source: trunk/sources/HeuristicLab.ExtLibs/HeuristicLab.AvalonEdit/5.0.1/AvalonEdit-5.0.1/Rendering/HeightTree.cs @ 12626

// 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.Collections.Generic;
using System.Diagnostics;
using System.Text;

using ICSharpCode.AvalonEdit.Document;
using ICSharpCode.AvalonEdit.Utils;

namespace ICSharpCode.AvalonEdit.Rendering
{
  /// <summary>
  /// Red-black tree similar to DocumentLineTree, augmented with collapsing and height data.
  /// </summary>
  sealed class HeightTree : ILineTracker, IDisposable
  {
    // TODO: Optimize this. This tree takes alot of memory.
    // (56 bytes for HeightTreeNode
    // We should try to get rid of the dictionary and find height nodes per index. (DONE!)
    // And we might do much better by compressing lines with the same height into a single node.
    // That would also improve load times because we would always start with just a single node.
    
    /* Idea:
     class NewHeightTreeNode {
      int totalCount; // =count+left.count+right.count
      int count; // one node can represent multiple lines
      double height; // height of each line in this node
      double totalHeight; // =(collapsedSections!=null?0:height*count) + left.totalHeight + right.totalHeight
      List<CollapsedSection> collapsedSections; // sections holding this line collapsed
      // no "nodeCollapsedSections"/"totalCollapsedSections":
      NewHeightTreeNode left, right, parent;
      bool color;
    }
    totalCollapsedSections: are hard to update and not worth the effort. O(n log n) isn't too bad for
     collapsing/uncollapsing, especially when compression reduces the n.
     */
    
    #region Constructor
    readonly TextDocument document;
    HeightTreeNode root;
    WeakLineTracker weakLineTracker;
    
    public HeightTree(TextDocument document, double defaultLineHeight)
    {
      this.document = document;
      weakLineTracker = WeakLineTracker.Register(document, this);
      this.DefaultLineHeight = defaultLineHeight;
      RebuildDocument();
    }
    
    public void Dispose()
    {
      if (weakLineTracker != null)
        weakLineTracker.Deregister();
      this.root = null;
      this.weakLineTracker = null;
    }
    
    double defaultLineHeight;
    
    public double DefaultLineHeight {
      get { return defaultLineHeight; }
      set {
        double oldValue = defaultLineHeight;
        if (oldValue == value)
          return;
        defaultLineHeight = value;
        // update the stored value in all nodes:
        foreach (var node in AllNodes) {
          if (node.lineNode.height == oldValue) {
            node.lineNode.height = value;
            UpdateAugmentedData(node, UpdateAfterChildrenChangeRecursionMode.IfRequired);
          }
        }
      }
    }
    
    HeightTreeNode GetNode(DocumentLine ls)
    {
      return GetNodeByIndex(ls.LineNumber - 1);
    }
    #endregion
    
    #region RebuildDocument
    void ILineTracker.ChangeComplete(DocumentChangeEventArgs e)
    {
    }
    
    void ILineTracker.SetLineLength(DocumentLine ls, int newTotalLength)
    {
    }
    
    /// <summary>
    /// Rebuild the tree, in O(n).
    /// </summary>
    public void RebuildDocument()
    {
      foreach (CollapsedLineSection s in GetAllCollapsedSections()) {
        s.Start = null;
        s.End = null;
      }
      
      HeightTreeNode[] nodes = new HeightTreeNode[document.LineCount];
      int lineNumber = 0;
      foreach (DocumentLine ls in document.Lines) {
        nodes[lineNumber++] = new HeightTreeNode(ls, defaultLineHeight);
      }
      Debug.Assert(nodes.Length > 0);
      // now build the corresponding balanced tree
      int height = DocumentLineTree.GetTreeHeight(nodes.Length);
      Debug.WriteLine("HeightTree will have height: " + height);
      root = BuildTree(nodes, 0, nodes.Length, height);
      root.color = BLACK;
      #if DEBUG
      CheckProperties();
      #endif
    }
    
    /// <summary>
    /// build a tree from a list of nodes
    /// </summary>
    HeightTreeNode BuildTree(HeightTreeNode[] nodes, int start, int end, int subtreeHeight)
    {
      Debug.Assert(start <= end);
      if (start == end) {
        return null;
      }
      int middle = (start + end) / 2;
      HeightTreeNode node = nodes[middle];
      node.left = BuildTree(nodes, start, middle, subtreeHeight - 1);
      node.right = BuildTree(nodes, middle + 1, end, subtreeHeight - 1);
      if (node.left != null) node.left.parent = node;
      if (node.right != null) node.right.parent = node;
      if (subtreeHeight == 1)
        node.color = RED;
      UpdateAugmentedData(node, UpdateAfterChildrenChangeRecursionMode.None);
      return node;
    }
    #endregion
    
