source: branches/2839_HiveProjectManagement/HeuristicLab.ExtLibs/HeuristicLab.AvalonEdit/5.0.1/AvalonEdit-5.0.1/Utils/Rope.cs @ 17991

// 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
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// DEALINGS IN THE SOFTWARE.

using System;
using System.Linq;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.Runtime.Serialization;
using System.Text;

namespace ICSharpCode.AvalonEdit.Utils
{
  /// <summary>
  /// A kind of List&lt;T&gt;, but more efficient for random insertions/removal.
  /// Also has cheap Clone() and SubRope() implementations.
  /// </summary>
  /// <remarks>
  /// This class is not thread-safe: multiple concurrent write operations or writes concurrent to reads have undefined behaviour.
  /// Concurrent reads, however, are safe.
  /// However, clones of a rope are safe to use on other threads even though they share data with the original rope.
  /// </remarks>
  [Serializable]
  [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1710:IdentifiersShouldHaveCorrectSuffix")]
  public sealed class Rope<T> : IList<T>, ICloneable
  {
    internal RopeNode<T> root;
    
    internal Rope(RopeNode<T> root)
    {
      this.root = root;
      root.CheckInvariants();
    }
    
    /// <summary>
    /// Creates a new rope representing the empty string.
    /// </summary>
    public Rope()
    {
      // we'll construct the empty rope as a clone of an imaginary static empty rope
      this.root = RopeNode<T>.emptyRopeNode;
      root.CheckInvariants();
    }
    
    /// <summary>
    /// Creates a rope from the specified input.
    /// This operation runs in O(N).
    /// </summary>
    /// <exception cref="ArgumentNullException">input is null.</exception>
    public Rope(IEnumerable<T> input)
    {
      if (input == null)
        throw new ArgumentNullException("input");
      Rope<T> inputRope = input as Rope<T>;
      if (inputRope != null) {
        // clone ropes instead of copying them
        inputRope.root.Publish();
        this.root = inputRope.root;
      } else {
        string text = input as string;
        if (text != null) {
          // if a string is IEnumerable<T>, then T must be char
          ((Rope<char>)(object)this).root = CharRope.InitFromString(text);
        } else {
          T[] arr = ToArray(input);
          this.root = RopeNode<T>.CreateFromArray(arr, 0, arr.Length);
        }
      }
      this.root.CheckInvariants();
    }
    
    /// <summary>
    /// Creates a rope from a part of the array.
    /// This operation runs in O(N).
    /// </summary>
    /// <exception cref="ArgumentNullException">input is null.</exception>
    public Rope(T[] array, int arrayIndex, int count)
    {
      VerifyArrayWithRange(array, arrayIndex, count);
      this.root = RopeNode<T>.CreateFromArray(array, arrayIndex, count);
      this.root.CheckInvariants();
    }
    
    /// <summary>
    /// Creates a new rope that lazily initalizes its content.
    /// </summary>
    /// <param name="length">The length of the rope that will be lazily loaded.</param>
    /// <param name="initializer">
    /// The callback that provides the content for this rope.
    /// <paramref name="initializer"/> will be called exactly once when the content of this rope is first requested.
    /// It must return a rope with the specified length.
    /// Because the initializer function is not called when a rope is cloned, and such clones may be used on another threads,
    /// it is possible for the initializer callback to occur on any thread.
    /// </param>
    /// <remarks>
    /// Any modifications inside the rope will also cause the content to be initialized.
    /// However, insertions at the beginning and the end, as well as inserting this rope into another or
    /// using the <see cref="Concat(Rope{T},Rope{T})"/> method, allows constructions of larger ropes where parts are
    /// lazily loaded.
    /// However, even methods like Concat may sometimes cause the initializer function to be called, e.g. when
    /// two short ropes are concatenated.
    /// </remarks>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures")]
    public Rope(int length, Func<Rope<T>> initializer)
    {
      if (initializer == null)
        throw new ArgumentNullException("initializer");
      if (length < 0)
        throw new ArgumentOutOfRangeException("length", length, "Length must not be negative");
      if (length == 0) {
        this.root = RopeNode<T>.emptyRopeNode;
      } else {
        this.root = new FunctionNode<T>(length, initializer);
      }
      this.root.CheckInvariants();
    }
    
    static T[] ToArray(IEnumerable<T> input)
    {
      T[] arr = input as T[];
      return arr ?? input.ToArray();
    }
    
    /// <summary>
    /// Clones the rope.
    /// This operation runs in linear time to the number of rope nodes touched since the last clone was created.
    /// If you count the per-node cost to the operation modifying the rope (doing this doesn't increase the complexity of the modification operations);
    /// the remainder of Clone() runs in O(1).
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public Rope<T> Clone()
    {
      // The Publish() call actually modifies this rope instance; but this modification is thread-safe
      // as long as the tree structure doesn't change during the operation.
      root.Publish();
      return new Rope<T>(root);
    }
    
    object ICloneable.Clone()
    {
      return this.Clone();
    }
    
    /// <summary>
    /// Resets the rope to an empty list.
    /// Runs in O(1).
    /// </summary>
    public void Clear()
    {
      root = RopeNode<T>.emptyRopeNode;
      OnChanged();
    }
    
