Add a state machine to AppLockFlowCoordinator. (#2166)

Fixes a bug when cancelling Face ID would loop back round to presenting Face ID.

ElementX/Sources/Services/AppLock/AppLockService.swift

@@ -38,6 +38,9 @@ class AppLockService: AppLockServiceProtocol {
         }
     }
     
+    private var isEnabledSubject: PassthroughSubject<Bool, Never> = .init()
+    var isEnabledPublisher: AnyPublisher<Bool, Never> { isEnabledSubject.eraseToAnyPublisher() }
+    
     var biometryType: LABiometryType {
         updateBiometrics()
         guard context.evaluatedPolicyDomainState != nil else { return .none }
@@ -71,6 +74,7 @@ class AppLockService: AppLockServiceProtocol {
         
         do {
             try keychainController.setPINCode(pinCode)
+            isEnabledSubject.send(true)
             return .success(())
         } catch {
             MXLog.error("Keychain access error: \(error)")
@@ -105,6 +109,7 @@ class AppLockService: AppLockServiceProtocol {
         keychainController.removePINCode()
         keychainController.removePINCodeBiometricState()
         appSettings.appLockNumberOfPINAttempts = 0
+        isEnabledSubject.send(false)
     }
     
     func applicationDidEnterBackground() {
@@ -128,30 +133,35 @@ class AppLockService: AppLockServiceProtocol {
             _ = enableBiometricUnlock()
         }
         
-        return completeUnlock()
+        completeUnlock()
+        return true
     }
     
-    func unlockWithBiometrics() async -> Bool {
+    func unlockWithBiometrics() async -> AppLockServiceBiometricResult {
         guard biometryType != .none, biometricUnlockEnabled else {
             MXLog.error("Biometric unlock not setup.")
-            return false
+            return .failed
         }
         
         guard biometricUnlockTrusted else {
             MXLog.error("Biometrics have changed. PIN should be shown.")
-            return false
+            return .failed
         }
         
         do {
             let context = unlockContext()
             guard try await context.evaluatePolicy(unlockPolicy, localizedReason: L10n.screenAppLockBiometricUnlockReasonIos) else {
                 MXLog.warning("\(context.biometryType) failed without error.")
-                return false
+                return .failed
             }
-            return completeUnlock()
+            completeUnlock()
+            return .unlocked
+        } catch LAError.systemCancel {
+            MXLog.error("\(context.biometryType) failed: The system cancelled.")
+            return .interrupted
         } catch {
             MXLog.error("\(context.biometryType) failed: \(error)")
-            return false
+            return .failed
         }
     }
     
@@ -180,9 +190,8 @@ class AppLockService: AppLockServiceProtocol {
     }
     
     /// Shared logic for completing an unlock via a PIN or biometrics.
-    private func completeUnlock() -> Bool {
+    private func completeUnlock() {
         timer.registerUnlock()
         appSettings.appLockNumberOfPINAttempts = 0
-        return true
     }
 }

ElementX/Sources/Services/AppLock/AppLockServiceProtocol.swift

@@ -30,6 +30,18 @@ enum AppLockServiceError: Error {
     case biometricUnlockNotSupported
 }
 
+/// The result of an attempt to unlock the app using Touch ID or Face ID.
+enum AppLockServiceBiometricResult {
+    /// Biometric lock was successful.
+    case unlocked
+    /// Biometric lock failed to authenticate the user. This represents any failure
+    /// other than the app being backgrounded during the authentication.
+    case failed
+    /// Biometric lock was interrupted by the system and did not complete. The expected
+    /// cause for this that the app was backgrounded whilst the request was in progress.
+    case interrupted
+}
+
 @MainActor
 protocol AppLockServiceProtocol: AnyObject {
     /// The use of a PIN code is mandatory for this device.
@@ -37,6 +49,9 @@ protocol AppLockServiceProtocol: AnyObject {
     /// The app has been configured to automatically lock with a PIN code.
     var isEnabled: Bool { get }
     
+    /// A publisher that advertises when the service has been enabled or disabled.
+    var isEnabledPublisher: AnyPublisher<Bool, Never> { get }
+    
     /// The type of biometric authentication supported by the device.
     var biometryType: LABiometryType { get }
     /// Whether or not the user has enabled unlock via TouchID, FaceID or (possibly) OpticID.
@@ -64,7 +79,7 @@ protocol AppLockServiceProtocol: AnyObject {
     /// Attempt to unlock the app with the supplied PIN code.
     func unlock(with pinCode: String) -> Bool
     /// Attempt to unlock the app using FaceID or TouchID.
-    func unlockWithBiometrics() async -> Bool
+    func unlockWithBiometrics() async -> AppLockServiceBiometricResult
     
     /// The number of attempts the user had made to unlock with a PIN code.
     ///