Contract Source Code:

/*
    Blank Token
*/

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.14;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/Strings.sol";
import "@openzeppelin/contracts/utils/Counters.sol";
import "@rari-capital/solmate/src/tokens/ERC721.sol";
import "./SignedAllowance.sol";
import "./Base64.sol";

/// @title Blank Token
/// @author of the contract filio.eth (twitter.com/filmakarov)

contract BlankToken is ERC721, Ownable, SignedAllowance {  

    using Strings for uint256;
    using Counters for Counters.Counter;

    /*///////////////////////////////////////////////////////////////
                                GENERAL STORAGE
    //////////////////////////////////////////////////////////////*/

    // _tokenIds.current() will always return the last minted tokenId # + 1
    // it is actually the amount of minted tokens as we mint consistently startin from #0
    Counters.Counter private _tokenIds;

    uint256 public constant MAX_ITEMS = 1400;

    string public baseURI;
    bool public saleState;
    bool public mergingActive;

    uint256 public totalBurned;
    
    /*///////////////////////////////////////////////////////////////
                                INITIALISATION
    //////////////////////////////////////////////////////////////*/

    constructor(string memory _myBase) ERC721("Blank Token", "BLT") {
            baseURI = _myBase; 
    }

    /*///////////////////////////////////////////////////////////////
                        MINTING LOGIC
    //////////////////////////////////////////////////////////////*/

    function mint(address to, uint256 nonce, bytes memory signature) public {
        require (saleState, "Presale not active");
 
        require(totalSupply() + 1 <= MAX_ITEMS, ">MaxSupply");
        
        // this will throw if the allowance has already been used or is not valid
        _useAllowance(to, nonce, signature);

        // If you try to re-enter here thru onERC721Received, function will revert
        // Counter won't increment and your token will be overminted by the next minter.
        // Your allowance will be marked as used at this moment, i.e. wasted 
        _safeMint(to, _tokenIds.current()); 
        _tokenIds.increment();        
    }

    // adminMint
    function adminMint(address to, uint256 qty) public onlyOwner {
        for (uint256 i = 0; i < qty; i++) {
            _safeMint(to, _tokenIds.current()); 
            _tokenIds.increment();
        }
    }

    // burn 2 get 1
    function mergeTokens(uint256 tokenId1, uint256 tokenId2) public {
        require(mergingActive, "Blank Token: Merging has not started yet");
        require(ownerOf(tokenId1) == msg.sender && ownerOf(tokenId2) == msg.sender, "Blank Token: must own tokens to merge");
        _burn(tokenId1);
        _burn(tokenId2);
        totalBurned += 2;

        // If you try to re-enter here thru onERC721Received, function will revert
        // Counter won't increment and your token will be overminted by the next minter.
        // So you will burn two of your tokens and get nothing, so you better do not try to re-enter 
        _safeMint(msg.sender, _tokenIds.current()); 
        _tokenIds.increment();
    }

    /*///////////////////////////////////////////////////////////////
                       PUBLIC METADATA VIEWS
    //////////////////////////////////////////////////////////////*/

    function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
        require(_exists(tokenId), "Blank token: this token does not exist");

        string memory json = string(abi.encodePacked('{"name": "Blank Token #', tokenId.toString(), '", "description": "Blank Studio is a curation platform enabling artists from a plethora of backgrounds to disrupt the digital world. Join our collective today to participate in future drops from our talented artists.", "external_url": "https://blankstudio.art", "image": "',baseURI, tokenMediaId(tokenId).toString(), '.mp4","attributes": [{"trait_type": "Category", "value": "', tokenCategory(tokenId) ,'"}]}'));
        return string(abi.encodePacked('data:application/json;base64,', Base64.encode(bytes(json))));

