contract ERC721Base is ERC721, ERC721Enumerable {
    // Token name
    string public name;

    // Token symbol
    string public symbol;

    //Token URI prefix
    string public tokenURIPrefix;

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

    /*
     *     bytes4(keccak256('name()')) == 0x06fdde03
     *     bytes4(keccak256('symbol()')) == 0x95d89b41
     *     bytes4(keccak256('tokenURI(uint256)')) == 0xc87b56dd
     *
     *     => 0x06fdde03 ^ 0x95d89b41 ^ 0xc87b56dd == 0x5b5e139f
     */
    bytes4 private constant _INTERFACE_ID_ERC721_METADATA = 0x5b5e139f;

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

        // register the supported interfaces to conform to ERC721 via ERC165
        _registerInterface(_INTERFACE_ID_ERC721_METADATA);
    }

    /**
     * @dev Internal function to set the token URI prefix.
     * @param _tokenURIPrefix string URI prefix to assign
     */
    function _setTokenURIPrefix(string memory _tokenURIPrefix) internal {
        tokenURIPrefix = _tokenURIPrefix;
    }

    /**
     * @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) external view returns (string memory) {
        require(_exists(tokenId), "ERC721Metadata: URI query for nonexistent token");
        return strConcat(tokenURIPrefix, _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), "ERC721Metadata: URI set of nonexistent token");
        _tokenURIs[tokenId] = uri;
    }

    /**
     * @dev Internal function to burn a specific token.
     * Reverts if the token does not exist.
     * Deprecated, use _burn(uint256) instead.
     * @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];
        }
    }

    function strConcat(string memory _a, string memory _b) internal pure returns (string memory) {
        bytes memory _ba = bytes(_a);
        bytes memory _bb = bytes(_b);
        bytes memory bab = new bytes(_ba.length + _bb.length);
        uint k = 0;
        for (uint i = 0; i < _ba.length; i++) bab[k++] = _ba[i];
        for (uint i = 0; i < _bb.length; i++) bab[k++] = _bb[i];
        return string(bab);
    }
}
/**
 * @title Full ERC721 Token with support for tokenURIPrefix
 * This implementation includes all the required and some optional functionality of the ERC721 standard
 * Moreover, it includes approve all functionality using operator terminology
 * @dev see https://eips.ethereum.org/EIPS/eip-721
 */
function tokenURI(uint256 tokenId) external view returns (string memory) {
    require(_exists(tokenId), "ERC721Metadata: URI query for nonexistent token");
    return strConcat(tokenURIPrefix, _tokenURIs[tokenId]);
}

/**
 * @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
 */