @param from The address which previously owned the token
        @param ids An array containing ids of each token being transferred (order and length must match values array)
        @param values An array containing amounts of each token being transferred (order and length must match ids array)
        @param data Additional data with no specified format
        @return `bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))` if transfer is allowed
    */
    function onERC1155BatchReceived(
        address operator,
        address from,
        uint256[] calldata ids,
        uint256[] calldata values,
        bytes calldata data
    )
        external
        returns(bytes4);
}

// File: @openzeppelin/contracts/introspection/ERC165.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./IERC165.sol";

/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts may inherit from this and call {_registerInterface} to declare
 * their support of an interface.
 */
abstract contract ERC165 is IERC165 {
    /*
     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
     */
    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;

    /**
     * @dev Mapping of interface ids to whether or not it's supported.
     */
    mapping(bytes4 => bool) private _supportedInterfaces;

    constructor () internal {
        // Derived contracts need only register support for their own interfaces,
        // we register support for ERC165 itself here
        _registerInterface(_INTERFACE_ID_ERC165);
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     *
     * Time complexity O(1), guaranteed to always use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return _supportedInterfaces[interfaceId];
    }

    /**
     * @dev Registers the contract as an implementer of the interface defined by
     * `interfaceId`. Support of the actual ERC165 interface is automatic and
     * registering its interface id is not required.
     *
     * See {IERC165-supportsInterface}.
     *
     * Requirements:
     *
     * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
     */
    function _registerInterface(bytes4 interfaceId) internal virtual {
        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
        _supportedInterfaces[interfaceId] = true;
    }
}

// File: @openzeppelin/contracts/introspection/IERC165.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

// File: @openzeppelin/contracts/token/ERC721/IERC721Receiver.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @title ERC721 token receiver interface
 * @dev Interface for any contract that wants to support safeTransfers
 * from ERC721 asset contracts.
 */
interface IERC721Receiver {
    /**
     * @dev Whenever an {IERC721} `tokenId` token is transferred to this contract via {IERC721-safeTransferFrom}
     * by `operator` from `from`, this function is called.
     *
     * It must return its Solidity selector to confirm the token transfer.
     * If any other value is returned or the interface is not implemented by the recipient, the transfer will be reverted.
     *
     * The selector can be obtained in Solidity with `IERC721.onERC721Received.selector`.
     */
    function onERC721Received(address operator, address from, uint256 tokenId, bytes calldata data) external returns (bytes4);
}

// File: @openzeppelin/contracts/token/ERC1155/IERC1155MetadataURI.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

import "./IERC1155.sol";

/**
 * @dev Interface of the optional ERC1155MetadataExtension interface, as defined
 * in the https://eips.ethereum.org/EIPS/eip-1155#metadata-extensions[EIP].
 *
 * _Available since v3.1._
 */
interface IERC1155MetadataURI is IERC1155 {
    /**
     * @dev Returns the URI for token type `id`.
     *
     * If the `\{id\}` substring is present in the URI, it must be replaced by
     * clients with the actual token type ID.
     */
    function uri(uint256 id) external view returns (string memory);
}

// File: @openzeppelin/contracts/token/ERC1155/ERC1155.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./IERC1155.sol";
import "./IERC1155MetadataURI.sol";
import "./IERC1155Receiver.sol";
import "../../utils/Context.sol";
import "../../introspection/ERC165.sol";
import "../../math/SafeMath.sol";
import "../../utils/Address.sol";

/**
 *
 * @dev Implementation of the basic standard multi-token.
 * See https://eips.ethereum.org/EIPS/eip-1155
 * Originally based on code by Enjin: https://github.com/enjin/erc-1155
 *
 * _Available since v3.1._
 */
contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
    using SafeMath for uint256;
    using Address for address;

    // Mapping from token ID to account balances
    mapping (uint256 => mapping(address => uint256)) private _balances;

    // Mapping from account to operator approvals
    mapping (address => mapping(address => bool)) private _operatorApprovals;

    // Used as the URI for all token types by relying on ID substitution, e.g. https://token-cdn-domain/{id}.json
    string private _uri;

    /*
     *     bytes4(keccak256('balanceOf(address,uint256)')) == 0x00fdd58e
     *     bytes4(keccak256('balanceOfBatch(address[],uint256[])')) == 0x4e1273f4
     *     bytes4(keccak256('setApprovalForAll(address,bool)')) == 0xa22cb465
     *     bytes4(keccak256('isApprovedForAll(address,address)')) == 0xe985e9c5
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256,uint256,bytes)')) == 0xf242432a
     *     bytes4(keccak256('safeBatchTransferFrom(address,address,uint256[],uint256[],bytes)')) == 0x2eb2c2d6
     *
     *     => 0x00fdd58e ^ 0x4e1273f4 ^ 0xa22cb465 ^
     *        0xe985e9c5 ^ 0xf242432a ^ 0x2eb2c2d6 == 0xd9b67a26
     */
    bytes4 private constant _INTERFACE_ID_ERC1155 = 0xd9b67a26;

    /*
     *     bytes4(keccak256('uri(uint256)')) == 0x0e89341c
     */
    bytes4 private constant _INTERFACE_ID_ERC1155_METADATA_URI = 0x0e89341c;

    /**
     * @dev See {_setURI}.
     */
    constructor (string memory uri_) public {
        _setURI(uri_);

        // register the supported interfaces to conform to ERC1155 via ERC165
        _registerInterface(_INTERFACE_ID_ERC1155);

        // register the supported interfaces to conform to ERC1155MetadataURI via ERC165
        _registerInterface(_INTERFACE_ID_ERC1155_METADATA_URI);
    }

    /**
     * @dev See {IERC1155MetadataURI-uri}.
     *
     * This implementation returns the same URI for *all* token types. It relies
     * on the token type ID substitution mechanism
     * https://eips.ethereum.org/EIPS/eip-1155#metadata[defined in the EIP].
     *
     * Clients calling this function must replace the `\{id\}` substring with the
     * actual token type ID.
     */
    function uri(uint256) external view virtual override returns (string memory) {
        return _uri;
    }

    /**
     * @dev See {IERC1155-balanceOf}.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     */
    function balanceOf(address account, uint256 id) public view virtual override returns (uint256) {
        require(account != address(0), "ERC1155: balance query for the zero address");
        return _balances[id][account];
    }

    /**
     * @dev See {IERC1155-balanceOfBatch}.
     *
     * Requirements:
     *
     * - `accounts` and `ids` must have the same length.
     */
    function balanceOfBatch(
        address[] memory accounts,
        uint256[] memory ids
    )
        public
        view
        virtual
        override
        returns (uint256[] memory)
    {
        require(accounts.length == ids.length, "ERC1155: accounts and ids length mismatch");

        uint256[] memory batchBalances = new uint256[](accounts.length);

        for (uint256 i = 0; i < accounts.length; ++i) {
            batchBalances[i] = balanceOf(accounts[i], ids[i]);
        }

        return batchBalances;
    }

    /**
     * @dev See {IERC1155-setApprovalForAll}.
     */
    function setApprovalForAll(address operator, bool approved) public virtual override {
        require(_msgSender() != operator, "ERC1155: setting approval status for self");

        _operatorApprovals[_msgSender()][operator] = approved;
        emit ApprovalForAll(_msgSender(), operator, approved);
    }

    /**
     * @dev See {IERC1155-isApprovedForAll}.
     */
    function isApprovedForAll(address account, address operator) public view virtual override returns (bool) {
        return _operatorApprovals[account][operator];
    }

    /**
     * @dev See {IERC1155-safeTransferFrom}.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 id,
        uint256 amount,
        bytes memory data
    )
        public
        virtual
        override
    {
        require(to != address(0), "ERC1155: transfer to the zero address");
        require(
            from == _msgSender() || isApprovedForAll(from, _msgSender()),
            "ERC1155: caller is not owner nor approved"
        );

        address operator = _msgSender();

        _beforeTokenTransfer(operator, from, to, _asSingletonArray(id), _asSingletonArray(amount), data);

        _balances[id][from] = _balances[id][from].sub(amount, "ERC1155: insufficient balance for transfer");
        _balances[id][to] = _balances[id][to].add(amount);

        emit TransferSingle(operator, from, to, id, amount);

        _doSafeTransferAcceptanceCheck(operator, from, to, id, amount, data);
    }

    /**
     * @dev See {IERC1155-safeBatchTransferFrom}.
     */
    function safeBatchTransferFrom(
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    )
        public
        virtual
        override
    {
        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");
        require(to != address(0), "ERC1155: transfer to the zero address");
        require(
            from == _msgSender() || isApprovedForAll(from, _msgSender()),
            "ERC1155: transfer caller is not owner nor approved"
        );

        address operator = _msgSender();

        _beforeTokenTransfer(operator, from, to, ids, amounts, data);

        for (uint256 i = 0; i < ids.length; ++i) {
            uint256 id = ids[i];
            uint256 amount = amounts[i];

            _balances[id][from] = _balances[id][from].sub(
                amount,
                "ERC1155: insufficient balance for transfer"
            );
            _balances[id][to] = _balances[id][to].add(amount);
        }

        emit TransferBatch(operator, from, to, ids, amounts);

        _doSafeBatchTransferAcceptanceCheck(operator, from, to, ids, amounts, data);
    }

    /**
     * @dev Sets a new URI for all token types, by relying on the token type ID
     * substitution mechanism
     * https://eips.ethereum.org/EIPS/eip-1155#metadata[defined in the EIP].
     *
     * By this mechanism, any occurrence of the `\{id\}` substring in either the
     * URI or any of the amounts in the JSON file at said URI will be replaced by
     * clients with the token type ID.
     *
     * For example, the `https://token-cdn-domain/\{id\}.json` URI would be
     * interpreted by clients as
     * `https://token-cdn-domain/000000000000000000000000000000000000000000000000000000000004cce0.json`
     * for token type ID 0x4cce0.
     *
     * See {uri}.
     *
     * Because these URIs cannot be meaningfully represented by the {u} event,
     * this function emits no events.
     */
    function _setURI(string memory newuri) internal virtual {
        _uri = newuri;
    }

    /**
     * @dev Creates `amount` tokens of token type `id`, and assigns them to `account`.
     *
     * Emits a {TransferSingle} event.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - If `account` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155Received} and return the
     * acceptance magic value.
     */
    function _mint(address account, uint256 id, uint256 amount, bytes memory data) internal virtual {
        require(account != address(0), "ERC1155: mint to the zero address");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, address(0), account, _asSingletonArray(id), _asSingletonArray(amount), data);

        _balances[id][account] = _balances[id][account].add(amount);
        emit TransferSingle(operator, address(0), account, id, amount);

        _doSafeTransferAcceptanceCheck(operator, address(0), account, id, amount, data);
    }

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_mint}.
     *
     * Requirements:
     *
     * - `ids` and `amounts` must have the same length.
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155BatchReceived} and return the
     * acceptance magic value.
     */
    function _mintBatch(address to, uint256[] memory ids, uint256[] memory amounts, bytes memory data) internal virtual {
        require(to != address(0), "ERC1155: mint to the zero address");
        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, address(0), to, ids, amounts, data);

        for (uint i = 0; i < ids.length; i++) {
            _balances[ids[i]][to] = amounts[i].add(_balances[ids[i]][to]);
        }

        emit TransferBatch(operator, address(0), to, ids, amounts);

        _doSafeBatchTransferAcceptanceCheck(operator, address(0), to, ids, amounts, data);
    }

    /**
     * @dev Destroys `amount` tokens of token type `id` from `account`
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens of token type `id`.
     */
    function _burn(address account, uint256 id, uint256 amount) internal virtual {
        require(account != address(0), "ERC1155: burn from the zero address");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, account, address(0), _asSingletonArray(id), _asSingletonArray(amount), "");

        _balances[id][account] = _balances[id][account].sub(
            amount,
            "ERC1155: burn amount exceeds balance"
        );

        emit TransferSingle(operator, account, address(0), id, amount);
    }

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_burn}.
     *
     * Requirements:
     *
     * - `ids` and `amounts` must have the same length.
     */
    function _burnBatch(address account, uint256[] memory ids, uint256[] memory amounts) internal virtual {
        require(account != address(0), "ERC1155: burn from the zero address");
        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, account, address(0), ids, amounts, "");

        for (uint i = 0; i < ids.length; i++) {
            _balances[ids[i]][account] = _balances[ids[i]][account].sub(
                amounts[i],
                "ERC1155: burn amount exceeds balance"
            );
        }

        emit TransferBatch(operator, account, address(0), ids, amounts);
    }

    /**
     * @dev Hook that is called before any token transfer. This includes minting
     * and burning, as well as batched variants.
     *
     * The same hook is called on both single and batched variants. For single
     * transfers, the length of the `id` and `amount` arrays will be 1.
     *
     * Calling conditions (for each `id` and `amount` pair):
     *
     * - When `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * of token type `id` will be  transferred to `to`.
     * - When `from` is zero, `amount` tokens of token type `id` will be minted
     * for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens of token type `id`
     * will be burned.
     * - `from` and `to` are never both zero.
     * - `ids` and `amounts` have the same, non-zero length.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(
        address operator,
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    )
        internal
        virtual
    { }

    function _doSafeTransferAcceptanceCheck(
        address operator,
        address from,
        address to,
        uint256 id,
        uint256 amount,
        bytes memory data
    )
        private
    {
        if (to.isContract()) {
            try IERC1155Receiver(to).onERC1155Received(operator, from, id, amount, data) returns (bytes4 response) {
                if (response != IERC1155Receiver(to).onERC1155Received.selector) {
                    revert("ERC1155: ERC1155Receiver rejected tokens");
                }
            } catch Error(string memory reason) {
                revert(reason);
            } catch {
                revert("ERC1155: transfer to non ERC1155Receiver implementer");
            }
        }
    }

    function _doSafeBatchTransferAcceptanceCheck(
        address operator,
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    )
        private
    {
        if (to.isContract()) {
            try IERC1155Receiver(to).onERC1155BatchReceived(operator, from, ids, amounts, data) returns (bytes4 response) {
                if (response != IERC1155Receiver(to).onERC1155BatchReceived.selector) {
                    revert("ERC1155: ERC1155Receiver rejected tokens");
                }
            } catch Error(string memory reason) {
                revert(reason);
            } catch {
                revert("ERC1155: transfer to non ERC1155Receiver implementer");
            }
        }
    }

    function _asSingletonArray(uint256 element) private pure returns (uint256[] memory) {
        uint256[] memory array = new uint256[](1);
        array[0] = element;

        return array;
    }
}

// File: @openzeppelin/contracts/utils/Address.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: @openzeppelin/contracts/token/ERC1155/ERC1155Pausable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./ERC1155.sol";
import "../../utils/Pausable.sol";