        //return string(abi.encodePacked(baseURI, tokenId.toString()));
    }

    function tokenMediaId(uint256 tokenId) internal pure returns (uint256) {
        if (tokenId < MAX_ITEMS) {
            return 0;
        } else {
            // from 1 to 5
            return random(string(abi.encodePacked("MEDIA ID", tokenId.toString()))) % 5 + 1;
        }
    }

    function tokenCategory(uint256 tokenId) internal pure returns (string memory) {
        string[6] memory categories = ["Blank Token", "Vinyl token: Focusing Partially", 
                                        "Vinyl token: Goon Squad", "Vinyl token: Snack",
                                        "Vinyl token: Sneep Deep", "Vinyl token: Stars Falling"];
        return categories[tokenMediaId(tokenId)];
    }

    function random(string memory input) internal pure returns (uint256) {
        return uint256(keccak256(abi.encodePacked(input)));
    }

    /*///////////////////////////////////////////////////////////////
                       VIEWS
    //////////////////////////////////////////////////////////////*/

    function totalSupply() public view returns (uint256) {
        return (_tokenIds.current() - totalBurned);
    }

    /// @notice Iterates over all the exisitng tokens and checks if they belong to the user
    /// This function uses very much resources.
    /// !!! NEVER USE this function with write transactions DIRECTLY. 
    /// Only read from it and then pass data to the write tx
    /// @param tokenOwner user to get tokens of
    /// @return the array of token IDs 
    function tokensOfOwner(address tokenOwner) external view returns(uint256[] memory) {
        uint256 tokenCount = _balanceOf[tokenOwner];
        if (tokenCount == 0) {
            // Return an empty array
            return new uint256[](0);
        } else {
            uint256[] memory result = new uint256[](tokenCount);
            uint256 resultIndex = 0;
            uint256 NFTId;
            for (NFTId = 0; NFTId < _tokenIds.current(); NFTId++) { 
                if (_exists(NFTId)) { 
                    if (_ownerOf[NFTId] == tokenOwner) {
                        result[resultIndex] = NFTId;
                        resultIndex++;
                    }
                } 
            }     
            return result;
        }
    }

    function _exists(uint256 tokenId) internal view returns (bool) {
        return (_ownerOf[tokenId] != address(0));
    }

    function ownerOf(uint256 tokenId) public view virtual override returns (address owner) {
        require (_exists(tokenId), "Blank Token: Not minted or burned");
        return (_ownerOf[tokenId]);
    }

    function nextTokenIndex() public view returns (uint256) {
        return _tokenIds.current();
    }

    /*///////////////////////////////////////////////////////////////
                       ADMIN FUNCTIONS
    //////////////////////////////////////////////////////////////*/
    
    function setBaseURI(string memory _newBaseURI) public onlyOwner {
        baseURI = _newBaseURI;
    }

    function switchSaleState() public onlyOwner {
        saleState = !saleState;
    }

    function switchMergeState() public onlyOwner {
        mergingActive = !mergingActive;
    }

    /// @notice sets allowance signer, this can be used to revoke all unused allowances already out there
    /// @param newSigner the new signer
    function setAllowancesSigner(address newSigner) external onlyOwner {
        _setAllowancesSigner(newSigner);
    }

    /// @notice Withdraws funds from the contract to msg.sender who is always the owner.
    /// No need to use reentrancy guard as receiver is always owner
    /// @param amt amount to withdraw in wei
    function withdraw(uint256 amt) public onlyOwner {
         address payable beneficiary = payable(owner());
        (bool success, ) = beneficiary.call{value: amt}("");
        if (!success) revert ("Withdrawal failed");
    }    

}

//   That's all, folks!

//SPDX-License-Identifier: MIT
pragma solidity ^0.8.11;

import '@openzeppelin/contracts/utils/cryptography/ECDSA.sol';

/// @title SignedAllowance
/// @author Simon Fremaux (@dievardump)
contract SignedAllowance {
    using ECDSA for bytes32;

    // list of already used allowances
    mapping(bytes32 => bool) public usedAllowances;

    // address used to sign the allowances
    address private _allowancesSigner;

    /// @notice Helper to know allowancesSigner address
    /// @return the allowance signer address
    function allowancesSigner() public view virtual returns (address) {
        return _allowancesSigner;
    }

