Support for Undo

Examples/Reminders/README.md

@@ -4,6 +4,10 @@ A rebuild of many of the features from Apple's [Reminders app][reminders-app-sto
 for reminders, lists and tags in a SQLite database, and uses foreign keys to express one-to-many
 and many-to-many relationships between the entities.
 
+The sample configures a default undo manager so local and synced changes can be undone/redone from
+the screen menu using Undo/Redo entries that trigger immediately. It also binds to Apple's
+`UndoManager` so system undo gestures (including shake to undo) work with the same stack.
+
 It also demonstrates how to perform very advanced queries in SQLite that would be impossible in
 SwiftData, such as using SQLite's `group_concat` function to fetch all reminders along with a 
 comma-separated list of all of its tags. SQLite is an incredibly powerful language, and one should

Examples/Reminders/ReminderForm.swift

@@ -169,7 +169,11 @@ struct ReminderFormView: View {
 
   private func saveButtonTapped() {
     withErrorReporting {
-      try database.write { db in
+      try database.writeWithUndoGroup(
+        reminder.id == nil
+          ? "Create reminder"
+          : "Edit reminder"
+      ) { db in
         let reminderID = try Reminder.upsert { reminder }
           .returning(\.id)
           .fetchOne(db)!

Examples/Reminders/ReminderRow.swift

@@ -76,14 +76,18 @@ struct ReminderRow: View {
     .swipeActions {
       Button("Delete", role: .destructive) {
         withErrorReporting {
-          try database.write { db in
+          try database.writeWithUndoGroup("Delete reminder") { db in
             try Reminder.delete(reminder).execute(db)
           }
         }
       }
       Button(reminder.isFlagged ? "Unflag" : "Flag") {
         withErrorReporting {
-          try database.write { db in
+          try database.writeWithUndoGroup(
+            reminder.isFlagged
+              ? "Unflag reminder"
+              : "Flag reminder"
+          ) { db in
             try Reminder
               .find(reminder.id)
               .update { $0.isFlagged.toggle() }
@@ -106,7 +110,11 @@ struct ReminderRow: View {
 
   private func completeButtonTapped() {
     withErrorReporting {
-      try database.write { db in
+      try database.writeWithUndoGroup(
+        reminder.isCompleted
+          ? "Mark reminder incomplete"
+          : "Mark reminder complete"
+      ) { db in
         try Reminder
           .find(reminder.id)
           .update { $0.toggleStatus() }

Examples/Reminders/RemindersApp.swift

@@ -14,11 +14,15 @@ struct RemindersApp: App {
   static let model = RemindersListsModel()
 
   @State var syncEngineDelegate = RemindersSyncEngineDelegate()
+  @State var undoManagerDelegate = RemindersUndoManagerDelegate()
 
   init() {
     if context == .live {
       try! prepareDependencies {
-        try $0.bootstrapDatabase(syncEngineDelegate: syncEngineDelegate)
+        try $0.bootstrapDatabase(
+          syncEngineDelegate: syncEngineDelegate,
+          undoManagerDelegate: undoManagerDelegate
+        )
       }
     }
   }
@@ -29,6 +33,7 @@ struct RemindersApp: App {
         NavigationStack {
           RemindersListsView(model: Self.model)
         }
+        .bindSQLiteUndoManagerToSystemUndo()
         .alert(
           "Reset local data?",
           isPresented: $syncEngineDelegate.isDeleteLocalDataAlertPresented
@@ -46,6 +51,18 @@ struct RemindersApp: App {
             """
           )
         }
+        .alert(item: $undoManagerDelegate.confirmationRequest) { request in
+          Alert(
+            title: Text(request.title),
+            message: Text(request.message),
+            primaryButton: .destructive(Text(request.confirmButtonTitle)) {
+              undoManagerDelegate.respondToConfirmation(confirmed: true)
+            },
+            secondaryButton: .cancel {
+              undoManagerDelegate.respondToConfirmation(confirmed: false)
+            }
+          )
+        }
       }
     }
   }
@@ -70,6 +87,103 @@ class RemindersSyncEngineDelegate: SyncEngineDelegate {
   }
 }
 
