// Contract: NFT
// Target function: function _transfer(address _to, uint256 _tokenId) internal
 /**
     * @dev Returns a distinct Uniform Resource Identifier (URI) for a given asset. It Throws if
     * `_tokenId` is not a valid NFT. URIs are defined in RFC3986. The URI may point to a JSON file
     * that conforms to the "ERC721 Metadata JSON Schema".
     * @return URI of _tokenId.
     */
    function tokenURI(uint256 _tokenId) external view returns (string memory);
}

/**
 * @dev A standard for detecting smart contract interfaces.
 * See: https://eips.ethereum.org/EIPS/eip-165.
 */
interface ERC165 {
    /**
     * @dev Checks if the smart contract includes a specific interface.
     * This function uses less than 30,000 gas.
     * @param _interfaceID The interface identifier, as specified in ERC-165.
     * @return True if _interfaceID is supported, false otherwise.
     */
    function supportsInterface(bytes4 _interfaceID)
        external
        view
        returns (bool);
}

/**
 * @dev Implementation of standard for detect smart contract interfaces.
 */
contract SupportsInterface is ERC165 {
    /**
     * @dev Mapping of supported intefraces. You must not set element 0xffffffff to true.
     */
    mapping(bytes4 => bool) internal supportedInterfaces;

    /**
     * @dev Contract constructor.
     */
    constructor() {
        supportedInterfaces[0x01ffc9a7] = true; // ERC165
    }

    /**
     * @dev Function to check which interfaces are suported by this contract.
     * @param _interfaceID Id of the interface.
     * @return True if _interfaceID is supported, false otherwise.
     */
    function supportsInterface(bytes4 _interfaceID)
        external
        view
        override
        returns (bool)
    {
        return supportedInterfaces[_interfaceID];
    }
}

/**
 * @dev ERC-721 non-fungible token standard.
 * See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md.
 */
interface ERC721 {
    /**
     * @dev Emits when ownership of any NFT changes by any mechanism. This event emits when NFTs are
     * created (`from` == 0) and destroyed (`to` == 0). Exception: during contract creation, any
     * number of NFTs may be created and assigned without emitting Transfer. At the time of any
     * transfer, the approved address for that NFT (if any) is reset to none.
     */
    event Transfer(
        address indexed _from,
        address indexed _to,
        uint256 indexed _tokenId
    );

    /**
     * @dev This emits when the approved address for an NFT is changed or reaffirmed. The zero
     * address indicates there is no approved address. When a Transfer event emits, this also
     * indicates that the approved address for that NFT (if any) is reset to none.
     */
    event Approval(
        address indexed _owner,
        address indexed _approved,
        uint256 indexed _tokenId
    );

    /**
     * @dev This emits when an operator is enabled or disabled for an owner. The operator can manage
     * all NFTs of the owner.
     */
    event ApprovalForAll(
        address indexed _owner,
        address indexed _operator,
        bool _approved
    );

    /**
     * @notice Throws unless `msg.sender` is the current owner, an authorized operator, or the
     * approved address for this NFT. Throws if `_from` is not the current owner. Throws if `_to` is
     * the zero address. Throws if `_tokenId` is not a valid NFT. When transfer is complete, this
     * function checks if `_to` is a smart contract (code size > 0). If so, it calls
     * `onERC721Received` on `_to` and throws if the return value is not
     * `bytes4(keccak256("onERC721Received(address,uint256,bytes)"))`.
     * @dev Transfers the ownership of an NFT from one address to another address. This function can
     * be changed to payable.
     * @param _from The current owner of the NFT.
     * @param _to The new owner.
     * @param _tokenId The NFT to transfer.
     * @param _data Additional data with no specified format, sent in call to `_to`.
     */
    function safeTransferFrom(
        address _from,
        address _to,
        uint256 _tokenId,
        bytes calldata _data
    ) external;

