// File: /contracts/pirate/PnG.sol



// SPDX-License-Identifier: MIT LICENSE

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/security/Pausable.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

import "./interfaces/IPnG.sol";
import "./interfaces/ITraits.sol";

import "./interfaces/IFleet.sol";


import "./utils/Accessable.sol";



contract TraitSelector {
    // list of probabilities for each trait type
    // 0 - 7 are associated with Galleons, 8 - 15 are associated with Pirates
    uint8[][16] public rarities;
    // list of aliases for Walker's Alias algorithm
    // 0 - 7 are associated with Galleons, 8-15 are associated with Pirates
    uint8[][16] public aliases;

    constructor() {
        // A.J. Walker's Alias Algorithm
        // Galleons

        // base
        rarities[0] = [ 245, 173, 255 ];
        aliases[0] =  [ 1, 2, 2 ];
        // deck
        rarities[1] = [ 252, 212, 255 ];
        aliases[1] =  [ 1, 2, 2 ];
        // sails
        rarities[2] =  [60,   2,  1,  86, 219,  17, 80, 73,86, 139, 54, 120,  86,  18, 66, 80,60, 119, 66,  86,  73, 192, 99,  3,33, 255];
        aliases[2] = [ 1, 13, 23,  1,  1, 23,  1,  1, 2,  2, 24, 23,  5, 24,  5,  5, 10, 10, 10, 10, 11,  1, 11, 24, 25, 25];
        // crowsNest
        rarities[3] = [ 9,  23, 119, 19,  74, 179, 10,  19,82,   6, 143,  8,   7,  40, 75,  71,52, 150,  10, 21, 150,  38, 17, 122,21, 255];
        aliases[3] = [ 2,  4,  4,  4,  8,  8, 10, 14,15, 17, 15, 17, 17, 19, 19, 19,20, 20, 20, 23, 21, 24, 25, 24,25, 25];
        // decor
        rarities[4] = [ 19, 59,  9, 21, 116,  46,  8, 30, 11, 45, 39,  49, 255, 21,163, 10, 26,  6, 202,  11];
        aliases[4] = [4,  4,  4,  5,  5,  7,  7, 11,  7, 10, 12, 12, 12, 10, 7, 10, 10, 11, 10, 11];
        // flags
        rarities[5] = [ 8,  64,  34, 104, 210, 189,  49, 159,  45, 146,  29,  31,  33,  61, 40,  69, 111,  29,  14, 221, 116, 150, 255, 232, 142];
        aliases[5] = [ 9,  9, 12, 12,  0,  0, 13,  0, 0, 12,  1,  1, 15, 16,  2, 17, 17, 22,  3,  1,  2,  6, 22,  0, 6];
        // bowsprit
        rarities[6] = [11,  23, 20,  49, 29,  9, 219, 159, 243,  85, 78,  11, 71, 42,  34,  14, 204,  61, 18, 151,  3,  2,  26,  27, 189, 255];
        aliases[6] = [3,  3,  3,  4,  6,  8,  7,  8,  9, 18,  9,  9, 25, 12, 12, 16,  9, 18, 25, 25, 18, 19, 23, 24,  9, 25];

        // empty
        rarities[7] = [255];
        aliases[7] = [0];

