// File: contracts/Hailstone.sol



//SPDX-License-Identifier: MIT
pragma solidity 0.8.10;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol";


// ABOUT: HAILSTONE is a work in solidity celebrating the Collatz conjecture.
//        https://en.wikipedia.org/wiki/Collatz_conjecture
//
//        HAILSTONE implements the Collatz algorithm in reverse to create a
//        path of NFTs away from the seed number 1

// HOW-TO: Each HAILSTONE NFT has a unique tokenId.
//
//         The last tokenId minted at any time becomes "head".
//
//         Head can be found by calling the head() function.
//
//         HAILSTONEs can be minted by calling the mint() function
//         while providing the next tokenId as the message value in wei.
//
//         The next tokenId/wei must be either:
//         head * 2
//         or
//         (head - 1) / 3    [if such a value exists, is odd, and not divisible by 3]
//
//         Thus the head will move up and down as a combination of human rationale
//         and the constraints of the algorithm. Together all minters will create
//         a unique Collatz path through the integers.
//
//         The Collatz algorithm and head value alone contain enough information
//         to traverse all previous HAILSTONE NFTs' tokenIds back to HAILSTONE 1.


contract Hailstone is ERC721Enumerable, Ownable, ReentrancyGuard {
    using Bitmask for uint256;

    uint constant MAX_UINT = 2**256 - 1;

    constructor()
    ERC721("HAILSTONE", "HAILS") {
        _mint(msg.sender, head);
    }


    ///////
    // Core
    ///////

    uint public head = 1;

    function mint() external payable nonReentrant() {
        uint msgValue = msg.value;

        if (msgValue == nextHigher(head) || msgValue == nextLower(head)) {
            checkGatewayTimeout();
            head = msgValue;
            _safeMint(_msgSender(), msgValue);
            return;
        }

        revert("message value was not a valid next step in sequence");
    }

    function nextHigher(uint _h) internal pure returns (uint) {
        return 2 * _h;
    }

    function nextLower(uint _h) internal pure returns (uint) {
        // Only proceed if (_h - 1) / 3 is an integer and is odd
        // NOTE: Because we first check that _h % 3 == 1 we know
        //       that _h / 3 will produce the same result as (_h - 1) / 3
        //       because the remainer of _h / 3 is always 1 and
        //       is always truncated in integer division by 3
        if (_h % 3 != 1 || (_h / 3) % 2 == 0) {
            return MAX_UINT;
        }

        // NOTE: Once you reach a head divisible by 3 you can only
        //       keep doubling forever *I think* (>_<). This is no fun
        //       so we catch this before we get to that situation.
        if (((_h / 3) % 3 == 0)) {
            return MAX_UINT;
        }

        // NOTE: (1 - 1) % 3 == 0, we don't want to go to 0 so we special-case reject 1->0
        // NOTE: 1->2->4->1 is a cycle, we break it by special-case rejecting 4->1
        if (_h == 1 || _h == 4) {
            return MAX_UINT;
        }

        return _h / 3;
    }

    function adminWithdraw(uint _amount) external {
        (bool success, ) = payable(owner()).call{ value: _amount }("");
        require(success, "nope");
    }


    ///////////////
    // Core [Extra]
    ///////////////

    bool public easyMode;

    function adminEasyMode(bool _b) external onlyOwner() {
        easyMode = _b;
    }

    modifier onlyEasyMode() {
        require(easyMode, "get head + use a calculator :)");
        _;
    }

    function getNextHigher() public view onlyEasyMode() returns (uint) {
        return nextHigher(head);
    }

    function getNextLower() public view onlyEasyMode() returns (uint) {
        return nextLower(head);
    }

    // NOTE: Never public visiblity, it makes things too easy, less dynamic, and less fun.
    function getCheapest(uint _head) internal pure returns (uint) {
        uint low = nextLower(_head);

        if (low != MAX_UINT) {
            return low;
        }

        return nextHigher(_head);
    }

    function previous(uint _n) external pure returns (uint) {
        // NOTE: if _n == 1, we go to 1->4->2->1->...