    /// @notice Helper that creates the message that signer needs to sign to allow a mint
    ///         this is usually also used when creating the allowances, to ensure "message"
    ///         is the same
    /// @param account the account to allow
    /// @param nonce the nonce
    /// @return the message to sign
    function createMessage(address account, uint256 nonce)
        public
        view
        returns (bytes32)
    {
        return keccak256(abi.encode(account, nonce, address(this)));
    }

    /// @notice Helper that creates a list of messages that signer needs to sign to allow mintings
    /// @param accounts the accounts to allow
    /// @param nonces the corresponding nonces
    /// @return messages the messages to sign
  /*  
    // function is commented out to save space in the contract
    // to batch create message will need to use for loop with the createMessage function

    function createMessages(address[] memory accounts, uint256[] memory nonces)
        external
        view
        returns (bytes32[] memory messages)
    {
        require(accounts.length == nonces.length, '!LENGTH_MISMATCH!');
        messages = new bytes32[](accounts.length);
        for (uint256 i; i < accounts.length; i++) {
            messages[i] = createMessage(accounts[i], nonces[i]);
        }
    } */

    /// @notice This function verifies that the current request is valid
    /// @dev It ensures that _allowancesSigner signed a message containing (account, nonce, address(this))
    ///      and that this message was not already used
    /// @param account the account the allowance is associated to
    /// @param nonce the nonce associated to this allowance
    /// @param signature the signature by the allowance signer wallet
    /// @return the message to mark as used
    function validateSignature(
        address account,
        uint256 nonce,
        bytes memory signature
    ) public view returns (bytes32) {
        return
            _validateSignature(account, nonce, signature, allowancesSigner());
    }

    /// @dev It ensures that signer signed a message containing (account, nonce, address(this))
    ///      and that this message was not already used
    /// @param account the account the allowance is associated to
    /// @param nonce the nonce associated to this allowance
    /// @param signature the signature by the allowance signer wallet
    /// @param signer the signer
    /// @return the message to mark as used
    function _validateSignature(
        address account,
        uint256 nonce,
        bytes memory signature,
        address signer
    ) internal view returns (bytes32) {
        bytes32 message = createMessage(account, nonce)
            .toEthSignedMessageHash();

        // verifies that the sha3(account, nonce, address(this)) has been signed by signer
        require(message.recover(signature) == signer, '!INVALID_SIGNATURE!');

        // verifies that the allowances was not already used
        require(usedAllowances[message] == false, '!ALREADY_USED!');

        return message;
    }

    /// @notice internal function that verifies an allowance and marks it as used
    ///         this function throws if signature is wrong or this nonce for this user has already been used
    /// @param account the account the allowance is associated to
    /// @param nonce the nonce
    /// @param signature the signature by the allowance wallet
    function _useAllowance(
        address account,
        uint256 nonce,
        bytes memory signature
    ) internal {
        bytes32 message = validateSignature(account, nonce, signature);
        usedAllowances[message] = true;
    }

    /// @notice Allows to change the allowance signer. This can be used to revoke any signed allowance not already used
    /// @param newSigner the new signer address
    function _setAllowancesSigner(address newSigner) internal {
        _allowancesSigner = newSigner;
    }
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/// @title Base64
/// @notice Provides a function for encoding some bytes in base64
/// @author Brecht Devos <brecht@loopring.org>
library Base64 {
    bytes internal constant TABLE = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    /// @notice Encodes some bytes to the base64 representation
    function encode(bytes memory data) internal pure returns (string memory) {
        uint256 len = data.length;
        if (len == 0) return "";

        // multiply by 4/3 rounded up
        uint256 encodedLen = 4 * ((len + 2) / 3);

