From ebf7c00eeb1a0e3fdf72c94eef1e75d92ccac0d8 Mon Sep 17 00:00:00 2001
From: Doug <6060466+pixlwave@users.noreply.github.com>
Date: Fri, 16 Aug 2024 11:25:36 +0100
Subject: [PATCH] Navigation support for upcoming Element Call Picture in
 Picture mode. (#3174)

---
 .../Sources/Application/AppSettings.swift     |  3 +
 .../Navigation/NavigationCoordinators.swift   | 73 ++++++++++++++++
 .../UserSessionFlowCoordinator.swift          | 22 ++++-
 .../Mocks/Generated/GeneratedMocks.swift      |  1 +
 .../CallScreen/CallScreenCoordinator.swift    | 12 +++
 .../Screens/CallScreen/CallScreenModels.swift |  4 +
 .../CallScreen/CallScreenViewModel.swift      | 46 ++++++++++
 .../Screens/CallScreen/View/CallScreen.swift  | 23 +++++
 .../RoomScreen/RoomScreenCoordinator.swift    |  2 +
 .../Screens/RoomScreen/RoomScreenModels.swift |  1 +
 .../RoomScreen/RoomScreenViewModel.swift      |  1 +
 .../ElementCall/ElementCallService.swift      |  2 +
 .../ElementCallServiceProtocol.swift          |  2 +
 .../NavigationSplitCoordinatorTests.swift     | 83 +++++++++++++++++++
 14 files changed, 273 insertions(+), 2 deletions(-)

diff --git a/ElementX/Sources/Application/AppSettings.swift b/ElementX/Sources/Application/AppSettings.swift
index 8e49a42c93..255960cc1e 100644
--- a/ElementX/Sources/Application/AppSettings.swift
+++ b/ElementX/Sources/Application/AppSettings.swift
@@ -288,6 +288,9 @@ final class AppSettings {
     
     @UserPreference(key: UserDefaultsKeys.timelineItemAuthenticityEnabled, defaultValue: false, storageType: .userDefaults(store))
     var timelineItemAuthenticityEnabled
+    
+    // Not user configurable as it depends on work in EC too.
+    let elementCallPictureInPictureEnabled = false
         
     #endif
     
diff --git a/ElementX/Sources/Application/Navigation/NavigationCoordinators.swift b/ElementX/Sources/Application/Navigation/NavigationCoordinators.swift
index 3ba5cf885c..e1ede6e032 100644
--- a/ElementX/Sources/Application/Navigation/NavigationCoordinators.swift
+++ b/ElementX/Sources/Application/Navigation/NavigationCoordinators.swift
@@ -115,6 +115,28 @@ class NavigationSplitCoordinator: CoordinatorProtocol, ObservableObject, CustomS
         fullScreenCoverModule?.coordinator
     }
     
+    @Published fileprivate var overlayModule: NavigationModule? {
+        didSet {
+            if let oldValue {
+                logPresentationChange("Remove overlay", oldValue)
+                oldValue.tearDown()
+            }
+            
+            if let overlayModule {
+                logPresentationChange("Set overlay", overlayModule)
+                overlayModule.coordinator?.start()
+            }
+        }
+    }
+    
+    /// The currently displayed overlay coordinator
+    var overlayCoordinator: (any CoordinatorProtocol)? {
+        overlayModule?.coordinator
+    }
+    
+    enum OverlayPresentationMode { case fullScreen, minimized }
+    @Published fileprivate var overlayPresentationMode: OverlayPresentationMode = .minimized
+    
     fileprivate var compactLayoutRootModule: NavigationModule? {
         if let sidebarNavigationStackCoordinator = sidebarModule?.coordinator as? NavigationStackCoordinator {
             if let sidebarRootModule = sidebarNavigationStackCoordinator.rootModule {
@@ -282,6 +304,47 @@ class NavigationSplitCoordinator: CoordinatorProtocol, ObservableObject, CustomS
             fullScreenCoverModule = NavigationModule(coordinator, dismissalCallback: dismissalCallback)
         }
     }
+    
+    /// Present an overlay on top of the split view
+    /// - Parameters:
+    ///   - coordinator: the coordinator to display
+    ///   - presentationMode: how the coordinator should be presented
+    ///   - animated: whether the transition should be animated
+    ///   - dismissalCallback: called when the overlay has been dismissed, programatically or otherwise
+    func setOverlayCoordinator(_ coordinator: (any CoordinatorProtocol)?,
+                               presentationMode: OverlayPresentationMode = .fullScreen,
+                               animated: Bool = true,
+                               dismissalCallback: (() -> Void)? = nil) {
+        guard let coordinator else {
+            overlayModule = nil
+            return
+        }
+        
+        if overlayModule?.coordinator === coordinator {
+            fatalError("Cannot use the same coordinator more than once")
+        }
+
+        var transaction = Transaction()
+        transaction.disablesAnimations = !animated
+
+        withTransaction(transaction) {
+            overlayPresentationMode = presentationMode
+            overlayModule = NavigationModule(coordinator, dismissalCallback: dismissalCallback)
+        }
+    }
+    
+    /// Updates the presentation of the overlay coordinator.
+    /// - Parameters:
+    ///   - mode: The type of presentation to use.
+    ///   - animated: whether the transition should be animated
+    func setOverlayPresentationMode(_ mode: OverlayPresentationMode, animated: Bool = true) {
+        var transaction = Transaction()
+        transaction.disablesAnimations = !animated
+        
+        withTransaction(transaction) {
+            overlayPresentationMode = mode
+        }
+    }
         
