// Vulnerability label: clean
pragma solidity ^0.4.24;

library Address {

  /**
   * Returns whether the target address is a contract
   * @dev This function will return false if invoked during the constructor of a contract,
   * as the code is not actually created until after the constructor finishes.
   * @param addr address to check
   * @return whether the target address is a contract
   */
    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.
        // solium-disable-next-line security/no-inline-assembly
        assembly { size := extcodesize(addr) }
        return size > 0;
    }

}

contract Ownable {

    address public owner;

    constructor() public {
        owner = msg.sender;
    }

    function setOwner(address _owner) public onlyOwner {
        owner = _owner;
    }

    function getOwner() public view returns (address) {
        return owner;
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

}

library SafeMath {

    /**
    * @dev Multiplies two numbers, throws on overflow.
    */
    function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {
        // Gas optimization: this is cheaper than asserting 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
        if (a == 0) {
            return 0;
        }

        c = a * b;
        assert(c / a == b);
        return c;
    }

    /**
    * @dev Integer division of two numbers, truncating the quotient.
    */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // assert(b > 0); // Solidity automatically throws when dividing by 0
        // uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold
        return a / b;
    }

    /**
    * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
    */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b <= a);
        return a - b;
    }

    /**
    * @dev Adds two numbers, throws on overflow.
    */
    function add(uint256 a, uint256 b) internal pure returns (uint256 c) {
        c = a + b;
        assert(c >= a);
        return c;
    }
}

library Strings {
    
  // via https://github.com/oraclize/ethereum-api/blob/master/oraclizeAPI_0.5.sol
  function strConcat(string _a, string _b, string _c, string _d, string _e) internal pure returns (string) {
      bytes memory _ba = bytes(_a);
      bytes memory _bb = bytes(_b);
      bytes memory _bc = bytes(_c);
      bytes memory _bd = bytes(_d);
      bytes memory _be = bytes(_e);
      string memory abcde = new string(_ba.length + _bb.length + _bc.length + _bd.length + _be.length);
      bytes memory babcde = bytes(abcde);
      uint k = 0;
      for (uint i = 0; i < _ba.length; i++) babcde[k++] = _ba[i];
      for (i = 0; i < _bb.length; i++) babcde[k++] = _bb[i];
      for (i = 0; i < _bc.length; i++) babcde[k++] = _bc[i];
      for (i = 0; i < _bd.length; i++) babcde[k++] = _bd[i];
      for (i = 0; i < _be.length; i++) babcde[k++] = _be[i];
      return string(babcde);
    }

    function strConcat(string _a, string _b, string _c, string _d) internal pure returns (string) {
        return strConcat(_a, _b, _c, _d, "");
    }

    function strConcat(string _a, string _b, string _c) internal pure returns (string) {
        return strConcat(_a, _b, _c, "", "");
    }

    function strConcat(string _a, string _b) internal pure returns (string) {
        return strConcat(_a, _b, "", "", "");
    }

    function uint2str(uint i) internal pure returns (string) {
        if (i == 0) return "0";
        uint j = i;
        uint len;
        while (j != 0){
            len++;
            j /= 10;
        }
        bytes memory bstr = new bytes(len);
        uint k = len - 1;
        while (i != 0){
            bstr[k--] = byte(48 + i % 10);
            i /= 10;
        }
        return string(bstr);
    }
}

interface IERC165 {

  /**
   * @notice Query if a contract implements an interface
   * @param _interfaceId The interface identifier, as specified in ERC-165
   * @dev Interface identification is specified in ERC-165. This function
   * uses less than 30,000 gas.
   */
  function supportsInterface(bytes4 _interfaceId) external view returns (bool);
  
}

contract IERC721Receiver {
    /**
    * @dev Magic value to be returned upon successful reception of an NFT
    *  Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`,
    *  which can be also obtained as `ERC721Receiver(0).onERC721Received.selector`
    */
    bytes4 internal constant ERC721_RECEIVED = 0x150b7a02;