    #region Insert/Remove lines
    void ILineTracker.BeforeRemoveLine(DocumentLine line)
    {
      HeightTreeNode node = GetNode(line);
      if (node.lineNode.collapsedSections != null) {
        foreach (CollapsedLineSection cs in node.lineNode.collapsedSections.ToArray()) {
          if (cs.Start == line && cs.End == line) {
            cs.Start = null;
            cs.End = null;
          } else if (cs.Start == line) {
            Uncollapse(cs);
            cs.Start = line.NextLine;
            AddCollapsedSection(cs, cs.End.LineNumber - cs.Start.LineNumber + 1);
          } else if (cs.End == line) {
            Uncollapse(cs);
            cs.End = line.PreviousLine;
            AddCollapsedSection(cs, cs.End.LineNumber - cs.Start.LineNumber + 1);
          }
        }
      }
      BeginRemoval();
      RemoveNode(node);
      // clear collapsedSections from removed line: prevent damage if removed line is in "nodesToCheckForMerging"
      node.lineNode.collapsedSections = null;
      EndRemoval();
    }
    
//    void ILineTracker.AfterRemoveLine(DocumentLine line)
//    {
//
//    }
    
    void ILineTracker.LineInserted(DocumentLine insertionPos, DocumentLine newLine)
    {
      InsertAfter(GetNode(insertionPos), newLine);
      #if DEBUG
      CheckProperties();
      #endif
    }
    
    HeightTreeNode InsertAfter(HeightTreeNode node, DocumentLine newLine)
    {
      HeightTreeNode newNode = new HeightTreeNode(newLine, defaultLineHeight);
      if (node.right == null) {
        if (node.lineNode.collapsedSections != null) {
          // we are inserting directly after node - so copy all collapsedSections
          // that do not end at node.
          foreach (CollapsedLineSection cs in node.lineNode.collapsedSections) {
            if (cs.End != node.documentLine)
              newNode.AddDirectlyCollapsed(cs);
          }
        }
        InsertAsRight(node, newNode);
      } else {
        node = node.right.LeftMost;
        if (node.lineNode.collapsedSections != null) {
          // we are inserting directly before node - so copy all collapsedSections
          // that do not start at node.
          foreach (CollapsedLineSection cs in node.lineNode.collapsedSections) {
            if (cs.Start != node.documentLine)
              newNode.AddDirectlyCollapsed(cs);
          }
        }
        InsertAsLeft(node, newNode);
      }
      return newNode;
    }
    #endregion
    
    #region Rotation callbacks
    enum UpdateAfterChildrenChangeRecursionMode
    {
      None,
      IfRequired,
      WholeBranch
    }
    
    static void UpdateAfterChildrenChange(HeightTreeNode node)
    {
      UpdateAugmentedData(node, UpdateAfterChildrenChangeRecursionMode.IfRequired);
    }
    
    static void UpdateAugmentedData(HeightTreeNode node, UpdateAfterChildrenChangeRecursionMode mode)
    {
      int totalCount = 1;
      double totalHeight = node.lineNode.TotalHeight;
      if (node.left != null) {
        totalCount += node.left.totalCount;
        totalHeight += node.left.totalHeight;
      }
      if (node.right != null) {
        totalCount += node.right.totalCount;
        totalHeight += node.right.totalHeight;
      }
      if (node.IsDirectlyCollapsed)
        totalHeight = 0;
      if (totalCount != node.totalCount
          || !totalHeight.IsClose(node.totalHeight)
          || mode == UpdateAfterChildrenChangeRecursionMode.WholeBranch)
      {
        node.totalCount = totalCount;
        node.totalHeight = totalHeight;
        if (node.parent != null && mode != UpdateAfterChildrenChangeRecursionMode.None)
          UpdateAugmentedData(node.parent, mode);
      }
    }
    
    void UpdateAfterRotateLeft(HeightTreeNode node)
    {
      // node = old parent
      // node.parent = pivot, new parent
      var collapsedP = node.parent.collapsedSections;
      var collapsedQ = node.collapsedSections;
      // move collapsedSections from old parent to new parent
      node.parent.collapsedSections = collapsedQ;
      node.collapsedSections = null;
      // split the collapsedSections from the new parent into its old children:
      if (collapsedP != null) {
        foreach (CollapsedLineSection cs in collapsedP) {
          if (node.parent.right != null)
            node.parent.right.AddDirectlyCollapsed(cs);
          node.parent.lineNode.AddDirectlyCollapsed(cs);
          if (node.right != null)
            node.right.AddDirectlyCollapsed(cs);
        }
      }
      MergeCollapsedSectionsIfPossible(node);
      