        // Pirates
        // skin
        rarities[8] = [ 255, 255, 255, 255, 255 ];
        aliases[8] =  [ 0, 1, 2, 3, 4 ];
        // clothes
        rarities[9] = [255, 153,  76, 128,128,  76, 255, 179, 76, 128];
        aliases[9] = [0, 2, 5, 2, 5,6, 6, 2, 4, 4];
        // hair
        rarities[10] = [216, 71, 67, 216, 54,152, 35, 55, 221, 34,255];
        aliases[10] = [ 1, 5, 1, 1, 6, 6, 7, 8, 10, 4, 10];
        // earrings
        rarities[11] = [35, 69, 126, 6, 42,  56, 57,  47, 134, 101, 208, 112,  142, 255, 169, 208,  78];
        aliases[11] = [2, 4,  3, 4,  5,  6,  7,  11, 7, 12, 7, 12, 13, 13, 7, 9,  9];
        // mouth
        rarities[12] = [80, 208,  43, 120,67, 139, 190, 255];
        aliases[12] = [ 1, 2, 3, 6, 2, 2, 7, 7];
        // eyes
        rarities[13] = [ 125, 134, 208,  23, 125, 179, 107, 118, 249, 171, 255, 200, 100, 225];
        aliases[13] = [1, 2, 2, 0, 2, 2, 9, 0, 5, 4, 4, 4, 4, 4];
        // weapon
        rarities[14] = [159, 229,  84,  93, 176, 53, 113, 123, 103,  94, 78,  96, 255];
        aliases[14] = [ 1, 2, 11, 2, 2, 9, 9, 9, 10, 10, 11, 12,12];
        //  alphaIndex
        rarities[15] = [ 173, 255, 163, 10 ];
        aliases[15] =  [ 1, 1, 0, 0 ];
    }


    /**
    * uses A.J. Walker's Alias algorithm for O(1) rarity table lookup
    * ensuring O(1) instead of O(n) reduces mint cost by more than 50%
    * probability & alias tables are generated off-chain beforehand
    * @param seed portion of the 256 bit seed to remove trait correlation
    * @param traitType the trait type to select a trait for 
    * @return the ID of the randomly selected trait
    */
    function selectTrait(uint16 seed, uint8 traitType) internal view returns (uint8) {
        uint8 trait = uint8(seed) % uint8(rarities[traitType].length);
        // If a selected random trait probability is selected (biased coin) return that trait
        if (seed >> 8 < rarities[traitType][trait]) return trait + 1;
        return aliases[traitType][trait] + 1;
    }

    /**
    * selects the species and all of its traits based on the seed value
    * @param seed a pseudorandom 256 bit number to derive traits from
    * @return t -  a struct of randomly selected traits
    */
    function selectTraits(uint256 seed) internal view returns (IPnG.GalleonPirate memory t) {    
        t.isGalleon = (seed & 0xFFFF) % 10 != 0;

        if (t.isGalleon) {
            seed >>= 16;
            t.base = selectTrait(uint16(seed & 0xFFFF), 0);

            seed >>= 16;
            t.deck = selectTrait(uint16(seed & 0xFFFF), 1);

            seed >>= 16;
            t.sails = selectTrait(uint16(seed & 0xFFFF), 2);

            seed >>= 16;
            t.crowsNest = selectTrait(uint16(seed & 0xFFFF), 3);

            seed >>= 16;
            t.decor = selectTrait(uint16(seed & 0xFFFF), 4);

            seed >>= 16;
            t.flags = selectTrait(uint16(seed & 0xFFFF), 5);

            seed >>= 16;
            t.bowsprit = selectTrait(uint16(seed & 0xFFFF), 6);

            seed >>= 16;
            t.alphaIndex = selectTrait(uint16(seed & 0xFFFF), 7) - 1;
            t.hat = t.alphaIndex;
        }
        else {
            seed >>= 16;
            t.skin = selectTrait(uint16(seed & 0xFFFF), 8);

            seed >>= 16;
            t.clothes = selectTrait(uint16(seed & 0xFFFF), 9);

            seed >>= 16;
            t.hair = selectTrait(uint16(seed & 0xFFFF), 10);

            seed >>= 16;
            t.earrings = selectTrait(uint16(seed & 0xFFFF), 11);

            seed >>= 16;
            t.mouth = selectTrait(uint16(seed & 0xFFFF), 12);

            seed >>= 16;
            t.eyes = selectTrait(uint16(seed & 0xFFFF), 13);

            seed >>= 16;
            t.weapon = selectTrait(uint16(seed & 0xFFFF), 14);

            seed >>= 16;
            t.alphaIndex = selectTrait(uint16(seed & 0xFFFF), 15) - 1;
            t.hat = t.alphaIndex;
        }

        return t;
    }
}



contract PnG is IPnG, ERC721, Accessable, Pausable, TraitSelector {
    uint256 constant MAX_INT = type(uint256).max;

    struct LastWrite {
        uint64 time;
        uint64 blockNum;
    }

    event GalleonMinted(uint256 indexed tokenId);
    event PirateMinted(uint256 indexed tokenId);

    event GalleonStolen(uint256 indexed tokenId);
    event PirateStolen(uint256 indexed tokenId);
    
    event GalleonBurned(uint256 indexed tokenId);
    event PirateBurned(uint256 indexed tokenId);

