misc: Implement Iterator approach for artists

First step towards improving sorting for Artists. Use the same iterator
approach as albums and tracks.

backend/mediaprovider/jellyfin/iterators.go

@@ -16,6 +16,8 @@ const (
 	AlbumSortArtistAZ       string = "Artist (A-Z)"
 	AlbumSortYearAscending  string = "Year (ascending)"
 	AlbumSortYearDescending string = "Year (descending)"
+
+	ArtistSortNameAZ string = "Name (A-Z)"
 )
 
 func (j *jellyfinMediaProvider) AlbumSortOrders() []string {
@@ -29,6 +31,12 @@ func (j *jellyfinMediaProvider) AlbumSortOrders() []string {
 	}
 }
 
+func (j *jellyfinMediaProvider) ArtistSortOrders() []string {
+	return []string{
+		ArtistSortNameAZ,
+	}
+}
+
 func (j *jellyfinMediaProvider) IterateAlbums(sortOrder string, filter mediaprovider.AlbumFilter) mediaprovider.AlbumIterator {
 	var jfSort jellyfin.Sort
 	switch sortOrder {
@@ -116,6 +124,32 @@ func (j *jellyfinMediaProvider) IterateTracks(searchQuery string) mediaprovider.
 	return helpers.NewTrackIterator(fetcher, j.prefetchCoverCB)
 }
 
+func (j *jellyfinMediaProvider) IterateArtists(sortOrder string) mediaprovider.ArtistIterator {
+	var jfSort jellyfin.Sort
+
+	if sortOrder == "" {
+		sortOrder = ArtistSortNameAZ // default
+	}
+	switch sortOrder {
+	case ArtistSortNameAZ:
+		jfSort.Field = jellyfin.SortByName
+		jfSort.Mode = jellyfin.SortAsc
+	}
+
+	fetcher := func(offs, limit int) ([]*mediaprovider.Artist, error) {
+		ar, err := j.client.GetAlbumArtists(jellyfin.QueryOpts{
+			Sort:   jfSort,
+			Paging: jellyfin.Paging{StartIndex: offs, Limit: limit},
+		})
+		if err != nil {
+			return nil, err
+		}
+		return sharedutil.MapSlice(ar, toArtist), nil
+	}
+
+	return helpers.NewArtistIterator(fetcher)
+}
+
 // Creates the Jellyfin filter to implement the given mediaprovider filter,
 // and zeros out the now-unneeded fields in the mediaprovider filter.
 func jfFilterFromFilter(filter *mediaprovider.AlbumFilter) jellyfin.Filter {

backend/mediaprovider/jellyfin/jellyfinmediaprovider.go

@@ -159,14 +159,6 @@ func (j *jellyfinMediaProvider) GetArtistInfo(artistID string) (*mediaprovider.A
 	}, nil
 }
 
-func (j *jellyfinMediaProvider) GetArtists() ([]*mediaprovider.Artist, error) {
-	ar, err := j.client.GetAlbumArtists(jellyfin.QueryOpts{})
-	if err != nil {
-		return nil, err
-	}
-	return sharedutil.MapSlice(ar, toArtist), nil
-}
-
 func (j *jellyfinMediaProvider) GetTrack(trackID string) (*mediaprovider.Track, error) {
 	tr, err := j.client.GetSong(trackID)
 	if err != nil {