    /**
    * @notice Handle the receipt of an NFT
    * @dev The ERC721 smart contract calls this function on the recipient
    * after a `safetransfer`. This function MAY throw to revert and reject the
    * transfer. Return of other than the magic value MUST result in the 
    * transaction being reverted.
    * Note: the 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 transfered
    * @param _data Additional data with no specified format
    * @return `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
    */
    function onERC721Received(
        address _operator,
        address _from,
        uint256 _tokenId,
        bytes memory _data
    )
        public
        returns(bytes4);
}

contract IERC721Holder is IERC721Receiver {

    function onERC721Received(address, address, uint256, bytes) public returns(bytes4) {
        return ERC721_RECEIVED;
    }

}

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);

    function balanceOf(address owner) public view returns (uint256 balance);
    function ownerOf(uint256 tokenId) public view returns (address owner);

    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 transferFrom(address from, address to, uint256 tokenId) public;
    function safeTransferFrom(address from, address to, uint256 tokenId) public;

    function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory data) public;

}

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);
}

contract IERC721Metadata is IERC721 {
    function name() external view returns (string memory _name);
    function symbol() external view returns (string memory _symbol);
    function tokenURI(uint256 _tokenId) public view returns (string memory);
}

contract SupportsInterfaceWithLookup is IERC165 {
    bytes4 public constant InterfaceId_ERC165 = 0x01ffc9a7;
    /**
    * 0x01ffc9a7 ===
    *   bytes4(keccak256('supportsInterface(bytes4)'))
    */

    /**
    * @dev a mapping of interface id to whether or not it's supported
    */
    mapping(bytes4 => bool) internal supportedInterfaces;

    /**
    * @dev A contract implementing SupportsInterfaceWithLookup
    * implement ERC165 itself
    */
    constructor() public {
        _registerInterface(InterfaceId_ERC165);
    }

    /**
    * @dev implement supportsInterface(bytes4) using a lookup table
    */
    function supportsInterface(bytes4 _interfaceId) external view returns (bool) {
        return supportedInterfaces[_interfaceId];
    }

    /**
    * @dev private method for registering an interface
    */
    function _registerInterface(bytes4 _interfaceId) internal {
        require(_interfaceId != 0xffffffff);
        supportedInterfaces[_interfaceId] = true;
    }
}

contract Delegate {

    function mint(address _sender, address _to) public returns (bool);

    function approve(address _sender, address _to, uint256 _tokenId) public returns (bool);

    function setApprovalForAll(address _sender, address _operator, bool _approved) public returns (bool);

    function transferFrom(address _sender, address _from, address _to, uint256 _tokenId) public returns (bool);
    
    function safeTransferFrom(address _sender, address _from, address _to, uint256 _tokenId) public returns (bool);

    function safeTransferFrom(address _sender, address _from, address _to, uint256 _tokenId, bytes memory _data) public returns (bool);

}

/**
 * @title ERC165
 * @author Matt Condon (@shrugs)
 * @dev Implements ERC165 using a lookup table.
 */
contract ERC165 is IERC165 {

    bytes4 private constant _InterfaceId_ERC165 = 0x01ffc9a7;
    /**
    * 0x01ffc9a7 ===
    *   bytes4(keccak256('supportsInterface(bytes4)'))
    */

    /**
    * @dev a mapping of interface id to whether or not it's supported
    */
    mapping(bytes4 => bool) private _supportedInterfaces;

    /**
    * @dev A contract implementing SupportsInterfaceWithLookup
    * implement ERC165 itself
    */
    constructor()
      internal
    {
        _registerInterface(_InterfaceId_ERC165);
    }

    /**
    * @dev implement supportsInterface(bytes4) using a lookup table
    */
    function supportsInterface(bytes4 interfaceId)
      external
      view
      returns (bool)
    {
        return _supportedInterfaces[interfaceId];
    }

    /**
    * @dev internal method for registering an interface
    */
    function _registerInterface(bytes4 interfaceId)
      internal
    {
        require(interfaceId != 0xffffffff);
        _supportedInterfaces[interfaceId] = true;
    }
}

contract ERC721 is ERC165, IERC721 {

    using SafeMath for uint256;
    using Address for address;

    // 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 => uint256) private _ownedTokensCount;

