source: trunk/HeuristicLab.ExtLibs/HeuristicLab.AvalonEdit/5.0.1/AvalonEdit-5.0.1/Editing/SelectionMouseHandler.cs

// Copyright (c) 2014 AlphaSierraPapa for the SharpDevelop Team
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

using System;
using System.ComponentModel;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media.TextFormatting;
using System.Windows.Threading;
using ICSharpCode.AvalonEdit.Document;
using ICSharpCode.AvalonEdit.Rendering;
using ICSharpCode.AvalonEdit.Utils;
#if NREFACTORY
using ICSharpCode.NRefactory.Editor;
#endif

namespace ICSharpCode.AvalonEdit.Editing
{
  /// <summary>
  /// Handles selection of text using the mouse.
  /// </summary>
  sealed class SelectionMouseHandler : ITextAreaInputHandler
  {
    #region enum SelectionMode
    enum SelectionMode
    {
      /// <summary>
      /// no selection (no mouse button down)
      /// </summary>
      None,
      /// <summary>
      /// left mouse button down on selection, might be normal click
      /// or might be drag'n'drop
      /// </summary>
      PossibleDragStart,
      /// <summary>
      /// dragging text
      /// </summary>
      Drag,
      /// <summary>
      /// normal selection (click+drag)
      /// </summary>
      Normal,
      /// <summary>
      /// whole-word selection (double click+drag or ctrl+click+drag)
      /// </summary>
      WholeWord,
      /// <summary>
      /// whole-line selection (triple click+drag)
      /// </summary>
      WholeLine,
      /// <summary>
      /// rectangular selection (alt+click+drag)
      /// </summary>
      Rectangular
    }
    #endregion
    
    readonly TextArea textArea;
    
    SelectionMode mode;
    AnchorSegment startWord;
    Point possibleDragStartMousePos;
    
    #region Constructor + Attach + Detach
    public SelectionMouseHandler(TextArea textArea)
    {
      if (textArea == null)
        throw new ArgumentNullException("textArea");
      this.textArea = textArea;
    }
    
    public TextArea TextArea {
      get { return textArea; }
    }
    
    public void Attach()
    {
      textArea.MouseLeftButtonDown += textArea_MouseLeftButtonDown;
      textArea.MouseMove += textArea_MouseMove;
      textArea.MouseLeftButtonUp += textArea_MouseLeftButtonUp;
      textArea.QueryCursor += textArea_QueryCursor;
      textArea.OptionChanged += textArea_OptionChanged;
      
      enableTextDragDrop = textArea.Options.EnableTextDragDrop;
      if (enableTextDragDrop) {
        AttachDragDrop();
      }
    }
    
    public void Detach()
    {
      mode = SelectionMode.None;
      textArea.MouseLeftButtonDown -= textArea_MouseLeftButtonDown;
      textArea.MouseMove -= textArea_MouseMove;
      textArea.MouseLeftButtonUp -= textArea_MouseLeftButtonUp;
      textArea.QueryCursor -= textArea_QueryCursor;
      textArea.OptionChanged -= textArea_OptionChanged;
      if (enableTextDragDrop) {
        DetachDragDrop();
      }
    }
    
    void AttachDragDrop()
    {
      textArea.AllowDrop = true;
      textArea.GiveFeedback += textArea_GiveFeedback;
      textArea.QueryContinueDrag += textArea_QueryContinueDrag;
      textArea.DragEnter += textArea_DragEnter;
      textArea.DragOver += textArea_DragOver;
      textArea.DragLeave += textArea_DragLeave;
      textArea.Drop += textArea_Drop;
    }
    
    void DetachDragDrop()
    {
      textArea.AllowDrop = false;
      textArea.GiveFeedback -= textArea_GiveFeedback;
      textArea.QueryContinueDrag -= textArea_QueryContinueDrag;
      textArea.DragEnter -= textArea_DragEnter;
      textArea.DragOver -= textArea_DragOver;
      textArea.DragLeave -= textArea_DragLeave;
      textArea.Drop -= textArea_Drop;
    }
    
    bool enableTextDragDrop;
    
    void textArea_OptionChanged(object sender, PropertyChangedEventArgs e)
    {
      bool newEnableTextDragDrop = textArea.Options.EnableTextDragDrop;
      if (newEnableTextDragDrop != enableTextDragDrop) {
        enableTextDragDrop = newEnableTextDragDrop;
        if (newEnableTextDragDrop)
          AttachDragDrop();
        else
          DetachDragDrop();
      }
    }
    #endregion
    