        // Add some extra buffer at the end
        bytes memory result = new bytes(encodedLen + 32);

        bytes memory table = TABLE;

        assembly {
            let tablePtr := add(table, 1)
            let resultPtr := add(result, 32)

            for {
                let i := 0
            } lt(i, len) {

            } {
                i := add(i, 3)
                let input := and(mload(add(data, i)), 0xffffff)

                let out := mload(add(tablePtr, and(shr(18, input), 0x3F)))
                out := shl(8, out)
                out := add(out, and(mload(add(tablePtr, and(shr(12, input), 0x3F))), 0xFF))
                out := shl(8, out)
                out := add(out, and(mload(add(tablePtr, and(shr(6, input), 0x3F))), 0xFF))
                out := shl(8, out)
                out := add(out, and(mload(add(tablePtr, and(input, 0x3F))), 0xFF))
                out := shl(224, out)

                mstore(resultPtr, out)

                resultPtr := add(resultPtr, 4)
            }

            switch mod(len, 3)
            case 1 {
                mstore(sub(resultPtr, 2), shl(240, 0x3d3d))
            }
            case 2 {
                mstore(sub(resultPtr, 1), shl(248, 0x3d))
            }

            mstore(result, encodedLen)
        }

        return string(result);
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (access/Ownable.sol)

pragma solidity ^0.8.0;

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

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

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

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _transferOwnership(_msgSender());
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        _checkOwner();
        _;
    }

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

    /**
     * @dev Throws if the sender is not the owner.
     */
    function _checkOwner() internal view virtual {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
    }

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

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

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (utils/Strings.sol)

pragma solidity ^0.8.0;

/**
 * @dev String operations.
 */
library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";
    uint8 private constant _ADDRESS_LENGTH = 20;

    /**
     * @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);
    }

    /**
     * @dev Converts an `address` with fixed length of 20 bytes to its not checksummed ASCII `string` hexadecimal representation.
     */
    function toHexString(address addr) internal pure returns (string memory) {
        return toHexString(uint256(uint160(addr)), _ADDRESS_LENGTH);
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Counters.sol)

pragma solidity ^0.8.0;

/**
 * @title Counters
 * @author Matt Condon (@shrugs)
 * @dev Provides counters that can only be incremented, decremented or reset. 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;`
 */
library Counters {
    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 {
        unchecked {
            counter._value += 1;
        }
    }

    function decrement(Counter storage counter) internal {
        uint256 value = counter._value;
        require(value > 0, "Counter: decrement overflow");
        unchecked {
            counter._value = value - 1;
        }
    }

    function reset(Counter storage counter) internal {
        counter._value = 0;
    }
}

// SPDX-License-Identifier: AGPL-3.0-only
pragma solidity >=0.8.0;

/// @notice Modern, minimalist, and gas efficient ERC-721 implementation.
/// @author Solmate (https://github.com/Rari-Capital/solmate/blob/main/src/tokens/ERC721.sol)
abstract contract ERC721 {
    /*//////////////////////////////////////////////////////////////
                                 EVENTS
    //////////////////////////////////////////////////////////////*/

    event Transfer(address indexed from, address indexed to, uint256 indexed id);

    event Approval(address indexed owner, address indexed spender, uint256 indexed id);

    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

    /*//////////////////////////////////////////////////////////////
                         METADATA STORAGE/LOGIC
    //////////////////////////////////////////////////////////////*/

    string public name;

    string public symbol;

    function tokenURI(uint256 id) public view virtual returns (string memory);

    /*//////////////////////////////////////////////////////////////
                      ERC721 BALANCE/OWNER STORAGE
    //////////////////////////////////////////////////////////////*/

    mapping(uint256 => address) internal _ownerOf;

    mapping(address => uint256) internal _balanceOf;

    function ownerOf(uint256 id) public view virtual returns (address owner) {
        require((owner = _ownerOf[id]) != address(0), "NOT_MINTED");
    }

    function balanceOf(address owner) public view virtual returns (uint256) {
        require(owner != address(0), "ZERO_ADDRESS");

        return _balanceOf[owner];
    }

    /*//////////////////////////////////////////////////////////////
                         ERC721 APPROVAL STORAGE
    //////////////////////////////////////////////////////////////*/

    mapping(uint256 => address) public getApproved;

    mapping(address => mapping(address => bool)) public isApprovedForAll;

    /*//////////////////////////////////////////////////////////////
                               CONSTRUCTOR
    //////////////////////////////////////////////////////////////*/

    constructor(string memory _name, string memory _symbol) {
        name = _name;
        symbol = _symbol;
    }

