Fix: Disable duplicate shortcut keys

AutoDarkModeApp/Strings/en-us/Resources.resw

@@ -370,6 +370,15 @@ Would you like to create an issue on the Auto Dark Mode repository?</value>
   <data name="Hotkeys" xml:space="preserve">
     <value>Hotkeys</value>
   </data>
+  <data name="HotkeyDuplicateErrorTitle" xml:space="preserve">
+    <value>Duplicate Hotkey</value>
+  </data>
+  <data name="HotkeyDuplicateErrorMessage" xml:space="preserve">
+    <value>This hotkey is already used by "{0}". Please choose a different key combination.</value>
+  </data>
+  <data name="HotkeyInvalidErrorMessage" xml:space="preserve">
+    <value>Invalid hotkey combination. Please include at least one non-modifier key (e.g., a letter, number, or function key).</value>
+  </data>
   <data name="IdleTime" xml:space="preserve">
     <value>Time in minutes before the system is considered idle</value>
   </data>

AutoDarkModeApp/UserControls/ShortcutDialogContentControl.xaml

@@ -10,6 +10,13 @@
 
     <StackPanel Orientation="Vertical" Spacing="16">
 
+        <InfoBar
+            x:Name="ErrorInfoBar"
+            IsClosable="False"
+            IsOpen="{x:Bind IsErrorVisible, Mode=OneWay}"
+            Message="{x:Bind ErrorMessage, Mode=OneWay}"
+            Severity="Error" />
+
         <TextBlock Text="{helpers:ResourceString Name=SelectTheKeyCombination}" TextWrapping="Wrap" />
 
         <ItemsControl

AutoDarkModeApp/UserControls/ShortcutDialogContentControl.xaml.cs

@@ -11,9 +11,32 @@ public sealed partial class ShortcutDialogContentControl : UserControl
     [GeneratedDependencyProperty]
     public partial string? CapturedHotkeys { get; set; }
 
+    [GeneratedDependencyProperty]
+    public partial bool HasNonModifierKey { get; set; }
+
+    [GeneratedDependencyProperty]
+    public partial bool IsErrorVisible { get; set; }
+
+    [GeneratedDependencyProperty]
+    public partial string? ErrorMessage { get; set; }
+
+    public Func<string?, (bool isDuplicate, string? conflictingName)>? ValidateHotkey { get; set; }
+
     private KeyboardHook? _keyboardHook;
     private bool _isCapturing;
 
+    public void ShowError(string message)
+    {
+        ErrorMessage = message;
+        IsErrorVisible = true;
+    }
+
+    public void HideError()
+    {
+        IsErrorVisible = false;
+        ErrorMessage = null;
+    }
+
     public void LoadFromKeyValue(string? hotkeyValue)
     {
         if (string.IsNullOrWhiteSpace(hotkeyValue))
@@ -86,13 +109,19 @@ private void OnKeyboardEvent(object? sender, KeyboardHookEventArgs e)
         }
 
         List<string> displayParts = [];
-        if (isCtrl) displayParts.Add("Ctrl");
-        if (isShift) displayParts.Add("Shift");
-        if (isAlt) displayParts.Add("Alt");
-        if (isWin) displayParts.Add("Win");
+        if (isCtrl)
+            displayParts.Add("Ctrl");
+        if (isShift)
+            displayParts.Add("Shift");
+        if (isAlt)
+            displayParts.Add("Alt");
+        if (isWin)
+            displayParts.Add("Win");
 
         var key = (VirtualKey)e.VirtualKeyCode;
-        if (!IsModifierKey(key))
+        HasNonModifierKey = !IsModifierKey(key);
+
+        if (HasNonModifierKey)
         {
             displayParts.Add(HotkeyStringConverter.GetKeyDisplayName(key));
         }
@@ -101,6 +130,23 @@ private void OnKeyboardEvent(object? sender, KeyboardHookEventArgs e)
         {
             CapturedHotkeys = string.Join(" + ", displayParts);
             HotkeyCombination = displayParts.Select(p => new SingleHotkeyDataObject { Key = p }).ToList();
+
+            if (ValidateHotkey is not null)
+            {
+                var (isDuplicate, conflictingName) = ValidateHotkey(CapturedHotkeys);
+                if (isDuplicate)
+                {
+                    ShowError(string.Format(ResourceExtensions.GetLocalized("HotkeyDuplicateErrorMessage"), conflictingName));
+                }
+                else
+                {
+                    HideError();
+                }
+            }
+            else
+            {
+                HideError();
+            }
         });
 
         e.Handled = true;

