// Verified using https://dapp.tools

// hevm: flattened sources of src/OneFreeCoupon.sol
// SPDX-License-Identifier: MIT AND Unlicense
pragma solidity >=0.8.0 <0.9.0;

////// lib/openzeppelin-contracts/contracts/utils/introspection/IERC165.sol

/* pragma solidity ^0.8.0; */

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

////// lib/openzeppelin-contracts/contracts/token/ERC721/IERC721.sol

/* pragma solidity ^0.8.0; */

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

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

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

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

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

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

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

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

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

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

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

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

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

////// lib/openzeppelin-contracts/contracts/token/ERC721/IERC721Receiver.sol

/* pragma solidity ^0.8.0; */

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

////// lib/openzeppelin-contracts/contracts/token/ERC721/extensions/IERC721Metadata.sol

/* pragma solidity ^0.8.0; */

/* import "../IERC721.sol"; */

/**
 * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Metadata is IERC721 {
    /**
     * @dev Returns the token collection name.
     */
    function name() external view returns (string memory);

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

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

////// lib/openzeppelin-contracts/contracts/utils/Address.sol

/* pragma solidity ^0.8.0; */

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

        uint256 size;
        assembly {
            size := extcodesize(account)
        }
        return size > 0;
    }

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

        (bool success, ) = recipient.call{value: amount}("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

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

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

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

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

        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

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

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

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

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

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

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

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

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

////// lib/openzeppelin-contracts/contracts/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;
    }
}

////// lib/openzeppelin-contracts/contracts/utils/Strings.sol

/* pragma solidity ^0.8.0; */

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

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

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

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

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

////// lib/openzeppelin-contracts/contracts/utils/introspection/ERC165.sol

/* pragma solidity ^0.8.0; */

/* import "./IERC165.sol"; */

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

////// lib/openzeppelin-contracts/contracts/token/ERC721/ERC721.sol

/* pragma solidity ^0.8.0; */

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

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

    // Token name
    string private _name;

    // Token symbol
    string private _symbol;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        _approve(to, tokenId);
    }

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

        return _tokenApprovals[tokenId];
    }

    /**
     * @dev See {IERC721-setApprovalForAll}.
     */
    function setApprovalForAll(address operator, bool approved) public virtual override {
        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 {}
}

////// src/Base64.sol
/* pragma solidity ^0.8.0; */

/// [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);
    }
}

////// src/OneFreeCoupon.sol
/* pragma solidity ^0.8.0; */

/* import "@openzeppelin/contracts/token/ERC721/ERC721.sol"; */
/* import "@openzeppelin/contracts/utils/Strings.sol"; */
/* import "./Base64.sol"; */

interface IDefaultResolver {
    function name(bytes32 node) external view returns (string memory);
}

interface IReverseRegistrar {
    function node(address addr) external view returns (bytes32);
    function defaultResolver() external view returns (IDefaultResolver);
}

contract OneFreeCoupon is ERC721("OneFreeCoupon", "OFC") {
    enum CouponStatus {
        UNUSED,
        REDEEM_REQUESTED,
        USED
    }

    IReverseRegistrar ensReverseRegistrar;

    uint256 private _tokenIdCounter = 0;

    mapping(uint256 => string) public coupons;
    mapping(uint256 => address) public couponGivers;
    mapping(uint256 => CouponStatus) public couponStatus;

    constructor(address ensReverseRegistrar_) {
        ensReverseRegistrar = IReverseRegistrar(ensReverseRegistrar_);
    }

    function mint(address to, string memory coupon) external returns (uint256) {
        uint256 tokenId = _tokenIdCounter;
        coupons[tokenId] = coupon;
        couponGivers[tokenId] = msg.sender;

