feat: add splash window.

src/Ursa/Windows/SplashWindow.cs

@@ -0,0 +1,56 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Interactivity;
+using Avalonia.Threading;
+
+namespace Ursa.Controls;
+
+public abstract class SplashWindow: Window
+{
+    public static readonly StyledProperty<TimeSpan?> CountDownProperty = AvaloniaProperty.Register<SplashWindow, TimeSpan?>(
+        nameof(CountDown));
+
+    public TimeSpan? CountDown
+    {
+        get => GetValue(CountDownProperty);
+        set => SetValue(CountDownProperty, value);
+    }
+
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+        if (CountDown != null && CountDown != TimeSpan.Zero)
+        {
+            DispatcherTimer.RunOnce(Close, CountDown.Value);
+        }
+    }
+
+    protected virtual Task<bool> CanClose() => Task.FromResult(true);
+    protected abstract Task<Window> CreateNextWindow();
+    
+    private bool _canClose;
+    
+    protected override sealed async void OnClosing(WindowClosingEventArgs e)
+    {
+        VerifyAccess();
+        if (!_canClose)
+        {
+            e.Cancel = true;
+            _canClose = await CanClose();
+            if (_canClose)
+            {
+                var nextWindow = await CreateNextWindow();
+                if (Application.Current?.ApplicationLifetime is IClassicDesktopStyleApplicationLifetime lifetime)
+                {
+                    lifetime.MainWindow = nextWindow;
+                }
+                nextWindow.Show();
+                Close();
+                return;
+            }
+        }
+        base.OnClosing(e);
+        
+    }
+}