      UpdateAfterChildrenChange(node);
      
      // not required: rotations only happen on insertions/deletions
      // -> totalCount changes -> the parent is always updated
      //UpdateAfterChildrenChange(node.parent);
    }
    
    void UpdateAfterRotateRight(HeightTreeNode node)
    {
      // node = old parent
      // node.parent = pivot, new parent
      var collapsedP = node.parent.collapsedSections;
      var collapsedQ = node.collapsedSections;
      // move collapsedSections from old parent to new parent
      node.parent.collapsedSections = collapsedQ;
      node.collapsedSections = null;
      // split the collapsedSections from the new parent into its old children:
      if (collapsedP != null) {
        foreach (CollapsedLineSection cs in collapsedP) {
          if (node.parent.left != null)
            node.parent.left.AddDirectlyCollapsed(cs);
          node.parent.lineNode.AddDirectlyCollapsed(cs);
          if (node.left != null)
            node.left.AddDirectlyCollapsed(cs);
        }
      }
      MergeCollapsedSectionsIfPossible(node);
      
      UpdateAfterChildrenChange(node);
      
      // not required: rotations only happen on insertions/deletions
      // -> totalCount changes -> the parent is always updated
      //UpdateAfterChildrenChange(node.parent);
    }
    
    // node removal:
    // a node in the middle of the tree is removed as following:
    //  its successor is removed
    //  it is replaced with its successor
    
    void BeforeNodeRemove(HeightTreeNode removedNode)
    {
      Debug.Assert(removedNode.left == null || removedNode.right == null);
      
      var collapsed = removedNode.collapsedSections;
      if (collapsed != null) {
        HeightTreeNode childNode = removedNode.left ?? removedNode.right;
        if (childNode != null) {
          foreach (CollapsedLineSection cs in collapsed)
            childNode.AddDirectlyCollapsed(cs);
        }
      }
      if (removedNode.parent != null)
        MergeCollapsedSectionsIfPossible(removedNode.parent);
    }
    
    void BeforeNodeReplace(HeightTreeNode removedNode, HeightTreeNode newNode, HeightTreeNode newNodeOldParent)
    {
      Debug.Assert(removedNode != null);
      Debug.Assert(newNode != null);
      while (newNodeOldParent != removedNode) {
        if (newNodeOldParent.collapsedSections != null) {
          foreach (CollapsedLineSection cs in newNodeOldParent.collapsedSections) {
            newNode.lineNode.AddDirectlyCollapsed(cs);
          }
        }
        newNodeOldParent = newNodeOldParent.parent;
      }
      if (newNode.collapsedSections != null) {
        foreach (CollapsedLineSection cs in newNode.collapsedSections) {
          newNode.lineNode.AddDirectlyCollapsed(cs);
        }
      }
      newNode.collapsedSections = removedNode.collapsedSections;
      MergeCollapsedSectionsIfPossible(newNode);
    }
    
    bool inRemoval;
    List<HeightTreeNode> nodesToCheckForMerging;
    
    void BeginRemoval()
    {
      Debug.Assert(!inRemoval);
      if (nodesToCheckForMerging == null) {
        nodesToCheckForMerging = new List<HeightTreeNode>();
      }
      inRemoval = true;
    }
    
    void EndRemoval()
    {
      Debug.Assert(inRemoval);
      inRemoval = false;
      foreach (HeightTreeNode node in nodesToCheckForMerging) {
        MergeCollapsedSectionsIfPossible(node);
      }
      nodesToCheckForMerging.Clear();
    }
    