        if (_n % 2 == 0) {
            return _n / 2;
        }

        return (3 * _n) + 1;
    }

    // NOTE: Not needed for current implementation, but maybe interesting..
    function getNth(uint _idx) public view returns (uint) {
        return getNthPure(_idx, totalSupply(), head);
    }

    function getNthPure(uint _idx, uint _supply, uint _head) public pure returns (uint v) {
        require(_idx > 0, "start counting at 1");
        require(_idx <= _supply, "idx can't be greater than supply");

        uint i = _supply;
        v = _head;

        while (true) {
            if (_idx == i) {
                return v;
            }

            if (v % 2 == 0) {
                v = v / 2;
            } else {
                v = 3 * v + 1;
            }

            i--;
        }
    }


    /////////////////////
    // Token URI and JSON
    /////////////////////

    function tokenURI(uint _tokenId) public view override returns (string memory output) {
        uint vis = customVis[_tokenId];
        string memory json = Base64.encode(bytes(string(abi.encodePacked(
            '{',
            getJsonName(_tokenId),
            getJsonDescription(_tokenId),
            getJsonImage(_tokenId),
            getJsonAnimation(_tokenId, vis),
            '}'
        ))));
        output = string(abi.encodePacked('data:application/json;base64,', json));
    }

    function getJsonName(uint _tokenId) internal pure returns (string memory) {
        return string(abi.encodePacked('"name": "HAILSTONE ', Conv.uintToString(_tokenId), '"'));
    }

    function getJsonDescription(uint _tokenId) internal pure returns (string memory) {
        return string(abi.encodePacked(',"description": "HAILSTONE ', Conv.uintToString(_tokenId), '"'));
    }

    function getJsonImage(uint _tokenId) internal pure returns (string memory) {
        return string(abi.encodePacked(',"image": "data:image/svg+xml;base64,', Base64.encode(bytes(HailImage.createSvgImage(_tokenId))), '"'));
    }

    function getJsonAnimation(uint _tokenId, uint _vis) internal view returns (string memory) {
        if (_vis.hasBit(FLAG_GRAPH_DISABLE)) {
            return "";
        }

        return string(abi.encodePacked(',"animation_url": "', createThreeGraph(_vis.hasBit(FLAG_GRAPH_LOG), head, _tokenId) ,'"'));
    }


    ///////////////////////
    // Visualization Custom
    ///////////////////////

    uint8 constant FLAG_GRAPH_DISABLE = 0;
    uint8 constant FLAG_GRAPH_LOG = 1;

    mapping(uint => uint) customVis;

    modifier onlyApprovedOrOwner(uint _tokenId) {
        require(_isApprovedOrOwner(_msgSender(), _tokenId), "must be token owner/approved");
        _;
    }

    // NOTE: Token owners can customize thier specific token's visualization. While this should generally be
    //       unnecessary it may be useful in the listed circumstances:

    //  - The three.js IPFS content becomes unavailable and the contract owner is unable or unwilling
    //    to correct this.
    function customGraphDisable(uint _tokenId, bool _b) external onlyApprovedOrOwner(_tokenId) {
        customVis[_tokenId] = customVis[_tokenId].chooseBit(FLAG_GRAPH_DISABLE, _b);
    }

    //  - A user prefers the three.js graph to begin rendering as logarithmic rather than linear
    //    depending on A E S T H E T I C S and the current size and shape of the hailstone path.
    function customGraphLog(uint _tokenId, bool _b) external onlyApprovedOrOwner(_tokenId) {
        customVis[_tokenId] = customVis[_tokenId].chooseBit(FLAG_GRAPH_LOG, _b);
    }


    ///////////////////////////////
    // Visualization Three.JS Graph
    ///////////////////////////////

    string systemThreeUri = "ipfs://QmQk6NT44gE2Wy2VEMV2kpptyaNBTZ4oSQ2vZosAPNg13W";

    function adminThreeUri(string calldata _threeUri) external onlyOwner() {
        systemThreeUri = _threeUri;
    }

    function createThreeGraph(bool _log, uint _head, uint _tokenId) internal view returns (string memory) {
        string memory logStr = "";
        if (_log) {
            logStr = "&log=1";
        }

        return string(abi.encodePacked(
            systemThreeUri,
            "?head=", Conv.uintToString(_head),
            "&target=", Conv.uintToString(_tokenId),
            "&network=1",   // PROD: network=1 for prod
            logStr
        ));
    }

    // Up - Log
    // Down - Lin
    // Left Left - ?
    // Right Right - ?


