Synchronize selected TOTP entries to Apple Watch (#55)

apple/Sources/Watch/IronStorageWatchApp.swift

@@ -1,7 +1,54 @@
 import SwiftUI
+import WatchConnectivity
+
+private final class WatchSnapshotTransport: NSObject, ObservableObject, WCSessionDelegate {
+    private static let snapshotKey = "de.rfc1437.ironstorage.watch.snapshot"
+    private static let deliveredReceiptKey = "de.rfc1437.ironstorage.watch.delivered"
+
+    override init() {
+        super.init()
+        guard WCSession.isSupported() else { return }
+        let session = WCSession.default
+        session.delegate = self
+        session.activate()
+    }
+
+    private func receive(_ applicationContext: [String: Any], session: WCSession) {
+        guard
+            applicationContext[Self.snapshotKey] is Data,
+            let receipt = applicationContext[Self.deliveredReceiptKey] as? Data
+        else { return }
+        let acknowledgement = [Self.deliveredReceiptKey: receipt]
+        if session.isReachable {
+            session.sendMessage(acknowledgement, replyHandler: nil) { _ in
+                session.transferUserInfo(acknowledgement)
+            }
+        } else {
+            session.transferUserInfo(acknowledgement)
+        }
+    }
+
+    func session(
+        _ session: WCSession,
+        activationDidCompleteWith activationState: WCSessionActivationState,
+        error: Error?
+    ) {
+        guard activationState == .activated, error == nil else { return }
+        receive(session.receivedApplicationContext, session: session)
+    }
+
+    func session(
+        _ session: WCSession,
+        didReceiveApplicationContext applicationContext: [String: Any]
+    ) {
+        receive(applicationContext, session: session)
+    }
+}
 
 @main
 struct IronStorageWatchApp: App {
+    @StateObject private var transport = WatchSnapshotTransport()
+
     var body: some Scene {
         WindowGroup {
             ContentUnavailableView("No TOTP Codes", systemImage: "timer")