    /**
     * @notice This works identically to the other function with an extra data parameter, except this
     * function just sets data to ""
     * @dev Transfers the ownership of an NFT from one address to another address. This function can
     * be changed to payable.
     * @param _from The current owner of the NFT.
     * @param _to The new owner.
     * @param _tokenId The NFT to transfer.
     */
    function safeTransferFrom(
        address _from,
        address _to,
        uint256 _tokenId
    ) external;

    /**
     * @notice The caller is responsible to confirm that `_to` is capable of receiving NFTs or else
     * they may be permanently lost.
     * @dev Throws unless `msg.sender` is the current owner, an authorized operator, or the approved
     * address for this NFT. Throws if `_from` is not the current owner. Throws if `_to` is the zero
     * address. Throws if `_tokenId` is not a valid NFT.  This function can be changed to payable.
     * @param _from The current owner of the NFT.
     * @param _to The new owner.
     * @param _tokenId The NFT to transfer.
     */
    function transferFrom(
        address _from,
        address _to,
        uint256 _tokenId
    ) external;

    /**
     * @notice The zero address indicates there is no approved address. Throws unless `msg.sender` is
     * the current NFT owner, or an authorized operator of the current owner.
     * @param _approved The new approved NFT controller.
     * @dev Set or reaffirm the approved address for an NFT. This function can be changed to payable.
     * @param _tokenId The NFT to approve.
     */
    function approve(address _approved, uint256 _tokenId) external;

    /**
     * @notice The contract MUST allow multiple operators per owner.
     * @dev Enables or disables approval for a third party ("operator") to manage all of
     * `msg.sender`'s assets. It also emits the ApprovalForAll event.
     * @param _operator Address to add to the set of authorized operators.
     * @param _approved True if the operators is approved, false to revoke approval.
     */
    function setApprovalForAll(address _operator, bool _approved) external;

    /**
     * @dev Returns the number of NFTs owned by `_owner`. NFTs assigned to the zero address are
     * considered invalid, and this function throws for queries about the zero address.
     * @notice Count all NFTs assigned to an owner.
     * @param _owner Address for whom to query the balance.
     * @return Balance of _owner.
     */
    function balanceOf(address _owner) external view returns (uint256);

    /**
     * @notice Find the owner of an NFT.
     * @dev Returns the address of the owner of the NFT. NFTs assigned to the zero address are
     * considered invalid, and queries about them do throw.
     * @param _tokenId The identifier for an NFT.
     * @return Address of _tokenId owner.
     */
    function ownerOf(uint256 _tokenId) external view returns (address);

    /**
     * @notice Throws if `_tokenId` is not a valid NFT.
     * @dev Get the approved address for a single NFT.
     * @param _tokenId The NFT to find the approved address for.
     * @return Address that _tokenId is approved for.
     */
    function getApproved(uint256 _tokenId) external view returns (address);

    /**
     * @notice Query if an address is an authorized operator for another address.
     * @dev Returns true if `_operator` is an approved operator for `_owner`, false otherwise.
     * @param _owner The address that owns the NFTs.
     * @param _operator The address that acts on behalf of the owner.
     * @return True if approved for all, false otherwise.
     */
    function isApprovedForAll(address _owner, address _operator)
        external
        view
        returns (bool);
}

/**
 * @dev Implementation of ERC-721 non-fungible token standard.
 */
contract NFToken is ERC721, SupportsInterface {
    using AddressUtils for address;

    /**
     * @dev List of revert message codes. Implementing dApp should handle showing the correct message.
     * Based on 0xcert framework error codes.
     */
    string constant ZERO_ADDRESS = "003001";
    string constant NOT_VALID_NFT = "003002";
    string constant NOT_OWNER_OR_OPERATOR = "003003";
    string constant NOT_OWNER_APPROVED_OR_OPERATOR = "003004";
    string constant NOT_ABLE_TO_RECEIVE_NFT = "003005";
    string constant NFT_ALREADY_EXISTS = "003006";
    string constant NOT_OWNER = "003007";
    string constant IS_OWNER = "003008";

