// File: @0xcert/ethereum-erc721/contracts/tokens/ERC721.sol

pragma solidity ^0.4.24;

/**
 * @dev ERC-721 non-fungible token standard. See https://goo.gl/pc9yoS.
 */
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
  );

  /**
   * @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.
   */
  function balanceOf(
    address _owner
  )
    external
    view
    returns (uint256);

  /**
   * @dev Returns the address of the owner of the NFT. NFTs assigned to zero address are considered
   * invalid, and queries about them do throw.
   * @param _tokenId The identifier for an NFT.
   */
  function ownerOf(
    uint256 _tokenId
  )
    external
    view
    returns (address);

  /**
   * @dev Transfers the ownership of an NFT from one address to another address.
   * @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)"))`.
   * @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 _data
  )
    external;

  /**
   * @dev Transfers the ownership of an NFT from one address to another address.
   * @notice This works identically to the other function with an extra data parameter, except this
   * function just sets data to ""
   * @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;

  /**
   * @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.
   * @notice The caller is responsible to confirm that `_to` is capable of receiving NFTs or else
   * they mayb be permanently lost.
   * @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;

  /**
   * @dev Set or reaffirm the approved address for an NFT.
   * @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.
   * @param _tokenId The NFT to approve.
   */
  function approve(
    address _approved,
    uint256 _tokenId
  )
    external;

  /**
   * @dev Enables or disables approval for a third party ("operator") to manage all of
   * `msg.sender`'s assets. It also emits the ApprovalForAll event.
   * @notice The contract MUST allow multiple operators per owner.
   * @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 Get the approved address for a single NFT.
   * @notice Throws if `_tokenId` is not a valid NFT.
   * @param _tokenId The NFT to find the approved address for.
   */
  function getApproved(
    uint256 _tokenId
  )
    external
    view
    returns (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.
   */
  function isApprovedForAll(
    address _owner,
    address _operator
  )
    external
    view
    returns (bool);

}

// File: @0xcert/ethereum-erc721/contracts/tokens/ERC721TokenReceiver.sol

pragma solidity ^0.4.24;

/**
 * @dev ERC-721 interface for accepting safe transfers. See https://goo.gl/pc9yoS.
 */
interface ERC721TokenReceiver {

  /**
   * @dev Handle the receipt of a NFT. The ERC721 smart contract calls this function on the
   * recipient after a `transfer`. This function MAY throw to revert and reject the transfer. Return
   * of other than the magic value MUST result in the transaction being reverted.
   * Returns `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))` unless throwing.
   * @notice The contract address is always the message sender. A wallet/broker/auction application
   * MUST implement the wallet interface if it will accept safe transfers.
   * @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.
   */
  function onERC721Received(
    address _operator,
    address _from,
    uint256 _tokenId,
    bytes _data
  )
    external
    returns(bytes4);
    
}

// File: @0xcert/ethereum-utils/contracts/math/SafeMath.sol

pragma solidity ^0.4.24;

/**
 * @dev Math operations with safety checks that throw on error. This contract is based
 * on the source code at https://goo.gl/iyQsmU.
 */
library SafeMath {

  /**
   * @dev Multiplies two numbers, throws on overflow.
   * @param _a Factor number.
   * @param _b Factor number.
   */
  function mul(
    uint256 _a,
    uint256 _b
  )
    internal
    pure
    returns (uint256)
  {
    if (_a == 0) {
      return 0;
    }
    uint256 c = _a * _b;
    assert(c / _a == _b);
    return c;
  }

  /**
   * @dev Integer division of two numbers, truncating the quotient.
   * @param _a Dividend number.
   * @param _b Divisor number.
   */
  function div(
    uint256 _a,
    uint256 _b
  )
    internal
    pure
    returns (uint256)
  {
    uint256 c = _a / _b;
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;
  }

  /**
   * @dev Substracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
   * @param _a Minuend number.
   * @param _b Subtrahend number.
   */
  function sub(
    uint256 _a,
    uint256 _b
  )
    internal
    pure
    returns (uint256)
  {
    assert(_b <= _a);
    return _a - _b;
  }

  /**
   * @dev Adds two numbers, throws on overflow.
   * @param _a Number.
   * @param _b Number.
   */
  function add(
    uint256 _a,
    uint256 _b
  )
    internal
    pure
    returns (uint256)
  {
    uint256 c = _a + _b;
    assert(c >= _a);
    return c;
  }

}

// File: @0xcert/ethereum-utils/contracts/utils/ERC165.sol

pragma solidity ^0.4.24;

/**
 * @dev A standard for detecting smart contract interfaces. See https://goo.gl/cxQCse.
 */
interface ERC165 {

  /**
   * @dev Checks if the smart contract includes a specific interface.
   * @notice This function uses less than 30,000 gas.
   * @param _interfaceID The interface identifier, as specified in ERC-165.
   */
  function supportsInterface(
    bytes4 _interfaceID
  )
    external
    view
    returns (bool);

