lightweight variant (#1)

Reviewed-on: #1
Co-authored-by: Aleksandr Neychev <alexnejchev73@gmail.com>

CursorLang.Settings/App.xaml.cs

@@ -0,0 +1,116 @@
+using System.Windows;
+using CursorLang.Core.Services;
+using CursorLang.Settings.Services;
+using CursorLang.Settings.ViewModels;
+using CursorLang.Settings.Views;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace CursorLang.Settings;
+
+/// <summary>
+/// The settings window as a process of its own.
+/// </summary>
+/// <remarks>
+/// It is started by the agent — from the tray menu, or straight away when the user
+/// launches the application themselves — and it ends when the window is closed. That
+/// is the whole point of the split: WPF costs around a hundred megabytes, and this way
+/// the system gets all of it back the moment the user is done, instead of the
+/// background process carrying it until sign-out.
+///
+/// Nothing here talks to the agent directly. Every edit goes into settings.json, and
+/// <see cref="SettingsService"/> nudges the agent to re-read it once the file is
+/// written. An agent that is not running is a normal case: the window works the same.
+/// </remarks>
+// ReSharper disable once RedundantExtendsListEntry
+public partial class App : Application
+{
+    private ServiceProvider? _services;
+    private SingleInstanceGate? _instanceGate;
+
+    protected override void OnStartup(StartupEventArgs e)
+    {
+        base.OnStartup(e);
+
+        var gate = new SingleInstanceGate(SingleInstanceGate.SettingsName);
+        if (!gate.TryAcquire(showRunningInstance: true))
+        {
+            gate.Dispose();
+            Shutdown();
+            return;
+        }
+
+        _instanceGate = gate;
+        _instanceGate.ActivationRequested += OnActivationRequested;
+
+        var services = new ServiceCollection();
+        ConfigureServices(services);
+        _services = services.BuildServiceProvider();
+
+        _services.GetRequiredService<SettingsService>().TrackChanges();
+        _services.GetRequiredService<ThemeService>();
+
+        MainWindow = _services.GetRequiredService<MainWindow>();
+
+        ShutdownMode = ShutdownMode.OnMainWindowClose;
+        MainWindow.Show();
+
+        _ = _services.GetRequiredService<SettingsViewModel>().InitializeAsync();
+        _ = _services.GetRequiredService<UpdateViewModel>().StartAsync();
+    }
+
+    protected override void OnExit(ExitEventArgs e)
+    {
+        _services?.Dispose();
+
+        if (_instanceGate is not null)
+        {
+            _instanceGate.ActivationRequested -= OnActivationRequested;
+            _instanceGate.Dispose();
+        }
+
+        base.OnExit(e);
+    }
+
+    internal static void ConfigureServices(IServiceCollection services)
+    {
+        services.AddSingleton(new UpdateOptions());
+
+        services.AddSingleton<SettingsService>();
+        services.AddSingleton(provider => provider.GetRequiredService<SettingsService>().Load());
+
+        services.AddSingleton<ThemeService>();
+        services.AddSingleton<IThemeService>(provider => provider.GetRequiredService<ThemeService>());
+
+        services.AddSingleton<MainWindowPlacement>();
+
+        services.AddSingleton<ILocalizationService, LocalizationService>();
+        services.AddSingleton<IStartupService, StartupService>();
+        services.AddSingleton<IUpdateService, UpdateService>();
+
+        services.AddSingleton<UpdateViewModel>();
+        services.AddSingleton<SettingsViewModel>();
+
+        services.AddSingleton<MainWindow>();
+    }
+
+    // A second launch — another click on "Settings" in the tray menu, say. The gate
+    // answers on a thread pool thread, and a window obeys only its own
+    private void OnActivationRequested(object? sender, EventArgs e) =>
+        Dispatcher.BeginInvoke(ShowMainWindow);
+
+    private void ShowMainWindow()
+    {
+        if (MainWindow is not { } window)
+        {
+            return;
+        }
+
+        if (window.WindowState == WindowState.Minimized)
+        {
+            window.WindowState = WindowState.Normal;
+        }
+
+        window.Show();
+        window.Activate();
+    }
+}