    /**
     * @dev Magic value of a smart contract that can receive NFT.
     * Equal to: bytes4(keccak256("onERC721Received(address,address,uint256,bytes)")).
     */
    bytes4 internal constant MAGIC_ON_ERC721_RECEIVED = 0x150b7a02;

    /**
     * @dev A mapping from NFT ID to the address that owns it.
     */
    mapping(uint256 => address) internal idToOwner;

    /**
     * @dev Mapping from NFT ID to approved address.
     */
    mapping(uint256 => address) internal idToApproval;

    /**
     * @dev Mapping from owner address to count of their tokens.
     */
    mapping(address => uint256) private ownerToNFTokenCount;

    /**
     * @dev Mapping from owner address to mapping of operator addresses.
     */
    mapping(address => mapping(address => bool)) internal ownerToOperators;

    /**
     * @dev Guarantees that the msg.sender is an owner or operator of the given NFT.
     * @param _tokenId ID of the NFT to validate.
     */
    modifier canOperate(uint256 _tokenId) {
        address tokenOwner = idToOwner[_tokenId];
        require(
            tokenOwner == msg.sender ||
                ownerToOperators[tokenOwner][msg.sender],
            NOT_OWNER_OR_OPERATOR
        );
        _;
    }

    /**
     * @dev Guarantees that the msg.sender is allowed to transfer NFT.
     * @param _tokenId ID of the NFT to transfer.
     */
    modifier canTransfer(uint256 _tokenId) {
        address tokenOwner = idToOwner[_tokenId];
        require(
            tokenOwner == msg.sender ||
                idToApproval[_tokenId] == msg.sender ||
                ownerToOperators[tokenOwner][msg.sender],
            NOT_OWNER_APPROVED_OR_OPERATOR
        );
        _;
    }

    /**
     * @dev Guarantees that _tokenId is a valid Token.
     * @param _tokenId ID of the NFT to validate.
     */
    modifier validNFToken(uint256 _tokenId) {
        require(idToOwner[_tokenId] != address(0), NOT_VALID_NFT);
        _;
    }

    /**
     * @dev Contract constructor.
     */
    constructor() {
        supportedInterfaces[0x80ac58cd] = true; // ERC721
    }

    /**
     * @notice Throws unless `msg.sender` is the current owner, an authorized operator, or the
     * approved address for this NFT. Throws if `_from` is not the current owner. Throws if `_to` is
     * the zero address. Throws if `_tokenId` is not a valid NFT. When transfer is complete, this
     * function checks if `_to` is a smart contract (code size > 0). If so, it calls
     * `onERC721Received` on `_to` and throws if the return value is not
     * `bytes4(keccak256("onERC721Received(address,uint256,bytes)"))`.
     * @dev Transfers the ownership of an NFT from one address to another address. This function can
     * be changed to payable.
     * @param _from The current owner of the NFT.
     * @param _to The new owner.
     * @param _tokenId The NFT to transfer.
     * @param _data Additional data with no specified format, sent in call to `_to`.
     */
    function safeTransferFrom(
        address _from,
        address _to,
        uint256 _tokenId,
        bytes calldata _data
    ) external override {
        _safeTransferFrom(_from, _to, _tokenId, _data);
    }

    /**
     * @notice This works identically to the other function with an extra data parameter, except this
     * function just sets data to "".
     * @dev Transfers the ownership of an NFT from one address to another address. This function can
     * be changed to payable.
     * @param _from The current owner of the NFT.
     * @param _to The new owner.
     * @param _tokenId The NFT to transfer.
     */
    function safeTransferFrom(
        address _from,
        address _to,
        uint256 _tokenId
    ) external override {
        _safeTransferFrom(_from, _to, _tokenId, "");
    }