    #region Dropping text
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
    void textArea_DragEnter(object sender, DragEventArgs e)
    {
      try {
        e.Effects = GetEffect(e);
        textArea.Caret.Show();
      } catch (Exception ex) {
        OnDragException(ex);
      }
    }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
    void textArea_DragOver(object sender, DragEventArgs e)
    {
      try {
        e.Effects = GetEffect(e);
      } catch (Exception ex) {
        OnDragException(ex);
      }
    }
    
    DragDropEffects GetEffect(DragEventArgs e)
    {
      if (e.Data.GetDataPresent(DataFormats.UnicodeText, true)) {
        e.Handled = true;
        int visualColumn;
        bool isAtEndOfLine;
        int offset = GetOffsetFromMousePosition(e.GetPosition(textArea.TextView), out visualColumn, out isAtEndOfLine);
        if (offset >= 0) {
          textArea.Caret.Position = new TextViewPosition(textArea.Document.GetLocation(offset), visualColumn) { IsAtEndOfLine = isAtEndOfLine };
          textArea.Caret.DesiredXPos = double.NaN;
          if (textArea.ReadOnlySectionProvider.CanInsert(offset)) {
            if ((e.AllowedEffects & DragDropEffects.Move) == DragDropEffects.Move
                && (e.KeyStates & DragDropKeyStates.ControlKey) != DragDropKeyStates.ControlKey)
            {
              return DragDropEffects.Move;
            } else {
              return e.AllowedEffects & DragDropEffects.Copy;
            }
          }
        }
      }
      return DragDropEffects.None;
    }
    
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
    void textArea_DragLeave(object sender, DragEventArgs e)
    {
      try {
        e.Handled = true;
        if (!textArea.IsKeyboardFocusWithin)
          textArea.Caret.Hide();
      } catch (Exception ex) {
        OnDragException(ex);
      }
    }
    
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
    void textArea_Drop(object sender, DragEventArgs e)
    {
      try {
        DragDropEffects effect = GetEffect(e);
        e.Effects = effect;
        if (effect != DragDropEffects.None) {
          string text = e.Data.GetData(DataFormats.UnicodeText, true) as string;
          if (text != null) {
            int start = textArea.Caret.Offset;
            if (mode == SelectionMode.Drag && textArea.Selection.Contains(start)) {
              Debug.WriteLine("Drop: did not drop: drop target is inside selection");
              e.Effects = DragDropEffects.None;
            } else {
              Debug.WriteLine("Drop: insert at " + start);
              
              bool rectangular = e.Data.GetDataPresent(RectangleSelection.RectangularSelectionDataType);
              
              string newLine = TextUtilities.GetNewLineFromDocument(textArea.Document, textArea.Caret.Line);
              text = TextUtilities.NormalizeNewLines(text, newLine);
              
              string pasteFormat;
              // fill the suggested DataFormat used for the paste action:
              if (rectangular)
                pasteFormat = RectangleSelection.RectangularSelectionDataType;
              else
                pasteFormat = DataFormats.UnicodeText;
              
              var pastingEventArgs = new DataObjectPastingEventArgs(e.Data, true, pasteFormat);
              textArea.RaiseEvent(pastingEventArgs);
              if (pastingEventArgs.CommandCancelled)
                return;
              
              // DataObject.PastingEvent handlers might have changed the format to apply.
              rectangular = pastingEventArgs.FormatToApply == RectangleSelection.RectangularSelectionDataType;
              
              // Mark the undo group with the currentDragDescriptor, if the drag
              // is originating from the same control. This allows combining
              // the undo groups when text is moved.
              textArea.Document.UndoStack.StartUndoGroup(this.currentDragDescriptor);
              try {
                if (rectangular && RectangleSelection.PerformRectangularPaste(textArea, textArea.Caret.Position, text, true)) {
                  
                } else {
                  textArea.Document.Insert(start, text);
                  textArea.Selection = Selection.Create(textArea, start, start + text.Length);
                }
              } finally {
                textArea.Document.UndoStack.EndUndoGroup();
              }
            }
            e.Handled = true;
          }
        }
      } catch (Exception ex) {
        OnDragException(ex);
      }
    }
    
    void OnDragException(Exception ex)
    {
      // WPF swallows exceptions during drag'n'drop or reports them incorrectly, so
      // we re-throw them later to allow the application's unhandled exception handler
      // to catch them
      textArea.Dispatcher.BeginInvoke(
        DispatcherPriority.Send,
        new Action(delegate {
                    throw new DragDropException("Exception during drag'n'drop", ex);
                   }));
    }
    
