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

Packages/AmphlifyKit/Sources/Sync/SyncEngine.swift

@@ -0,0 +1,39 @@
+import Domain
+import Store
+
+public actor SyncEngine {
+    private let library: any Library
+    private let batchSize = 500
+
+    public init(library: any Library) {
+        self.library = library
+    }
+
+    public func sync(_ source: any LibrarySource) async throws {
+        do {
+            try await pull(source, since: library.cursor(for: source.id))
+        } catch SourceError.cannotCalculateChanges {
+            try await pull(source, since: nil)
+        }
+    }
+
+    private func pull(_ source: any LibrarySource, since cursor: Cursor?) async throws {
+        var batch: [Change] = []
+        for try await change in source.changes(since: cursor) {
+            if case let .checkpoint(next) = change {
+                await library.apply(batch)
+                batch.removeAll(keepingCapacity: true)
+                await library.setCursor(next, for: source.id)
+            } else {
+                batch.append(change)
+                if batch.count >= batchSize {
+                    await library.apply(batch)
+                    batch.removeAll(keepingCapacity: true)
+                }
+            }
+        }
+        if !batch.isEmpty {
+            await library.apply(batch)
+        }
+    }
+}