public static function add_line(string $log) : string {
        if (empty(self::$taskloginfo)) {
            return $log;
        }

        if (empty(self::$fh)) {
            return $log;
        }

        if (self::is_current_output_buffer()) {
            fwrite(self::$fh, $log);
        }

        return $log;
    }