     // MARK: - CoordinatorProtocol
     
@@ -385,6 +448,16 @@ private struct NavigationSplitCoordinatorView: View {
             module.coordinator?.toPresentable()
                 .id(module.id)
         }
+        .overlay {
+            Group {
+                if let coordinator = navigationSplitCoordinator.overlayModule?.coordinator {
+                    coordinator.toPresentable()
+                        .opacity(navigationSplitCoordinator.overlayPresentationMode == .minimized ? 0 : 1)
+                        .transition(.opacity)
+                }
+            }
+            .animation(.elementDefault, value: navigationSplitCoordinator.overlayPresentationMode)
+        }
         // Handle `horizontalSizeClass` changes breaking the navigation bar
         // https://github.com/element-hq/element-x-ios/issues/617
         .onChange(of: horizontalSizeClass) { value in
diff --git a/ElementX/Sources/FlowCoordinators/UserSessionFlowCoordinator.swift b/ElementX/Sources/FlowCoordinators/UserSessionFlowCoordinator.swift
index 9d98247dee..5c8da5b603 100644
--- a/ElementX/Sources/FlowCoordinators/UserSessionFlowCoordinator.swift
+++ b/ElementX/Sources/FlowCoordinators/UserSessionFlowCoordinator.swift
@@ -14,6 +14,7 @@
 // limitations under the License.
 //
 
+import AVKit
 import Combine
 import SwiftUI
 
@@ -557,7 +558,14 @@ class UserSessionFlowCoordinator: FlowCoordinatorProtocol {
         
     // MARK: Calls
     
+    private var callScreenPictureInPictureController: AVPictureInPictureController?
     private func presentCallScreen(roomProxy: RoomProxyProtocol) {
+        guard elementCallService.ongoingCallRoomID != roomProxy.id else {
+            MXLog.info("Returning to existing call.")
+            callScreenPictureInPictureController?.stopPictureInPicture()
+            return
+        }
+        
         let colorScheme: ColorScheme = appMediator.windowManager.mainWindow.traitCollection.userInterfaceStyle == .light ? .light : .dark
         let callScreenCoordinator = CallScreenCoordinator(parameters: .init(elementCallService: elementCallService,
                                                                             clientProxy: userSession.clientProxy,
@@ -565,19 +573,29 @@ class UserSessionFlowCoordinator: FlowCoordinatorProtocol {
                                                                             clientID: InfoPlistReader.main.bundleIdentifier,
                                                                             elementCallBaseURL: appSettings.elementCallBaseURL,
                                                                             elementCallBaseURLOverride: appSettings.elementCallBaseURLOverride,
+                                                                            elementCallPictureInPictureEnabled: appSettings.elementCallPictureInPictureEnabled,
                                                                             colorScheme: colorScheme,
                                                                             appHooks: appHooks))
         
