Show add comment glyph for the current mouse line

Author: jcansdale

src/GitHub.InlineReviews/GitHub.InlineReviews.csproj

@@ -82,6 +82,7 @@
     <Compile Include="InlineReviewsPackage.cs" />
     <Compile Include="Models\InlineCommentThreadModel.cs" />
     <Compile Include="Models\PullRequestSessionFile.cs" />
+    <Compile Include="Tags\MouseEnterAndLeaveEventRouter.cs" />
     <Compile Include="Peek\InlineCommentPeekableItem.cs" />
     <Compile Include="Peek\InlineCommentPeekableItemSource.cs" />
     <Compile Include="Peek\InlineCommentPeekableItemSourceProvider.cs" />

src/GitHub.InlineReviews/InlineCommentMarginProvider.cs

@@ -58,8 +58,14 @@ IWpfTextViewMargin CreateMargin<TGlyphTag>(IGlyphFactory<TGlyphTag> glyphFactory
             IWpfTextViewHost wpfTextViewHost, IWpfTextViewMargin parent, IEditorFormatMap editorFormatMap) where TGlyphTag : ITag
         {
             var tagAggregator = tagAggregatorFactory.CreateTagAggregator<TGlyphTag>(wpfTextViewHost.TextView);
-            return new GlyphMargin<TGlyphTag>(wpfTextViewHost, glyphFactory, gridFactory, tagAggregator, editorFormatMap,
+            var margin = new GlyphMargin<TGlyphTag>(wpfTextViewHost, glyphFactory, gridFactory, tagAggregator, editorFormatMap,
                 IsMarginVisible, MarginPropertiesName, MarginName, true, 17.0);
+
+            var router = new MouseEnterAndLeaveEventRouter<AddInlineCommentGlyph>();
+            wpfTextViewHost.TextView.VisualElement.MouseMove += (t, e) => router.MouseMove(margin.VisualElement, e);
+            wpfTextViewHost.TextView.VisualElement.MouseLeave += (t, e) => router.MouseLeave(margin.VisualElement, e);
+
+            return margin;
         }
 
         bool IsMarginVisible(ITextBuffer buffer)

src/GitHub.InlineReviews/Tags/MouseEnterAndLeaveEventRouter.cs

@@ -0,0 +1,99 @@
+using System;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Input;
+
+namespace GitHub.InlineReviews.Tags
+{
+    class MouseEnterAndLeaveEventRouter<T> where T : FrameworkElement
+    {
+        T previousMouseOverElement;
+
+        public void MouseMove(object target, MouseEventArgs e)
+        {
+            T mouseOverElement = null;
+            Action<T> visitAction = element =>
+            {
+                mouseOverElement = element;
+            };
+
+            var visitor = new Visitor(e, visitAction);
+            visitor.Visit(target);
+
+            if (mouseOverElement != previousMouseOverElement)
+            {
+                MouseLeave(previousMouseOverElement, e);
+                MouseEnter(mouseOverElement, e);
+            }
+        }
+
+        public void MouseLeave(object target, MouseEventArgs e)
+        {
+            MouseLeave(previousMouseOverElement, e);
+        }
+
+        void MouseEnter(T element, MouseEventArgs e)
+        {
+            element?.RaiseEvent(new MouseEventArgs(e.MouseDevice, e.Timestamp)
+            {
+                RoutedEvent = Mouse.MouseEnterEvent,
+            });
+
+            previousMouseOverElement = element;
+        }
+
+        void MouseLeave(T element, MouseEventArgs e)
+        {
+            element?.RaiseEvent(new MouseEventArgs(e.MouseDevice, e.Timestamp)
+            {
+                RoutedEvent = Mouse.MouseLeaveEvent,
+            });
+
+            previousMouseOverElement = null;
+        }
+
+        class Visitor
+        {
+            MouseEventArgs mouseEventArgs;
+            Action<T> action;
+
+            internal Visitor(MouseEventArgs mouseEventArgs, Action<T> action)
+            {
+                this.mouseEventArgs = mouseEventArgs;
+                this.action = action;
+            }
+
+            internal void Visit(object obj)
+            {
+                if (obj is Panel)
+                {
+                    Visit((Panel)obj);
+                    return;
+                }
+
+                if (obj is T)
+                {
+                    Visit((T)obj);
+                    return;
+                }
+            }
+
+            internal void Visit(Panel panel)
+            {
+                foreach (var child in panel.Children)
+                {
+                    Visit(child);
+                }
+            }
+
+            internal void Visit(T element)
+            {
+                var point = mouseEventArgs.GetPosition(element);
+                if (point.Y >= 0 && point.Y < element.ActualHeight)
+                {
+                    action(element);
+                }
+            }
+        }
+    }
+}