    void MergeCollapsedSectionsIfPossible(HeightTreeNode node)
    {
      Debug.Assert(node != null);
      if (inRemoval) {
        nodesToCheckForMerging.Add(node);
        return;
      }
      // now check if we need to merge collapsedSections together
      bool merged = false;
      var collapsedL = node.lineNode.collapsedSections;
      if (collapsedL != null) {
        for (int i = collapsedL.Count - 1; i >= 0; i--) {
          CollapsedLineSection cs = collapsedL[i];
          if (cs.Start == node.documentLine || cs.End == node.documentLine)
            continue;
          if (node.left == null
              || (node.left.collapsedSections != null && node.left.collapsedSections.Contains(cs)))
          {
            if (node.right == null
                || (node.right.collapsedSections != null && node.right.collapsedSections.Contains(cs)))
            {
              // all children of node contain cs: -> merge!
              if (node.left != null) node.left.RemoveDirectlyCollapsed(cs);
              if (node.right != null) node.right.RemoveDirectlyCollapsed(cs);
              collapsedL.RemoveAt(i);
              node.AddDirectlyCollapsed(cs);
              merged = true;
            }
          }
        }
        if (collapsedL.Count == 0)
          node.lineNode.collapsedSections = null;
      }
      if (merged && node.parent != null) {
        MergeCollapsedSectionsIfPossible(node.parent);
      }
    }
    #endregion
    
    #region GetNodeBy... / Get...FromNode
    HeightTreeNode GetNodeByIndex(int index)
    {
      Debug.Assert(index >= 0);
      Debug.Assert(index < root.totalCount);
      HeightTreeNode node = root;
      while (true) {
        if (node.left != null && index < node.left.totalCount) {
          node = node.left;
        } else {
          if (node.left != null) {
            index -= node.left.totalCount;
          }
          if (index == 0)
            return node;
          index--;
          node = node.right;
        }
      }
    }
    
    HeightTreeNode GetNodeByVisualPosition(double position)
    {
      HeightTreeNode node = root;
      while (true) {
        double positionAfterLeft = position;
        if (node.left != null) {
          positionAfterLeft -= node.left.totalHeight;
          if (positionAfterLeft < 0) {
            // Descend into left
            node = node.left;
            continue;
          }
        }
        double positionBeforeRight = positionAfterLeft - node.lineNode.TotalHeight;
        if (positionBeforeRight < 0) {
          // Found the correct node
          return node;
        }
        if (node.right == null || node.right.totalHeight == 0) {
          // Can happen when position>node.totalHeight,
          // i.e. at the end of the document, or due to rounding errors in previous loop iterations.
          
          // If node.lineNode isn't collapsed, return that.
          // Also return node.lineNode if there is no previous node that we could return instead.
          if (node.lineNode.TotalHeight > 0 || node.left == null)
            return node;
          // Otherwise, descend into left (find the last non-collapsed node)
          node = node.left;
        } else {
          // Descend into right
          position = positionBeforeRight;
          node = node.right;
        }
      }
    }
    
    static double GetVisualPositionFromNode(HeightTreeNode node)
    {
      double position = (node.left != null) ? node.left.totalHeight : 0;
      while (node.parent != null) {
        if (node.IsDirectlyCollapsed)
          position = 0;
        if (node == node.parent.right) {
          if (node.parent.left != null)
            position += node.parent.left.totalHeight;
          position += node.parent.lineNode.TotalHeight;
        }
        node = node.parent;
      }
      return position;
    }
    #endregion
    
    #region Public methods
    public DocumentLine GetLineByNumber(int number)
    {
      return GetNodeByIndex(number - 1).documentLine;
    }
    
    public DocumentLine GetLineByVisualPosition(double position)
    {
      return GetNodeByVisualPosition(position).documentLine;
    }
    
    public double GetVisualPosition(DocumentLine line)
    {
      return GetVisualPositionFromNode(GetNode(line));
    }
    
    public double GetHeight(DocumentLine line)
    {
      return GetNode(line).lineNode.height;
    }
    
    public void SetHeight(DocumentLine line, double val)
    {
      var node = GetNode(line);
      node.lineNode.height = val;
      UpdateAfterChildrenChange(node);
    }
    
    public bool GetIsCollapsed(int lineNumber)
    {
      var node = GetNodeByIndex(lineNumber - 1);
      return node.lineNode.IsDirectlyCollapsed || GetIsCollapedFromNode(node);
    }
    
    /// <summary>
    /// Collapses the specified text section.
    /// Runtime: O(log n)
    /// </summary>
    public CollapsedLineSection CollapseText(DocumentLine start, DocumentLine end)
    {
      if (!document.Lines.Contains(start))
        throw new ArgumentException("Line is not part of this document", "start");
      if (!document.Lines.Contains(end))
        throw new ArgumentException("Line is not part of this document", "end");
      int length = end.LineNumber - start.LineNumber + 1;
      if (length < 0)
        throw new ArgumentException("start must be a line before end");
      CollapsedLineSection section = new CollapsedLineSection(this, start, end);
      AddCollapsedSection(section, length);
      #if DEBUG
      CheckProperties();
      #endif
      return section;
    }
    #endregion
    
