feat(*): subsonic client with avfoundation playback and apple music ui

Packages/AmphlifyKit/Sources/Playback/SilentEngine.swift

@@ -0,0 +1,56 @@
+import Foundation
+
+public actor SilentEngine: OutputEngine {
+    public nonisolated let events: AsyncStream<OutputEvent>
+    private let continuation: AsyncStream<OutputEvent>.Continuation
+    private var item: QueueItem?
+    private var position: TimeInterval = 0
+    private var startedAt: ContinuousClock.Instant?
+    private var timer: Task<Void, Never>?
+
+    public init() {
+        (events, continuation) = AsyncStream<OutputEvent>.makeStream()
+    }
+
+    public func load(_ item: QueueItem, at position: TimeInterval) {
+        timer?.cancel()
+        self.item = item
+        self.position = position
+        startedAt = nil
+    }
+
+    public func play() {
+        guard let item, startedAt == nil else { return }
+        startedAt = .now
+        let remaining = max(item.track.duration - position, 0)
+        timer = Task { [continuation] in
+            try? await Task.sleep(for: .seconds(remaining))
+            guard !Task.isCancelled else { return }
+            continuation.yield(.finished(item.id))
+        }
+    }
+
+    public func pause() {
+        timer?.cancel()
+        if let startedAt {
+            let elapsed = ContinuousClock.now - startedAt
+            position += Double(elapsed.components.seconds) + Double(elapsed.components.attoseconds) / 1e18
+        }
+        startedAt = nil
+    }
+
+    public func seek(to position: TimeInterval) {
+        let wasPlaying = startedAt != nil
+        pause()
+        self.position = position
+        if wasPlaying {
+            play()
+        }
+    }
+
+    public func stop() {
+        timer?.cancel()
+        item = nil
+        startedAt = nil
+    }
+}