Improve hotkey capture and validation

MainWindow.xaml

@@ -81,7 +81,8 @@
                         </Grid.RowDefinitions>
 
                         <TextBlock Text="Hotkey" VerticalAlignment="Center" Margin="0,0,8,8"/>
-                        <TextBox x:Name="HotkeyBox" Grid.Column="1" Margin="0,0,0,8"/>
+                        <TextBox x:Name="HotkeyBox" Grid.Column="1" Margin="0,0,0,8"
+                                 PreviewKeyDown="HotkeyBox_PreviewKeyDown"/>
 
                         <TextBlock Text="Default for New Items" Grid.Row="1" VerticalAlignment="Center" Margin="0,0,8,0"/>
                         <ComboBox x:Name="DisplayModeBox" Grid.Row="1" Grid.Column="1"/>

MainWindow.xaml.cs

@@ -312,13 +312,78 @@ public partial class MainWindow : Window
             return;
         }
 
-        controller.Config.Hotkey = string.IsNullOrWhiteSpace(HotkeyBox.Text) ? "Ctrl+Alt+Space" : HotkeyBox.Text.Trim();
+        controller.Config.Hotkey = string.IsNullOrWhiteSpace(HotkeyBox.Text)
+            ? "Ctrl+Alt+Space"
+            : HotkeyService.Normalize(HotkeyBox.Text.Trim());
         controller.Config.DisplayMode = DisplayModeBox.SelectedItem is LauncherDisplayMode mode
             ? mode
             : LauncherDisplayMode.LargeIconWithText;
         ApplyCurrentItem();
     }
 
+    private void HotkeyBox_PreviewKeyDown(object sender, System.Windows.Input.KeyEventArgs e)
+    {
+        Key key = e.Key == Key.System ? e.SystemKey : e.Key;
+        if (key == Key.ImeProcessed)
+        {
+            key = e.ImeProcessedKey;
+        }
+
+        if (key is Key.LeftCtrl or Key.RightCtrl or Key.LeftAlt or Key.RightAlt or Key.LeftShift or Key.RightShift
+            or Key.LWin or Key.RWin)
+        {
+            e.Handled = true;
+            return;
+        }
+
+        if (key is Key.Back or Key.Delete or Key.Escape)
+        {
+            HotkeyBox.Text = "";
+            e.Handled = true;
+            return;
+        }
+
+        ModifierKeys modifiers = Keyboard.Modifiers;
+        if (modifiers == ModifierKeys.None)
+        {
+            StatusText.Text = "Press a hotkey with Ctrl, Alt, Shift, or Win plus another key.";
+            e.Handled = true;
+            return;
+        }
+
+        HotkeyBox.Text = FormatHotkey(modifiers, key);
+        HotkeyBox.CaretIndex = HotkeyBox.Text.Length;
+        StatusText.Text = "Click Save to apply the new hotkey.";
+        e.Handled = true;
+    }
+
+    private static string FormatHotkey(ModifierKeys modifiers, Key key)
+    {
+        List<string> parts = [];
+        if (modifiers.HasFlag(ModifierKeys.Control))
+        {
+            parts.Add("Ctrl");
+        }
+
+        if (modifiers.HasFlag(ModifierKeys.Alt))
+        {
+            parts.Add("Alt");
+        }
+
+        if (modifiers.HasFlag(ModifierKeys.Shift))
+        {
+            parts.Add("Shift");
+        }
+
+        if (modifiers.HasFlag(ModifierKeys.Windows))
+        {
+            parts.Add("Win");
+        }
+
+        parts.Add(key.ToString());
+        return string.Join("+", parts);
+    }
+
     private void LoadStartupState()
     {
         isLoadingStartupState = true;
@@ -569,9 +634,24 @@ public partial class MainWindow : Window
             return;
         }
 
-        ApplyConfigFields();
+        string previousHotkey = controller.Config.Hotkey;
-        ConfigService.Save(controller.Config);
+        try
-        controller.ReloadConfig();
+        {
+            ApplyConfigFields();
+            ConfigService.Save(controller.Config);
+            controller.ReloadConfig();
+        }
+        catch (Exception ex) when (ex is FormatException or InvalidOperationException)
+        {
+            controller.Config.Hotkey = previousHotkey;
+            ConfigService.Save(controller.Config);
+            controller.ReloadConfig();
+            HotkeyBox.Text = previousHotkey;
+            MessageBox.Show($"Could not apply hotkey.\n\n{ex.Message}", "Taskbar Launcher");
+            StatusText.Text = $"Hotkey was not changed. Current hotkey: {previousHotkey}";
+            return;
+        }
+
         LauncherItem? reloadedSelection = selectedPath is null ? null : FindItemByPath(controller.Config.Items, selectedPath);
         RefreshView(reloadedSelection);
         StatusText.Text = reloadedSelection is null