}

// File: @0xcert/ethereum-utils/contracts/utils/SupportsInterface.sol

pragma solidity ^0.4.24;


/**
 * @dev Implementation of standard for detect smart contract interfaces.
 */
contract SupportsInterface is
  ERC165
{

  /**
   * @dev Mapping of supported intefraces.
   * @notice You must not set element 0xffffffff to true.
   */
  mapping(bytes4 => bool) internal supportedInterfaces;

  /**
   * @dev Contract constructor.
   */
  constructor()
    public
  {
    supportedInterfaces[0x01ffc9a7] = true; // ERC165
  }

  /**
   * @dev Function to check which interfaces are suported by this contract.
   * @param _interfaceID Id of the interface.
   */
  function supportsInterface(
    bytes4 _interfaceID
  )
    external
    view
    returns (bool)
  {
    return supportedInterfaces[_interfaceID];
  }

}

// File: @0xcert/ethereum-utils/contracts/utils/AddressUtils.sol

pragma solidity ^0.4.24;

/**
 * @dev Utility library of inline functions on addresses.
 */
library AddressUtils {

  /**
   * @dev Returns whether the target address is a contract.
   * @param _addr Address to check.
   */
  function isContract(
    address _addr
  )
    internal
    view
    returns (bool)
  {
    uint256 size;

    /**
     * XXX Currently there is no better way to check if there is a contract in an address than to
     * check the size of the code at that address.
     * See https://ethereum.stackexchange.com/a/14016/36603 for more details about how this works.
     * TODO: Check this again before the Serenity release, because all addresses will be
     * contracts then.
     */
    assembly { size := extcodesize(_addr) } // solium-disable-line security/no-inline-assembly
    return size > 0;
  }

}

// File: @0xcert/ethereum-erc721/contracts/tokens/NFToken.sol

pragma solidity ^0.4.24;






/**
 * @dev Implementation of ERC-721 non-fungible token standard.
 */
contract NFToken is
  ERC721,
  SupportsInterface
{
  using SafeMath for uint256;
  using AddressUtils for address;

  /**
   * @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 idToApprovals;

   /**
   * @dev Mapping from owner address to count of his tokens.
   */
  mapping (address => uint256) internal ownerToNFTokenCount;

  /**
   * @dev Mapping from owner address to mapping of operator addresses.
   */
  mapping (address => mapping (address => bool)) internal ownerToOperators;

  /**
   * @dev Magic value of a smart contract that can recieve NFT.
   * Equal to: bytes4(keccak256("onERC721Received(address,address,uint256,bytes)")).
   */
  bytes4 constant MAGIC_ON_ERC721_RECEIVED = 0x150b7a02;

  /**
   * @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.
   * @param _from Sender of NFT (if address is zero address it indicates token creation).
   * @param _to Receiver of NFT (if address is zero address it indicates token destruction).
   * @param _tokenId The NFT that got transfered.
   */
  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.
   * @param _owner Owner of NFT.
   * @param _approved Address that we are approving.
   * @param _tokenId NFT which we are approving.
   */
  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.
   * @param _owner Owner of NFT.
   * @param _operator Address to which we are setting operator rights.
   * @param _approved Status of operator rights(true if operator rights are given and false if
   * revoked).
   */
  event ApprovalForAll(
    address indexed _owner,
    address indexed _operator,
    bool _approved
  );

  /**
   * @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]);
    _;
  }

  /**
   * @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
      || getApproved(_tokenId) == msg.sender
      || ownerToOperators[tokenOwner][msg.sender]
    );

    _;
  }

  /**
   * @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));
    _;
  }

  /**
   * @dev Contract constructor.
   */
  constructor()
    public
  {
    supportedInterfaces[0x80ac58cd] = true; // ERC721
  }

  /**
   * @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.
   */
  function balanceOf(
    address _owner
  )
    external
    view
    returns (uint256)
  {
    require(_owner != address(0));
    return ownerToNFTokenCount[_owner];
  }

  /**
   * @dev Returns the address of the owner of the NFT. NFTs assigned to zero address are considered
   * invalid, and queries about them do throw.
   * @param _tokenId The identifier for an NFT.
   */
  function ownerOf(
    uint256 _tokenId
  )
    external
    view
    returns (address _owner)
  {
    _owner = idToOwner[_tokenId];
    require(_owner != address(0));
  }

  /**
   * @dev Transfers the ownership of an NFT from one address to another address.
   * @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)"))`.
   * @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 _data
  )
    external
  {
    _safeTransferFrom(_from, _to, _tokenId, _data);
  }

  /**
   * @dev Transfers the ownership of an NFT from one address to another address.
   * @notice This works identically to the other function with an extra data parameter, except this
   * function just sets data to ""
   * @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
  {
    _safeTransferFrom(_from, _to, _tokenId, "");
  }