    #region LineCount & TotalHeight
    public int LineCount {
      get {
        return root.totalCount;
      }
    }
    
    public double TotalHeight {
      get {
        return root.totalHeight;
      }
    }
    #endregion
    
    #region GetAllCollapsedSections
    IEnumerable<HeightTreeNode> AllNodes {
      get {
        if (root != null) {
          HeightTreeNode node = root.LeftMost;
          while (node != null) {
            yield return node;
            node = node.Successor;
          }
        }
      }
    }
    
    internal IEnumerable<CollapsedLineSection> GetAllCollapsedSections()
    {
      List<CollapsedLineSection> emptyCSList = new List<CollapsedLineSection>();
      return System.Linq.Enumerable.Distinct(
        System.Linq.Enumerable.SelectMany(
          AllNodes, node => System.Linq.Enumerable.Concat(node.lineNode.collapsedSections ?? emptyCSList,
                                                          node.collapsedSections ?? emptyCSList)
        ));
    }
    #endregion
    
    #region CheckProperties
    #if DEBUG
    [Conditional("DATACONSISTENCYTEST")]
    internal void CheckProperties()
    {
      CheckProperties(root);
      
      foreach (CollapsedLineSection cs in GetAllCollapsedSections()) {
        Debug.Assert(GetNode(cs.Start).lineNode.collapsedSections.Contains(cs));
        Debug.Assert(GetNode(cs.End).lineNode.collapsedSections.Contains(cs));
        int endLine = cs.End.LineNumber;
        for (int i = cs.Start.LineNumber; i <= endLine; i++) {
          CheckIsInSection(cs, GetLineByNumber(i));
        }
      }
      
      // check red-black property:
      int blackCount = -1;
      CheckNodeProperties(root, null, RED, 0, ref blackCount);
    }
    
    void CheckIsInSection(CollapsedLineSection cs, DocumentLine line)
    {
      HeightTreeNode node = GetNode(line);
      if (node.lineNode.collapsedSections != null && node.lineNode.collapsedSections.Contains(cs))
        return;
      while (node != null) {
        if (node.collapsedSections != null && node.collapsedSections.Contains(cs))
          return;
        node = node.parent;
      }
      throw new InvalidOperationException(cs + " not found for line " + line);
    }
    
    void CheckProperties(HeightTreeNode node)
    {
      int totalCount = 1;
      double totalHeight = node.lineNode.TotalHeight;
      if (node.lineNode.IsDirectlyCollapsed)
        Debug.Assert(node.lineNode.collapsedSections.Count > 0);
      if (node.left != null) {
        CheckProperties(node.left);
        totalCount += node.left.totalCount;
        totalHeight += node.left.totalHeight;
        
        CheckAllContainedIn(node.left.collapsedSections, node.lineNode.collapsedSections);
      }
      if (node.right != null) {
        CheckProperties(node.right);
        totalCount += node.right.totalCount;
        totalHeight += node.right.totalHeight;
        
        CheckAllContainedIn(node.right.collapsedSections, node.lineNode.collapsedSections);
      }
      if (node.left != null && node.right != null) {
        if (node.left.collapsedSections != null && node.right.collapsedSections != null) {
          var intersection = System.Linq.Enumerable.Intersect(node.left.collapsedSections, node.right.collapsedSections);
          Debug.Assert(System.Linq.Enumerable.Count(intersection) == 0);
        }
      }
      if (node.IsDirectlyCollapsed) {
        Debug.Assert(node.collapsedSections.Count > 0);
        totalHeight = 0;
      }
      Debug.Assert(node.totalCount == totalCount);
      Debug.Assert(node.totalHeight.IsClose(totalHeight));
    }
    
    /// <summary>
    /// Checks that all elements in list1 are contained in list2.
    /// </summary>
    static void CheckAllContainedIn(IEnumerable<CollapsedLineSection> list1, ICollection<CollapsedLineSection> list2)
    {
      if (list1 == null) list1 = new List<CollapsedLineSection>();
      if (list2 == null) list2 = new List<CollapsedLineSection>();
      foreach (CollapsedLineSection cs in list1) {
        Debug.Assert(list2.Contains(cs));
      }
    }
    
    /*
    1. A node is either red or black.
    2. The root is black.
    3. All leaves are black. (The leaves are the NIL children.)
    4. Both children of every red node are black. (So every red node must have a black parent.)
    5. Every simple path from a node to a descendant leaf contains the same number of black nodes. (Not counting the leaf node.)
     */
    void CheckNodeProperties(HeightTreeNode node, HeightTreeNode parentNode, bool parentColor, int blackCount, ref int expectedBlackCount)
    {
      if (node == null) return;
      