/**
 * @dev ERC1155 token with pausable token transfers, minting and burning.
 *
 * Useful for scenarios such as preventing trades until the end of an evaluation
 * period, or having an emergency switch for freezing all token transfers in the
 * event of a large bug.
 *
 * _Available since v3.1._
 */
abstract contract ERC1155Pausable is ERC1155, Pausable {
    /**
     * @dev See {ERC1155-_beforeTokenTransfer}.
     *
     * Requirements:
     *
     * - the contract must not be paused.
     */
    function _beforeTokenTransfer(
        address operator,
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    )
        internal
        virtual
        override
    {
        super._beforeTokenTransfer(operator, from, to, ids, amounts, data);

        require(!paused(), "ERC1155Pausable: token transfer while paused");
    }
}

// File: @openzeppelin/contracts/utils/Pausable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./Context.sol";

/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
abstract contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);

    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);

    bool private _paused;

    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor () internal {
        _paused = false;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view virtual returns (bool) {
        return _paused;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        require(!paused(), "Pausable: paused");
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        require(paused(), "Pausable: not paused");
        _;
    }

    /**
     * @dev Triggers stopped state.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }

    /**
     * @dev Returns to normal state.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}

// File: @openzeppelin/contracts/token/ERC721/ERC721Pausable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./ERC721.sol";
import "../../utils/Pausable.sol";

/**
 * @dev ERC721 token with pausable token transfers, minting and burning.
 *
 * Useful for scenarios such as preventing trades until the end of an evaluation
 * period, or having an emergency switch for freezing all token transfers in the
 * event of a large bug.
 */
abstract contract ERC721Pausable is ERC721, Pausable {
    /**
     * @dev See {ERC721-_beforeTokenTransfer}.
     *
     * Requirements:
     *
     * - the contract must not be paused.
     */
    function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal virtual override {
        super._beforeTokenTransfer(from, to, tokenId);

        require(!paused(), "ERC721Pausable: token transfer while paused");
    }
}

// File: @openzeppelin/contracts/token/ERC721/ERC721.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../utils/Context.sol";
import "./IERC721.sol";
import "./IERC721Metadata.sol";
import "./IERC721Enumerable.sol";
import "./IERC721Receiver.sol";
import "../../introspection/ERC165.sol";
import "../../math/SafeMath.sol";
import "../../utils/Address.sol";
import "../../utils/EnumerableSet.sol";
import "../../utils/EnumerableMap.sol";
import "../../utils/Strings.sol";

/**
 * @title ERC721 Non-Fungible Token Standard basic implementation
 * @dev see https://eips.ethereum.org/EIPS/eip-721
 */
contract ERC721 is Context, ERC165, IERC721, IERC721Metadata, IERC721Enumerable {
    using SafeMath for uint256;
    using Address for address;
    using EnumerableSet for EnumerableSet.UintSet;
    using EnumerableMap for EnumerableMap.UintToAddressMap;
    using Strings for uint256;

    // Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
    // which can be also obtained as `IERC721Receiver(0).onERC721Received.selector`
    bytes4 private constant _ERC721_RECEIVED = 0x150b7a02;

    // Mapping from holder address to their (enumerable) set of owned tokens
    mapping (address => EnumerableSet.UintSet) private _holderTokens;

    // Enumerable mapping from token ids to their owners
    EnumerableMap.UintToAddressMap private _tokenOwners;

    // Mapping from token ID to approved address
    mapping (uint256 => address) private _tokenApprovals;

    // Mapping from owner to operator approvals
    mapping (address => mapping (address => bool)) private _operatorApprovals;

    // Token name
    string private _name;

    // Token symbol
    string private _symbol;

    // Optional mapping for token URIs
    mapping (uint256 => string) private _tokenURIs;

    // Base URI
    string private _baseURI;

    /*
     *     bytes4(keccak256('balanceOf(address)')) == 0x70a08231
     *     bytes4(keccak256('ownerOf(uint256)')) == 0x6352211e
     *     bytes4(keccak256('approve(address,uint256)')) == 0x095ea7b3
     *     bytes4(keccak256('getApproved(uint256)')) == 0x081812fc
     *     bytes4(keccak256('setApprovalForAll(address,bool)')) == 0xa22cb465
     *     bytes4(keccak256('isApprovedForAll(address,address)')) == 0xe985e9c5
     *     bytes4(keccak256('transferFrom(address,address,uint256)')) == 0x23b872dd
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256)')) == 0x42842e0e
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256,bytes)')) == 0xb88d4fde
     *
     *     => 0x70a08231 ^ 0x6352211e ^ 0x095ea7b3 ^ 0x081812fc ^
     *        0xa22cb465 ^ 0xe985e9c5 ^ 0x23b872dd ^ 0x42842e0e ^ 0xb88d4fde == 0x80ac58cd
     */
    bytes4 private constant _INTERFACE_ID_ERC721 = 0x80ac58cd;

    /*
     *     bytes4(keccak256('name()')) == 0x06fdde03
     *     bytes4(keccak256('symbol()')) == 0x95d89b41
     *     bytes4(keccak256('tokenURI(uint256)')) == 0xc87b56dd
     *
     *     => 0x06fdde03 ^ 0x95d89b41 ^ 0xc87b56dd == 0x5b5e139f
     */
    bytes4 private constant _INTERFACE_ID_ERC721_METADATA = 0x5b5e139f;

    /*
     *     bytes4(keccak256('totalSupply()')) == 0x18160ddd
     *     bytes4(keccak256('tokenOfOwnerByIndex(address,uint256)')) == 0x2f745c59
     *     bytes4(keccak256('tokenByIndex(uint256)')) == 0x4f6ccce7
     *
     *     => 0x18160ddd ^ 0x2f745c59 ^ 0x4f6ccce7 == 0x780e9d63
     */
    bytes4 private constant _INTERFACE_ID_ERC721_ENUMERABLE = 0x780e9d63;

    /**
     * @dev Initializes the contract by setting a `name` and a `symbol` to the token collection.
     */
    constructor (string memory name_, string memory symbol_) public {
        _name = name_;
        _symbol = symbol_;

        // register the supported interfaces to conform to ERC721 via ERC165
        _registerInterface(_INTERFACE_ID_ERC721);
        _registerInterface(_INTERFACE_ID_ERC721_METADATA);
        _registerInterface(_INTERFACE_ID_ERC721_ENUMERABLE);
    }

    /**
     * @dev See {IERC721-balanceOf}.
     */
    function balanceOf(address owner) public view virtual override returns (uint256) {
        require(owner != address(0), "ERC721: balance query for the zero address");
        return _holderTokens[owner].length();
    }

    /**
     * @dev See {IERC721-ownerOf}.
     */
    function ownerOf(uint256 tokenId) public view virtual override returns (address) {
        return _tokenOwners.get(tokenId, "ERC721: owner query for nonexistent token");
    }

    /**
     * @dev See {IERC721Metadata-name}.
     */
    function name() public view virtual override returns (string memory) {
        return _name;
    }

    /**
     * @dev See {IERC721Metadata-symbol}.
     */
    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev See {IERC721Metadata-tokenURI}.
     */
    function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
        require(_exists(tokenId), "ERC721Metadata: URI query for nonexistent token");

        string memory _tokenURI = _tokenURIs[tokenId];
        string memory base = baseURI();

        // If there is no base URI, return the token URI.
        if (bytes(base).length == 0) {
            return _tokenURI;
        }
        // If both are set, concatenate the baseURI and tokenURI (via abi.encodePacked).
        if (bytes(_tokenURI).length > 0) {
            return string(abi.encodePacked(base, _tokenURI));
        }
        // If there is a baseURI but no tokenURI, concatenate the tokenID to the baseURI.
        return string(abi.encodePacked(base, tokenId.toString()));
    }

    /**
    * @dev Returns the base URI set via {_setBaseURI}. This will be
    * automatically added as a prefix in {tokenURI} to each token's URI, or
    * to the token ID if no specific URI is set for that token ID.
    */
    function baseURI() public view virtual returns (string memory) {
        return _baseURI;
    }

    /**
     * @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) public view virtual override returns (uint256) {
        return _holderTokens[owner].at(index);
    }

    /**
     * @dev See {IERC721Enumerable-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        // _tokenOwners are indexed by tokenIds, so .length() returns the number of tokenIds
        return _tokenOwners.length();
    }

    /**
     * @dev See {IERC721Enumerable-tokenByIndex}.
     */
    function tokenByIndex(uint256 index) public view virtual override returns (uint256) {
        (uint256 tokenId, ) = _tokenOwners.at(index);
        return tokenId;
    }

    /**
     * @dev See {IERC721-approve}.
     */
    function approve(address to, uint256 tokenId) public virtual override {
        address owner = ERC721.ownerOf(tokenId);
        require(to != owner, "ERC721: approval to current owner");

        require(_msgSender() == owner || ERC721.isApprovedForAll(owner, _msgSender()),
            "ERC721: approve caller is not owner nor approved for all"
        );

        _approve(to, tokenId);
    }

    /**
     * @dev See {IERC721-getApproved}.
     */
    function getApproved(uint256 tokenId) public view virtual override returns (address) {
        require(_exists(tokenId), "ERC721: approved query for nonexistent token");

        return _tokenApprovals[tokenId];
    }

    /**
     * @dev See {IERC721-setApprovalForAll}.
     */
    function setApprovalForAll(address operator, bool approved) public virtual override {
        require(operator != _msgSender(), "ERC721: approve to caller");

        _operatorApprovals[_msgSender()][operator] = approved;
        emit ApprovalForAll(_msgSender(), operator, approved);
    }

    /**
     * @dev See {IERC721-isApprovedForAll}.
     */
    function isApprovedForAll(address owner, address operator) public view virtual override returns (bool) {
        return _operatorApprovals[owner][operator];
    }

    /**
     * @dev See {IERC721-transferFrom}.
     */
    function transferFrom(address from, address to, uint256 tokenId) public virtual override {
        //solhint-disable-next-line max-line-length
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");

        _transfer(from, to, tokenId);
    }

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(address from, address to, uint256 tokenId) public virtual override {
        safeTransferFrom(from, to, tokenId, "");
    }

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public virtual override {
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");
        _safeTransfer(from, to, tokenId, _data);
    }

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
     * are aware of the ERC721 protocol to prevent tokens from being forever locked.
     *
     * `_data` is additional data, it has no specified format and it is sent in call to `to`.
     *
     * This internal function is equivalent to {safeTransferFrom}, and can be used to e.g.
     * implement alternative mechanisms to perform token transfer, such as signature-based.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function _safeTransfer(address from, address to, uint256 tokenId, bytes memory _data) internal virtual {
        _transfer(from, to, tokenId);
        require(_checkOnERC721Received(from, to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");
    }

    /**
     * @dev Returns whether `tokenId` exists.
     *
     * Tokens can be managed by their owner or approved accounts via {approve} or {setApprovalForAll}.
     *
     * Tokens start existing when they are minted (`_mint`),
     * and stop existing when they are burned (`_burn`).
     */
    function _exists(uint256 tokenId) internal view virtual returns (bool) {
        return _tokenOwners.contains(tokenId);
    }

    /**
     * @dev Returns whether `spender` is allowed to manage `tokenId`.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function _isApprovedOrOwner(address spender, uint256 tokenId) internal view virtual returns (bool) {
        require(_exists(tokenId), "ERC721: operator query for nonexistent token");
        address owner = ERC721.ownerOf(tokenId);
        return (spender == owner || getApproved(tokenId) == spender || ERC721.isApprovedForAll(owner, spender));
    }

    /**
     * @dev Safely mints `tokenId` and transfers it to `to`.
     *
     * Requirements:
     d*
     * - `tokenId` must not exist.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function _safeMint(address to, uint256 tokenId) internal virtual {
        _safeMint(to, tokenId, "");
    }

    /**
     * @dev Same as {xref-ERC721-_safeMint-address-uint256-}[`_safeMint`], with an additional `data` parameter which is
     * forwarded in {IERC721Receiver-onERC721Received} to contract recipients.
     */
    function _safeMint(address to, uint256 tokenId, bytes memory _data) internal virtual {
        _mint(to, tokenId);
        require(_checkOnERC721Received(address(0), to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");
    }