         callScreenCoordinator.actions
             .sink { [weak self] action in
+                guard let self else { return }
                 switch action {
+                case .pictureInPictureStarted(let controller):
+                    MXLog.info("Hiding call for PiP presentation.")
+                    callScreenPictureInPictureController = controller
+                    navigationSplitCoordinator.setOverlayPresentationMode(.minimized)
+                case .pictureInPictureStopped:
+                    MXLog.info("Restoring call after PiP presentation.")
+                    navigationSplitCoordinator.setOverlayPresentationMode(.fullScreen)
+                    callScreenPictureInPictureController = nil
                 case .dismiss:
-                    self?.navigationSplitCoordinator.setSheetCoordinator(nil)
+                    navigationSplitCoordinator.setOverlayCoordinator(nil)
                 }
             }
             .store(in: &cancellables)
         
-        navigationSplitCoordinator.setSheetCoordinator(callScreenCoordinator, animated: true)
+        navigationSplitCoordinator.setOverlayCoordinator(callScreenCoordinator, animated: true)
         
         analytics.track(screen: .RoomCall)
     }
diff --git a/ElementX/Sources/Mocks/Generated/GeneratedMocks.swift b/ElementX/Sources/Mocks/Generated/GeneratedMocks.swift
index 08780c2e11..1cf8b8ea70 100644
--- a/ElementX/Sources/Mocks/Generated/GeneratedMocks.swift
+++ b/ElementX/Sources/Mocks/Generated/GeneratedMocks.swift
@@ -4894,6 +4894,7 @@ class ElementCallServiceMock: ElementCallServiceProtocol {
         set(value) { underlyingActions = value }
     }
     var underlyingActions: AnyPublisher<ElementCallServiceAction, Never>!
+    var ongoingCallRoomID: String?
 
     //MARK: - setClientProxy
 
diff --git a/ElementX/Sources/Screens/CallScreen/CallScreenCoordinator.swift b/ElementX/Sources/Screens/CallScreen/CallScreenCoordinator.swift
index bfdc7299d8..13b13b0e34 100644
--- a/ElementX/Sources/Screens/CallScreen/CallScreenCoordinator.swift
+++ b/ElementX/Sources/Screens/CallScreen/CallScreenCoordinator.swift
@@ -14,6 +14,7 @@
 // limitations under the License.
 //
 
+import AVKit
 import Combine
 import SwiftUI
 
@@ -24,11 +25,17 @@ struct CallScreenCoordinatorParameters {
     let clientID: String
     let elementCallBaseURL: URL
     let elementCallBaseURLOverride: URL?
+    let elementCallPictureInPictureEnabled: Bool
     let colorScheme: ColorScheme
     let appHooks: AppHooks
 }
 
 enum CallScreenCoordinatorAction {
+    /// The call is still ongoing but the user wishes to navigate around the app.
+    case pictureInPictureStarted(AVPictureInPictureController?)
+    /// The call is hidden and the user wishes to return to it.
+    case pictureInPictureStopped
+    /// The call is finished and the screen is done with.
     case dismiss
 }
 
@@ -48,6 +55,7 @@ final class CallScreenCoordinator: CoordinatorProtocol {
                                         clientID: parameters.clientID,
                                         elementCallBaseURL: parameters.elementCallBaseURL,
                                         elementCallBaseURLOverride: parameters.elementCallBaseURLOverride,
+                                        elementCallPictureInPictureEnabled: parameters.elementCallPictureInPictureEnabled,
                                         colorScheme: parameters.colorScheme,
                                         appHooks: parameters.appHooks)
     }
@@ -57,6 +65,10 @@ final class CallScreenCoordinator: CoordinatorProtocol {
             guard let self else { return }
             
             switch action {
+            case .pictureInPictureStarted(let controller):
+                actionsSubject.send(.pictureInPictureStarted(controller))
+            case .pictureInPictureStopped:
+                actionsSubject.send(.pictureInPictureStopped)
             case .dismiss:
                 actionsSubject.send(.dismiss)
             }
diff --git a/ElementX/Sources/Screens/CallScreen/CallScreenModels.swift b/ElementX/Sources/Screens/CallScreen/CallScreenModels.swift
index c9098b11cd..2007ee04ec 100644
--- a/ElementX/Sources/Screens/CallScreen/CallScreenModels.swift
+++ b/ElementX/Sources/Screens/CallScreen/CallScreenModels.swift
@@ -14,9 +14,12 @@
 // limitations under the License.
 //
 
