// File: contracts/8_ERC721AuctionNonceTransferProxySupport/AuctionERC721SaleNonceHolder.sol



pragma solidity ^0.5.0;
pragma experimental ABIEncoderV2;

/**
 * @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);
}

/**
 * @dev Required interface of an ERC721 compliant contract.
 */
contract IERC721 is IERC165 {
    event Transfer(
        address indexed from,
        address indexed to,
        uint256 indexed tokenId
    );
    event Approval(
        address indexed owner,
        address indexed approved,
        uint256 indexed tokenId
    );
    event ApprovalForAll(
        address indexed owner,
        address indexed operator,
        bool approved
    );

    /**
     * @dev Returns the number of NFTs in `owner`'s account.
     */
    function balanceOf(address owner) public view returns (uint256 balance);

    /**
     * @dev Returns the owner of the NFT specified by `tokenId`.
     */
    function ownerOf(uint256 tokenId) public view returns (address owner);

    /**
     * @dev Transfers a specific NFT (`tokenId`) from one account (`from`) to
     * another (`to`).
     *
     *
     *
     * Requirements:
     * - `from`, `to` cannot be zero.
     * - `tokenId` must be owned by `from`.
     * - If the caller is not `from`, it must be have been allowed to move this
     * NFT by either {approve} or {setApprovalForAll}.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId
    ) public;

    /**
     * @dev Transfers a specific NFT (`tokenId`) from one account (`from`) to
     * another (`to`).
     *
     * Requirements:
     * - If the caller is not `from`, it must be approved to move this NFT by
     * either {approve} or {setApprovalForAll}.
     */
    function transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) public;

    function approve(address to, uint256 tokenId) public;

    function getApproved(uint256 tokenId)
        public
        view
        returns (address operator);

    function setApprovalForAll(address operator, bool _approved) public;

    function isApprovedForAll(address owner, address operator)
        public
        view
        returns (bool);

    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        bytes memory data
    ) public;
}

/**
 * @title ERC721 token receiver interface
 * @dev Interface for any contract that wants to support safeTransfers
 * from ERC721 asset contracts.
 */
contract IERC721Receiver {
    /**
     * @notice Handle the receipt of an NFT
     * @dev The ERC721 smart contract calls this function on the recipient
     * after a {IERC721-safeTransferFrom}. This function MUST return the function selector,
     * otherwise the caller will revert the transaction. The selector to be
     * returned can be obtained as `this.onERC721Received.selector`. This
     * function MAY throw to revert and reject the transfer.
     * Note: the ERC721 contract address is always the message sender.
     * @param operator The address which called `safeTransferFrom` function
     * @param from The address which previously owned the token
     * @param tokenId The NFT identifier which is being transferred
     * @param data Additional data with no specified format
     * @return bytes4 `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
     */
    function onERC721Received(
        address operator,
        address from,
        uint256 tokenId,
        bytes memory data
    ) public returns (bytes4);
}

/*
 * @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 GSN 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.
 */
contract Context {
    // Empty internal constructor, to prevent people from mistakenly deploying
    // an instance of this contract, which should be used via inheritance.
    constructor() internal {}

    // solhint-disable-previous-line no-empty-blocks

    function _msgSender() internal view returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

/**
 * @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.
 *
 * 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.
 */
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() internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Returns true if the caller is the current owner.
     */
    function isOwner() public view returns (bool) {
        return _msgSender() == _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 onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = 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 onlyOwner {
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     */
    function _transferOwnership(address newOwner) internal {
        require(
            newOwner != address(0),
            "Ownable: new owner is the zero address"
        );
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

/**
 * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
contract IERC721Metadata is IERC721 {
    function name() external view returns (string memory);

    function symbol() external view returns (string memory);

    function tokenURI(uint256 tokenId) external view returns (string memory);
}

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @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) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @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 sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     *
     * _Available since v2.4.0._
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @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) {
        // 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 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts 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) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts 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.
     *
     * _Available since v2.4.0._
     */
    function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts 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 mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message 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.
     *
     * _Available since v2.4.0._
     */
    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

/**
 * @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) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash =
            0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            codehash := extcodehash(account)
        }
        return (codehash != accountHash && codehash != 0x0);
    }

    /**
     * @dev Converts an `address` into `address payable`. Note that this is
     * simply a type cast: the actual underlying value is not changed.
     *
     * _Available since v2.4.0._
     */
    function toPayable(address account)
        internal
        pure
        returns (address payable)
    {
        return address(uint160(account));
    }

    /**
     * @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].
     *
     * _Available since v2.4.0._
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(
            address(this).balance >= amount,
            "Address: insufficient balance"
        );

        // solhint-disable-next-line avoid-call-value
        (bool success, ) = recipient.call.value(amount)("");
        require(
            success,
            "Address: unable to send value, recipient may have reverted"
        );
    }
}

/**
 * @title Counters
 * @author Matt Condon (@shrugs)
 * @dev Provides counters that can only be incremented or decremented by one. 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;`
 * Since it is not possible to overflow a 256 bit integer with increments of one, `increment` can skip the {SafeMath}
 * overflow check, thereby saving gas. This does assume however correct usage, in that the underlying `_value` is never
 * directly accessed.
 */
library Counters {
    using SafeMath for uint256;

    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 {
        // The {SafeMath} overflow check can be skipped here, see the comment at the top
        counter._value += 1;
    }

    function decrement(Counter storage counter) internal {
        counter._value = counter._value.sub(1);
    }
}

/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts may inherit from this and call {_registerInterface} to declare
 * their support of an interface.
 */
contract ERC165 is IERC165 {
    /*
     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
     */
    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;

    /**
     * @dev Mapping of interface ids to whether or not it's supported.
     */
    mapping(bytes4 => bool) private _supportedInterfaces;

    constructor() internal {
        // Derived contracts need only register support for their own interfaces,
        // we register support for ERC165 itself here
        _registerInterface(_INTERFACE_ID_ERC165);
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     *
     * Time complexity O(1), guaranteed to always use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId)
        external
        view
        returns (bool)
    {
        return _supportedInterfaces[interfaceId];
    }

    /**
     * @dev Registers the contract as an implementer of the interface defined by
     * `interfaceId`. Support of the actual ERC165 interface is automatic and
     * registering its interface id is not required.
     *
     * See {IERC165-supportsInterface}.
     *
     * Requirements:
     *
     * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
     */
    function _registerInterface(bytes4 interfaceId) internal {
        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
        _supportedInterfaces[interfaceId] = true;
    }
}

/**
 * @title ERC721 Non-Fungible Token Standard basic implementation
 * @dev see https://eips.ethereum.org/EIPS/eip-721
 */
contract ERC721 is Context, ERC165, IERC721 {
    using SafeMath for uint256;
    using Address for address;
    using Counters for Counters.Counter;

    // Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
    // which can be also obtained as `IERC721Receiver(0).onERC721Received.selector`
    bytes4 private constant _ERC721_RECEIVED = 0x150b7a02;

    // Mapping from token ID to owner
    mapping(uint256 => address) private _tokenOwner;

    // Mapping from token ID to approved address
    mapping(uint256 => address) private _tokenApprovals;

    // Mapping from owner to number of owned token
    mapping(address => Counters.Counter) private _ownedTokensCount;

    // Mapping from owner to operator approvals
    mapping(address => mapping(address => bool)) private _operatorApprovals;

    /*
     *     bytes4(keccak256('balanceOf(address)')) == 0x70a08231
     *     bytes4(keccak256('ownerOf(uint256)')) == 0x6352211e
     *     bytes4(keccak256('approve(address,uint256)')) == 0x095ea7b3
     *     bytes4(keccak256('getApproved(uint256)')) == 0x081812fc
     *     bytes4(keccak256('setApprovalForAll(address,bool)')) == 0xa22cb465
     *     bytes4(keccak256('isApprovedForAll(address,address)')) == 0xe985e9c5
     *     bytes4(keccak256('transferFrom(address,address,uint256)')) == 0x23b872dd
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256)')) == 0x42842e0e
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256,bytes)')) == 0xb88d4fde
     *
     *     => 0x70a08231 ^ 0x6352211e ^ 0x095ea7b3 ^ 0x081812fc ^
     *        0xa22cb465 ^ 0xe985e9c ^ 0x23b872dd ^ 0x42842e0e ^ 0xb88d4fde == 0x80ac58cd
     */
    bytes4 private constant _INTERFACE_ID_ERC721 = 0x80ac58cd;

    constructor() public {
        // register the supported interfaces to conform to ERC721 via ERC165
        _registerInterface(_INTERFACE_ID_ERC721);
    }

