// 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);
}

// File: @openzeppelin/contracts/token/ERC721/IERC721.sol

pragma solidity ^0.8.0;

/**
 * @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


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


pragma solidity ^0.8.0;

/**
 * @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


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);
    }

    function _verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) private 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/Context.sol


pragma solidity ^0.8.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

// File: @openzeppelin/contracts/utils/Strings.sol


pragma solidity ^0.8.0;

/**
 * @dev String operations.
 */
library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";

    /**
     * @dev Converts a `uint256` to its ASCII `string` decimal representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        while (value != 0) {
            digits -= 1;
            buffer[digits] = bytes1(uint8(48 + uint256(value % 10)));
            value /= 10;
        }
        return string(buffer);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        if (value == 0) {
            return "0x00";
        }
        uint256 temp = value;
        uint256 length = 0;
        while (temp != 0) {
            length++;
            temp >>= 8;
        }
        return toHexString(value, length);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
     */
    function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
        bytes memory buffer = new bytes(2 * length + 2);
        buffer[0] = "0";
        buffer[1] = "x";
        for (uint256 i = 2 * length + 1; i > 1; --i) {
            buffer[i] = _HEX_SYMBOLS[value & 0xf];
            value >>= 4;
        }
        require(value == 0, "Strings: hex length insufficient");
        return string(buffer);
    }
}

// File: @openzeppelin/contracts/utils/introspection/ERC165.sol


pragma solidity ^0.8.0;

/**
 * @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/token/ERC721/ERC721.sol


pragma solidity ^0.8.0;







/**
 * @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(to).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/access/Ownable.sol


pragma solidity ^0.8.0;

/**
 * @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/utils/Counters.sol


pragma solidity ^0.8.0;

/**
 * @title Counters
 * @author Matt Condon (@shrugs)
 * @dev Provides counters that can only be incremented, decremented or reset. This can be used e.g. to track the number
 * of elements in a mapping, issuing ERC721 ids, or counting request ids.
 *
 * Include with `using Counters for Counters.Counter;`
 */
library Counters {
    struct Counter {
        // This variable should never be directly accessed by users of the library: interactions must be restricted to
        // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
        // this feature: see https://github.com/ethereum/solidity/issues/4637
        uint256 _value; // default: 0
    }

    function current(Counter storage counter) internal view returns (uint256) {
        return counter._value;
    }

    function increment(Counter storage counter) internal {
        unchecked {
            counter._value += 1;
        }
    }

    function decrement(Counter storage counter) internal {
        uint256 value = counter._value;
        require(value > 0, "Counter: decrement overflow");
        unchecked {
            counter._value = value - 1;
        }
    }

    function reset(Counter storage counter) internal {
        counter._value = 0;
    }
}

// File: @openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol

pragma solidity ^0.8.0;

/**
 * @dev ERC721 token with storage based token URI management.
 */
abstract contract ERC721URIStorage is ERC721 {
    using Strings for uint256;

    // Optional mapping for token URIs
    mapping(uint256 => string) private _tokenURIs;

    /**
     * @dev See {IERC721Metadata-tokenURI}.
     */
    function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
        require(_exists(tokenId), "ERC721URIStorage: URI query for nonexistent token");

        string memory _tokenURI = _tokenURIs[tokenId];
        string memory base = _baseURI();

        // If there is no base URI, return the token URI.
        if (bytes(base).length == 0) {
            return _tokenURI;
        }
        // If both are set, concatenate the baseURI and tokenURI (via abi.encodePacked).
        if (bytes(_tokenURI).length > 0) {
            return string(abi.encodePacked(base, _tokenURI));
        }

        return super.tokenURI(tokenId);
    }

    /**
     * @dev Sets `_tokenURI` as the tokenURI of `tokenId`.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function _setTokenURI(uint256 tokenId, string memory _tokenURI) internal virtual {
        require(_exists(tokenId), "ERC721URIStorage: URI set of nonexistent token");
        _tokenURIs[tokenId] = _tokenURI;
    }

    /**
     * @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 override {
        super._burn(tokenId);

        if (bytes(_tokenURIs[tokenId]).length != 0) {
            delete _tokenURIs[tokenId];
        }
    }
}

