minstrel/internal/library/tracknumber.go

package library

import (
	"strconv"
	"strings"

	"github.com/dhowden/tag"
)

// ReadTrackAndDisc reads a file's track and disc numbers. dhowden/tag reads a
// Vorbis TRACKNUMBER or DISCNUMBER only as a bare number, but taggers also
// write "3/20" there (as Minstrel's own importer once did), and that
// reads as 0. For Vorbis the number before the slash is taken instead.
func ReadTrackAndDisc(m tag.Metadata) (track, disc int) {
	track, _ = m.Track()
	disc, _ = m.Disc()
	if m.Format() != tag.VORBIS {
		return track, disc
	}
	raw := m.Raw()
	if track == 0 {
		track = leadingNumber(raw["tracknumber"])
	}
	if disc == 0 {
		disc = leadingNumber(raw["discnumber"])
	}
	return track, disc
}

// leadingNumber is the number in a tag value of "3" or "3/20"; 0 for
// anything else.
func leadingNumber(v any) int {
	s, _ := v.(string)
	before, _, _ := strings.Cut(s, "/")
	n, err := strconv.Atoi(strings.TrimSpace(before))
	if err != nil || n < 0 {
		return 0
	}
	return n
}