Fixes #4456 - Clear MouseGrabView in App.End (#4460)

* Fixed MouseGrabView bug.

Added extensive test coverage for `Keyboard`, `Mouse`, `Timeout`, and `Popover` functionalities, including edge cases and concurrent access. Introduced parameterized and data-driven tests to reduce redundancy and improve clarity.

Refactored codebase for modularity and maintainability,
introducing new namespaces and reorganizing classes. Enhanced `MouseImpl`, `KeyboardImpl`, and `Runnable` implementations with improved event handling, thread safety, and support for the Terminal.Gui Cancellable Work Pattern (CWP).

Removed deprecated code and legacy tests, such as `LogarithmicTimeout` and `SmoothAcceleratingTimeout`. Fixed bugs related to mouse grabbing during drag operations and unbalanced `ApplicationImpl.Begin/End` calls. Improved documentation and code readability with modern C# features.

* Code cleanup.

* Update Tests/UnitTestsParallelizable/Application/Runnable/RunnableIntegrationTests.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Improve null handling and simplify test setup

In `MouseImpl.cs`, added an early `return` after the `UngrabMouse()`
call within the `if (view is null)` block to prevent further execution
when `view` is `null`, improving null reference handling.

In `RunnableIntegrationTests.cs`, removed the initialization of the
`IApplication` object (`app`) from the `MultipleRunnables_IndependentResults`
test method, simplifying the test setup and focusing on runnable behavior.

* Code cleanup

* API doc link cleanup

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Tests/UnitTestsParallelizable/Application/Mouse/ApplicationMouseEnterLeaveTests.cs