// File: contracts/SeahorseNFT.sol

pragma solidity 0.8.4;
// ERC721URIStorage is the contract from openzeppelin for v0.8 that includes the metadata 
contract SeahorseNFT is ERC721URIStorage {
    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;

    // Data of each NFT
    struct TokenData {
        address payable creator; // creator of the NFT
        uint256 royalties;       // royalties to be paid to NFT creator on a resale. In basic points
        string lockedContent;    // Content that is locked until the token is sold, and then will be visible to the owner
    }
    mapping(uint256 => TokenData) tokens;

    constructor(string memory name_, string memory symbol_) ERC721(name_, symbol_) {}

    function getCreator(uint256 _tokenId) public view returns (address) {
        return tokens[_tokenId].creator;
    }

    // returns in basic points the royalties of a token
    function getRoyalties(uint256 _tokenId) public view returns (uint256) {
        return tokens[_tokenId].royalties;
    }

    // mints the NFT and save the data in the "tokens" map
    function createItem(string memory _tokenURI, uint256 _royalties, string memory _lockedContent)
        public
        returns (uint256)
    {
        require(_royalties <=5000, "Max royalties are 50%");

        _tokenIds.increment();

        uint256 newItemId = _tokenIds.current();
        _mint(msg.sender, newItemId);
        _setTokenURI(newItemId, _tokenURI);

        tokens[newItemId] = TokenData({ creator: payable(msg.sender), royalties: _royalties, lockedContent:_lockedContent});
    
        return newItemId;
    }

    // returns the string "locked", only available for the owner
    function unlockContent(uint256 _tokenId) public view returns (string memory)
    {
        require(this.ownerOf(_tokenId) == msg.sender, "Not the owner");
        return tokens[_tokenId].lockedContent;
    }
}

// File: @openzeppelin/contracts/utils/math/SafeMath.sol

pragma solidity ^0.8.0;

// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is no longer needed starting with Solidity 0.8. The compiler
 * now has built in overflow checking.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
            // benefit is lost if 'b' is also tested.
            // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
            if (a == 0) return (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        return a + b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return a - b;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        return a * b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a / b;
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}

// File: @openzeppelin/contracts/security/ReentrancyGuard.sol

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: contracts/Engine.sol

pragma solidity 0.8.4;

//import "./AddressUtils.sol";
contract Engine is Ownable, ReentrancyGuard {
    using SafeMath for uint256;

    event OfferCreated(
        uint256 _tokenId,
        address _creator,
        address _asset,
        uint256 numCopies,
        uint256 amount,
        bool isSale
    );
    // Event triggered when an auction is created
    event AuctionCreated(
        uint256 _auctionId,
        address _creator,
        uint256 _tokenId,
        uint256 _startPrice
    );
    // Event triggered when an auction receives a bid
    event AuctionBid(uint256 _index, address _bidder, uint256 amount);
    // Event triggered when an ended auction winner claims the NFT
    event Claim(uint256 auctionIndex, address claimer);
    // Event triggered when an auction received a bid that implies sending funds back to previous best bidder
    event ReturnBidFunds(uint256 _index, address _bidder, uint256 amount);
    // Event triggered when a royalties payment is generated, either on direct sales or on auctions
    event Royalties(address receiver, uint256 amount);
    // Event triggered when a payment to the owner is generated, either on direct sales or on auctions.assetAddress
    // This event is useful to check that all the payments funds are the right ones.
    event PaymentToOwner(
        address receiver,
        uint256 amount,
        //    uint256 paidByCustomer,
        uint256 commission,
        uint256 royalties,
        uint256 safetyCheckValue
    );
    event Buy(uint256 _index, address buyer, uint256 _amount);
    // Fired when setCommission is called
    event SetCommission(uint256 oldCommission, uint256 newCommission);

