lightweight variant (#1)

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

CursorLang.Core/Threading/MessageTimer.cs

@@ -0,0 +1,70 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Core.Threading;
+
+/// <summary>
+/// A timer that ticks on the message loop — the agent's stand-in for
+/// <c>DispatcherTimer</c>.
+/// </summary>
+/// <remarks>
+/// <c>SetTimer</c> with a null window binds the timer to the thread rather than to a
+/// window, and <c>DispatchMessage</c> calls the callback straight from the loop. The
+/// upshot is the same as with a dispatcher timer: the tick arrives on the thread that
+/// owns the hook and the popup, so nothing needs marshalling and nothing races.
+///
+/// The callback lives in a field for the reason a hook procedure does: the only
+/// reference to it is held by Win32, and a collected delegate takes the process down
+/// with it at the first tick.
+/// </remarks>
+internal sealed class MessageTimer : IDisposable
+{
+    /// <summary>Windows will not go below this, and pretending otherwise misleads.</summary>
+    private const uint MinimumIntervalMilliseconds = 10;
+
+    private readonly TimerProc _callback;
+
+    private nuint _id;
+
+    internal MessageTimer() => _callback = OnTimer;
+
+    internal event EventHandler? Tick;
+
+    internal TimeSpan Interval { get; set; } = TimeSpan.FromMilliseconds(100);
+
+    internal bool IsRunning => _id != 0;
+
+    /// <summary>Starts the timer, or restarts it from zero when it is already running.</summary>
+    internal void Start()
+    {
+        Stop();
+
+        var milliseconds = (uint)Math.Clamp(
+            Math.Round(Interval.TotalMilliseconds), MinimumIntervalMilliseconds, int.MaxValue);
+
+        _id = SetTimer(IntPtr.Zero, 0, milliseconds, _callback);
+    }
+
+    internal void Stop()
+    {
+        if (_id == 0)
+        {
+            return;
+        }
+
+        KillTimer(IntPtr.Zero, _id);
+        _id = 0;
+    }
+
+    public void Dispose() => Stop();
+
+    private void OnTimer(IntPtr window, uint message, nuint id, uint time) =>
+        Tick?.Invoke(this, EventArgs.Empty);
+
+    private delegate void TimerProc(IntPtr hWnd, uint message, nuint idEvent, uint time);
+
+    [DllImport("user32.dll", SetLastError = true)]
+    private static extern nuint SetTimer(IntPtr hWnd, nuint nIDEvent, uint uElapse, TimerProc lpTimerFunc);
+
+    [DllImport("user32.dll", SetLastError = true)]
+    private static extern bool KillTimer(IntPtr hWnd, nuint uIDEvent);
+}