Implement switching between previous programs via just alt

DD2Switcher/Program.cs

@@ -4,12 +4,16 @@ using System.Diagnostics;
 using System.Linq;
 using System.Runtime.InteropServices;
 using System.Windows.Forms;
+using System.Threading;
 
 namespace DD2Switcher {
     internal static class Program {
         private static int NumProc = 19;
         private static Process[] windows = new Process[NumProc];
         private static int ActiveIndex = -1;
+        private static int PreviousIndex = -1;
+        private static bool AltPressed = false;
+        private static Timer AltTimer;
 
         private static readonly IntPtr defaultAffinity = new(0xFF000000);
         private static readonly IntPtr fullAffinity = new(0xFFFFFFFF);
@@ -221,6 +225,7 @@ namespace DD2Switcher {
                 Console.WriteLine($"Window at index {index} does not exist, removing from tracked windows");
                 windows[index] = null;
             } else {
+                PreviousIndex = ActiveIndex;
                 SetForegroundWindow(window.MainWindowHandle);
                 ActiveIndex = index;
                 AdjustAffinities();
@@ -228,6 +233,38 @@ namespace DD2Switcher {
             }
         }
 
+        private static void TabToPrevious() {
+            if (PreviousIndex == -1) {
+                Console.WriteLine("No previous window to switch to");
+                return;
+            }
+            CleanWindows();
+            Console.WriteLine($"Tab to previous window at index {PreviousIndex}");
+
+            var window = windows[PreviousIndex];
+            if (window == null || window.MainWindowHandle == IntPtr.Zero) {
+                Console.WriteLine(
+                    $"Previous window at index {PreviousIndex} does not exist, removing from tracked windows");
+                windows[PreviousIndex] = null;
+                PreviousIndex = -1;
+            } else {
+                var tempIndex = ActiveIndex;
+                SetForegroundWindow(window.MainWindowHandle);
+                ActiveIndex = PreviousIndex;
+                PreviousIndex = tempIndex;
+                AdjustAffinities();
+                AdjustPriorities();
+            }
+        }
+
+        private static void OnAltTimer() {
+            if (AltPressed) {
+                AltPressed = false;
+                AltTimer.Stop();
+                TabToPrevious();
+            }
+        }
+
         private static bool IsCapsLockOn() {
             return (GetKeyState(0x14) & 1) == 1;
         }
@@ -245,7 +282,10 @@ namespace DD2Switcher {
                     Process.GetCurrentProcess().Kill();
                 }
 
+            AltTimer = new Timer(OnAltTimer, null, Timeout.Infinite, Timeout.Infinite);
+
             HotKeyManager.RegisterHotKey(Keys.Capital, KeyModifiers.NoRepeat);
+            HotKeyManager.RegisterHotKey(Keys.Menu, KeyModifiers.NoRepeat);
             // Register main number keys (0-9)
             for (int i = 0; i < 10; i++) HotKeyManager.RegisterHotKey(Keys.D0 + i, KeyModifiers.Alt);
 
@@ -261,6 +301,17 @@ namespace DD2Switcher {
                 //   return;
                 // }
 
+                if (e.Key == Keys.Menu && e.Modifiers == KeyModifiers.NoRepeat) {
+                    AltPressed = true;
+                    AltTimer.Change(150, Timeout.Infinite);
+                    return;
+                }
+
+                if (e.Modifiers == KeyModifiers.Alt) {
+                    AltPressed = false;
+                    AltTimer.Stop();
+                }
+
                 int index;
                 if (e.Key >= Keys.D0 && e.Key <= Keys.D9) {
                     index = e.Key - Keys.D0;