class Color

class Color {
    
    /**
     * Validates whether a hexadecimal color value is syntactically correct.
     *
     * @param $hex
     *   The hexadecimal string to validate. May contain a leading '#'. May use
     *   the shorthand notation (e.g., '123' for '112233').
     *
     * @return bool
     *   TRUE if $hex is valid or FALSE if it is not.
     */
    public static function validateHex($hex) {
        if (!is_string($hex)) {
            return FALSE;
        }
        return preg_match('/^[#]?([0-9a-fA-F]{3}){1,2}$/', $hex) === 1;
    }
    
    /**
     * Parses a hexadecimal color string like '#abc' or '#aabbcc'.
     *
     * @param string $hex
     *   The hexadecimal color string to parse.
     *
     * @return array
     *   An array containing the values for 'red', 'green', 'blue'.
     *
     * @throws \InvalidArgumentException
     */
    public static function hexToRgb($hex) {
        if (!self::validateHex($hex)) {
            throw new \InvalidArgumentException("'{$hex}' is not a valid hex value.");
        }
        // Ignore '#' prefixes.
        $hex = ltrim($hex, '#');
        // Convert shorthands like '#abc' to '#aabbcc'.
        if (strlen($hex) == 3) {
            $hex = $hex[0] . $hex[0] . $hex[1] . $hex[1] . $hex[2] . $hex[2];
        }
        $c = hexdec($hex);
        return [
            'red' => $c >> 16 & 0xff,
            'green' => $c >> 8 & 0xff,
            'blue' => $c & 0xff,
        ];
    }
    
    /**
     * Converts RGB color arrays or strings to lowercase CSS notation.
     *
     * @param array|string $input
     *   The value to convert. If the value is an array the first three elements
     *   will be used as the red, green and blue components. String values in CSS
     *   notation like '10, 20, 30' are also supported.
     *
     * @return string
     *   The lowercase simple color representation of the given color.
     */
    public static function rgbToHex($input) {
        // Remove named array keys if input comes from Color::hex2rgb().
        if (is_array($input)) {
            $rgb = array_values($input);
        }
        elseif (is_string($input)) {
            preg_match('/(\\d+), ?(\\d+), ?(\\d+)/', $input, $rgb);
            array_shift($rgb);
        }
        $out = 0;
        foreach ($rgb as $k => $v) {
            $out |= $v << 16 - $k * 8;
        }
        return '#' . str_pad(dechex($out), 6, 0, STR_PAD_LEFT);
    }
    
    /**
     * Normalize the hex color length to 6 characters for comparison.
     *
     * @param string $hex
     *   The hex color to normalize.
     *
     * @return string
     *   The 6 character hex color.
     */
    public static function normalizeHexLength($hex) {
        // Ignore '#' prefixes.
        $hex = ltrim($hex, '#');
        if (strlen($hex) === 3) {
            $hex[5] = $hex[2];
            $hex[4] = $hex[2];
            $hex[3] = $hex[1];
            $hex[2] = $hex[1];
            $hex[1] = $hex[0];
        }
        return '#' . $hex;
    }

}