fix: Add cloning logic to filters, make providers not update original filter

backend/mediaprovider/helpers/iterators.go

@@ -195,6 +195,8 @@ func (n nilFilter[M]) IsNil() bool { return true }
 
 func (n nilFilter[M]) Matches(*M) bool { return true }
 
+func (n nilFilter[M]) Clone() mediaprovider.MediaFilter[M, nilFilterOptions] { return n }
+
 func (n nilFilter[M]) Options() nilFilterOptions { return nilFilterOptions{} }
 
-func (n nilFilter[M]) SetOptions(o nilFilterOptions) {}
+func (n nilFilter[M]) SetOptions(options nilFilterOptions) {}

backend/mediaprovider/jellyfin/iterators.go

@@ -58,7 +58,7 @@ func (j *jellyfinMediaProvider) IterateAlbums(sortOrder string, filter mediaprov
 		jfSort.Field = jellyfin.SortByYear
 		jfSort.Mode = jellyfin.SortDesc
 	}
-	jfFilt := jfFilterFromFilter(filter)
+	jfFilt, modifiedFilter := jfFilterFromFilter(filter)
 
 	fetcher := func(offs, limit int) ([]*mediaprovider.Album, error) {
 		al, err := j.client.GetAlbums(jellyfin.QueryOpts{
@@ -84,9 +84,9 @@ func (j *jellyfinMediaProvider) IterateAlbums(sortOrder string, filter mediaprov
 			}
 			return sharedutil.MapSlice(al, toAlbum), nil
 		}
-		return helpers.NewRandomAlbumIter(determFetcher, fetcher, filter, j.prefetchCoverCB)
+		return helpers.NewRandomAlbumIter(determFetcher, fetcher, modifiedFilter, j.prefetchCoverCB)
 	}
-	return helpers.NewAlbumIterator(fetcher, filter, j.prefetchCoverCB)
+	return helpers.NewAlbumIterator(fetcher, modifiedFilter, j.prefetchCoverCB)
 }
 
 func (j *jellyfinMediaProvider) SearchAlbums(searchQuery string, filter mediaprovider.AlbumFilter) mediaprovider.AlbumIterator {
@@ -151,15 +151,20 @@ func (j *jellyfinMediaProvider) IterateArtists(sortOrder string) mediaprovider.A
 }
 
 // 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 {
+// and returns a modified mediaprovider filter, with now-unneeded fields zeroed out.
+func jfFilterFromFilter(filter mediaprovider.AlbumFilter) (jellyfin.Filter, mediaprovider.AlbumFilter) {
 	var jfFilt jellyfin.Filter
 
-	filterOptions := filter.Options()
+	// Clone the original filter to not modify its options.
+	// Set filters must be maintained in the original filter, as they are used for the UI.
+	// Modified filter options are used to ignore further filtering that was already handled by the
+	// Jellyfin API.
+	modifiedFilter := filter.Clone()
+	filterOptions := modifiedFilter.Options()
 
 	if filterOptions.ExcludeUnfavorited {
 		jfFilt.Favorite = true
-		filterOptions.ExcludeUnfavorited = false // Jellyfin will handle this filter
+		filterOptions.ExcludeUnfavorited = false
 	}
 	if filterOptions.MinYear > 0 && filterOptions.MaxYear > 0 {
 		jfFilt.YearRange = [2]int{filterOptions.MinYear, filterOptions.MaxYear}
@@ -174,7 +179,6 @@ func jfFilterFromFilter(filter mediaprovider.AlbumFilter) jellyfin.Filter {
 	jfFilt.Genres = filterOptions.Genres
 	filterOptions.Genres = nil
 
-	filter.SetOptions(filterOptions)
-
-	return jfFilt
+	modifiedFilter.SetOptions(filterOptions)
+	return jfFilt, modifiedFilter
 }

backend/mediaprovider/mediaprovider.go

@@ -18,6 +18,7 @@ type TrackIterator = MediaIterator[Track]
 type MediaFilter[M, F any] interface {
 	Options() F
 	SetOptions(F)
+	Clone() MediaFilter[M, F]
 	IsNil() bool
 	Matches(*M) bool
 }
@@ -33,6 +34,19 @@ type AlbumFilterOptions struct {
 	ExcludeUnfavorited bool // mut. exc. with ExcludeFavorited
 }
 
+// Clone returns a deep copy of the filter options
+func (o AlbumFilterOptions) Clone() AlbumFilterOptions {
+	genres := make([]string, len(o.Genres))
+	copy(genres, o.Genres)
+	return AlbumFilterOptions{
+		MinYear:            o.MinYear,
+		MaxYear:            o.MaxYear,
+		Genres:             genres,
+		ExcludeFavorited:   o.ExcludeFavorited,
+		ExcludeUnfavorited: o.ExcludeUnfavorited,
+	}
+}
+
 type albumFilter struct {
 	options AlbumFilterOptions
 }
@@ -45,8 +59,13 @@ func (a albumFilter) Options() AlbumFilterOptions {
 	return a.options
 }
 
-func (a *albumFilter) SetOptions(o AlbumFilterOptions) {
-	a.options = o
+func (a *albumFilter) SetOptions(options AlbumFilterOptions) {
+	a.options = options
+}
+
+// Clone returns a deep copy of the filter
+func (a albumFilter) Clone() AlbumFilter {
+	return NewAlbumFilter(a.options.Clone())
 }
 
 // Returns true if the filter is the nil filter - i.e. matches everything

backend/mediaprovider/subsonic/albumiterator.go

@@ -68,18 +68,22 @@ func (s *subsonicMediaProvider) IterateAlbums(sortOrder string, filter mediaprov
 		// but servers do internally match against all the genres the album is categorized with.
 		// So we must not additionally filter by genre to avoid excluding results where
 		// the single genre returned by Subsonic isn't the one we're iterating on.
-		filterOptions.Genres = nil
+		modifiedFilter := filter.Clone()
+		modifiedOptions := modifiedFilter.Options()
+		modifiedOptions.Genres = nil
+		modifiedFilter.SetOptions(modifiedOptions)
 		fetchFn := func(offset, limit int) ([]*subsonic.AlbumID3, error) {
 			return s.client.GetAlbumList2("byGenre",
 				map[string]string{"genre": genre, "offset": strconv.Itoa(offset), "limit": strconv.Itoa(limit)})
 		}
-		filter.SetOptions(filterOptions)
-		return helpers.NewAlbumIterator(makeFetchFn(fetchFn), filter, s.prefetchCoverCB)
+		return helpers.NewAlbumIterator(makeFetchFn(fetchFn), modifiedFilter, s.prefetchCoverCB)
 	}
 	if sortOrder == "" && filterOptions.ExcludeUnfavorited {
-		filterOptions.ExcludeUnfavorited = false // we're already filtering by this
-		filter.SetOptions(filterOptions)
-		return s.baseIterFromSimpleSortOrder("starred", filter)
+		modifiedFilter := filter.Clone()
+		modifiedOptions := modifiedFilter.Options()
+		modifiedOptions.ExcludeUnfavorited = false // we're already filtering by this
+		modifiedFilter.SetOptions(modifiedOptions)
+		return s.baseIterFromSimpleSortOrder("starred", modifiedFilter)
 	}
 	if sortOrder == "" {
 		sortOrder = AlbumSortRecentlyAdded // default