    /**
     * @notice The caller is responsible to confirm that `_to` is capable of receiving NFTs or else
     * they may be permanently lost.
     * @dev Throws unless `msg.sender` is the current owner, an authorized operator, or the approved
     * address for this NFT. Throws if `_from` is not the current owner. Throws if `_to` is the zero
     * address. Throws if `_tokenId` is not a valid NFT. This function can be changed to payable.
     * @param _from The current owner of the NFT.
     * @param _to The new owner.
     * @param _tokenId The NFT to transfer.
     */
    function transferFrom(
        address _from,
        address _to,
        uint256 _tokenId
    ) external override canTransfer(_tokenId) validNFToken(_tokenId) {
        address tokenOwner = idToOwner[_tokenId];
        require(tokenOwner == _from, NOT_OWNER);
        require(_to != address(0), ZERO_ADDRESS);

        _transfer(_to, _tokenId);
    }

    /**
     * @notice The zero address indicates there is no approved address. Throws unless `msg.sender` is
     * the current NFT owner, or an authorized operator of the current owner.
     * @dev Set or reaffirm the approved address for an NFT. This function can be changed to payable.
     * @param _approved Address to be approved for the given NFT ID.
     * @param _tokenId ID of the token to be approved.
     */
    function approve(address _approved, uint256 _tokenId)
        external
        override
        canOperate(_tokenId)
        validNFToken(_tokenId)
    {
        address tokenOwner = idToOwner[_tokenId];
        require(_approved != tokenOwner, IS_OWNER);

        idToApproval[_tokenId] = _approved;
        emit Approval(tokenOwner, _approved, _tokenId);
    }

    /**
     * @notice This works even if sender doesn't own any tokens at the time.
     * @dev Enables or disables approval for a third party ("operator") to manage all of
     * `msg.sender`'s assets. It also emits the ApprovalForAll event.
     * @param _operator Address to add to the set of authorized operators.
     * @param _approved True if the operators is approved, false to revoke approval.
     */
    function setApprovalForAll(address _operator, bool _approved)
        external
        override
    {
        ownerToOperators[msg.sender][_operator] = _approved;
        emit ApprovalForAll(msg.sender, _operator, _approved);
    }

    /**
     * @dev Returns the number of NFTs owned by `_owner`. NFTs assigned to the zero address are
     * considered invalid, and this function throws for queries about the zero address.
     * @param _owner Address for whom to query the balance.
     * @return Balance of _owner.
     */
    function balanceOf(address _owner)
        external
        view
        override
        returns (uint256)
    {
        require(_owner != address(0), ZERO_ADDRESS);
        return _getOwnerNFTCount(_owner);
    }

    /**
     * @dev Returns the address of the owner of the NFT. NFTs assigned to the zero address are
     * considered invalid, and queries about them do throw.
     * @param _tokenId The identifier for an NFT.
     * @return _owner Address of _tokenId owner.
     */
    function ownerOf(uint256 _tokenId)
        external
        view
        override
        returns (address _owner)
    {
        _owner = idToOwner[_tokenId];
        require(_owner != address(0), NOT_VALID_NFT);
    }

    /**
     * @notice Throws if `_tokenId` is not a valid NFT.
     * @dev Get the approved address for a single NFT.
     * @param _tokenId ID of the NFT to query the approval of.
     * @return Address that _tokenId is approved for.
     */
    function getApproved(uint256 _tokenId)
        external
        view
        override
        validNFToken(_tokenId)
        returns (address)
    {
        return idToApproval[_tokenId];
    }

    /**
     * @dev Checks if `_operator` is an approved operator for `_owner`.
     * @param _owner The address that owns the NFTs.
     * @param _operator The address that acts on behalf of the owner.
     * @return True if approved for all, false otherwise.
     */
    function isApprovedForAll(address _owner, address _operator)
        external
        view
        override
        returns (bool)
    {
        return ownerToOperators[_owner][_operator];
    }