}

	if opts.FileNameFunc == nil {
		opts.FileNameFunc = defaultFilenameFunc
	}

	pr, pw := xioutil.WaitPipe()

	w := &Writer{
		opts: opts,
		pw:   pw,
		pr:   pr,
	}

	if w.f == nil {
		if err := w.rotate(); err != nil {
			return nil, fmt.Errorf("Failed to create log file: %w", err)
		}
	}

	go w.listen()