Intercept back button when leaving an unsaved custom list

ios/MullvadVPN.xcodeproj/project.pbxproj

@@ -539,6 +539,7 @@
 		7A6F2FAB2AFD3097006D0856 /* CustomDNSCellFactory.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7A6F2FAA2AFD3097006D0856 /* CustomDNSCellFactory.swift */; };
 		7A6F2FAD2AFD3DA7006D0856 /* CustomDNSViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7A6F2FAC2AFD3DA7006D0856 /* CustomDNSViewController.swift */; };
 		7A6F2FAF2AFE36E7006D0856 /* VPNSettingsInfoButtonItem.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7A6F2FAE2AFE36E7006D0856 /* VPNSettingsInfoButtonItem.swift */; };
+		7A7907332BC0280A00B61F81 /* InterceptibleNavigationController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7A7907322BC0280A00B61F81 /* InterceptibleNavigationController.swift */; };
 		7A7AD28D29DC677800480EF1 /* FirstTimeLaunch.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7A7AD28C29DC677800480EF1 /* FirstTimeLaunch.swift */; };
 		7A818F1F29F0305800C7F0F4 /* RootConfiguration.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7A818F1E29F0305800C7F0F4 /* RootConfiguration.swift */; };
 		7A83A0C62B29A750008B5CE7 /* APIAccessMethodsTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7A83A0C52B29A750008B5CE7 /* APIAccessMethodsTests.swift */; };
@@ -1803,6 +1804,7 @@
 		7A6F2FAA2AFD3097006D0856 /* CustomDNSCellFactory.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CustomDNSCellFactory.swift; sourceTree = "<group>"; };
 		7A6F2FAC2AFD3DA7006D0856 /* CustomDNSViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CustomDNSViewController.swift; sourceTree = "<group>"; };
 		7A6F2FAE2AFE36E7006D0856 /* VPNSettingsInfoButtonItem.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = VPNSettingsInfoButtonItem.swift; sourceTree = "<group>"; };
+		7A7907322BC0280A00B61F81 /* InterceptibleNavigationController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = InterceptibleNavigationController.swift; sourceTree = "<group>"; };
 		7A7AD28C29DC677800480EF1 /* FirstTimeLaunch.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FirstTimeLaunch.swift; sourceTree = "<group>"; };
 		7A818F1E29F0305800C7F0F4 /* RootConfiguration.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RootConfiguration.swift; sourceTree = "<group>"; };
 		7A83A0C52B29A750008B5CE7 /* APIAccessMethodsTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = APIAccessMethodsTests.swift; sourceTree = "<group>"; };
@@ -2692,6 +2694,7 @@
 				58138E60294871C600684F0C /* DeviceDataThrottling.swift */,
 				7A7AD28C29DC677800480EF1 /* FirstTimeLaunch.swift */,
 				582AE30F2440A6CA00E6733A /* InputTextFormatter.swift */,
+				7A7907322BC0280A00B61F81 /* InterceptibleNavigationController.swift */,
 				58DFF7D12B0256A300F864E0 /* MarkdownStylingOptions.swift */,
 				58CC40EE24A601900019D96E /* ObserverList.swift */,
 			);
@@ -5459,6 +5462,7 @@
 				7A42DEC92A05164100B209BE /* SettingsInputCell.swift in Sources */,
 				5803B4B22940A48700C23744 /* TunnelStore.swift in Sources */,
 				586A950F29012BEE007BAF2B /* AddressCacheTracker.swift in Sources */,
+				7A7907332BC0280A00B61F81 /* InterceptibleNavigationController.swift in Sources */,
 				F02F41A02B9723AF00625A4F /* AddLocationsViewController.swift in Sources */,
 				587B753D2666468F00DEF7E9 /* NotificationController.swift in Sources */,
 			);