    // Status of an auction, calculated using the start date, the duration and the current timeblock
    enum Status {
        pending,
        active,
        finished
    }
    // Data of an auction
    struct Auction {
        address assetAddress; // token address
        uint256 assetId; // token id
        address payable creator; // creator of the auction, which is the token owner
        uint256 startTime; // time (unix, in seconds) where the auction will start
        uint256 duration; // duration in seconds of the auction
        uint256 currentBidAmount; // amount in ETH of the current bid amount
        address payable currentBidOwner; // address of the user who places the best bid
        uint256 bidCount; // number of bids of the auction
    }
    Auction[] public auctions;

    uint256 public commission = 0; // this is the commission in basic points that will charge the marketplace by default.
    uint256 public accumulatedCommission = 0; // this is the amount in ETH accumulated on marketplace wallet
    uint256 public totalSales = 0;

    struct Offer {
        address assetAddress; // address of the token
        uint256 tokenId; // the tokenId returned when calling "createItem"
        address payable creator; // who creates the offer
        uint256 price; // price of each token
        bool isOnSale; // is on sale or not
        bool isAuction; // is this offer is for an auction
        uint256 idAuction; // the id of the auction
    }
    mapping(uint256 => Offer) public offers;

    // Every time a token is put on sale, an offer is created. An offer can be a direct sale, an auction
    // or a combination of both.
    function createOffer(
        address _assetAddress, // address of the token
        uint256 _tokenId, // tokenId
        bool _isDirectSale, // true if can be bought on a direct sale
        bool _isAuction, // true if can be bought in an auction
        uint256 _price, // price that if paid in a direct sale, transfers the NFT
        uint256 _startPrice, // minimum price on the auction
        uint256 _startTime, // time when the auction will start. Check the format with frontend
        uint256 _duration // duration in seconds of the auction
    ) public {
        ERC721 asset = ERC721(_assetAddress);
        require(asset.ownerOf(_tokenId) == msg.sender, "Not the owner");
        require(
            asset.getApproved(_tokenId) == address(this),
            "NFT not approved"
        );
        // Could not be used to update an existing offer (#02)
        Offer memory previous = offers[_tokenId];
        require(
            previous.isOnSale == false && previous.isAuction == false,
            "An active offer already exists"
        );

        // First create the offer
        Offer memory offer = Offer({
            assetAddress: _assetAddress,
            tokenId: _tokenId,
            creator: payable(msg.sender),
            price: _price,
            isOnSale: _isDirectSale,
            isAuction: _isAuction,
            idAuction: 0
        });
        // only if the offer has the "is_auction" flag, add the auction to the list
        if (_isAuction) {
            offer.idAuction = createAuction(
                _assetAddress,
                _tokenId,
                _startPrice,
                _startTime,
                _duration
            );
        }
        offers[_tokenId] = offer;
        emit OfferCreated(
            _tokenId,
            msg.sender,
            _assetAddress,
            1,
            _price,
            _isDirectSale
        );
    }

    // returns the auctionId from the offerId
    function getAuctionId(uint256 _tokenId) public view returns (uint256) {
        Offer memory offer = offers[_tokenId];
        return offer.idAuction;
    }

    // this method returns the current date and time of the blockchain. Used also to check the contract is alive
    function ahora() public view returns (uint256) {
        return block.timestamp;
    }

    // Remove an auction from the offer that did not have previous bids. Beware could be a direct sale
    function removeFromAuction(uint256 _tokenId) public {
        Offer memory offer = offers[_tokenId];
        require(msg.sender == offer.creator, "You are not the owner");
        Auction memory auction = auctions[offer.idAuction];
        require(auction.bidCount == 0, "Bids existing");
        offer.isAuction = false;
        offer.idAuction = 0;
        offers[_tokenId] = offer;
    }

    // remove a direct sale from an offer. Beware that could be an auction for the token
    function removeFromSale(uint256 _tokenId) public {
        Offer memory offer = offers[_tokenId];
        require(msg.sender == offer.creator, "You are not the owner");
        offer.isOnSale = false;
        offers[_tokenId] = offer;
    }

    // Changes the default commission. Only the owner of the marketplace can do that. In basic points
    function setCommission(uint256 _commission) public onlyOwner {
        require(_commission <= 5000, "Commission too high");
        emit SetCommission(
            commission,
            _commission
        );
        commission = _commission;
    }

