feat: implement audio fade in/out

InfinifiIOS/PlaybackManager.swift

@@ -7,27 +7,37 @@ enum PlaybackState {
     case loading
 }
 
-@MainActor
 class PlaybackManager: ObservableObject {
     @Published var playbackState: PlaybackState = .paused
     @Published var hasError = false
 
     private var audioPlayer = AVPlayer()
+    private var fadeInTimer: Timer?
+    private var fadeOutTimer: Timer?
+    private var scheduledFadeOutTimer: Timer?
 
     func nextTrack() {
         playbackState = .loading
         Task {
-            try await loadCurrentTrack()
-            playbackState = .playing
+            try await loadAndPlayNextTrack()
+            await MainActor.run {
+                playbackState = .playing
+            }
         }
     }
 
     func stop() {
         playbackState = .paused
+        fadeInTimer?.invalidate()
+        fadeInTimer = nil
+        fadeOutTimer?.invalidate()
+        fadeOutTimer = nil
+        scheduledFadeOutTimer?.invalidate()
+        scheduledFadeOutTimer = nil
         audioPlayer.pause()
     }
 
-    private nonisolated func loadCurrentTrack() async throws {
+    private nonisolated func loadAndPlayNextTrack() async throws {
         let now = Date().timeIntervalSince1970
         guard let url = URL(string: "https://infinifi.cafe/current.mp3?t=\(now)") else {
             return
@@ -41,11 +51,19 @@ class PlaybackManager: ObservableObject {
         }
 
         let playerItem = AVPlayerItem(asset: asset)
-
         NotificationCenter.default.addObserver(self, selector: #selector(playbackFinished), name: AVPlayerItem.didPlayToEndTimeNotification, object: playerItem)
 
-        await audioPlayer.replaceCurrentItem(with: playerItem)
+        audioPlayer.volume = 0.0
+
+        audioPlayer.replaceCurrentItem(with: playerItem)
         await audioPlayer.play()
+
+        DispatchQueue.main.async {
+            self.fadeInAudio()
+            self.scheduledFadeOutTimer = Timer.scheduledTimer(withTimeInterval: 55, repeats: false) { _ in
+                self.fadeOutAudio()
+            }
+        }
     }
 
     @objc
@@ -55,4 +73,22 @@ class PlaybackManager: ObservableObject {
             nextTrack()
         }
     }
+
+    private func fadeInAudio() {
+        fadeInTimer = Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) { timer in
+            self.audioPlayer.volume += 0.01
+            if self.audioPlayer.volume >= 1.0 {
+                timer.invalidate()
+            }
+        }
+    }
+
+    private func fadeOutAudio() {
+        fadeOutTimer = Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) { timer in
+            self.audioPlayer.volume -= 0.02
+            if self.audioPlayer.volume <= 0 {
+                timer.invalidate()
+            }
+        }
+    }
 }