// File: /Users/csessa/dev/yearn-truffle-verify2/contracts/CollectableDust.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.12;

import "@openzeppelin/contracts/utils/Address.sol";
import "@openzeppelin/contracts/utils/EnumerableSet.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

import "../interfaces/ICollectableDust.sol";

abstract contract CollectableDust is ICollectableDust {
    using EnumerableSet for EnumerableSet.AddressSet;

    address public constant ETH_ADDRESS = 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;
    EnumerableSet.AddressSet internal protocolTokens;

    constructor() public {}

    function _addProtocolToken(address _token) internal {
        require(!protocolTokens.contains(_token), "collectable-dust::token-is-part-of-the-protocol");
        protocolTokens.add(_token);
    }

    function _removeProtocolToken(address _token) internal {
        require(protocolTokens.contains(_token), "collectable-dust::token-not-part-of-the-protocol");
        protocolTokens.remove(_token);
    }

    function _sendDust(
        address _to,
        address _token,
        uint256 _amount
    ) internal {
        require(_to != address(0), "collectable-dust::cant-send-dust-to-zero-address");
        require(!protocolTokens.contains(_token), "collectable-dust::token-is-part-of-the-protocol");
        if (_token == ETH_ADDRESS) {
            payable(_to).transfer(_amount);
        } else {
            IERC20(_token).transfer(_to, _amount);
        }
        emit DustSent(_to, _token, _amount);
    }
}

// File: /Users/csessa/dev/yearn-truffle-verify2/contracts/Governable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.12;

import "../interfaces/IGovernable.sol";

abstract contract Governable is IGovernable {
    address public governor;
    address public pendingGovernor;

    constructor(address _governor) public {
        require(_governor != address(0), "governable::governor-should-not-be-zero-address");
        governor = _governor;
    }

    function _setPendingGovernor(address _pendingGovernor) internal {
        require(_pendingGovernor != address(0), "governable::pending-governor-should-not-be-zero-address");
        pendingGovernor = _pendingGovernor;
        emit PendingGovernorSet(_pendingGovernor);
    }

    function _acceptGovernor() internal {
        governor = pendingGovernor;
        pendingGovernor = address(0);
        emit GovernorAccepted();
    }

    modifier onlyGovernor {
        require(msg.sender == governor, "governable::only-governor");
        _;
    }

    modifier onlyPendingGovernor {
        require(msg.sender == pendingGovernor, "governable::only-pending-governor");
        _;
    }
}

// File: /Users/csessa/dev/yearn-truffle-verify2/contracts/HegicBot.sol



// SPDX-License-Identifier: GPL-3.0
pragma solidity 0.6.12;
pragma experimental ABIEncoderV2;

import "@openzeppelin/contracts/math/SafeMath.sol";
import "@openzeppelin/contracts/utils/Address.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721Holder.sol";
import "@openzeppelin/contracts/utils/Counters.sol";

import "../interfaces/IHegicNFT.sol";
import "../interfaces/IHegicBot.sol";
import "../interfaces/IPriceProvider.sol";
import "./Governable.sol";
import "./CollectableDust.sol";

contract HegicBot is IHegicBot, Governable, CollectableDust, ERC721Holder {
    using Address for address;
    using SafeMath for uint256;
    using Counters for Counters.Counter;

    uint256 public FEE_MAX = 10000;
    uint256 public workFee = 100;

    uint256 public maxTimeToMaturity = 15 minutes;

    IHegicNFT public ethNft;
    IPriceProvider public priceProvider;
    address public keeper;

    Counters.Counter private _trackedTokenIds;
    mapping(uint256 => TrackedToken) public trackedTokens;

    constructor(IHegicNFT _ethNft, IPriceProvider _priceProvider) public Governable(msg.sender) CollectableDust() {
        ethNft = _ethNft;
        priceProvider = _priceProvider;
    }

    function track(uint256 tokenId, uint256 priceTarget) external override returns (uint256 trackedTokenId) {
        require(ethNft.isValidToken(tokenId), "tokenId invalid");

        ethNft.safeTransferFrom(msg.sender, address(this), tokenId);