    // called in a direct sale by the customer. Transfer the nft to the customer, the royalties (if any)
    // to the token creator, the commission for the marketplace is keeped on the contract and the remaining
    // funds are transferred to the token owner.
    // is there is an auction open, the last bid amount is sent back to the last bidder
    // After that, the offer is cleared.
    function buy(uint256 _tokenId) external payable nonReentrant {
        address buyer = msg.sender;
        uint256 paidPrice = msg.value;

        Offer memory offer = offers[_tokenId];
        require(offer.isOnSale == true, "NFT not in direct sale");
        uint256 price = offer.price;
        require(paidPrice >= price, "Price is not enough");

        //if there is a bid and the auction is closed but not claimed, give priority to claim
        require(
            !(offer.isAuction == true &&
                isFinished(offer.idAuction) &&
                auctions[offer.idAuction].bidCount > 0),
            "Claim asset from auction has priority"
        );

        emit Claim(_tokenId, buyer);
        SeahorseNFT asset = SeahorseNFT(offer.assetAddress);
        asset.safeTransferFrom(offer.creator, buyer, _tokenId);

        // now, pay the amount - commission - royalties to the auction creator
        address payable creatorNFT = payable(asset.getCreator(_tokenId));

        uint256 commissionToPay = (paidPrice.mul(commission)) / 10000;
        uint256 royaltiesToPay = 0;
        if (creatorNFT != offer.creator) {
            // It is a resale. Transfer royalties
            royaltiesToPay =
                (paidPrice.mul(asset.getRoyalties(_tokenId))) /
                10000;

            (bool success, ) = creatorNFT.call{value: royaltiesToPay}("");
            require(success, "Transfer failed.");

            emit Royalties(creatorNFT, royaltiesToPay);
        }
        uint256 amountToPay = paidPrice.sub(commissionToPay).sub(
            royaltiesToPay
        );

        (bool success2, ) = offer.creator.call{value: amountToPay}("");
        require(success2, "Transfer failed.");
        emit PaymentToOwner(
            offer.creator,
            amountToPay,
            //     paidPrice,
            commissionToPay,
            royaltiesToPay,
            amountToPay + ((paidPrice * commission) / 10000) // using safemath will trigger an error because of stack size
        );

        // is there is an auction open, we have to give back the last bid amount to the last bidder
        if (offer.isAuction == true) {
            Auction memory auction = auctions[offer.idAuction];
            // #4. Only if there is at least a bid and the bid amount > 0, give it back to last bidder
            if (auction.currentBidAmount != 0 && auction.bidCount > 0) {
                // return funds to the previuos bidder
                (bool success3, ) = auction.currentBidOwner.call{
                    value: auction.currentBidAmount
                }("");
                require(success3, "Transfer failed.");
                emit ReturnBidFunds(
                    offer.idAuction,
                    auction.currentBidOwner,
                    auction.currentBidAmount
                );
            }
        }

        emit Buy(_tokenId, msg.sender, msg.value);

        accumulatedCommission = accumulatedCommission.add(commissionToPay);

        offer.isAuction = false;
        offer.isOnSale = false;
        offers[_tokenId] = offer;

        totalSales = totalSales.add(msg.value);
    }

    // Creates an auction for a token. It is linked to an offer
    function createAuction(
        address _assetAddress, // address of the SeahorseNFT token
        uint256 _assetId, // id of the NFT
        uint256 _startPrice, // minimum price
        uint256 _startTime, // time when the auction will start. Check with frontend because is unix time in seconds, not millisecs!
        uint256 _duration // duration in seconds of the auction
    ) private returns (uint256) {
        if (_startTime == 0) {
            _startTime = block.timestamp;
        }

