When retrieving images from external sources, avoid calling it again if data is already cached locally.

Relates to https://github.com/navidrome/navidrome/issues/2130#issuecomment-1412742918

core/artwork/cache_warmer.go

@@ -48,7 +48,15 @@ type cacheWarmer struct {
 	wakeSignal chan struct{}
 }
 
+var ignoredIds = map[string]struct{}{
+	consts.VariousArtistsID: {},
+	consts.UnknownArtistID:  {},
+}
+
 func (a *cacheWarmer) PreCache(artID model.ArtworkID) {
+	if _, shouldIgnore := ignoredIds[artID.ID]; shouldIgnore {
+		return
+	}
 	a.mutex.Lock()
 	defer a.mutex.Unlock()
 	a.buffer[artID] = struct{}{}

core/artwork/reader_artist.go

@@ -42,7 +42,9 @@ func newArtistReader(ctx context.Context, artwork *artwork, artID model.ArtworkI
 		em:     em,
 		artist: *ar,
 	}
-	a.cacheKey.lastUpdate = ar.ExternalInfoUpdatedAt
+	// TODO Find a way to factor in the ExternalUpdateInfoAt in the cache key. Problem is that it can
+	// change _after_ retrieving from external sources, making the key invalid
+	//a.cacheKey.lastUpdate = ar.ExternalInfoUpdatedAt
 	var files []string
 	var paths []string
 	for _, al := range als {
@@ -64,10 +66,10 @@ func newArtistReader(ctx context.Context, artwork *artwork, artID model.ArtworkI
 func (a *artistReader) Key() string {
 	hash := md5.Sum([]byte(conf.Server.Agents + conf.Server.Spotify.ID))
 	return fmt.Sprintf(
-		"%s.%x.%t ",
+		"%s.%t.%x",
 		a.cacheKey.Key(),
-		hash,
 		conf.Server.EnableExternalServices,
+		hash,
 	)
 }