Improve caching and UI sync

- Add skip operation guard to prevent concurrent track changes
- Implement aggressive prefetch (3 tracks ahead instead of 1)
- Add peek_upcoming method to queue for multi-track prefetch

src-tauri/src/commands/playback.rs

@@ -103,67 +103,74 @@ async fn download_audio(url: &str) -> Result<Vec<u8>, String> {
     Ok(bytes.to_vec())
 }
 
-/// Spawn background task to prefetch next track
+/// Number of tracks to prefetch ahead
+const PREFETCH_COUNT: usize = 3;
+
+/// Spawn background tasks to prefetch upcoming tracks
 fn spawn_prefetch(
     client: Arc<Mutex<QobuzClient>>,
     cache: Arc<AudioCache>,
     queue: &QueueManager,
 ) {
-    // Get next track from queue
-    let next_track = match queue.peek_next() {
-        Some(t) => t,
-        None => {
-            log::debug!("No next track to prefetch");
-            return;
-        }
-    };
+    // Get upcoming tracks from queue
+    let upcoming_tracks = queue.peek_upcoming(PREFETCH_COUNT);
 
-    let track_id = next_track.id;
-    let track_title = next_track.title.clone();
-
-    // Check if already cached or being fetched
-    if cache.contains(track_id) {
-        log::debug!("Next track {} already cached", track_id);
+    if upcoming_tracks.is_empty() {
+        log::debug!("No upcoming tracks to prefetch");
         return;
     }
 
-    if cache.is_fetching(track_id) {
-        log::debug!("Next track {} already being fetched", track_id);
-        return;
+    for track in upcoming_tracks {
+        let track_id = track.id;
+        let track_title = track.title.clone();
+
+        // Check if already cached or being fetched
+        if cache.contains(track_id) {
+            log::debug!("Track {} already cached", track_id);
+            continue;
+        }
+
+        if cache.is_fetching(track_id) {
+            log::debug!("Track {} already being fetched", track_id);
+            continue;
+        }
+
+        // Mark as fetching
+        cache.mark_fetching(track_id);
+
+        let client_clone = client.clone();
+        let cache_clone = cache.clone();
+
+        log::info!("Prefetching track: {} - {}", track_id, track_title);
+
+        // Spawn background task for each track
+        tokio::spawn(async move {
+            let result = async {
+                let client_guard = client_clone.lock().await;
+                let stream_url = client_guard
+                    .get_stream_url_with_fallback(track_id, Quality::HiRes)
+                    .await
+                    .map_err(|e| format!("Failed to get stream URL: {}", e))?;
+                drop(client_guard);
+
+                let data = download_audio(&stream_url.url).await?;
+                Ok::<Vec<u8>, String>(data)
+            }
+            .await;
+
+            match result {
+                Ok(data) => {
+                    cache_clone.insert(track_id, data);
+                    log::info!("Prefetch complete for track {}", track_id);
+                }
+                Err(e) => {
+                    log::warn!("Prefetch failed for track {}: {}", track_id, e);
+                }
+            }
+
+            cache_clone.unmark_fetching(track_id);
+        });
     }
-
-    // Mark as fetching
-    cache.mark_fetching(track_id);
-
-    log::info!("Prefetching next track: {} - {}", track_id, track_title);
-
-    // Spawn background task
-    tokio::spawn(async move {
-        let result = async {
-            let client_guard = client.lock().await;
-            let stream_url = client_guard
-                .get_stream_url_with_fallback(track_id, Quality::HiRes)
-                .await
-                .map_err(|e| format!("Failed to get stream URL: {}", e))?;
-            drop(client_guard);
-
-            let data = download_audio(&stream_url.url).await?;
-            Ok::<Vec<u8>, String>(data)
-        }
-        .await;
-
-        match result {
-            Ok(data) => {
-                cache.insert(track_id, data);
-                log::info!("Prefetch complete for track {}", track_id);
-            }
-            Err(e) => {
-                log::warn!("Prefetch failed for track {}: {}", track_id, e);
-            }
-        }
-
-        cache.unmark_fetching(track_id);
-    });
 }
 
 /// Pause playback

src-tauri/src/queue/mod.rs

@@ -201,6 +201,53 @@ impl QueueManager {
         next_idx.and_then(|idx| state.tracks.get(idx).cloned())
     }
 
+    /// Get multiple upcoming tracks without advancing (for prefetching)
+    pub fn peek_upcoming(&self, count: usize) -> Vec<QueueTrack> {
+        let state = self.state.lock().unwrap();
+        if state.tracks.is_empty() || count == 0 {
+            return Vec::new();
+        }
+
+        // Don't return upcoming if repeat one (same track always)
+        if state.repeat == RepeatMode::One {
+            return Vec::new();
+        }
+
+        let mut result = Vec::with_capacity(count);
+
+        if state.shuffle {
+            let start_pos = state.shuffle_position + 1;
+            for i in 0..count {
+                let pos = start_pos + i;
+                if pos < state.shuffle_order.len() {
+                    if let Some(track) = state.tracks.get(state.shuffle_order[pos]) {
+                        result.push(track.clone());
+                    }
+                } else if state.repeat == RepeatMode::All {
+                    // Wrap around
+                    let wrapped_pos = pos % state.shuffle_order.len();
+                    if let Some(track) = state.tracks.get(state.shuffle_order[wrapped_pos]) {
+                        result.push(track.clone());
+                    }
+                }
+            }
+        } else {
+            let start_idx = state.current_index.map(|i| i + 1).unwrap_or(0);
+            for i in 0..count {
+                let idx = start_idx + i;
+                if idx < state.tracks.len() {
+                    result.push(state.tracks[idx].clone());
+                } else if state.repeat == RepeatMode::All {
+                    // Wrap around
+                    let wrapped_idx = idx % state.tracks.len();
+                    result.push(state.tracks[wrapped_idx].clone());
+                }
+            }
+        }
+
+        result
+    }
+
     /// Advance to next track and return it
     pub fn next(&self) -> Option<QueueTrack> {
         let mut state = self.state.lock().unwrap();

src/routes/+page.svelte

@@ -398,13 +398,14 @@
 
   // Skip track handlers - wired to backend queue
   async function handleSkipBack() {
-    if (!currentTrack) return;
+    if (!currentTrack || isSkipping) return;
     // If more than 3 seconds in, restart track; otherwise go to previous
     if (currentTime > 3) {
       handleSeek(0);
       return;
     }
 
+    isSkipping = true;
     try {
       const prevTrack = await invoke<BackendQueueTrack | null>('previous_track');
       if (prevTrack) {
@@ -416,12 +417,15 @@
     } catch (err) {
       console.error('Failed to go to previous track:', err);
       showToast('Failed to go to previous track', 'error');
+    } finally {
+      isSkipping = false;
     }
   }
 
   async function handleSkipForward() {
-    if (!currentTrack) return;
+    if (!currentTrack || isSkipping) return;
 
+    isSkipping = true;
     try {
       const nextTrackResult = await invoke<BackendQueueTrack | null>('next_track');
       if (nextTrackResult) {
@@ -435,6 +439,8 @@
     } catch (err) {
       console.error('Failed to go to next track:', err);
       showToast('Failed to go to next track', 'error');
+    } finally {
+      isSkipping = false;
     }
   }
 
@@ -671,6 +677,7 @@
   let pollInterval: ReturnType<typeof setInterval> | null = null;
 
   let isAdvancingTrack = false; // Prevent multiple advances
+  let isSkipping = false; // Prevent concurrent skip operations
 
   async function pollPlaybackState() {
     if (!currentTrack) return;