refactor: make PlayerViewModel single source of truth for all playback state

Music/Services/AudioService.swift

@@ -25,6 +25,7 @@ final class AudioService {
     private var pendingSeekTime: Double?
 
     var onTrackFinished: (() -> Void)?
+    var onPlaybackStateChanged: (() -> Void)?
 
     func play(url: URL) {
         cleanup()
@@ -42,6 +43,7 @@ final class AudioService {
             if let dur = self.player?.currentItem?.duration, dur.isValid, !dur.isIndefinite {
                 self.duration = dur.seconds
             }
+            self.onPlaybackStateChanged?()
         }
 
         endObserver = NotificationCenter.default.addObserver(
@@ -51,21 +53,25 @@ final class AudioService {
         ) { [weak self] _ in
             self?.isPlaying = false
             self?.currentTime = 0
+            self?.onPlaybackStateChanged?()
             self?.onTrackFinished?()
         }
 
         player?.play()
         isPlaying = true
+        onPlaybackStateChanged?()
     }
 
     func pause() {
         player?.pause()
         isPlaying = false
+        onPlaybackStateChanged?()
     }
 
     func resume() {
         player?.play()
         isPlaying = true
+        onPlaybackStateChanged?()
     }
 
     func togglePlayPause() {
@@ -144,6 +150,7 @@ final class AudioService {
         isPlaying = false
         currentTime = 0
         duration = 0
+        onPlaybackStateChanged?()
     }
 
     private func cleanup() {

Music/ViewModels/PlayerViewModel.swift

@@ -1,11 +1,19 @@
 import Foundation
 import Observation
 
+protocol RemoteCommandSender: AnyObject {
+    func sendCommand(_ command: RemoteCommand)
+}
+
 @Observable
 final class PlayerViewModel {
     var currentTrack: Track?
     var currentIndex: Int?
     var isShuffled = false
+    var isPlaying = false
+    var currentTime: Double = 0
+    var duration: Double = 0
+    var volume: Float = 0.65
 
     private(set) var queue: [Track] = []
     private var originalQueue: [Track] = []
@@ -13,6 +21,11 @@ final class PlayerViewModel {
     private let db: DatabaseService?
     private var halfwayReported = false
 
+    private var remoteClient: RemoteCommandSender?
+    var trackResolver: ((Int64) -> Track?)?
+
+    private var isRemote: Bool { remoteClient != nil }
+
     init(audio: AudioService, db: DatabaseService?) {
         self.audio = audio
         self.db = db
@@ -20,8 +33,26 @@ final class PlayerViewModel {
         audio.onTrackFinished = { [weak self] in
             self?.trackDidFinish()
         }
+
+        audio.onPlaybackStateChanged = { [weak self] in
+            self?.syncFromAudio()
+        }
     }
 
+    // MARK: - Audio Sync
+
+    private func syncFromAudio() {
+        guard !isRemote else { return }
+        isPlaying = audio.isPlaying
+        if !audio.isScrubbing {
+            currentTime = audio.currentTime
+        }
+        duration = audio.duration
+        checkHalfway()
+    }
+
+    // MARK: - Queue Management
+
     func setQueue(_ tracks: [Track]) {
         originalQueue = tracks
         if isShuffled {
@@ -34,28 +65,81 @@ final class PlayerViewModel {
         }
     }
 
+    // MARK: - Playback Controls
+
     func play(_ track: Track) {
         currentTrack = track
         currentIndex = queue.firstIndex(where: { $0.id == track.id })
         halfwayReported = false
+        isPlaying = true
+        currentTime = 0
+
+        if let client = remoteClient {
+            guard let trackId = track.id else { return }
+            client.sendCommand(.play(trackId: trackId, queueIds: queue.compactMap(\.id)))
+        } else {
+            guard let url = URL(string: track.fileURL) else { return }
+            audio.play(url: url)
+        }
+    }
+
+    func togglePlayPause() {
+        if isPlaying { pause() } else { resume() }
+    }
+
+    func pause() {
+        isPlaying = false
+        if let client = remoteClient { client.sendCommand(.pause) } else { audio.pause() }
+    }
+
+    func resume() {
+        isPlaying = true
+        if let client = remoteClient { client.sendCommand(.resume) } else { audio.resume() }
+    }
+
+    func seek(to position: Double) {
+        currentTime = position
+        if let client = remoteClient { client.sendCommand(.seek(position: position)) } else { audio.seek(to: position) }
+    }
 