    /**
     * @dev Mints `tokenId` and transfers it to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {_safeMint} whenever possible
     *
     * Requirements:
     *
     * - `tokenId` must not exist.
     * - `to` cannot be the zero address.
     *
     * Emits a {Transfer} event.
     */
    function _mint(address to, uint256 tokenId) internal virtual {
        require(to != address(0), "ERC721: mint to the zero address");
        require(!_exists(tokenId), "ERC721: token already minted");

        _beforeTokenTransfer(address(0), to, tokenId);

        _holderTokens[to].add(tokenId);

        _tokenOwners.set(tokenId, to);

        emit Transfer(address(0), to, tokenId);
    }

    /**
     * @dev Destroys `tokenId`.
     * The approval is cleared when the token is burned.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     *
     * Emits a {Transfer} event.
     */
    function _burn(uint256 tokenId) internal virtual {
        address owner = ERC721.ownerOf(tokenId); // internal owner

        _beforeTokenTransfer(owner, address(0), tokenId);

        // Clear approvals
        _approve(address(0), tokenId);

        // Clear metadata (if any)
        if (bytes(_tokenURIs[tokenId]).length != 0) {
            delete _tokenURIs[tokenId];
        }

        _holderTokens[owner].remove(tokenId);

        _tokenOwners.remove(tokenId);

        emit Transfer(owner, address(0), tokenId);
    }

    /**
     * @dev Transfers `tokenId` from `from` to `to`.
     *  As opposed to {transferFrom}, this imposes no restrictions on msg.sender.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     *
     * Emits a {Transfer} event.
     */
    function _transfer(address from, address to, uint256 tokenId) internal virtual {
        require(ERC721.ownerOf(tokenId) == from, "ERC721: transfer of token that is not own"); // internal owner
        require(to != address(0), "ERC721: transfer to the zero address");

        _beforeTokenTransfer(from, to, tokenId);

        // Clear approvals from the previous owner
        _approve(address(0), tokenId);

        _holderTokens[from].remove(tokenId);
        _holderTokens[to].add(tokenId);

        _tokenOwners.set(tokenId, to);

        emit Transfer(from, to, tokenId);
    }

    /**
     * @dev Sets `_tokenURI` as the tokenURI of `tokenId`.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function _setTokenURI(uint256 tokenId, string memory _tokenURI) internal virtual {
        require(_exists(tokenId), "ERC721Metadata: URI set of nonexistent token");
        _tokenURIs[tokenId] = _tokenURI;
    }

    /**
     * @dev Internal function to set the base URI for all token IDs. It is
     * automatically added as a prefix to the value returned in {tokenURI},
     * or to the token ID if {tokenURI} is empty.
     */
    function _setBaseURI(string memory baseURI_) internal virtual {
        _baseURI = baseURI_;
    }

    /**
     * @dev Internal function to invoke {IERC721Receiver-onERC721Received} on a target address.
     * The call is not executed if the target address is not a contract.
     *
     * @param from address representing the previous owner of the given token ID
     * @param to target address that will receive the tokens
     * @param tokenId uint256 ID of the token to be transferred
     * @param _data bytes optional data to send along with the call
     * @return bool whether the call correctly returned the expected magic value
     */
    function _checkOnERC721Received(address from, address to, uint256 tokenId, bytes memory _data)
        private returns (bool)
    {
        if (!to.isContract()) {
            return true;
        }
        bytes memory returndata = to.functionCall(abi.encodeWithSelector(
            IERC721Receiver(to).onERC721Received.selector,
            _msgSender(),
            from,
            tokenId,
            _data
        ), "ERC721: transfer to non ERC721Receiver implementer");
        bytes4 retval = abi.decode(returndata, (bytes4));
        return (retval == _ERC721_RECEIVED);
    }

    function _approve(address to, uint256 tokenId) private {
        _tokenApprovals[tokenId] = to;
        emit Approval(ERC721.ownerOf(tokenId), to, tokenId); // internal owner
    }

    /**
     * @dev Hook that is called before any token transfer. This includes minting
     * and burning.
     *
     * Calling conditions:
     *
     * - When `from` and `to` are both non-zero, ``from``'s `tokenId` will be
     * transferred to `to`.
     * - When `from` is zero, `tokenId` will be minted for `to`.
     * - When `to` is zero, ``from``'s `tokenId` will be burned.
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal virtual { }
}

// File: @openzeppelin/contracts/token/ERC721/IERC721Metadata.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

import "./IERC721.sol";

/**
 * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Metadata is IERC721 {

    /**
     * @dev Returns the token collection name.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the token collection symbol.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the Uniform Resource Identifier (URI) for `tokenId` token.
     */
    function tokenURI(uint256 tokenId) external view returns (string memory);
}

// File: @openzeppelin/contracts/token/ERC721/IERC721Enumerable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

import "./IERC721.sol";

/**
 * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Enumerable is IERC721 {

    /**
     * @dev Returns the total amount of tokens stored by the contract.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns a token ID owned by `owner` at a given `index` of its token list.
     * Use along with {balanceOf} to enumerate all of ``owner``'s tokens.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) external view returns (uint256 tokenId);

    /**
     * @dev Returns a token ID at a given `index` of all the tokens stored by the contract.
     * Use along with {totalSupply} to enumerate all tokens.
     */
    function tokenByIndex(uint256 index) external view returns (uint256);
}