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
    void textArea_GiveFeedback(object sender, GiveFeedbackEventArgs e)
    {
      try {
        e.UseDefaultCursors = true;
        e.Handled = true;
      } catch (Exception ex) {
        OnDragException(ex);
      }
    }
    
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
    void textArea_QueryContinueDrag(object sender, QueryContinueDragEventArgs e)
    {
      try {
        if (e.EscapePressed) {
          e.Action = DragAction.Cancel;
        } else if ((e.KeyStates & DragDropKeyStates.LeftMouseButton) != DragDropKeyStates.LeftMouseButton) {
          e.Action = DragAction.Drop;
        } else {
          e.Action = DragAction.Continue;
        }
        e.Handled = true;
      } catch (Exception ex) {
        OnDragException(ex);
      }
    }
    #endregion
    
    #region Start Drag
    object currentDragDescriptor;
    
    void StartDrag()
    {
      // prevent nested StartDrag calls
      mode = SelectionMode.Drag;
      
      // mouse capture and Drag'n'Drop doesn't mix
      textArea.ReleaseMouseCapture();
      
      DataObject dataObject = textArea.Selection.CreateDataObject(textArea);
      
      DragDropEffects allowedEffects = DragDropEffects.All;
      var deleteOnMove = textArea.Selection.Segments.Select(s => new AnchorSegment(textArea.Document, s)).ToList();
      foreach (ISegment s in deleteOnMove) {
        ISegment[] result = textArea.GetDeletableSegments(s);
        if (result.Length != 1 || result[0].Offset != s.Offset || result[0].EndOffset != s.EndOffset) {
          allowedEffects &= ~DragDropEffects.Move;
        }
      }
      
      var copyingEventArgs = new DataObjectCopyingEventArgs(dataObject, true);
      textArea.RaiseEvent(copyingEventArgs);
      if (copyingEventArgs.CommandCancelled)
        return;
      
      object dragDescriptor = new object();
      this.currentDragDescriptor = dragDescriptor;
      
      DragDropEffects resultEffect;
      using (textArea.AllowCaretOutsideSelection()) {
        var oldCaretPosition = textArea.Caret.Position;
        try {
          Debug.WriteLine("DoDragDrop with allowedEffects=" + allowedEffects);
          resultEffect = DragDrop.DoDragDrop(textArea, dataObject, allowedEffects);
          Debug.WriteLine("DoDragDrop done, resultEffect=" + resultEffect);
        } catch (COMException ex) {
          // ignore COM errors - don't crash on badly implemented drop targets
          Debug.WriteLine("DoDragDrop failed: " + ex.ToString());
          return;
        }
        if (resultEffect == DragDropEffects.None) {
          // reset caret if drag was aborted
          textArea.Caret.Position = oldCaretPosition;
        }
      }
      
      this.currentDragDescriptor = null;
      
      if (deleteOnMove != null && resultEffect == DragDropEffects.Move && (allowedEffects & DragDropEffects.Move) == DragDropEffects.Move) {
        bool draggedInsideSingleDocument = (dragDescriptor == textArea.Document.UndoStack.LastGroupDescriptor);
        if (draggedInsideSingleDocument)
          textArea.Document.UndoStack.StartContinuedUndoGroup(null);
        textArea.Document.BeginUpdate();
        try {
          foreach (ISegment s in deleteOnMove) {
            textArea.Document.Remove(s.Offset, s.Length);
          }
        } finally {
          textArea.Document.EndUpdate();
          if (draggedInsideSingleDocument)
            textArea.Document.UndoStack.EndUndoGroup();
        }
      }
    }
    #endregion
    