        _trackedTokenIds.increment();
        trackedTokenId = _trackedTokenIds.current();
        TrackedToken memory trackedToken = TrackedToken(msg.sender, tokenId, priceTarget);
        trackedTokens[trackedTokenId] = trackedToken;

        emit TokenTracked(msg.sender, tokenId, trackedTokenId, priceTarget);
    }

    function changeTargetPrice(uint256 trackedTokenId, uint256 newTargetPrice) external override {
        TrackedToken storage trackedToken = trackedTokens[trackedTokenId];
        require(trackedToken.owner == msg.sender, "!owner");

        trackedToken.priceTarget = newTargetPrice;

        emit TargetPriceChanged(msg.sender, trackedToken.tokenId, trackedTokenId, newTargetPrice);
    }

    function untrack(uint256 trackedTokenId) external override returns (bool) {
        TrackedToken memory trackedToken = trackedTokens[trackedTokenId];
        require(trackedToken.owner == msg.sender, "!owner");

        ethNft.safeTransferFrom(address(this), msg.sender, trackedToken.tokenId);
        delete trackedTokens[trackedTokenId];
        emit TokenUntracked(msg.sender, trackedToken.tokenId, trackedTokenId);

        return true;
    }

    function exercisable(uint256 trackedTokenId) external view override returns (bool) {
        TrackedToken memory trackedToken = trackedTokens[trackedTokenId];
        Option memory option = ethNft.getUnderlyingOptionParams(trackedToken.tokenId);

        // return false if option is not active
        if (option.expiration < block.timestamp || option.state != State.Active) {
            return false;
        }

        (, int256 latestPrice, , , ) = priceProvider.latestRoundData();
        uint256 currentPrice = uint256(latestPrice);

        bool ITM = false;

        if (option.optionType == OptionType.Call) {
            ITM = currentPrice > option.strike;
        } else if (option.optionType == OptionType.Put) {
            ITM = currentPrice < option.strike;
        }

        // if option is In The Money and the msg.sender is the owner, it is exercisable
        if (ITM && (trackedToken.owner == msg.sender)) {
            return true;
        }

        // if option is In The Money and the option is going to expire in the next minutes
        if (ITM && (option.expiration.sub(maxTimeToMaturity) <= block.timestamp)) {
            return true;
        }

        // regular behavior: exersisable only when spot reached target price
        if (option.optionType == OptionType.Call) {
            return currentPrice >= trackedToken.priceTarget;
        } else if (option.optionType == OptionType.Put) {
            return currentPrice <= trackedToken.priceTarget;
        }

        return false;
    }

    function exercise(uint256 trackedTokenId) external override returns (address, uint256) {
        require(this.exercisable(trackedTokenId), "trackedTokenId not exercisable");

        TrackedToken memory trackedToken = trackedTokens[trackedTokenId];

        ethNft.exerciseOption(trackedToken.tokenId);

        uint256 grossProfit = address(this).balance;
        uint256 ownerFee = grossProfit.mul(workFee).div(FEE_MAX);
        require(ownerFee > 0, "profit==0");

        payable(governor).transfer(ownerFee);

        uint256 netProfit = address(this).balance;
        if (msg.sender == keeper) {
            payable(keeper).transfer(netProfit);
        } else {
            payable(trackedToken.owner).transfer(netProfit);
        }

        delete trackedTokens[trackedTokenId];

        emit TrackedTokenExercised(msg.sender, trackedToken.tokenId, trackedTokenId, grossProfit);

        return (trackedToken.owner, netProfit);
    }

    function setWorkFee(uint256 _workFee) external override onlyGovernor {
        require(_workFee > 0 && _workFee <= 10000);
        workFee = _workFee;
        emit WorkFeeSet(_workFee);
    }

    function setKeeper(address _keeper) external override onlyGovernor {
        keeper = _keeper;
        emit KeeperSet(_keeper);
    }

    function setMaxTimeToMaturity(uint256 _newTTM) external override onlyGovernor {
        maxTimeToMaturity = _newTTM;
        emit TTMSet(_newTTM);
    }

    // Governable
    function setPendingGovernor(address _pendingGovernor) external override onlyGovernor {
        _setPendingGovernor(_pendingGovernor);
    }

    function acceptGovernor() external override onlyPendingGovernor {
        _acceptGovernor();
    }

    // Collectable Dust
    function sendDust(
        address _to,
        address _token,
        uint256 _amount
    ) external override onlyGovernor {
        _sendDust(_to, _token, _amount);
    }

    receive() external payable {}
}

// File: /Users/csessa/dev/yearn-truffle-verify2/interfaces/ICollectableDust.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.6.12;

interface ICollectableDust {
    event DustSent(address _to, address token, uint256 amount);

    function sendDust(
        address _to,
        address _token,
        uint256 _amount
    ) external;
}

