feat(cast): add position tracking and auto-advance for Chromecast

- Add cast_get_position command for Chromecast media position
- Add CastPositionInfo struct with position, duration, player_state, idle_reason
- Extend position polling to work with both DLNA and Chromecast
- Detect track end on Chromecast via IDLE state with FINISHED reason
- Unify polling logic for both protocols

cpvsc

src-tauri/src/cast/chromecast_thread.rs

@@ -9,7 +9,7 @@ use std::time::Duration;
 
 use crate::cast::device::CastDeviceConnection;
 use crate::cast::errors::CastError;
-use crate::cast::{CastStatus, MediaMetadata};
+use crate::cast::{CastStatus, MediaMetadata, CastPositionInfo};
 
 /// Commands sent to the Chromecast thread
 pub enum CastCommand {
@@ -24,6 +24,9 @@ pub enum CastCommand {
     GetStatus {
         reply: Sender<Result<CastStatus, CastError>>,
     },
+    GetMediaPosition {
+        reply: Sender<Result<CastPositionInfo, CastError>>,
+    },
     LoadMedia {
         url: String,
         content_type: String,
@@ -188,6 +191,17 @@ impl ChromecastHandle {
             .recv()
             .map_err(|_| CastError::Connection("Thread response error".to_string()))?
     }
+
+    /// Get media position for seekbar updates
+    pub fn get_media_position(&self) -> Result<CastPositionInfo, CastError> {
+        let (reply_tx, reply_rx) = mpsc::channel();
+        self.sender
+            .send(CastCommand::GetMediaPosition { reply: reply_tx })
+            .map_err(|_| CastError::Connection("Thread communication error".to_string()))?;
+        reply_rx
+            .recv()
+            .map_err(|_| CastError::Connection("Thread response error".to_string()))?
+    }
 }
 
 impl Drop for ChromecastHandle {
@@ -248,6 +262,14 @@ fn chromecast_thread_main(receiver: Receiver<CastCommand>) {
                 let _ = reply.send(result);
             }
 
+            CastCommand::GetMediaPosition { reply } => {
+                let result = match connection.as_mut() {
+                    Some(conn) => conn.get_media_position(),
+                    None => Err(CastError::NotConnected),
+                };
+                let _ = reply.send(result);
+            }
+
             CastCommand::LoadMedia {
                 url,
                 content_type,

src-tauri/src/cast/commands.rs

@@ -7,7 +7,7 @@ use tokio::sync::Mutex;
 use crate::api::models::Quality;
 use crate::AppState;
 use crate::cast::{
-    CastError, CastStatus, DeviceDiscovery, DiscoveredDevice, MediaMetadata, MediaServer,
+    CastError, CastStatus, CastPositionInfo, DeviceDiscovery, DiscoveredDevice, MediaMetadata, MediaServer,
 };
 use crate::cast::chromecast_thread::ChromecastHandle;
 use crate::library::{AudioFormat, LibraryState};
@@ -110,6 +110,11 @@ pub async fn cast_get_status(state: State<'_, CastState>) -> Result<CastStatus,
     state.chromecast.get_status().map_err(|e| e.to_string())
 }
 
+#[tauri::command]
+pub async fn cast_get_position(state: State<'_, CastState>) -> Result<CastPositionInfo, String> {
+    state.chromecast.get_media_position().map_err(|e| e.to_string())
+}
+
 // === Playback ===
 
 #[tauri::command]

src-tauri/src/cast/device.rs

@@ -3,7 +3,7 @@
 use serde::{Deserialize, Serialize};
 
 use rust_cast::CastDevice;
-use rust_cast::channels::media::{Image, Media, Metadata, MusicTrackMediaMetadata, StreamType};
+use rust_cast::channels::media::{Image, Media, Metadata, MusicTrackMediaMetadata, StreamType, PlayerState, IdleReason};
 use rust_cast::channels::receiver::{CastDeviceApp, Status as ReceiverStatus};
 
 use crate::cast::CastError;
@@ -20,6 +20,15 @@ pub struct MediaMetadata {
     pub duration_secs: Option<u64>,
 }
 