      Debug.Assert(node.parent == parentNode);
      
      if (parentColor == RED) {
        Debug.Assert(node.color == BLACK);
      }
      if (node.color == BLACK) {
        blackCount++;
      }
      if (node.left == null && node.right == null) {
        // node is a leaf node:
        if (expectedBlackCount == -1)
          expectedBlackCount = blackCount;
        else
          Debug.Assert(expectedBlackCount == blackCount);
      }
      CheckNodeProperties(node.left, node, node.color, blackCount, ref expectedBlackCount);
      CheckNodeProperties(node.right, node, node.color, blackCount, ref expectedBlackCount);
    }
    
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
    public string GetTreeAsString()
    {
      StringBuilder b = new StringBuilder();
      AppendTreeToString(root, b, 0);
      return b.ToString();
    }
    
    static void AppendTreeToString(HeightTreeNode node, StringBuilder b, int indent)
    {
      if (node.color == RED)
        b.Append("RED   ");
      else
        b.Append("BLACK ");
      b.AppendLine(node.ToString());
      indent += 2;
      if (node.left != null) {
        b.Append(' ', indent);
        b.Append("L: ");
        AppendTreeToString(node.left, b, indent);
      }
      if (node.right != null) {
        b.Append(' ', indent);
        b.Append("R: ");
        AppendTreeToString(node.right, b, indent);
      }
    }
    #endif
    #endregion
    
    #region Red/Black Tree
    const bool RED = true;
    const bool BLACK = false;
    
    void InsertAsLeft(HeightTreeNode parentNode, HeightTreeNode newNode)
    {
      Debug.Assert(parentNode.left == null);
      parentNode.left = newNode;
      newNode.parent = parentNode;
      newNode.color = RED;
      UpdateAfterChildrenChange(parentNode);
      FixTreeOnInsert(newNode);
    }
    
    void InsertAsRight(HeightTreeNode parentNode, HeightTreeNode newNode)
    {
      Debug.Assert(parentNode.right == null);
      parentNode.right = newNode;
      newNode.parent = parentNode;
      newNode.color = RED;
      UpdateAfterChildrenChange(parentNode);
      FixTreeOnInsert(newNode);
    }
    
    void FixTreeOnInsert(HeightTreeNode node)
    {
      Debug.Assert(node != null);
      Debug.Assert(node.color == RED);
      Debug.Assert(node.left == null || node.left.color == BLACK);
      Debug.Assert(node.right == null || node.right.color == BLACK);
      
      HeightTreeNode parentNode = node.parent;
      if (parentNode == null) {
        // we inserted in the root -> the node must be black
        // since this is a root node, making the node black increments the number of black nodes
        // on all paths by one, so it is still the same for all paths.
        node.color = BLACK;
        return;
      }
      if (parentNode.color == BLACK) {
        // if the parent node where we inserted was black, our red node is placed correctly.
        // since we inserted a red node, the number of black nodes on each path is unchanged
        // -> the tree is still balanced
        return;
      }
      // parentNode is red, so there is a conflict here!
      
      // because the root is black, parentNode is not the root -> there is a grandparent node
      HeightTreeNode grandparentNode = parentNode.parent;
      HeightTreeNode uncleNode = Sibling(parentNode);
      if (uncleNode != null && uncleNode.color == RED) {
        parentNode.color = BLACK;
        uncleNode.color = BLACK;
        grandparentNode.color = RED;
        FixTreeOnInsert(grandparentNode);
        return;
      }
      // now we know: parent is red but uncle is black
      // First rotation:
      if (node == parentNode.right && parentNode == grandparentNode.left) {
        RotateLeft(parentNode);
        node = node.left;
      } else if (node == parentNode.left && parentNode == grandparentNode.right) {
        RotateRight(parentNode);
        node = node.right;
      }
      // because node might have changed, reassign variables:
      parentNode = node.parent;
      grandparentNode = parentNode.parent;
      
      // Now recolor a bit:
      parentNode.color = BLACK;
      grandparentNode.color = RED;
      // Second rotation:
      if (node == parentNode.left && parentNode == grandparentNode.left) {
        RotateRight(grandparentNode);
      } else {
        // because of the first rotation, this is guaranteed:
        Debug.Assert(node == parentNode.right && parentNode == grandparentNode.right);
        RotateLeft(grandparentNode);
      }
    }
    
    void RemoveNode(HeightTreeNode removedNode)
    {
      if (removedNode.left != null && removedNode.right != null) {
        // replace removedNode with it's in-order successor
        