-        guard let url = URL(string: track.fileURL) else { return }
-        audio.play(url: url)
+    func setVolume(_ level: Float) {
+        volume = level
+        if let client = remoteClient { client.sendCommand(.setVolume(level: level)) } else { audio.volume = level }
+    }
+
+    func beginScrubbing() {
+        if !isRemote { audio.beginScrubbing() }
+    }
+
+    func scrub(to position: Double) {
+        currentTime = position
+        if !isRemote { audio.scrub(to: position) }
+    }
+
+    func endScrubbing(at position: Double) {
+        currentTime = position
+        if let client = remoteClient { client.sendCommand(.seek(position: position)) } else { audio.endScrubbing(at: position) }
     }
 
     func next() {
+        if let client = remoteClient {
+            client.sendCommand(.next)
+            return
+        }
         guard let idx = currentIndex else { return }
         let nextIdx = idx + 1
         if nextIdx < queue.count {
             play(queue[nextIdx])
         } else {
-            audio.stop()
-            currentTrack = nil
-            currentIndex = nil
+            stop()
         }
     }
 
     func previous() {
+        if let client = remoteClient {
+            client.sendCommand(.previous)
+            return
+        }
         guard let idx = currentIndex else { return }
         let prevIdx = max(0, idx - 1)
         play(queue[prevIdx])
@@ -63,6 +147,10 @@ final class PlayerViewModel {
 
     func toggleShuffle() {
         isShuffled.toggle()
+        if let client = remoteClient {
+            client.sendCommand(.toggleShuffle)
+            return
+        }
         if isShuffled {
             queue = buildShuffledQueue(from: originalQueue, startingWith: currentTrack)
         } else {
@@ -73,10 +161,62 @@ final class PlayerViewModel {
         }
     }
 
+    func stop() {
+        isPlaying = false
+        currentTime = 0
+        duration = 0
+        currentTrack = nil
+        currentIndex = nil
+        if !isRemote { audio.stop() }
+    }
+
+    // MARK: - Remote Mode
+
+    func enterRemoteMode(client: RemoteCommandSender) {
+        audio.stop()
+        remoteClient = client
+        currentTrack = nil
+        currentIndex = nil
+        isPlaying = false
+        currentTime = 0
+        duration = 0
+        queue = []
+        originalQueue = []
+    }
+
+    func exitRemoteMode() {
+        remoteClient = nil
+        trackResolver = nil
+        currentTrack = nil
+        currentIndex = nil
+        isPlaying = false
+        currentTime = 0
+        duration = 0
+        queue = []
+        originalQueue = []
+    }
+
+    func applyRemoteState(_ state: PlaybackStatePayload) {
+        guard isRemote else { return }
+        isPlaying = state.isPlaying
+        currentTime = state.currentTime
+        duration = state.duration
+        volume = state.volume
+        isShuffled = state.isShuffled
+
+        if let trackId = state.trackId, currentTrack?.id != trackId {
+            currentTrack = trackResolver?(trackId)
+        } else if state.trackId == nil {
+            currentTrack = nil
+        }
+    }
+
+    // MARK: - Internal
+
     func checkHalfway() {
         guard !halfwayReported,
-              audio.duration > 0,
-              audio.currentTime >= audio.duration * 0.5,
+              duration > 0,
+              currentTime >= duration * 0.5,
               let track = currentTrack,
               let trackId = track.id else { return }
 
@@ -86,6 +226,7 @@ final class PlayerViewModel {
     }
 
     private func trackDidFinish() {
+        guard !isRemote else { return }
         if let track = currentTrack, let trackId = track.id, !halfwayReported {
             let newCount = track.playCount + 1
             try? db?.updatePlayStats(trackId: trackId, playCount: newCount, lastPlayedAt: Date())