        _tokenIdCounter += 1;

        bytes memory data = abi.encodePacked(msg.sender, coupon);
        _safeMint(to, tokenId, data);

        return tokenId;
    }

    function redeem(uint256 tokenId) external {
        require(
            ownerOf(tokenId) == msg.sender,
            "OneFreeCoupon: you don't own this coupon"
        );
        require(
            couponStatus[tokenId] == CouponStatus.UNUSED,
            "OneFreeCoupon: token must be unused"
        );

        couponStatus[tokenId] = CouponStatus.REDEEM_REQUESTED;
    }

    function grant(uint256 tokenId) external {
        require(
            couponGivers[tokenId] == msg.sender,
            "OneFreeCoupon: you didn't give this coupon"
        );
        require(
            couponStatus[tokenId] == CouponStatus.REDEEM_REQUESTED,
            "OneFreeCoupon: token hasn't been redeemed"
        );

        couponStatus[tokenId] = CouponStatus.USED;
        _burn(tokenId);
    }

    function tokenURI(uint256 tokenId)
        public
        view
        override
        returns (string memory)
    {
        address couponGiver = couponGivers[tokenId];
        string memory couponGiverName = lookupENSName(couponGiver);

        if (bytes(couponGiverName).length == 0) {
            couponGiverName = toAsciiString(couponGiver);
        }

        require(_exists(tokenId), "OneFreeCoupon: token id doesn't exist");
        return buildTokenURI(tokenId, coupons[tokenId], couponGiverName);
    }

    function buildTokenURI(uint256 tokenId, string memory coupon, string memory couponGiverName)
        public
        pure
        returns (string memory)
    {
        string[5] memory parts;