        HeightTreeNode leftMost = removedNode.right.LeftMost;
        HeightTreeNode parentOfLeftMost = leftMost.parent;
        RemoveNode(leftMost); // remove leftMost from its current location
        
        BeforeNodeReplace(removedNode, leftMost, parentOfLeftMost);
        // and overwrite the removedNode with it
        ReplaceNode(removedNode, leftMost);
        leftMost.left = removedNode.left;
        if (leftMost.left != null) leftMost.left.parent = leftMost;
        leftMost.right = removedNode.right;
        if (leftMost.right != null) leftMost.right.parent = leftMost;
        leftMost.color = removedNode.color;
        
        UpdateAfterChildrenChange(leftMost);
        if (leftMost.parent != null) UpdateAfterChildrenChange(leftMost.parent);
        return;
      }
      
      // now either removedNode.left or removedNode.right is null
      // get the remaining child
      HeightTreeNode parentNode = removedNode.parent;
      HeightTreeNode childNode = removedNode.left ?? removedNode.right;
      BeforeNodeRemove(removedNode);
      ReplaceNode(removedNode, childNode);
      if (parentNode != null) UpdateAfterChildrenChange(parentNode);
      if (removedNode.color == BLACK) {
        if (childNode != null && childNode.color == RED) {
          childNode.color = BLACK;
        } else {
          FixTreeOnDelete(childNode, parentNode);
        }
      }
    }
    
    void FixTreeOnDelete(HeightTreeNode node, HeightTreeNode parentNode)
    {
      Debug.Assert(node == null || node.parent == parentNode);
      if (parentNode == null)
        return;
      
      // warning: node may be null
      HeightTreeNode sibling = Sibling(node, parentNode);
      if (sibling.color == RED) {
        parentNode.color = RED;
        sibling.color = BLACK;
        if (node == parentNode.left) {
          RotateLeft(parentNode);
        } else {
          RotateRight(parentNode);
        }
        
        sibling = Sibling(node, parentNode); // update value of sibling after rotation
      }
      
      if (parentNode.color == BLACK
          && sibling.color == BLACK
          && GetColor(sibling.left) == BLACK
          && GetColor(sibling.right) == BLACK)
      {
        sibling.color = RED;
        FixTreeOnDelete(parentNode, parentNode.parent);
        return;
      }
      
      if (parentNode.color == RED
          && sibling.color == BLACK
          && GetColor(sibling.left) == BLACK
          && GetColor(sibling.right) == BLACK)
      {
        sibling.color = RED;
        parentNode.color = BLACK;
        return;
      }
      
      if (node == parentNode.left &&
          sibling.color == BLACK &&
          GetColor(sibling.left) == RED &&
          GetColor(sibling.right) == BLACK)
      {
        sibling.color = RED;
        sibling.left.color = BLACK;
        RotateRight(sibling);
      }
      else if (node == parentNode.right &&
               sibling.color == BLACK &&
               GetColor(sibling.right) == RED &&
               GetColor(sibling.left) == BLACK)
      {
        sibling.color = RED;
        sibling.right.color = BLACK;
        RotateLeft(sibling);
      }
      sibling = Sibling(node, parentNode); // update value of sibling after rotation
      
      sibling.color = parentNode.color;
      parentNode.color = BLACK;
      if (node == parentNode.left) {
        if (sibling.right != null) {
          Debug.Assert(sibling.right.color == RED);
          sibling.right.color = BLACK;
        }
        RotateLeft(parentNode);
      } else {
        if (sibling.left != null) {
          Debug.Assert(sibling.left.color == RED);
          sibling.left.color = BLACK;
        }
        RotateRight(parentNode);
      }
    }
    
    void ReplaceNode(HeightTreeNode replacedNode, HeightTreeNode newNode)
    {
      if (replacedNode.parent == null) {
        Debug.Assert(replacedNode == root);
        root = newNode;
      } else {
        if (replacedNode.parent.left == replacedNode)
          replacedNode.parent.left = newNode;
        else
          replacedNode.parent.right = newNode;
      }
      if (newNode != null) {
        newNode.parent = replacedNode.parent;
      }
      replacedNode.parent = null;
    }
    
    void RotateLeft(HeightTreeNode p)
    {
      // let q be p's right child
      HeightTreeNode q = p.right;
      Debug.Assert(q != null);
      Debug.Assert(q.parent == p);
      // set q to be the new root
      ReplaceNode(p, q);
      