  /**
   * @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.
   * @notice The caller is responsible to confirm that `_to` is capable of receiving NFTs or else
   * they maybe be permanently lost.
   * @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
    canTransfer(_tokenId)
    validNFToken(_tokenId)
  {
    address tokenOwner = idToOwner[_tokenId];
    require(tokenOwner == _from);
    require(_to != address(0));

    _transfer(_to, _tokenId);
  }

  /**
   * @dev Set or reaffirm the approved address for an NFT.
   * @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 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
    canOperate(_tokenId)
    validNFToken(_tokenId)
  {
    address tokenOwner = idToOwner[_tokenId];
    require(_approved != tokenOwner);

    idToApprovals[_tokenId] = _approved;
    emit Approval(tokenOwner, _approved, _tokenId);
  }

  /**
   * @dev Enables or disables approval for a third party ("operator") to manage all of
   * `msg.sender`'s assets. It also emits the ApprovalForAll event.
   * @notice This works even if sender doesn't own any tokens at the time.
   * @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
  {
    require(_operator != address(0));
    ownerToOperators[msg.sender][_operator] = _approved;
    emit ApprovalForAll(msg.sender, _operator, _approved);
  }

  /**
   * @dev Get the approved address for a single NFT.
   * @notice Throws if `_tokenId` is not a valid NFT.
   * @param _tokenId ID of the NFT to query the approval of.
   */
  function getApproved(
    uint256 _tokenId
  )
    public
    view
    validNFToken(_tokenId)
    returns (address)
  {
    return idToApprovals[_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.
   */
  function isApprovedForAll(
    address _owner,
    address _operator
  )
    external
    view
    returns (bool)
  {
    require(_owner != address(0));
    require(_operator != address(0));
    return ownerToOperators[_owner][_operator];
  }

  /**
   * @dev Actually perform the safeTransferFrom.
   * @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 _data
  )
    internal
    canTransfer(_tokenId)
    validNFToken(_tokenId)
  {
    address tokenOwner = idToOwner[_tokenId];
    require(tokenOwner == _from);
    require(_to != address(0));

    _transfer(_to, _tokenId);

    if (_to.isContract()) {
      bytes4 retval = ERC721TokenReceiver(_to).onERC721Received(msg.sender, _from, _tokenId, _data);
      require(retval == MAGIC_ON_ERC721_RECEIVED);
    }
  }

  /**
   * @dev Actually preforms the transfer.
   * @notice Does NO checks.
   * @param _to Address of a new owner.
   * @param _tokenId The NFT that is being transferred.
   */
  function _transfer(
    address _to,
    uint256 _tokenId
  )
    private
  {
    address from = idToOwner[_tokenId];
    clearApproval(_tokenId);

    removeNFToken(from, _tokenId);
    addNFToken(_to, _tokenId);

    emit Transfer(from, _to, _tokenId);
  }
   
  /**
   * @dev Mints a new NFT.
   * @notice This is a private function which should be called from user-implemented external
   * mint function. Its purpose is to show and properly initialize data structures when using this
   * implementation.
   * @param _to The address that will own the minted NFT.
   * @param _tokenId of the NFT to be minted by the msg.sender.
   */
  function _mint(
    address _to,
    uint256 _tokenId
  )
    internal
  {
    require(_to != address(0));
    require(_tokenId != 0);
    require(idToOwner[_tokenId] == address(0));

    addNFToken(_to, _tokenId);

    emit Transfer(address(0), _to, _tokenId);
  }

  /**
   * @dev Burns a NFT.
   * @notice This is a private function which should be called from user-implemented external
   * burn function. Its purpose is to show and properly initialize data structures when using this
   * implementation.
   * @param _owner Address of the NFT owner.
   * @param _tokenId ID of the NFT to be burned.
   */
  function _burn(
    address _owner,
    uint256 _tokenId
  )
    validNFToken(_tokenId)
    internal
  {
    clearApproval(_tokenId);
    removeNFToken(_owner, _tokenId);
    emit Transfer(_owner, address(0), _tokenId);
  }

  /** 
   * @dev Clears the current approval of a given NFT ID.
   * @param _tokenId ID of the NFT to be transferred.
   */
  function clearApproval(
    uint256 _tokenId
  )
    private
  {
    if(idToApprovals[_tokenId] != 0)
    {
      delete idToApprovals[_tokenId];
    }
  }

  /**
   * @dev Removes a NFT from owner.
   * @notice Use and override this function with caution. Wrong usage can have serious consequences.
   * @param _from Address from wich we want to remove the NFT.
   * @param _tokenId Which NFT we want to remove.
   */
  function removeNFToken(
    address _from,
    uint256 _tokenId
  )
   internal
  {
    require(idToOwner[_tokenId] == _from);
    assert(ownerToNFTokenCount[_from] > 0);
    ownerToNFTokenCount[_from] = ownerToNFTokenCount[_from].sub(1);
    delete idToOwner[_tokenId];
  }

