private static function getUuidV4($bytes)
    {
        // set version to 0100
        $bytes[6] = chr(ord($bytes[6]) & 0x0f | 0x40);
        // set bits 6-7 to 10
        $bytes[8] = chr(ord($bytes[8]) & 0x3f | 0x80);
        return vsprintf('%s%s-%s-%s-%s-%s%s%s', str_split(bin2hex($bytes), 4));
    }