@@ -0,0 +1,454 @@
+#nullable enable
+using System.ComponentModel;
+
+namespace ApplicationTests.Mouse;
+
+[Trait ("Category", "Input")]
+public class ApplicationMouseEnterLeaveTests
+{
+    private class TestView : View
+    {
+        public TestView ()
+        {
+            X = 1;
+            Y = 1;
+            Width = 1;
+            Height = 1;
+        }
+
+       // public bool CancelOnEnter { get; }
+        public int OnMouseEnterCalled { get; private set; }
+        public int OnMouseLeaveCalled { get; private set; }
+
+        protected override bool OnMouseEnter (CancelEventArgs eventArgs)
+        {
+            OnMouseEnterCalled++;
+           // eventArgs.Cancel = CancelOnEnter;
+
+            base.OnMouseEnter (eventArgs);
+
+            return eventArgs.Cancel;
+        }
+
+        protected override void OnMouseLeave ()
+        {
+            OnMouseLeaveCalled++;
+
+            base.OnMouseLeave ();
+        }
+    }
+
+    [Fact]
+    public void RaiseMouseEnterLeaveEvents_MouseEntersView_CallsOnMouseEnter ()
+    {
+        IApplication? app = Application.Create ();
+        Runnable<bool> runnable = new () { Frame = new (0, 0, 10, 10) };
+        app.Begin (runnable);
+
+        // Arrange
+        var view = new TestView ();
+        runnable.Add (view);
+        var mousePosition = new Point (1, 1);
+        List<View?> currentViewsUnderMouse = [view];
+
+        var mouseEvent = new MouseEventArgs
+        {
+            Position = mousePosition,
+            ScreenPosition = mousePosition
+        };
+
+        app.Mouse.CachedViewsUnderMouse.Clear ();
+
+        try
+        {
+            // Act
+            app.Mouse.RaiseMouseEnterLeaveEvents (mousePosition, currentViewsUnderMouse);
+
+            // Assert
+            Assert.Equal (1, view.OnMouseEnterCalled);
+        }
+        finally
+        {
+            // Cleanup
+            app.Mouse.ResetState ();
+        }
+    }
+
+    [Fact]
+    public void RaiseMouseEnterLeaveEvents_MouseLeavesView_CallsOnMouseLeave ()
+    {
+        // Arrange
+        IApplication? app = Application.Create ();
+        Runnable<bool> runnable = new () { Frame = new (0, 0, 10, 10) };
+        app.Begin (runnable);
+
+        var view = new TestView ();
+        runnable.Add (view);
+        var mousePosition = new Point (0, 0);
+        List<View?> currentViewsUnderMouse = new ();
+        var mouseEvent = new MouseEventArgs ();
+
+        app.Mouse.CachedViewsUnderMouse.Clear ();
+        app.Mouse.CachedViewsUnderMouse.Add (view);
+
+        // Act
+        app.Mouse.RaiseMouseEnterLeaveEvents (mousePosition, currentViewsUnderMouse);
+
+        // Assert
+        Assert.Equal (0, view.OnMouseEnterCalled);
+        Assert.Equal (1, view.OnMouseLeaveCalled);
+    }
+
+    [Fact]
+    public void RaiseMouseEnterLeaveEvents_MouseMovesBetweenAdjacentViews_CallsOnMouseEnterAndLeave ()
+    {
+        // Arrange
+        IApplication? app = Application.Create ();
+        Runnable<bool> runnable = new () { Frame = new (0, 0, 10, 10) };
+        app.Begin (runnable);
+        var view1 = new TestView (); // at 1,1 to 2,2
+
+        var view2 = new TestView () // at 2,2 to 3,3
+        {
+            X = 2,
+            Y = 2
+        };
+        runnable.Add (view1);
+        runnable.Add (view2);
+
+        app.Mouse.CachedViewsUnderMouse.Clear ();
+
+        // Act
+        var mousePosition = new Point (0, 0);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (0, view1.OnMouseEnterCalled);
+        Assert.Equal (0, view1.OnMouseLeaveCalled);
+        Assert.Equal (0, view2.OnMouseEnterCalled);
+        Assert.Equal (0, view2.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (1, 1);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (0, view1.OnMouseLeaveCalled);
+        Assert.Equal (0, view2.OnMouseEnterCalled);
+        Assert.Equal (0, view2.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (2, 2);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (1, view1.OnMouseLeaveCalled);
+        Assert.Equal (1, view2.OnMouseEnterCalled);
+        Assert.Equal (0, view2.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (3, 3);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                                mousePosition,
+                                                runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (1, view1.OnMouseLeaveCalled);
+        Assert.Equal (1, view2.OnMouseEnterCalled);
+        Assert.Equal (1, view2.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (0, 0);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (1, view1.OnMouseLeaveCalled);
+        Assert.Equal (1, view2.OnMouseEnterCalled);
+        Assert.Equal (1, view2.OnMouseLeaveCalled);
+
+    }
+
+    [Fact]
+    public void RaiseMouseEnterLeaveEvents_NoViewsUnderMouse_DoesNotCallOnMouseEnterOrLeave ()
+    {
+        // Arrange
+        IApplication? app = Application.Create ();
+        Runnable<bool> runnable = new () { Frame = new (0, 0, 10, 10) };
+        app.Begin (runnable);
+        var view = new TestView ();
+        runnable.Add (view);
+        var mousePosition = new Point (0, 0);
+        List<View?> currentViewsUnderMouse = new ();
+        var mouseEvent = new MouseEventArgs ();
+
+        app.Mouse.CachedViewsUnderMouse.Clear ();
+
+        // Act
+        app.Mouse.RaiseMouseEnterLeaveEvents (mousePosition, currentViewsUnderMouse);
+
+        // Assert
+        Assert.Equal (0, view.OnMouseEnterCalled);
+        Assert.Equal (0, view.OnMouseLeaveCalled);
+
+    }
+
+    [Fact]