    /**
     * @dev Gets the balance of the specified address.
     * @param owner address to query the balance of
     * @return uint256 representing the amount owned by the passed address
     */
    function balanceOf(address owner) public view returns (uint256) {
        require(
            owner != address(0),
            "ERC721: balance query for the zero address"
        );

        return _ownedTokensCount[owner].current();
    }

    /**
     * @dev Gets the owner of the specified token ID.
     * @param tokenId uint256 ID of the token to query the owner of
     * @return address currently marked as the owner of the given token ID
     */
    function ownerOf(uint256 tokenId) public view returns (address) {
        address owner = _tokenOwner[tokenId];
        require(
            owner != address(0),
            "ERC721: owner query for nonexistent token"
        );

        return owner;
    }

    /**
     * @dev Approves another address to transfer the given token ID
     * The zero address indicates there is no approved address.
     * There can only be one approved address per token at a given time.
     * Can only be called by the token owner or an approved operator.
     * @param to address to be approved for the given token ID
     * @param tokenId uint256 ID of the token to be approved
     */
    function approve(address to, uint256 tokenId) public {
        address owner = 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"
        );

        _tokenApprovals[tokenId] = to;
        emit Approval(owner, to, tokenId);
    }

    /**
     * @dev Gets the approved address for a token ID, or zero if no address set
     * Reverts if the token ID does not exist.
     * @param tokenId uint256 ID of the token to query the approval of
     * @return address currently approved for the given token ID
     */
    function getApproved(uint256 tokenId) public view returns (address) {
        require(
            _exists(tokenId),
            "ERC721: approved query for nonexistent token"
        );

        return _tokenApprovals[tokenId];
    }

    /**
     * @dev Sets or unsets the approval of a given operator
     * An operator is allowed to transfer all tokens of the sender on their behalf.
     * @param to operator address to set the approval
     * @param approved representing the status of the approval to be set
     */
    function setApprovalForAll(address to, bool approved) public {
        require(to != _msgSender(), "ERC721: approve to caller");

        _operatorApprovals[_msgSender()][to] = approved;
        emit ApprovalForAll(_msgSender(), to, approved);
    }

    /**
     * @dev Tells whether an operator is approved by a given owner.
     * @param owner owner address which you want to query the approval of
     * @param operator operator address which you want to query the approval of
     * @return bool whether the given operator is approved by the given owner
     */
    function isApprovedForAll(address owner, address operator)
        public
        view
        returns (bool)
    {
        return _operatorApprovals[owner][operator];
    }

    /**
     * @dev Transfers the ownership of a given token ID to another address.
     * Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
     * Requires the msg.sender to be the owner, approved, or operator.
     * @param from current owner of the token
     * @param to address to receive the ownership of the given token ID
     * @param tokenId uint256 ID of the token to be transferred
     */
    function transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) public {
        //solhint-disable-next-line max-line-length
        require(
            _isApprovedOrOwner(_msgSender(), tokenId),
            "ERC721: transfer caller is not owner nor approved"
        );

        _transferFrom(from, to, tokenId);
    }

    /**
     * @dev Safely transfers the ownership of a given token ID to another address
     * If the target address is a contract, it must implement {IERC721Receiver-onERC721Received},
     * which is called upon a safe transfer, and return the magic value
     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
     * the transfer is reverted.
     * Requires the msg.sender to be the owner, approved, or operator
     * @param from current owner of the token
     * @param to address to receive the ownership of the given token ID
     * @param tokenId uint256 ID of the token to be transferred
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId
    ) public {
        safeTransferFrom(from, to, tokenId, "");
    }

    /**
     * @dev Safely transfers the ownership of a given token ID to another address
     * If the target address is a contract, it must implement {IERC721Receiver-onERC721Received},
     * which is called upon a safe transfer, and return the magic value
     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
     * the transfer is reverted.
     * Requires the _msgSender() to be the owner, approved, or operator
     * @param from current owner of the token
     * @param to address to receive the ownership of the given token ID
     * @param tokenId uint256 ID of the token to be transferred
     * @param _data bytes data to send along with a safe transfer check
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        bytes memory _data
    ) public {
        require(
            _isApprovedOrOwner(_msgSender(), tokenId),
            "ERC721: transfer caller is not owner nor approved"
        );
        _safeTransferFrom(from, to, tokenId, _data);
    }

    /**
     * @dev Safely transfers the ownership of a given token ID to another address
     * If the target address is a contract, it must implement `onERC721Received`,
     * which is called upon a safe transfer, and return the magic value
     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
     * the transfer is reverted.
     * Requires the msg.sender to be the owner, approved, or operator
     * @param from current owner of the token
     * @param to address to receive the ownership of the given token ID
     * @param tokenId uint256 ID of the token to be transferred
     * @param _data bytes data to send along with a safe transfer check
     */
    function _safeTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        bytes memory _data
    ) internal {
        _transferFrom(from, to, tokenId);
        require(
            _checkOnERC721Received(from, to, tokenId, _data),
            "ERC721: transfer to non ERC721Receiver implementer"
        );
    }

    /**
     * @dev Returns whether the specified token exists.
     * @param tokenId uint256 ID of the token to query the existence of
     * @return bool whether the token exists
     */
    function _exists(uint256 tokenId) internal view returns (bool) {
        address owner = _tokenOwner[tokenId];
        return owner != address(0);
    }

    /**
     * @dev Returns whether the given spender can transfer a given token ID.
     * @param spender address of the spender to query
     * @param tokenId uint256 ID of the token to be transferred
     * @return bool whether the msg.sender is approved for the given token ID,
     * is an operator of the owner, or is the owner of the token
     */
    function _isApprovedOrOwner(address spender, uint256 tokenId)
        internal
        view
        returns (bool)
    {
        require(
            _exists(tokenId),
            "ERC721: operator query for nonexistent token"
        );
        address owner = ownerOf(tokenId);
        return (spender == owner ||
            getApproved(tokenId) == spender ||
            isApprovedForAll(owner, spender));
    }

    /**
     * @dev Internal function to safely mint a new token.
     * Reverts if the given token ID already exists.
     * If the target address is a contract, it must implement `onERC721Received`,
     * which is called upon a safe transfer, and return the magic value
     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
     * the transfer is reverted.
     * @param to The address that will own the minted token
     * @param tokenId uint256 ID of the token to be minted
     */
    function _safeMint(address to, uint256 tokenId) internal {
        _safeMint(to, tokenId, "");
    }

    /**
     * @dev Internal function to safely mint a new token.
     * Reverts if the given token ID already exists.
     * If the target address is a contract, it must implement `onERC721Received`,
     * which is called upon a safe transfer, and return the magic value
     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
     * the transfer is reverted.
     * @param to The address that will own the minted token
     * @param tokenId uint256 ID of the token to be minted
     * @param _data bytes data to send along with a safe transfer check
     */
    function _safeMint(
        address to,
        uint256 tokenId,
        bytes memory _data
    ) internal {
        _mint(to, tokenId);
        require(
            _checkOnERC721Received(address(0), to, tokenId, _data),
            "ERC721: transfer to non ERC721Receiver implementer"
        );
    }

    /**
     * @dev Internal function to mint a new token.
     * Reverts if the given token ID already exists.
     * @param to The address that will own the minted token
     * @param tokenId uint256 ID of the token to be minted
     */
    function _mint(address to, uint256 tokenId) internal {
        require(to != address(0), "ERC721: mint to the zero address");
        require(!_exists(tokenId), "ERC721: token already minted");

