trimmed down metadata & own extractor for vobis(flac)

internal/metadata/vobis.go

@@ -2,12 +2,89 @@ package metadata
 
 import (
 	"log/slog"
+	"os"
 	"strconv"
 
 	"github.com/go-flac/flacvorbis/v2"
 	"github.com/go-flac/go-flac/v2"
 )
 
+func readVorbisMetadata(file string) (*Metadata, error) {
+	f, err := os.Open(file)
+	if err != nil {
+		return nil, err
+	}
+
+	defer f.Close()
+
+	flacFile, err := flac.ParseMetadata(f)
+	if err != nil {
+		return nil, err
+	}
+
+	cmt, err := findVobisMetadata(*flacFile)
+	if err != nil {
+		return nil, err
+	}
+
+	titles, err := cmt.Get(flacvorbis.FIELD_TITLE)
+	if err != nil {
+		return nil, err
+	}
+	var title *string
+	if len(titles) > 0 {
+		title = &titles[0]
+	}
+
+	albums, err := cmt.Get(flacvorbis.FIELD_ALBUM)
+	if err != nil {
+		return nil, err
+	}
+	var album *string
+	if len(albums) > 0 {
+		album = &albums[0]
+	}
+
+	artists, err := cmt.Get(flacvorbis.FIELD_ARTIST)
+	if err != nil {
+		return nil, err
+	}
+
+	albumArtists, err := cmt.Get("ALBUMARTIST")
+	if err != nil {
+		return nil, err
+	}
+
+	comments, err := cmt.Get("COMMENT")
+	if err != nil {
+		return nil, err
+	}
+	var comment *string
+	if len(comments) > 0 {
+		comment = &comments[0]
+	}
+
+	metadata := &Metadata{
+		Title:       title,
+		Artist:      artists,
+		Album:       album,
+		AlbumArtist: albumArtists,
+		Comment:     comment,
+	}
+
+	return metadata, nil
+}
+
+func findVobisMetadata(f flac.File) (*flacvorbis.MetaDataBlockVorbisComment, error) {
+	for _, meta := range f.Meta {
+		if meta.Type == flac.VorbisComment {
+			return flacvorbis.ParseFromMetaDataBlock(*meta)
+		}
+	}
+
+	return nil, nil
+}
+
 func updateFlacMetadata(m Metadata, input, output string) error {
 	f, err := flac.ParseFile(input)
 	if err != nil {
@@ -36,13 +113,25 @@ func updateFlacMetadata(m Metadata, input, output string) error {
 func createVorbisMetaBlock(m Metadata) flacvorbis.MetaDataBlockVorbisComment {
 	vorbisMeta := flacvorbis.New()
 
-	vorbisMeta.Add(flacvorbis.FIELD_TITLE, m.Title)
-	vorbisMeta.Add(flacvorbis.FIELD_ALBUM, m.Album)
-	vorbisMeta.Add("COMMENT", m.Comment)
-	vorbisMeta.Add("TRACKNUMBER", strconv.Itoa(m.Track))
-	vorbisMeta.Add("TOTALTRACKS", strconv.Itoa(m.TotalTracks))
-	vorbisMeta.Add("DISCNUMBER", strconv.Itoa(m.Disc))
-	vorbisMeta.Add("TOTALDISCS", strconv.Itoa(m.TotalDiscs))
+	if m.Title != nil {
+		vorbisMeta.Add(flacvorbis.FIELD_TITLE, *m.Title)
+	}
+
+	if m.Album != nil {
+		vorbisMeta.Add(flacvorbis.FIELD_ALBUM, *m.Album)
+	}
+
+	if m.Comment != nil {
+		vorbisMeta.Add("COMMENT", *m.Comment)
+	}
+
+	if m.Track != 0 {
+		vorbisMeta.Add("TRACKNUMBER", strconv.Itoa(m.Track))
+	}
+
+	if m.TotalTracks != 0 {
+		vorbisMeta.Add("TOTALTRACKS", strconv.Itoa(m.TotalTracks))
+	}
 
 	for _, artist := range m.Artist {
 		vorbisMeta.Add(flacvorbis.FIELD_ARTIST, artist)