    // max number of tokens that can be minted: 50000 in production
    uint256 public maxTokens;
    // number of tokens that can be claimed for a fee: 10,000
    uint256 public PAID_TOKENS;
    // number of tokens have been minted so far
    uint16 public override minted;

    // tokenId -> traits
    mapping(uint256 => GalleonPirate) private tokenTraits;
    // tokenHash -> tokenId
    mapping(uint256 => uint256) public existingCombinations;
    // Tracks the last block and timestamp that a caller has written to state.
    // Disallow some access to functions if they occur while a change is being written.
    mapping(address => LastWrite) private lastWriteAddress;
    mapping(uint256 => LastWrite) private lastWriteToken;

    // reference to the Fleet contract to allow transfers to it without approval
    IFleet public fleet;
    ITraits public traits;

    constructor(uint256 _maxTokens) ERC721("Pirate Game", "PnG") {
        maxTokens = _maxTokens;
        PAID_TOKENS = _maxTokens / 5;
        _pause();
    }

    /** MODIFIERS */

    modifier requireContractsSet() {
        require(address(traits) != address(0) && address(fleet) != address(0), "Contracts not set");
        _;
    }

    modifier blockIfChangingAddress() {
        require(isAdmin(_msgSender()) || lastWriteAddress[tx.origin].blockNum < block.number, "Cannot interact in the current block");
        _;
    }

    modifier blockIfChangingToken(uint256 tokenId) {
        require(isAdmin(_msgSender()) || lastWriteToken[tokenId].blockNum < block.number, "Cannot interact in the current block");
        _;
    }

    function setContracts(address _traits, address _fleet) external onlyOwner {
        traits = ITraits(_traits);
        fleet = IFleet(_fleet);
    }

    /** EXTERNAL */

    function getTokenWriteBlock(uint256 tokenId) external view override
        onlyAdmin
        returns(uint64) 
    {
        return lastWriteToken[tokenId].blockNum;
    }

    /** 
    * Mint a token - any payment / game logic should be handled in the game contract. 
    * This will just generate random traits and mint a token to a designated address.
    */
    function mint(address recipient, uint256 seed) external override 
        whenNotPaused 
        onlyAdmin
    {
        require(minted + 1 <= maxTokens, "All tokens minted");
        minted++;
        generate(minted, seed);
        if(tx.origin != recipient && recipient != address(fleet)) {
            // Stolen!
            if(tokenTraits[minted].isGalleon) {
                emit GalleonStolen(minted);
            }
            else {
                emit PirateStolen(minted);
            }
        }
        _safeMint(recipient, minted);
    }

    /** 
    * Burn a token - any game logic should be handled before this function.
    */
    function burn(uint256 tokenId) external override 
        whenNotPaused 
        onlyAdmin
    {
        require(ownerOf(tokenId) == tx.origin, "Oops you don't own that");
        if(tokenTraits[tokenId].isGalleon) {
            emit GalleonBurned(tokenId);
        }
        else {
            emit PirateBurned(tokenId);
        }
        _burn(tokenId);
    }

    function updateOriginAccess(uint16[] memory tokenIds) external override 
        onlyAdmin
    {
        uint64 blockNum = uint64(block.number);
        uint64 time = uint64(block.timestamp);
        lastWriteAddress[tx.origin] = LastWrite(time, blockNum);
        for (uint256 i = 0; i < tokenIds.length; i++) {
            lastWriteToken[tokenIds[i]] = LastWrite(time, blockNum);
        }
    }

    function transferFrom( address from, address to, uint256 tokenId) 
        public 
        virtual 
        override(ERC721, IERC721) 
        blockIfChangingToken(tokenId) 
    {
        // allow admin contracts to be send without approval
        if(!isAdmin(_msgSender())) {
            require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");
        }
        _transfer(from, to, tokenId);
    }