    /////////////////////
    // Gateway Management
    /////////////////////

    function checkGatewayTimeout() internal view {
        // PROD: uncomment for prod
        require(balanceOf(msg.sender) < 2, "client gateway timeout"); // The Tourist [Chorus]
    }


    ////////////////////
    // Contract Metadata
    ////////////////////

    string systemContractImageUri = "ipfs://Qmc1ku4XyZyVrtgppnw3VpmQdg7hpZfppdsxGPNd97yddc";

    function adminContractImageUri(string calldata _contractImageUri) external onlyOwner() {
        systemContractImageUri = _contractImageUri;
    }

    function contractURI() public view returns (string memory output) {
        string memory json = Base64.encode(bytes(string(abi.encodePacked(
            '{'
                '"name": "HAILSTONE", '
                '"description": "HAILSTONE is a work in solidity celebrating the Collatz conjecture.", '
                '"image": "', systemContractImageUri, '" '
            '}'
        ))));

        output = string(abi.encodePacked('data:application/json;base64,', json));
    }
}


//////////////////////////
// Visualization SVG Image
//////////////////////////

library HailImage {
    function createSvgImage(uint _tokenId) external pure returns (string memory) {
        return string(abi.encodePacked(
            '<svg xmlns="http://www.w3.org/2000/svg" preserveAspectRatio="xMinYMin meet" viewBox="0 0 350 350">'
            '<style>'
                '@font-face {'
                    'font-family: "zen_kaku_gothic_new_light";'
                    'src: url(data:application/font-woff2;charset=utf-8;base64,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) format("woff2");'
                    'font-weight: light;'
                    'font-style: normal;'
                '} '
                '.base { fill: #222222; font-family: zen_kaku_gothic_new_light, sans-serif; text-anchor: middle } '
                '.tit { font-size: 30px; } '
                '.num { font-size: 32px; } '
                '.poly { fill: #22222244; transform-origin: center; } '
            '</style>'
            '<rect width="100%" height="100%" fill="#dbd8d6" />'
            '<text x="175" y="52" class="base tit">HAILSTONE</text>'
            '<text x="175" y="97" class="base num">', Conv.uintToString(_tokenId), '</text>'
            '<g transform-origin="center" transform="translate(0,20)">',
            polyLayer(_tokenId, 13, 11, true),
            polyLayer(_tokenId, 19, 17, true),
            polyLayer(_tokenId, 29, 23, true),
            extraPolys(_tokenId),
            '</g></svg>'
        ));
    }



    function extraPolys(uint _tokenId) internal pure returns (string memory out) {
        uint dig = countDigits(_tokenId);
        out = string(abi.encodePacked(
            polyLayer(_tokenId, 37, 31, dig > 2),
            polyLayer(_tokenId, 41, 43, dig > 3),
            polyLayer(_tokenId, 53, 47, dig > 5),
            polyLayer(_tokenId, 61, 59, dig > 10),
            polyLayer(_tokenId, 71, 67, dig > 15)
        ));
    }

    function polyLayer(uint _tokenId, uint _modX, uint _modY, bool _active) internal pure returns (string memory) {
        if (!_active) {
            return "";
        }

        return string(abi.encodePacked(
            '<polygon class="poly" points="175,173 177,175, 175,177 173,175" transform="scale(',
            Conv.uintToString(_tokenId % _modX),
            ',',
            Conv.uintToString(_tokenId % _modY),
            ')" />'
        ));
    }

    function countDigits(uint n) internal pure returns (uint r) {
        while (n > 0) {
            r += 1;
            n /= 10;
        }
    }

    function createContractImage() external pure returns (string memory) {
        return string(abi.encodePacked(
            '<svg xmlns="http://www.w3.org/2000/svg" preserveAspectRatio="xMinYMin meet" viewBox="0 0 350 350">'
            '<style>'
                '.poly { fill: #22222244; transform-origin: center; } '
            '</style>'
            '<rect width="100%" height="100%" fill="#dbd8d6" />'
            '<polygon class="poly" points="175,173 177,175, 175,177 173,175" transform="scale(13, 11)" />'
            '<polygon class="poly" points="175,173 177,175, 175,177 173,175" transform="scale(19, 17)" />'
            '<polygon class="poly" points="175,173 177,175, 175,177 173,175" transform="scale(29, 23)" />'
            '<polygon class="poly" points="175,173 177,175, 175,177 173,175" transform="scale(37, 31)" />'
            '<polygon class="poly" points="175,173 177,175, 175,177 173,175" transform="scale(43, 41)" />'
            '<polygon class="poly" points="175,173 177,175, 175,177 173,175" transform="scale(53, 47)" />'
            '<polygon class="poly" points="175,173 177,175, 175,177 173,175" transform="scale(61, 59)" />'
            '<polygon class="poly" points="175,173 177,175, 175,177 173,175" transform="scale(71, 67)" />'
            '</svg>'
        ));
    }
}