        _tokenOwner[tokenId] = to;
        _ownedTokensCount[to].increment();

        emit Transfer(address(0), to, tokenId);
    }

    /**
     * @dev Internal function to burn a specific token.
     * Reverts if the token does not exist.
     * Deprecated, use {_burn} instead.
     * @param owner owner of the token to burn
     * @param tokenId uint256 ID of the token being burned
     */
    function _burn(address owner, uint256 tokenId) internal {
        require(
            ownerOf(tokenId) == owner,
            "ERC721: burn of token that is not own"
        );

        _clearApproval(tokenId);

        _ownedTokensCount[owner].decrement();
        _tokenOwner[tokenId] = address(0);

        emit Transfer(owner, address(0), tokenId);
    }

    /**
     * @dev Internal function to burn a specific token.
     * Reverts if the token does not exist.
     * @param tokenId uint256 ID of the token being burned
     */
    function _burn(uint256 tokenId) internal {
        _burn(ownerOf(tokenId), tokenId);
    }

    /**
     * @dev Internal function to transfer ownership of a given token ID to another address.
     * As opposed to {transferFrom}, this imposes no restrictions on msg.sender.
     * @param from current owner of the token
     * @param to address to receive the ownership of the given token ID
     * @param tokenId uint256 ID of the token to be transferred
     */
    function _transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) internal {
        require(
            ownerOf(tokenId) == from,
            "ERC721: transfer of token that is not own"
        );
        require(to != address(0), "ERC721: transfer to the zero address");

        _clearApproval(tokenId);

        _ownedTokensCount[from].decrement();
        _ownedTokensCount[to].increment();

        _tokenOwner[tokenId] = to;

        emit Transfer(from, 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.
     *
     * This is an internal detail of the `ERC721` contract and its use is deprecated.
     * @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
    ) internal returns (bool) {
        if (!to.isContract()) {
            return true;
        }
        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) =
            to.call(
                abi.encodeWithSelector(
                    IERC721Receiver(to).onERC721Received.selector,
                    _msgSender(),
                    from,
                    tokenId,
                    _data
                )
            );
        if (!success) {
            if (returndata.length > 0) {
                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert("ERC721: transfer to non ERC721Receiver implementer");
            }
        } else {
            bytes4 retval = abi.decode(returndata, (bytes4));
            return (retval == _ERC721_RECEIVED);
        }
    }

    /**
     * @dev Private function to clear current approval of a given token ID.
     * @param tokenId uint256 ID of the token to be transferred
     */
    function _clearApproval(uint256 tokenId) private {
        if (_tokenApprovals[tokenId] != address(0)) {
            _tokenApprovals[tokenId] = address(0);
        }
    }
}

/**
 * @title ERC721 Burnable Token
 * @dev ERC721 Token that can be irreversibly burned (destroyed).
 */
contract ERC721Burnable is Context, ERC721 {
    /**
     * @dev Burns a specific ERC721 token.
     * @param tokenId uint256 id of the ERC721 token to be burned.
     */
    function burn(uint256 tokenId) public {
        //solhint-disable-next-line max-line-length
        require(
            _isApprovedOrOwner(_msgSender(), tokenId),
            "ERC721Burnable: caller is not owner nor approved"
        );
        _burn(tokenId);
    }
}

/**
 * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
contract IERC721Enumerable is IERC721 {
    function totalSupply() public view returns (uint256);

    function tokenOfOwnerByIndex(address owner, uint256 index)
        public
        view
        returns (uint256 tokenId);

    function tokenByIndex(uint256 index) public view returns (uint256);
}

/**
 * @title ERC-721 Non-Fungible Token with optional enumeration extension logic
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
contract ERC721Enumerable is Context, ERC165, ERC721, IERC721Enumerable {
    // Mapping from owner to list of owned token IDs
    mapping(address => uint256[]) private _ownedTokens;

    // Mapping from token ID to index of the owner tokens list
    mapping(uint256 => uint256) private _ownedTokensIndex;

    // Array with all token ids, used for enumeration
    uint256[] private _allTokens;

    // Mapping from token id to position in the allTokens array
    mapping(uint256 => uint256) private _allTokensIndex;

    /*
     *     bytes4(keccak256('totalSupply()')) == 0x18160ddd
     *     bytes4(keccak256('tokenOfOwnerByIndex(address,uint256)')) == 0x2f745c59
     *     bytes4(keccak256('tokenByIndex(uint256)')) == 0x4f6ccce7
     *
     *     => 0x18160ddd ^ 0x2f745c59 ^ 0x4f6ccce7 == 0x780e9d63
     */
    bytes4 private constant _INTERFACE_ID_ERC721_ENUMERABLE = 0x780e9d63;

    /**
     * @dev Constructor function.
     */
    constructor() public {
        // register the supported interface to conform to ERC721Enumerable via ERC165
        _registerInterface(_INTERFACE_ID_ERC721_ENUMERABLE);
    }

    /**
     * @dev Gets the token ID at a given index of the tokens list of the requested owner.
     * @param owner address owning the tokens list to be accessed
     * @param index uint256 representing the index to be accessed of the requested tokens list
     * @return uint256 token ID at the given index of the tokens list owned by the requested address
     */
    function tokenOfOwnerByIndex(address owner, uint256 index)
        public
        view
        returns (uint256)
    {
        require(
            index < balanceOf(owner),
            "ERC721Enumerable: owner index out of bounds"
        );
        return _ownedTokens[owner][index];
    }

    /**
     * @dev Gets the total amount of tokens stored by the contract.
     * @return uint256 representing the total amount of tokens
     */
    function totalSupply() public view returns (uint256) {
        return _allTokens.length;
    }

    /**
     * @dev Gets the token ID at a given index of all the tokens in this contract
     * Reverts if the index is greater or equal to the total number of tokens.
     * @param index uint256 representing the index to be accessed of the tokens list
     * @return uint256 token ID at the given index of the tokens list
     */
    function tokenByIndex(uint256 index) public view returns (uint256) {
        require(
            index < totalSupply(),
            "ERC721Enumerable: global index out of bounds"
        );
        return _allTokens[index];
    }

    /**
     * @dev Internal function to transfer ownership of a given token ID to another address.
     * As opposed to transferFrom, this imposes no restrictions on msg.sender.
     * @param from current owner of the token
     * @param to address to receive the ownership of the given token ID
     * @param tokenId uint256 ID of the token to be transferred
     */
    function _transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) internal {
        super._transferFrom(from, to, tokenId);

        _removeTokenFromOwnerEnumeration(from, tokenId);

        _addTokenToOwnerEnumeration(to, tokenId);
    }

    /**
     * @dev Internal function to mint a new token.
     * Reverts if the given token ID already exists.
     * @param to address the beneficiary that will own the minted token
     * @param tokenId uint256 ID of the token to be minted
     */
    function _mint(address to, uint256 tokenId) internal {
        super._mint(to, tokenId);

        _addTokenToOwnerEnumeration(to, tokenId);

        _addTokenToAllTokensEnumeration(tokenId);
    }

    /**
     * @dev Internal function to burn a specific token.
     * Reverts if the token does not exist.
     * Deprecated, use {ERC721-_burn} instead.
     * @param owner owner of the token to burn
     * @param tokenId uint256 ID of the token being burned
     */
    function _burn(address owner, uint256 tokenId) internal {
        super._burn(owner, tokenId);

        _removeTokenFromOwnerEnumeration(owner, tokenId);
        // Since tokenId will be deleted, we can clear its slot in _ownedTokensIndex to trigger a gas refund
        _ownedTokensIndex[tokenId] = 0;

        _removeTokenFromAllTokensEnumeration(tokenId);
    }

    /**
     * @dev Gets the list of token IDs of the requested owner.
     * @param owner address owning the tokens
     * @return uint256[] List of token IDs owned by the requested address
     */
    function _tokensOfOwner(address owner)
        internal
        view
        returns (uint256[] storage)
    {
        return _ownedTokens[owner];
    }