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

    bytes4 private constant _InterfaceId_ERC721 = 0x80ac58cd;
    /*
    * 0x80ac58cd ===
    *   bytes4(keccak256('balanceOf(address)')) ^
    *   bytes4(keccak256('ownerOf(uint256)')) ^
    *   bytes4(keccak256('approve(address,uint256)')) ^
    *   bytes4(keccak256('getApproved(uint256)')) ^
    *   bytes4(keccak256('setApprovalForAll(address,bool)')) ^
    *   bytes4(keccak256('isApprovedForAll(address,address)')) ^
    *   bytes4(keccak256('transferFrom(address,address,uint256)')) ^
    *   bytes4(keccak256('safeTransferFrom(address,address,uint256)')) ^
    *   bytes4(keccak256('safeTransferFrom(address,address,uint256,bytes)'))
    */

    constructor()
        public
    {
        // register the supported interfaces to conform to ERC721 via ERC165
        _registerInterface(_InterfaceId_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));
        return _ownedTokensCount[owner];
    }

    /**
    * @dev Gets the owner of the specified token ID
    * @param tokenId uint256 ID of the token to query the owner of
    * @return owner 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));
        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);
        require(msg.sender == owner || isApprovedForAll(owner, msg.sender));

        _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));
        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 != msg.sender);
        _operatorApprovals[msg.sender][to] = approved;
        emit ApprovalForAll(msg.sender, 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
    {
        require(_isApprovedOrOwner(msg.sender, tokenId));
        require(to != address(0));

        _clearApproval(from, tokenId);
        _removeTokenFrom(from, tokenId);
        _addTokenTo(to, tokenId);

        emit Transfer(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 `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
    {
        // solium-disable-next-line arg-overflow
        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 `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
    )
        public
    {
        transferFrom(from, to, tokenId);
        // solium-disable-next-line arg-overflow
        require(_checkAndCallSafeTransfer(from, to, tokenId, _data));
    }

    /**
    * @dev Returns whether the specified token exists
    * @param tokenId uint256 ID of the token to query the existence of
    * @return 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)
    {
        address owner = ownerOf(tokenId);
        // Disable solium check because of
        // https://github.com/duaraghav8/Solium/issues/175
        // solium-disable-next-line operator-whitespace
        return (
        spender == owner ||
        getApproved(tokenId) == spender ||
        isApprovedForAll(owner, spender)
        );
    }

    /**
    * @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 by the msg.sender
    */
    function _mint(address to, uint256 tokenId) internal {
        require(to != address(0));
        _addTokenTo(to, tokenId);
        emit Transfer(address(0), to, 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 by the msg.sender
    */
    function _burn(address owner, uint256 tokenId) internal {
        _clearApproval(owner, tokenId);
        _removeTokenFrom(owner, tokenId);
        emit Transfer(owner, address(0), tokenId);
    }

    /**
    * @dev Internal function to clear current approval of a given token ID
    * Reverts if the given address is not indeed the owner of the token
    * @param owner owner of the token
    * @param tokenId uint256 ID of the token to be transferred
    */
    function _clearApproval(address owner, uint256 tokenId) internal {
        require(ownerOf(tokenId) == owner);
        if (_tokenApprovals[tokenId] != address(0)) {
            _tokenApprovals[tokenId] = address(0);
        }
    }

    /**
    * @dev Internal function to add a token ID to the list of a given address
    * @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 _addTokenTo(address to, uint256 tokenId) internal {
        require(_tokenOwner[tokenId] == address(0));
        _tokenOwner[tokenId] = to;
        _ownedTokensCount[to] = _ownedTokensCount[to].add(1);
    }

    /**
    * @dev Internal function to remove a token ID from the list of a given address
    * @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 _removeTokenFrom(address from, uint256 tokenId) internal {
        require(ownerOf(tokenId) == from);
        _ownedTokensCount[from] = _ownedTokensCount[from].sub(1);
        _tokenOwner[tokenId] = address(0);
    }