    #region QueryCursor
    // provide the IBeam Cursor for the text area
    void textArea_QueryCursor(object sender, QueryCursorEventArgs e)
    {
      if (!e.Handled) {
        if (mode != SelectionMode.None || !enableTextDragDrop) {
          e.Cursor = Cursors.IBeam;
          e.Handled = true;
        } else if (textArea.TextView.VisualLinesValid) {
          // Only query the cursor if the visual lines are valid.
          // If they are invalid, the cursor will get re-queried when the visual lines
          // get refreshed.
          Point p = e.GetPosition(textArea.TextView);
          if (p.X >= 0 && p.Y >= 0 && p.X <= textArea.TextView.ActualWidth && p.Y <= textArea.TextView.ActualHeight) {
            int visualColumn;
            bool isAtEndOfLine;
            int offset = GetOffsetFromMousePosition(e, out visualColumn, out isAtEndOfLine);
            if (textArea.Selection.Contains(offset))
              e.Cursor = Cursors.Arrow;
            else
              e.Cursor = Cursors.IBeam;
            e.Handled = true;
          }
        }
      }
    }
    #endregion
    
    #region LeftButtonDown
    void textArea_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
      mode = SelectionMode.None;
      if (!e.Handled && e.ChangedButton == MouseButton.Left) {
        ModifierKeys modifiers = Keyboard.Modifiers;
        bool shift = (modifiers & ModifierKeys.Shift) == ModifierKeys.Shift;
        if (enableTextDragDrop && e.ClickCount == 1 && !shift) {
          int visualColumn;
          bool isAtEndOfLine;
          int offset = GetOffsetFromMousePosition(e, out visualColumn, out isAtEndOfLine);
          if (textArea.Selection.Contains(offset)) {
            if (textArea.CaptureMouse()) {
              mode = SelectionMode.PossibleDragStart;
              possibleDragStartMousePos = e.GetPosition(textArea);
            }
            e.Handled = true;
            return;
          }
        }
        
        var oldPosition = textArea.Caret.Position;
        SetCaretOffsetToMousePosition(e);
        
        
        if (!shift) {
          textArea.ClearSelection();
        }
        if (textArea.CaptureMouse()) {
          if ((modifiers & ModifierKeys.Alt) == ModifierKeys.Alt && textArea.Options.EnableRectangularSelection) {
            mode = SelectionMode.Rectangular;
            if (shift && textArea.Selection is RectangleSelection) {
              textArea.Selection = textArea.Selection.StartSelectionOrSetEndpoint(oldPosition, textArea.Caret.Position);
            }
          } else if (e.ClickCount == 1 && ((modifiers & ModifierKeys.Control) == 0)) {
            mode = SelectionMode.Normal;
            if (shift && !(textArea.Selection is RectangleSelection)) {
              textArea.Selection = textArea.Selection.StartSelectionOrSetEndpoint(oldPosition, textArea.Caret.Position);
            }
          } else {
            SimpleSegment startWord;
            if (e.ClickCount == 3) {
              mode = SelectionMode.WholeLine;
              startWord = GetLineAtMousePosition(e);
            } else {
              mode = SelectionMode.WholeWord;
              startWord = GetWordAtMousePosition(e);
            }
            if (startWord == SimpleSegment.Invalid) {
              mode = SelectionMode.None;
              textArea.ReleaseMouseCapture();
              return;
            }
            if (shift && !textArea.Selection.IsEmpty) {
              if (startWord.Offset < textArea.Selection.SurroundingSegment.Offset) {
                textArea.Selection = textArea.Selection.SetEndpoint(new TextViewPosition(textArea.Document.GetLocation(startWord.Offset)));
              } else if (startWord.EndOffset > textArea.Selection.SurroundingSegment.EndOffset) {
                textArea.Selection = textArea.Selection.SetEndpoint(new TextViewPosition(textArea.Document.GetLocation(startWord.EndOffset)));
              }
              this.startWord = new AnchorSegment(textArea.Document, textArea.Selection.SurroundingSegment);
            } else {
              textArea.Selection = Selection.Create(textArea, startWord.Offset, startWord.EndOffset);
              this.startWord = new AnchorSegment(textArea.Document, startWord.Offset, startWord.Length);
            }
          }
        }
      }
      e.Handled = true;
    }
    #endregion
    