// File: @openzeppelin/contracts/utils/EnumerableMap.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Library for managing an enumerable variant of Solidity's
 * https://solidity.readthedocs.io/en/latest/types.html#mapping-types[`mapping`]
 * type.
 *
 * Maps have the following properties:
 *
 * - Entries are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Entries are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableMap for EnumerableMap.UintToAddressMap;
 *
 *     // Declare a set state variable
 *     EnumerableMap.UintToAddressMap private myMap;
 * }
 * ```
 *
 * As of v3.0.0, only maps of type `uint256 -> address` (`UintToAddressMap`) are
 * supported.
 */
library EnumerableMap {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Map type with
    // bytes32 keys and values.
    // The Map implementation uses private functions, and user-facing
    // implementations (such as Uint256ToAddressMap) are just wrappers around
    // the underlying Map.
    // This means that we can only create new EnumerableMaps for types that fit
    // in bytes32.

    struct MapEntry {
        bytes32 _key;
        bytes32 _value;
    }

    struct Map {
        // Storage of map keys and values
        MapEntry[] _entries;

        // Position of the entry defined by a key in the `entries` array, plus 1
        // because index 0 means a key is not in the map.
        mapping (bytes32 => uint256) _indexes;
    }

    /**
     * @dev Adds a key-value pair to a map, or updates the value for an existing
     * key. O(1).
     *
     * Returns true if the key was added to the map, that is if it was not
     * already present.
     */
    function _set(Map storage map, bytes32 key, bytes32 value) private returns (bool) {
        // We read and store the key's index to prevent multiple reads from the same storage slot
        uint256 keyIndex = map._indexes[key];

        if (keyIndex == 0) { // Equivalent to !contains(map, key)
            map._entries.push(MapEntry({ _key: key, _value: value }));
            // The entry is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            map._indexes[key] = map._entries.length;
            return true;
        } else {
            map._entries[keyIndex - 1]._value = value;
            return false;
        }
    }

    /**
     * @dev Removes a key-value pair from a map. O(1).
     *
     * Returns true if the key was removed from the map, that is if it was present.
     */
    function _remove(Map storage map, bytes32 key) private returns (bool) {
        // We read and store the key's index to prevent multiple reads from the same storage slot
        uint256 keyIndex = map._indexes[key];

        if (keyIndex != 0) { // Equivalent to contains(map, key)
            // To delete a key-value pair from the _entries array in O(1), we swap the entry to delete with the last one
            // in the array, and then remove the last entry (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = keyIndex - 1;
            uint256 lastIndex = map._entries.length - 1;

            // When the entry to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            MapEntry storage lastEntry = map._entries[lastIndex];

            // Move the last entry to the index where the entry to delete is
            map._entries[toDeleteIndex] = lastEntry;
            // Update the index for the moved entry
            map._indexes[lastEntry._key] = toDeleteIndex + 1; // All indexes are 1-based

            // Delete the slot where the moved entry was stored
            map._entries.pop();

            // Delete the index for the deleted slot
            delete map._indexes[key];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the key is in the map. O(1).
     */
    function _contains(Map storage map, bytes32 key) private view returns (bool) {
        return map._indexes[key] != 0;
    }

    /**
     * @dev Returns the number of key-value pairs in the map. O(1).
     */
    function _length(Map storage map) private view returns (uint256) {
        return map._entries.length;
    }

   /**
    * @dev Returns the key-value pair stored at position `index` in the map. O(1).
    *
    * Note that there are no guarantees on the ordering of entries inside the
    * array, and it may change when more entries are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function _at(Map storage map, uint256 index) private view returns (bytes32, bytes32) {
        require(map._entries.length > index, "EnumerableMap: index out of bounds");

        MapEntry storage entry = map._entries[index];
        return (entry._key, entry._value);
    }

    /**
     * @dev Tries to returns the value associated with `key`.  O(1).
     * Does not revert if `key` is not in the map.
     */
    function _tryGet(Map storage map, bytes32 key) private view returns (bool, bytes32) {
        uint256 keyIndex = map._indexes[key];
        if (keyIndex == 0) return (false, 0); // Equivalent to contains(map, key)
        return (true, map._entries[keyIndex - 1]._value); // All indexes are 1-based
    }

    /**
     * @dev Returns the value associated with `key`.  O(1).
     *
     * Requirements:
     *
     * - `key` must be in the map.
     */
    function _get(Map storage map, bytes32 key) private view returns (bytes32) {
        uint256 keyIndex = map._indexes[key];
        require(keyIndex != 0, "EnumerableMap: nonexistent key"); // Equivalent to contains(map, key)
        return map._entries[keyIndex - 1]._value; // All indexes are 1-based
    }

    /**
     * @dev Same as {_get}, with a custom error message when `key` is not in the map.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {_tryGet}.
     */
    function _get(Map storage map, bytes32 key, string memory errorMessage) private view returns (bytes32) {
        uint256 keyIndex = map._indexes[key];
        require(keyIndex != 0, errorMessage); // Equivalent to contains(map, key)
        return map._entries[keyIndex - 1]._value; // All indexes are 1-based
    }

    // UintToAddressMap

    struct UintToAddressMap {
        Map _inner;
    }

    /**
     * @dev Adds a key-value pair to a map, or updates the value for an existing
     * key. O(1).
     *
     * Returns true if the key was added to the map, that is if it was not
     * already present.
     */
    function set(UintToAddressMap storage map, uint256 key, address value) internal returns (bool) {
        return _set(map._inner, bytes32(key), bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the key was removed from the map, that is if it was present.
     */
    function remove(UintToAddressMap storage map, uint256 key) internal returns (bool) {
        return _remove(map._inner, bytes32(key));
    }

    /**
     * @dev Returns true if the key is in the map. O(1).
     */
    function contains(UintToAddressMap storage map, uint256 key) internal view returns (bool) {
        return _contains(map._inner, bytes32(key));
    }

    /**
     * @dev Returns the number of elements in the map. O(1).
     */
    function length(UintToAddressMap storage map) internal view returns (uint256) {
        return _length(map._inner);
    }

   /**
    * @dev Returns the element stored at position `index` in the set. O(1).
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(UintToAddressMap storage map, uint256 index) internal view returns (uint256, address) {
        (bytes32 key, bytes32 value) = _at(map._inner, index);
        return (uint256(key), address(uint160(uint256(value))));
    }

    /**
     * @dev Tries to returns the value associated with `key`.  O(1).
     * Does not revert if `key` is not in the map.
     *
     * _Available since v3.4._
     */
    function tryGet(UintToAddressMap storage map, uint256 key) internal view returns (bool, address) {
        (bool success, bytes32 value) = _tryGet(map._inner, bytes32(key));
        return (success, address(uint160(uint256(value))));
    }

    /**
     * @dev Returns the value associated with `key`.  O(1).
     *
     * Requirements:
     *
     * - `key` must be in the map.
     */
    function get(UintToAddressMap storage map, uint256 key) internal view returns (address) {
        return address(uint160(uint256(_get(map._inner, bytes32(key)))));
    }

    /**
     * @dev Same as {get}, with a custom error message when `key` is not in the map.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryGet}.
     */
    function get(UintToAddressMap storage map, uint256 key, string memory errorMessage) internal view returns (address) {
        return address(uint160(uint256(_get(map._inner, bytes32(key), errorMessage))));
    }
}

// File: @openzeppelin/contracts/utils/Strings.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev String operations.
 */
library Strings {
    /**
     * @dev Converts a `uint256` to its ASCII `string` representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        uint256 index = digits - 1;
        temp = value;
        while (temp != 0) {
            buffer[index--] = bytes1(uint8(48 + temp % 10));
            temp /= 10;
        }
        return string(buffer);
    }
}

// File: @openzeppelin/contracts/token/ERC721/ERC721Burnable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../utils/Context.sol";
import "./ERC721.sol";

/**
 * @title ERC721 Burnable Token
 * @dev ERC721 Token that can be irreversibly burned (destroyed).
 */
abstract contract ERC721Burnable is Context, ERC721 {
    /**
     * @dev Burns `tokenId`. See {ERC721-_burn}.
     *
     * Requirements:
     *
     * - The caller must own `tokenId` or be an approved operator.
     */
    function burn(uint256 tokenId) public virtual {
        //solhint-disable-next-line max-line-length
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721Burnable: caller is not owner nor approved");
        _burn(tokenId);
    }
}

// File: @openzeppelin/contracts/presets/ERC721PresetMinterPauserAutoId.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../access/AccessControl.sol";
import "../utils/Context.sol";
import "../utils/Counters.sol";
import "../token/ERC721/ERC721.sol";
import "../token/ERC721/ERC721Burnable.sol";
import "../token/ERC721/ERC721Pausable.sol";

/**
 * @dev {ERC721} token, including:
 *
 *  - ability for holders to burn (destroy) their tokens
 *  - a minter role that allows for token minting (creation)
 *  - a pauser role that allows to stop all token transfers
 *  - token ID and URI autogeneration
 *
 * This contract uses {AccessControl} to lock permissioned functions using the
 * different roles - head to its documentation for details.
 *
 * The account that deploys the contract will be granted the minter and pauser
 * roles, as well as the default admin role, which will let it grant both minter
 * and pauser roles to other accounts.
 */
contract ERC721PresetMinterPauserAutoId is Context, AccessControl, ERC721Burnable, ERC721Pausable {
    using Counters for Counters.Counter;

    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
    bytes32 public constant PAUSER_ROLE = keccak256("PAUSER_ROLE");

    Counters.Counter private _tokenIdTracker;

    /**
     * @dev Grants `DEFAULT_ADMIN_ROLE`, `MINTER_ROLE` and `PAUSER_ROLE` to the
     * account that deploys the contract.
     *
     * Token URIs will be autogenerated based on `baseURI` and their token IDs.
     * See {ERC721-tokenURI}.
     */
    constructor(string memory name, string memory symbol, string memory baseURI) public ERC721(name, symbol) {
        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());

        _setupRole(MINTER_ROLE, _msgSender());
        _setupRole(PAUSER_ROLE, _msgSender());

        _setBaseURI(baseURI);
    }

    /**
     * @dev Creates a new token for `to`. Its token ID will be automatically
     * assigned (and available on the emitted {IERC721-Transfer} event), and the token
     * URI autogenerated based on the base URI passed at construction.
     *
     * See {ERC721-_mint}.
     *
     * Requirements:
     *
     * - the caller must have the `MINTER_ROLE`.
     */
    function mint(address to) public virtual {
        require(hasRole(MINTER_ROLE, _msgSender()), "ERC721PresetMinterPauserAutoId: must have minter role to mint");

        // We cannot just use balanceOf to create the new tokenId because tokens
        // can be burned (destroyed), so we need a separate counter.
        _mint(to, _tokenIdTracker.current());
        _tokenIdTracker.increment();
    }

    /**
     * @dev Pauses all token transfers.
     *
     * See {ERC721Pausable} and {Pausable-_pause}.
     *
     * Requirements:
     *
     * - the caller must have the `PAUSER_ROLE`.
     */
    function pause() public virtual {
        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC721PresetMinterPauserAutoId: must have pauser role to pause");
        _pause();
    }

    /**
     * @dev Unpauses all token transfers.
     *
     * See {ERC721Pausable} and {Pausable-_unpause}.
     *
     * Requirements:
     *
     * - the caller must have the `PAUSER_ROLE`.
     */
    function unpause() public virtual {
        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC721PresetMinterPauserAutoId: must have pauser role to unpause");
        _unpause();
    }

    function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal virtual override(ERC721, ERC721Pausable) {
        super._beforeTokenTransfer(from, to, tokenId);
    }
}

// File: @openzeppelin/contracts/access/AccessControl.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../utils/EnumerableSet.sol";
import "../utils/Address.sol";
import "../utils/Context.sol";

/**
 * @dev Contract module that allows children to implement role-based access
 * control mechanisms.
 *
 * Roles are referred to by their `bytes32` identifier. These should be exposed
 * in the external API and be unique. The best way to achieve this is by
 * using `public constant` hash digests:
 *
 * ```
 * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
 * ```
 *
 * Roles can be used to represent a set of permissions. To restrict access to a
 * function call, use {hasRole}:
 *
 * ```
 * function foo() public {
 *     require(hasRole(MY_ROLE, msg.sender));
 *     ...
 * }
 * ```
 *
 * Roles can be granted and revoked dynamically via the {grantRole} and
 * {revokeRole} functions. Each role has an associated admin role, and only
 * accounts that have a role's admin role can call {grantRole} and {revokeRole}.
 *
 * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
 * that only accounts with this role will be able to grant or revoke other
 * roles. More complex role relationships can be created by using
 * {_setRoleAdmin}.
 *
 * WARNING: The `DEFAULT_ADMIN_ROLE` is also its own admin: it has permission to
 * grant and revoke this role. Extra precautions should be taken to secure
 * accounts that have been granted it.
 */
abstract contract AccessControl is Context {
    using EnumerableSet for EnumerableSet.AddressSet;
    using Address for address;

    struct RoleData {
        EnumerableSet.AddressSet members;
        bytes32 adminRole;
    }

    mapping (bytes32 => RoleData) private _roles;

    bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;

    /**
     * @dev Emitted when `newAdminRole` is set as ``role``'s admin role, replacing `previousAdminRole`
     *
     * `DEFAULT_ADMIN_ROLE` is the starting admin for all roles, despite
     * {RoleAdminChanged} not being emitted signaling this.
     *
     * _Available since v3.1._
     */
    event RoleAdminChanged(bytes32 indexed role, bytes32 indexed previousAdminRole, bytes32 indexed newAdminRole);

    /**
     * @dev Emitted when `account` is granted `role`.
     *
     * `sender` is the account that originated the contract call, an admin role
     * bearer except when using {_setupRole}.
     */
    event RoleGranted(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Emitted when `account` is revoked `role`.
     *
     * `sender` is the account that originated the contract call:
     *   - if using `revokeRole`, it is the admin role bearer
     *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
     */
    event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) public view returns (bool) {
        return _roles[role].members.contains(account);
    }

    /**
     * @dev Returns the number of accounts that have `role`. Can be used
     * together with {getRoleMember} to enumerate all bearers of a role.
     */
    function getRoleMemberCount(bytes32 role) public view returns (uint256) {
        return _roles[role].members.length();
    }

    /**
     * @dev Returns one of the accounts that have `role`. `index` must be a
     * value between 0 and {getRoleMemberCount}, non-inclusive.
     *
     * Role bearers are not sorted in any particular way, and their ordering may
     * change at any point.
     *
     * WARNING: When using {getRoleMember} and {getRoleMemberCount}, make sure
     * you perform all queries on the same block. See the following