    /*//////////////////////////////////////////////////////////////
                              ERC721 LOGIC
    //////////////////////////////////////////////////////////////*/

    function approve(address spender, uint256 id) public virtual {
        address owner = _ownerOf[id];

        require(msg.sender == owner || isApprovedForAll[owner][msg.sender], "NOT_AUTHORIZED");

        getApproved[id] = spender;

        emit Approval(owner, spender, id);
    }

    function setApprovalForAll(address operator, bool approved) public virtual {
        isApprovedForAll[msg.sender][operator] = approved;

        emit ApprovalForAll(msg.sender, operator, approved);
    }

    function transferFrom(
        address from,
        address to,
        uint256 id
    ) public virtual {
        require(from == _ownerOf[id], "WRONG_FROM");

        require(to != address(0), "INVALID_RECIPIENT");

        require(
            msg.sender == from || isApprovedForAll[from][msg.sender] || msg.sender == getApproved[id],
            "NOT_AUTHORIZED"
        );

        // Underflow of the sender's balance is impossible because we check for
        // ownership above and the recipient's balance can't realistically overflow.
        unchecked {
            _balanceOf[from]--;

            _balanceOf[to]++;
        }

        _ownerOf[id] = to;

        delete getApproved[id];

        emit Transfer(from, to, id);
    }

    function safeTransferFrom(
        address from,
        address to,
        uint256 id
    ) public virtual {
        transferFrom(from, to, id);

        require(
            to.code.length == 0 ||
                ERC721TokenReceiver(to).onERC721Received(msg.sender, from, id, "") ==
                ERC721TokenReceiver.onERC721Received.selector,
            "UNSAFE_RECIPIENT"
        );
    }

    function safeTransferFrom(
        address from,
        address to,
        uint256 id,
        bytes calldata data
    ) public virtual {
        transferFrom(from, to, id);

        require(
            to.code.length == 0 ||
                ERC721TokenReceiver(to).onERC721Received(msg.sender, from, id, data) ==
                ERC721TokenReceiver.onERC721Received.selector,
            "UNSAFE_RECIPIENT"
        );
    }

    /*//////////////////////////////////////////////////////////////
                              ERC165 LOGIC
    //////////////////////////////////////////////////////////////*/

    function supportsInterface(bytes4 interfaceId) public view virtual returns (bool) {
        return
            interfaceId == 0x01ffc9a7 || // ERC165 Interface ID for ERC165
            interfaceId == 0x80ac58cd || // ERC165 Interface ID for ERC721
            interfaceId == 0x5b5e139f; // ERC165 Interface ID for ERC721Metadata
    }

    /*//////////////////////////////////////////////////////////////
                        INTERNAL MINT/BURN LOGIC
    //////////////////////////////////////////////////////////////*/

    function _mint(address to, uint256 id) internal virtual {
        require(to != address(0), "INVALID_RECIPIENT");

        require(_ownerOf[id] == address(0), "ALREADY_MINTED");

        // Counter overflow is incredibly unrealistic.
        unchecked {
            _balanceOf[to]++;
        }

        _ownerOf[id] = to;

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

    function _burn(uint256 id) internal virtual {
        address owner = _ownerOf[id];

        require(owner != address(0), "NOT_MINTED");

        // Ownership check above ensures no underflow.
        unchecked {
            _balanceOf[owner]--;
        }

        delete _ownerOf[id];

        delete getApproved[id];

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

    /*//////////////////////////////////////////////////////////////
                        INTERNAL SAFE MINT LOGIC
    //////////////////////////////////////////////////////////////*/

    function _safeMint(address to, uint256 id) internal virtual {
        _mint(to, id);

        require(
            to.code.length == 0 ||
                ERC721TokenReceiver(to).onERC721Received(msg.sender, address(0), id, "") ==
                ERC721TokenReceiver.onERC721Received.selector,
            "UNSAFE_RECIPIENT"
        );
    }

    function _safeMint(
        address to,
        uint256 id,
        bytes memory data
    ) internal virtual {
        _mint(to, id);

        require(
            to.code.length == 0 ||
                ERC721TokenReceiver(to).onERC721Received(msg.sender, address(0), id, data) ==
                ERC721TokenReceiver.onERC721Received.selector,
            "UNSAFE_RECIPIENT"
        );
    }
}