+import AVKit
 import Foundation
 
 enum CallScreenViewModelAction {
+    case pictureInPictureStarted(AVPictureInPictureController?)
+    case pictureInPictureStopped
     case dismiss
 }
 
@@ -39,4 +42,5 @@ struct Bindings {
 
 enum CallScreenViewAction {
     case urlChanged(URL?)
+    case navigateBack
 }
diff --git a/ElementX/Sources/Screens/CallScreen/CallScreenViewModel.swift b/ElementX/Sources/Screens/CallScreen/CallScreenViewModel.swift
index a33536e721..d6fc6abe09 100644
--- a/ElementX/Sources/Screens/CallScreen/CallScreenViewModel.swift
+++ b/ElementX/Sources/Screens/CallScreen/CallScreenViewModel.swift
@@ -14,6 +14,7 @@
 // limitations under the License.
 //
 
+import AVKit
 import CallKit
 import Combine
 import SwiftUI
@@ -23,6 +24,7 @@ typealias CallScreenViewModelType = StateStoreViewModel<CallScreenViewState, Cal
 class CallScreenViewModel: CallScreenViewModelType, CallScreenViewModelProtocol {
     private let elementCallService: ElementCallServiceProtocol
     private let roomProxy: RoomProxyProtocol
+    private let isPictureInPictureEnabled: Bool
     
     private let widgetDriver: ElementCallWidgetDriverProtocol
     
@@ -45,12 +47,14 @@ class CallScreenViewModel: CallScreenViewModelType, CallScreenViewModelProtocol
          clientID: String,
          elementCallBaseURL: URL,
          elementCallBaseURLOverride: URL?,
+         elementCallPictureInPictureEnabled: Bool,
          colorScheme: ColorScheme,
          appHooks: AppHooks) {
         guard let deviceID = clientProxy.deviceID else { fatalError("Missing device ID for the call.") }
         
         self.elementCallService = elementCallService
         self.roomProxy = roomProxy
+        isPictureInPictureEnabled = elementCallPictureInPictureEnabled
         
         widgetDriver = roomProxy.elementCallWidgetDriver(deviceID: deviceID)
         
@@ -151,6 +155,23 @@ class CallScreenViewModel: CallScreenViewModelType, CallScreenViewModelProtocol
                     syncUpdateCancellable = nil
                 }
             }, receiveValue: { _ in })
+        
+        // Use did start otherwise there's a black box left on the screen during the pip controller animation.
+        NotificationCenter.default.publisher(for: .init("AVPictureInPictureControllerDidStartNotification"))
+            .sink { [weak self] notification in
+                guard let self else { return }
+                let controller = notification.object as? AVPictureInPictureController
+                actionsSubject.send(.pictureInPictureStarted(controller))
+            }
+            .store(in: &cancellables)
+        
+        NotificationCenter.default.publisher(for: .init("AVPictureInPictureControllerWillStopNotification"))
+            .sink { [weak self] _ in
+                guard let self else { return }
+                actionsSubject.send(.pictureInPictureStopped)
+                Task { try await self.state.bindings.javaScriptEvaluator?("controls.disableCompatPip()") }
+            }
+            .store(in: &cancellables)
     }
     
     override func process(viewAction: CallScreenViewAction) {
@@ -158,6 +179,8 @@ class CallScreenViewModel: CallScreenViewModelType, CallScreenViewModelProtocol
         case .urlChanged(let url):
             guard let url else { return }
             MXLog.info("URL changed to: \(url)")
+        case .navigateBack:
+            handleBackwardsNavigation()
         }
     }
     
@@ -171,6 +194,29 @@ class CallScreenViewModel: CallScreenViewModelType, CallScreenViewModelProtocol
     