     * https://forum.openzeppelin.com/t/iterating-over-elements-on-enumerableset-in-openzeppelin-contracts/2296[forum post]
     * for more information.
     */
    function getRoleMember(bytes32 role, uint256 index) public view returns (address) {
        return _roles[role].members.at(index);
    }

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) public view returns (bytes32) {
        return _roles[role].adminRole;
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function grantRole(bytes32 role, address account) public virtual {
        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to grant");

        _grantRole(role, account);
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function revokeRole(bytes32 role, address account) public virtual {
        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to revoke");

        _revokeRole(role, account);
    }

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been granted `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     */
    function renounceRole(bytes32 role, address account) public virtual {
        require(account == _msgSender(), "AccessControl: can only renounce roles for self");

        _revokeRole(role, account);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event. Note that unlike {grantRole}, this function doesn't perform any
     * checks on the calling account.
     *
     * [WARNING]
     * ====
     * This function should only be called from the constructor when setting
     * up the initial roles for the system.
     *
     * Using this function in any other way is effectively circumventing the admin
     * system imposed by {AccessControl}.
     * ====
     */
    function _setupRole(bytes32 role, address account) internal virtual {
        _grantRole(role, account);
    }

    /**
     * @dev Sets `adminRole` as ``role``'s admin role.
     *
     * Emits a {RoleAdminChanged} event.
     */
    function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
        emit RoleAdminChanged(role, _roles[role].adminRole, adminRole);
        _roles[role].adminRole = adminRole;
    }

    function _grantRole(bytes32 role, address account) private {
        if (_roles[role].members.add(account)) {
            emit RoleGranted(role, account, _msgSender());
        }
    }

    function _revokeRole(bytes32 role, address account) private {
        if (_roles[role].members.remove(account)) {
            emit RoleRevoked(role, account, _msgSender());
        }
    }
}

// File: @openzeppelin/contracts/utils/Counters.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../math/SafeMath.sol";

/**
 * @title Counters
 * @author Matt Condon (@shrugs)
 * @dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number
 * of elements in a mapping, issuing ERC721 ids, or counting request ids.
 *
 * Include with `using Counters for Counters.Counter;`
 * Since it is not possible to overflow a 256 bit integer with increments of one, `increment` can skip the {SafeMath}
 * overflow check, thereby saving gas. This does assume however correct usage, in that the underlying `_value` is never
 * directly accessed.
 */
library Counters {
    using SafeMath for uint256;

    struct Counter {
        // This variable should never be directly accessed by users of the library: interactions must be restricted to
        // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
        // this feature: see https://github.com/ethereum/solidity/issues/4637
        uint256 _value; // default: 0
    }

    function current(Counter storage counter) internal view returns (uint256) {
        return counter._value;
    }

    function increment(Counter storage counter) internal {
        // The {SafeMath} overflow check can be skipped here, see the comment at the top
        counter._value += 1;
    }

    function decrement(Counter storage counter) internal {
        counter._value = counter._value.sub(1);
    }
}

// File: contracts/VNFTGov.sol



pragma solidity ^0.6.0;

interface IVNFT {
    function balanceOf(address owner) external view returns (uint256 balance);

    function tokenOfOwnerByIndex(address owner, uint256 index)
        external
        view
        returns (uint256 id);

    function vnftScore(uint256 _tokenId) external view returns (uint256 _score);

    function timeVnftBorn(uint256 _tokenId)
        external
        view
        returns (uint256 _born);
}

interface IVNFTx {
    function getHp(uint256 _tokenId) external view returns (uint256 _hp);
}

import "@openzeppelin/contracts/math/SafeMath.sol";

contract VNFTGov {
    using SafeMath for uint256;

    IVNFT vnft = IVNFT(0x57f0B53926dd62f2E26bc40B30140AbEA474DA94);
    IVNFTx vnftx = IVNFTx(0x14d4D06B8e8df9B85A37D622aA95784a4FCcB130);

    constructor() public {}

    function getVotes(address voter) public view returns (uint256) {
        uint256 balance = vnft.balanceOf(voter);
        uint256 votes = 0;
        for (uint256 index = 0; index < balance; index++) {
            uint256 pet = vnft.tokenOfOwnerByIndex(voter, index);
            uint256 hp = vnftx.getHp(pet);
            if (hp >= 90) {
                uint256 age = (now.sub(vnft.timeVnftBorn(pet))).div(1 weeks);
                uint256 score = vnft.vnftScore(pet);
                votes = votes.add((age.mul(score)));
            }
        }
        return (votes);
    }
}

// File: contracts/Vesting.sol



pragma solidity ^0.6.0;

import "../interfaces/IMuse.sol";
import "@openzeppelin/contracts/math/SafeMath.sol";

contract Vesting {
    using SafeMath for uint256;

    IMuse public token;

    uint256 public duration = 365;
    uint256 public timeStarted;

    address public dao = 0x0f4676178b5c53Ae0a655f1B19A96387E4b8B5f2;
    address public a = 0x230A9678009e797a8ea77D449a18C28A25b363dd;
    address public b = 0x889551682afc348e298Cf1BbB2D981592409C9D0;
    uint256 public paid;
    mapping(address => uint256) public shouldGet;

    address owner;

    constructor(address _token) public {
        timeStarted = now;
        token = IMuse(_token);
        owner = msg.sender;
        shouldGet[dao] = 100000 * 10**18;
    }

    // only daves wallet can cashout this vested allocation as it's for dao and daves.
    function claimVestedTokens() external {
        require(owner == msg.sender, "!forbidden");
        require(shouldGet[dao] >= paid, "Finished vesting");
        uint256 _amount = getAllocation();

        if (paid + _amount >= 100000 * 10**18) {
            // Case where we didnd withdraw all but passed the 1 year
            _amount = 100000 * 10**18 - paid;
        }
        paid += _amount;

        uint256 eachShares = _amount.div(2);

        token.mint(a, eachShares);
        token.mint(b, eachShares);
        // send vest to contract wallet for future dao
        token.mint(dao, _amount);
    }

    //@TODO check my math
    function getAllocation() public view returns (uint256) {
        uint256 perDay = shouldGet[dao].div(duration);
        uint256 daysPassed = (now.sub(timeStarted)).div(1 days);
        uint256 amount = (daysPassed.mul(perDay)).sub(paid);
        return amount;
    }
}

// File: interfaces/IMuse.sol



pragma solidity ^0.6.0;

// Interface for our erc20 token
interface IMuse {
    function totalSupply() external view returns (uint256);

    function balanceOf(address tokenOwner)
        external
        view
        returns (uint256 balance);

    function allowance(address tokenOwner, address spender)
        external
        view
        returns (uint256 remaining);

    function transfer(address to, uint256 tokens)
        external
        returns (bool success);

    function approve(address spender, uint256 tokens)
        external
        returns (bool success);

    function transferFrom(
        address from,
        address to,
        uint256 tokens
    ) external returns (bool success);

    function mintingFinished() external view returns (bool);

    function mint(address to, uint256 amount) external;

    function burn(uint256 amount) external;

    function burnFrom(address account, uint256 amount) external;
}

// File: contracts/MasterChef.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/token/ERC20/SafeERC20.sol";
import "@openzeppelin/contracts/utils/EnumerableSet.sol";
import "@openzeppelin/contracts/math/SafeMath.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "../interfaces/IMuse.sol";

contract MasterChef is Ownable {
    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    struct UserInfo {
        uint256 amount;
        uint256 rewardDebt;
    }

    struct PoolInfo {
        IERC20 lpToken;
        uint256 allocPoint;
        uint256 lastRewardBlock;
        uint256 accMusePerShare;
    }

    // The MUSE TOKEN!
    IMuse public muse;
    // Dev address.
    address public devaddr;
    // Block number when bonus MUSE period ends.
    uint256 public bonusEndBlock;
    // MUSE tokens created per block.
    uint256 public musePerBlock;
    // Bonus muliplier for early MUSE makers.
    uint256 public constant BONUS_MULTIPLIER = 10;

    // Info of each pool.
    PoolInfo[] public poolInfo;
    // Info of each user that stakes LP tokens.
    mapping(uint256 => mapping(address => UserInfo)) public userInfo;
    // Total allocation points. Must be the sum of all allocation points in all pools.
    uint256 public totalAllocPoint = 0;
    // The block number when MUSE mining starts.
    uint256 public startBlock;

    event Deposit(address indexed user, uint256 indexed pid, uint256 amount);
    event Withdraw(address indexed user, uint256 indexed pid, uint256 amount);
    event EmergencyWithdraw(
        address indexed user,
        uint256 indexed pid,
        uint256 amount
    );

    constructor(
        IMuse _muse,
        address _devaddr,
        uint256 _musePerBlock,
        uint256 _startBlock,
        uint256 _bonusEndBlock
    ) public {
        muse = _muse;
        devaddr = _devaddr;
        musePerBlock = _musePerBlock;
        bonusEndBlock = _bonusEndBlock;
        startBlock = _startBlock;
    }

    function poolLength() external view returns (uint256) {
        return poolInfo.length;
    }

    // Add a new lp to the pool. Can only be called by the owner.
    // XXX DO NOT add the same LP token more than once. Rewards will be messed up if you do.
    function add(
        uint256 _allocPoint,
        IERC20 _lpToken,
        bool _withUpdate
    ) public onlyOwner {
        if (_withUpdate) {
            massUpdatePools();
        }
        uint256 lastRewardBlock =
            block.number > startBlock ? block.number : startBlock;
        totalAllocPoint = totalAllocPoint.add(_allocPoint);
        poolInfo.push(
            PoolInfo({
                lpToken: _lpToken,
                allocPoint: _allocPoint,
                lastRewardBlock: lastRewardBlock,
                accMusePerShare: 0
            })
        );
    }

    // Update the given pool's MUSE allocation point. Can only be called by the owner.
    function set(
        uint256 _pid,
        uint256 _allocPoint,
        bool _withUpdate
    ) public onlyOwner {
        if (_withUpdate) {
            massUpdatePools();
        }
        totalAllocPoint = totalAllocPoint.sub(poolInfo[_pid].allocPoint).add(
            _allocPoint
        );
        poolInfo[_pid].allocPoint = _allocPoint;
    }

    // Return reward multiplier over the given _from to _to block.
    function getMultiplier(uint256 _from, uint256 _to)
        public
        view
        returns (uint256)
    {
        if (_to <= bonusEndBlock) {
            return _to.sub(_from).mul(BONUS_MULTIPLIER);
        } else if (_from >= bonusEndBlock) {
            return _to.sub(_from);
        } else {
            return
                bonusEndBlock.sub(_from).mul(BONUS_MULTIPLIER).add(
                    _to.sub(bonusEndBlock)
                );
        }
    }

    function pendingMuse(uint256 _pid, address _user)
        external
        view
        returns (uint256)
    {
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][_user];
        uint256 accMusePerShare = pool.accMusePerShare;
        uint256 lpSupply = pool.lpToken.balanceOf(address(this));
        if (block.number > pool.lastRewardBlock && lpSupply != 0) {
            uint256 multiplier =
                getMultiplier(pool.lastRewardBlock, block.number);
            uint256 museReward =
                multiplier.mul(musePerBlock).mul(pool.allocPoint).div(
                    totalAllocPoint
                );
            accMusePerShare = accMusePerShare.add(
                museReward.mul(1e12).div(lpSupply)
            );
        }
        return user.amount.mul(accMusePerShare).div(1e12).sub(user.rewardDebt);
    }

    function massUpdatePools() public {
        uint256 length = poolInfo.length;
        for (uint256 pid = 0; pid < length; ++pid) {
            updatePool(pid);
        }
    }

    function updatePool(uint256 _pid) public {
        PoolInfo storage pool = poolInfo[_pid];
        if (block.number <= pool.lastRewardBlock) {
            return;
        }
        uint256 lpSupply = pool.lpToken.balanceOf(address(this));
        if (lpSupply == 0) {
            pool.lastRewardBlock = block.number;
            return;
        }
        uint256 multiplier = getMultiplier(pool.lastRewardBlock, block.number);
        uint256 museReward =
            multiplier.mul(musePerBlock).mul(pool.allocPoint).div(
                totalAllocPoint
            );
        muse.mint(devaddr, museReward.div(10));
        muse.mint(address(this), museReward);
        pool.accMusePerShare = pool.accMusePerShare.add(
            museReward.mul(1e12).div(lpSupply)
        );
        pool.lastRewardBlock = block.number;
    }

    // Deposit LP tokens to MasterChef for MUSE allocation.
    function deposit(uint256 _pid, uint256 _amount) public {
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][msg.sender];
        updatePool(_pid);
        if (user.amount > 0) {
            uint256 pending =
                user.amount.mul(pool.accMusePerShare).div(1e12).sub(
                    user.rewardDebt
                );
            if (pending > 0) {
                safeMuseTransfer(msg.sender, pending);
            }
        }
        if (_amount > 0) {
            pool.lpToken.safeTransferFrom(
                address(msg.sender),
                address(this),
                _amount
            );
            user.amount = user.amount.add(_amount);
        }
        user.rewardDebt = user.amount.mul(pool.accMusePerShare).div(1e12);
        emit Deposit(msg.sender, _pid, _amount);
    }

    // Withdraw LP tokens from MasterChef.
    function withdraw(uint256 _pid, uint256 _amount) public {
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][msg.sender];
        require(user.amount >= _amount, "withdraw: not good");
        updatePool(_pid);
        uint256 pending =
            user.amount.mul(pool.accMusePerShare).div(1e12).sub(
                user.rewardDebt
            );
        if (pending > 0) {
            safeMuseTransfer(msg.sender, pending);
        }
        if (_amount > 0) {
            user.amount = user.amount.sub(_amount);
            pool.lpToken.safeTransfer(address(msg.sender), _amount);
        }
        user.rewardDebt = user.amount.mul(pool.accMusePerShare).div(1e12);
        emit Withdraw(msg.sender, _pid, _amount);
    }

    // Withdraw without caring about rewards. EMERGENCY ONLY.
    function emergencyWithdraw(uint256 _pid) public {
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][msg.sender];
        uint256 amount = user.amount;
        user.amount = 0;
        user.rewardDebt = 0;
        pool.lpToken.safeTransfer(address(msg.sender), amount);
        emit EmergencyWithdraw(msg.sender, _pid, amount);
    }

    function safeMuseTransfer(address _to, uint256 _amount) internal {
        uint256 museBal = muse.balanceOf(address(this));
        if (_amount > museBal) {
            muse.transfer(_to, museBal);
        } else {
            muse.transfer(_to, _amount);
        }
    }

    // Update dev address by the previous dev.
    function dev(address _devaddr) public {
        require(msg.sender == devaddr, "dev: wut?");
        devaddr = _devaddr;
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: @openzeppelin/contracts/token/ERC20/SafeERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./IERC20.sol";
import "../../math/SafeMath.sol";
import "../../utils/Address.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: contracts/UpgradeableBeacon.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "@openzeppelin/contracts/proxy/IBeacon.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/Address.sol";

/**
 * @dev This contract is used in conjunction with one or more instances of {BeaconProxy} to determine their
 * implementation contract, which is where they will delegate all function calls.
 *
 * An owner is able to change the implementation the beacon points to, thus upgrading the proxies that use this beacon.a
 */
contract UpgradeableBeacon is IBeacon, Ownable {
    address private _implementation;