  /**
   * @dev Assignes a new NFT to owner.
   * @notice Use and override this function with caution. Wrong usage can have serious consequences.
   * @param _to Address to wich we want to add the NFT.
   * @param _tokenId Which NFT we want to add.
   */
  function addNFToken(
    address _to,
    uint256 _tokenId
  )
    internal
  {
    require(idToOwner[_tokenId] == address(0));

    idToOwner[_tokenId] = _to;
    ownerToNFTokenCount[_to] = ownerToNFTokenCount[_to].add(1);
  }

}

// File: @0xcert/ethereum-erc721/contracts/tokens/ERC721Metadata.sol

pragma solidity ^0.4.24;

/**
 * @dev Optional metadata extension for ERC-721 non-fungible token standard.
 * See https://goo.gl/pc9yoS.
 */
interface ERC721Metadata {

  /**
   * @dev Returns a descriptive name for a collection of NFTs in this contract.
   */
  function name()
    external
    view
    returns (string _name);

  /**
   * @dev Returns a abbreviated name for a collection of NFTs in this contract.
   */
  function symbol()
    external
    view
    returns (string _symbol);

  /**
   * @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".
   */
  function tokenURI(uint256 _tokenId)
    external
    view
    returns (string);

}

// File: @0xcert/ethereum-erc721/contracts/tokens/NFTokenMetadata.sol

pragma solidity ^0.4.24;



/**
 * @dev Optional metadata implementation for ERC-721 non-fungible token standard.
 */
contract NFTokenMetadata is
  NFToken,
  ERC721Metadata
{

  /**
   * @dev A descriptive name for a collection of NFTs.
   */
  string internal nftName;

  /**
   * @dev An abbreviated name for NFTokens.
   */
  string internal nftSymbol;

  /**
   * @dev Mapping from NFT ID to metadata uri.
   */
  mapping (uint256 => string) internal idToUri;

  /**
   * @dev Contract constructor.
   * @notice When implementing this contract don't forget to set nftName and nftSymbol.
   */
  constructor()
    public
  {
    supportedInterfaces[0x5b5e139f] = true; // ERC721Metadata
  }

  /**
   * @dev Burns a NFT.
   * @notice This is a internal function which should be called from user-implemented external
   * burn function. Its purpose is to show and properly initialize data structures when using this
   * implementation.
   * @param _owner Address of the NFT owner.
   * @param _tokenId ID of the NFT to be burned.
   */
  function _burn(
    address _owner,
    uint256 _tokenId
  )
    internal
  {
    super._burn(_owner, _tokenId);

    if (bytes(idToUri[_tokenId]).length != 0) {
      delete idToUri[_tokenId];
    }
  }

  /**
   * @dev Set a distinct URI (RFC 3986) for a given NFT ID.
   * @notice this is a internal function which should be called from user-implemented external
   * function. Its purpose is to show and properly initialize data structures when using this
   * implementation.
   * @param _tokenId Id for which we want uri.
   * @param _uri String representing RFC 3986 URI.
   */
  function _setTokenUri(
    uint256 _tokenId,
    string _uri
  )
    validNFToken(_tokenId)
    internal
  {
    idToUri[_tokenId] = _uri;
  }

  /**
   * @dev Returns a descriptive name for a collection of NFTokens.
   */
  function name()
    external
    view
    returns (string _name)
  {
    _name = nftName;
  }

  /**
   * @dev Returns an abbreviated name for NFTokens.
   */
  function symbol()
    external
    view
    returns (string _symbol)
  {
    _symbol = nftSymbol;
  }

  /**
   * @dev A distinct URI (RFC 3986) for a given NFT.
   * @param _tokenId Id for which we want uri.
   */
  function tokenURI(
    uint256 _tokenId
  )
    validNFToken(_tokenId)
    external
    view
    returns (string)
  {
    return idToUri[_tokenId];
  }

}

// File: @0xcert/ethereum-erc721/contracts/tokens/ERC721Enumerable.sol

pragma solidity ^0.4.24;

/**
 * @dev Optional enumeration extension for ERC-721 non-fungible token standard.
 * See https://goo.gl/pc9yoS.
 */
interface ERC721Enumerable {

  /**
   * @dev Returns a count of valid NFTs tracked by this contract, where each one of them has an
   * assigned and queryable owner not equal to the zero address.
   */
  function totalSupply()
    external
    view
    returns (uint256);

  /**
   * @dev Returns the token identifier for the `_index`th NFT. Sort order is not specified.
   * @param _index A counter less than `totalSupply()`.
   */
  function tokenByIndex(
    uint256 _index
  )
    external
    view
    returns (uint256);

