refactor: decouple tag writers from deezer models

internal/tag/id3v2.go

@@ -0,0 +1,70 @@
+package tag
+
+import (
+	"fmt"
+	"strconv"
+
+	"github.com/bogem/id3v2/v2"
+)
+
+type id3v2Tagger struct {
+	tag *id3v2.Tag
+}
+
+func (t *id3v2Tagger) write(m Metadata) error {
+	defer t.tag.Close()
+
+	duration, err := strconv.Atoi(m.Duration)
+	if err != nil {
+		return err
+	}
+	length := fmt.Sprintf("%d", duration*1000)
+
+	if m.Album != nil {
+		t.addTag("TRCK", m.TrackNumber)
+		t.addTag("TPE2", m.Album.Artist)
+		t.addTag("TALB", m.Album.Title)
+		t.addTag("TPUB", m.Album.Label)
+		t.addTag("TDOR", m.Album.OriginalReleaseDate)
+		t.addTag("TYER", m.Album.ReleaseDate)
+		t.addTag("COMM", m.Album.ProducerLine)
+		t.addTag("TCOP", m.Album.Copyright)
+	}
+
+	t.addTag("TPE1", m.Artists)
+	t.addTag("TIT2", m.Title)
+	t.addTag("TCOM", m.Composers)
+	t.addTag("TEXT", m.Lyricists)
+	t.addTag("TCON", m.Genre)
+	t.addTag("TLEN", length)
+	t.addTag("TBPM", m.BPM)
+	t.addTag("TKEY", m.Key)
+	t.addTXXX("GAIN", m.Gain)
+	t.addTXXX("ISRC", m.ISRC)
+
+	t.tag.AddAttachedPicture(id3v2.PictureFrame{
+		Encoding:    t.tag.DefaultEncoding(),
+		MimeType:    "image/jpeg",
+		PictureType: id3v2.PTFrontCover,
+		Description: "Cover",
+		Picture:     m.Cover,
+	})
+
+	return t.tag.Save()
+}
+
+func (t *id3v2Tagger) addTag(name, value string) {
+	if value != "" {
+		t.tag.AddTextFrame(name, t.tag.DefaultEncoding(), value)
+	}
+}
+
+func (t *id3v2Tagger) addTXXX(description, value string) {
+	if value != "" {
+		t.tag.AddUserDefinedTextFrame(id3v2.UserDefinedTextFrame{
+			Encoding:    t.tag.DefaultEncoding(),
+			Description: description,
+			Value:       value,
+		})
+	}
+}