    /**
     * @dev Private function to add a token to this extension's ownership-tracking data structures.
     * @param to address representing the new owner of the given token ID
     * @param tokenId uint256 ID of the token to be added to the tokens list of the given address
     */
    function _addTokenToOwnerEnumeration(address to, uint256 tokenId) private {
        _ownedTokensIndex[tokenId] = _ownedTokens[to].length;
        _ownedTokens[to].push(tokenId);
    }

    /**
     * @dev Private function to add a token to this extension's token tracking data structures.
     * @param tokenId uint256 ID of the token to be added to the tokens list
     */
    function _addTokenToAllTokensEnumeration(uint256 tokenId) private {
        _allTokensIndex[tokenId] = _allTokens.length;
        _allTokens.push(tokenId);
    }

    /**
     * @dev Private function to remove a token from this extension's ownership-tracking data structures. Note that
     * while the token is not assigned a new owner, the `_ownedTokensIndex` mapping is _not_ updated: this allows for
     * gas optimizations e.g. when performing a transfer operation (avoiding double writes).
     * This has O(1) time complexity, but alters the order of the _ownedTokens array.
     * @param from address representing the previous owner of the given token ID
     * @param tokenId uint256 ID of the token to be removed from the tokens list of the given address
     */
    function _removeTokenFromOwnerEnumeration(address from, uint256 tokenId)
        private
    {
        // To prevent a gap in from's tokens array, we store the last token in the index of the token to delete, and
        // then delete the last slot (swap and pop).

        uint256 lastTokenIndex = _ownedTokens[from].length.sub(1);
        uint256 tokenIndex = _ownedTokensIndex[tokenId];

        // When the token to delete is the last token, the swap operation is unnecessary
        if (tokenIndex != lastTokenIndex) {
            uint256 lastTokenId = _ownedTokens[from][lastTokenIndex];

            _ownedTokens[from][tokenIndex] = lastTokenId; // Move the last token to the slot of the to-delete token
            _ownedTokensIndex[lastTokenId] = tokenIndex; // Update the moved token's index
        }

        // This also deletes the contents at the last position of the array
        _ownedTokens[from].length--;

        // Note that _ownedTokensIndex[tokenId] hasn't been cleared: it still points to the old slot (now occupied by
        // lastTokenId, or just over the end of the array if the token was the last one).
    }

    /**
     * @dev Private function to remove a token from this extension's token tracking data structures.
     * This has O(1) time complexity, but alters the order of the _allTokens array.
     * @param tokenId uint256 ID of the token to be removed from the tokens list
     */
    function _removeTokenFromAllTokensEnumeration(uint256 tokenId) private {
        // To prevent a gap in the tokens array, we store the last token in the index of the token to delete, and
        // then delete the last slot (swap and pop).

        uint256 lastTokenIndex = _allTokens.length.sub(1);
        uint256 tokenIndex = _allTokensIndex[tokenId];

        // When the token to delete is the last token, the swap operation is unnecessary. However, since this occurs so
        // rarely (when the last minted token is burnt) that we still do the swap here to avoid the gas cost of adding
        // an 'if' statement (like in _removeTokenFromOwnerEnumeration)
        uint256 lastTokenId = _allTokens[lastTokenIndex];

        _allTokens[tokenIndex] = lastTokenId; // Move the last token to the slot of the to-delete token
        _allTokensIndex[lastTokenId] = tokenIndex; // Update the moved token's index

        // This also deletes the contents at the last position of the array
        _allTokens.length--;
        _allTokensIndex[tokenId] = 0;
    }
}

library UintLibrary {
    function toString(uint256 _i) internal pure returns (string memory) {
        if (_i == 0) {
            return "0";
        }
        uint256 j = _i;
        uint256 len;
        while (j != 0) {
            len++;
            j /= 10;
        }
        bytes memory bstr = new bytes(len);
        uint256 k = len - 1;
        while (_i != 0) {
            bstr[k--] = byte(uint8(48 + (_i % 10)));
            _i /= 10;
        }
        return string(bstr);
    }
}

library StringLibrary {
    using UintLibrary for uint256;

    function append(string memory _a, string memory _b)
        internal
        pure
        returns (string memory)
    {
        bytes memory _ba = bytes(_a);
        bytes memory _bb = bytes(_b);
        bytes memory bab = new bytes(_ba.length + _bb.length);
        uint256 k = 0;
        for (uint256 i = 0; i < _ba.length; i++) bab[k++] = _ba[i];
        for (uint256 i = 0; i < _bb.length; i++) bab[k++] = _bb[i];
        return string(bab);
    }

    function append(
        string memory _a,
        string memory _b,
        string memory _c
    ) internal pure returns (string memory) {
        bytes memory _ba = bytes(_a);
        bytes memory _bb = bytes(_b);
        bytes memory _bc = bytes(_c);
        bytes memory bbb = new bytes(_ba.length + _bb.length + _bc.length);
        uint256 k = 0;
        for (uint256 i = 0; i < _ba.length; i++) bbb[k++] = _ba[i];
        for (uint256 i = 0; i < _bb.length; i++) bbb[k++] = _bb[i];
        for (uint256 i = 0; i < _bc.length; i++) bbb[k++] = _bc[i];
        return string(bbb);
    }

    function recover(
        string memory message,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal pure returns (address) {
        bytes memory msgBytes = bytes(message);
        bytes memory fullMessage =
            concat(
                bytes("\x19Ethereum Signed Message:\n"),
                bytes(msgBytes.length.toString()),
                msgBytes,
                new bytes(0),
                new bytes(0),
                new bytes(0),
                new bytes(0)
            );
        return ecrecover(keccak256(fullMessage), v, r, s);
    }

    function getAddress(
        bytes memory generatedBytes,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal pure returns (address) {
        bytes memory msgBytes = generatedBytes;
        bytes memory fullMessage =
            concat(
                bytes("\x19Ethereum Signed Message:\n"),
                bytes(msgBytes.length.toString()),
                msgBytes,
                new bytes(0),
                new bytes(0),
                new bytes(0),
                new bytes(0)
            );
        return ecrecover(keccak256(fullMessage), v, r, s);
    }

    function concat(
        bytes memory _ba,
        bytes memory _bb,
        bytes memory _bc,
        bytes memory _bd,
        bytes memory _be,
        bytes memory _bf,
        bytes memory _bg
    ) internal pure returns (bytes memory) {
        bytes memory resultBytes =
            new bytes(
                _ba.length +
                    _bb.length +
                    _bc.length +
                    _bd.length +
                    _be.length +
                    _bf.length +
                    _bg.length
            );
        uint256 k = 0;
        for (uint256 i = 0; i < _ba.length; i++) resultBytes[k++] = _ba[i];
        for (uint256 i = 0; i < _bb.length; i++) resultBytes[k++] = _bb[i];
        for (uint256 i = 0; i < _bc.length; i++) resultBytes[k++] = _bc[i];
        for (uint256 i = 0; i < _bd.length; i++) resultBytes[k++] = _bd[i];
        for (uint256 i = 0; i < _be.length; i++) resultBytes[k++] = _be[i];
        for (uint256 i = 0; i < _bf.length; i++) resultBytes[k++] = _bf[i];
        for (uint256 i = 0; i < _bg.length; i++) resultBytes[k++] = _bg[i];
        return resultBytes;
    }
}

contract HasContractURI is ERC165 {
    string public contractURI;

    /*
     * bytes4(keccak256('contractURI()')) == 0xe8a3d485
     */
    bytes4 private constant _INTERFACE_ID_CONTRACT_URI = 0xe8a3d485;

    constructor(string memory _contractURI) public {
        contractURI = _contractURI;
        _registerInterface(_INTERFACE_ID_CONTRACT_URI);
    }

    /**
     * @dev Internal function to set the contract URI
     * @param _contractURI string URI prefix to assign
     */
    function _setContractURI(string memory _contractURI) internal {
        contractURI = _contractURI;
    }
}

contract HasTokenURI {
    using StringLibrary for string;

    //Token URI prefix
    string public tokenURIPrefix;