     // MARK: - Private
     
+    private func handleBackwardsNavigation() {
+        #if targetEnvironment(simulator)
+        if UIDevice.current.isPhone {
+            MXLog.warning("The iPhone simulator doesn't support PiP.")
+            actionsSubject.send(.dismiss)
+            return
+        }
+        #endif
+        
+        guard isPictureInPictureEnabled, state.url != nil else {
+            actionsSubject.send(.dismiss)
+            return
+        }
+        
+        Task {
+            try await state.bindings.javaScriptEvaluator?("controls.enableCompatPip()")
+            // Enable this check when implemented on web.
+            // if result as? Bool != true {
+            //    actionsSubject.send(.dismiss)
+            // }
+        }
+    }
+    
     private func setAudioEnabled(_ enabled: Bool) async {
         let message = ElementCallWidgetMessage(direction: .toWidget,
                                                action: .mediaState,
diff --git a/ElementX/Sources/Screens/CallScreen/View/CallScreen.swift b/ElementX/Sources/Screens/CallScreen/View/CallScreen.swift
index 2ddd464369..27eea19c11 100644
--- a/ElementX/Sources/Screens/CallScreen/View/CallScreen.swift
+++ b/ElementX/Sources/Screens/CallScreen/View/CallScreen.swift
@@ -15,6 +15,7 @@
 //
 
 import Combine
+import SFSafeSymbols
 import SwiftUI
 import WebKit
 
@@ -22,6 +23,26 @@ struct CallScreen: View {
     @ObservedObject var context: CallScreenViewModel.Context
     
     var body: some View {
+        NavigationStack {
+            content
+                .frame(maxWidth: .infinity, maxHeight: .infinity)
+                .background(Color.compound.bgCanvasDefault.ignoresSafeArea())
+                .navigationBarTitleDisplayMode(.inline)
+                .toolbar {
+                    ToolbarItem(placement: .cancellationAction) {
+                        Button { context.send(viewAction: .navigateBack) } label: {
+                            Image(systemSymbol: .chevronBackward)
+                                .fontWeight(.semibold)
+                        }
+                        .offset(y: -8)
+                        // .padding(.leading, -8) // Fixes the button alignment, but harder to tap.
+                    }
+                }
+        }
+    }
+    
+    @ViewBuilder
+    var content: some View {
         if context.viewState.url == nil {
             ProgressView()
         } else {
@@ -187,6 +208,7 @@ struct CallScreen_Previews: PreviewProvider {
     static let viewModel = {
         let clientProxy = ClientProxyMock()
         clientProxy.getElementWellKnownReturnValue = .success(nil)
+        clientProxy.deviceID = "call-device-id"
         
         let roomProxy = RoomProxyMock()
         roomProxy.sendCallNotificationIfNeeededReturnValue = .success(())
@@ -204,6 +226,7 @@ struct CallScreen_Previews: PreviewProvider {
                                    clientID: "io.element.elementx",
                                    elementCallBaseURL: "https://call.element.io",
                                    elementCallBaseURLOverride: nil,
+                                   elementCallPictureInPictureEnabled: false,
                                    colorScheme: .light,
                                    appHooks: AppHooks())
     }()
diff --git a/ElementX/Sources/Screens/RoomScreen/RoomScreenCoordinator.swift b/ElementX/Sources/Screens/RoomScreen/RoomScreenCoordinator.swift
index 97b37686b9..98b0fb5030 100644
--- a/ElementX/Sources/Screens/RoomScreen/RoomScreenCoordinator.swift
+++ b/ElementX/Sources/Screens/RoomScreen/RoomScreenCoordinator.swift
@@ -156,6 +156,8 @@ final class RoomScreenCoordinator: CoordinatorProtocol {
                     actionsSubject.send(.presentRoomDetails)
                 case .displayCall:
                     actionsSubject.send(.presentCallScreen)
+                case .removeComposerFocus:
+                    composerViewModel.process(timelineAction: .removeFocus)
                 }
             }
             .store(in: &cancellables)
diff --git a/ElementX/Sources/Screens/RoomScreen/RoomScreenModels.swift b/ElementX/Sources/Screens/RoomScreen/RoomScreenModels.swift
index f4d4bd31ef..866d1252e2 100644
--- a/ElementX/Sources/Screens/RoomScreen/RoomScreenModels.swift
+++ b/ElementX/Sources/Screens/RoomScreen/RoomScreenModels.swift
@@ -22,6 +22,7 @@ enum RoomScreenViewModelAction {
     case displayPinnedEventsTimeline
     case displayRoomDetails
     case displayCall
+    case removeComposerFocus
 }
 
