Re-parent notification controller between primary and secondary containers on iPad based on environment (compact, regular)

2 files changed, 105 insertions, 2 deletions

diff --git a/ios/MullvadVPN/Coordinators/App/ApplicationCoordinator.swift b/ios/MullvadVPN/Coordinators/App/ApplicationCoordinator.swift
index 7bdff9081a..53032583d1 100644
--- a/ios/MullvadVPN/Coordinators/App/ApplicationCoordinator.swift
+++ b/ios/MullvadVPN/Coordinators/App/ApplicationCoordinator.swift
@@ -115,7 +115,7 @@ final class ApplicationCoordinator: Coordinator, Presenting, RootContainerViewCo
             setupSplitView()
         }
 
-        primaryNavigationContainer.notificationController = notificationController
+        setNotificationControllerParent(isPrimary: true)
 
         continueFlow(animated: false)
     }
@@ -341,6 +341,7 @@ final class ApplicationCoordinator: Coordinator, Presenting, RootContainerViewCo
     private func beginHorizontalFlow(animated: Bool, completion: @escaping () -> Void) {
         if isPad, secondaryNavigationContainer.presentingViewController == nil {
             secondaryRootConfiguration.apply(to: secondaryNavigationContainer)
+            addSecondaryContextPresentationStyleObserver()
 
             primaryNavigationContainer.present(
                 secondaryNavigationContainer,
@@ -362,12 +363,75 @@ final class ApplicationCoordinator: Coordinator, Presenting, RootContainerViewCo
      */
     private func endHorizontalFlow(animated: Bool = true, completion: (() -> Void)? = nil) {
         if isPad {
-            secondaryNavigationContainer.dismiss(animated: animated, completion: completion)
+            removeSecondaryContextPresentationStyleObserver()
+
+            secondaryNavigationContainer.dismiss(animated: animated) {
+                // Put notification controller back into primary container.
+                self.setNotificationControllerParent(isPrimary: true)
+
+                completion?()
+            }
         } else {
             completion?()
         }
     }
 
+    /**
+     Assigns notification controller to either primary or secondary container making sure that only one of them holds
+     the reference.
+     */
+    private func setNotificationControllerParent(isPrimary: Bool) {
+        if isPrimary {
+            secondaryNavigationContainer.notificationController = nil
+            primaryNavigationContainer.notificationController = notificationController
+        } else {
+            primaryNavigationContainer.notificationController = nil
+            secondaryNavigationContainer.notificationController = notificationController
+        }
+    }
+
+    /**
+     Start observing secondary context presentation style which is in compact environment turns into fullscreen
+     and otherwise looks like formsheet.
+
+     In response to compact environment and fullscreen presentation, the observer re-assigns notification controller
+     from primary to secondary context to mimic the look and feel of iPhone app. The opposite is also true, that it
+     will make sure that notification controller is presented within primary context when secondary context is in
+     formsheet presentation style.
+     */
+    private func addSecondaryContextPresentationStyleObserver() {
+        removeSecondaryContextPresentationStyleObserver()
+
+        NotificationCenter.default.addObserver(
+            self,
+            selector: #selector(formSheetControllerWillChangeFullscreenPresentation(_:)),
+            name: FormsheetPresentationController.willChangeFullScreenPresentation,
+            object: secondaryNavigationContainer
+        )
+    }
+
+    /**
+     Stop observing secondary context presentation style.
+     */
+    private func removeSecondaryContextPresentationStyleObserver() {
+        NotificationCenter.default.removeObserver(
+            self,
+            name: FormsheetPresentationController.willChangeFullScreenPresentation,
+            object: secondaryNavigationContainer
+        )
+    }
+
+    /**
+     This method is called in response to changes in fullscreen presentation style of form sheet presentation
+     controller.
+     */
+    @objc private func formSheetControllerWillChangeFullscreenPresentation(_ note: Notification) {
+        guard let isFullscreenNumber = note
+            .userInfo?[SecondaryContextPresentationController.isFullScreenUserInfoKey] as? NSNumber else { return }
+
+        setNotificationControllerParent(isPrimary: !isFullscreenNumber.boolValue)
+    }
+
     private var isPad: Bool {
         return UIDevice.current.userInterfaceIdiom == .pad
     }
diff --git a/ios/MullvadVPN/Presentation controllers/FormsheetPresentationController.swift b/ios/MullvadVPN/Presentation controllers/FormsheetPresentationController.swift
index 047fd84bca..97ab75fefc 100644
--- a/ios/MullvadVPN/Presentation controllers/FormsheetPresentationController.swift
+++ b/ios/MullvadVPN/Presentation controllers/FormsheetPresentationController.swift
@@ -16,6 +16,23 @@ private let animationDuration: TimeInterval = 0.5
  Custom implementation of a formsheet presentation controller.
  */
 class FormsheetPresentationController: UIPresentationController {
+    /**
+     Name of notification posted when fullscreen presentation changes, including during initial presentation.
+     */
+    static let willChangeFullScreenPresentation = Notification
+        .Name(rawValue: "FormsheetPresentationControllerWillChangeFullScreenPresentation")
+
+    /**
+     User info key passed along with `willChangeFullScreenPresentation` notification that contains boolean value that
+     indicates if presentation controller is using fullscreen presentation.
+     */
+    static let isFullScreenUserInfoKey = "isFullScreen"
+
+    /**
+     Last known presentation style used to prevent emitting duplicate `willChangeFullScreenPresentation` notifications.
+     */
+    private var lastKnownIsInFullScreen: Bool?
+
     private let dimmingView: UIView = {
         let dimmingView = UIView()
         dimmingView.backgroundColor = .black
@@ -85,6 +102,8 @@ class FormsheetPresentationController: UIPresentationController {
         } else {
             revealDimmingView()
         }
+
+        postFullscreenPresentationWillChangeIfNeeded()
     }
 
     override func presentationTransitionDidEnd(_ completed: Bool) {
@@ -112,6 +131,26 @@ class FormsheetPresentationController: UIPresentationController {
             dimmingView.removeFromSuperview()
         }
     }
+
+    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
+        super.traitCollectionDidChange(previousTraitCollection)
+
+        postFullscreenPresentationWillChangeIfNeeded()
+    }
+
+    private func postFullscreenPresentationWillChangeIfNeeded() {
+        let currentIsInFullScreen = isInFullScreenPresentation
+
+        guard lastKnownIsInFullScreen != currentIsInFullScreen else { return }
+
+        lastKnownIsInFullScreen = currentIsInFullScreen
+
+        NotificationCenter.default.post(
+            name: Self.willChangeFullScreenPresentation,
+            object: presentedViewController,
+            userInfo: [Self.isFullScreenUserInfoKey: NSNumber(booleanLiteral: currentIsInFullScreen)]
+        )
+    }
 }
 
 class FormsheetTransitioningDelegate: NSObject, UIViewControllerTransitioningDelegate {