    // Optional mapping for token URIs
    mapping(uint256 => string) private _tokenURIs;

    constructor(string memory _tokenURIPrefix) public {
        tokenURIPrefix = _tokenURIPrefix;
    }

    /**
     * @dev Returns an URI for a given token ID.
     * Throws if the token ID does not exist. May return an empty string.
     * @param tokenId uint256 ID of the token to query
     */
    function _tokenURI(uint256 tokenId) internal view returns (string memory) {
        return tokenURIPrefix.append(_tokenURIs[tokenId]);
    }

    /**
     * @dev Internal function to set the token URI for a given token.
     * Reverts if the token ID does not exist.
     * @param tokenId uint256 ID of the token to set its URI
     * @param uri string URI to assign
     */
    function _setTokenURI(uint256 tokenId, string memory uri) internal {
        _tokenURIs[tokenId] = uri;
    }

    /**
     * @dev Internal function to set the token URI prefix.
     * @param _tokenURIPrefix string URI prefix to assign
     */
    function _setTokenURIPrefix(string memory _tokenURIPrefix) internal {
        tokenURIPrefix = _tokenURIPrefix;
    }

    function _clearTokenURI(uint256 tokenId) internal {
        if (bytes(_tokenURIs[tokenId]).length != 0) {
            delete _tokenURIs[tokenId];
        }
    }
}

contract HasSecondarySaleFees is ERC165 {
    event SecondarySaleFees(
        uint256 tokenId,
        address[] recipients,
        uint256[] bps
    );

    /*
     * bytes4(keccak256('getFeeBps(uint256)')) == 0x0ebd4c7f
     * bytes4(keccak256('getFeeRecipients(uint256)')) == 0xb9c4d9fb
     *
     * => 0x0ebd4c7f ^ 0xb9c4d9fb == 0xb7799584
     */
    bytes4 private constant _INTERFACE_ID_FEES = 0xb7799584;

    constructor() public {
        _registerInterface(_INTERFACE_ID_FEES);
    }

    function getFeeRecipients(uint256 id)
        public
        view
        returns (address payable[] memory);

    function getFeeBps(uint256 id) public view returns (uint256[] memory);
}

/**
 * @title Full ERC721 Token with support for tokenURIPrefix
 * This implementation includes all the required and some optional functionality of the ERC721 standard
 * Moreover, it includes approve all functionality using operator terminology
 * @dev see https://eips.ethereum.org/EIPS/eip-721
 */
contract ERC721Base is
    HasSecondarySaleFees,
    ERC721,
    HasContractURI,
    HasTokenURI,
    ERC721Enumerable
{
    // Token name
    string public name;

    // Token symbol
    string public symbol;

    struct Fee {
        address payable recipient;
        uint256 value;
    }

    // id => fees
    mapping(uint256 => Fee[]) public fees;

    /*
     *     bytes4(keccak256('name()')) == 0x06fdde03
     *     bytes4(keccak256('symbol()')) == 0x95d89b41
     *     bytes4(keccak256('tokenURI(uint256)')) == 0xc87b56dd
     *
     *     => 0x06fdde03 ^ 0x95d89b41 ^ 0xc87b56dd == 0x5b5e139f
     */
    bytes4 private constant _INTERFACE_ID_ERC721_METADATA = 0x5b5e139f;

    /**
     * @dev Constructor function
     */
    constructor(
        string memory _name,
        string memory _symbol,
        string memory contractURI,
        string memory _tokenURIPrefix
    ) public HasContractURI(contractURI) HasTokenURI(_tokenURIPrefix) {
        name = _name;
        symbol = _symbol;

        // register the supported interfaces to conform to ERC721 via ERC165
        _registerInterface(_INTERFACE_ID_ERC721_METADATA);
    }

    function getFeeRecipients(uint256 id)
        public
        view
        returns (address payable[] memory)
    {
        Fee[] memory _fees = fees[id];
        address payable[] memory result = new address payable[](_fees.length);
        for (uint256 i = 0; i < _fees.length; i++) {
            result[i] = _fees[i].recipient;
        }
        return result;
    }

    function getFeeBps(uint256 id) public view returns (uint256[] memory) {
        Fee[] memory _fees = fees[id];
        uint256[] memory result = new uint256[](_fees.length);
        for (uint256 i = 0; i < _fees.length; i++) {
            result[i] = _fees[i].value;
        }
        return result;
    }

    function _mint(
        address to,
        uint256 tokenId,
        Fee[] memory _fees
    ) internal {
        _mint(to, tokenId);
        address[] memory recipients = new address[](_fees.length);
        uint256[] memory bps = new uint256[](_fees.length);
        for (uint256 i = 0; i < _fees.length; i++) {
            require(
                _fees[i].recipient != address(0x0),
                "Recipient should be present"
            );
            require(_fees[i].value != 0, "Fee value should be positive");
            fees[tokenId].push(_fees[i]);
            recipients[i] = _fees[i].recipient;
            bps[i] = _fees[i].value;
        }
        if (_fees.length > 0) {
            emit SecondarySaleFees(tokenId, recipients, bps);
        }
    }

    /**
     * @dev Returns an URI for a given token ID.
     * Throws if the token ID does not exist. May return an empty string.
     * @param tokenId uint256 ID of the token to query
     */
    function tokenURI(uint256 tokenId) external view returns (string memory) {
        require(
            _exists(tokenId),
            "ERC721Metadata: URI query for nonexistent token"
        );
        return super._tokenURI(tokenId);
    }

    /**
     * @dev Internal function to set the token URI for a given token.
     * Reverts if the token ID does not exist.
     * @param tokenId uint256 ID of the token to set its URI
     * @param uri string URI to assign
     */
    function _setTokenURI(uint256 tokenId, string memory uri) internal {
        require(
            _exists(tokenId),
            "ERC721Metadata: URI set of nonexistent token"
        );
        super._setTokenURI(tokenId, uri);
    }

    /**
     * @dev Internal function to burn a specific token.
     * Reverts if the token does not exist.
     * Deprecated, use _burn(uint256) instead.
     * @param owner owner of the token to burn
     * @param tokenId uint256 ID of the token being burned by the msg.sender
     */
    function _burn(address owner, uint256 tokenId) internal {
        super._burn(owner, tokenId);
        _clearTokenURI(tokenId);
    }
}

/**
 * @title MintableToken
 * @dev anyone can mint token.
 */
contract MintableToken is
    Ownable,
    IERC721,
    IERC721Metadata,
    ERC721Burnable,
    ERC721Base
{
    constructor(
        string memory name,
        string memory symbol,
        address newOwner,
        string memory contractURI,
        string memory tokenURIPrefix
    ) public ERC721Base(name, symbol, contractURI, tokenURIPrefix) {
        _registerInterface(bytes4(keccak256("MINT_WITH_ADDRESS")));
        transferOwnership(newOwner);
    }

    function mint(
        uint256 tokenId,
        uint8 v,
        bytes32 r,
        bytes32 s,
        Fee[] memory _fees,
        string memory tokenURI
    ) public {
        require(
            owner() ==
                ecrecover(keccak256(abi.encodePacked(this, tokenId)), v, r, s),
            "owner should sign tokenId"
        );
        _mint(msg.sender, tokenId, _fees);
        _setTokenURI(tokenId, tokenURI);
    }

    function setTokenURIPrefix(string memory tokenURIPrefix) public onlyOwner {
        _setTokenURIPrefix(tokenURIPrefix);
    }

    function setContractURI(string memory contractURI) public onlyOwner {
        _setContractURI(contractURI);
    }
}

library AddressLibrary {
    function toString(address _addr) internal pure returns (string memory) {
        bytes32 value = bytes32(uint256(_addr));
        bytes memory alphabet = "0123456789abcdef";
        bytes memory str = new bytes(42);
        str[0] = "0";
        str[1] = "x";
        for (uint256 i = 0; i < 20; i++) {
            str[2 + i * 2] = alphabet[uint8(value[i + 12] >> 4)];
            str[3 + i * 2] = alphabet[uint8(value[i + 12] & 0x0f)];
        }
        return string(str);
    }
}

contract AbstractSale is Ownable {
    using UintLibrary for uint256;
    using AddressLibrary for address;
    using StringLibrary for string;
    using SafeMath for uint256;

    bytes4 private constant _INTERFACE_ID_FEES = 0xb7799584;
    uint256 private constant maxBuyerFeePercentage = 10000;

    uint256 public buyerFee = 0;
    address payable public beneficiary;