+@MainActor
+@Observable
+final class RemindersUndoManagerDelegate: SQLiteData.UndoManagerDelegate {
+  enum ConfirmationReason {
+    /// The group itself came from syncing.
+    case syncOrigin
+    /// The group is local but remote sync changes have arrived since.
+    case syncChangesSinceRedo
+  }
+
+  struct ConfirmationRequest: Identifiable {
+    let action: UndoAction
+    let group: UndoGroup
+    let reason: ConfirmationReason
+    var id: UUID { group.id }
+    var title: String {
+      switch action {
+      case .undo: "Undo \"\(group.description)\"?"
+      case .redo: "Redo \"\(group.description)\"?"
+      }
+    }
+    var message: String {
+      switch reason {
+      case .syncOrigin:
+        "This change came from syncing. Are you sure you want to continue?"
+      case .syncChangesSinceRedo:
+        """
+        Changes from another device or user have been applied since this action and could \
+        potentially conflict with the changes you are trying to redo.
+        """
+      }
+    }
+    var confirmButtonTitle: String {
+      switch action {
+      case .undo: "Undo"
+      case .redo: "Redo"
+      }
+    }
+  }
+
+  var confirmationRequest: ConfirmationRequest?
+  private var confirmationContinuation: CheckedContinuation<Bool, Never>?
+
+  func undoManager(
+    _ undoManager: SQLiteData.UndoManager,
+    willPerform action: UndoAction,
+    for group: UndoGroup,
+    performAction: @isolated(any) @Sendable () async throws -> Void
+  ) async throws {
+    guard let reason = confirmationReason(
+      undoManager: undoManager, action: action, group: group
+    ) else {
+      try await performAction()
+      return
+    }
+    if await requestConfirmation(action: action, group: group, reason: reason) {
+      try await performAction()
+    }
+  }
+
+  func respondToConfirmation(confirmed: Bool) {
+    confirmationContinuation?.resume(returning: confirmed)
+    confirmationContinuation = nil
+    confirmationRequest = nil
+  }
+
+  private func confirmationReason(
+    undoManager: SQLiteData.UndoManager,
+    action: UndoAction,
+    group: UndoGroup
+  ) -> ConfirmationReason? {
+    if action == .undo && group.isSharedZoneChange {
+      return .syncOrigin
+    }
+    if action == .redo && undoManager.hasSyncChangesSince(group) {
+      return .syncChangesSinceRedo
+    }
+    return nil
+  }
+
+  private func requestConfirmation(
+    action: UndoAction,
+    group: UndoGroup,
+    reason: ConfirmationReason
+  ) async -> Bool {
+    if confirmationContinuation != nil {
+      respondToConfirmation(confirmed: false)
+    }
+    return await withCheckedContinuation { continuation in
+      confirmationContinuation = continuation
+      confirmationRequest = ConfirmationRequest(
+        action: action, group: group, reason: reason
+      )
+    }
+  }
+}
+
 class AppDelegate: UIResponder, UIApplicationDelegate, ObservableObject {
   func application(
     _ application: UIApplication,

Examples/Reminders/RemindersDetail.swift

@@ -50,7 +50,7 @@ class RemindersDetailModel: HashableObject {
 
   func move(from source: IndexSet, to destination: Int) async {
     withErrorReporting {
-      try database.write { db in
+      try database.writeWithUndoGroup("Reorder reminders") { db in
         var ids = reminderRows.map(\.reminder.id)
         ids.move(fromOffsets: source, toOffset: destination)
         try Reminder
@@ -252,6 +252,9 @@ struct RemindersDetailView: View {
             }
           }
           Menu {
+            UndoMenuItems()
+              .tint(model.detailType.color)
+            Divider()
             Group {
               Menu {
                 ForEach(RemindersDetailModel.Ordering.allCases, id: \.self) { ordering in

Examples/Reminders/RemindersListForm.swift

@@ -77,7 +77,11 @@ struct RemindersListForm: View {
         Button("Save") {
           Task { [remindersList, coverImageData] in
             await withErrorReporting {
-              try await database.write { db in
+              try await database.writeWithUndoGroup(
+                remindersList.id == nil
+                  ? "Create list"
+                  : "Edit list"
+              ) { db in
                 let remindersListID =
                   try RemindersList
                   .upsert { remindersList }