    /** INTERNAL */

    /**
    * generates traits for a specific token, checking to make sure it's unique
    * @param tokenId the id of the token to generate traits for
    * @param seed a pseudorandom 256 bit number to derive traits from
    * @return t - a struct of traits for the given token ID
    */
    function generate(uint256 tokenId, uint256 seed) internal returns (GalleonPirate memory t) {
        t = selectTraits(seed);
        if (existingCombinations[structToHash(t)] == 0) {
            tokenTraits[tokenId] = t;
            existingCombinations[structToHash(t)] = tokenId;

            if(t.isGalleon)
                emit GalleonMinted(tokenId);
            else
                emit PirateMinted(tokenId);

            return t;
        }

        if (seed == MAX_INT)
            return generate(tokenId, 1);
        else
            return generate(tokenId, seed+1);
    }

    /**
    * converts a struct to a 256 bit hash to check for uniqueness
    * @param s the struct to pack into a hash
    * @return the 256 bit hash of the struct
    */
    function structToHash(GalleonPirate memory s) internal pure returns (uint256) {
        if (s.isGalleon) {
            return uint256(keccak256(abi.encodePacked(
                s.isGalleon,
                // Galleon
                s.base,
                s.deck,
                s.sails,
                s.crowsNest,
                s.decor,
                s.flags,
                s.bowsprit
        )));
        } else {
            return uint256(keccak256(abi.encodePacked(
                s.isGalleon,
                s.skin,
                s.clothes,
                s.hair,
                s.earrings,
                s.mouth,
                s.eyes,
                s.weapon,
                s.hat,
                s.alphaIndex
            )));
        }
    }

    /** READ */

    function isGalleon(uint256 tokenId) external view override 
        blockIfChangingToken(tokenId) 
        returns (bool) 
    {
        IPnG.GalleonPirate memory s = tokenTraits[tokenId];
        return s.isGalleon;
    }

    function getMaxTokens() external view override returns (uint256) {
        return maxTokens;
    }

    function getPaidTokens() external view override returns (uint256) {
        return PAID_TOKENS;
    }

    /** ADMIN */

    /**
    * updates the number of tokens for sale
    */
    function _setTokensAmount(uint16 _paidTokens, uint16 _maxTokens) external onlyAdmin {
        PAID_TOKENS = _paidTokens;
        maxTokens = _maxTokens;
    }

    /**
    * enables owner to pause / unpause minting
    */
    function _setPaused(bool _paused) external requireContractsSet onlyAdmin {
        if (_paused) _pause();
        else _unpause();
    }


    /** Traits */

    function getTokenTraits(uint256 tokenId) external view override 
        blockIfChangingAddress 
        blockIfChangingToken(tokenId) 
        returns (GalleonPirate memory) 
    {
        return tokenTraits[tokenId];
    }

    function tokenURI(uint256 tokenId) public view override 
        blockIfChangingAddress 
        blockIfChangingToken(tokenId) 
        returns (string memory) 
    {
        require(_exists(tokenId), "Token ID does not exist");
        return traits.tokenURI(tokenId);
    }


    function totalSupply() public view returns (uint256) {
        return minted;
    }

    
    function balanceOf(address owner) public view virtual override(ERC721, IERC721) 
        blockIfChangingAddress 
        returns (uint256) 
    {
        // checking on this address in the same block it's being modified
        require(
            isAdmin(_msgSender()) || lastWriteAddress[owner].blockNum < block.number, 
            "Cannot interact in the current block"
        );
        return super.balanceOf(owner);
    }


    function ownerOf(uint256 tokenId) public view virtual override(ERC721, IERC721) 
        blockIfChangingAddress 
        blockIfChangingToken(tokenId) 
        returns (address) 
    {
        address addr = super.ownerOf(tokenId);
        // checking on this address in the same block it's being modified
        require(
            isAdmin(_msgSender()) || lastWriteAddress[addr].blockNum < block.number, 
            "Cannot interact in the current block"
        );
        return addr;
    }


