vector-im/element-x-ios/issues/31 - Implement simple SaS sesson verification

* vector-im/element-x-ios/issues/31 - Session verification unit and UI tests
* Fix ImageAnonymizer tests when running on Apple Silicon
* Rename SessionVerification to SessionVerificationScreen

ElementX/Sources/Services/Session/UserSession.swift

@@ -7,13 +7,64 @@
 //
 
 import Foundation
+import Combine
 
 class UserSession: UserSessionProtocol {
+    private var cancellables = Set<AnyCancellable>()
+    private var checkForSessionVerificationControllerCancellable: AnyCancellable?
+    
     let clientProxy: ClientProxyProtocol
     let mediaProvider: MediaProviderProtocol
+    let callbacks = PassthroughSubject<UserSessionCallback, Never>()
+    private(set) var sessionVerificationController: SessionVerificationControllerProxyProtocol?
     
     init(clientProxy: ClientProxyProtocol, mediaProvider: MediaProviderProtocol) {
         self.clientProxy = clientProxy
         self.mediaProvider = mediaProvider
+        
+        setupSessionVerificationWatchdog()
+    }
+    
+    // MARK: - Private
+    
+    private func setupSessionVerificationWatchdog() {
+        checkForSessionVerificationControllerCancellable = clientProxy.callbacks
+            .receive(on: DispatchQueue.main)
+            .sink { [weak self] callback in
+                if case .receivedSyncUpdate = callback {
+                    self?.attemptSessionVerification()
+                }
+            }
+    }
+    
+    private func attemptSessionVerification() {
+        Task {
+            switch await clientProxy.sessionVerificationControllerProxy() {
+            case .success(let sessionVerificationController):
+                tearDownSessionVerificationControllerWatchdog()
+                
+                if !sessionVerificationController.isVerified {
+                    callbacks.send(.sessionVerificationNeeded)
+                }
+                
+                self.sessionVerificationController = sessionVerificationController
+                
+                sessionVerificationController.callbacks.sink { callback in
+                    switch callback {
+                    case .finished:
+                        self.callbacks.send(.didVerifySession)
+                    default:
+                        break
+                    }
+                }.store(in: &cancellables)
+                
+            case .failure(let error):
+                MXLog.error("Failed getting session verification controller with error: \(error). Will retry on the next sync update.")
+            }
+        }
+    }
+    
+    private func tearDownSessionVerificationControllerWatchdog() {
+        checkForSessionVerificationControllerCancellable = nil
     }
 }