/// @notice A generic interface for a contract which properly accepts ERC721 tokens.
/// @author Solmate (https://github.com/Rari-Capital/solmate/blob/main/src/tokens/ERC721.sol)
abstract contract ERC721TokenReceiver {
    function onERC721Received(
        address,
        address,
        uint256,
        bytes calldata
    ) external virtual returns (bytes4) {
        return ERC721TokenReceiver.onERC721Received.selector;
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.3) (utils/cryptography/ECDSA.sol)

pragma solidity ^0.8.0;

import "../Strings.sol";

/**
 * @dev Elliptic Curve Digital Signature Algorithm (ECDSA) operations.
 *
 * These functions can be used to verify that a message was signed by the holder
 * of the private keys of a given address.
 */
library ECDSA {
    enum RecoverError {
        NoError,
        InvalidSignature,
        InvalidSignatureLength,
        InvalidSignatureS,
        InvalidSignatureV
    }

    function _throwError(RecoverError error) private pure {
        if (error == RecoverError.NoError) {
            return; // no error: do nothing
        } else if (error == RecoverError.InvalidSignature) {
            revert("ECDSA: invalid signature");
        } else if (error == RecoverError.InvalidSignatureLength) {
            revert("ECDSA: invalid signature length");
        } else if (error == RecoverError.InvalidSignatureS) {
            revert("ECDSA: invalid signature 's' value");
        } else if (error == RecoverError.InvalidSignatureV) {
            revert("ECDSA: invalid signature 'v' value");
        }
    }

    /**
     * @dev Returns the address that signed a hashed message (`hash`) with
     * `signature` or error string. This address can then be used for verification purposes.
     *
     * The `ecrecover` EVM opcode allows for malleable (non-unique) signatures:
     * this function rejects them by requiring the `s` value to be in the lower
     * half order, and the `v` value to be either 27 or 28.
     *
     * IMPORTANT: `hash` _must_ be the result of a hash operation for the
     * verification to be secure: it is possible to craft signatures that
     * recover to arbitrary addresses for non-hashed data. A safe way to ensure
     * this is by receiving a hash of the original message (which may otherwise
     * be too long), and then calling {toEthSignedMessageHash} on it.
     *
     * Documentation for signature generation:
     * - with https://web3js.readthedocs.io/en/v1.3.4/web3-eth-accounts.html#sign[Web3.js]
     * - with https://docs.ethers.io/v5/api/signer/#Signer-signMessage[ethers]
     *
     * _Available since v4.3._
     */
    function tryRecover(bytes32 hash, bytes memory signature) internal pure returns (address, RecoverError) {
        if (signature.length == 65) {
            bytes32 r;
            bytes32 s;
            uint8 v;
            // ecrecover takes the signature parameters, and the only way to get them
            // currently is to use assembly.
            /// @solidity memory-safe-assembly
            assembly {
                r := mload(add(signature, 0x20))
                s := mload(add(signature, 0x40))
                v := byte(0, mload(add(signature, 0x60)))
            }
            return tryRecover(hash, v, r, s);
        } else {
            return (address(0), RecoverError.InvalidSignatureLength);
        }
    }

    /**
     * @dev Returns the address that signed a hashed message (`hash`) with
     * `signature`. This address can then be used for verification purposes.
     *
     * The `ecrecover` EVM opcode allows for malleable (non-unique) signatures:
     * this function rejects them by requiring the `s` value to be in the lower
     * half order, and the `v` value to be either 27 or 28.
     *
     * IMPORTANT: `hash` _must_ be the result of a hash operation for the
     * verification to be secure: it is possible to craft signatures that
     * recover to arbitrary addresses for non-hashed data. A safe way to ensure
     * this is by receiving a hash of the original message (which may otherwise
     * be too long), and then calling {toEthSignedMessageHash} on it.
     */
    function recover(bytes32 hash, bytes memory signature) internal pure returns (address) {
        (address recovered, RecoverError error) = tryRecover(hash, signature);
        _throwError(error);
        return recovered;
    }

