add new lyricsmanager missed in last commit

backend/lyricsmanager.go

@@ -0,0 +1,75 @@
+package backend
+
+import (
+	"context"
+	"log"
+	"sync"
+
+	"github.com/dweymouth/supersonic/backend/mediaprovider"
+)
+
+type LyricsManager struct {
+	sm     *ServerManager
+	lrclib *LrcLibFetcher
+
+	// right now only one song can have lyrics being fetched
+	// at any given time (b/c we only show lyrics for the currently playing song)
+	lock                  sync.Mutex
+	fetchInProgressID     string
+	fetchInProgressCancel context.CancelFunc
+	cbs                   []func(string, *mediaprovider.Lyrics)
+}
+
+func NewLyricsManager(sm *ServerManager, lrclib *LrcLibFetcher) *LyricsManager {
+	return &LyricsManager{
+		sm:     sm,
+		lrclib: lrclib,
+	}
+}
+
+func (lm *LyricsManager) FetchLyricsAsync(song *mediaprovider.Track, cb func(string, *mediaprovider.Lyrics)) {
+	lm.lock.Lock()
+	defer lm.lock.Unlock()
+
+	if lm.fetchInProgressID == song.ID {
+		lm.cbs = append(lm.cbs, cb)
+		return
+	}
+	lm.fetchInProgressID = song.ID
+
+	if lm.fetchInProgressCancel != nil {
+		lm.fetchInProgressCancel()
+	}
+	lm.cbs = []func(string, *mediaprovider.Lyrics){cb}
+	ctx, cancel := context.WithCancel(context.Background())
+	lm.fetchInProgressCancel = cancel
+	go lm.fetchLyrics(ctx, song, func(id string, lyrics *mediaprovider.Lyrics) {
+		lm.lock.Lock()
+		defer lm.lock.Unlock()
+		for _, cb := range lm.cbs {
+			cb(id, lyrics)
+		}
+	})
+}
+
+func (lm *LyricsManager) fetchLyrics(ctx context.Context, song *mediaprovider.Track, cb func(string, *mediaprovider.Lyrics)) {
+	var lyrics *mediaprovider.Lyrics
+	var err error
+	if lp, ok := lm.sm.Server.(mediaprovider.LyricsProvider); ok {
+		if lyrics, err = lp.GetLyrics(song); err != nil {
+			log.Printf("Error fetching lyrics: %v", err)
+		}
+	}
+	if lyrics == nil && lm.lrclib != nil {
+		lyrics, err = lm.lrclib.FetchLrcLibLyrics(song.Title, song.ArtistNames[0], song.Album, int(song.Duration.Seconds()))
+		if err != nil {
+			log.Println(err.Error())
+		}
+	}
+	select {
+	case <-ctx.Done():
+		return
+	default:
+		cb(song.ID, lyrics)
+	}
+}