refine iOS swipe flow interaction

mobile/ios-app/Core/Media/PlayerCoordinator.swift

@@ -8,14 +8,24 @@ final class PlayerCoordinator: ObservableObject {
 
     @Published var isPlaying = false
     @Published var playbackPositionMs: Int = 0
+    @Published var playbackCompletionCount = 0
+
+    private var playbackEndObserver: NSObjectProtocol?
 
     init() {
         self.player = AVPlayer()
         self.player.actionAtItemEnd = .pause
     }
 
+    deinit {
+        if let playbackEndObserver {
+            NotificationCenter.default.removeObserver(playbackEndObserver)
+        }
+    }
+
     func prepareForPreview(url: URL, startTimeMs: Int = 0) {
         player.replaceCurrentItem(with: AVPlayerItem(url: url))
+        observePlaybackEnd(for: player.currentItem)
         let startTime = CMTime(seconds: Double(startTimeMs) / 1_000.0, preferredTimescale: 1_000)
         player.seek(to: startTime)
         player.play()
@@ -50,4 +60,26 @@ final class PlayerCoordinator: ObservableObject {
     func restart(url: URL, startTimeMs: Int = 0) {
         prepareForPreview(url: url, startTimeMs: startTimeMs)
     }
+
+    private func observePlaybackEnd(for item: AVPlayerItem?) {
+        if let playbackEndObserver {
+            NotificationCenter.default.removeObserver(playbackEndObserver)
+            self.playbackEndObserver = nil
+        }
+
+        guard let item else {
+            return
+        }
+
+        playbackEndObserver = NotificationCenter.default.addObserver(
+            forName: .AVPlayerItemDidPlayToEndTime,
+            object: item,
+            queue: .main
+        ) { [weak self] _ in
+            Task { @MainActor [weak self] in
+                self?.isPlaying = false
+                self?.playbackCompletionCount += 1
+            }
+        }
+    }
 }