 enum RoomScreenViewAction {
diff --git a/ElementX/Sources/Screens/RoomScreen/RoomScreenViewModel.swift b/ElementX/Sources/Screens/RoomScreen/RoomScreenViewModel.swift
index 41106e2218..a2fead44e9 100644
--- a/ElementX/Sources/Screens/RoomScreen/RoomScreenViewModel.swift
+++ b/ElementX/Sources/Screens/RoomScreen/RoomScreenViewModel.swift
@@ -84,6 +84,7 @@ class RoomScreenViewModel: RoomScreenViewModelType, RoomScreenViewModelProtocol
             actionsSubject.send(.displayRoomDetails)
         case .displayCall:
             actionsSubject.send(.displayCall)
+            actionsSubject.send(.removeComposerFocus)
             analyticsService.trackInteraction(name: .MobileRoomCallButton)
         }
     }
diff --git a/ElementX/Sources/Services/ElementCall/ElementCallService.swift b/ElementX/Sources/Services/ElementCall/ElementCallService.swift
index 2390a3d0a8..5accc97d87 100644
--- a/ElementX/Sources/Services/ElementCall/ElementCallService.swift
+++ b/ElementX/Sources/Services/ElementCall/ElementCallService.swift
@@ -59,6 +59,8 @@ class ElementCallService: NSObject, ElementCallServiceProtocol, PKPushRegistryDe
     
     private var ongoingCallID: CallID?
     
+    var ongoingCallRoomID: String? { ongoingCallID?.roomID }
+    
     private let actionsSubject: PassthroughSubject<ElementCallServiceAction, Never> = .init()
     var actions: AnyPublisher<ElementCallServiceAction, Never> {
         actionsSubject.eraseToAnyPublisher()
diff --git a/ElementX/Sources/Services/ElementCall/ElementCallServiceProtocol.swift b/ElementX/Sources/Services/ElementCall/ElementCallServiceProtocol.swift
index 1c47b23f0b..c58a683945 100644
--- a/ElementX/Sources/Services/ElementCall/ElementCallServiceProtocol.swift
+++ b/ElementX/Sources/Services/ElementCall/ElementCallServiceProtocol.swift
@@ -26,6 +26,8 @@ enum ElementCallServiceAction {
 protocol ElementCallServiceProtocol {
     var actions: AnyPublisher<ElementCallServiceAction, Never> { get }
     
+    var ongoingCallRoomID: String? { get }
+    
     func setClientProxy(_ clientProxy: ClientProxyProtocol)
     
     func setupCallSession(roomID: String, roomDisplayName: String) async
diff --git a/UnitTests/Sources/NavigationSplitCoordinatorTests.swift b/UnitTests/Sources/NavigationSplitCoordinatorTests.swift
index cc5b7181e0..cc12ea20b6 100644
--- a/UnitTests/Sources/NavigationSplitCoordinatorTests.swift
+++ b/UnitTests/Sources/NavigationSplitCoordinatorTests.swift
@@ -99,6 +99,52 @@ class NavigationSplitCoordinatorTests: XCTestCase {
         assertCoordinatorsEqual(someOtherSheetCoordinator, navigationSplitCoordinator.sheetCoordinator)
     }
     
