Added application session services, along with initial restore and tracker implementations.

Harmonia.WinUI/MainWindow.xaml.cs

@@ -1,3 +1,5 @@
+using Harmonia.WinUI.Session;
+using Microsoft.UI.Windowing;
 using Microsoft.UI.Xaml;
 
 namespace Harmonia.WinUI;
@@ -6,10 +8,17 @@ public sealed partial class MainWindow : Window
 {
     private const string ApplicationTitle = "Harmonia";
 
-    public MainWindow()
+    private readonly ISessionService _sessionService;
+
+    private bool _isSaved;
+
+    public MainWindow(ISessionService sessionService)
     {
+        _sessionService = sessionService;
+
         InitializeComponent();
         InitializeTitleBar();
+        InitializeWindowState();
     }
 
     private void InitializeTitleBar()
@@ -18,4 +27,39 @@ public sealed partial class MainWindow : Window
         ExtendsContentIntoTitleBar = true;
         SetTitleBar(AppTitleBar);
     }
+
+    private void InitializeWindowState()
+    {
+        if (AppWindow.Presenter is OverlappedPresenter presenter && _sessionService.Session.Window.IsMaximized)
+        {
+            presenter.Maximize();
+        }
+
+        AppWindow.Changed += OnAppWindowChanged;
+    }
+
+    private void OnAppWindowChanged(AppWindow sender, AppWindowChangedEventArgs args)
+    {
+        if (sender.Presenter is not OverlappedPresenter presenter)
+            return;
+
+        // Ignore the minimized state so a minimize-then-close doesn't lose the maximized flag.
+        if (presenter.State is OverlappedPresenterState.Minimized)
+            return;
+
+        _sessionService.Session.Window.IsMaximized = presenter.State == OverlappedPresenterState.Maximized;
+    }
+
+    private async void OnMainWindowClosed(object sender, WindowEventArgs args)
+    {
+        if (_isSaved)
+            return;
+
+        args.Handled = true;
+
+        await _sessionService.SaveAsync();
+
+        _isSaved = true;
+        Close();
+    }
 }