Services/HotkeyService.cs

@@ -1,4 +1,5 @@
 using System.Runtime.InteropServices;
+using System.ComponentModel;
 using System.Windows;
 using System.Windows.Input;
 using System.Windows.Interop;
@@ -17,6 +18,7 @@ public sealed class HotkeyService : IDisposable
 
     public void Register(string hotkey)
     {
+        ParseHotkey(hotkey, out uint modifiers, out uint key);
         Unregister();
 
         window = new Window
@@ -37,8 +39,13 @@ public sealed class HotkeyService : IDisposable
             source = HwndSource.FromHwnd(helper.Handle);
             source?.AddHook(WndProc);
 
-            ParseHotkey(hotkey, out uint modifiers, out uint key);
+            if (!RegisterHotKey(helper.Handle, HotkeyId, modifiers, key))
-            RegisterHotKey(helper.Handle, HotkeyId, modifiers, key);
+            {
+                int error = Marshal.GetLastWin32Error();
+                throw new InvalidOperationException(
+                    $"Windows could not register hotkey '{Normalize(hotkey)}'. It may already be used by another app.",
+                    new Win32Exception(error));
+            }
         };
 
         window.Show();
@@ -78,12 +85,47 @@ public sealed class HotkeyService : IDisposable
         return IntPtr.Zero;
     }
 
+    public static string Normalize(string hotkey)
+    {
+        ParseHotkey(hotkey, out uint modifiers, out uint key);
+        Key parsedKey = KeyInterop.KeyFromVirtualKey((int)key);
+        List<string> parts = [];
+
+        if ((modifiers & 0x0002) != 0)
+        {
+            parts.Add("Ctrl");
+        }
+
+        if ((modifiers & 0x0001) != 0)
+        {
+            parts.Add("Alt");
+        }
+
+        if ((modifiers & 0x0004) != 0)
+        {
+            parts.Add("Shift");
+        }
+
+        if ((modifiers & 0x0008) != 0)
+        {
+            parts.Add("Win");
+        }
+
+        parts.Add(parsedKey.ToString());
+        return string.Join("+", parts);
+    }
+
     private static void ParseHotkey(string hotkey, out uint modifiers, out uint key)
     {
         modifiers = 0;
-        key = (uint)KeyInterop.VirtualKeyFromKey(Key.Space);
+        key = 0;
 
-        foreach (string part in hotkey.Split('+', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries))
+        string[] parts = hotkey
+            .Replace(",", "+", StringComparison.Ordinal)
+            .Replace(" ", "+", StringComparison.Ordinal)
+            .Split('+', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries);
+
+        foreach (string part in parts)
         {
             if (part.Equals("Ctrl", StringComparison.OrdinalIgnoreCase) || part.Equals("Control", StringComparison.OrdinalIgnoreCase))
             {
@@ -101,11 +143,45 @@ public sealed class HotkeyService : IDisposable
             {
                 modifiers |= 0x0008;
             }
-            else if (Enum.TryParse(part, true, out Key parsedKey))
+            else if (TryParseKey(part, out Key parsedKey))
             {
                 key = (uint)KeyInterop.VirtualKeyFromKey(parsedKey);
             }
+            else
+            {
+                throw new FormatException($"'{part}' is not a valid hotkey key.");
+            }
         }
+
+        if (modifiers == 0)
+        {
+            throw new FormatException("Hotkeys must include at least one modifier: Ctrl, Alt, Shift, or Win.");
+        }
+
+        if (key == 0)
+        {
+            throw new FormatException("Hotkeys must include a final key, such as Space, S, F12, or D1.");
+        }
+    }
+
+    private static bool TryParseKey(string value, out Key key)
+    {
+        if (Enum.TryParse(value, true, out key))
+        {
+            return true;
+        }
+
+        if (value.Length == 1 && char.IsLetter(value[0]))
+        {
+            return Enum.TryParse(value.ToUpperInvariant(), out key);
+        }
+
+        if (value.Length == 1 && char.IsDigit(value[0]))
+        {
+            return Enum.TryParse($"D{value}", out key);
+        }
+
+        return false;
     }
 
     [DllImport("user32.dll", SetLastError = true)]