refactor(lyrics): centralize lyric kind constants

The "main"/"translation"/"pronunciation" kind values were redefined in
three places (ttmlLyricKind* in the TTML parser, lyricsfileKindMain in the
Lyricsfile parser, and inline literals in the subsonic response builder).
Define them once as model.LyricKind* (kept as wire-compatible string values)
plus a LyricKindOrMain helper, and use them everywhere a kind is produced,
defaulted, or filtered. No wire-facing types change.

model/lyrics.go

@@ -45,6 +45,23 @@ type Lyrics struct {
 	Synced        bool    `structs:"synced"                  json:"synced"`
 }
 
+// Lyric kinds, as defined by the OpenSubsonic songLyrics v2 contract. These are
+// the canonical wire values; keep them in sync with the spec.
+const (
+	LyricKindMain          = "main"
+	LyricKindTranslation   = "translation"
+	LyricKindPronunciation = "pronunciation"
+)
+
+// LyricKindOrMain returns kind, defaulting to LyricKindMain when empty. A blank
+// kind means an untyped (single-track) lyric, which the contract treats as main.
+func LyricKindOrMain(kind string) string {
+	if strings.TrimSpace(kind) == "" {
+		return LyricKindMain
+	}
+	return kind
+}
+
 // support the standard [mm:ss.mm], as well as [hh:*] and [*.mmm]
 const timeRegexString = `\[([0-9]{1,2}:)?([0-9]{1,2}):([0-9]{1,2})(\.[0-9]{1,3})?\]`
 

model/lyrics_ttml.go

@@ -21,10 +21,7 @@ const (
 	defaultTTMLSubFrameRate = 1.0
 	defaultTTMLTickRate     = 1.0
 
-	ttmlLyricKindMain          = "main"
-	ttmlLyricKindTranslation   = "translation"
-	ttmlLyricKindPronunciation = "pronunciation"
-	ttmlBackgroundAgentPrefix  = "__nd_bg__|"
+	ttmlBackgroundAgentPrefix = "__nd_bg__|"
 )
 
 var offsetTimeRegex = regexp.MustCompile(`^([0-9]+(?:\.[0-9]+)?)(h|m|s|ms|f|t)$`)
@@ -157,9 +154,9 @@ func (p *ttmlParser) parseElement(start xml.StartElement, parent ttmlTimingConte
 
 	switch local {
 	case "translation":
-		return p.parseMetadataTrack(start, parent, ttmlLyricKindTranslation)
+		return p.parseMetadataTrack(start, parent, LyricKindTranslation)
 	case "transliteration":
-		return p.parseMetadataTrack(start, parent, ttmlLyricKindPronunciation)
+		return p.parseMetadataTrack(start, parent, LyricKindPronunciation)
 	case "agent":
 		return p.parseAgentDefinition(start)
 	}
@@ -582,15 +579,15 @@ func (p *ttmlParser) toLyricList() LyricList {
 			continue
 		}
 		res = append(res, p.finalizeLyrics(Lyrics{
-			Kind:   ttmlLyricKindMain,
+			Kind:   LyricKindMain,
 			Lang:   lang,
 			Line:   lines,
 			Synced: linesAreSynced(lines),
 		}))
 	}
 
-	res = append(res, p.buildMetadataLyrics(ttmlLyricKindTranslation, p.translationLangOrder, p.translationEntriesByLg)...)
-	res = append(res, p.buildMetadataLyrics(ttmlLyricKindPronunciation, p.pronunciationLangOrder, p.pronunciationEntriesByLg)...)
+	res = append(res, p.buildMetadataLyrics(LyricKindTranslation, p.translationLangOrder, p.translationEntriesByLg)...)
+	res = append(res, p.buildMetadataLyrics(LyricKindPronunciation, p.pronunciationLangOrder, p.pronunciationEntriesByLg)...)
 	return res
 }
 
@@ -854,12 +851,12 @@ func (p *ttmlParser) addMetadataEntry(kind string, lang string, entry ttmlMetada
 	p.metadataSeq++
 
 	switch kind {
-	case ttmlLyricKindTranslation:
+	case LyricKindTranslation:
 		if _, ok := p.translationEntriesByLg[lang]; !ok {
 			p.translationLangOrder = append(p.translationLangOrder, lang)
 		}
 		p.translationEntriesByLg[lang] = append(p.translationEntriesByLg[lang], entry)
-	case ttmlLyricKindPronunciation:
+	case LyricKindPronunciation:
 		if _, ok := p.pronunciationEntriesByLg[lang]; !ok {
 			p.pronunciationLangOrder = append(p.pronunciationLangOrder, lang)
 		}

model/lyricsfile.go

@@ -35,7 +35,7 @@ func ParseLyricsfile(text string) (LyricList, error) {
 		DisplayArtist: str.SanitizeText(doc.Metadata.Artist),
 		DisplayTitle:  str.SanitizeText(doc.Metadata.Title),
 		Lang:          normalizeLyricsfileLang(doc.Metadata.Language),
-		Kind:          lyricsfileKindMain,
+		Kind:          LyricKindMain,
 	}
 	if doc.Metadata.OffsetMs != 0 {
 		off := doc.Metadata.OffsetMs
@@ -62,10 +62,7 @@ func ParseLyricsfile(text string) (LyricList, error) {
 	return LyricList{NormalizeLyrics(lyrics)}, nil
 }
 
-const (
-	lyricsfileVersion  = "1.0"
-	lyricsfileKindMain = "main"
-)
+const lyricsfileVersion = "1.0"
 
 type lyricsfileDocument struct {
 	Version  string                `yaml:"version"`

server/subsonic/helpers.go

@@ -581,11 +581,7 @@ func buildStructuredLyric(mf *model.MediaFile, lyrics model.Lyrics, enhanced boo
 	}
 
 	if enhanced {
-		kind := strings.TrimSpace(lyrics.Kind)
-		if kind == "" {
-			kind = "main"
-		}
-		structured.Kind = kind
+		structured.Kind = model.LyricKindOrMain(lyrics.Kind)
 		if len(cueLines) > 0 && len(responseAgents) > 0 {
 			structured.Agents = responseAgents
 		}
@@ -637,10 +633,9 @@ func buildLyricsList(mf *model.MediaFile, lyricsList model.LyricList, enhanced b
 	if enhanced {
 		filtered = lyricsList
 	} else {
-		// Without enhanced, only return "main" kind entries
+		// Without enhanced, only return main-kind entries (a blank kind is main).
 		for _, l := range lyricsList {
-			kind := strings.TrimSpace(l.Kind)
-			if kind == "" || kind == "main" {
+			if model.LyricKindOrMain(l.Kind) == model.LyricKindMain {
 				filtered = append(filtered, l)
 			}
 		}