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/library-store.ts

@@ -0,0 +1,168 @@
+import { EventsOn } from '@runtime/runtime';
+import { GetAllTracks, GetAllAlbums } from '@go/library/Library';
+import type { library } from '@go/models';
+import { Events } from '../events';
+
+type ViewName = 'tracks' | 'albums';
+
+type Subscriber = () => void;
+
+class LibraryStore {
+    private tracks: library.Track[] | null = null;
+    private albums: library.Album[] | null = null;
+
+    private tracksLoading = false;
+    private albumsLoading = false;
+
+    private scrollPositions: Record<ViewName, number> = {
+        tracks: 0,
+        albums: 0,
+    };
+
+    private subscribers = new Set<Subscriber>();
+
+    constructor() {
+        EventsOn(Events.LibraryScanComplete, () => {
+            this.invalidate();
+        });
+    }
+
+    // ===================================================================
+    // DATA ACCESS
+    // Returns cached data or fetches from backend on first access.
+    // ===================================================================
+
+    async getTracks(): Promise<library.Track[]> {
+        if (this.tracks !== null) {
+            return this.tracks;
+        }
+
+        if (this.tracksLoading) {
+            return this.waitForTracks();
+        }
+
+        this.tracksLoading = true;
+        this.notify();
+
+        try {
+            const tracks = await GetAllTracks();
+            this.tracks = tracks;
+
+            return tracks;
+        } finally {
+            this.tracksLoading = false;
+            this.notify();
+        }
+    }
+
+    async getAlbums(): Promise<library.Album[]> {
+        if (this.albums !== null) {
+            return this.albums;
+        }
+
+        if (this.albumsLoading) {
+            return this.waitForAlbums();
+        }
+
+        this.albumsLoading = true;
+        this.notify();
+
+        try {
+            const albums = await GetAllAlbums();
+            this.albums = albums;
+
+            return albums;
+        } finally {
+            this.albumsLoading = false;
+            this.notify();
+        }
+    }
+
+    // ===================================================================
+    // STATE ACCESSORS
+    // Synchronous access for controllers that need current cached values.
+    // ===================================================================
+
+    getCachedTracks(): library.Track[] | null {
+        return this.tracks;
+    }
+
+    getCachedAlbums(): library.Album[] | null {
+        return this.albums;
+    }
+
+    isTracksLoading(): boolean {
+        return this.tracksLoading;
+    }
+
+    isAlbumsLoading(): boolean {
+        return this.albumsLoading;
+    }
+
+    // ===================================================================
+    // SCROLL POSITION
+    // ===================================================================
+
+    getScrollPosition(view: ViewName): number {
+        return this.scrollPositions[view];
+    }
+
+    setScrollPosition(view: ViewName, offset: number): void {
+        this.scrollPositions[view] = offset;
+    }
+
+    // ===================================================================
+    // INVALIDATION
+    // ===================================================================
+
+    private invalidate(): void {
+        this.tracks = null;
+        this.albums = null;
+        this.scrollPositions = { tracks: 0, albums: 0 };
+        this.notify();
+    }
+
+    // ===================================================================
+    // SUBSCRIPTION SYSTEM
+    // ===================================================================
+
+    subscribe(callback: Subscriber): () => void {
+        this.subscribers.add(callback);
+
+        return () => this.subscribers.delete(callback);
+    }
+
+    private notify(): void {
+        this.subscribers.forEach((callback) => callback());
+    }
+
+    // ===================================================================
+    // HELPERS
+    // Wait for an in-flight fetch to complete.
+    // ===================================================================
+
+    private waitForTracks(): Promise<library.Track[]> {
+        return new Promise((resolve) => {
+            const unsub = this.subscribe(() => {
+                if (!this.tracksLoading && this.tracks !== null) {
+                    unsub();
+                    resolve(this.tracks);
+                }
+            });
+        });
+    }
+
+    private waitForAlbums(): Promise<library.Album[]> {
+        return new Promise((resolve) => {
+            const unsub = this.subscribe(() => {
+                if (!this.albumsLoading && this.albums !== null) {
+                    unsub();
+                    resolve(this.albums);
+                }
+            });
+        });
+    }
+}
+
+// Singleton instance.
+export const libraryStore = new LibraryStore();