  /**
   * @dev Returns the token identifier for the `_index`th NFT assigned to `_owner`. Sort order is
   * not specified. It throws if `_index` >= `balanceOf(_owner)` or if `_owner` is the zero address,
   * representing invalid NFTs.
   * @param _owner An address where we are interested in NFTs owned by them.
   * @param _index A counter less than `balanceOf(_owner)`.
   */
  function tokenOfOwnerByIndex(
    address _owner,
    uint256 _index
  )
    external
    view
    returns (uint256);

}

// File: @0xcert/ethereum-erc721/contracts/tokens/NFTokenEnumerable.sol

pragma solidity ^0.4.24;



/**
 * @dev Optional enumeration implementation for ERC-721 non-fungible token standard.
 */
contract NFTokenEnumerable is
  NFToken,
  ERC721Enumerable
{

  /**
   * @dev Array of all NFT IDs.
   */
  uint256[] internal tokens;

  /**
   * @dev Mapping from token ID its index in global tokens array.
   */
  mapping(uint256 => uint256) internal idToIndex;

  /**
   * @dev Mapping from owner to list of owned NFT IDs.
   */
  mapping(address => uint256[]) internal ownerToIds;

  /**
   * @dev Mapping from NFT ID to its index in the owner tokens list.
   */
  mapping(uint256 => uint256) internal idToOwnerIndex;

  /**
   * @dev Contract constructor.
   */
  constructor()
    public
  {
    supportedInterfaces[0x780e9d63] = true; // ERC721Enumerable
  }

  /**
   * @dev Mints a new NFT.
   * @notice This is a private function which should be called from user-implemented external
   * mint function. Its purpose is to show and properly initialize data structures when using this
   * implementation.
   * @param _to The address that will own the minted NFT.
   * @param _tokenId of the NFT to be minted by the msg.sender.
   */
  function _mint(
    address _to,
    uint256 _tokenId
  )
    internal
  {
    super._mint(_to, _tokenId);
    tokens.push(_tokenId);
    idToIndex[_tokenId] = tokens.length.sub(1);
  }

  /**
   * @dev Burns a NFT.
   * @notice This is a private function which should be called from user-implemented external
   * burn function. Its purpose is to show and properly initialize data structures when using this
   * implementation.
   * @param _owner Address of the NFT owner.
   * @param _tokenId ID of the NFT to be burned.
   */
  function _burn(
    address _owner,
    uint256 _tokenId
  )
    internal
  {
    super._burn(_owner, _tokenId);
    assert(tokens.length > 0);

    uint256 tokenIndex = idToIndex[_tokenId];
    // Sanity check. This could be removed in the future.
    assert(tokens[tokenIndex] == _tokenId);
    uint256 lastTokenIndex = tokens.length.sub(1);
    uint256 lastToken = tokens[lastTokenIndex];

    tokens[tokenIndex] = lastToken;

    tokens.length--;
    // Consider adding a conditional check for the last token in order to save GAS.
    idToIndex[lastToken] = tokenIndex;
    idToIndex[_tokenId] = 0;
  }

  /**
   * @dev Removes a NFT from an address.
   * @notice Use and override this function with caution. Wrong usage can have serious consequences.
   * @param _from Address from wich we want to remove the NFT.
   * @param _tokenId Which NFT we want to remove.
   */
  function removeNFToken(
    address _from,
    uint256 _tokenId
  )
   internal
  {
    super.removeNFToken(_from, _tokenId);
    assert(ownerToIds[_from].length > 0);

    uint256 tokenToRemoveIndex = idToOwnerIndex[_tokenId];
    uint256 lastTokenIndex = ownerToIds[_from].length.sub(1);
    uint256 lastToken = ownerToIds[_from][lastTokenIndex];

    ownerToIds[_from][tokenToRemoveIndex] = lastToken;

    ownerToIds[_from].length--;
    // Consider adding a conditional check for the last token in order to save GAS.
    idToOwnerIndex[lastToken] = tokenToRemoveIndex;
    idToOwnerIndex[_tokenId] = 0;
  }

  /**
   * @dev Assignes a new NFT to an address.
   * @notice Use and override this function with caution. Wrong usage can have serious consequences.
   * @param _to Address to wich we want to add the NFT.
   * @param _tokenId Which NFT we want to add.
   */
  function addNFToken(
    address _to,
    uint256 _tokenId
  )
    internal
  {
    super.addNFToken(_to, _tokenId);

    uint256 length = ownerToIds[_to].length;
    ownerToIds[_to].push(_tokenId);
    idToOwnerIndex[_tokenId] = length;
  }

  /**
   * @dev Returns the count of all existing NFTokens.
   */
  function totalSupply()
    external
    view
    returns (uint256)
  {
    return tokens.length;
  }