    #region Mouse Position <-> Text coordinates
    SimpleSegment GetWordAtMousePosition(MouseEventArgs e)
    {
      TextView textView = textArea.TextView;
      if (textView == null) return SimpleSegment.Invalid;
      Point pos = e.GetPosition(textView);
      if (pos.Y < 0)
        pos.Y = 0;
      if (pos.Y > textView.ActualHeight)
        pos.Y = textView.ActualHeight;
      pos += textView.ScrollOffset;
      VisualLine line = textView.GetVisualLineFromVisualTop(pos.Y);
      if (line != null) {
        int visualColumn = line.GetVisualColumn(pos, textArea.Selection.EnableVirtualSpace);
        int wordStartVC = line.GetNextCaretPosition(visualColumn + 1, LogicalDirection.Backward, CaretPositioningMode.WordStartOrSymbol, textArea.Selection.EnableVirtualSpace);
        if (wordStartVC == -1)
          wordStartVC = 0;
        int wordEndVC = line.GetNextCaretPosition(wordStartVC, LogicalDirection.Forward, CaretPositioningMode.WordBorderOrSymbol, textArea.Selection.EnableVirtualSpace);
        if (wordEndVC == -1)
          wordEndVC = line.VisualLength;
        int relOffset = line.FirstDocumentLine.Offset;
        int wordStartOffset = line.GetRelativeOffset(wordStartVC) + relOffset;
        int wordEndOffset = line.GetRelativeOffset(wordEndVC) + relOffset;
        return new SimpleSegment(wordStartOffset, wordEndOffset - wordStartOffset);
      } else {
        return SimpleSegment.Invalid;
      }
    }
    
    SimpleSegment GetLineAtMousePosition(MouseEventArgs e)
    {
      TextView textView = textArea.TextView;
      if (textView == null) return SimpleSegment.Invalid;
      Point pos = e.GetPosition(textView);
      if (pos.Y < 0)
        pos.Y = 0;
      if (pos.Y > textView.ActualHeight)
        pos.Y = textView.ActualHeight;
      pos += textView.ScrollOffset;
      VisualLine line = textView.GetVisualLineFromVisualTop(pos.Y);
      if (line != null) {
        return new SimpleSegment(line.StartOffset, line.LastDocumentLine.EndOffset - line.StartOffset);
      } else {
        return SimpleSegment.Invalid;
      }
    }
    
    int GetOffsetFromMousePosition(MouseEventArgs e, out int visualColumn, out bool isAtEndOfLine)
    {
      return GetOffsetFromMousePosition(e.GetPosition(textArea.TextView), out visualColumn, out isAtEndOfLine);
    }
    
    int GetOffsetFromMousePosition(Point positionRelativeToTextView, out int visualColumn, out bool isAtEndOfLine)
    {
      visualColumn = 0;
      TextView textView = textArea.TextView;
      Point pos = positionRelativeToTextView;
      if (pos.Y < 0)
        pos.Y = 0;
      if (pos.Y > textView.ActualHeight)
        pos.Y = textView.ActualHeight;
      pos += textView.ScrollOffset;
      if (pos.Y > textView.DocumentHeight)
        pos.Y = textView.DocumentHeight - ExtensionMethods.Epsilon;
      VisualLine line = textView.GetVisualLineFromVisualTop(pos.Y);
      if (line != null) {
        visualColumn = line.GetVisualColumn(pos, textArea.Selection.EnableVirtualSpace, out isAtEndOfLine);
        return line.GetRelativeOffset(visualColumn) + line.FirstDocumentLine.Offset;
      }
      isAtEndOfLine = false;
      return -1;
    }
    
    int GetOffsetFromMousePositionFirstTextLineOnly(Point positionRelativeToTextView, out int visualColumn)
    {
      visualColumn = 0;
      TextView textView = textArea.TextView;
      Point pos = positionRelativeToTextView;
      if (pos.Y < 0)
        pos.Y = 0;
      if (pos.Y > textView.ActualHeight)
        pos.Y = textView.ActualHeight;
      pos += textView.ScrollOffset;
      if (pos.Y > textView.DocumentHeight)
        pos.Y = textView.DocumentHeight - ExtensionMethods.Epsilon;
      VisualLine line = textView.GetVisualLineFromVisualTop(pos.Y);
      if (line != null) {
        visualColumn = line.GetVisualColumn(line.TextLines.First(), pos.X, textArea.Selection.EnableVirtualSpace);
        return line.GetRelativeOffset(visualColumn) + line.FirstDocumentLine.Offset;
      }
      return -1;
    }
    #endregion
    