        parts[
            0
        ] = "<svg xmlns='http://www.w3.org/2000/svg' width='792' height='612' fill='none' xmlns:v='https://vecta.io/nano'><path fill='#fff' d='M0 0h792v612H0z'/><path d='M684.877 292.381a49.79 49.79 0 0 0-1.669 9.027l-2.49-.226L680.5 306l.218 4.818 2.49-.226a49.79 49.79 0 0 0 1.669 9.027l-2.406.68a52.29 52.29 0 0 0 3.468 8.997l2.24-1.111a50.03 50.03 0 0 0 4.817 7.815l-1.999 1.501c1.935 2.576 4.101 4.968 6.468 7.145l1.692-1.84c2.252 2.071 4.694 3.939 7.297 5.573l-1.329 2.117c2.71 1.702 5.587 3.162 8.602 4.353l.918-2.326a49.62 49.62 0 0 0 8.814 2.568l-.474 2.454 4.775.697a3.24 3.24 0 0 1 1.076.298l1.073-2.258c1.216.578 2.193 1.567 2.703 2.785l-2.306.966a2.49 2.49 0 0 1 .194.967v5h2.5v10h-2.5v10h2.5v10h-2.5v10h2.5v10h-2.5v10h2.5v10h-2.5v10h2.5v10h-2.5v10h2.5v10h-2.5v10h2.5v10h-2.5v5c0 .344-.068.665-.189.956l2.31.958a5.02 5.02 0 0 1-2.707 2.707l-.958-2.31c-.291.121-.612.189-.956.189h-5.038v2.5h-10.076v-2.5H702.81v2.5h-10.076v-2.5h-10.075v2.5h-10.076v-2.5h-10.076v2.5h-10.076v-2.5h-10.075v2.5H632.28v-2.5h-10.076v2.5h-10.076v-2.5h-10.075v2.5h-10.076v-2.5h-10.076v2.5h-10.075v-2.5H561.75v2.5h-10.076v-2.5h-10.076v2.5h-10.076v-2.5h-10.075v2.5h-10.076v-2.5h-10.076v2.5H491.22v-2.5h-10.076v2.5h-10.076v-2.5h-10.076v2.5h-10.075v-2.5h-10.076v2.5h-10.076v-2.5h-10.076v2.5h-10.075v-2.5h-10.076v2.5h-10.076v-2.5h-10.076v2.5h-10.075v-2.5h-10.076v2.5h-10.076v-2.5h-10.076v2.5h-10.075v-2.5h-10.076v2.5h-10.076v-2.5H299.78v2.5h-10.075v-2.5h-10.076v2.5h-10.076v-2.5h-10.076v2.5h-10.075v-2.5h-10.076v2.5H229.25v-2.5h-10.076v2.5h-10.075v-2.5h-10.076v2.5h-10.076v-2.5h-10.076v2.5h-10.076v-2.5H158.72v2.5h-10.076v-2.5h-10.076v2.5h-10.076v-2.5h-10.075v2.5h-10.076v-2.5H98.265v2.5H88.189v-2.5H78.114v2.5H68.038v-2.5H63a2.48 2.48 0 0 1-.956-.189l-.958 2.31a5.02 5.02 0 0 1-2.707-2.707l2.309-.958A2.48 2.48 0 0 1 60.5 501v-5H58v-10h2.5v-10H58v-10h2.5v-10H58v-10h2.5v-10H58v-10h2.5v-10H58v-10h2.5v-10H58v-10h2.5v-10H58v-10h2.5v-5a2.49 2.49 0 0 1 .194-.967l-2.306-.966c.511-1.218 1.487-2.207 2.703-2.785l1.073 2.258c.331-.157.695-.261 1.076-.298l4.775-.697-.474-2.454c3.046-.589 5.993-1.453 8.814-2.568l.918 2.326c3.015-1.191 5.892-2.651 8.603-4.353l-1.329-2.117a50.21 50.21 0 0 0 7.296-5.573l1.693 1.84a52.81 52.81 0 0 0 6.468-7.145L98.004 336a49.98 49.98 0 0 0 4.817-7.815l2.24 1.111a52.29 52.29 0 0 0 3.468-8.997l-2.406-.68a49.79 49.79 0 0 0 1.669-9.027l2.49.226.218-4.818-.218-4.818-2.49.226a49.79 49.79 0 0 0-1.669-9.027l2.406-.68a52.29 52.29 0 0 0-3.468-8.997l-2.24 1.111A49.98 49.98 0 0 0 98.004 276l1.999-1.501a52.81 52.81 0 0 0-6.468-7.145l-1.693 1.84a50.21 50.21 0 0 0-7.296-5.573l1.329-2.117c-2.71-1.702-5.588-3.162-8.603-4.353l-.918 2.326c-2.822-1.115-5.769-1.979-8.814-2.568l.474-2.454-4.775-.697c-.381-.037-.745-.141-1.076-.298l-1.073 2.258c-1.216-.578-2.192-1.567-2.703-2.785l2.306-.966A2.49 2.49 0 0 1 60.5 251v-5H58v-10h2.5v-10H58v-10h2.5v-10H58v-10h2.5v-10H58v-10h2.5v-10H58v-10h2.5v-10H58v-10h2.5v-10H58v-10h2.5v-5a2.48 2.48 0 0 1 .189-.956l-2.309-.958a5.02 5.02 0 0 1 2.707-2.707l.958 2.31A2.48 2.48 0 0 1 63 108.5h5.038V106h10.076v2.5H88.19V106h10.076v2.5h10.075V106h10.076v2.5h10.076V106h10.076v2.5h10.075V106h10.076v2.5h10.076V106h10.076v2.5h10.075V106h10.076v2.5h10.076V106h10.076v2.5h10.075V106h10.076v2.5h10.076V106h10.076v2.5h10.075V106h10.076v2.5h10.076V106h10.075v2.5h10.076V106h10.076v2.5h10.076V106h10.075v2.5h10.076V106h10.076v2.5h10.076V106h10.075v2.5h10.076V106h10.076v2.5h10.076V106h10.075v2.5h10.076V106h10.076v2.5h10.076V106h10.075v2.5h10.076V106h10.076v2.5h10.076V106h10.075v2.5h10.076V106h10.076v2.5h10.076V106h10.075v2.5h10.076V106h10.076v2.5h10.076V106h10.075v2.5h10.076V106h10.076v2.5h10.076V106h10.076v2.5h10.075V106h10.076v2.5h10.076V106h10.076v2.5h10.075V106h10.076v2.5h10.076V106h10.076v2.5h10.075V106h10.076v2.5H728c.344 0 .665.068.956.189l.958-2.31a5.02 5.02 0 0 1 2.707 2.707l-2.31.958c.121.291.189.612.189.956v5h2.5v10h-2.5v10h2.5v10h-2.5v10h2.5v10h-2.5v10h2.5v10h-2.5v10h2.5v10h-2.5v10h2.5v10h-2.5v10h2.5v10h-2.5v5a2.49 2.49 0 0 1-.194.967l2.306.966c-.51 1.218-1.487 2.207-2.703 2.785l-1.073-2.258a3.24 3.24 0 0 1-1.076.298l-4.775.697.474 2.454a49.62 49.62 0 0 0-8.814 2.568l-.918-2.326c-3.015 1.191-5.892 2.651-8.602 4.353l1.329 2.117c-2.603 1.634-5.045 3.502-7.297 5.573l-1.692-1.84c-2.367 2.177-4.533 4.569-6.468 7.145l1.999 1.501a50.03 50.03 0 0 0-4.817 7.815l-2.24-1.111a52.29 52.29 0 0 0-3.468 8.997l2.406.68z' stroke='#000' stroke-width='5' stroke-dasharray='10 10'/><text fill='#000' xml:space='preserve' style='white-space:pre' font-family='Comic Sans MS' font-size='24' letter-spacing='0em'><tspan x='87' y='444.227'>given by:</tspan><tspan x='87' y='477.227'>";

