fix(dock): address reviewer feedback on drag-and-drop highlighting

src/Editor/Ghost.Editor/View/Controls/DockLayout.cs

@@ -17,13 +17,15 @@ public sealed partial class DockLayout : Control
 {
     private const string PART_ROOT_GRID = "PART_RootGrid";
     private const string PART_DROP_TARGET_OVERLAY = "PART_DropTargetOverlay";
+    private const string DRAG_PROPERTY_DOCK_TAB = "DockTab";
     private const double MIN_PANE_SIZE = 100;
     private const double SPLITTER_THICKNESS = 4;
+    private const double DROP_EDGE_THRESHOLD = 0.25;
 
     private FrameworkElement? _dropTargetOverlay;
     private readonly HashSet<DockNode> _subscribedNodes = new();
 
-    internal enum DockPosition { Center, Top, Bottom, Left, Right, None }
+    public enum DockPosition { Center, Top, Bottom, Left, Right, None }
 
     public DockLayout()
     {
@@ -32,6 +34,19 @@ public sealed partial class DockLayout : Control
         Unloaded += OnUnloaded;
     }
 
+    /// <summary>
+    /// Calculates the dock position based on the relative position within a target element.
+    /// Precedence: Left/Right win over Top/Bottom at corners.
+    /// </summary>
+    public static DockPosition CalculateDockPosition(double width, double height, double x, double y, double threshold)
+    {
+        if (x < width * threshold) return DockPosition.Left;
+        if (x > width * (1 - threshold)) return DockPosition.Right;
+        if (y < height * threshold) return DockPosition.Top;
+        if (y > height * (1 - threshold)) return DockPosition.Bottom;
+        return DockPosition.Center;
+    }
+
     private void OnLoaded(object sender, RoutedEventArgs e)
     {
         if (Root != null)
@@ -302,38 +317,40 @@ public sealed partial class DockLayout : Control
     {
         _draggedItem = args.Item;
         _sourceNode = sender.Tag as DockPanelNode;
-        args.Data.Properties.Add("DockTab", _draggedItem); // Identify our drag
+        args.Data.Properties.Add(DRAG_PROPERTY_DOCK_TAB, _draggedItem); // Identify our drag
     }
 
     private void TabView_DragOver(object sender, DragEventArgs e)
     {
-        if (e.DataView.Properties.ContainsKey("DockTab") && sender is FrameworkElement targetElement)
+        if (e.DataView.Properties.ContainsKey(DRAG_PROPERTY_DOCK_TAB) && sender is FrameworkElement targetElement)
         {
             e.AcceptedOperation = global::Windows.ApplicationModel.DataTransfer.DataPackageOperation.Move;
 
             var position = e.GetPosition(targetElement);
-            double width = targetElement.ActualWidth;
+            var newPosition = CalculateDockPosition(targetElement.ActualWidth, targetElement.ActualHeight, position.X, position.Y, DROP_EDGE_THRESHOLD);
-            double height = targetElement.ActualHeight;
-
-            double edgeThreshold = 0.25; // 25% of edge triggers split
-
-            if (position.X < width * edgeThreshold) _currentDropPosition = DockPosition.Left;
-            else if (position.X > width * (1 - edgeThreshold)) _currentDropPosition = DockPosition.Right;
-            else if (position.Y < height * edgeThreshold) _currentDropPosition = DockPosition.Top;
-            else if (position.Y > height * (1 - edgeThreshold)) _currentDropPosition = DockPosition.Bottom;
-            else _currentDropPosition = DockPosition.Center;
 
+            if (newPosition != _currentDropPosition)
+            {
+                _currentDropPosition = newPosition;
                 UpdateDropOverlay(targetElement, _currentDropPosition);
             }
         }
+    }
 
     private void TabView_DragLeave(object sender, DragEventArgs e)
+    {
+        ClearDragState();
+    }
+
+    private void ClearDragState()
     {
         if (_dropTargetOverlay != null)
         {
             _dropTargetOverlay.Visibility = Visibility.Collapsed;
-            _currentDropPosition = DockPosition.None;
         }
+        _currentDropPosition = DockPosition.None;
+        _draggedItem = null;
+        _sourceNode = null;
     }
 
     private void UpdateDropOverlay(FrameworkElement targetElement, DockPosition position)
@@ -375,6 +392,7 @@ public sealed partial class DockLayout : Control
     // Add a dummy TabView_Drop method so it compiles, we will implement it in Task 6
     private void TabView_Drop(object sender, DragEventArgs e)
     {
+        ClearDragState();
     }
 
     protected override void OnApplyTemplate()

src/Test/Ghost.UnitTest/DockLayoutTest.cs

@@ -0,0 +1,62 @@
+using Ghost.Editor.View.Controls;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Ghost.UnitTest;
+
+[TestClass]
+public class DockLayoutTest
+{
+    private const double THRESHOLD = 0.25;
+
+    [TestMethod]
+    public void TestCalculateDockPosition_Center()
+    {
+        // 100x100, threshold 0.25 -> Center is [25, 75]
+        var pos = DockLayout.CalculateDockPosition(100, 100, 50, 50, THRESHOLD);
+        Assert.AreEqual(DockLayout.DockPosition.Center, pos);
+    }
+
+    [TestMethod]
+    public void TestCalculateDockPosition_Left()
+    {
+        var pos = DockLayout.CalculateDockPosition(100, 100, 10, 50, THRESHOLD);
+        Assert.AreEqual(DockLayout.DockPosition.Left, pos);
+    }
+
+    [TestMethod]
+    public void TestCalculateDockPosition_Right()
+    {
+        var pos = DockLayout.CalculateDockPosition(100, 100, 90, 50, THRESHOLD);
+        Assert.AreEqual(DockLayout.DockPosition.Right, pos);
+    }
+
+    [TestMethod]
+    public void TestCalculateDockPosition_Top()
+    {
+        var pos = DockLayout.CalculateDockPosition(100, 100, 50, 10, THRESHOLD);
+        Assert.AreEqual(DockLayout.DockPosition.Top, pos);
+    }
+
+    [TestMethod]
+    public void TestCalculateDockPosition_Bottom()
+    {
+        var pos = DockLayout.CalculateDockPosition(100, 100, 50, 90, THRESHOLD);
+        Assert.AreEqual(DockLayout.DockPosition.Bottom, pos);
+    }
+
+    [TestMethod]
+    public void TestCalculateDockPosition_CornerPrecedence_LeftTop()
+    {
+        // (10, 10) is in both Left and Top zones.
+        // Current implementation: Left/Right win over Top/Bottom.
+        var pos = DockLayout.CalculateDockPosition(100, 100, 10, 10, THRESHOLD);
+        Assert.AreEqual(DockLayout.DockPosition.Left, pos);
+    }
+
+    [TestMethod]
+    public void TestCalculateDockPosition_CornerPrecedence_RightBottom()
+    {
+        var pos = DockLayout.CalculateDockPosition(100, 100, 90, 90, THRESHOLD);
+        Assert.AreEqual(DockLayout.DockPosition.Right, pos);
+    }
+}

src/Test/Ghost.UnitTest/Ghost.UnitTest.csproj

@@ -16,6 +16,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\Editor\Ghost.Editor.Core\Ghost.Editor.Core.csproj" />
+    <ProjectReference Include="..\..\Editor\Ghost.Editor\Ghost.Editor.csproj" />
   </ItemGroup>
 
   <ItemGroup>