+/// Media position info for seekbar updates
+#[derive(Debug, Clone, Serialize)]
+pub struct CastPositionInfo {
+    pub position_secs: f64,
+    pub duration_secs: f64,
+    pub player_state: String,
+    pub idle_reason: Option<String>,
+}
+
 /// Device status for frontend
 #[derive(Debug, Clone, Serialize)]
 pub struct CastStatus {
@@ -208,6 +217,56 @@ impl CastDeviceConnection {
         Ok(())
     }
 
+    /// Get current media position for seekbar updates
+    pub fn get_media_position(&mut self) -> Result<CastPositionInfo, CastError> {
+        let session = self.session.as_ref().ok_or(CastError::NotConnected)?;
+        let destination = &session.transport_id;
+
+        let status = self
+            .device
+            .media
+            .get_status(destination.as_str(), None)
+            .map_err(|e| CastError::Media(e.to_string()))?;
+
+        // Get the first media entry (current playing item)
+        if let Some(entry) = status.entries.first() {
+            let player_state = match entry.player_state {
+                PlayerState::Idle => "IDLE",
+                PlayerState::Playing => "PLAYING",
+                PlayerState::Paused => "PAUSED",
+                PlayerState::Buffering => "BUFFERING",
+            };
+
+            let idle_reason = entry.idle_reason.as_ref().map(|r| match r {
+                IdleReason::Cancelled => "CANCELLED".to_string(),
+                IdleReason::Interrupted => "INTERRUPTED".to_string(),
+                IdleReason::Finished => "FINISHED".to_string(),
+                IdleReason::Error => "ERROR".to_string(),
+            });
+
+            let duration = entry.media.as_ref()
+                .and_then(|m| m.duration)
+                .unwrap_or(0.0) as f64;
+
+            let position = entry.current_time.unwrap_or(0.0) as f64;
+
+            Ok(CastPositionInfo {
+                position_secs: position,
+                duration_secs: duration,
+                player_state: player_state.to_string(),
+                idle_reason,
+            })
+        } else {
+            // No media playing
+            Ok(CastPositionInfo {
+                position_secs: 0.0,
+                duration_secs: 0.0,
+                player_state: "IDLE".to_string(),
+                idle_reason: None,
+            })
+        }
+    }
+
     fn ensure_session(&mut self) -> Result<(), CastError> {
         if self.session.is_some() {
             return Ok(());

src-tauri/src/cast/mod.rs

@@ -10,7 +10,7 @@ pub mod airplay;
 pub mod dlna;
 
 pub use commands::CastState;
-pub use device::{CastDeviceConnection, CastStatus, MediaMetadata};
+pub use device::{CastDeviceConnection, CastStatus, MediaMetadata, CastPositionInfo};
 pub use discovery::{DeviceDiscovery, DiscoveredDevice};
 pub use errors::CastError;
 pub use media_server::MediaServer;

src-tauri/src/lib.rs

@@ -619,6 +619,7 @@ pub fn run() {
             cast::commands::cast_connect,
             cast::commands::cast_disconnect,
             cast::commands::cast_get_status,
+            cast::commands::cast_get_position,
             cast::commands::cast_play_track,
             cast::commands::cast_play_local_track,
             cast::commands::cast_play,

src/lib/stores/castStore.ts

@@ -250,8 +250,8 @@ export async function castTrack(
     };
     notifyListeners();
     
-    // Start position polling for DLNA
-    if (state.protocol === 'dlna') {
+    // Start position polling for DLNA and Chromecast
+    if (state.protocol === 'dlna' || state.protocol === 'chromecast') {
       startPositionPolling();
     }
   } catch (err) {
@@ -401,50 +401,77 @@ export function setOnCastTrackEnded(callback: (() => Promise<void>) | null): voi
 }
 
 /**
- * Start polling for DLNA position updates
+ * Start polling for cast position updates (DLNA and Chromecast)
  */
 export function startPositionPolling(): void {
   if (positionPollInterval) return;
-  if (state.protocol !== 'dlna') return;
+  if (state.protocol !== 'dlna' && state.protocol !== 'chromecast') return;
 
