contract ERC721Tradable is ERC721Full, Ownable {
    using Strings for string;

    address proxyRegistryAddress;
    uint256 private _currentTokenId = 0;

    constructor(
        string memory _name,
        string memory _symbol,
        address _proxyRegistryAddress
    ) public ERC721Full(_name, _symbol) {
        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 pure 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);
    }
}
/**
 * @title ERC721Tradable
 * ERC721Tradable - ERC721 contract that whitelists a trading address, and has minting functionality.
 */
function _incrementTokenId() private {
        _currentTokenId++;
    }
/**
 * @dev increments the value of _currentTokenId
 */