      // set p's right child to be q's left child
      p.right = q.left;
      if (p.right != null) p.right.parent = p;
      // set q's left child to be p
      q.left = p;
      p.parent = q;
      UpdateAfterRotateLeft(p);
    }
    
    void RotateRight(HeightTreeNode p)
    {
      // let q be p's left child
      HeightTreeNode q = p.left;
      Debug.Assert(q != null);
      Debug.Assert(q.parent == p);
      // set q to be the new root
      ReplaceNode(p, q);
      
      // set p's left child to be q's right child
      p.left = q.right;
      if (p.left != null) p.left.parent = p;
      // set q's right child to be p
      q.right = p;
      p.parent = q;
      UpdateAfterRotateRight(p);
    }
    
    static HeightTreeNode Sibling(HeightTreeNode node)
    {
      if (node == node.parent.left)
        return node.parent.right;
      else
        return node.parent.left;
    }
    
    static HeightTreeNode Sibling(HeightTreeNode node, HeightTreeNode parentNode)
    {
      Debug.Assert(node == null || node.parent == parentNode);
      if (node == parentNode.left)
        return parentNode.right;
      else
        return parentNode.left;
    }
    
    static bool GetColor(HeightTreeNode node)
    {
      return node != null ? node.color : BLACK;
    }
    #endregion
    
    #region Collapsing support
    static bool GetIsCollapedFromNode(HeightTreeNode node)
    {
      while (node != null) {
        if (node.IsDirectlyCollapsed)
          return true;
        node = node.parent;
      }
      return false;
    }
    
    internal void AddCollapsedSection(CollapsedLineSection section, int sectionLength)
    {
      AddRemoveCollapsedSection(section, sectionLength, true);
    }
    
    void AddRemoveCollapsedSection(CollapsedLineSection section, int sectionLength, bool add)
    {
      Debug.Assert(sectionLength > 0);
      
      HeightTreeNode node = GetNode(section.Start);
      // Go up in the tree.
      while (true) {
        // Mark all middle nodes as collapsed
        if (add)
          node.lineNode.AddDirectlyCollapsed(section);
        else
          node.lineNode.RemoveDirectlyCollapsed(section);
        sectionLength -= 1;
        if (sectionLength == 0) {
          // we are done!
          Debug.Assert(node.documentLine == section.End);
          break;
        }
        // Mark all right subtrees as collapsed.
        if (node.right != null) {
          if (node.right.totalCount < sectionLength) {
            if (add)
              node.right.AddDirectlyCollapsed(section);
            else
              node.right.RemoveDirectlyCollapsed(section);
            sectionLength -= node.right.totalCount;
          } else {
            // mark partially into the right subtree: go down the right subtree.
            AddRemoveCollapsedSectionDown(section, node.right, sectionLength, add);
            break;
          }
        }
        // go up to the next node
        HeightTreeNode parentNode = node.parent;
        Debug.Assert(parentNode != null);
        while (parentNode.right == node) {
          node = parentNode;
          parentNode = node.parent;
          Debug.Assert(parentNode != null);
        }
        node = parentNode;
      }
      UpdateAugmentedData(GetNode(section.Start), UpdateAfterChildrenChangeRecursionMode.WholeBranch);
      UpdateAugmentedData(GetNode(section.End), UpdateAfterChildrenChangeRecursionMode.WholeBranch);
    }
    
    static void AddRemoveCollapsedSectionDown(CollapsedLineSection section, HeightTreeNode node, int sectionLength, bool add)
    {
      while (true) {
        if (node.left != null) {
          if (node.left.totalCount < sectionLength) {
            // mark left subtree
            if (add)
              node.left.AddDirectlyCollapsed(section);
            else
              node.left.RemoveDirectlyCollapsed(section);
            sectionLength -= node.left.totalCount;
          } else {
            // mark only inside the left subtree
            node = node.left;
            Debug.Assert(node != null);
            continue;
          }
        }
        if (add)
          node.lineNode.AddDirectlyCollapsed(section);
        else
          node.lineNode.RemoveDirectlyCollapsed(section);
        sectionLength -= 1;
        if (sectionLength == 0) {
          // done!
          Debug.Assert(node.documentLine == section.End);
          break;
        }
        // mark inside right subtree:
        node = node.right;
        Debug.Assert(node != null);
      }
    }
    
    public void Uncollapse(CollapsedLineSection section)
    {
      int sectionLength = section.End.LineNumber - section.Start.LineNumber + 1;
      AddRemoveCollapsedSection(section, sectionLength, false);
      // do not call CheckProperties() in here - Uncollapse is also called during line removals
    }
    #endregion
  }
}