    function tokenByIndex(uint256 index) public view returns (uint256) {
        require(
            isAdmin(_msgSender()) || lastWriteToken[index+1].blockNum < block.number, 
            "Cannot interact in the current block"
        );
        return index + 1;
    }


    function approve(address to, uint256 tokenId) public virtual override(ERC721, IERC721) 
        blockIfChangingToken(tokenId) 
    {
        super.approve(to, tokenId);
    }


    function getApproved(uint256 tokenId) public view virtual override(ERC721, IERC721) 
        blockIfChangingToken(tokenId) 
        returns (address) 
    {
        return super.getApproved(tokenId);
    }


    function setApprovalForAll(address operator, bool approved) 
        public virtual override(ERC721, IERC721) 
        blockIfChangingAddress 
    {
        super.setApprovalForAll(operator, approved);
    }


    function isApprovedForAll(address owner, address operator) 
        public view virtual override(ERC721, IERC721) 
        blockIfChangingAddress 
        returns (bool) 
    {
        return super.isApprovedForAll(owner, operator);
    }
    

    function safeTransferFrom( address from, address to, uint256 tokenId) 
        public virtual override(ERC721, IERC721) 
        blockIfChangingToken(tokenId) 
    {
        super.safeTransferFrom(from, to, tokenId);
    }


    function safeTransferFrom( address from, address to, uint256 tokenId, bytes memory _data)
        public virtual override(ERC721, IERC721) 
        blockIfChangingToken(tokenId) 
    {
        super.safeTransferFrom(from, to, tokenId, _data);
    }


    /**
     * allows owner to withdraw funds from minting
     */
    function _withdraw() external onlyTokenClaimer {
        payable(_msgSender()).transfer(address(this).balance);
    }
}
// File: /contracts/pirate/utils/Accessable.sol



// SPDX-License-Identifier: MIT LICENSE

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/utils/Context.sol";


contract Owned is Context {
    address private _contractOwner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    constructor() { 
        _contractOwner = payable(_msgSender()); 
    }

    function owner() public view virtual returns(address) {
        return _contractOwner;
    }

    function _transferOwnership(address newOwner) external virtual onlyOwner {
        require(newOwner != address(0), "Owned: Address can not be 0x0");
        __transferOwnership(newOwner);
    }


    function _renounceOwnership() external virtual onlyOwner {
        __transferOwnership(address(0));
    }

    function __transferOwnership(address _to) internal {
        emit OwnershipTransferred(owner(), _to);
        _contractOwner = _to;
    }


    modifier onlyOwner() {
        require(_msgSender() == _contractOwner, "Owned: Only owner can operate");
        _;
    }
}



contract Accessable is Owned {
    mapping(address => bool) private _admins;
    mapping(address => bool) private _tokenClaimers;

    constructor() {
        _admins[_msgSender()] = true;
        _tokenClaimers[_msgSender()] = true;
    }

    function isAdmin(address user) public view returns(bool) {
        return _admins[user];
    }

    function isTokenClaimer(address user) public view returns(bool) {
        return _tokenClaimers[user];
    }


    function _setAdmin(address _user, bool _isAdmin) external onlyOwner {
        _admins[_user] = _isAdmin;
        require( _admins[owner()], "Accessable: Contract owner must be an admin" );
    }

    function _setTokenClaimer(address _user, bool _isTokenCalimer) external onlyOwner {
        _tokenClaimers[_user] = _isTokenCalimer;
        require( _tokenClaimers[owner()], "Accessable: Contract owner must be an token claimer" );
    }


    modifier onlyAdmin() {
        require(_admins[_msgSender()], "Accessable: Only admin can operate");
        _;
    }

    modifier onlyTokenClaimer() {
        require(_tokenClaimers[_msgSender()], "Accessable: Only Token Claimer can operate");
        _;
    }
}
// File: /contracts/pirate/interfaces/ITraits.sol