////////////////////
// Support Libraries
////////////////////

library Conv {
    // Copied from 'Loot', ty!
    function uintToString(uint256 value) internal pure returns (string memory) {
    // Inspired by OraclizeAPI's implementation - MIT license
    // 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);
    }
}


/// [MIT License]
/// @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);
    }
}


/**
* @title Library implementing bitmask operations
* @author TruSet, modified by hailstone authors
* @dev A maximum of 256 bits can be operated on when storing bits in a uint256, so the bitIndex is a uint8
*/
library Bitmask {
    function hasBit(uint256 bits, uint8 bitIndex) internal pure returns (bool) {
        return (bits & (uint(1) << bitIndex)) > 0;
    }

    function setBit(uint256 bits, uint8 bitIndex) internal pure returns (uint256) {
        uint256 bit = (uint(1) << bitIndex);
        return bits | bit;
    }

    function unsetBit(uint256 bits, uint8 bitIndex) internal pure returns (uint256) {
        uint256 bitmask = ~(uint(1) << bitIndex);
        return bits & bitmask;
    }

    // added by hailstone authors
    function chooseBit(uint256 bits, uint8 bitIndex, bool b) internal pure returns (uint256) {
        if (b) {
            return setBit(bits, bitIndex);
        }

        return unsetBit(bits, bitIndex);
    }
}


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



// SPDX-License-Identifier: MIT

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() {
        _setOwner(_msgSender());
    }

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

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

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

    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor() {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

// File: @openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../ERC721.sol";
import "./IERC721Enumerable.sol";

/**
 * @dev This implements an optional extension of {ERC721} defined in the EIP that adds
 * enumerability of all the token ids in the contract as well as all token ids owned by each
 * account.
 */
abstract contract ERC721Enumerable is ERC721, IERC721Enumerable {
    // Mapping from owner to list of owned token IDs
    mapping(address => mapping(uint256 => uint256)) private _ownedTokens;

    // Mapping from token ID to index of the owner tokens list
    mapping(uint256 => uint256) private _ownedTokensIndex;

    // Array with all token ids, used for enumeration
    uint256[] private _allTokens;

    // Mapping from token id to position in the allTokens array
    mapping(uint256 => uint256) private _allTokensIndex;

    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC721) returns (bool) {
        return interfaceId == type(IERC721Enumerable).interfaceId || super.supportsInterface(interfaceId);
    }

    /**
     * @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) public view virtual override returns (uint256) {
        require(index < ERC721.balanceOf(owner), "ERC721Enumerable: owner index out of bounds");
        return _ownedTokens[owner][index];
    }

    /**
     * @dev See {IERC721Enumerable-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _allTokens.length;
    }

    /**
     * @dev See {IERC721Enumerable-tokenByIndex}.
     */
    function tokenByIndex(uint256 index) public view virtual override returns (uint256) {
        require(index < ERC721Enumerable.totalSupply(), "ERC721Enumerable: global index out of bounds");
        return _allTokens[index];
    }

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

        if (from == address(0)) {
            _addTokenToAllTokensEnumeration(tokenId);
        } else if (from != to) {
            _removeTokenFromOwnerEnumeration(from, tokenId);
        }
        if (to == address(0)) {
            _removeTokenFromAllTokensEnumeration(tokenId);
        } else if (to != from) {
            _addTokenToOwnerEnumeration(to, tokenId);
        }
    }

    /**
     * @dev Private function to add a token to this extension's ownership-tracking data structures.
     * @param to address representing the new owner of the given token ID
     * @param tokenId uint256 ID of the token to be added to the tokens list of the given address
     */
    function _addTokenToOwnerEnumeration(address to, uint256 tokenId) private {
        uint256 length = ERC721.balanceOf(to);
        _ownedTokens[to][length] = tokenId;
        _ownedTokensIndex[tokenId] = length;
    }