        Auction memory auction = Auction({
            creator: payable(msg.sender),
            assetAddress: _assetAddress,
            assetId: _assetId,
            startTime: _startTime,
            duration: _duration,
            currentBidAmount: _startPrice,
            currentBidOwner: payable(address(0)),
            bidCount: 0
        });
        auctions.push(auction);
        uint256 index = auctions.length.sub(1);

        emit AuctionCreated(index, auction.creator, _assetId, _startPrice);

        return index;
    }

    // At the end of the call, the amount is saved on the marketplace wallet and the previous bid amount is returned to old bidder
    // except in the case of the first bid, as could exists a minimum price set by the creator as first bid.
    function bid(uint256 auctionIndex) public payable nonReentrant {
        Auction storage auction = auctions[auctionIndex];
        require(auction.creator != address(0), "Cannot bid. Error in auction");
        require(isActive(auctionIndex), "Bid not active");
        require(msg.value > auction.currentBidAmount, "Bid too low");
        // we got a better bid. Return funds to the previous best bidder
        // and register the sender as `currentBidOwner`

        // this check is for not transferring back funds on the first bid, as the fist bid is the minimum price set by the auction creator
        // and the bid owner is address(0)
        if (
            auction.currentBidAmount != 0 &&
            auction.currentBidOwner != address(0)
        ) {
            // return funds to the previuos bidder
            (bool success, ) = auction.currentBidOwner.call{
                value: auction.currentBidAmount
            }("");
            require(success, "Transfer failed.");
            emit ReturnBidFunds(
                auctionIndex,
                auction.currentBidOwner,
                auction.currentBidAmount
            );
        }
        // register new bidder
        auction.currentBidAmount = msg.value;
        auction.currentBidOwner = payable(msg.sender);
        auction.bidCount = auction.bidCount.add(1);

        emit AuctionBid(auctionIndex, msg.sender, msg.value);
    }

    function getTotalAuctions() public view returns (uint256) {
        return auctions.length;
    }

    function isActive(uint256 _auctionIndex) public view returns (bool) {
        return getStatus(_auctionIndex) == Status.active;
    }

    function isFinished(uint256 _auctionIndex) public view returns (bool) {
        return getStatus(_auctionIndex) == Status.finished;
    }

    // The auctions did not be affected if the current time is 15 seconds wrong
    // So, according to Consensys security advices, it is safe using block.timestamp
    function getStatus(uint256 _auctionIndex) public view returns (Status) {
        Auction storage auction = auctions[_auctionIndex];
        if (block.timestamp < auction.startTime) {
            return Status.pending;
        } else if (block.timestamp < auction.startTime.add(auction.duration)) {
            return Status.active;
        } else {
            return Status.finished;
        }
    }

    // returns the end date of the auction, in unix time using seconds
    function endDate(uint256 _auctionIndex) public view returns (uint256) {
        Auction storage auction = auctions[_auctionIndex];
        return auction.startTime.add(auction.duration);
    }

    // returns the user with the best bid until now on an auction
    function getCurrentBidOwner(uint256 _auctionIndex)
        public
        view
        returns (address)
    {
        return auctions[_auctionIndex].currentBidOwner;
    }

    // returns the amount in ETH of the best bid until now on an auction
    function getCurrentBidAmount(uint256 _auctionIndex)
        public
        view
        returns (uint256)
    {
        return auctions[_auctionIndex].currentBidAmount;
    }

    // returns the number of bids of an auction (0 by default)
    function getBidCount(uint256 _auctionIndex) public view returns (uint256) {
        return auctions[_auctionIndex].bidCount;
    }

    // returns the winner of an auction once the auction finished
    function getWinner(uint256 auctionIndex) public view returns (address) {
        require(isFinished(auctionIndex), "Auction not finished yet");
        return auctions[auctionIndex].currentBidOwner;
    }

    // called when the auction is finished by the user who won the auction
    // transfer the nft to the caller, the royalties (if any) to the nft creator
    // the commission of the marketplace is calculated, and the remaining funds
    // are transferred to the token owner
    // After this, the offer is disabled
    function closeAuction(uint256 auctionIndex) public {
        //    address winner = getWinner(auctionIndex);
        //    require(winner == msg.sender, "You are not the winner of the auction");
        auctionTransferAsset(auctionIndex);
    }

    function automaticSetWinner(uint256 auctionIndex) public onlyOwner {
        auctionTransferAsset(auctionIndex);
    }

    function auctionTransferAsset(uint256 auctionIndex) private nonReentrant {
        // require(isFinished(auctionIndex), "The auction is still active");
        address winner = getWinner(auctionIndex);