    /* An ECDSA signature. */
    struct Sig {
        /* v parameter */
        uint8 v;
        /* r parameter */
        bytes32 r;
        /* s parameter */
        bytes32 s;
    }

    constructor(address payable _beneficiary) public {
        beneficiary = _beneficiary;
    }

    function setBuyerFee(uint256 _buyerFee) public onlyOwner {
        require(
            _buyerFee <= maxBuyerFeePercentage,
            "max buyer percentage can't be more than 10000"
        );
        buyerFee = _buyerFee;
    }

    function setBeneficiary(address payable _beneficiary) public onlyOwner {
        beneficiary = _beneficiary;
    }

    function prepareMessage(
        address token,
        uint256 tokenId,
        uint256 bid,
        uint256 sellerFee,
        uint256 nonce
    ) internal pure returns (string memory) {
        string memory result =
            string(
                strConcat(
                    bytes(token.toString()),
                    bytes(". tokenId: "),
                    bytes(tokenId.toString()),
                    bytes(". bid: "),
                    bytes(bid.toString()),
                    bytes(". nonce: "),
                    bytes(nonce.toString())
                )
            );
        if (sellerFee != 0) {
            return result.append(". sellerFee: ", sellerFee.toString());
        } else {
            return result;
        }
    }

    function strConcat(
        bytes memory _ba,
        bytes memory _bb,
        bytes memory _bc,
        bytes memory _bd,
        bytes memory _be,
        bytes memory _bf,
        bytes memory _bg
    ) internal pure returns (bytes memory) {
        bytes memory resultBytes =
            new bytes(
                _ba.length +
                    _bb.length +
                    _bc.length +
                    _bd.length +
                    _be.length +
                    _bf.length +
                    _bg.length
            );
        uint256 k = 0;
        for (uint256 i = 0; i < _ba.length; i++) resultBytes[k++] = _ba[i];
        for (uint256 i = 0; i < _bb.length; i++) resultBytes[k++] = _bb[i];
        for (uint256 i = 0; i < _bc.length; i++) resultBytes[k++] = _bc[i];
        for (uint256 i = 0; i < _bd.length; i++) resultBytes[k++] = _bd[i];
        for (uint256 i = 0; i < _be.length; i++) resultBytes[k++] = _be[i];
        for (uint256 i = 0; i < _bf.length; i++) resultBytes[k++] = _bf[i];
        for (uint256 i = 0; i < _bg.length; i++) resultBytes[k++] = _bg[i];
        return resultBytes;
    }

    function transferEther(
        IERC165 token,
        uint256 tokenId,
        address payable owner,
        uint256 total,
        uint256 sellerFee
    ) internal {
        uint256 value = transferFeeToBeneficiary(total, sellerFee);
        if (token.supportsInterface(_INTERFACE_ID_FEES)) {
            HasSecondarySaleFees withFees =
                HasSecondarySaleFees(address(token));
            address payable[] memory recipients =
                withFees.getFeeRecipients(tokenId);
            uint256[] memory fees = withFees.getFeeBps(tokenId);
            require(fees.length == recipients.length);
            for (uint256 i = 0; i < fees.length; i++) {
                (uint256 newValue, uint256 current) =
                    subFee(
                        value,
                        total.mul(fees[i]).div(maxBuyerFeePercentage)
                    );
                value = newValue;
                recipients[i].transfer(current);
            }
        }
        owner.transfer(value);
    }

    function transferFeeToBeneficiary(uint256 total, uint256 sellerFee)
        internal
        returns (uint256)
    {
        (uint256 value, uint256 sellerFeeValue) =
            subFee(total, total.mul(sellerFee).div(maxBuyerFeePercentage));
        uint256 buyerFeeValue = total.mul(buyerFee).div(maxBuyerFeePercentage);
        uint256 beneficiaryFee = buyerFeeValue.add(sellerFeeValue);
        if (beneficiaryFee > 0) {
            beneficiary.transfer(beneficiaryFee);
        }
        return value;
    }

    function subFee(uint256 value, uint256 fee) internal pure returns (uint256 newValue, uint256 realFee) {
        if (value > fee) {
            newValue = value - fee;
            realFee = fee;
        } else {
            newValue = 0;
            realFee = value;
        }
    }
}

/**
    @title ERC-1155 Multi Token Standard
    @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1155.md
    Note: The ERC-165 identifier for this interface is 0xd9b67a26.
 */
contract IERC1155 is IERC165 {
    /**
        @dev Either `TransferSingle` or `TransferBatch` MUST emit when tokens are transferred, including zero value transfers as well as minting or burning (see "Safe Transfer Rules" section of the standard).
        The `_operator` argument MUST be msg.sender.
        The `_from` argument MUST be the address of the holder whose balance is decreased.
        The `_to` argument MUST be the address of the recipient whose balance is increased.
        The `_id` argument MUST be the token type being transferred.
        The `_value` argument MUST be the number of tokens the holder balance is decreased by and match what the recipient balance is increased by.
        When minting/creating tokens, the `_from` argument MUST be set to `0x0` (i.e. zero address).
        When burning/destroying tokens, the `_to` argument MUST be set to `0x0` (i.e. zero address).
    */
    event TransferSingle(
        address indexed _operator,
        address indexed _from,
        address indexed _to,
        uint256 _id,
        uint256 _value
    );

    /**
        @dev Either `TransferSingle` or `TransferBatch` MUST emit when tokens are transferred, including zero value transfers as well as minting or burning (see "Safe Transfer Rules" section of the standard).
        The `_operator` argument MUST be msg.sender.
        The `_from` argument MUST be the address of the holder whose balance is decreased.
        The `_to` argument MUST be the address of the recipient whose balance is increased.
        The `_ids` argument MUST be the list of tokens being transferred.
        The `_values` argument MUST be the list of number of tokens (matching the list and order of tokens specified in _ids) the holder balance is decreased by and match what the recipient balance is increased by.
        When minting/creating tokens, the `_from` argument MUST be set to `0x0` (i.e. zero address).
        When burning/destroying tokens, the `_to` argument MUST be set to `0x0` (i.e. zero address).
    */
    event TransferBatch(
        address indexed _operator,
        address indexed _from,
        address indexed _to,
        uint256[] _ids,
        uint256[] _values
    );

    /**
        @dev MUST emit when approval for a second party/operator address to manage all tokens for an owner address is enabled or disabled (absense of an event assumes disabled).
    */
    event ApprovalForAll(
        address indexed _owner,
        address indexed _operator,
        bool _approved
    );

    /**
        @dev MUST emit when the URI is updated for a token ID.
        URIs are defined in RFC 3986.
        The URI MUST point a JSON file that conforms to the "ERC-1155 Metadata URI JSON Schema".
    */
    event URI(string _value, uint256 indexed _id);

    /**
        @notice Transfers `_value` amount of an `_id` from the `_from` address to the `_to` address specified (with safety call).
        @dev Caller must be approved to manage the tokens being transferred out of the `_from` account (see "Approval" section of the standard).
        MUST revert if `_to` is the zero address.
        MUST revert if balance of holder for token `_id` is lower than the `_value` sent.
        MUST revert on any other error.
        MUST emit the `TransferSingle` event to reflect the balance change (see "Safe Transfer Rules" section of the standard).
        After the above conditions are met, this function MUST check if `_to` is a smart contract (e.g. code size > 0). If so, it MUST call `onERC1155Received` on `_to` and act appropriately (see "Safe Transfer Rules" section of the standard).
        @param _from    Source address
        @param _to      Target address
        @param _id      ID of the token type
        @param _value   Transfer amount
        @param _data    Additional data with no specified format, MUST be sent unaltered in call to `onERC1155Received` on `_to`
    */
    function safeTransferFrom(
        address _from,
        address _to,
        uint256 _id,
        uint256 _value,
        bytes calldata _data
    ) external;

