Introduce a kill switch for the new feature

DuckDuckGo/AppDelegate.swift

@@ -22,12 +22,12 @@ import Core
 
 enum AppBehavior: String {
 
-    case existing
-    case stateMachine
+    case old
+    case new
 
 }
 
-protocol DDGAppDelegate {
+protocol DDGApp {
 
     var privacyProDataReporter: PrivacyProDataReporting? { get }
 
@@ -51,18 +51,16 @@ protocol DDGAppDelegate {
         realDelegate.privacyProDataReporter
     }
 
+    func forceOldAppDelegate() {
+        BoolFileMarker(name: .forceOldAppDelegate)?.mark()
+    }
+
     private let appBehavior: AppBehavior = {
-        guard !ProcessInfo().arguments.contains("testing") else { return .existing }
-        if let appBehavior = AppDependencyProvider.shared.appSettings.appBehavior {
-            return appBehavior
-        }
-        let appBehavior: AppBehavior = Double.random(in: 0..<1) < 0.2 ? .stateMachine : .existing // 20% of users will run through new flow
-        AppDependencyProvider.shared.appSettings.appBehavior = appBehavior
-        return appBehavior
+        BoolFileMarker(name: .forceOldAppDelegate)?.isPresent == true ? .old : .new
     }()
 
-    private lazy var realDelegate: UIApplicationDelegate & DDGAppDelegate = {
-        if appBehavior == .existing {
+    private lazy var realDelegate: UIApplicationDelegate & DDGApp = {
+        if appBehavior == .old {
             return OldAppDelegate(with: self)
         } else {
             return NewAppDelegate()
@@ -161,3 +159,9 @@ extension Error {
     }
 
 }
+
+private extension BoolFileMarker.Name {
+
+    static let forceOldAppDelegate = BoolFileMarker.Name(rawValue: "force-old-app-delegate")
+
+}

DuckDuckGo/AppLifecycle/AppStates/Active.swift

@@ -121,6 +121,7 @@ struct Active: AppState {
     private func activateApp(isTesting: Bool = false) {
         guard !isTesting else { return } // Leaving this as is for now to ensure this code is never executed, regardless of where it's called from.
         // In the future, we may consider creating separate states specifically for testing purposes.
+
         StorageInconsistencyMonitor().didBecomeActive(isProtectedDataAvailable: application.isProtectedDataAvailable)
         appDependencies.syncService.initializeIfNeeded()
         appDependencies.syncDataProviders.setUpDatabaseCleanersIfNeeded(syncService: appDependencies.syncService)

DuckDuckGo/AppLifecycle/AppStates/Background.swift

@@ -21,6 +21,7 @@ import Foundation
 import Combine
 import DDGSync
 import UIKit
+import Core
 
 struct Background: AppState {
 
@@ -70,6 +71,15 @@ struct Background: AppState {
         privacyProDataReporter.saveApplicationLastSessionEnded()
 
         resetAppStartTime()
+
+        // Kill switch for the new app delegate:
+        // If the .forceOldAppDelegate flag is set in the config, we mark a file as present.
+        // This switches the app to the old mode and silently crashes it in the background.
+        // When reopened, the app will reliably run the old flow.
+        if ContentBlocking.shared.privacyConfigurationManager.privacyConfig.isEnabled(featureKey: .forceOldAppDelegate) {
+            (UIApplication.shared.delegate as? AppDelegate)?.forceOldAppDelegate()
+            fatalError() // we silently crash in the background
+        }
     }
 
     private mutating func suspendSync(syncService: DDGSync) {

DuckDuckGo/NewAppDelegate.swift

@@ -19,12 +19,12 @@
 
 import UIKit
 
-final class NewAppDelegate: NSObject, UIApplicationDelegate, DDGAppDelegate {
+final class NewAppDelegate: NSObject, UIApplicationDelegate, DDGApp {
 
     private let appStateMachine: AppStateMachine = AppStateMachine()
 
     var privacyProDataReporter: PrivacyProDataReporting? {
-        (appStateMachine.currentState as? Active)?.appDependencies.privacyProDataReporter // just for now, we have to get rid of this antipattern
+        (appStateMachine.currentState as? Active)?.appDependencies.privacyProDataReporter // just for now, we have to get rid of this anti pattern
     }
 
     func initialize() { } // init code will happen inside AppStateMachine/Init state .init()
@@ -35,7 +35,9 @@ final class NewAppDelegate: NSObject, UIApplicationDelegate, DDGAppDelegate {
     }
 
     func applicationDidBecomeActive(_ application: UIApplication) {
-        appStateMachine.handle(.activating)
+        if !ProcessInfo().arguments.contains("testing") {
+            appStateMachine.handle(.activating)
+        }
     }
 
     func applicationWillResignActive(_ application: UIApplication) {

DuckDuckGo/OldAppDelegate.swift

@@ -1,5 +1,5 @@
 //
-//  AppDelegate.swift
+//  OldAppDelegate.swift
 //  DuckDuckGo
 //
 //  Copyright © 2017 DuckDuckGo. All rights reserved.
@@ -42,7 +42,7 @@ import WebKit
 import os.log
 
 @MainActor
-final class OldAppDelegate: NSObject, UIApplicationDelegate, DDGAppDelegate {
+final class OldAppDelegate: NSObject, UIApplicationDelegate, DDGApp {
 
     private var testing = false
     var appIsLaunching = false

DuckDuckGoTests/AppSettingsMock.swift

@@ -22,7 +22,7 @@ import Foundation
 @testable import DuckDuckGo
 
 class AppSettingsMock: AppSettings {
-    var appBehavior: DuckDuckGo.AppBehavior? = .existing
+    var appBehavior: DuckDuckGo.AppBehavior? = .new
 
     var defaultTextZoomLevel: DuckDuckGo.TextZoomLevel = .percent100