// SPDX-License-Identifier: MIT LICENSE 

pragma solidity ^0.8.0;

interface ITraits {
    function tokenURI(uint256 tokenId) external view returns (string memory);
}
// File: /contracts/pirate/interfaces/IPnG.sol



// SPDX-License-Identifier: MIT LICENSE

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC721/IERC721.sol";

interface IPnG is IERC721 {

    struct GalleonPirate {
        bool isGalleon;

        // Galleon traits
        uint8 base;
        uint8 deck;
        uint8 sails;
        uint8 crowsNest;
        uint8 decor;
        uint8 flags;
        uint8 bowsprit;

        // Pirate traits
        uint8 skin;
        uint8 clothes;
        uint8 hair;
        uint8 earrings;
        uint8 mouth;
        uint8 eyes;
        uint8 weapon;
        uint8 hat;
        uint8 alphaIndex;
    }


    function updateOriginAccess(uint16[] memory tokenIds) external;

    function totalSupply() external view returns(uint256);

    function mint(address recipient, uint256 seed) external;
    function burn(uint256 tokenId) external;
    function minted() external view returns (uint16);

    function getMaxTokens() external view returns (uint256);
    function getPaidTokens() external view returns (uint256);
    function getTokenTraits(uint256 tokenId) external view returns (GalleonPirate memory);
    function getTokenWriteBlock(uint256 tokenId) external view returns(uint64);
    function isGalleon(uint256 tokenId) external view returns(bool);
}
// File: /contracts/pirate/interfaces/IFleet.sol



// SPDX-License-Identifier: MIT LICENSE 

pragma solidity ^0.8.0;

interface IFleet {
    function addManyToFleet(address account, uint16[] calldata tokenIds) external;
    function randomPirateOwner(uint256 seed) external view returns (address);
}
// File: @openzeppelin/contracts/utils/introspection/IERC165.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (utils/introspection/IERC165.sol)

pragma solidity ^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/utils/introspection/ERC165.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (utils/introspection/ERC165.sol)

pragma solidity ^0.8.0;

import "./IERC165.sol";

/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts that want to implement ERC165 should inherit from this contract and override {supportsInterface} to check
 * for the additional interface id that will be supported. For example:
 *
 * ```solidity
 * function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
 *     return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
 * }
 * ```
 *
 * Alternatively, {ERC165Storage} provides an easier to use but more expensive implementation.
 */
abstract contract ERC165 is IERC165 {
    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IERC165).interfaceId;
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (utils/Strings.sol)

pragma solidity ^0.8.0;

/**
 * @dev String operations.
 */
library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";

    /**
     * @dev Converts a `uint256` to its ASCII `string` decimal 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);
        while (value != 0) {
            digits -= 1;
            buffer[digits] = bytes1(uint8(48 + uint256(value % 10)));
            value /= 10;
        }
        return string(buffer);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        if (value == 0) {
            return "0x00";
        }
        uint256 temp = value;
        uint256 length = 0;
        while (temp != 0) {
            length++;
            temp >>= 8;
        }
        return toHexString(value, length);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
     */
    function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
        bytes memory buffer = new bytes(2 * length + 2);
        buffer[0] = "0";
        buffer[1] = "x";
        for (uint256 i = 2 * length + 1; i > 1; --i) {
            buffer[i] = _HEX_SYMBOLS[value & 0xf];
            value >>= 4;
        }
        require(value == 0, "Strings: hex length insufficient");
        return string(buffer);
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (utils/Context.sol)

pragma solidity ^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 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) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (utils/Address.sol)

pragma solidity ^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;
        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");

        (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");

        (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");

        (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");

        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal 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

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (token/ERC721/extensions/IERC721Metadata.sol)

pragma solidity ^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/IERC721Receiver.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (token/ERC721/IERC721Receiver.sol)

pragma solidity ^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/ERC721/IERC721.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (token/ERC721/IERC721.sol)

pragma solidity ^0.8.0;

import "../../utils/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/ERC721/ERC721.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (token/ERC721/ERC721.sol)

pragma solidity ^0.8.0;

import "./IERC721.sol";
import "./IERC721Receiver.sol";
import "./extensions/IERC721Metadata.sol";
import "../../utils/Address.sol";
import "../../utils/Context.sol";
import "../../utils/Strings.sol";
import "../../utils/introspection/ERC165.sol";