    /**
     * @dev Emitted when the implementation returned by the beacon is changed.
     */
    event Upgraded(address indexed implementation);

    /**
     * @dev Sets the address of the initial implementation, and the deployer account as the owner who can upgrade the
     * beacon.
     */
    constructor(address implementation_) public {
        _setImplementation(implementation_);
    }

    /**
     * @dev Returns the current implementation address.
     */
    function implementation() public view virtual override returns (address) {
        return _implementation;
    }

    /**
     * @dev Upgrades the beacon to a new implementation.
     *
     * Emits an {Upgraded} event.
     *
     * Requirements:
     *
     * - msg.sender must be the owner of the contract.
     * - `newImplementation` must be a contract.
     */
    function upgradeTo(address newImplementation) public virtual onlyOwner {
        _setImplementation(newImplementation);
        emit Upgraded(newImplementation);
    }

    /**
     * @dev Sets the implementation contract address for this beacon
     *
     * Requirements:
     *
     * - `newImplementation` must be a contract.
     */
    function _setImplementation(address newImplementation) private {
        require(
            Address.isContract(newImplementation),
            "UpgradeableBeacon: implementation is not a contract"
        );
        _implementation = newImplementation;
    }
}

// File: @openzeppelin/contracts/proxy/IBeacon.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev This is the interface that {BeaconProxy} expects of its beacon.
 */
interface IBeacon {
    /**
     * @dev Must return an address that can be used as a delegate call target.
     *
     * {BeaconProxy} will check that this address is a contract.
     */
    function implementation() external view returns (address);
}

// File: @openzeppelin/contracts/presets/ERC1155PresetMinterPauser.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../access/AccessControl.sol";
import "../utils/Context.sol";
import "../token/ERC1155/ERC1155.sol";
import "../token/ERC1155/ERC1155Burnable.sol";
import "../token/ERC1155/ERC1155Pausable.sol";

/**
 * @dev {ERC1155} token, including:
 *
 *  - ability for holders to burn (destroy) their tokens
 *  - a minter role that allows for token minting (creation)
 *  - a pauser role that allows to stop all token transfers
 *
 * This contract uses {AccessControl} to lock permissioned functions using the
 * different roles - head to its documentation for details.
 *
 * The account that deploys the contract will be granted the minter and pauser
 * roles, as well as the default admin role, which will let it grant both minter
 * and pauser roles to other accounts.
 */
contract ERC1155PresetMinterPauser is Context, AccessControl, ERC1155Burnable, ERC1155Pausable {
    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
    bytes32 public constant PAUSER_ROLE = keccak256("PAUSER_ROLE");

    /**
     * @dev Grants `DEFAULT_ADMIN_ROLE`, `MINTER_ROLE`, and `PAUSER_ROLE` to the account that
     * deploys the contract.
     */
    constructor(string memory uri) public ERC1155(uri) {
        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());

        _setupRole(MINTER_ROLE, _msgSender());
        _setupRole(PAUSER_ROLE, _msgSender());
    }

    /**
     * @dev Creates `amount` new tokens for `to`, of token type `id`.
     *
     * See {ERC1155-_mint}.
     *
     * Requirements:
     *
     * - the caller must have the `MINTER_ROLE`.
     */
    function mint(address to, uint256 id, uint256 amount, bytes memory data) public virtual {
        require(hasRole(MINTER_ROLE, _msgSender()), "ERC1155PresetMinterPauser: must have minter role to mint");

        _mint(to, id, amount, data);
    }

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] variant of {mint}.
     */
    function mintBatch(address to, uint256[] memory ids, uint256[] memory amounts, bytes memory data) public virtual {
        require(hasRole(MINTER_ROLE, _msgSender()), "ERC1155PresetMinterPauser: must have minter role to mint");

        _mintBatch(to, ids, amounts, data);
    }

    /**
     * @dev Pauses all token transfers.
     *
     * See {ERC1155Pausable} and {Pausable-_pause}.
     *
     * Requirements:
     *
     * - the caller must have the `PAUSER_ROLE`.
     */
    function pause() public virtual {
        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC1155PresetMinterPauser: must have pauser role to pause");
        _pause();
    }

    /**
     * @dev Unpauses all token transfers.
     *
     * See {ERC1155Pausable} and {Pausable-_unpause}.
     *
     * Requirements:
     *
     * - the caller must have the `PAUSER_ROLE`.
     */
    function unpause() public virtual {
        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC1155PresetMinterPauser: must have pauser role to unpause");
        _unpause();
    }

    function _beforeTokenTransfer(
        address operator,
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    )
        internal virtual override(ERC1155, ERC1155Pausable)
    {
        super._beforeTokenTransfer(operator, from, to, ids, amounts, data);
    }
}

// File: @openzeppelin/contracts/token/ERC1155/ERC1155Burnable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./ERC1155.sol";

/**
 * @dev Extension of {ERC1155} that allows token holders to destroy both their
 * own tokens and those that they have been approved to use.
 *
 * _Available since v3.1._
 */
abstract contract ERC1155Burnable is ERC1155 {
    function burn(address account, uint256 id, uint256 value) public virtual {
        require(
            account == _msgSender() || isApprovedForAll(account, _msgSender()),
            "ERC1155: caller is not owner nor approved"
        );

        _burn(account, id, value);
    }

    function burnBatch(address account, uint256[] memory ids, uint256[] memory values) public virtual {
        require(
            account == _msgSender() || isApprovedForAll(account, _msgSender()),
            "ERC1155: caller is not owner nor approved"
        );

        _burnBatch(account, ids, values);
    }
}

// File: contracts/Test1155.sol



pragma solidity ^0.6.0;

import "@openzeppelin/contracts/presets/ERC1155PresetMinterPauser.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract Test1155 is ERC1155PresetMinterPauser, Ownable {
    constructor()
        public
        // start contract
        ERC1155PresetMinterPauser("https://ck.io/api/")
    {}

    function setBaseURI(string memory baseURI_) public onlyOwner {
        _setURI(baseURI_);
    }
}

// File: @openzeppelin/contracts/presets/ERC20PresetMinterPauser.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../access/AccessControl.sol";
import "../utils/Context.sol";
import "../token/ERC20/ERC20.sol";
import "../token/ERC20/ERC20Burnable.sol";
import "../token/ERC20/ERC20Pausable.sol";

/**
 * @dev {ERC20} token, including:
 *
 *  - ability for holders to burn (destroy) their tokens
 *  - a minter role that allows for token minting (creation)
 *  - a pauser role that allows to stop all token transfers
 *
 * This contract uses {AccessControl} to lock permissioned functions using the
 * different roles - head to its documentation for details.
 *
 * The account that deploys the contract will be granted the minter and pauser
 * roles, as well as the default admin role, which will let it grant both minter
 * and pauser roles to other accounts.
 */
contract ERC20PresetMinterPauser is Context, AccessControl, ERC20Burnable, ERC20Pausable {
    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
    bytes32 public constant PAUSER_ROLE = keccak256("PAUSER_ROLE");

    /**
     * @dev Grants `DEFAULT_ADMIN_ROLE`, `MINTER_ROLE` and `PAUSER_ROLE` to the
     * account that deploys the contract.
     *
     * See {ERC20-constructor}.
     */
    constructor(string memory name, string memory symbol) public ERC20(name, symbol) {
        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());

        _setupRole(MINTER_ROLE, _msgSender());
        _setupRole(PAUSER_ROLE, _msgSender());
    }

    /**
     * @dev Creates `amount` new tokens for `to`.
     *
     * See {ERC20-_mint}.
     *
     * Requirements:
     *
     * - the caller must have the `MINTER_ROLE`.
     */
    function mint(address to, uint256 amount) public virtual {
        require(hasRole(MINTER_ROLE, _msgSender()), "ERC20PresetMinterPauser: must have minter role to mint");
        _mint(to, amount);
    }

    /**
     * @dev Pauses all token transfers.
     *
     * See {ERC20Pausable} and {Pausable-_pause}.
     *
     * Requirements:
     *
     * - the caller must have the `PAUSER_ROLE`.
     */
    function pause() public virtual {
        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC20PresetMinterPauser: must have pauser role to pause");
        _pause();
    }

    /**
     * @dev Unpauses all token transfers.
     *
     * See {ERC20Pausable} and {Pausable-_unpause}.
     *
     * Requirements:
     *
     * - the caller must have the `PAUSER_ROLE`.
     */
    function unpause() public virtual {
        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC20PresetMinterPauser: must have pauser role to unpause");
        _unpause();
    }

    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual override(ERC20, ERC20Pausable) {
        super._beforeTokenTransfer(from, to, amount);
    }
}

// File: @openzeppelin/contracts/token/ERC20/ERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../utils/Context.sol";
import "./IERC20.sol";
import "../../math/SafeMath.sol";

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name_, string memory symbol_) public {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view virtual returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * Requirements:
     *
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal virtual {
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}

// File: @openzeppelin/contracts/token/ERC20/ERC20Burnable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../utils/Context.sol";
import "./ERC20.sol";

/**
 * @dev Extension of {ERC20} that allows token holders to destroy both their own
 * tokens and those that they have an allowance for, in a way that can be
 * recognized off-chain (via event analysis).
 */
abstract contract ERC20Burnable is Context, ERC20 {
    using SafeMath for uint256;

    /**
     * @dev Destroys `amount` tokens from the caller.
     *
     * See {ERC20-_burn}.
     */
    function burn(uint256 amount) public virtual {
        _burn(_msgSender(), amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, deducting from the caller's
     * allowance.
     *
     * See {ERC20-_burn} and {ERC20-allowance}.
     *
     * Requirements:
     *
     * - the caller must have allowance for ``accounts``'s tokens of at least
     * `amount`.
     */
    function burnFrom(address account, uint256 amount) public virtual {
        uint256 decreasedAllowance = allowance(account, _msgSender()).sub(amount, "ERC20: burn amount exceeds allowance");

        _approve(account, _msgSender(), decreasedAllowance);
        _burn(account, amount);
    }
}

// File: @openzeppelin/contracts/token/ERC20/ERC20Pausable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./ERC20.sol";
import "../../utils/Pausable.sol";

/**
 * @dev ERC20 token with pausable token transfers, minting and burning.
 *
 * Useful for scenarios such as preventing trades until the end of an evaluation
 * period, or having an emergency switch for freezing all token transfers in the
 * event of a large bug.
 */
abstract contract ERC20Pausable is ERC20, Pausable {
    /**
     * @dev See {ERC20-_beforeTokenTransfer}.
     *
     * Requirements:
     *
     * - the contract must not be paused.
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual override {
        super._beforeTokenTransfer(from, to, amount);

        require(!paused(), "ERC20Pausable: token transfer while paused");
    }
}

// File: contracts/ERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/math/SafeMath.sol";

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is  IERC20 {
    using SafeMath for uint256;

    mapping(address => uint256) private _balances;

    mapping(address => mapping(address => uint256)) private _allowances;

    uint256 public override totalSupply;

    string public name;
    string public symbol;
    uint8 public decimals;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor() public {}


    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount)
        public
        virtual
        override
        returns (bool)
    {
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender)
        public
        view
        virtual
        override
        returns (uint256)
    {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount)
        public
        virtual
        override
        returns (bool)
    {
        _approve(msg.sender, spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20};
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(
            sender,
            msg.sender,
            _allowances[sender][msg.sender].sub(
                amount,
                "ERC20: transfer amount exceeds allowance"
            )
        );
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue)
        public
        virtual
        returns (bool)
    {
        _approve(
            msg.sender,
            spender,
            _allowances[msg.sender][spender].add(addedValue)
        );
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue)
        public
        virtual
        returns (bool)
    {
        _approve(
            msg.sender,
            spender,
            _allowances[msg.sender][spender].sub(
                subtractedValue,
                "ERC20: decreased allowance below zero"
            )
        );
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(
        address sender,
        address recipient,
        uint256 amount
    ) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender].sub(
            amount,
            "ERC20: transfer amount exceeds balance"
        );
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        totalSupply = totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _balances[account] = _balances[account].sub(
            amount,
            "ERC20: burn amount exceeds balance"
        );
        totalSupply = totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {}

    // Added from import "@openzeppelin/contracts/token/ERC20/ERC20Burnable.sol";

    function burn(uint256 amount) public virtual {
        _burn(msg.sender, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, deducting from the caller's
     * allowance.
     *
     * See {ERC20-_burn} and {ERC20-allowance}.
     *
     * Requirements:
     *
     * - the caller must have allowance for ``accounts``'s tokens of at least
     * `amount`.
     */
    function burnFrom(address account, uint256 amount) public virtual {
        uint256 decreasedAllowance =
            allowance(account, msg.sender).sub(
                amount,
                "ERC20: burn amount exceeds allowance"
            );

        _approve(account, msg.sender, decreasedAllowance);
        _burn(account, amount);
    }
}

// File: contracts/NFT20.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/presets/ERC20PresetMinterPauser.sol";

contract NFT20 is ERC20PresetMinterPauser {
    // Cap at 1 million
    uint256 internal _cap = 1000000 * 10**18;

    constructor() public ERC20PresetMinterPauser("NFT20", "NFT20") {}

    /**
     * @dev Returns the cap on the token's total supply.
     */
    function cap() public view returns (uint256) {
        return _cap;
    }

    // change cap in case of decided by the community
    function changeCap(uint256 _newCap) external {
        require(
            hasRole(MINTER_ROLE, _msgSender()),
            "ERC20PresetMinterPauser: must have minter role to mint"
        );
        _cap = _newCap;
    }

    /**
     * @dev See {ERC20-_beforeTokenTransfer}.
     *
     * Requirements:
     *
     * - minted tokens must not cause the total supply to go over the cap.
     */
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual override(ERC20PresetMinterPauser) {
        super._beforeTokenTransfer(from, to, amount);

        if (from == address(0)) {
            // When minting tokens
            require(
                totalSupply().add(amount) <= _cap,
                "ERC20Capped: cap exceeded"
            );
        }
    }
}

// File: contracts/Test721.sol



pragma solidity ^0.6.0;

import "@openzeppelin/contracts/presets/ERC721PresetMinterPauserAutoId.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract Test721 is ERC721PresetMinterPauserAutoId, Ownable {
    constructor()
        public
        // start contract
        ERC721PresetMinterPauserAutoId("Land", "Land", "https://land.io/api/")
    {}

    // in case of need to change the URL of the api to get metadata