+    public void RaiseMouseEnterLeaveEvents_MouseMovesBetweenOverlappingPeerViews_CallsOnMouseEnterAndLeave ()
+    {
+        // Arrange
+        IApplication? app = Application.Create ();
+        Runnable<bool> runnable = new () { Frame = new (0, 0, 10, 10) };
+        app.Begin (runnable);
+
+        var view1 = new TestView
+        {
+            Width = 2
+        }; // at 1,1 to 3,2
+
+        var view2 = new TestView () // at 2,2 to 4,3
+        {
+            Width = 2,
+            X = 2,
+            Y = 2
+        };
+        runnable.Add (view1);
+        runnable.Add (view2);
+
+        app.Mouse.CachedViewsUnderMouse.Clear ();
+
+        // Act
+        var mousePosition = new Point (0, 0);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (0, view1.OnMouseEnterCalled);
+        Assert.Equal (0, view1.OnMouseLeaveCalled);
+        Assert.Equal (0, view2.OnMouseEnterCalled);
+        Assert.Equal (0, view2.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (1, 1);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (0, view1.OnMouseLeaveCalled);
+        Assert.Equal (0, view2.OnMouseEnterCalled);
+        Assert.Equal (0, view2.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (2, 2);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (1, view1.OnMouseLeaveCalled);
+        Assert.Equal (1, view2.OnMouseEnterCalled);
+        Assert.Equal (0, view2.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (3, 3);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (1, view1.OnMouseLeaveCalled);
+        Assert.Equal (1, view2.OnMouseEnterCalled);
+        Assert.Equal (1, view2.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (0, 0);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (1, view1.OnMouseLeaveCalled);
+        Assert.Equal (1, view2.OnMouseEnterCalled);
+        Assert.Equal (1, view2.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (2, 2);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (1, view1.OnMouseLeaveCalled);
+        Assert.Equal (2, view2.OnMouseEnterCalled);
+        Assert.Equal (1, view2.OnMouseLeaveCalled);
+
+    }
+
+    [Fact]
+    public void RaiseMouseEnterLeaveEvents_MouseMovesBetweenOverlappingSubViews_CallsOnMouseEnterAndLeave ()
+    {
+        // Arrange
+        IApplication? app = Application.Create ();
+        Runnable<bool> runnable = new () { Frame = new (0, 0, 10, 10) };
+        app.Begin (runnable);
+
+        var view1 = new TestView
+        {
+            Id = "view1",
+            Width = 2,
+            Height = 2,
+            Arrangement = ViewArrangement.Overlapped
+        }; // at 1,1 to 3,3 (screen)
+
+        var subView = new TestView
+        {
+            Id = "subView",
+            Width = 2,
+            Height = 2,
+            X = 1,
+            Y = 1,
+            Arrangement = ViewArrangement.Overlapped
+        }; // at 2,2 to 4,4 (screen)
+        view1.Add (subView);
+        runnable.Add (view1);
+
+        app.Mouse.CachedViewsUnderMouse.Clear ();
+
+        Assert.Equal (1, view1.FrameToScreen ().X);
+        Assert.Equal (2, subView.FrameToScreen ().X);
+
+        // Act
+        var mousePosition = new Point (0, 0);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (0, view1.OnMouseEnterCalled);
+        Assert.Equal (0, view1.OnMouseLeaveCalled);
+        Assert.Equal (0, subView.OnMouseEnterCalled);
+        Assert.Equal (0, subView.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (1, 1);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (0, view1.OnMouseLeaveCalled);
+        Assert.Equal (0, subView.OnMouseEnterCalled);
+        Assert.Equal (0, subView.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (2, 2);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (0, view1.OnMouseLeaveCalled);
+        Assert.Equal (1, subView.OnMouseEnterCalled);
+        Assert.Equal (0, subView.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (0, 0);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (1, view1.OnMouseEnterCalled);
+        Assert.Equal (1, view1.OnMouseLeaveCalled);
+        Assert.Equal (1, subView.OnMouseEnterCalled);
+        Assert.Equal (1, subView.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (2, 2);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (2, view1.OnMouseEnterCalled);
+        Assert.Equal (1, view1.OnMouseLeaveCalled);
+        Assert.Equal (2, subView.OnMouseEnterCalled);
+        Assert.Equal (1, subView.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (3, 3);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (2, view1.OnMouseEnterCalled);
+        Assert.Equal (2, view1.OnMouseLeaveCalled);
+        Assert.Equal (2, subView.OnMouseEnterCalled);
+        Assert.Equal (2, subView.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (0, 0);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (2, view1.OnMouseEnterCalled);
+        Assert.Equal (2, view1.OnMouseLeaveCalled);
+        Assert.Equal (2, subView.OnMouseEnterCalled);
+        Assert.Equal (2, subView.OnMouseLeaveCalled);
+
+        // Act
+        mousePosition = new (2, 2);
+
+        app.Mouse.RaiseMouseEnterLeaveEvents (
+                                              mousePosition,
+                                              runnable.GetViewsUnderLocation (mousePosition, ViewportSettingsFlags.TransparentMouse));
+
+        // Assert
+        Assert.Equal (3, view1.OnMouseEnterCalled);
+        Assert.Equal (2, view1.OnMouseLeaveCalled);
+        Assert.Equal (3, subView.OnMouseEnterCalled);
+        Assert.Equal (2, subView.OnMouseLeaveCalled);
+
+    }
+}