  /**
   * @dev Returns NFT ID by its index.
   * @param _index A counter less than `totalSupply()`.
   */
  function tokenByIndex(
    uint256 _index
  )
    external
    view
    returns (uint256)
  {
    require(_index < tokens.length);
    // Sanity check. This could be removed in the future.
    assert(idToIndex[tokens[_index]] == _index);
    return tokens[_index];
  }

  /**
   * @dev returns the n-th NFT ID from a list of owner's tokens.
   * @param _owner Token owner's address.
   * @param _index Index number representing n-th token in owner's list of tokens.
   */
  function tokenOfOwnerByIndex(
    address _owner,
    uint256 _index
  )
    external
    view
    returns (uint256)
  {
    require(_index < ownerToIds[_owner].length);
    return ownerToIds[_owner][_index];
  }

}

// File: @0xcert/ethereum-utils/contracts/ownership/Ownable.sol

pragma solidity ^0.4.24;

/**
 * @dev The contract has an owner address, and provides basic authorization control whitch
 * simplifies the implementation of user permissions. This contract is based on the source code
 * at https://goo.gl/n2ZGVt.
 */
contract Ownable {
  address public owner;

  /**
   * @dev An event which is triggered when the owner is changed.
   * @param previousOwner The address of the previous owner.
   * @param newOwner The address of the new owner.
   */
  event OwnershipTransferred(
    address indexed previousOwner,
    address indexed newOwner
  );

  /**
   * @dev The constructor sets the original `owner` of the contract to the sender account.
   */
  constructor()
    public
  {
    owner = msg.sender;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param _newOwner The address to transfer ownership to.
   */
  function transferOwnership(
    address _newOwner
  )
    onlyOwner
    public
  {
    require(_newOwner != address(0));
    emit OwnershipTransferred(owner, _newOwner);
    owner = _newOwner;
  }

}

// File: @0xcert/ethereum-utils/contracts/ownership/Claimable.sol

pragma solidity ^0.4.24;


/**
 * @dev The contract has an owner address, and provides basic authorization control whitch
 * simplifies the implementation of user permissions. This contract is based on the source code
 * at goo.gl/CfEAkv and upgrades Ownable contracts with additional claim step which makes ownership
 * transfers less prone to errors.
 */
contract Claimable is Ownable {
  address public pendingOwner;

  /**
   * @dev An event which is triggered when the owner is changed.
   * @param previousOwner The address of the previous owner.
   * @param newOwner The address of the new owner.
   */
  event OwnershipTransferred(
    address indexed previousOwner,
    address indexed newOwner
  );

  /**
   * @dev Allows the current owner to give new owner ability to claim the ownership of the contract.
   * This differs from the Owner's function in that it allows setting pedingOwner address to 0x0,
   * which effectively cancels an active claim.
   * @param _newOwner The address which can claim ownership of the contract.
   */
  function transferOwnership(
    address _newOwner
  )
    onlyOwner
    public
  {
    pendingOwner = _newOwner;
  }

  /**
   * @dev Allows the current pending owner to claim the ownership of the contract. It emits
   * OwnershipTransferred event and resets pending owner to 0.
   */
  function claimOwnership()
    public
  {
    require(msg.sender == pendingOwner);
    address previousOwner = owner;
    owner = pendingOwner;
    pendingOwner = 0;
    emit OwnershipTransferred(previousOwner, owner);
  }
}

// File: contracts/Adminable.sol

pragma solidity ^0.4.24;


/**
 * @title Adminable
 * @dev Allows to manage privilages to special contract functionality.
 */
contract Adminable is Claimable {
  mapping(address => uint) public adminsMap;
  address[] public adminList;

  /**
   * @dev Returns true, if provided address has special privilages, otherwise false
   * @param adminAddress - address to check
   */
  function isAdmin(address adminAddress)
    public
    view
    returns(bool isIndeed)
  {
    if (adminAddress == owner) return true;

    if (adminList.length == 0) return false;
    return (adminList[adminsMap[adminAddress]] == adminAddress);
  }

  /**
   * @dev Grants special rights for address holder
   * @param adminAddress - address of future admin
   */
  function addAdmin(address adminAddress)
    public
    onlyOwner
    returns(uint index)
  {
    require(!isAdmin(adminAddress), "Address already has admin rights!");

    adminsMap[adminAddress] = adminList.push(adminAddress)-1;

    return adminList.length-1;
  }

  /**
   * @dev Removes special rights for provided address
   * @param adminAddress - address of current admin
   */
  function removeAdmin(address adminAddress)
    public
    onlyOwner
    returns(uint index)
  {
    // we can not remove owner from admin role
    require(owner != adminAddress, "Owner can not be removed from admin role!");
    require(isAdmin(adminAddress), "Provided address is not admin.");

    uint rowToDelete = adminsMap[adminAddress];
    address keyToMove = adminList[adminList.length-1];
    adminList[rowToDelete] = keyToMove;
    adminsMap[keyToMove] = rowToDelete;
    adminList.length--;

    return rowToDelete;
  }

  /**
   * @dev modifier Throws if called by any account other than the owner.
   */
  modifier onlyAdmin() {
    require(isAdmin(msg.sender), "Can be executed only by admin accounts!");
    _;
  }
}