Examples/Reminders/RemindersListRow.swift

@@ -35,7 +35,7 @@ struct RemindersListRow: View {
     .swipeActions {
       Button {
         withErrorReporting {
-          try database.write { db in
+          try database.writeWithUndoGroup("Delete list") { db in
             try RemindersList.delete(remindersList)
               .execute(db)
           }

Examples/Reminders/RemindersLists.swift

@@ -55,6 +55,10 @@ class RemindersListsModel {
 
   @ObservationIgnored
   @Dependency(\.defaultDatabase) private var database
+  @ObservationIgnored
+  @Dependency(\.defaultUndoManager) private var undoManager
+  @ObservationIgnored
+  private var undoEventsTask: Task<Void, Never>?
 
   func statTapped(_ detailType: RemindersDetailModel.DetailType) {
     destination = .detail(RemindersDetailModel(detailType: detailType))
@@ -81,7 +85,7 @@ class RemindersListsModel {
   func deleteTags(atOffsets offsets: IndexSet) {
     withErrorReporting {
       let tagTitles = offsets.map { tags[$0].title }
-      try database.write { db in
+      try database.writeWithUndoGroup("Delete tags") { db in
         try Tag
           .where { $0.title.in(tagTitles) }
           .delete()
@@ -91,6 +95,7 @@ class RemindersListsModel {
   }
 
   func onAppear() {
+    observeUndoEventsIfNeeded()
     withErrorReporting {
       try Tips.configure()
     }
@@ -121,7 +126,7 @@ class RemindersListsModel {
 
   func move(from source: IndexSet, to destination: Int) {
     withErrorReporting {
-      try database.write { db in
+      try database.writeWithUndoGroup("Reorder lists") { db in
         var ids = remindersLists.map(\.remindersList.id)
         ids.move(fromOffsets: source, toOffset: destination)
         try RemindersList
@@ -143,12 +148,46 @@ class RemindersListsModel {
 
   #if DEBUG
     func seedDatabaseButtonTapped() {
-      withErrorReporting {
-        try database.seedSampleData()
+      Task {
+        withErrorReporting {
+          try database.writeWithoutUndoGroup {
+            try database.seedSampleData()
+          }
+        }
       }
     }
   #endif
 
+  deinit {
+    undoEventsTask?.cancel()
+  }
+
+  private func observeUndoEventsIfNeeded() {
+    guard undoEventsTask == nil, let undoManager else { return }
+    undoEventsTask = Task { [weak self] in
+      guard let self else { return }
+      for await event in undoManager.events {
+        await self.handleUndoEvent(event)
+      }
+    }
+  }
+
+  private func handleUndoEvent(_ event: UndoEvent) async {
+    guard event.kind == .undo else { return }
+    guard event.affectedRows.contains(where: { $0.tableName == RemindersList.tableName }) else { return }
+    guard case let .detail(detailModel)? = destination else { return }
+    guard case let .remindersList(remindersList) = detailModel.detailType else { return }
+
+    await withErrorReporting {
+      let isStillPresent = try await database.read { db in
+        try RemindersList.find(remindersList.id).fetchOne(db) != nil
+      }
+      if !isStillPresent {
+        destination = nil
+      }
+    }
+  }
+
   @CasePathable
   enum Destination {
     case detail(RemindersDetailModel)
@@ -312,9 +351,11 @@ struct RemindersListsView: View {
     }
     .listStyle(.insetGrouped)
     .toolbar {
-      #if DEBUG
-        ToolbarItem(placement: .automatic) {
-          Menu {
+      ToolbarItem(placement: .primaryAction) {
+        Menu {
+          UndoMenuItems()
+          #if DEBUG
+            Divider()
             Button {
               model.seedDatabaseButtonTapped()
             } label: {
@@ -335,12 +376,12 @@ struct RemindersListsView: View {
               Text("\(syncEngine.isRunning ? "Stop" : "Start") synchronizing")
               Image(systemName: syncEngine.isRunning ? "stop" : "play")
             }
-          } label: {
-            Image(systemName: "ellipsis.circle")
-          }
-          .popoverTip(model.seedDatabaseTip)
+          #endif
+        } label: {
+          Image(systemName: "ellipsis.circle")
         }
-      #endif
+        .popoverTip(model.seedDatabaseTip)
+      }
       ToolbarItem(placement: .bottomBar) {
         HStack {
           Button {