TestCon.sol

pragma solidity >=0.4.21 <0.7.0;

import "./TradableERC.sol";

contract TestCon is TradeableERC721Token {
  constructor(address _proxyRegistryAddress) TradeableERC721Token("EggGame", "Egg", _proxyRegistryAddress) public { }

  uint storedData;

  function set(uint x) public {
    storedData = x;
  }

  function get() public view returns (uint) {
    return storedData;
  }
}

TradeableERC721Token.sol

pragma solidity ^0.5.0;

import "../client/node_modules/@openzeppelin/contracts/ownership/Ownable.sol";
import "../client/node_modules/@openzeppelin/contracts/token/ERC721/ERC721Full.sol";


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

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

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

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

    function uint2str(uint _i) internal pure returns (string memory _uintAsString) {
        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(uint8(48 + _i % 10));
            _i /= 10;
        }
        return string(bstr);
    }
}

contract OwnableDelegateProxy { }

contract ProxyRegistry {
    mapping(address => OwnableDelegateProxy) public proxies;
}

/**
 * @title TradeableERC721Token
 * TradeableERC721Token - ERC721 contract that whitelists a trading address, and has minting functionality.
 */
contract TradeableERC721Token is ERC721Full, Ownable {
  using Strings for string;

  address proxyRegistryAddress;
  uint256 private _currentTokenId = 0;

  constructor(string memory _name, string memory _symbol, address _proxyRegistryAddress) ERC721Full(_name, _symbol) public {
    proxyRegistryAddress = _proxyRegistryAddress;
  }

  /**
    * @dev Mints a token to an address with a tokenURI.
    * @param _to address of the future owner of the token
    */
  function mintTo(address _to) public onlyOwner {
    uint256 newTokenId = _getNextTokenId();
    _mint(_to, newTokenId);
    _incrementTokenId();
  }

  /**
    * @dev calculates the next token ID based on value of _currentTokenId 
    * @return uint256 for the next token ID
    */
  function _getNextTokenId() private view returns (uint256) {
    return _currentTokenId.add(1);
  }

  /**
    * @dev increments the value of _currentTokenId 
    */
  function _incrementTokenId() private  {
    _currentTokenId++;
  }

  function baseTokenURI() public view returns (string memory) {
    return "";
  }

  function tokenURI(uint256 _tokenId) external view returns (string memory) {
    return Strings.strConcat(
        baseTokenURI(),
        Strings.uint2str(_tokenId)
    );
  }

  /**
   * Override isApprovedForAll to whitelist user's OpenSea proxy accounts to enable gas-less listings.
   */
  function isApprovedForAll(
    address owner,
    address operator
  )
    public
    view
    returns (bool)
  {
    // Whitelist OpenSea proxy contract for easy trading.
    ProxyRegistry proxyRegistry = ProxyRegistry(proxyRegistryAddress);
    if (address(proxyRegistry.proxies(owner)) == operator) {
        return true;
    }

    return super.isApprovedForAll(owner, operator);
  }
}