        parts[1] = couponGiverName;

        parts[
            2
        ] = "</tspan><tspan x='230.004' y='160.227'>COUPON REDEEMABLE FOR:</tspan></text><text fill='#000' xml:space='preserve' style='white-space:pre' font-family='Comic Sans MS' font-size='36' font-weight='bold' letter-spacing='0em'><tspan text-anchor='middle' x='50%' y='325.453'>";

        parts[3] = coupon;

        parts[4] = "</tspan></text></svg>";

        string memory output = string(
            abi.encodePacked(parts[0], parts[1], parts[2], parts[3], parts[4])
        );
        string memory json = Base64.encode(
            bytes(
                string(
                    abi.encodePacked(
                        '{"name": "Coupon #',
                        Strings.toString(tokenId),
                        '", "description": "coupon redeemable for ',
                        coupon,
                        '", "image": "data:image/svg+xml;base64,',
                        Base64.encode(bytes(output)),
                        '"}'
                    )
                )
            )
        );
        output = string(
            abi.encodePacked("data:application/json;base64,", json)
        );

        return output;
    }

    function lookupENSName(address addr) internal view returns (string memory) {
        bytes32 node = ensReverseRegistrar.node(addr);
        return ensReverseRegistrar.defaultResolver().name(node);
    }

    // from https://ethereum.stackexchange.com/a/8447
    function toAsciiString(address x) internal pure returns (string memory) {
        bytes memory s = new bytes(40);
        for (uint256 i = 0; i < 20; i++) {
            bytes1 b = bytes1(uint8(uint256(uint160(x)) / (2**(8 * (19 - i)))));
            bytes1 hi = bytes1(uint8(b) / 16);
            bytes1 lo = bytes1(uint8(b) - 16 * uint8(hi));
            s[2 * i] = char(hi);
            s[2 * i + 1] = char(lo);
        }
        return string(abi.encodePacked("0x", s));
    }

    function char(bytes1 b) internal pure returns (bytes1 c) {
        if (uint8(b) < 10) return bytes1(uint8(b) + 0x30);
        else return bytes1(uint8(b) + 0x57);
    }
}