// File: contracts/MarbleNFTInterface.sol

pragma solidity ^0.4.24;

/**
 * @title Marble NFT Interface
 * @dev Defines Marbles unique extension of NFT.
 * ...It contains methodes returning core properties what describe Marble NFTs and provides management options to create,
 * burn NFT or change approvals of it.
 */
interface MarbleNFTInterface {

  /**
   * @dev Mints Marble NFT.
   * @notice This is a external function which should be called just by the owner of contract or any other user who has priviladge of being resposible
   * of creating valid Marble NFT. Valid token contains all neccessary information to be able recreate marble card image.
   * @param _tokenId The ID of new NFT.
   * @param _owner Address of the NFT owner.
   * @param _uri Unique URI proccessed by Marble services to be sure it is valid NFTs DNA. Most likely it is URL pointing to some website address.
   * @param _metadataUri URI pointing to "ERC721 Metadata JSON Schema"
   * @param _tokenId ID of the NFT to be burned.
   */
  function mint(
    uint256 _tokenId,
    address _owner,
    address _creator,
    string _uri,
    string _metadataUri,
    uint256 _created
  )
    external;

  /**
   * @dev Burns Marble NFT. Should be fired only by address with proper authority as contract owner or etc.
   * @param _tokenId ID of the NFT to be burned.
   */
  function burn(
    uint256 _tokenId
  )
    external;

  /**
   * @dev Allowes to change approval for change of ownership even when sender is not NFT holder. Sender has to have special role granted by contract to use this tool.
   * @notice Careful with this!!!! :))
   * @param _tokenId ID of the NFT to be updated.
   * @param _approved ETH address what supposed to gain approval to take ownership of NFT.
   */
  function forceApproval(
    uint256 _tokenId,
    address _approved
  )
    external;

  /**
   * @dev Returns properties used for generating NFT metadata image (a.k.a. card).
   * @param _tokenId ID of the NFT.
   */
  function tokenSource(uint256 _tokenId)
    external
    view
    returns (
      string uri,
      address creator,
      uint256 created
    );

  /**
   * @dev Returns ID of NFT what matches provided source URI.
   * @param _uri URI of source website.
   */
  function tokenBySourceUri(string _uri)
    external
    view
    returns (uint256 tokenId);

  /**
   * @dev Returns all properties of Marble NFT. Lets call it Marble NFT Model with properties described below:
   * @param _tokenId ID  of NFT
   * Returned model:
   * uint256 id ID of NFT
   * string uri  URI of source website. Website is used to mine data to crate NFT metadata image.
   * string metadataUri URI to NFT metadata assets. In our case to our websevice providing JSON with additional information based on "ERC721 Metadata JSON Schema".
   * address owner NFT owner address.
   * address creator Address of creator of this NFT. It means that this addres placed sourceURI to candidate contract.
   * uint256 created Date and time of creation of NFT candidate.
   *
   * (id, uri, metadataUri, owner, creator, created)
   */
  function getNFT(uint256 _tokenId)
    external
    view
    returns(
      uint256 id,
      string uri,
      string metadataUri,
      address owner,
      address creator,
      uint256 created
    );


    /**
     * @dev Transforms URI to hash.
     * @param _uri URI to be transformed to hash.
     */
    function getSourceUriHash(string _uri)
      external
      view
      returns(uint256 hash);
}

// File: contracts/MarbleNFT.sol

pragma solidity ^0.4.24;





/**
 * @title MARBLE NFT CONTRACT
 * @notice We omit a fallback function to prevent accidental sends to this contract.
 */
contract MarbleNFT is
  Adminable,
  NFTokenMetadata,
  NFTokenEnumerable,
  MarbleNFTInterface
{

  /*
   * @dev structure storing additional information about created NFT
   * uri: URI used as source/key/representation of NFT, it can be considered as tokens DNA
   * creator:  address of candidate creator - a.k.a. address of person who initialy provided source URI
   * created: date of NFT creation
   */
  struct MarbleNFTSource {

    // URI used as source/key of NFT, we can consider it as tokens DNA
    string uri;

    // address of candidate creator - a.k.a. address of person who initialy provided source URI
    address creator;

    // date of NFT creation
    uint256 created;
  }

  /**
   * @dev Mapping from NFT ID to marble NFT source.
   */
  mapping (uint256 => MarbleNFTSource) public idToMarbleNFTSource;
  /**
   * @dev Mapping from marble NFT source uri hash TO NFT ID .
   */
  mapping (uint256 => uint256) public sourceUriHashToId;

  constructor()
    public
  {
    nftName = "MARBLE-NFT";
    nftSymbol = "MRBLNFT";
  }