AutoDarkModeApp/ViewModels/HotkeysViewModel.cs

@@ -102,6 +102,47 @@ public void UpdateHotkeyValue(string tag, string? value)
         SafeSaveBuilder();
     }
 
+    public (bool isDuplicate, string? conflictingName) IsDuplicateHotkey(string currentTag, string? newKeys)
+    {
+        if (string.IsNullOrWhiteSpace(newKeys))
+        {
+            return (false, null);
+        }
+
+        var normalizedNewKeys = newKeys.Trim();
+
+        var allHotkeys = new[]
+        {
+            (Tag: "ForceLight", Keys: _builder.Config.Hotkeys.ForceLight, Name: "ForceLight"),
+            (Tag: "ForceDark", Keys: _builder.Config.Hotkeys.ForceDark, Name: "ForceDark"),
+            (Tag: "StopForcing", Keys: _builder.Config.Hotkeys.NoForce, Name: "StopForcing"),
+            (Tag: "ToggleTheme", Keys: _builder.Config.Hotkeys.ToggleTheme, Name: "ToggleTheme"),
+            (Tag: "AutomaticThemeSwitch", Keys: _builder.Config.Hotkeys.ToggleAutoThemeSwitch, Name: "AutomaticThemeSwitch"),
+            (Tag: "PauseAutoThemeSwitching", Keys: _builder.Config.Hotkeys.TogglePostpone, Name: "PauseAutoThemeSwitching"),
+        };
+
+        foreach (var hotkey in allHotkeys)
+        {
+            if (hotkey.Tag == currentTag)
+            {
+                continue;
+            }
+
+            if (string.IsNullOrWhiteSpace(hotkey.Keys))
+            {
+                continue;
+            }
+
+            if (hotkey.Keys.Trim().Equals(normalizedNewKeys, StringComparison.OrdinalIgnoreCase))
+            {
+                var displayName = HotkeysCollection?.FirstOrDefault(h => h.Tag == hotkey.Tag)?.DisplayName ?? hotkey.Name;
+                return (true, displayName);
+            }
+        }
+
+        return (false, null);
+    }
+
     public HotkeysViewModel(IErrorService errorService)
     {
         _dispatcherQueue = Microsoft.UI.Dispatching.DispatcherQueue.GetForCurrentThread();

AutoDarkModeApp/Views/HotkeysPage.xaml.cs

@@ -24,6 +24,7 @@ private async void EditHotkeysButton_Click(object sender, RoutedEventArgs e)
 
         var keyValue = ViewModel.GetHotkeyValue(hotkeyData.Tag);
         var dialogContent = new ShortcutDialogContentControl();
+        dialogContent.ValidateHotkey = (newKeys) => ViewModel.IsDuplicateHotkey(hotkeyData.Tag, newKeys);
 
         if (keyValue is not null)
         {
@@ -42,18 +43,32 @@ private async void EditHotkeysButton_Click(object sender, RoutedEventArgs e)
             Content = dialogContent,
         };
 
+        shortcutDialog.Closing += (dialog, args) =>
+        {
+            if (args.Result == ContentDialogResult.Primary)
+            {
+                if (!dialogContent.HasNonModifierKey)
+                {
+                    dialogContent.ShowError("HotkeyInvalidErrorMessage".GetLocalized());
+                }
+                if (dialogContent.IsErrorVisible)
+                {
+                    args.Cancel = true;
+                }
+            }
+        };
+
         var result = await shortcutDialog.ShowAsync();
         if (result == ContentDialogResult.Secondary)
         {
             dialogContent.HotkeyCombination?.Clear();
             dialogContent.CapturedHotkeys = null;
         }
-        else if (result != ContentDialogResult.Primary)
+
+        if (result == ContentDialogResult.Primary || result == ContentDialogResult.Secondary)
         {
-            return;
+            ViewModel.UpdateHotkeyValue(hotkeyData.Tag, dialogContent.CapturedHotkeys);
         }
-
-        ViewModel.UpdateHotkeyValue(hotkeyData.Tag, dialogContent.CapturedHotkeys);
     }
 
     private async void SaveSettingsButton_Click(object sender, RoutedEventArgs e)