    #region MouseMove
    void textArea_MouseMove(object sender, MouseEventArgs e)
    {
      if (e.Handled)
        return;
      if (mode == SelectionMode.Normal || mode == SelectionMode.WholeWord || mode == SelectionMode.WholeLine || mode == SelectionMode.Rectangular) {
        e.Handled = true;
        if (textArea.TextView.VisualLinesValid) {
          // If the visual lines are not valid, don't extend the selection.
          // Extending the selection forces a VisualLine refresh, and it is sufficient
          // to do that on MouseUp, we don't have to do it every MouseMove.
          ExtendSelectionToMouse(e);
        }
      } else if (mode == SelectionMode.PossibleDragStart) {
        e.Handled = true;
        Vector mouseMovement = e.GetPosition(textArea) - possibleDragStartMousePos;
        if (Math.Abs(mouseMovement.X) > SystemParameters.MinimumHorizontalDragDistance
            || Math.Abs(mouseMovement.Y) > SystemParameters.MinimumVerticalDragDistance)
        {
          StartDrag();
        }
      }
    }
    #endregion
    
    #region ExtendSelection
    void SetCaretOffsetToMousePosition(MouseEventArgs e)
    {
      SetCaretOffsetToMousePosition(e, null);
    }
    
    void SetCaretOffsetToMousePosition(MouseEventArgs e, ISegment allowedSegment)
    {
      int visualColumn;
      bool isAtEndOfLine;
      int offset;
      if (mode == SelectionMode.Rectangular) {
        offset = GetOffsetFromMousePositionFirstTextLineOnly(e.GetPosition(textArea.TextView), out visualColumn);
        isAtEndOfLine = true;
      } else {
        offset = GetOffsetFromMousePosition(e, out visualColumn, out isAtEndOfLine);
      }
      if (allowedSegment != null) {
        offset = offset.CoerceValue(allowedSegment.Offset, allowedSegment.EndOffset);
      }
      if (offset >= 0) {
        textArea.Caret.Position = new TextViewPosition(textArea.Document.GetLocation(offset), visualColumn) { IsAtEndOfLine = isAtEndOfLine };
        textArea.Caret.DesiredXPos = double.NaN;
      }
    }
    
    void ExtendSelectionToMouse(MouseEventArgs e)
    {
      TextViewPosition oldPosition = textArea.Caret.Position;
      if (mode == SelectionMode.Normal || mode == SelectionMode.Rectangular) {
        SetCaretOffsetToMousePosition(e);
        if (mode == SelectionMode.Normal && textArea.Selection is RectangleSelection)
          textArea.Selection = new SimpleSelection(textArea, oldPosition, textArea.Caret.Position);
        else if (mode == SelectionMode.Rectangular && !(textArea.Selection is RectangleSelection))
          textArea.Selection = new RectangleSelection(textArea, oldPosition, textArea.Caret.Position);
        else
          textArea.Selection = textArea.Selection.StartSelectionOrSetEndpoint(oldPosition, textArea.Caret.Position);
      } else if (mode == SelectionMode.WholeWord || mode == SelectionMode.WholeLine) {
        var newWord = (mode == SelectionMode.WholeLine) ? GetLineAtMousePosition(e) : GetWordAtMousePosition(e);
        if (newWord != SimpleSegment.Invalid) {
          textArea.Selection = Selection.Create(textArea,
                                                Math.Min(newWord.Offset, startWord.Offset),
                                                Math.Max(newWord.EndOffset, startWord.EndOffset));
          // Set caret offset, but limit the caret to stay inside the selection.
          // in whole-word selection, it's otherwise possible that we get the caret outside the
          // selection - but the TextArea doesn't like that and will reset the selection, causing
          // flickering.
          SetCaretOffsetToMousePosition(e, textArea.Selection.SurroundingSegment);
        }
      }
      textArea.Caret.BringCaretToView(5.0);
    }
    #endregion
    
    #region MouseLeftButtonUp
    void textArea_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
    {
      if (mode == SelectionMode.None || e.Handled)
        return;
      e.Handled = true;
      if (mode == SelectionMode.PossibleDragStart) {
        // -> this was not a drag start (mouse didn't move after mousedown)
        SetCaretOffsetToMousePosition(e);
        textArea.ClearSelection();
      } else if (mode == SelectionMode.Normal || mode == SelectionMode.WholeWord || mode == SelectionMode.WholeLine || mode == SelectionMode.Rectangular) {
        ExtendSelectionToMouse(e);
      }
      mode = SelectionMode.None;
      textArea.ReleaseMouseCapture();
    }
    #endregion
  }
}