Introduce BiometricsAuthenticationPresenter

Riot/Modules/SetPinCode/SetupBiometrics/BiometricsAuthenticationPresenter.swift

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+// 
+// Copyright 2020 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
+import LocalAuthentication
+
+enum BiometricsAuthenticationPresenterError: Error {
+    case unknown
+}
+
+/// Presenter for user authentication with biometry.
+final class BiometricsAuthenticationPresenter {
+
+    /// Whether the presenter currently showing the biometrics setup or unlock dialog.
+    /// Showing biometrics dialog will cause the app to resign active.
+    /// This property can be used in order to distinguish real resignations and biometrics case.
+    static private(set) var isPresentingBiometricsAuth: Bool = false
+    
+    /// Presents the user authentication with biometry.
+    /// - Parameters:
+    ///   - message: The app-provided reason for requesting authentication, which displays in the authentication dialog presented to the user.
+    ///   - completion: A closure that is executed when policy evaluation finishes. Will be called in main thread.
+    func present(with message: String, completion: @escaping (Result<Void, Error>) -> Void) {
+        //  do not present if already presented
+        guard !BiometricsAuthenticationPresenter.isPresentingBiometricsAuth else {
+            return
+        }
+        BiometricsAuthenticationPresenter.isPresentingBiometricsAuth = true
+
+        LAContext().evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: message) { (success, error) in
+            if success {
+                // Complete after a little delay
+                DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
+                    BiometricsAuthenticationPresenter.isPresentingBiometricsAuth = false
+                    completion(.success(Void()))
+                }
+            } else {
+                let finalError: Error
+                
+                if let error = error {
+                    finalError = error
+                } else {
+                    finalError = BiometricsAuthenticationPresenterError.unknown
+                }
+                
+                DispatchQueue.main.async {
+                    BiometricsAuthenticationPresenter.isPresentingBiometricsAuth = false
+                    completion(.failure(finalError))
+                }
+            }
+        }
+    }
+}