    /**
        @notice Transfers `_values` amount(s) of `_ids` from the `_from` address to the `_to` address specified (with safety call).
        @dev Caller must be approved to manage the tokens being transferred out of the `_from` account (see "Approval" section of the standard).
        MUST revert if `_to` is the zero address.
        MUST revert if length of `_ids` is not the same as length of `_values`.
        MUST revert if any of the balance(s) of the holder(s) for token(s) in `_ids` is lower than the respective amount(s) in `_values` sent to the recipient.
        MUST revert on any other error.
        MUST emit `TransferSingle` or `TransferBatch` event(s) such that all the balance changes are reflected (see "Safe Transfer Rules" section of the standard).
        Balance changes and events MUST follow the ordering of the arrays (_ids[0]/_values[0] before _ids[1]/_values[1], etc).
        After the above conditions for the transfer(s) in the batch are met, this function MUST check if `_to` is a smart contract (e.g. code size > 0). If so, it MUST call the relevant `ERC1155TokenReceiver` hook(s) on `_to` and act appropriately (see "Safe Transfer Rules" section of the standard).
        @param _from    Source address
        @param _to      Target address
        @param _ids     IDs of each token type (order and length must match _values array)
        @param _values  Transfer amounts per token type (order and length must match _ids array)
        @param _data    Additional data with no specified format, MUST be sent unaltered in call to the `ERC1155TokenReceiver` hook(s) on `_to`
    */
    function safeBatchTransferFrom(
        address _from,
        address _to,
        uint256[] calldata _ids,
        uint256[] calldata _values,
        bytes calldata _data
    ) external;

    /**
        @notice Get the balance of an account's Tokens.
        @param _owner  The address of the token holder
        @param _id     ID of the Token
        @return        The _owner's balance of the Token type requested
     */
    function balanceOf(address _owner, uint256 _id)
        external
        view
        returns (uint256);

    /**
        @notice Get the balance of multiple account/token pairs
        @param _owners The addresses of the token holders
        @param _ids    ID of the Tokens
        @return        The _owner's balance of the Token types requested (i.e. balance for each (owner, id) pair)
     */
    function balanceOfBatch(address[] calldata _owners, uint256[] calldata _ids)
        external
        view
        returns (uint256[] memory);

    /**
        @notice Enable or disable approval for a third party ("operator") to manage all of the caller's tokens.
        @dev MUST emit the ApprovalForAll event on success.
        @param _operator  Address to add to the set of authorized operators
        @param _approved  True if the operator is approved, false to revoke approval
    */
    function setApprovalForAll(address _operator, bool _approved) external;

    /**
        @notice Queries the approval status of an operator for a given owner.
        @param _owner     The owner of the Tokens
        @param _operator  Address of authorized operator
        @return           True if the operator is approved, false if not
    */
    function isApprovedForAll(address _owner, address _operator)
        external
        view
        returns (bool);
}

/**
 * @title Roles
 * @dev Library for managing addresses assigned to a Role.
 */
library Roles {
    struct Role {
        mapping(address => bool) bearer;
    }

    /**
     * @dev Give an account access to this role.
     */
    function add(Role storage role, address account) internal {
        require(!has(role, account), "Roles: account already has role");
        role.bearer[account] = true;
    }

    /**
     * @dev Remove an account's access to this role.
     */
    function remove(Role storage role, address account) internal {
        require(has(role, account), "Roles: account does not have role");
        role.bearer[account] = false;
    }

    /**
     * @dev Check if an account has this role.
     * @return bool
     */
    function has(Role storage role, address account)
        internal
        view
        returns (bool)
    {
        require(account != address(0), "Roles: account is the zero address");
        return role.bearer[account];
    }
}

contract OperatorRole is Context {
    using Roles for Roles.Role;

    event OperatorAdded(address indexed account);
    event OperatorRemoved(address indexed account);

    Roles.Role private _operators;

    constructor() internal {}

    modifier onlyOperator() {
        require(
            isOperator(_msgSender()),
            "OperatorRole: caller does not have the Operator role"
        );
        _;
    }

    function isOperator(address account) public view returns (bool) {
        return _operators.has(account);
    }

    function _addOperator(address account) internal {
        _operators.add(account);
        emit OperatorAdded(account);
    }

    function _removeOperator(address account) internal {
        _operators.remove(account);
        emit OperatorRemoved(account);
    }
}

contract OwnableOperatorRole is Ownable, OperatorRole {
    function addOperator(address account) public onlyOwner {
        _addOperator(account);
    }

    function removeOperator(address account) public onlyOwner {
        _removeOperator(account);
    }
}

contract TransferProxy is OwnableOperatorRole {
    function erc721safeTransferFrom(
        IERC721 token,
        address from,
        address to,
        uint256 tokenId
    ) external onlyOperator {
        token.safeTransferFrom(from, to, tokenId);
    }

    function erc1155safeTransferFrom(
        IERC1155 token,
        address _from,
        address _to,
        uint256 _id,
        uint256 _value,
        bytes calldata _data
    ) external onlyOperator {
        token.safeTransferFrom(_from, _to, _id, _value, _data);
    }
}

contract IERC721Sale {
    function getNonce(IERC721 token, uint256 tokenId)
        public
        view
        returns (uint256);
}

contract ERC721SaleNonceHolder is OwnableOperatorRole {
    mapping(bytes32 => uint256) public nonces;
    IERC721Sale public previous;

    constructor(IERC721Sale _previous) public {
        previous = _previous;
    }

    function getNonce(IERC721 token, uint256 tokenId)
        public
        view
        returns (uint256)
    {
        uint256 newNonce = nonces[getPositionKey(token, tokenId)];
        if (newNonce != 0) {
            return newNonce;
        }
        if (address(previous) == address(0x0)) {
            return 0;
        }
        return previous.getNonce(token, tokenId);
    }

    function setNonce(
        IERC721 token,
        uint256 tokenId,
        uint256 nonce
    ) public onlyOperator {
        nonces[getPositionKey(token, tokenId)] = nonce;
    }

    function getPositionKey(IERC721 token, uint256 tokenId)
        public
        pure
        returns (bytes32)
    {
        return keccak256(abi.encodePacked(token, tokenId));
    }
}

interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract AuctionERC20TransferProxy is OwnableOperatorRole {
    function erc20safeTransferFrom(IERC20 token, address from, address to, uint256 value) external onlyOperator {
        require(token.transferFrom(from, to, value), "failure while transferring");
    }
    
    function userBalance(IERC20 token, address user) external view returns(uint256) {
        return token.balanceOf(user);
    }
}

contract AuctionERC721SaleNonceHolder is OwnableOperatorRole {
    mapping(bytes32 => uint256) public nonces;

    function getNonce(IERC721 token, uint256 tokenId) view public returns (uint256) {
        uint256 newNonce = nonces[getPositionKey(token, tokenId)];
        if (newNonce != 0) {
            return newNonce;
        }
        return 0;
    }

    function setNonce(IERC721 token, uint256 tokenId, uint256 nonce) public onlyOperator {
        nonces[getPositionKey(token, tokenId)] = nonce;
    }

    function getPositionKey(IERC721 token, uint256 tokenId) pure public returns (bytes32) {
        return keccak256(abi.encodePacked(token, tokenId));
    }
}

interface ERC721TokenInter {
  function getFeeBps(uint256) external view returns (uint256[] memory);
  function getFeeRecipients(uint256) external view returns (address[] memory);
}

contract AuctionERC721 is Ownable, IERC721Receiver, AbstractSale {
    using AddressLibrary for address;
    using UintLibrary for uint256;
    using StringLibrary for string;
    uint256 private constant maxBuyerFeePercentage = 10000;
    address public systemSigner;

    event AuctionClosed(
        address indexed token,
        uint256 indexed tokenId,
        address seller,
        address buyer,
        address erc20Token,
        uint256 price,
        uint256 nonce
    );
    
    event CancelAuction(
        address indexed token,
        uint256 indexed tokenId,
        address seller,
        uint256 nonce
    );
    
    event SystemSignerChanged(
        address oldSigner,
        address newSigner
    );

