Move everything back to original positions if error

Author: tznind

src/Operations/DragOperation.cs

@@ -287,4 +287,13 @@ private void ContinueDrag(DragMemento mem, Point dest)
 
         this.DestinationY = dest.Y;
     }
+
+    /// <summary>
+    /// Restores all mementos to original locations
+    /// </summary>
+    /// <exception cref="NotImplementedException"></exception>
+    public void Abandon()
+    {
+        UndoImpl();
+    }
 }

src/UI/Editor.cs

@@ -26,7 +26,7 @@ namespace TerminalGuiDesigner.UI;
 /// application.  Hooks key and mouse events and mounts as a sub-view whatever file
 /// the user opens.
 /// </summary>
-public class Editor : Toplevel
+public class Editor : Toplevel, IErrorReporter
 {
     private KeyMap keyMap;
     private readonly KeyboardManager keyboardManager;
@@ -82,7 +82,10 @@ public Editor()
         LoadKeyMap();
 
         this.keyboardManager = new KeyboardManager(this.keyMap);
-        this.mouseManager = new MouseManager();
+        this.mouseManager = new MouseManager()
+        {
+            ErrorReporter = this
+        };
         this.Closing += this.Editor_Closing;
 
         this.BuildRootMenu();
@@ -1177,7 +1180,7 @@ private void Delete()
         }
     }
 
-    private void ShowErrorThatViewIsUsedByOthers(Design[] usedBy)
+    public void ShowErrorThatViewIsUsedByOthers(Design[] usedBy)
     {
         if (usedBy.Length == 1)
         {
@@ -1504,4 +1507,4 @@ private void ShowEditProperties(Design d)
         var edit = new EditDialog(d);
         Application.Run(edit, this.ErrorHandler);
     }
-}
+}

src/UI/IErrorReporter.cs

@@ -0,0 +1,6 @@
+namespace TerminalGuiDesigner.UI;
+
+public interface IErrorReporter
+{
+    public void ShowErrorThatViewIsUsedByOthers(Design[] usedBy);
+}

src/UI/MouseManager.cs

@@ -33,6 +33,12 @@ public class MouseManager
     /// </summary>
     public Rectangle? SelectionBox => RectExtensions.FromBetweenPoints(this.selectionStart, this.selectionEnd);
 
+    /// <summary>
+    /// Set to report impossible commands as they are executed i.e. to give info
+    /// to user about why operation failed etc.
+    /// </summary>
+    public IErrorReporter? ErrorReporter;
+
     /// <summary>
     /// Responds to <see cref="Application.MouseEvent"/>(by changing a 'drag a box' selection area
     /// or starting a resize etc).
@@ -198,12 +204,12 @@ public void HandleMouse(MouseEventArgs m, Design viewBeingEdited)
                     // we are dragging into a new container
                     this.dragOperation.DropInto = into.View;
 
-                   /*
-                    TODO: Do this
-                    if (this.dragOperation.IsImpossible)
+                   
+                    if (this.dragOperation.IsImpossible && this.dragOperation.PreventDrag.Any())
                     {
-                        Editor.FlashMessageIfAble($"{Editor.Error}")
-                    }*/
+                        ErrorReporter?.ShowErrorThatViewIsUsedByOthers(this.dragOperation.PreventDrag);
+                        this.dragOperation.Abandon();
+                    }
 
                     // end drag
                     OperationManager.Instance.Do(this.dragOperation);