feat(subsonic): implement indexBasedQueue extension (#4244)

* redo this whole PR, but clearner now that better errata is in

* update play queue types

server/subsonic/bookmarks.go

@@ -91,7 +91,7 @@ func (api *Router) GetPlayQueue(r *http.Request) (*responses.Subsonic, error) {
 		Current:   currentID,
 		Position:  pq.Position,
 		Username:  user.UserName,
-		Changed:   &pq.UpdatedAt,
+		Changed:   pq.UpdatedAt,
 		ChangedBy: pq.ChangedBy,
 	}
 	return response, nil
@@ -135,3 +135,74 @@ func (api *Router) SavePlayQueue(r *http.Request) (*responses.Subsonic, error) {
 	}
 	return newResponse(), nil
 }
+
+func (api *Router) GetPlayQueueByIndex(r *http.Request) (*responses.Subsonic, error) {
+	user, _ := request.UserFrom(r.Context())
+
+	repo := api.ds.PlayQueue(r.Context())
+	pq, err := repo.RetrieveWithMediaFiles(user.ID)
+	if err != nil && !errors.Is(err, model.ErrNotFound) {
+		return nil, err
+	}
+	if pq == nil || len(pq.Items) == 0 {
+		return newResponse(), nil
+	}
+
+	response := newResponse()
+
+	var index *int
+	if len(pq.Items) > 0 {
+		index = &pq.Current
+	}
+
+	response.PlayQueueByIndex = &responses.PlayQueueByIndex{
+		Entry:        slice.MapWithArg(pq.Items, r.Context(), childFromMediaFile),
+		CurrentIndex: index,
+		Position:     pq.Position,
+		Username:     user.UserName,
+		Changed:      pq.UpdatedAt,
+		ChangedBy:    pq.ChangedBy,
+	}
+	return response, nil
+}
+
+func (api *Router) SavePlayQueueByIndex(r *http.Request) (*responses.Subsonic, error) {
+	p := req.Params(r)
+	ids, _ := p.Strings("id")
+
+	position := p.Int64Or("position", 0)
+
+	var err error
+	var currentIndex int
+
+	if len(ids) > 0 {
+		currentIndex, err = p.Int("currentIndex")
+		if err != nil || currentIndex < 0 || currentIndex >= len(ids) {
+			return nil, newError(responses.ErrorMissingParameter, "missing parameter index, err: %s", err)
+		}
+	}
+
+	items := slice.Map(ids, func(id string) model.MediaFile {
+		return model.MediaFile{ID: id}
+	})
+
+	user, _ := request.UserFrom(r.Context())
+	client, _ := request.ClientFrom(r.Context())
+
+	pq := &model.PlayQueue{
+		UserID:    user.ID,
+		Current:   currentIndex,
+		Position:  position,
+		ChangedBy: client,
+		Items:     items,
+		CreatedAt: time.Time{},
+		UpdatedAt: time.Time{},
+	}
+
+	repo := api.ds.PlayQueue(r.Context())
+	err = repo.Store(pq)
+	if err != nil {
+		return nil, err
+	}
+	return newResponse(), nil
+}