    /**
     * @dev Overload of {ECDSA-tryRecover} that receives the `r` and `vs` short-signature fields separately.
     *
     * See https://eips.ethereum.org/EIPS/eip-2098[EIP-2098 short signatures]
     *
     * _Available since v4.3._
     */
    function tryRecover(
        bytes32 hash,
        bytes32 r,
        bytes32 vs
    ) internal pure returns (address, RecoverError) {
        bytes32 s = vs & bytes32(0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff);
        uint8 v = uint8((uint256(vs) >> 255) + 27);
        return tryRecover(hash, v, r, s);
    }

    /**
     * @dev Overload of {ECDSA-recover} that receives the `r and `vs` short-signature fields separately.
     *
     * _Available since v4.2._
     */
    function recover(
        bytes32 hash,
        bytes32 r,
        bytes32 vs
    ) internal pure returns (address) {
        (address recovered, RecoverError error) = tryRecover(hash, r, vs);
        _throwError(error);
        return recovered;
    }

    /**
     * @dev Overload of {ECDSA-tryRecover} that receives the `v`,
     * `r` and `s` signature fields separately.
     *
     * _Available since v4.3._
     */
    function tryRecover(
        bytes32 hash,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal pure returns (address, RecoverError) {
        // EIP-2 still allows signature malleability for ecrecover(). Remove this possibility and make the signature
        // unique. Appendix F in the Ethereum Yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), defines
        // the valid range for s in (301): 0 < s < secp256k1n ÷ 2 + 1, and for v in (302): v ∈ {27, 28}. Most
        // signatures from current libraries generate a unique signature with an s-value in the lower half order.
        //
        // If your library generates malleable signatures, such as s-values in the upper range, calculate a new s-value
        // with 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141 - s1 and flip v from 27 to 28 or
        // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
        // these malleable signatures as well.
        if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) {
            return (address(0), RecoverError.InvalidSignatureS);
        }
        if (v != 27 && v != 28) {
            return (address(0), RecoverError.InvalidSignatureV);
        }

        // If the signature is valid (and not malleable), return the signer address
        address signer = ecrecover(hash, v, r, s);
        if (signer == address(0)) {
            return (address(0), RecoverError.InvalidSignature);
        }

        return (signer, RecoverError.NoError);
    }

    /**
     * @dev Overload of {ECDSA-recover} that receives the `v`,
     * `r` and `s` signature fields separately.
     */
    function recover(
        bytes32 hash,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal pure returns (address) {
        (address recovered, RecoverError error) = tryRecover(hash, v, r, s);
        _throwError(error);
        return recovered;
    }

    /**
     * @dev Returns an Ethereum Signed Message, created from a `hash`. This
     * produces hash corresponding to the one signed with the
     * https://eth.wiki/json-rpc/API#eth_sign[`eth_sign`]
     * JSON-RPC method as part of EIP-191.
     *
     * See {recover}.
     */
    function toEthSignedMessageHash(bytes32 hash) internal pure returns (bytes32) {
        // 32 is the length in bytes of hash,
        // enforced by the type signature above
        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));
    }

    /**
     * @dev Returns an Ethereum Signed Message, created from `s`. This
     * produces hash corresponding to the one signed with the
     * https://eth.wiki/json-rpc/API#eth_sign[`eth_sign`]
     * JSON-RPC method as part of EIP-191.
     *
     * See {recover}.
     */
    function toEthSignedMessageHash(bytes memory s) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n", Strings.toString(s.length), s));
    }

    /**
     * @dev Returns an Ethereum Signed Typed Data, created from a
     * `domainSeparator` and a `structHash`. This produces hash corresponding
     * to the one signed with the
     * https://eips.ethereum.org/EIPS/eip-712[`eth_signTypedData`]
     * JSON-RPC method as part of EIP-712.
     *
     * See {recover}.
     */
    function toTypedDataHash(bytes32 domainSeparator, bytes32 structHash) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (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;
    }
}