frontend fixes

album artist gets populated with artist as fallback (frontend also uses
this as display name fallback for albums). added scroll position
persistence when switching main views. also added frontend cache for
faster switching.

frontend/src/store/controllers/library-controller.ts

@@ -0,0 +1,81 @@
+import type { ReactiveController, ReactiveControllerHost } from 'lit';
+import type { library } from '@go/models';
+import { libraryStore } from '../library-store';
+
+type ViewName = 'tracks' | 'albums';
+
+/**
+ * LibraryController connects a Lit component to the LibraryStore.
+ *
+ * Usage in a component:
+ *
+ *   private library = new LibraryController(this);
+ *
+ *   async connectedCallback() {
+ *     super.connectedCallback();
+ *     this.tracks = await this.library.getTracks();
+ *   }
+ */
+export class LibraryController implements ReactiveController {
+    private host: ReactiveControllerHost;
+    private unsubscribe?: () => void;
+
+    constructor(host: ReactiveControllerHost) {
+        this.host = host;
+        host.addController(this);
+    }
+
+    // ===================================================================
+    // LIFECYCLE HOOKS
+    // ===================================================================
+
+    hostConnected(): void {
+        this.unsubscribe = libraryStore.subscribe(() => {
+            this.host.requestUpdate();
+        });
+    }
+
+    hostDisconnected(): void {
+        this.unsubscribe?.();
+    }
+
+    // ===================================================================
+    // DATA ACCESS
+    // ===================================================================
+
+    async getTracks(): Promise<library.Track[]> {
+        return libraryStore.getTracks();
+    }
+
+    async getAlbums(): Promise<library.Album[]> {
+        return libraryStore.getAlbums();
+    }
+
+    get cachedTracks(): library.Track[] | null {
+        return libraryStore.getCachedTracks();
+    }
+
+    get cachedAlbums(): library.Album[] | null {
+        return libraryStore.getCachedAlbums();
+    }
+
+    get tracksLoading(): boolean {
+        return libraryStore.isTracksLoading();
+    }
+
+    get albumsLoading(): boolean {
+        return libraryStore.isAlbumsLoading();
+    }
+
+    // ===================================================================
+    // SCROLL POSITION
+    // ===================================================================
+
+    getScrollPosition(view: ViewName): number {
+        return libraryStore.getScrollPosition(view);
+    }
+
+    setScrollPosition(view: ViewName, offset: number): void {
+        libraryStore.setScrollPosition(view, offset);
+    }
+}