Fix state machine crashes & background tasks (#343)

* Fix `UIApplication.shared` after moving to SwiftUI app

* Do not autoplay videos on background

* Move app state changes into the app coordinator

* Add application background task, move into the suspended state more accurately

* Add changelog

* Fix most of the linter errors

* Strip suspended state from state machine

* Fix build

* Clear audio session warning

* Update AppCoordinator.swift

* Update AppCoordinator.swift

* Swift format

ElementX/Sources/Services/UserSession/UserSessionFlowCoordinator.swift

@@ -36,7 +36,6 @@ class UserSessionFlowCoordinator: CoordinatorProtocol {
         self.bugReportService = bugReportService
         
         setupStateMachine()
-        startObservingApplicationState()
     }
     
     func start() {
@@ -84,11 +83,6 @@ class UserSessionFlowCoordinator: CoordinatorProtocol {
             case (.feedbackScreen, .dismissedFeedbackScreen, .homeScreen):
                 break
                 
-            case (_, .resignActive, .suspended):
-                self.pause()
-            case (_, .becomeActive, _):
-                self.resume()
-                
             default:
                 fatalError("Unknown transition: \(context)")
             }
@@ -98,17 +92,6 @@ class UserSessionFlowCoordinator: CoordinatorProtocol {
             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()
@@ -247,24 +230,4 @@ class UserSessionFlowCoordinator: CoordinatorProtocol {
             self?.stateMachine.processEvent(.dismissedFeedbackScreen)
         }
     }
-    
-    // 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/Services/UserSession/UserSessionFlowCoordinatorStateMachine.swift

@@ -38,9 +38,6 @@ class UserSessionFlowCoordinatorStateMachine {
         
         /// Showing the settings screen
         case settingsScreen
-
-        /// Application has been suspended
-        case suspended
     }
 
     /// Events that can be triggered on the AppCoordinator state machine
@@ -68,22 +65,15 @@ class UserSessionFlowCoordinatorStateMachine {
         case showSessionVerificationScreen
         /// Session verification has finished
         case dismissedSessionVerificationScreen
-
-        /// Application goes into inactive state
-        case resignActive
-        /// Application goes into active state
-        case becomeActive
     }
     
     private let stateMachine: StateMachine<State, Event>
-    private var stateBeforeSuspension: State?
     
     init() {
         stateMachine = StateMachine(state: .initial)
         configure()
     }
 
-    // swiftlint:disable:next cyclomatic_complexity
     private func configure() {
         stateMachine.addRoutes(event: .start, transitions: [.initial => .homeScreen])
 
@@ -109,18 +99,6 @@ class UserSessionFlowCoordinatorStateMachine {
             case (.dismissedSessionVerificationScreen, .sessionVerificationScreen):
                 return .homeScreen
                 
-            case (.resignActive, _):
-                self.stateBeforeSuspension = fromState
-                return .suspended
-            case (.becomeActive, _):
-                // Cannot become active if not previously suspended
-                // Happens when the app is backgrounded before the session is setup
-                guard let previousState = self.stateBeforeSuspension else {
-                    return self.stateMachine.state
-                }
-                
-                return previousState
-                
             default:
                 return nil
             }