    /**
    * @dev Internal function to invoke `onERC721Received` on a target address
    * The call is not executed if the target address is not a contract
    * @param from address representing the previous owner of the given token ID
    * @param to target address that will receive the tokens
    * @param tokenId uint256 ID of the token to be transferred
    * @param _data bytes optional data to send along with the call
    * @return whether the call correctly returned the expected magic value
    */
    function _checkAndCallSafeTransfer(
        address from,
        address to,
        uint256 tokenId,
        bytes memory _data
    )
        internal
        returns (bool)
    {
        if (!to.isContract()) {
            return true;
        }
        bytes4 retval = IERC721Receiver(to).onERC721Received(
        msg.sender, from, tokenId, _data);
        return (retval == _ERC721_RECEIVED);
    }
}

contract ERC721Enumerable is 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 private constant _InterfaceId_ERC721Enumerable = 0x780e9d63;
    /**
    * 0x780e9d63 ===
    *   bytes4(keccak256('totalSupply()')) ^
    *   bytes4(keccak256('tokenOfOwnerByIndex(address,uint256)')) ^
    *   bytes4(keccak256('tokenByIndex(uint256)'))
    */

    /**
    * @dev Constructor function
    */
    constructor() public {
        // register the supported interface to conform to ERC721 via ERC165
        _registerInterface(_InterfaceId_ERC721Enumerable);
    }

    /**
    * @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));
        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());
        return _allTokens[index];
    }

    /**
    * @dev Internal function to add a token ID to the list of a given address
    * @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 _addTokenTo(address to, uint256 tokenId) internal {
        super._addTokenTo(to, tokenId);
        uint256 length = _ownedTokens[to].length;
        _ownedTokens[to].push(tokenId);
        _ownedTokensIndex[tokenId] = length;
    }

    /**
    * @dev Internal function to remove a token ID from the list of a given address
    * @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 _removeTokenFrom(address from, uint256 tokenId) internal {
        super._removeTokenFrom(from, tokenId);

        // To prevent a gap in the array, we store the last token in the index of the token to delete, and
        // then delete the last slot.
        uint256 tokenIndex = _ownedTokensIndex[tokenId];
        uint256 lastTokenIndex = _ownedTokens[from].length.sub(1);
        uint256 lastToken = _ownedTokens[from][lastTokenIndex];

        _ownedTokens[from][tokenIndex] = lastToken;
        // This also deletes the contents at the last position of the array
        _ownedTokens[from].length--;

        // Note that this will handle single-element arrays. In that case, both tokenIndex and lastTokenIndex are going to
        // be zero. Then we can make sure that we will remove tokenId from the ownedTokens list since we are first swapping
        // the lastToken to the first position, and then dropping the element placed in the last position of the list

        _ownedTokensIndex[tokenId] = 0;
        _ownedTokensIndex[lastToken] = tokenIndex;
    }

    /**
    * @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 by the msg.sender
    */
    function _mint(address to, uint256 tokenId) internal {
        super._mint(to, tokenId);

        _allTokensIndex[tokenId] = _allTokens.length;
        _allTokens.push(tokenId);
    }

    /**
    * @dev Internal function to burn a specific token
    * Reverts if the token does not exist
    * @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);

        // Reorg all tokens array
        uint256 tokenIndex = _allTokensIndex[tokenId];
        uint256 lastTokenIndex = _allTokens.length.sub(1);
        uint256 lastToken = _allTokens[lastTokenIndex];

        _allTokens[tokenIndex] = lastToken;
        _allTokens[lastTokenIndex] = 0;

        _allTokens.length--;
        _allTokensIndex[tokenId] = 0;
        _allTokensIndex[lastToken] = tokenIndex;
    }
}


contract ERC721Metadata is ERC165, ERC721, IERC721Metadata {
    // Token name
    string internal _name;

    // Token symbol
    string internal _symbol;

    // Optional mapping for token URIs
    mapping(uint256 => string) private _tokenURIs;

    bytes4 private constant InterfaceId_ERC721Metadata = 0x5b5e139f;
    /**
    * 0x5b5e139f ===
    *   bytes4(keccak256('name()')) ^
    *   bytes4(keccak256('symbol()')) ^
    *   bytes4(keccak256('tokenURI(uint256)'))
    */