-  console.log('[CastStore] Starting DLNA position polling');
+  console.log(`[CastStore] Starting ${state.protocol?.toUpperCase()} position polling`);
   trackEndDetected = false;
   lastTransportState = 'PLAYING';
   
   positionPollInterval = setInterval(async () => {
-    if (!state.isConnected || state.protocol !== 'dlna') {
+    if (!state.isConnected || (state.protocol !== 'dlna' && state.protocol !== 'chromecast')) {
       stopPositionPolling();
       return;
     }
 
     try {
-      const positionInfo = await invoke<{
-        position_secs: number;
-        duration_secs: number;
-        transport_state: string;
-      }>('dlna_get_position');
+      let positionSecs = 0;
+      let durationSecs = 0;
+      let transportState = 'PLAYING';
+      let idleReason: string | null = null;
 
-      const wasPlaying = state.isPlaying;
-      const isNowPlaying = positionInfo.transport_state === 'PLAYING';
-      const transportState = positionInfo.transport_state;
+      if (state.protocol === 'dlna') {
+        const positionInfo = await invoke<{
+          position_secs: number;
+          duration_secs: number;
+          transport_state: string;
+        }>('dlna_get_position');
+        
+        positionSecs = positionInfo.position_secs;
+        durationSecs = positionInfo.duration_secs;
+        transportState = positionInfo.transport_state;
+      } else if (state.protocol === 'chromecast') {
+        const positionInfo = await invoke<{
+          position_secs: number;
+          duration_secs: number;
+          player_state: string;
+          idle_reason: string | null;
+        }>('cast_get_position');
+        
+        positionSecs = positionInfo.position_secs;
+        durationSecs = positionInfo.duration_secs;
+        transportState = positionInfo.player_state;
+        idleReason = positionInfo.idle_reason;
+      }
+
+      const isNowPlaying = transportState === 'PLAYING';
 
       state = {
         ...state,
-        positionSecs: positionInfo.position_secs,
-        durationSecs: positionInfo.duration_secs,
+        positionSecs,
+        durationSecs,
         isPlaying: isNowPlaying
       };
       
       notifyListeners();
 
-      // Detect track ended: was PLAYING, now STOPPED, and position is near end or reset to 0
-      const isNearEnd = positionInfo.duration_secs > 0 && 
-        (positionInfo.position_secs >= positionInfo.duration_secs - 2 || positionInfo.position_secs === 0);
+      // Detect track ended based on protocol
+      let trackEnded = false;
       
-      if (lastTransportState === 'PLAYING' && 
-          (transportState === 'STOPPED' || transportState === 'NO_MEDIA_PRESENT') && 
-          !trackEndDetected) {
-        console.log('[CastStore] DLNA track ended, transport:', transportState, 'position:', positionInfo.position_secs);
+      if (state.protocol === 'dlna') {
+        // DLNA: was PLAYING, now STOPPED or NO_MEDIA_PRESENT
+        trackEnded = lastTransportState === 'PLAYING' && 
+          (transportState === 'STOPPED' || transportState === 'NO_MEDIA_PRESENT');
+      } else if (state.protocol === 'chromecast') {
+        // Chromecast: IDLE state with FINISHED reason
+        trackEnded = transportState === 'IDLE' && idleReason === 'FINISHED';
+      }
+      
+      if (trackEnded && !trackEndDetected) {
+        console.log(`[CastStore] ${state.protocol?.toUpperCase()} track ended, state:`, transportState, 'idle_reason:', idleReason);
         trackEndDetected = true;
         
         if (onCastTrackEnded) {
@@ -473,7 +500,7 @@ export function startPositionPolling(): void {
  */
 export function stopPositionPolling(): void {
   if (positionPollInterval) {
-    console.log('[CastStore] Stopping DLNA position polling');
+    console.log('[CastStore] Stopping position polling');
     clearInterval(positionPollInterval);
     positionPollInterval = null;
   }