ios/MullvadVPN/Classes/InterceptibleNavigationController.swift

@@ -0,0 +1,36 @@
+//
+//  InterceptibleNavigationController.swift
+//  MullvadVPN
+//
+//  Created by Jon Petersson on 2024-04-05.
+//  Copyright © 2024 Mullvad VPN AB. All rights reserved.
+//
+
+import UIKit
+
+class InterceptibleNavigationController: CustomNavigationController {
+    var shouldPopViewController: ((UIViewController) -> Bool)?
+    var shouldPopToViewController: ((UIViewController) -> Bool)?
+
+    // Called when popping the topmost view controller in the stack, eg. by pressing a navigation
+    // bar back button.
+    override func popViewController(animated: Bool) -> UIViewController? {
+        guard let viewController = viewControllers.last else { return nil }
+
+        if shouldPopViewController?(viewController) ?? true {
+            return super.popViewController(animated: animated)
+        } else {
+            return nil
+        }
+    }
+
+    // Called when popping to a specific view controller, eg. by long pressing a navigation bar
+    // back button (revealing a navigation menu) and selecting a destination view controller.
+    override func popToViewController(_ viewController: UIViewController, animated: Bool) -> [UIViewController]? {
+        if shouldPopToViewController?(viewController) ?? true {
+            return super.popToViewController(viewController, animated: animated)
+        } else {
+            return nil
+        }
+    }
+}

ios/MullvadVPN/Coordinators/CustomLists/AddCustomListCoordinator.swift

@@ -84,17 +84,10 @@ extension AddCustomListCoordinator: CustomListViewControllerDelegate {
         let coordinator = AddLocationsCoordinator(
             navigationController: navigationController,
             nodes: nodes,
-            customList: list
+            subject: subject
         )
 
-        coordinator.didFinish = { [weak self] locationsCoordinator, customList in
-            guard let self else { return }
-            subject.send(CustomListViewModel(
-                id: customList.id,
-                name: customList.name,
-                locations: customList.locations,
-                tableSections: subject.value.tableSections
-            ))
+        coordinator.didFinish = { locationsCoordinator in
             locationsCoordinator.removeFromParent()
         }
 

ios/MullvadVPN/Coordinators/CustomLists/AddLocationsCoordinator.swift

@@ -6,6 +6,7 @@
 //  Copyright © 2024 Mullvad VPN AB. All rights reserved.
 //
 
+import Combine
 import MullvadSettings
 import MullvadTypes
 import Routing
@@ -14,9 +15,9 @@ import UIKit
 class AddLocationsCoordinator: Coordinator, Presentable, Presenting {
     private let navigationController: UINavigationController
     private let nodes: [LocationNode]
-    private var customList: CustomList
+    private var subject: CurrentValueSubject<CustomListViewModel, Never>
 
-    var didFinish: ((AddLocationsCoordinator, CustomList) -> Void)?
+    var didFinish: ((AddLocationsCoordinator) -> Void)?
 
     var presentedViewController: UIViewController {
         navigationController
@@ -25,17 +26,17 @@ class AddLocationsCoordinator: Coordinator, Presentable, Presenting {
     init(
         navigationController: UINavigationController,
         nodes: [LocationNode],
-        customList: CustomList
+        subject: CurrentValueSubject<CustomListViewModel, Never>
     ) {
         self.navigationController = navigationController
         self.nodes = nodes
-        self.customList = customList
+        self.subject = subject
     }
 
     func start() {
         let controller = AddLocationsViewController(
             allLocationsNodes: nodes,
-            customList: customList
+            subject: subject
         )
         controller.delegate = self
 
@@ -51,11 +52,7 @@ class AddLocationsCoordinator: Coordinator, Presentable, Presenting {
 }
 
 extension AddLocationsCoordinator: AddLocationsViewControllerDelegate {
-    func didUpdateSelectedLocations(locations: [RelayLocation]) {
-        customList.locations = locations
-    }
-
     func didBack() {
-        didFinish?(self, customList)
+        didFinish?(self)
     }
 }

ios/MullvadVPN/Coordinators/CustomLists/AddLocationsDataSource.swift

@@ -6,6 +6,7 @@
 //  Copyright © 2024 Mullvad VPN AB. All rights reserved.
 //
 
+import Combine
 import MullvadSettings
 import MullvadTypes
 import UIKit
@@ -15,20 +16,21 @@ class AddLocationsDataSource:
     LocationDiffableDataSourceProtocol {
     private var customListLocationNode: CustomListLocationNode
     private let nodes: [LocationNode]
-    var didUpdateCustomList: ((CustomListLocationNode) -> Void)?
+    private let subject: CurrentValueSubject<CustomListViewModel, Never>
     let tableView: UITableView
     let sections: [LocationSection]
 