    // To Transfer NFT
    TransferProxy public transferProxy;

    // To Transfer ERC20
    AuctionERC20TransferProxy public erc20TransferProxy;

    // Auction Nonce Holder
    AuctionERC721SaleNonceHolder public nonceHolder;

    constructor(TransferProxy _transferProxy, AuctionERC20TransferProxy _erc20TransferProxy, AuctionERC721SaleNonceHolder _nonceHolder, address payable beneficiary, address _systemSigner) public AbstractSale(beneficiary) {
        transferProxy = _transferProxy;
        erc20TransferProxy = _erc20TransferProxy;
        nonceHolder = _nonceHolder;
        systemSigner = _systemSigner;
    }
    
    function changeSystemSigner(address _newSystemSigner) public {
        require(owner() == msg.sender, "only owner can call");
        require(_newSystemSigner != address(0), "New signer can't be zero address");
        systemSigner = _newSystemSigner;
        emit SystemSignerChanged(systemSigner, _newSystemSigner);
    }
    
    struct Asset {
        address token;
        uint256 assetTokenId;
    }
    
    struct Trade {
        address payable seller;
        address payable buyer;
        uint256 reservedPrice;
        uint256 offeredPrice;
        address erc20Token;
        uint256 sellerFee;
        string auctionStart;
        string auctionEnd;
    }
    
    struct BuyerSig {
        uint8 v;
        bytes32 r;
        bytes32 s;
    }
    
    struct SystemSig {
        uint8 v;
        bytes32 r;
        bytes32 s;
    }

    function closeAuction(Asset memory asset, Trade memory trade, BuyerSig memory buyerSig, SystemSig memory systemSig) public payable {
        // Check if the called is the owner of NFT
        address payable seller = address(uint160(IERC721(asset.token).ownerOf(asset.assetTokenId)));
        require(seller == msg.sender, "NFT owner is not a seller");
        
        // Check if the Auction reached reserved price
        require(trade.offeredPrice >= trade.reservedPrice, "Reserved Price haven't met");
        
        // get Nonce of token
        uint256 nonce = nonceHolder.getNonce(IERC721(asset.token), asset.assetTokenId);
        
        // Validate Trade Value of Buyer & Balance of Buyer
        require(validateTradeValue(trade.offeredPrice, IERC20(trade.erc20Token), trade.buyer), "Buyer don't have enough balance");
        
        verifyBidderSign(asset, trade, buyerSig, nonce);
        verifySystemSign(asset, trade, systemSig, nonce);
        
        // Transfer NFT
        transferERC721NFT(IERC721(asset.token), trade.buyer, asset.assetTokenId);
        
        uint256 offeredPrice = trade.offeredPrice;
        uint256 sellerFeeToSlash = transferERC20FeeToBeneficiary(offeredPrice, trade.sellerFee, trade.erc20Token, trade.buyer);
        
        // Transfer Createor Royalty to Creator
        uint256 creatorFee = getCreatorFee(asset.token, asset.assetTokenId);
        address creator = getCreator(asset.token, asset.assetTokenId);
        uint256 creatorSlash = offeredPrice.mul(creatorFee).div(maxBuyerFeePercentage);
        erc20TransferProxy.erc20safeTransferFrom(IERC20(trade.erc20Token), trade.buyer, creator, creatorSlash);
        
        // Transfer Seller
        uint256 sellerSlash = offeredPrice.sub(creatorSlash).sub(sellerFeeToSlash);
        erc20TransferProxy.erc20safeTransferFrom(IERC20(trade.erc20Token), trade.buyer, msg.sender, sellerSlash);

        // Increases the nonce
        changeNonce(asset.token, asset.assetTokenId, nonce);
        emitAuction(asset, trade, trade.buyer, nonce + 1);
    }
    
    function verifyBidderSign(Asset memory asset, Trade memory trade, BuyerSig memory buyerSig, uint256 nonce) internal pure {
        string memory messageSigned = prepareMessage(address(asset.token), asset.assetTokenId, trade.offeredPrice, trade.sellerFee, nonce);
        address isBidder = StringLibrary.recover(messageSigned, buyerSig.v, buyerSig.r, buyerSig.s);
        require(trade.buyer == isBidder, "owner should sign correct message");
    }
    
    function verifySystemSign(Asset memory asset, Trade memory trade, SystemSig memory systemSig, uint256 nonce) internal view {
        address isSystemSigner = StringLibrary.getAddress(abi.encodePacked(IERC721(asset.token), asset.assetTokenId, msg.sender, trade.buyer, IERC20(trade.erc20Token), trade.offeredPrice, trade.auctionStart, trade.auctionEnd, nonce), systemSig.v, systemSig.r, systemSig.s);
        require(systemSigner == isSystemSigner, "system signer should sign correct message");
    }
    
    function transferERC20FeeToBeneficiary(uint256 price, uint256 sellerFee, address erc20Token, address buyer) internal returns (uint256) {
        // Transfer PlatformBuyerFee to Beneficiary
        uint256 platformBuyerFee = price.mul(buyerFee).div(maxBuyerFeePercentage);
        erc20TransferProxy.erc20safeTransferFrom(IERC20(erc20Token), buyer, beneficiary, platformBuyerFee);
        
        // Transfer PlatformSellerFee to Beneficiary
        uint256 platformSellerFee = price.mul(sellerFee).div(maxBuyerFeePercentage);
        if(sellerFee > 0) {
            erc20TransferProxy.erc20safeTransferFrom(IERC20(erc20Token), buyer, beneficiary, platformSellerFee);   
        }
        
        return platformSellerFee;
    }
    
    function changeNonce(address token, uint256 tokenId, uint256 nonce) internal {
        nonceHolder.setNonce(IERC721(token), tokenId, nonce+1);
    }
    
    function emitAuction(Asset memory asset, Trade memory trade, address buyer, uint256 nonce) internal {
        emit AuctionClosed(address(asset.token), asset.assetTokenId, msg.sender, buyer, address(trade.erc20Token), trade.offeredPrice, nonce);
    }
    
    function validateTradeValue(uint256 offeredPrice, IERC20 erc20Token, address buyer) internal view returns (bool) {
        uint256 priceWithBuyerFee = offeredPrice.mul(buyerFee);
        uint256 buyerFeeValue = priceWithBuyerFee.div(maxBuyerFeePercentage);
        uint256 totalTradeValue = offeredPrice.add(buyerFeeValue);
        uint256 buyerErc20TokenBalance = erc20TransferProxy.userBalance(erc20Token, buyer);
        return buyerErc20TokenBalance >= totalTradeValue;
    }
    
    function transferERC721NFT(IERC721 token, address buyer, uint256 tokenId) internal {
        transferProxy.erc721safeTransferFrom(token, msg.sender, buyer, tokenId);
    }
    
    function getCreatorFee(address erc721Adddress, uint256 tokenId) internal view returns (uint256) {
        uint256[] memory fees = ERC721TokenInter(erc721Adddress).getFeeBps(tokenId);
        return fees[0];
    }
    
    function getCreator(address erc721Adddress, uint256 tokenId) internal view returns (address) {
        address[] memory creators = ERC721TokenInter(erc721Adddress).getFeeRecipients(tokenId);
        return creators[0];
    }
    
    function cancelAuction(IERC721 token, uint256 tokenId) public {
        address owner = token.ownerOf(tokenId);
        require(owner == msg.sender, "not an owner");
        uint256 nonce = nonceHolder.getNonce(token, tokenId) + 1;
        nonceHolder.setNonce(token, tokenId, nonce);
        emit CancelAuction(address(token), tokenId, owner, nonce);
    }

    function onERC721Received(address, address, uint256, bytes memory) public returns (bytes4) {
        return this.onERC721Received.selector;
    }
}