modified PopupLayout

CursorLang/Services/KeyboardLayoutService.cs

@@ -27,29 +27,54 @@ public sealed class KeyboardLayoutOptions
 public sealed class KeyboardLayoutService : IKeyboardLayoutService, IDisposable
 {
     private readonly DispatcherTimer _pollTimer;
+    private readonly Func<IntPtr> _getForegroundWindow;
+    private readonly Func<int> _getActiveLocaleId;
+    private readonly Action _requestNextLayout;
+
     private int _lastLocaleId = -1;
     private IntPtr _lastForegroundWindow;
 
     public KeyboardLayoutService(KeyboardLayoutOptions options)
+        : this(
+            options,
+            KeyboardLayoutNative.GetForegroundWindow,
+            KeyboardLayoutNative.GetActiveLocaleId,
+            KeyboardLayoutNative.RequestNextLayout)
     {
+    }
+
+    /// <summary>
+    /// Takes the sources of system information explicitly: in tests the layout and the
+    /// active window are not provided by Windows.
+    /// </summary>
+    internal KeyboardLayoutService(
+        KeyboardLayoutOptions options,
+        Func<IntPtr> getForegroundWindow,
+        Func<int> getActiveLocaleId,
+        Action requestNextLayout)
+    {
+        _getForegroundWindow = getForegroundWindow;
+        _getActiveLocaleId = getActiveLocaleId;
+        _requestNextLayout = requestNextLayout;
+
         _pollTimer = new DispatcherTimer { Interval = options.PollInterval };
         _pollTimer.Tick += OnTick;
     }
 
     public event EventHandler<LayoutChangedEventArgs>? LayoutChanged;
 
-    public KeyboardLayout Current => KeyboardLayout.FromLocaleId(KeyboardLayoutNative.GetActiveLocaleId());
+    public KeyboardLayout Current => KeyboardLayout.FromLocaleId(_getActiveLocaleId());
 
     public void Start()
     {
-        _lastForegroundWindow = KeyboardLayoutNative.GetForegroundWindow();
-        _lastLocaleId = KeyboardLayoutNative.GetActiveLocaleId();
+        _lastForegroundWindow = _getForegroundWindow();
+        _lastLocaleId = _getActiveLocaleId();
         _pollTimer.Start();
     }
 
     public void Stop() => _pollTimer.Stop();
 
-    public void SwitchToNext() => KeyboardLayoutNative.RequestNextLayout();
+    public void SwitchToNext() => _requestNextLayout();
 
     public void Dispose()
     {
@@ -57,9 +82,14 @@ public sealed class KeyboardLayoutService : IKeyboardLayoutService, IDisposable
         _pollTimer.Tick -= OnTick;
     }
 
-    private void OnTick(object? sender, EventArgs e)
+    private void OnTick(object? sender, EventArgs e) => Poll();
+
+    // A single poll step. Called by the timer, and in tests — directly:
+    // there is no point waiting for a tick to check how the reason for a layout
+    // change is decided
+    internal void Poll()
     {
-        IntPtr foreground = KeyboardLayoutNative.GetForegroundWindow();
+        IntPtr foreground = _getForegroundWindow();
         if (foreground == IntPtr.Zero)
         {
             return;
@@ -68,7 +98,7 @@ public sealed class KeyboardLayoutService : IKeyboardLayoutService, IDisposable
         bool appSwitched = foreground != _lastForegroundWindow;
         _lastForegroundWindow = foreground;
 
-        int localeId = KeyboardLayoutNative.GetActiveLocaleId();
+        int localeId = _getActiveLocaleId();
         if (localeId == _lastLocaleId)
         {
             return;