     init(
         tableView: UITableView,
         allLocationNodes: [LocationNode],
-        customList: CustomList
+        subject: CurrentValueSubject<CustomListViewModel, Never>
     ) {
         self.tableView = tableView
         self.nodes = allLocationNodes
+        self.subject = subject
 
         self.customListLocationNode = CustomListLocationNodeBuilder(
-            customList: customList,
+            customList: subject.value.customList,
             allLocations: self.nodes
         ).customListLocationNode
 
@@ -51,10 +53,12 @@ class AddLocationsDataSource:
         reloadWithSelectedLocations()
     }
 
+    // Called from `LocationDiffableDataSourceProtocol`.
     func nodeShowsChildren(_ node: LocationNode) -> Bool {
         isLocationInCustomList(node: node)
     }
 
+    // Called from `LocationDiffableDataSourceProtocol`.
     func nodeShouldBeSelected(_ node: LocationNode) -> Bool {
         customListLocationNode.children.contains(node)
     }
@@ -149,7 +153,10 @@ extension AddLocationsDataSource: LocationCellDelegate {
             customListLocationNode.remove(selectedLocation: item.node, with: locationList)
         }
         updateDataSnapshot(with: [locationList], completion: {
-            self.didUpdateCustomList?(self.customListLocationNode)
+            let locations = self.customListLocationNode.children.reduce([]) { partialResult, locationNode in
+                partialResult + locationNode.locations
+            }
+            self.subject.value.locations = locations
         })
     }
 }

ios/MullvadVPN/Coordinators/CustomLists/AddLocationsViewController.swift

@@ -6,19 +6,19 @@
 //  Copyright © 2024 Mullvad VPN AB. All rights reserved.
 //
 
+import Combine
 import MullvadSettings
 import MullvadTypes
 import UIKit
 
 protocol AddLocationsViewControllerDelegate: AnyObject {
-    func didUpdateSelectedLocations(locations: [RelayLocation])
     func didBack()
 }
 
 class AddLocationsViewController: UIViewController {
     private var dataSource: AddLocationsDataSource?
     private let nodes: [LocationNode]
-    private let customList: CustomList
+    private let subject: CurrentValueSubject<CustomListViewModel, Never>
 
     weak var delegate: AddLocationsViewControllerDelegate?
     private let tableView: UITableView = {
@@ -33,10 +33,10 @@ class AddLocationsViewController: UIViewController {
 
     init(
         allLocationsNodes: [LocationNode],
-        customList: CustomList
+        subject: CurrentValueSubject<CustomListViewModel, Never>
     ) {
         self.nodes = allLocationsNodes
-        self.customList = customList
+        self.subject = subject
         super.init(nibName: nil, bundle: nil)
     }
 
@@ -70,17 +70,8 @@ class AddLocationsViewController: UIViewController {
         dataSource = AddLocationsDataSource(
             tableView: tableView,
             allLocationNodes: nodes.copy(),
-            customList: customList
+            subject: subject
         )
-
-        dataSource?.didUpdateCustomList = { [weak self] customListLocationNode in
-            guard let self else { return }
-            delegate?.didUpdateSelectedLocations(
-                locations: customListLocationNode.children.reduce([]) { partialResult, locationNode in
-                    partialResult + locationNode.locations
-                }
-            )
-        }
     }
 }
 

ios/MullvadVPN/Coordinators/CustomLists/CustomListViewController.swift

@@ -27,6 +27,14 @@ class CustomListViewController: UIViewController {
     private let alertPresenter: AlertPresenter
     private var validationErrors: Set<CustomListFieldValidationError> = []
 
