library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";

    /**
     * @dev Converts a `uint256` to its ASCII `string` decimal representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        while (value != 0) {
            digits -= 1;
            buffer[digits] = bytes1(uint8(48 + uint256(value % 10)));
            value /= 10;
        }
        return string(buffer);
    }

    /**
     * Length
     * 
     * Returns the length of the specified string
     * 
     * @param _base When being used for a data type this is the extended object
     *              otherwise this is the string to be measured
     * @return uint The length of the passed string
     */
    function length(string memory _base)
        internal
        pure
        returns (uint) {
        bytes memory _baseBytes = bytes(_base);
        return _baseBytes.length;
    }

    /**
     * Sub String
     * 
     * Extracts the part of a string based on the desired length and offset. The
     * offset and length must not exceed the lenth of the base string.
     * 
     * @param _base When being used for a data type this is the extended object
     *              otherwise this is the string that will be used for 
     *              extracting the sub string from
     * @param _length The length of the sub string to be extracted from the base
     * @param _offset The starting point to extract the sub string from
     * @return string The extracted sub string
     */
    function _substring(string memory _base, int _length, int _offset)
        internal
        pure
        returns (string memory) {
        bytes memory _baseBytes = bytes(_base);

        assert(uint(_offset + _length) <= _baseBytes.length);

        string memory _tmp = new string(uint(_length));
        bytes memory _tmpBytes = bytes(_tmp);

        uint j = 0;
        for (uint i = uint(_offset); i < uint(_offset + _length); i++) {
            _tmpBytes[j++] = _baseBytes[i];
        }

        return string(_tmpBytes);
    }

    /**
     * Index Of
     *
     * Locates and returns the position of a character within a string
     * 
     * @param _base When being used for a data type this is the extended object
     *              otherwise this is the string acting as the haystack to be
     *              searched
     * @param _value The needle to search for, at present this is currently
     *               limited to one character
     * @return int The position of the needle starting from 0 and returning -1
     *             in the case of no matches found
     */
    function indexOf(string memory _base, string memory _value)
        internal
        pure
        returns (int) {
        return _indexOf(_base, _value, 0);
    }

    /**
     * Index Of
     *
     * Locates and returns the position of a character within a string starting
     * from a defined offset
     * 
     * @param _base When being used for a data type this is the extended object
     *              otherwise this is the string acting as the haystack to be
     *              searched
     * @param _value The needle to search for, at present this is currently
     *               limited to one character
     * @param _offset The starting point to start searching from which can start
     *                from 0, but must not exceed the length of the string
     * @return int The position of the needle starting from 0 and returning -1
     *             in the case of no matches found
     */
    function _indexOf(string memory _base, string memory _value, uint _offset)
        internal
        pure
        returns (int) {
        bytes memory _baseBytes = bytes(_base);
        bytes memory _valueBytes = bytes(_value);

        assert(_valueBytes.length == 1);

        for (uint i = _offset; i < _baseBytes.length; i++) {
            if (_baseBytes[i] == _valueBytes[0]) {
                return int(i);
            }
        }

        return -1;
    }
}
/**
 * @dev String operations.
 */
function _indexOf(string memory _base, string memory _value, uint _offset)
    internal
    pure
    returns (int) {
    bytes memory _baseBytes = bytes(_base);
    bytes memory _valueBytes = bytes(_value);

    assert(_valueBytes.length == 1);

    for (uint i = _offset; i < _baseBytes.length; i++) {
        if (_baseBytes[i] == _valueBytes[0]) {
            return int(i);
        }
    }

    return -1;
}

/**
 * Index Of
 *
 * Locates and returns the position of a character within a string starting
 * from a defined offset
 * 
 * @param _base When being used for a data type this is the extended object
 *              otherwise this is the string acting as the haystack to be
 *              searched
 * @param _value The needle to search for, at present this is currently
 *               limited to one character
 * @param _offset The starting point to start searching from which can start
 *                from 0, but must not exceed the length of the string
 * @return int The position of the needle starting from 0 and returning -1
 *             in the case of no matches found
 */