MaximumFileSize int64

	// FileNameFunc specifies the name a new file will take.
	// FileNameFunc must ensure collisions in filenames do not occur.
	// Do not rely on timestamps to be unique, high throughput writes
	// may fall on the same timestamp.
	// Eg.
	// 	2020-03-28_15-00-945-<random-hash>.log
	// When FileNameFunc is not specified, DefaultFilenameFunc will be used.
	FileNameFunc func() string

	if lgDir == "" {
		return os.Stderr, nil
	}
	lgDirAbs, err := filepath.Abs(lgDir)
	if err != nil {
		return nil, err
	}
	lgSize := ctx.Int("log-size")

	var fileNameFunc func() string
	if ctx.IsSet("log-prefix") {
		fileNameFunc = func() string {
			return fmt.Sprintf("%s-%s.log", ctx.String("log-prefix"), fmt.Sprintf("%X", time.Now().UTC().UnixNano()))
		}
	}

	output, err := logger.NewDir(logger.Options{