lightweight variant (#1)

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

CursorLang.Settings.Tests/Interop/ForegroundWindowTests.cs

@@ -0,0 +1,159 @@
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Interop;
+using CursorLang.Core.Interop;
+using CursorLang.Settings.Interop;
+using CursorLang.Settings.Tests.Infrastructure;
+
+namespace CursorLang.Settings.Tests.Interop;
+
+/// <summary>
+/// Checks that need a real foreground window with an input field: the caret
+/// and the layout switch live exactly there.
+/// </summary>
+/// <remarks>
+/// Windows does not always allow a window to come forward — when the screen is
+/// locked, say, or when the run happens in a session without a desktop. In
+/// those cases the check reports itself as skipped rather than failed: there
+/// would be nothing to verify.
+/// </remarks>
+public sealed class ForegroundWindowTests
+{
+    [Fact]
+    public void The_caret_in_an_input_field_is_found()
+    {
+        Sta.Run(() =>
+        {
+            using var input = new InputWindow();
+            input.RequireForeground();
+
+            PopupWindowNative.Rect? caret = CaretNative.TryGetCaretRect();
+
+            if (caret is null)
+            {
+                Assert.Skip("The input field did not report the caret position");
+            }
+
+            // The caret has to sit inside the input window and to have a height
+            PopupWindowNative.Rect bounds = WindowPlacementNative.TryGetBounds(input.Handle)!.Value;
+
+            Assert.True(caret.Value.Bottom > caret.Value.Top);
+            Assert.InRange(caret.Value.Left, bounds.Left, bounds.Right);
+            Assert.InRange(caret.Value.Top, bounds.Top, bounds.Bottom);
+        });
+    }
+
+    [Fact]
+    public void The_tooltip_at_the_caret_lands_next_to_it()
+    {
+        Sta.Run(() =>
+        {
+            using var input = new InputWindow();
+            input.RequireForeground();
+
+            PopupWindowNative.Rect? caret = CaretNative.TryGetCaretRect();
+            if (caret is null)
+            {
+                Assert.Skip("The input field did not report the caret position");
+            }
+
+            PopupWindowNative.Rect field =
+                WindowPlacementNative.TryGetBounds(input.Handle)!.Value;
+
+            Assert.True(CaretNative.IsInside(caret.Value, field),
+                "the caret reported by the input field is outside that field");
+        });
+    }
+
+    // The request to switch the layout goes to the window holding the input
+    // focus, so it only concerns the test window itself
+    [Fact]
+    public void The_request_to_change_the_layout_reaches_its_own_window()
+    {
+        Sta.Run(() =>
+        {
+            using var input = new InputWindow();
+            input.RequireForeground();
+
+            int before = KeyboardLayoutNative.GetActiveLocaleId();
+
+            KeyboardLayoutNative.RequestNextLayout();
+            Sta.Pause(TimeSpan.FromMilliseconds(150));
+
+            int after = KeyboardLayoutNative.GetActiveLocaleId();
+
+            Assert.InRange(after, 1, 0xFFFF);
+
+            if (after == before)
+            {
+                // The system may hold a single layout — there is nothing to switch to
+                return;
+            }
+
+            // Bring the layout back around the circle to where it was
+            for (int i = 0; i < 8 && KeyboardLayoutNative.GetActiveLocaleId() != before; i++)
+            {
+                KeyboardLayoutNative.RequestNextLayout();
+                Sta.Pause(TimeSpan.FromMilliseconds(150));
+            }
+        });
+    }
+
+    /// <summary>A window with an input field brought to the foreground.</summary>
+    private sealed class InputWindow : IDisposable
+    {
+        private readonly Window _window;
+
+        internal InputWindow()
+        {
+            var box = new TextBox { Text = "check", FontSize = 20 };
+
+            _window = new Window
+            {
+                Width = 400,
+                Height = 200,
+                ShowInTaskbar = false,
+                WindowStartupLocation = WindowStartupLocation.Manual,
+                Left = 100,
+                Top = 100,
+                Topmost = true,
+                Content = box,
+            };
+
+            _window.Show();
+            Handle = new WindowInteropHelper(_window).Handle;
+
+            // Windows grants the right to bring a window forward neither to
+            // everyone nor at once, so it takes a few attempts
+            for (int attempt = 0; attempt < 10; attempt++)
+            {
+                _window.Activate();
+                box.Focus();
+                box.CaretIndex = box.Text.Length;
+
+                Sta.Pause(TimeSpan.FromMilliseconds(50));
+
+                if (KeyboardLayoutNative.GetForegroundWindow() == Handle)
+                {
+                    break;
+                }
+            }
+
+            // The caret does not appear at the same instant as the focus
+            Sta.Pause(TimeSpan.FromMilliseconds(100));
+        }
+
+        internal IntPtr Handle { get; }
+
+        /// <summary>Skips the check if the window never became the foreground one.</summary>
+        internal void RequireForeground()
+        {
+            if (KeyboardLayoutNative.GetForegroundWindow() != Handle)
+            {
+                Assert.Skip("The window could not be brought to the foreground");
+            }
+        }
+
+        public void Dispose() => _window.Close();
+    }
+}