+    func testFullScreenCover() {
+        let sidebarCoordinator = SomeTestCoordinator()
+        navigationSplitCoordinator.setSidebarCoordinator(sidebarCoordinator)
+        let detailCoordinator = SomeTestCoordinator()
+        navigationSplitCoordinator.setDetailCoordinator(detailCoordinator)
+        
+        let fullScreenCoordinator = SomeTestCoordinator()
+        navigationSplitCoordinator.setFullScreenCoverCoordinator(fullScreenCoordinator)
+        
+        assertCoordinatorsEqual(sidebarCoordinator, navigationSplitCoordinator.sidebarCoordinator)
+        assertCoordinatorsEqual(detailCoordinator, navigationSplitCoordinator.detailCoordinator)
+        assertCoordinatorsEqual(fullScreenCoordinator, navigationSplitCoordinator.fullScreenCoverCoordinator)
+        
+        navigationSplitCoordinator.setFullScreenCoverCoordinator(nil)
+        
+        assertCoordinatorsEqual(sidebarCoordinator, navigationSplitCoordinator.sidebarCoordinator)
+        assertCoordinatorsEqual(detailCoordinator, navigationSplitCoordinator.detailCoordinator)
+        XCTAssertNil(navigationSplitCoordinator.fullScreenCoverCoordinator)
+    }
+    
+    func testOverlay() {
+        let sidebarCoordinator = SomeTestCoordinator()
+        navigationSplitCoordinator.setSidebarCoordinator(sidebarCoordinator)
+        let detailCoordinator = SomeTestCoordinator()
+        navigationSplitCoordinator.setDetailCoordinator(detailCoordinator)
+        
+        let overlayCoordinator = SomeTestCoordinator()
+        navigationSplitCoordinator.setOverlayCoordinator(overlayCoordinator)
+        
+        assertCoordinatorsEqual(sidebarCoordinator, navigationSplitCoordinator.sidebarCoordinator)
+        assertCoordinatorsEqual(detailCoordinator, navigationSplitCoordinator.detailCoordinator)
+        assertCoordinatorsEqual(overlayCoordinator, navigationSplitCoordinator.overlayCoordinator)
+        
+        // The coordinator should still be retained when changing the presentation mode.
+        navigationSplitCoordinator.setOverlayPresentationMode(.minimized)
+        assertCoordinatorsEqual(overlayCoordinator, navigationSplitCoordinator.overlayCoordinator)
+        navigationSplitCoordinator.setOverlayPresentationMode(.fullScreen)
+        assertCoordinatorsEqual(overlayCoordinator, navigationSplitCoordinator.overlayCoordinator)
+        
+        navigationSplitCoordinator.setOverlayCoordinator(nil)
+        
+        assertCoordinatorsEqual(sidebarCoordinator, navigationSplitCoordinator.sidebarCoordinator)
+        assertCoordinatorsEqual(detailCoordinator, navigationSplitCoordinator.detailCoordinator)
+        XCTAssertNil(navigationSplitCoordinator.overlayCoordinator)
+    }
+    
     func testSidebarReplacementCallbacks() {
         let sidebarCoordinator = SomeTestCoordinator()
         
@@ -135,6 +181,43 @@ class NavigationSplitCoordinatorTests: XCTestCase {
         waitForExpectations(timeout: 1.0)
     }
     
+    func testFullScreenCoverDismissalCallback() {
+        let fullScreenCoordinator = SomeTestCoordinator()
+        
+        let expectation = expectation(description: "Wait for callback")
+        navigationSplitCoordinator.setFullScreenCoverCoordinator(fullScreenCoordinator) {
+            expectation.fulfill()
+        }
+        
+        navigationSplitCoordinator.setFullScreenCoverCoordinator(nil)
+        waitForExpectations(timeout: 1.0)
+    }
+    
+    func testOverlayDismissalCallback() {
+        let overlayCoordinator = SomeTestCoordinator()
+        
+        let expectation = expectation(description: "Wait for callback")
+        navigationSplitCoordinator.setOverlayCoordinator(overlayCoordinator) {
+            expectation.fulfill()
+        }
+        
+        navigationSplitCoordinator.setOverlayCoordinator(nil)
+        waitForExpectations(timeout: 1.0)
+    }
+    
+    func testOverlayDismissalCallbackWhenChangingMode() {
+        let overlayCoordinator = SomeTestCoordinator()
+        
+        let expectation = expectation(description: "Wait for callback")
+        expectation.isInverted = true
+        navigationSplitCoordinator.setOverlayCoordinator(overlayCoordinator) {
+            expectation.fulfill()
+        }
+        
+        navigationSplitCoordinator.setOverlayPresentationMode(.minimized)
+        waitForExpectations(timeout: 1.0)
+    }
+    
     func testEmbeddedStackPresentsSheetThroughSplit() {
         let sidebarNavigationStackCoordinator = NavigationStackCoordinator(navigationSplitCoordinator: navigationSplitCoordinator)
         sidebarNavigationStackCoordinator.setRootCoordinator(SomeTestCoordinator())