/**
 * @dev Implementation of https://eips.ethereum.org/EIPS/eip-721[ERC721] Non-Fungible Token Standard, including
 * the Metadata extension, but not including the Enumerable extension, which is available separately as
 * {ERC721Enumerable}.
 */
contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
    using Address for address;
    using Strings for uint256;

    // Token name
    string private _name;

    // Token symbol
    string private _symbol;

    // Mapping from token ID to owner address
    mapping(uint256 => address) private _owners;

    // Mapping owner address to token count
    mapping(address => uint256) private _balances;

    // 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;

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

    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override(ERC165, IERC165) returns (bool) {
        return
            interfaceId == type(IERC721).interfaceId ||
            interfaceId == type(IERC721Metadata).interfaceId ||
            super.supportsInterface(interfaceId);
    }

    /**
     * @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 _balances[owner];
    }

    /**
     * @dev See {IERC721-ownerOf}.
     */
    function ownerOf(uint256 tokenId) public view virtual override returns (address) {
        address owner = _owners[tokenId];
        require(owner != address(0), "ERC721: owner query for nonexistent token");
        return owner;
    }

    /**
     * @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 baseURI = _baseURI();
        return bytes(baseURI).length > 0 ? string(abi.encodePacked(baseURI, tokenId.toString())) : "";
    }

    /**
     * @dev Base URI for computing {tokenURI}. If set, the resulting URI for each
     * token will be the concatenation of the `baseURI` and the `tokenId`. Empty
     * by default, can be overriden in child contracts.
     */
    function _baseURI() internal view virtual returns (string memory) {
        return "";
    }

    /**
     * @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 || 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 {
        _setApprovalForAll(_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 _owners[tokenId] != address(0);
    }

    /**
     * @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 || isApprovedForAll(owner, spender));
    }

    /**
     * @dev Safely mints `tokenId` and transfers it to `to`.
     *
     * Requirements:
     *
     * - `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);

        _balances[to] += 1;
        _owners[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);

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

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

        _balances[owner] -= 1;
        delete _owners[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");
        require(to != address(0), "ERC721: transfer to the zero address");

        _beforeTokenTransfer(from, to, tokenId);

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

        _balances[from] -= 1;
        _balances[to] += 1;
        _owners[tokenId] = to;

        emit Transfer(from, to, tokenId);
    }

    /**
     * @dev Approve `to` to operate on `tokenId`
     *
     * Emits a {Approval} event.
     */
    function _approve(address to, uint256 tokenId) internal virtual {
        _tokenApprovals[tokenId] = to;
        emit Approval(ERC721.ownerOf(tokenId), to, tokenId);
    }

    /**
     * @dev Approve `operator` to operate on all of `owner` tokens
     *
     * Emits a {ApprovalForAll} event.
     */
    function _setApprovalForAll(
        address owner,
        address operator,
        bool approved
    ) internal virtual {
        require(owner != operator, "ERC721: approve to caller");
        _operatorApprovals[owner][operator] = approved;
        emit ApprovalForAll(owner, operator, approved);
    }

    /**
     * @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()) {
            try IERC721Receiver(to).onERC721Received(_msgSender(), from, tokenId, _data) returns (bytes4 retval) {
                return retval == IERC721Receiver.onERC721Received.selector;
            } catch (bytes memory reason) {
                if (reason.length == 0) {
                    revert("ERC721: transfer to non ERC721Receiver implementer");
                } else {
                    assembly {
                        revert(add(32, reason), mload(reason))
                    }
                }
            }
        } else {
            return true;
        }
    }

    /**
     * @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` 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 tokenId
    ) internal virtual {}
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (security/Pausable.sol)

pragma solidity ^0.8.0;

import "../utils/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() {
        _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());
    }
}