Stop syncing on resign active and start again on resume (#232)

ElementX/Sources/UserSession/UserSessionFlowCoordinator.swift

@@ -38,6 +38,7 @@ class UserSessionFlowCoordinator: Coordinator {
         self.bugReportService = bugReportService
         
         setupStateMachine()
+        startObservingApplicationState()
     }
     
     func start() {
@@ -48,6 +49,7 @@ class UserSessionFlowCoordinator: Coordinator {
         
     // MARK: - Private
     
+    // swiftlint:disable:next cyclomatic_complexity
     private func setupStateMachine() {
         stateMachine.addTransitionHandler { [weak self] context in
             guard let self else { return }
@@ -56,7 +58,7 @@ class UserSessionFlowCoordinator: Coordinator {
             case (.initial, .start, .homeScreen):
                 self.presentHomeScreen()
                 
-            case(_, _, .roomScreen(let roomId)):
+            case(.homeScreen, .showRoomScreen, .roomScreen(let roomId)):
                 self.presentRoomWithIdentifier(roomId)
             case(.roomScreen(let roomId), .dismissedRoomScreen, .homeScreen):
                 self.tearDownDismissedRoomScreen(roomId)
@@ -70,6 +72,10 @@ class UserSessionFlowCoordinator: Coordinator {
                 self.presentSettingsScreen()
             case (.settingsScreen, .dismissedSettingsScreen, .homeScreen):
                 self.dismissSettingsScreen()
+            case (_, .resignActive, .suspended):
+                self.pause()
+            case (_, .becomeActive, _):
+                self.resume()
                 
             default:
                 fatalError("Unknown transition: \(context)")
@@ -80,6 +86,17 @@ class UserSessionFlowCoordinator: Coordinator {
             fatalError("Failed transition with context: \(context)")
         }
     }
+
+    private func startObservingApplicationState() {
+        NotificationCenter.default.addObserver(self,
+                                               selector: #selector(applicationWillResignActive),
+                                               name: UIApplication.willResignActiveNotification,
+                                               object: nil)
+        NotificationCenter.default.addObserver(self,
+                                               selector: #selector(applicationDidBecomeActive),
+                                               name: UIApplication.didBecomeActiveNotification,
+                                               object: nil)
+    }
     
     private func presentHomeScreen() {
         userSession.clientProxy.startSync()
@@ -272,4 +289,24 @@ class UserSessionFlowCoordinator: Coordinator {
         navigationRouter.dismissModule()
         remove(childCoordinator: bugReportCoordinator)
     }
+
+    // MARK: - Application State
+
+    private func pause() {
+        userSession.clientProxy.stopSync()
+    }
+
+    private func resume() {
+        userSession.clientProxy.startSync()
+    }
+
+    @objc
+    private func applicationWillResignActive() {
+        stateMachine.processEvent(.resignActive)
+    }
+
+    @objc
+    private func applicationDidBecomeActive() {
+        stateMachine.processEvent(.becomeActive)
+    }
 }

ElementX/Sources/UserSession/UserSessionFlowCoordinatorStateMachine.swift

@@ -35,6 +35,9 @@ class UserSessionFlowCoordinatorStateMachine {
         
         /// Showing the settings screen
         case settingsScreen
+
+        /// Application has been suspended
+        case suspended
     }
 
     /// Events that can be triggered on the AppCoordinator state machine
@@ -57,24 +60,37 @@ class UserSessionFlowCoordinatorStateMachine {
         case showSettingsScreen
         /// The settings screen has been dismissed
         case dismissedSettingsScreen
+
+        /// Application goes into inactive state
+        case resignActive
+        /// Application goes into active state
+        case becomeActive
     }
     
     private let stateMachine: StateMachine<State, Event>
+    private var stateBeforeSuspension: State = .initial
     
     init() {
-        stateMachine = StateMachine(state: .initial) { machine in
-            machine.addRoutes(event: .start, transitions: [.initial => .homeScreen])
+        stateMachine = StateMachine(state: .initial)
+        configure()
+    }
 
-            // Transitions with associated values need to be handled through `addRouteMapping`
-            machine.addRouteMapping { event, fromState, _ in
-                switch (event, fromState) {
-                case (.showRoomScreen(let roomId), .homeScreen):
-                    return .roomScreen(roomId: roomId)
-                case (.dismissedRoomScreen, .roomScreen):
-                    return .homeScreen
-                default:
-                    return nil
-                }
+    private func configure() {
+        stateMachine.addRoutes(event: .start, transitions: [.initial => .homeScreen])
+
+        stateMachine.addRouteMapping { event, fromState, _ in
+            switch (event, fromState) {
+            case (.showRoomScreen(let roomId), .homeScreen):
+                return .roomScreen(roomId: roomId)
+            case (.dismissedRoomScreen, .roomScreen):
+                return .homeScreen
+            case (.resignActive, _):
+                self.stateBeforeSuspension = fromState
+                return .suspended
+            case (.becomeActive, .suspended):
+                return self.stateBeforeSuspension
+            default:
+                return nil
             }
         }
     }