Alsing.SourceCode.SyntaxDocument.Undo C# (CSharp) Метод

        public TextPoint Undo()
        {
            if (UndoStep == 0)
                return new TextPoint(-1, -1);


            UndoBlockCollection ActionGroup = UndoBuffer[UndoStep - 1];
            UndoBlock undo = ActionGroup[0];

            for (int i = ActionGroup.Count - 1; i >= 0; i--)
            {
                undo = ActionGroup[i];
                //TextPoint tp=new TextPoint (undo.Position.X,undo.Position.Y);
                switch (undo.Action)
                {
                    case UndoAction.DeleteRange:
                        InsertText(undo.Text, undo.Position.X, undo.Position.Y, false);
                        break;
                    case UndoAction.InsertRange:
                        {
                            TextRange r = GetRangeFromText(undo.Text, undo.Position.X, undo.Position.Y);
                            DeleteRange(r, false);
                        }
                        break;
                    default:
                        break;
                }
            }

            UndoStep--;
            ResetVisibleRows();

            //no undo steps left , the document is not dirty
            if (UndoStep == 0)
                Modified = false;

            var tp = new TextPoint(undo.Position.X, undo.Position.Y);
            OnUndoBufferChanged();
            return tp;
        }