    /**
    * @dev Constructor function
    */
    constructor(string memory name, string memory symbol) public {
        _name = name;
        _symbol = symbol;

        // register the supported interfaces to conform to ERC721 via ERC165
        _registerInterface(InterfaceId_ERC721Metadata);
    }

    /**
    * @dev Gets the token name
    * @return string representing the token name
    */
    function name() external view returns (string memory) {
        return _name;
    }

    /**
    * @dev Gets the token symbol
    * @return string representing the token symbol
    */
    function symbol() external view returns (string memory) {
        return _symbol;
    }

    /**
    * @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) public view returns (string memory) {
        require(_exists(tokenId));
        return _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 {
        require(_exists(tokenId));
        _tokenURIs[tokenId] = uri;
    }

    /**
    * @dev Internal function to burn a specific token
    * Reverts if the token does not exist
    * @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);

        // Clear metadata (if any)
        if (bytes(_tokenURIs[tokenId]).length != 0) {
            delete _tokenURIs[tokenId];
        }
    }
}

contract ERC721Full is ERC721, ERC721Enumerable, ERC721Metadata {
  
    constructor(string memory name, string memory symbol) ERC721Metadata(name, symbol) public {

    }

}

contract Collectables is ERC721Full("GU Collectable", "TRINKET"), Ownable {

    using Strings for string;

    // delegate item specific storage/logic to other contracts
    // one main contract manages transfers etc
    mapping(uint32 => address) public delegates;

    // use uint32s instead of addresses to reduce the storage size needed
    // individual token properties should be stored in the delegate contract
    uint32[] public collectables;
    uint public delegateCount;

    event DelegateAdded(address indexed delegate, uint32 indexed delegateID);

    function addDelegate(address delegate) public onlyOwner {
        uint32 delegateID = uint32(delegateCount++);
        // should never happen, but check anyway
        require(delegates[delegateID] == address(0), "delegate is already set for collectable type");
        delegates[delegateID] = delegate;
        emit DelegateAdded(delegate, delegateID);
    }

    function mint(uint32 delegateID, address to) public returns (uint) {
        Delegate delegate = getDelegate(delegateID);
        require(delegate.mint(msg.sender, to), "delegate could not mint token");
        uint id = collectables.push(delegateID) - 1;
        super._mint(to, id);
        return id;
    }

    function transferFrom(address from, address to, uint256 tokenId) public {
        Delegate delegate = getTokenDelegate(tokenId);
        require(delegate.transferFrom(msg.sender, from, to, tokenId), "could not transfer token");
        super.transferFrom(from, to, tokenId);
    }

    function approve(address to, uint256 tokenId) public {
        Delegate delegate = getTokenDelegate(tokenId);
        require(delegate.approve(msg.sender, to, tokenId), "could not approve token");
        super.approve(to, tokenId);
    }

    function safeTransferFrom(address from, address to, uint256 tokenId, bytes data) public {
        Delegate delegate = getTokenDelegate(tokenId);
        require(delegate.safeTransferFrom(msg.sender, from, to, tokenId, data), "could not safe transfer token");
        super.safeTransferFrom(from, to, tokenId, data);
    }

    function safeTransferFrom(address from, address to, uint256 tokenId) public {
        Delegate delegate = getTokenDelegate(tokenId);
        require(delegate.safeTransferFrom(msg.sender, from, to, tokenId), "could not safe transfer token");
        super.safeTransferFrom(from, to, tokenId);
    }

    function getTokenDelegate(uint id) public view returns (Delegate) {
        address d = delegates[collectables[id]];
        require(d != address(0), "invalid delegate");
        return Delegate(d);
    }

    function getDelegate(uint32 id) public view returns (Delegate) {
        address d = delegates[id];
        require(d != address(0), "invalid delegate");
        return Delegate(d);
    }

    string public constant tokenMetadataBaseURI = "https://api.godsunchained.com/collectable/";

    function tokenURI(uint256 _tokenId) public view returns (string memory) {
        require(_exists(_tokenId), "token doesn't exist");
        return Strings.strConcat(
            tokenMetadataBaseURI,
            Strings.uint2str(_tokenId)
        );
    }

    

}