    /**
     * @dev Private function to add a token to this extension's token tracking data structures.
     * @param tokenId uint256 ID of the token to be added to the tokens list
     */
    function _addTokenToAllTokensEnumeration(uint256 tokenId) private {
        _allTokensIndex[tokenId] = _allTokens.length;
        _allTokens.push(tokenId);
    }

    /**
     * @dev Private function to remove a token from this extension's ownership-tracking data structures. Note that
     * while the token is not assigned a new owner, the `_ownedTokensIndex` mapping is _not_ updated: this allows for
     * gas optimizations e.g. when performing a transfer operation (avoiding double writes).
     * This has O(1) time complexity, but alters the order of the _ownedTokens array.
     * @param from address representing the previous owner of the given token ID
     * @param tokenId uint256 ID of the token to be removed from the tokens list of the given address
     */
    function _removeTokenFromOwnerEnumeration(address from, uint256 tokenId) private {
        // To prevent a gap in from's tokens array, we store the last token in the index of the token to delete, and
        // then delete the last slot (swap and pop).

        uint256 lastTokenIndex = ERC721.balanceOf(from) - 1;
        uint256 tokenIndex = _ownedTokensIndex[tokenId];

        // When the token to delete is the last token, the swap operation is unnecessary
        if (tokenIndex != lastTokenIndex) {
            uint256 lastTokenId = _ownedTokens[from][lastTokenIndex];

            _ownedTokens[from][tokenIndex] = lastTokenId; // Move the last token to the slot of the to-delete token
            _ownedTokensIndex[lastTokenId] = tokenIndex; // Update the moved token's index
        }

        // This also deletes the contents at the last position of the array
        delete _ownedTokensIndex[tokenId];
        delete _ownedTokens[from][lastTokenIndex];
    }

    /**
     * @dev Private function to remove a token from this extension's token tracking data structures.
     * This has O(1) time complexity, but alters the order of the _allTokens array.
     * @param tokenId uint256 ID of the token to be removed from the tokens list
     */
    function _removeTokenFromAllTokensEnumeration(uint256 tokenId) private {
        // To prevent a gap in the tokens array, we store the last token in the index of the token to delete, and
        // then delete the last slot (swap and pop).

        uint256 lastTokenIndex = _allTokens.length - 1;
        uint256 tokenIndex = _allTokensIndex[tokenId];

        // When the token to delete is the last token, the swap operation is unnecessary. However, since this occurs so
        // rarely (when the last minted token is burnt) that we still do the swap here to avoid the gas cost of adding
        // an 'if' statement (like in _removeTokenFromOwnerEnumeration)
        uint256 lastTokenId = _allTokens[lastTokenIndex];

        _allTokens[tokenIndex] = lastTokenId; // Move the last token to the slot of the to-delete token
        _allTokensIndex[lastTokenId] = tokenIndex; // Update the moved token's index

        // This also deletes the contents at the last position of the array
        delete _allTokensIndex[tokenId];
        _allTokens.pop();
    }
}

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



// SPDX-License-Identifier: MIT

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/token/ERC721/ERC721.sol



// SPDX-License-Identifier: MIT

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 {
        require(operator != _msgSender(), "ERC721: approve to caller");

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

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

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

        _transfer(from, to, tokenId);
    }

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

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

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

    /**
     * @dev Returns whether `tokenId` exists.
     *
     * Tokens can be managed by their owner or approved accounts via {approve} or {setApprovalForAll}.
     *
     * Tokens start existing when they are minted (`_mint`),
     * and stop existing when they are burned (`_burn`).
     */
    function _exists(uint256 tokenId) internal view virtual returns (bool) {
        return _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 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/token/ERC721/extensions/IERC721Enumerable.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC721.sol";

/**
 * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Enumerable is IERC721 {
    /**
     * @dev Returns the total amount of tokens stored by the contract.
     */
    function totalSupply() external view returns (uint256);

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

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

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



// SPDX-License-Identifier: MIT

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/IERC721Receiver.sol



// SPDX-License-Identifier: MIT

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/extensions/IERC721Metadata.sol



// SPDX-License-Identifier: MIT

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/utils/Address.sol



// SPDX-License-Identifier: MIT

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/utils/Strings.sol



// SPDX-License-Identifier: MIT

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/introspection/ERC165.sol



// SPDX-License-Identifier: MIT

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/introspection/IERC165.sol



// SPDX-License-Identifier: MIT

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);
}