    function setBaseURI(string memory baseURI_) public onlyOwner {
        _setBaseURI(baseURI_);
    }
}

// File: contracts/NFT20Factory.sol



// pragma solidity ^0.6.0;

// import "@openzeppelin/contracts-upgradeable/proxy/Initializable.sol";

// import "@openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol";
// import "@openzeppelin/contracts-upgradeable/math/SafeMathUpgradeable.sol";
// import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

// import "./NFT20Pair.sol";
// // import "../interfaces/INFT20Pair.sol";
// interface INFT20Pair {


//  function setParams(
//         uint256 _nftType,
//         string calldata name,
//         string calldata symbol
//             ) external;

//     function getInfos()
//         external
//         view
//         returns (
//             uint256 _type,
//             string memory _name,
//             string memory _symbol,
//             uint256 _supply
//         );
// }

// contract NFT20Factory is Initializable, OwnableUpgradeable {
//     using SafeMathUpgradeable for uint256;

//     // keep track of nft address to pair address
//     mapping(address => address) public nftToToken;
//     mapping(uint256 => address) public indexToNft;

//     uint256 public counter;
//     uint256 public fee;

//     event pairCreated(
//         address indexed originalNFT,
//         address newPair,
//         uint256 _type
//     );

//     constructor() public {}

//     function initialize() public initializer {
//         OwnableUpgradeable.__Ownable_init();
//         fee = 5;
//     }

//     function nft20Pair(
//         string calldata name,
//         address _nftOrigin,
//         uint256 _nftType
//     ) external {
//         // if pair exists then throw.
//         require(
//             nftToToken[_nftOrigin] == address(0),
//             "A token for this NFT already exists"
//         );

//         NFT20Pair _nft20pair = new NFT20Pair();

//         _nft20pair.init(
//             string(abi.encodePacked("NFT20 ", name)),
//             string(abi.encodePacked(name, "20")),
//             _nftOrigin,
//             _nftType
//         );
//         nftToToken[_nftOrigin] = address(_nft20pair);
//         indexToNft[counter] = _nftOrigin;
//         counter = counter + 1;
//         emit pairCreated(_nftOrigin, address(_nft20pair), _nftType);
//     }

//     function getPairByNftAddress(uint256 index)
//         public
//         view
//         returns (
//             address _nft20pair,
//             address _originalNft,
//             uint256 _type,
//             string memory _name,
//             string memory _symbol,
//             uint256 _supply
//         )
//     {
//         _originalNft = indexToNft[index];
//         _nft20pair = nftToToken[_originalNft];
//         (_type, _name, _symbol, _supply) = INFT20Pair(_nft20pair).getInfos();
//     }

//     // this is to sset value in case we decided to change tokens given to a tokenizing project.
//     function setValue(
//         address _pair,
//         uint256 _nftType,
//         string calldata _name,
//         string calldata _symbol
//     ) external onlyOwner {
//         INFT20Pair(_pair).setParams(_nftType, _name, _symbol);
//     }

//     function setFee(uint256 _fee) external onlyOwner {
//         fee = _fee;
//     }

//     function recoverERC20(address tokenAddress, uint256 tokenAmount)
//         public
//         onlyOwner
//     {
//         IERC20(tokenAddress).transfer(owner(), tokenAmount);
//     }
// }

// File: contracts/NFT20FactoryV2.sol



// pragma solidity ^0.6.0;

// import "@openzeppelin/contracts-upgradeable/proxy/Initializable.sol";

// import "@openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol";
// import "@openzeppelin/contracts-upgradeable/math/SafeMathUpgradeable.sol";
// import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
// import "@openzeppelin/contracts-upgradeable/utils/AddressUpgradeable.sol";

// import "../interfaces/INFT20Pair.sol";

// import "@openzeppelin/contracts/proxy/BeaconProxy.sol";

// contract NFT20FactoryV2 is Initializable, OwnableUpgradeable {
//     using SafeMathUpgradeable for uint256;

//     // keep track of nft address to pair address
//     mapping(address => address) public nftToToken;
//     mapping(uint256 => address) public indexToNft;

//     uint256 public counter;
//     uint256 public fee;

//     event pairCreated(
//         address indexed originalNFT,
//         address newPair,
//         uint256 _type
//     );

//     using AddressUpgradeable for address;
//     address public logic;

//     constructor() public {}

//     function nft20Pair(
//         string memory name,
//         address _nftOrigin,
//         uint256 _nftType
//     ) public payable {
//         bytes memory initData =
//             abi.encodeWithSignature(
//                 "init(string,string,address,uint256)",
//                 string(abi.encodePacked("NFT20 ", name)),
//                 string(abi.encodePacked(name, "20")),
//                 _nftOrigin,
//                 _nftType
//             );

//         address instance = address(new BeaconProxy(logic, ""));

//         instance.functionCallWithValue(initData, msg.value);

//         nftToToken[_nftOrigin] = instance;
//         indexToNft[counter] = _nftOrigin;
//         counter = counter + 1;
//         emit pairCreated(_nftOrigin, instance, _nftType);
//     }

//     function getPairByNftAddress(uint256 index)
//         public
//         view
//         returns (
//             address _nft20pair,
//             address _originalNft,
//             uint256 _type,
//             string memory _name,
//             string memory _symbol,
//             uint256 _supply
//         )
//     {
//         _originalNft = indexToNft[index];
//         _nft20pair = nftToToken[_originalNft];
//         (_type, _name, _symbol, _supply) = INFT20Pair(_nft20pair).getInfos();
//     }

//     // this is to sset value in case we decided to change tokens given to a tokenizing project.
//     function setValue(
//         address _pair,
//         uint256 _nftType,
//         string calldata _name,
//         string calldata _symbol,
//         uint256 _value
//     ) external onlyOwner {
//         INFT20Pair(_pair).setParams(_nftType, _name, _symbol, _value);
//     }

//     function setFee(uint256 _fee) external onlyOwner {
//         fee = _fee;
//     }

//     function recoverERC20(address tokenAddress, uint256 tokenAmount)
//         public
//         onlyOwner
//     {
//         IERC20(tokenAddress).transfer(owner(), tokenAmount);
//     }

//     function changeLogic(address _newLogic) external onlyOwner {
//         logic = _newLogic;
//     }
// }

// File: contracts/NFT20FactoryV3.sol



// pragma solidity ^0.6.0;

// import "@openzeppelin/contracts-upgradeable/proxy/Initializable.sol";

// import "@openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol";
// import "@openzeppelin/contracts-upgradeable/math/SafeMathUpgradeable.sol";
// import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
// import "@openzeppelin/contracts-upgradeable/utils/AddressUpgradeable.sol";

// import "../interfaces/INFT20Pair.sol";

// import "@openzeppelin/contracts/proxy/BeaconProxy.sol";

// contract NFT20FactoryV3 is Initializable, OwnableUpgradeable {
//     using SafeMathUpgradeable for uint256;

//     // keep track of nft address to pair address
//     mapping(address => address) public nftToToken;
//     mapping(uint256 => address) public indexToNft;

//     uint256 public counter;
//     uint256 public fee;

//     event pairCreated(
//         address indexed originalNFT,
//         address newPair,
//         uint256 _type
//     );

//     using AddressUpgradeable for address;
//     address public logic;

//     constructor() public {}

//     function nft20Pair(
//         string memory name,
//         address _nftOrigin,
//         uint256 _nftType
//     ) public payable {
//         require(nftToToken[_nftOrigin] == address(0));
//         bytes memory initData =
//             abi.encodeWithSignature(
//                 "init(string,string,address,uint256)",
//                 string(abi.encodePacked("NFT20 ", name)),
//                 string(abi.encodePacked(name, "20")),
//                 _nftOrigin,
//                 _nftType
//             );

//         address instance = address(new BeaconProxy(logic, ""));

//         instance.functionCallWithValue(initData, msg.value);

//         nftToToken[_nftOrigin] = instance;
//         indexToNft[counter] = _nftOrigin;
//         counter = counter + 1;
//         emit pairCreated(_nftOrigin, instance, _nftType);
//     }

//     function getPairByNftAddress(uint256 index)
//         public
//         view
//         returns (
//             address _nft20pair,
//             address _originalNft,
//             uint256 _type,
//             string memory _name,
//             string memory _symbol,
//             uint256 _supply
//         )
//     {
//         _originalNft = indexToNft[index];
//         _nft20pair = nftToToken[_originalNft];
//         (_type, _name, _symbol, _supply) = INFT20Pair(_nft20pair).getInfos();
//     }

//     // this is to sset value in case we decided to change tokens given to a tokenizing project.
//     function setValue(
//         address _pair,
//         uint256 _nftType,
//         string calldata _name,
//         string calldata _symbol,
//         uint256 _value
//     ) external onlyOwner {
//         INFT20Pair(_pair).setParams(_nftType, _name, _symbol, _value);
//     }

//     function setFee(uint256 _fee) external onlyOwner {
//         fee = _fee;
//     }

//     function recoverERC20(address tokenAddress, uint256 tokenAmount)
//         public
//         onlyOwner
//     {
//         IERC20(tokenAddress).transfer(owner(), tokenAmount);
//     }

//     function changeLogic(address _newLogic) external onlyOwner {
//         logic = _newLogic;
//     }

//     function fix() external onlyOwner {
//         nftToToken[
//             address(0xC2C747E0F7004F9E8817Db2ca4997657a7746928)
//         ] = address(0xc2BdE1A2fA26890c8E6AcB10C91CC6D9c11F4a73);
//         counter = counter - 1;
//     }
// }

// File: contracts/NFT20FactoryV4.sol



// pragma solidity ^0.6.0;

// import "@openzeppelin/contracts-upgradeable/proxy/Initializable.sol";

// import "@openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol";
// import "@openzeppelin/contracts-upgradeable/math/SafeMathUpgradeable.sol";
// import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
// import "@openzeppelin/contracts-upgradeable/utils/AddressUpgradeable.sol";

// import "../interfaces/INFT20Pair.sol";

// import "@openzeppelin/contracts/proxy/BeaconProxy.sol";

// contract NFT20FactoryV4 is Initializable, OwnableUpgradeable {
//     using SafeMathUpgradeable for uint256;

//     // keep track of nft address to pair address
//     mapping(address => address) public nftToToken;
//     mapping(uint256 => address) public indexToNft;

//     uint256 public counter;
//     uint256 public fee;

//     event pairCreated(
//         address indexed originalNFT,
//         address newPair,
//         uint256 _type
//     );

//     using AddressUpgradeable for address;
//     address public logic;

//     constructor() public {}

//     function nft20Pair(
//         string memory name,
//         address _nftOrigin,
//         uint256 _nftType
//     ) public payable {
//         require(nftToToken[_nftOrigin] == address(0));
//         bytes memory initData =
//             abi.encodeWithSignature(
//                 "init(string,string,address,uint256)",
//                 string(abi.encodePacked("NFT20 ", name)),
//                 string(abi.encodePacked(name, "20")),
//                 _nftOrigin,
//                 _nftType
//             );

//         address instance = address(new BeaconProxy(logic, ""));

//         instance.functionCallWithValue(initData, msg.value);

//         nftToToken[_nftOrigin] = instance;
//         indexToNft[counter] = _nftOrigin;
//         counter = counter + 1;
//         emit pairCreated(_nftOrigin, instance, _nftType);
//     }

//     function getPairByNftAddress(uint256 index)
//         public
//         view
//         returns (
//             address _nft20pair,
//             address _originalNft,
//             uint256 _type,
//             string memory _name,
//             string memory _symbol,
//             uint256 _supply
//         )
//     {
//         _originalNft = indexToNft[index];
//         _nft20pair = nftToToken[_originalNft];
//         (_type, _name, _symbol, _supply) = INFT20Pair(_nft20pair).getInfos();
//     }

//     // this is to sset value in case we decided to change tokens given to a tokenizing project.
//     function setValue(
//         address _pair,
//         uint256 _nftType,
//         string calldata _name,
//         string calldata _symbol,
//         uint256 _value
//     ) external onlyOwner {
//         INFT20Pair(_pair).setParams(_nftType, _name, _symbol, _value);
//     }

//     function setFee(uint256 _fee) external onlyOwner {
//         fee = _fee;
//     }

//     function recoverERC20(address tokenAddress, uint256 tokenAmount)
//         public
//         onlyOwner
//     {
//         IERC20(tokenAddress).transfer(owner(), tokenAmount);
//     }

//     function changeLogic(address _newLogic) external onlyOwner {
//         logic = _newLogic;
//     }
// }

// File: contracts/NFT20Pair.sol



// pragma solidity ^0.6.0;

// // ERC721
// import "@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol";
// import "@openzeppelin/contracts/token/ERC721/IERC721.sol";

// // ERC1155
// import "@openzeppelin/contracts/token/ERC1155/ERC1155Receiver.sol";
// import "@openzeppelin/contracts/token/ERC1155/IERC1155.sol";

// import "./ERC20.sol";

// import "@openzeppelin/contracts/utils/EnumerableSet.sol";

// interface IFactory {
//     function fee() external view returns (uint256);
// }

// contract NFT20Pair is ERC20, IERC721Receiver, ERC1155Receiver {
//     address public factory;
//     address public nftAddress;
//     uint256 public nftType;
//     uint256 public nftValue;

//     mapping(uint256 => uint256) public track1155;

//     using EnumerableSet for EnumerableSet.UintSet;
//     EnumerableSet.UintSet lockedNfts;

//     event Withdraw(uint256[] indexed _tokenIds, uint256[] indexed amounts);

//     // create new token
//     constructor() public {}

//     function init(
//         string memory _name,
//         string memory _symbol,
//         address _nftAddress,
//         uint256 _nftType
//     ) public payable {
//         require(factory == address(0)); //Watch out TEST this is so we can init several time
//         factory = msg.sender;
//         nftType = _nftType;
//         name = _name;
//         symbol = _symbol;
//         decimals = 18;
//         nftAddress = _nftAddress;
//         nftValue = 100 * 10**18;
//     }

//     function getInfos()
//         public
//         view
//         returns (
//             uint256 _type,
//             string memory _name,
//             string memory _symbol,
//             uint256 _supply
//         )
//     {
//         _type = nftType;
//         _name = name;
//         _symbol = symbol;
//         _supply = totalSupply / 100 ether;
//     }

//     // withdraw nft and burn tokens
//     function withdraw(uint256[] calldata _tokenIds, uint256[] calldata amounts)
//         external
//     {
//         if (nftType == 1155) {
//             if (_tokenIds.length == 1) {
//                 _burn(msg.sender, nftValue.mul(amounts[0]));
//                 _withdraw1155(
//                     address(this),
//                     msg.sender,
//                     _tokenIds[0],
//                     amounts[0]
//                 );
//             } else {
//                 _batchWithdraw1155(
//                     address(this),
//                     msg.sender,
//                     _tokenIds,
//                     amounts
//                 );
//             }
//         } else if (nftType == 721) {
//             _burn(msg.sender, nftValue.mul(_tokenIds.length));
//             for (uint256 i = 0; i < _tokenIds.length; i++) {
//                 _withdraw721(address(this), msg.sender, _tokenIds[i]);
//             }
//         }

//         emit Withdraw(_tokenIds, amounts);
//     }

//     function _withdraw1155(
//         address _from,
//         address _to,
//         uint256 _tokenId,
//         uint256 value
//     ) internal {
//         track1155[_tokenId] = track1155[_tokenId].sub(value);
//         if (track1155[_tokenId] == 0) {
//             lockedNfts.remove(_tokenId);
//         }
//         IERC1155(nftAddress).safeTransferFrom(_from, _to, _tokenId, value, "");
//     }

//     function _batchWithdraw1155(
//         address _from,
//         address _to,
//         uint256[] memory ids,
//         uint256[] memory amounts
//     ) internal {
