fix(launcher): close LA4 review findings

src/AcDream.Launcher/MainWindow.axaml.cs

@@ -1,5 +1,7 @@
+using System.ComponentModel;
 using AcDream.Launcher.ViewModels;
 using Avalonia.Controls;
+using Avalonia.Input;
 using Avalonia.Markup.Xaml;
 using Avalonia.Threading;
 
@@ -8,6 +10,9 @@ namespace AcDream.Launcher;
 public sealed partial class MainWindow : Window
 {
     private readonly DispatcherTimer _statusTimer;
+    private LauncherWindowViewModel? _observedViewModel;
+    private Control? _focusBeforeModal;
+    private bool _wasModalOpen;
 
     public MainWindow()
     {
@@ -17,6 +22,7 @@ public sealed partial class MainWindow : Window
             Interval = TimeSpan.FromMilliseconds(250),
         };
         _statusTimer.Tick += OnStatusTimerTick;
+        DataContextChanged += OnDataContextChanged;
         Opened += OnOpened;
         Closed += OnClosed;
     }
@@ -27,6 +33,8 @@ public sealed partial class MainWindow : Window
     {
         _statusTimer.Stop();
         _statusTimer.Tick -= OnStatusTimerTick;
+        DataContextChanged -= OnDataContextChanged;
+        ObserveViewModel(null);
         Opened -= OnOpened;
         Closed -= OnClosed;
     }
@@ -38,4 +46,92 @@ public sealed partial class MainWindow : Window
             viewModel.PollStatus();
         }
     }
+
+    private void OnDataContextChanged(object? sender, EventArgs e) =>
+        ObserveViewModel(DataContext as LauncherWindowViewModel);
+
+    private void ObserveViewModel(LauncherWindowViewModel? viewModel)
+    {
+        if (ReferenceEquals(_observedViewModel, viewModel))
+        {
+            return;
+        }
+
+        if (_observedViewModel is not null)
+        {
+            _observedViewModel.PropertyChanged -= OnViewModelPropertyChanged;
+        }
+
+        _observedViewModel = viewModel;
+        if (_observedViewModel is not null)
+        {
+            _observedViewModel.PropertyChanged += OnViewModelPropertyChanged;
+        }
+
+        _wasModalOpen = viewModel?.IsModalOpen == true;
+    }
+
+    private void OnViewModelPropertyChanged(object? sender, PropertyChangedEventArgs e)
+    {
+        if (e.PropertyName != nameof(LauncherWindowViewModel.IsModalOpen)
+            || sender is not LauncherWindowViewModel viewModel)
+        {
+            return;
+        }
+
+        bool isModalOpen = viewModel.IsModalOpen;
+        if (isModalOpen && !_wasModalOpen)
+        {
+            _focusBeforeModal = TopLevel.GetTopLevel(this)?.FocusManager?.GetFocusedElement() as Control;
+            Dispatcher.UIThread.Post(() => FocusActiveModal(viewModel));
+        }
+        else if (!isModalOpen && _wasModalOpen)
+        {
+            Control? focusToRestore = _focusBeforeModal;
+            _focusBeforeModal = null;
+            Dispatcher.UIThread.Post(() =>
+            {
+                if (focusToRestore?.Focus() != true)
+                {
+                    ProfilesTree.Focus();
+                }
+            });
+        }
+
+        _wasModalOpen = isModalOpen;
+    }
+
+    private void FocusActiveModal(LauncherWindowViewModel viewModel)
+    {
+        if (viewModel.EditorDialog.IsOpen)
+        {
+            Control target = viewModel.EditorDialog.Kind switch
+            {
+                ProfileEditorKind.AddServer or ProfileEditorKind.EditServer => ServerNameTextBox,
+                ProfileEditorKind.AddAccount or ProfileEditorKind.EditAccount => AccountNameTextBox,
+                ProfileEditorKind.AddCharacter or ProfileEditorKind.EditCharacter => CharacterNameTextBox,
+                _ => EditorSubmitButton,
+            };
+            target.Focus();
+        }
+        else if (viewModel.FirstRunWizardShell.IsOpen)
+        {
+            FirstRunCloseButton.Focus();
+        }
+        else if (viewModel.UpdatePromptShell.IsOpen)
+        {
+            UpdateCloseButton.Focus();
+        }
+    }
+
+    private void OnModalKeyDown(object? sender, KeyEventArgs e)
+    {
+        if (e.Key != Key.Escape || DataContext is not LauncherWindowViewModel viewModel)
+        {
+            return;
+        }
+
+        viewModel.CloseActiveModal();
+        e.Handled = true;
+    }
 }