Nudge the clock with the arrow keys

DesktopClock.Tests/WindowUtilTests.cs

@@ -1,7 +1,37 @@
+using System.Windows.Input;
+
 namespace DesktopClock.Tests;
 
 public class WindowUtilTests
 {
+    [Theory]
+    [InlineData(Key.Left, ModifierKeys.None, -1, 0)]
+    [InlineData(Key.Right, ModifierKeys.None, 1, 0)]
+    [InlineData(Key.Up, ModifierKeys.None, 0, -1)]
+    [InlineData(Key.Down, ModifierKeys.None, 0, 1)]
+    [InlineData(Key.Left, ModifierKeys.Shift, -10, 0)]
+    [InlineData(Key.Right, ModifierKeys.Shift, 10, 0)]
+    [InlineData(Key.Up, ModifierKeys.Shift, 0, -10)]
+    [InlineData(Key.Down, ModifierKeys.Shift, 0, 10)]
+    public void GetKeyboardNudge_ArrowKeys_MoveByStep(Key key, ModifierKeys modifiers, double expectedX, double expectedY)
+    {
+        var nudge = WindowUtil.GetKeyboardNudge(key, modifiers);
+
+        Assert.Equal(expectedX, nudge.X);
+        Assert.Equal(expectedY, nudge.Y);
+    }
+
+    [Theory]
+    [InlineData(Key.Enter)]
+    [InlineData(Key.A)]
+    [InlineData(Key.Space)]
+    public void GetKeyboardNudge_OtherKeys_DoNotMove(Key key)
+    {
+        var nudge = WindowUtil.GetKeyboardNudge(key, ModifierKeys.None);
+
+        Assert.Equal(default, nudge);
+    }
+
     private const int WsExTransparent = 0x00000020;
     private const int WsExToolWindow = 0x00000080;
     private const int WsExAppWindow = 0x00040000;

DesktopClock/MainWindow.xaml.cs

@@ -429,6 +429,30 @@ private void Window_KeyDown(object sender, KeyEventArgs e)
                     break;
             }
         }
+        else if (Keyboard.Modifiers is ModifierKeys.None or ModifierKeys.Shift)
+        {
+            NudgeWindow(e);
+        }
+    }
+
+    /// <summary>
+    /// Moves the clock with the arrow keys as a precise, mouse-free alternative to dragging.
+    /// </summary>
+    private void NudgeWindow(KeyEventArgs e)
+    {
+        // The keyboard respects the same lock as the mouse.
+        if (!Settings.Default.DragToMove)
+            return;
+
+        var nudge = WindowUtil.GetKeyboardNudge(e.Key, Keyboard.Modifiers);
+        if (nudge == default)
+            return;
+
+        Left += nudge.X;
+        Top += nudge.Y;
+
+        PixelShifter?.UpdateBasePosition(this);
+        e.Handled = true;
     }
 
     private void OpenUrl(string url)

DesktopClock/Utilities/WindowUtil.cs

@@ -1,12 +1,40 @@
 using System;
 using System.Runtime.InteropServices;
 using System.Windows;
+using System.Windows.Input;
 using System.Windows.Interop;
 
 namespace DesktopClock;
 
 public static class WindowUtil
 {
+    /// <summary>
+    /// How far one arrow key press moves the window.
+    /// </summary>
+    public const double NudgeStep = 1;
+
+    /// <summary>
+    /// How far an arrow key press moves the window while Shift is held.
+    /// </summary>
+    public const double LargeNudgeStep = 10;
+
+    /// <summary>
+    /// Returns how far an arrow key should move the window, or zero for other keys.
+    /// </summary>
+    public static Vector GetKeyboardNudge(Key key, ModifierKeys modifiers)
+    {
+        var step = modifiers == ModifierKeys.Shift ? LargeNudgeStep : NudgeStep;
+
+        return key switch
+        {
+            Key.Left => new Vector(-step, 0),
+            Key.Right => new Vector(step, 0),
+            Key.Up => new Vector(0, -step),
+            Key.Down => new Vector(0, step),
+            _ => default,
+        };
+    }
+
     private const int GWL_EXSTYLE = -20;
     private const int WS_EX_TRANSPARENT = 0x00000020;
     private const int WS_EX_TOOLWINDOW = 0x00000080;