//         uint256 qty = 0;
//         for (uint256 i = 0; i < ids.length; i++) {
//             track1155[ids[i]] = track1155[ids[i]].sub(amounts[i]);
//             if (track1155[ids[i]] == 0) {
//                 lockedNfts.remove(ids[i]);
//             }
//             qty = qty + amounts[i];
//         }
//         // burn tokens
//         _burn(msg.sender, nftValue.mul(qty));

//         IERC1155(nftAddress).safeBatchTransferFrom(
//             _from,
//             _to,
//             ids,
//             amounts,
//             "0x0"
//         );
//     }

//     //@feature requires aproval for all before
//     function multi721Deposit(uint256[]  calldata _ids) public {
//         for (uint256 i = 0; i < _ids.length; i++) {
//         IERC721(nftAddress).safeTransferFrom(msg.sender, address(this), _ids[i]);
//         } 
//     }

//     function swap721(uint256 _in, uint256 _out) external {
//         require(nftType == 721, "!error");
//         lockedNfts.add(_in);
//         lockedNfts.remove(_out);

//         // requires user approval
//         IERC721(nftAddress).transferFrom(msg.sender, address(this), _in);

//         IERC721(nftAddress).safeTransferFrom(address(this), msg.sender, _out);
//     }

//     function swap1155(
//         uint256[] calldata in_ids,
//         uint256[] calldata in_amounts,
//         uint256[] calldata out_ids,
//         uint256[] calldata out_amounts
//     ) external {
//         require(nftType == 1155, "!error");

//         uint256 ins;
//         uint256 outs;

//         for (uint256 i = 0; i < in_ids.length; i++) {
//             ins = ins.add(in_amounts[i]);
//         }
//         for (uint256 i = 0; i < out_ids.length; i++) {
//             outs = outs.add(out_amounts[i]);
//             track1155[out_ids[i]] = track1155[out_ids[i]].sub(out_amounts[i]);
//             if (track1155[out_ids[i]] == 0) {
//                 lockedNfts.remove(out_ids[i]);
//             }
//         }

//         require(ins == outs, "Need to swap same amount of NFTs");

//         IERC1155(nftAddress).safeBatchTransferFrom(
//             address(this),
//             msg.sender,
//             out_ids,
//             out_amounts,
//             "0x0"
//         );
//         IERC1155(nftAddress).safeBatchTransferFrom(
//             msg.sender,
//             address(this),
//             in_ids,
//             in_amounts,
//             "INTERNAL"
//         );
//     }

//     function _withdraw721(
//         address _from,
//         address _to,
//         uint256 _tokenId
//     ) internal {
//         lockedNfts.remove(_tokenId);
//         IERC721(nftAddress).safeTransferFrom(_from, _to, _tokenId);
//     }

//     function onERC721Received(
//         address operator,
//         address,
//         uint256 tokenId,
//         bytes memory
//     ) public virtual override returns (bytes4) {
//         require(nftAddress == msg.sender, "forbidden");
//         deposit721(operator, tokenId);
//         return this.onERC721Received.selector;
//     }

//     function onERC1155Received(
//         address operator,
//         address,
//         uint256 id,
//         uint256 value,
//         bytes memory data
//     ) public virtual override returns (bytes4) {
//         require(nftAddress == msg.sender, "forbidden");
//         if (keccak256(data) != keccak256("INTERNAL")) {
//             if (!lockedNfts.contains(id)) {
//                 lockedNfts.add(id);
//             }

//             track1155[id] = track1155[id].add(value);
//             uint256 fee = IFactory(factory).fee();
//             _mint(factory, (nftValue.mul(value)).mul(fee).div(100));
//             _mint(
//                 operator,
//                 (nftValue.mul(value)).mul(uint256(100).sub(fee)).div(100)
//             );
//         }
//         return this.onERC1155Received.selector;
//     }

//     function onERC1155BatchReceived(
//         address operator,
//         address,
//         uint256[] memory ids,
//         uint256[] memory values,
//         bytes memory data
//     ) public virtual override returns (bytes4) {
//         require(nftType == 1155, "forbidden");
//         require(nftAddress == msg.sender, "forbidden");
//         if (keccak256(data) != keccak256("INTERNAL")) {
//             uint256 qty = 0;

//             for (uint256 i = 0; i < ids.length; i++) {
//                 if (!lockedNfts.contains(ids[i])) {
//                     lockedNfts.add(ids[i]);
//                 }

//                 qty = qty + values[i];
//                 track1155[ids[i]] = track1155[ids[i]].add(values[i]);
//             }
//             uint256 fee = IFactory(factory).fee();
//             _mint(
//                 operator,
//                 (nftValue.mul(qty)).mul(uint256(100).sub(fee)).div(100)
//             );
//             _mint(factory, (nftValue.mul(qty)).mul(fee).div(100));
//         }
//         return this.onERC1155BatchReceived.selector;
//     }

//     // to deposit old erc721
//     function tokenize721(uint256 tokenId) external {
//         IERC721(nftAddress).transferFrom(msg.sender, address(this), tokenId);
//         deposit721(msg.sender, tokenId);
//     }

//     function deposit721(address operator, uint256 tokenId) internal {
//         require(!lockedNfts.contains(tokenId), "forbidden");
//         lockedNfts.add(tokenId);
//         uint256 fee = IFactory(factory).fee();
//         _mint(factory, nftValue.mul(fee).div(100));
//         _mint(operator, nftValue.mul(uint256(100).sub(fee)).div(100));
//     }

//     // set new price
//     function setParams(
//         uint256 _nftType,
//         string calldata _name,
//         string calldata _symbol,
//         uint256 _nftValue
//     ) external {
//         require(msg.sender == factory, "!authorized");
//         nftType = _nftType;
//         name = _name;
//         symbol = _symbol;
//         nftValue = _nftValue;
//     }
// }

// File: contracts/NFTLP.sol



// // SPDX-License-Identifier: MIT
// pragma solidity ^0.6.0;

// import "@openzeppelin/contracts/utils/Counters.sol";
// import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
// import "@openzeppelin/contracts/token/ERC20/SafeERC20.sol";
// import "@openzeppelin/contracts/math/SafeMath.sol";

// import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
// import "@openzeppelin/contracts/token/ERC721/ERC721Burnable.sol";

// contract NFTLP is ERC721Burnable {
//     using SafeMath for uint256;
//     using SafeERC20 for IERC20;

//     using Counters for Counters.Counter;

//     Counters.Counter private _tokenIdTracker;

//     struct NFTDetails {
//         address erc20address; //Address of LP token contract
//         uint256 amount; // amount lp tokens staked
//         uint256 block; //block the nft was minted at
//     }

//     mapping(uint256 => NFTDetails) private nftDetails;

//     // total staked per token address
//     mapping(address => uint256) public totalStaked;

//     constructor(string memory baseURI_) public ERC721("NFT20", "NFT20") {
//         _setBaseURI(baseURI_);
//     }

//     function getNFTInfo(uint256 _nftId)
//         public
//         view
//         returns (
//             address _erc20address,
//             uint256 _amount,
//             uint256 _block
//         )
//     {
//         NFTDetails storage nft = nftDetails[_nftId];
//         _erc20address = nft.erc20address;
//         _amount = nft.amount;
//         _block = nft.block;
//     }

//     // deposit LP tokens and get NFT representation
//     function deposit(address erc20address, uint256 amount) external {
//         // deposit lp tokens into contract
//         IERC20(erc20address).safeTransferFrom(
//             address(msg.sender),
//             address(this),
//             amount
//         );

//         nftDetails[_tokenIdTracker.current()] = NFTDetails(
//             erc20address,
//             amount,
//             block.number
//         );

//         totalStaked[erc20address] = totalStaked[erc20address].add(amount);

//         // give minter role to this contract
//         _mint(msg.sender, _tokenIdTracker.current());

//         _tokenIdTracker.increment();
//     }

//     // instead of withdraw I am overriding the burn function from NFTs.
//     // this is because if there was withdraw and someone executes burn, it would burn the token and
//     // not delete the struct or make blance go down or send LP tokens back.
//     // not sure about this let me know.
//     function burn(uint256 tokenId) public override {
//         //solhint-disable-next-line max-line-length
//         require(
//             _isApprovedOrOwner(_msgSender(), tokenId),
//             "ERC721Burnable: caller is not owner nor approved"
//         );

//         NFTDetails storage nft = nftDetails[tokenId];

//         totalStaked[nft.erc20address] = totalStaked[nft.erc20address].sub(
//             nft.amount
//         );

//         // Send lp tokens to user
//         IERC20(nft.erc20address).transfer(msg.sender, nft.amount);

//         // delete data
//         delete nftDetails[tokenId];
//         _burn(tokenId);
//     }




// // SPDX-License-Identifier: AGPL-3.0-or-later
// pragma solidity ^0.6.8;
// pragma experimental ABIEncoderV2;

// import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
// import "@openzeppelin/contracts/token/ERC20/SafeERC20.sol";
// import "@openzeppelin/contracts/token/ERC721/IERC721.sol";
// import "@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol";
// import "@openzeppelin/contracts/token/ERC1155/IERC1155.sol";
// import "@openzeppelin/contracts/token/ERC1155/ERC1155Receiver.sol";

// contract MultiAssetSwapper is ReentrancyGuard, ERC1155Receiver, IERC721Receiver {

//   using SafeERC20 for IERC20;
//   using SafeMath for uint256;

//   struct Swap {
//     address proposer;
//     address[] tokenAddresses;
//     uint256[] amounts;
//     uint256[] ids;
//     bool[] isERC20;
//     // 0 to (numToSwapFor-1) are the proposer's assets
//     // numToSwapFor to (tokenAddresses.length-1) are the desired assets
//     uint256 numToSwapFor;
//   }

  

//   uint256 public currSwapIndex;
//   mapping(uint256 => Swap) swapRecords;

//   constructor() public {}

//   // Accepts safe ERC-721 transfers
//   function onERC721Received(address operator, address from, uint256 tokenId, bytes calldata data) external override returns (bytes4) {
//     return this.onERC721Received.selector;
//   }

//   // From: https://docs.gnosis.io/conditionaltokens/docs/ctftutorial13/
//   function onERC1155Received(address operator, address from, uint256 id, uint256 value, bytes calldata data) external override returns(bytes4) {
//       return this.onERC1155BatchReceived.selector;
//   }

//   function onERC1155BatchReceived( address operator, address from, uint256[] calldata ids, uint256[] calldata values, bytes calldata data )
//   external override returns(bytes4) {
//         return this.onERC1155BatchReceived.selector;
//     }

//   function _transferAsset(address a, uint256 amount, uint256 id, bool isERC20, address receiver) internal {
//     // Normal ERC-20 transfer
//     if (isERC20) {
//       IERC20(a).safeTransferFrom(msg.sender, receiver, amount);
//     }
//     else {
//       // If amount is greater than 0, we do ERC-1155 transfer
//       if (amount > 0) {
//         IERC1155(a).safeTransferFrom(msg.sender, receiver, id, amount, "");
//       }
//       else {
//         IERC721(a).safeTransferFrom(msg.sender, receiver, id);
//       }
//     }
//   }

//   function _transferAssetBack(address a, uint256 amount, uint256 id, bool isERC20, address receiver) internal {
//     // Normal ERC-20 transfer
//     if (isERC20) {
//       IERC20(a).safeTransfer(receiver, amount);
//     }
//     else {
//       // If amount is greater than 0, we do ERC-1155 transfer
//       if (amount > 0) {
//         IERC1155(a).safeTransferFrom(address(this), receiver, id, amount, "");
//       }
//       else {
//         IERC721(a).safeTransferFrom(address(this), receiver, id);
//       }
//     }
//   }

//   function proposeSwap(address[] calldata tokenAddresses,
//                        uint256[] calldata amounts,
//                        uint256[] calldata ids,
//                        bool[] calldata isERC20,
//                        uint256 numToSwapFor) external nonReentrant {
//     require((tokenAddresses.length == amounts.length), "diff lengths");
//     require((tokenAddresses.length == ids.length), "diff lengths");
//     require((tokenAddresses.length == isERC20.length), "diff lengths");
//     require((numToSwapFor < tokenAddresses.length), "nothing desired");
//     for (uint256 index = 0; index < numToSwapFor; index.add(1)) {
//       _transferAsset(tokenAddresses[index], amounts[index], ids[index], isERC20[index], address(this));
//     }
//     currSwapIndex = currSwapIndex.add(1);
//     swapRecords[currSwapIndex] = Swap(
//       msg.sender,
//       tokenAddresses,
//       amounts,
//       ids,
//       isERC20,
//       numToSwapFor
//     );
//   }

//   function removeSwap(uint256 swapId) external nonReentrant {
//     Swap storage swapItem = swapRecords[swapId];
//     require((swapItem.proposer == msg.sender), "not proposer");

//     // Move assets back
//     for (uint256 index = 0; index < swapItem.numToSwapFor; index.add(1)) {
//       _transferAssetBack(swapItem.tokenAddresses[index], swapItem.amounts[index], swapItem.ids[index], swapItem.isERC20[index], msg.sender);
//     }

//     // Remove storage slot
//     delete swapRecords[swapId];
//   }

//   function takeSwap(uint256 swapId) external nonReentrant {
//     Swap storage swapItem = swapRecords[swapId];
//     // Send all of the desired stuff to the proposer of the swap
//     for (uint256 index = swapItem.numToSwapFor; index < swapItem.tokenAddresses.length; index.add(1)) {
//       _transferAsset(swapItem.tokenAddresses[index], swapItem.amounts[index], swapItem.ids[index], swapItem.isERC20[index], swapItem.proposer);
//     }
//     // Send all of the escrowed stuff to the taker
//     for (uint256 index = 9; index < swapItem.numToSwapFor; index.add(1)) {
//       _transferAsset(swapItem.tokenAddresses[index], swapItem.amounts[index], swapItem.ids[index], swapItem.isERC20[index], msg.sender);
//     }

//     // Remove storage slot
//     delete swapRecords[swapId];
//   }


 

// }

// File: contracts/Proxy.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @title Proxy
 * @dev Implements delegation of calls to other contracts, with proper
 * forwarding of return values and bubbling of failures.
 * It defines a fallback function that delegates all calls to the address
 * returned by the abstract _implementation() internal function.
 */
abstract contract Proxy {
    /**
     * @dev Fallback function.
     * Implemented entirely in `_fallback`.
     */
    fallback() external payable {
        _fallback();
    }

    /**
     * @dev Receive function.
     * Implemented entirely in `_fallback`.
     */
    receive() external payable {
        _fallback();
    }

    /**
     * @return The Address of the implementation.
     */
    function _implementation() internal virtual view returns (address);

    /**
     * @dev Delegates execution to an implementation contract.
     * This is a low level function that doesn't return to its internal call site.
     * It will return to the external caller whatever the implementation returns.
     * @param implementation Address to delegate.
     */
    function _delegate(address implementation) internal {
        assembly {
            // Copy msg.data. We take full control of memory in this inline assembly
            // block because it will not return to Solidity code. We overwrite the
            // Solidity scratch pad at memory position 0.
            calldatacopy(0, 0, calldatasize())

            // Call the implementation.
            // out and outsize are 0 because we don't know the size yet.
            let result := delegatecall(
                gas(),
                implementation,
                0,
                calldatasize(),
                0,
                0
            )

            // Copy the returned data.
            returndatacopy(0, 0, returndatasize())

            switch result
                // delegatecall returns 0 on error.
                case 0 {
                    revert(0, returndatasize())
                }
                default {
                    return(0, returndatasize())
                }
        }
    }

    /**
     * @dev Function that is run as the first thing in the fallback function.
     * Can be redefined in derived contracts to add functionality.
     * Redefinitions must call super._willFallback().
     */
    function _willFallback() internal virtual {}

    /**
     * @dev fallback implementation.
     * Extracted to enable manual triggering.
     */
    function _fallback() internal {
        _willFallback();
        _delegate(_implementation());
    }
}