// File: /Users/csessa/dev/yearn-truffle-verify2/interfaces/IGovernable.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.6.12;

interface IGovernable {
    event PendingGovernorSet(address pendingGovernor);
    event GovernorAccepted();

    function setPendingGovernor(address _pendingGovernor) external;

    function acceptGovernor() external;
}

// File: /Users/csessa/dev/yearn-truffle-verify2/interfaces/IHegic.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.6.12;
pragma experimental ABIEncoderV2;

enum State {Inactive, Active, Exercised, Expired}
enum OptionType {Invalid, Put, Call}

struct Option {
    State state;
    address payable holder;
    uint256 strike;
    uint256 amount;
    uint256 lockedAmount;
    uint256 premium;
    uint256 expiration;
    OptionType optionType;
}

interface IHegicPool {
    function totalBalance() external view returns (uint256 amount);

    function availableBalance() external view returns (uint256 amount);
}

interface IHegicOptions {
    function pool() external view returns (address poolAddress);

    function unlockAll(uint256[] calldata optionsIDs) external;

    function options(uint256) external view returns (Option memory);
}

// File: /Users/csessa/dev/yearn-truffle-verify2/interfaces/IHegicBot.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.6.12;
pragma experimental ABIEncoderV2;

struct TrackedToken {
    address owner;
    uint256 tokenId;
    uint256 priceTarget;
}

interface IHegicBot {
    event TokenTracked(
        address indexed account,
        uint256 indexed tokenId,
        uint256 indexed trackedTokenId,
        uint256 targetPrice
    );

    event TargetPriceChanged (
        address indexed account,
        uint256 indexed tokenId,
        uint256 indexed trackedTokenId,
        uint256 newTargetPrice
    );

    event TokenUntracked(
        address indexed account,
        uint256 indexed tokenId,
        uint256 indexed trackedTokenId
    );

    event TrackedTokenExercised(
        address indexed account,
        uint256 indexed tokenId,
        uint256 indexed trackedTokenId,
        uint256 grossProfit
    );

    event WorkFeeSet(uint256 workFee);
    event KeeperSet(address keeper);
    event TTMSet(uint256 newTTM);

    function track(uint256, uint256) external returns (uint256);

    function untrack(uint256) external returns (bool);

    function changeTargetPrice(uint256, uint256) external;

    function exercisable(uint256) external view returns (bool);

    function exercise(uint256) external returns (address, uint256);

    function setWorkFee(uint256) external;

    function setKeeper(address) external;

    function setMaxTimeToMaturity(uint256) external;

}

// File: /Users/csessa/dev/yearn-truffle-verify2/interfaces/IHegicNFT.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.6.12;
pragma experimental ABIEncoderV2;

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

interface IHegicNFT is IERC721 {
    function tokenizeOption(uint256, address) external returns (uint256);

    function isValidToken(uint256) external view returns (bool);

    function getUnderlyingOptionParams(uint256) external view returns (Option memory);

    function exerciseOption(uint256) external returns (uint256);
}

// File: /Users/csessa/dev/yearn-truffle-verify2/interfaces/IPriceProvider.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.6.12;
pragma experimental ABIEncoderV2;

interface IPriceProvider {
    function latestRoundData()
        external
        view
        returns (
            uint80 roundId,
            int256 answer,
            uint256 startedAt,
            uint256 updatedAt,
            uint80 answeredInRound
        );
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @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/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @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, 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) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * 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);
        uint256 c = a - b;

        return c;
    }

    /**
     * @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) {
        // 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 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts 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) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message 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, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts 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) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message 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, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @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/ERC721/ERC721Holder.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

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/token/ERC721/IERC721.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.2;

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

/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721 is IERC165 {
    /**
     * @dev Emitted when `tokenId` token is transfered 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/ERC721/IERC721Receiver.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @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/utils/Address.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.2;

/**
 * @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) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
    }

    /**
     * @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");
        return _functionCallWithValue(target, data, value, errorMessage);
    }

    function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

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: @openzeppelin/contracts/utils/EnumerableSet.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @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 v3.0.0, only sets of type `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];
    }

    // 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(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(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(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(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));
    }
}