        Auction storage auction = auctions[auctionIndex];

        // the token could be sold in direct sale or the owner cancelled the auction
        Offer memory offer = offers[auction.assetId];
        require(offer.isAuction == true, "NFT not in auction");

        if (auction.bidCount > 0) {
            SeahorseNFT asset = SeahorseNFT(auction.assetAddress);

            // #3, check if the asset owner had removed their approval or the offer creator is not the token owner anymore.
            require(
                asset.getApproved(auction.assetId) == address(this),
                "NFT not approved"
            );
            require(
                asset.ownerOf(auction.assetId) == auction.creator,
                "Auction creator is not nft owner"
            );

            asset.safeTransferFrom(auction.creator, winner, auction.assetId);

            emit Claim(auctionIndex, winner);

            // now, pay the amount - commission - royalties to the auction creator
            address payable creatorNFT = payable(
                asset.getCreator(auction.assetId)
            );
            uint256 commissionToPay = (
                auction.currentBidAmount.mul(commission)
            ) / 10000;
            uint256 royaltiesToPay = 0;
            if (creatorNFT != auction.creator) {
                // It is a resale. Transfer royalties
                royaltiesToPay =
                    (
                        auction.currentBidAmount.mul(
                            asset.getRoyalties(auction.assetId)
                        )
                    ) /
                    10000;
                creatorNFT.transfer(royaltiesToPay);
                emit Royalties(creatorNFT, royaltiesToPay);
            }
            uint256 amountToPay = auction
                .currentBidAmount
                .sub(commissionToPay)
                .sub(royaltiesToPay);

            (bool success, ) = auction.creator.call{value: amountToPay}("");
            require(success, "Transfer failed.");
            emit PaymentToOwner(
                auction.creator,
                amountToPay,
                //  auction.currentBidAmount,
                commissionToPay,
                royaltiesToPay,
                amountToPay + commissionToPay + royaltiesToPay
            );

            accumulatedCommission = accumulatedCommission.add(commissionToPay);

            totalSales = totalSales.add(auction.currentBidAmount);
        }

        offer.isAuction = false;
        offer.isOnSale = false;
        offers[auction.assetId] = offer;
    }

    //Call this method
    function cancelAuctionOfToken(uint256 _tokenId)
        external
        onlyOwner
        nonReentrant
    {
        Offer memory offer = offers[_tokenId];
        // is there is an auction open, we have to give back the last bid amount to the last bidder
        require(offer.isAuction, "Offer is not an auction");
        Auction memory auction = auctions[offer.idAuction];

        if (auction.bidCount > 0) returnLastBid(offer, auction);

        offer.isAuction = false;
        offers[_tokenId] = offer;
    }

    function returnLastBid(Offer memory offer, Auction memory auction)
        internal
    {
        // is there is an auction open, we have to give back the last bid amount to the last bidder
        require(offer.isAuction, "Offer is not an auction");
        // #4. Only if there is at least a bid and the bid amount > 0, give it back to last bidder
        require(
            auction.currentBidAmount != 0 &&
                auction.bidCount > 0 &&
                auction.currentBidOwner != address(0),
            "No bids yet"
        );
        require(
            offer.creator != auction.currentBidOwner,
            "Offer owner cannot retrieve own funds"
        );
        // return funds to the previuos bidder
        (bool success3, ) = auction.currentBidOwner.call{
            value: auction.currentBidAmount
        }("");
        require(success3, "Transfer failed.");
        emit ReturnBidFunds(
            offer.idAuction,
            auction.currentBidOwner,
            auction.currentBidAmount
        );
    }

    // This method is only callable by the marketplace owner and transfer funds from
    // the marketplace to the caller.
    // It us used to move the funds from the marketplace to the investors
    function extractBalance() public nonReentrant onlyOwner {
        address payable me = payable(msg.sender);
        (bool success, ) = me.call{value: accumulatedCommission}("");
        require(success, "Transfer failed.");
        accumulatedCommission = 0;
    }
}