  /**
   * @dev Mints a new NFT.
   * @param _tokenId The unique number representing NFT
   * @param _owner Holder of Marble NFT
   * @param _creator Creator of Marble NFT
   * @param _uri URI representing NFT
   * @param _metadataUri URI pointing to "ERC721 Metadata JSON Schema"
   * @param _created date of creation of NFT candidate
   */
  function mint(
    uint256 _tokenId,
    address _owner,
    address _creator,
    string _uri,
    string _metadataUri,
    uint256 _created
  )
    external
    onlyAdmin
  {
    uint256 uriHash = _getSourceUriHash(_uri);

    require(uriHash != _getSourceUriHash(""), "NFT URI can not be empty!");
    require(sourceUriHashToId[uriHash] == 0, "NFT with same URI already exists!");

    _mint(_owner, _tokenId);
    _setTokenUri(_tokenId, _metadataUri);

    idToMarbleNFTSource[_tokenId] = MarbleNFTSource(_uri, _creator, _created);
    sourceUriHashToId[uriHash] = _tokenId;
  }

  /**
   * @dev Burns NFT. Sadly, trully.. ...probably someone marbled something ugly!!!! :)
   * @param _tokenId ID of ugly NFT
   */
  function burn(
    uint256 _tokenId
  )
    external
    onlyAdmin
  {
    address owner = idToOwner[_tokenId];

    MarbleNFTSource memory marbleNFTSource = idToMarbleNFTSource[_tokenId];

    if (bytes(marbleNFTSource.uri).length != 0) {
      uint256 uriHash = _getSourceUriHash(marbleNFTSource.uri);
      delete sourceUriHashToId[uriHash];
      delete idToMarbleNFTSource[_tokenId];
    }

    _burn(owner, _tokenId);
  }

  /**
   * @dev Tool to manage misstreated NFTs or to be able to extend our services for new cool stuff like auctions, weird games and so on......
   * @param _tokenId ID of the NFT to be update.
   * @param _approved Address to replace current approved address on NFT
   */
  function forceApproval(
    uint256 _tokenId,
    address _approved
  )
    external
    onlyAdmin
  {
    address tokenOwner = idToOwner[_tokenId];
    require(_approved != tokenOwner,"Owner can not be become new owner!");

    idToApprovals[_tokenId] = _approved;
    emit Approval(tokenOwner, _approved, _tokenId);
  }

  /**
   * @dev Returns model of Marble NFT source properties
   * @param _tokenId ID of the NFT
   */
  function tokenSource(uint256 _tokenId)
    external
    view
    returns (
      string uri,
      address creator,
      uint256 created)
  {
    MarbleNFTSource memory marbleNFTSource = idToMarbleNFTSource[_tokenId];
    return (marbleNFTSource.uri, marbleNFTSource.creator, marbleNFTSource.created);
  }

  /**
   * @dev Returns token ID related to provided source uri
   * @param _uri URI representing created NFT
   */
  function tokenBySourceUri(string _uri)
    external
    view
    returns (uint256 tokenId)
  {
    return sourceUriHashToId[_getSourceUriHash(_uri)];
  }

  /**
   * @dev Returns whole Marble NFT model
   * --------------------
   *   MARBLE NFT MODEL
   * --------------------
   * uint256 id NFT unique identification
   * string uri NFT source URI, source is whole site what was proccessed by marble to create this NFT, it is URI representation of NFT (call it DNA)
   * string metadataUri  URI pointint to token NFT metadata shcema
   * address owner Current NFT owner
   * address creator First NFT owner
   * uint256 created Date of NFT candidate creation
   *
   * (id, uri, metadataUri, owner, creator, created)
   */
  function getNFT(uint256 _tokenId)
    external
    view
    returns(
      uint256 id,
      string uri,
      string metadataUri,
      address owner,
      address creator,
      uint256 created
    )
  {

    MarbleNFTSource memory marbleNFTSource = idToMarbleNFTSource[_tokenId];

    return (
      _tokenId,
      marbleNFTSource.uri,
      idToUri[_tokenId],
      idToOwner[_tokenId],
      marbleNFTSource.creator,
      marbleNFTSource.created);
  }


  /**
   * @dev Transforms URI to hash.
   * @param _uri URI to be transformed to hash.
   */
  function getSourceUriHash(string _uri)
     external
     view
     returns(uint256 hash)
  {
     return _getSourceUriHash(_uri);
  }

  /**
   * @dev Transforms URI to hash.
   * @param _uri URI to be transformed to hash.
   */
  function _getSourceUriHash(string _uri)
    internal
    pure
    returns(uint256 hash)
  {
    return uint256(keccak256(abi.encodePacked(_uri)));
  }
}