+    private var persistedCustomList: CustomList? {
+        return interactor.fetchAll().first(where: { $0.id == subject.value.id })
+    }
+
+    private var customListHasUnsavedChanges: Bool {
+        return persistedCustomList != subject.value.customList
+    }
+
     private lazy var cellConfiguration: CustomListCellConfiguration = {
         CustomListCellConfiguration(tableView: tableView, subject: subject)
     }()
@@ -91,9 +99,38 @@ class CustomListViewController: UIViewController {
     }
 
     private func configureNavigationItem() {
+        if let navigationController = navigationController as? InterceptibleNavigationController {
+            interceptNavigation(navigationController)
+        }
+
+        navigationController?.interactivePopGestureRecognizer?.delegate = self
         navigationItem.rightBarButtonItem = saveBarButton
     }
 
+    private func interceptNavigation(_ navigationController: InterceptibleNavigationController) {
+        navigationController.shouldPopViewController = { [weak self] viewController in
+            guard
+                let self,
+                viewController is Self,
+                customListHasUnsavedChanges
+            else { return true }
+
+            self.onUnsavedChanges()
+            return false
+        }
+
+        navigationController.shouldPopToViewController = { [weak self] viewController in
+            guard
+                let self,
+                viewController is ListCustomListViewController,
+                customListHasUnsavedChanges
+            else { return true }
+
+            self.onUnsavedChanges()
+            return false
+        }
+    }
+
     private func configureTableView() {
         tableView.delegate = dataSourceConfiguration
         tableView.backgroundColor = .secondaryColor
@@ -195,4 +232,68 @@ class CustomListViewController: UIViewController {
 
         alertPresenter.showAlert(presentation: presentation, animated: true)
     }
+
+    @objc private func onUnsavedChanges() {
+        let message = NSMutableAttributedString(
+            markdownString: NSLocalizedString(
+                "CUSTOM_LISTS_UNSAVED_CHANGES_PROMPT",
+                tableName: "CustomLists",
+                value: "You have unsaved changes.",
+                comment: ""
+            ),
+            options: MarkdownStylingOptions(font: .preferredFont(forTextStyle: .body))
+        )
+
+        let presentation = AlertPresentation(
+            id: "api-custom-lists-unsaved-changes-alert",
+            icon: .alert,
+            attributedMessage: message,
+            buttons: [
+                AlertAction(
+                    title: NSLocalizedString(
+                        "CUSTOM_LISTS_DISCARD_CHANGES_BUTTON",
+                        tableName: "CustomLists",
+                        value: "Discard changes",
+                        comment: ""
+                    ),
+                    style: .destructive,
+                    handler: {
+                        // Reset subject/view model to no longer having unsaved changes.
+                        if let persistedCustomList = self.persistedCustomList {
+                            self.subject.value.update(with: persistedCustomList)
+                        }
+                        self.delegate?.customListDidSave(self.subject.value.customList)
+                    }
+                ),
+                AlertAction(
+                    title: NSLocalizedString(
+                        "CUSTOM_LISTS_BACK_TO_EDITING_BUTTON",
+                        tableName: "CustomLists",
+                        value: "Back to editing",
+                        comment: ""
+                    ),
+                    style: .default
+                ),
+            ]
+        )
+
+        alertPresenter.showAlert(presentation: presentation, animated: true)
+    }
+}
+
+extension CustomListViewController: UIGestureRecognizerDelegate {
+    // For some reason, intercepting `popViewController(animated: Bool)` in `InterceptibleNavigationController`
+    // by SWIPING back leads to weird behaviour where subsequent navigation seem to happen systemwise but not
+    // UI-wise. This leads to the UI freezing up, and the only remedy is to restart the app.
+    //
+    // To get around this issue we can intercept the back swipe gesture and manually perform the transtion
+    // instead, thereby bypassing the inner mechanisms that go out of sync.
+    func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
+        guard gestureRecognizer == navigationController?.interactivePopGestureRecognizer else {
+            return true
+        }
+
+        navigationController?.popViewController(animated: true)
+        return false
+    }
 }

ios/MullvadVPN/Coordinators/CustomLists/CustomListViewModel.swift

@@ -18,4 +18,9 @@ struct CustomListViewModel {
     var customList: CustomList {
         CustomList(id: id, name: name, locations: locations)
     }
+
+    mutating func update(with list: CustomList) {
+        name = list.name
+        locations = list.locations
+    }
 }