fix: nextup can have undefined parent id

Next up was called for each library, while the function itself overwrote the whole state. This resulted in nextUp being populated by the latest library fetched.
I reduced it to a single call cause removing the parentId gets us the classic Next Up experience from web.

Other improvements:

- Merge promises together
- Better function names and null checks

frontend/src/store/userLibraries.ts

@@ -124,7 +124,7 @@ class UserLibrariesStore {
     useSnackbar(t('errors.anErrorHappened'), 'error');
   };
 
-  private _fetchUserViews = async (): Promise<void> => {
+  private _updateUserViews = async (): Promise<void> => {
     const remote = useRemote();
 
     try {
@@ -134,13 +134,13 @@ class UserLibrariesStore {
           userId: remote.auth.currentUserId || ''
         });
 
-      this._state.value.views = userViewsResponse.data.Items || [];
+      this._state.value.views = userViewsResponse.data.Items ?? [];
     } catch (error) {
       this._onError(error);
     }
   };
 
-  private _fetchAudioResumes = async (): Promise<void> => {
+  private _updateAudioResumes = async (): Promise<void> => {
     const remote = useRemote();
 
     try {
@@ -160,15 +160,13 @@ class UserLibrariesStore {
         })
       ).data.Items;
 
-      if (audioResumes) {
-        this._state.value.homeSections.audioResumes = audioResumes;
-      }
+      this._state.value.homeSections.audioResumes = audioResumes ?? [];
     } catch (error) {
       this._onError(error);
     }
   };
 
-  private _fetchVideoResumes = async (): Promise<void> => {
+  private _updateVideoResumes = async (): Promise<void> => {
     const remote = useRemote();
 
     try {
@@ -188,15 +186,13 @@ class UserLibrariesStore {
         })
       ).data.Items;
 
-      if (videoResumes) {
-        this._state.value.homeSections.videoResumes = videoResumes;
-      }
+      this._state.value.homeSections.videoResumes = videoResumes ?? [];
     } catch (error) {
       this._onError(error);
     }
   };
 
-  private _fetchUpNext = async (libraryId: string): Promise<void> => {
+  private _updateUpNext = async (libraryId?: string): Promise<void> => {
     const remote = useRemote();
 
     try {
@@ -215,15 +211,16 @@ class UserLibrariesStore {
         })
       ).data.Items;
 
-      if (upNext) {
-        this._state.value.homeSections.upNext = upNext;
-      }
+      this._state.value.homeSections.upNext = [
+        ...this._state.value.homeSections.upNext,
+        ...(upNext ?? [])
+      ];
     } catch (error) {
       this._onError(error);
     }
   };
 
-  private _fetchLatestMedia = async (libraryId: string): Promise<void> => {
+  private _updateLatestMedia = async (libraryId: string): Promise<void> => {
     const remote = useRemote();
 
     try {
@@ -248,7 +245,7 @@ class UserLibrariesStore {
     }
   };
 
-  private _fetchIndexCarouselItems = async (): Promise<void> => {
+  private _updateIndexCarouselItems = async (): Promise<void> => {
     const remote = useRemote();
 
     try {
@@ -262,27 +259,31 @@ class UserLibrariesStore {
         })
       ).data;
 
-      if (carouselItems) {
-        this._state.value.carouselItems = carouselItems;
-      }
+      this._state.value.carouselItems = carouselItems;
     } catch (error) {
       this._onError(error);
     }
   };
 
   public refresh = async (): Promise<void> => {
-    await this._fetchUserViews();
-    await this._fetchAudioResumes();
-    await this._fetchVideoResumes();
-    await this._fetchIndexCarouselItems();
+    this._state.value.homeSections.upNext = [];
+
+    const promises: Promise<void>[] = [
+      this._updateUserViews(),
+      this._updateAudioResumes(),
+      this._updateVideoResumes(),
+      this._updateIndexCarouselItems(),
+      this._updateUpNext()
+    ];
 
     for (const library of this.libraries) {
       if (library.Id) {
-        await this._fetchUpNext(library.Id);
-        await this._fetchLatestMedia(library.Id);
+        promises.push(this._updateLatestMedia(library.Id));
       }
     }
 
+    await Promise.all(promises);
+
     this._state.value.isReady = true;
   };