Initial service implementation for using a PIN code. (#1912)

* Initial service implementation for using a PIN code.

* Tweak Danger for commit size

600-800 lines is perfectly normal for our PRs, up it to 1000.

ElementX/Sources/Services/AppLock/AppLockService.swift

@@ -16,14 +16,33 @@
 
 import LocalAuthentication
 
+enum AppLockServiceError: Error {
+    /// The operation failed to access the keychain.
+    case keychainError
+    /// The PIN code was rejected because it isn't long enough, or contains invalid characters.
+    case invalidPIN
+    /// The PIN code was rejected as an insecure choice.
+    case weakPIN
+}
+
 @MainActor
 protocol AppLockServiceProtocol {
     /// The app has been configured to automatically lock with a PIN code.
     var isEnabled: Bool { get }
-    /// The app can additionally be unlocked using FaceID or TouchID.
-    var supportsBiometrics: Bool { get }
-    /// The app should be unlocked with a PIN code/biometrics before being presented.
-    var needsUnlock: Bool { 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.
+    var biometricUnlockEnabled: Bool { get set }
+    
+    /// Sets the user's PIN code used to unlock the app.
+    func setupPINCode(_ pinCode: String) -> Result<Void, AppLockServiceError>
+    /// Disables the App Lock feature, removing the user's stored PIN code.
+    func disable()
+    
+    /// Informs the service that the app has entered the background.
+    func applicationDidEnterBackground()
+    /// Decides whether the app should be unlocked with a PIN code/biometrics on foregrounding.
+    func computeNeedsUnlock(willEnterForegroundAt date: Date) -> Bool
     
     /// Attempt to unlock the app with the supplied PIN code.
     func unlock(with pinCode: String) -> Bool
@@ -31,25 +50,80 @@ protocol AppLockServiceProtocol {
     func unlockWithBiometrics() -> Bool
 }
 
+/// The service responsible for locking and unlocking the app.
 class AppLockService: AppLockServiceProtocol {
     private let keychainController: KeychainControllerProtocol
     private let appSettings: AppSettings
+    private let context = LAContext()
     
-    var isEnabled: Bool { appSettings.appLockFlowEnabled }
-    var supportsBiometrics: Bool { true }
-    var needsUnlock: Bool { true }
+    private let timer: AppLockTimer
+    
+    var isEnabled: Bool {
+        do {
+            guard appSettings.appLockFlowEnabled else { return false }
+            return try keychainController.containsPINCode()
+        } catch {
+            MXLog.error("Keychain access error: \(error)")
+            MXLog.error("Locking the app.")
+            return true
+        }
+    }
+    
+    var biometryType: LABiometryType { context.biometryType }
+    var biometricUnlockEnabled = false // Needs to be stored, not sure if in the keychain or defaults yet.
     
     init(keychainController: KeychainControllerProtocol, appSettings: AppSettings) {
         self.keychainController = keychainController
         self.appSettings = appSettings
+        timer = AppLockTimer(gracePeriod: appSettings.appLockGracePeriod)
+    }
+    
+    func setupPINCode(_ pinCode: String) -> Result<Void, AppLockServiceError> {
+        guard validate(pinCode) else { return .failure(.invalidPIN) }
+        guard !appSettings.appLockPINCodeBlockList.contains(pinCode) else { return .failure(.weakPIN) }
+        
+        do {
+            try keychainController.setPINCode(pinCode)
+            return .success(())
+        } catch {
+            MXLog.error("Keychain access error: \(error)")
+            return .failure(.keychainError)
+        }
+    }
+    
+    func disable() {
+        biometricUnlockEnabled = false
+        keychainController.removePINCode()
+    }
+    
+    func applicationDidEnterBackground() {
+        timer.applicationDidEnterBackground()
+    }
+    
+    func computeNeedsUnlock(willEnterForegroundAt date: Date) -> Bool {
+        timer.computeLockState(willEnterForegroundAt: date)
     }
     
     func unlock(with pinCode: String) -> Bool {
-        true
+        guard pinCode == keychainController.pinCode() else { return false }
+        return completeUnlock()
     }
     
     func unlockWithBiometrics() -> Bool {
-        guard supportsBiometrics else { return false }
+        guard biometryType != .none, biometricUnlockEnabled else { return false }
+        return completeUnlock()
+    }
+    
+    // MARK: - Private
+    
+    /// Ensures that a provided PIN code is long enough and only contains digits.
+    private func validate(_ pinCode: String) -> Bool {
+        pinCode.count == 4 && pinCode.allSatisfy(\.isNumber)
+    }
+    
+    /// Shared logic for completing an unlock via a PIN or biometry.
+    private func completeUnlock() -> Bool {
+        timer.registerUnlock()
         return true
     }
 }

ElementX/Sources/Services/AppLock/AppLockTimer.swift

@@ -0,0 +1,62 @@
+//
+// Copyright 2023 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+
+/// A timer that adds a grace-period to the app before locking it.
+class AppLockTimer {
+    /// The amount of time the app should remain unlocked for whilst backgrounded.
+    let gracePeriod: TimeInterval
+    
+    /// Whether the timer considers the app to be locked or not.
+    ///
+    /// Internally this value may be incorrect, always call `needsUnlock` to get the correct value.
+    private var isLocked = true
+    /// The date when the app was last backgrounded whilst in an unlocked state.
+    private var lastUnlockedBackground: Date?
+    
+    /// Creates a new timer.
+    /// - Parameter gracePeriod: The amount of time the app should remain unlocked for whilst backgrounded.
+    init(gracePeriod: TimeInterval) {
+        self.gracePeriod = 180
+    }
+    
+    /// Signals to the timer to track how long the app will be backgrounded for.
+    func applicationDidEnterBackground(date: Date = .now) {
+        // Only update the last background date if the app is currently unlocked.
+        guard !isLocked else { return }
+        lastUnlockedBackground = date
+    }
+    
+    /// Asks the timer to recompute the lock state on foregrounding.
+    func computeLockState(willEnterForegroundAt date: Date) -> Bool {
+        guard !isLocked, let lastUnlockedBackground else { return true }
+        
+        isLocked = date.timeIntervalSince(lastUnlockedBackground) >= gracePeriod
+        
+        // Don't allow changing the device's clock to unlock the app.
+        if date < lastUnlockedBackground {
+            isLocked = true
+        }
+        
+        return isLocked
+    }
+    
+    /// Registers a successful unlock with the timer.
+    func registerUnlock() {
+        isLocked = false
+    }
+}