    /// <summary>
    /// Gets the length of the rope.
    /// Runs in O(1).
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public int Length {
      get { return root.length; }
    }
    
    /// <summary>
    /// Gets the length of the rope.
    /// Runs in O(1).
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public int Count {
      get { return root.length; }
    }
    
    /// <summary>
    /// Inserts another rope into this rope.
    /// Runs in O(lg N + lg M), plus a per-node cost as if <c>newElements.Clone()</c> was called.
    /// </summary>
    /// <exception cref="ArgumentNullException">newElements is null.</exception>
    /// <exception cref="ArgumentOutOfRangeException">index or length is outside the valid range.</exception>
    public void InsertRange(int index, Rope<T> newElements)
    {
      if (index < 0 || index > this.Length) {
        throw new ArgumentOutOfRangeException("index", index, "0 <= index <= " + this.Length.ToString(CultureInfo.InvariantCulture));
      }
      if (newElements == null)
        throw new ArgumentNullException("newElements");
      newElements.root.Publish();
      root = root.Insert(index, newElements.root);
      OnChanged();
    }
    
    /// <summary>
    /// Inserts new elemetns into this rope.
    /// Runs in O(lg N + M), where N is the length of this rope and M is the number of new elements.
    /// </summary>
    /// <exception cref="ArgumentNullException">newElements is null.</exception>
    /// <exception cref="ArgumentOutOfRangeException">index or length is outside the valid range.</exception>
    public void InsertRange(int index, IEnumerable<T> newElements)
    {
      if (newElements == null)
        throw new ArgumentNullException("newElements");
      Rope<T> newElementsRope = newElements as Rope<T>;
      if (newElementsRope != null) {
        InsertRange(index, newElementsRope);
      } else {
        T[] arr = ToArray(newElements);
        InsertRange(index, arr, 0, arr.Length);
      }
    }
    
    /// <summary>
    /// Inserts new elements into this rope.
    /// Runs in O(lg N + M), where N is the length of this rope and M is the number of new elements.
    /// </summary>
    /// <exception cref="ArgumentNullException">newElements is null.</exception>
    /// <exception cref="ArgumentOutOfRangeException">index or length is outside the valid range.</exception>
    public void InsertRange(int index, T[] array, int arrayIndex, int count)
    {
      if (index < 0 || index > this.Length) {
        throw new ArgumentOutOfRangeException("index", index, "0 <= index <= " + this.Length.ToString(CultureInfo.InvariantCulture));
      }
      VerifyArrayWithRange(array, arrayIndex, count);
      if (count > 0) {
        root = root.Insert(index, array, arrayIndex, count);
        OnChanged();
      }
    }
    
    /// <summary>
    /// Appends multiple elements to the end of this rope.
    /// Runs in O(lg N + M), where N is the length of this rope and M is the number of new elements.
    /// </summary>
    /// <exception cref="ArgumentNullException">newElements is null.</exception>
    public void AddRange(IEnumerable<T> newElements)
    {
      InsertRange(this.Length, newElements);
    }
    
    /// <summary>
    /// Appends another rope to the end of this rope.
    /// Runs in O(lg N + lg M), plus a per-node cost as if <c>newElements.Clone()</c> was called.
    /// </summary>
    /// <exception cref="ArgumentNullException">newElements is null.</exception>
    public void AddRange(Rope<T> newElements)
    {
      InsertRange(this.Length, newElements);
    }
    
    /// <summary>
    /// Appends new elements to the end of this rope.
    /// Runs in O(lg N + M), where N is the length of this rope and M is the number of new elements.
    /// </summary>
    /// <exception cref="ArgumentNullException">array is null.</exception>
    public void AddRange(T[] array, int arrayIndex, int count)
    {
      InsertRange(this.Length, array, arrayIndex, count);
    }
    
    /// <summary>
    /// Removes a range of elements from the rope.
    /// Runs in O(lg N).
    /// </summary>
    /// <exception cref="ArgumentOutOfRangeException">offset or length is outside the valid range.</exception>
    public void RemoveRange(int index, int count)
    {
      VerifyRange(index, count);
      if (count > 0) {
        root = root.RemoveRange(index, count);
        OnChanged();
      }
    }
    
    /// <summary>
    /// Copies a range of the specified array into the rope, overwriting existing elements.
    /// Runs in O(lg N + M).
    /// </summary>
    public void SetRange(int index, T[] array, int arrayIndex, int count)
    {
      VerifyRange(index, count);
      VerifyArrayWithRange(array, arrayIndex, count);
      if (count > 0) {
        root = root.StoreElements(index, array, arrayIndex, count);
        OnChanged();
      }
    }
    
    /// <summary>
    /// Creates a new rope and initializes it with a part of this rope.
    /// Runs in O(lg N) plus a per-node cost as if <c>this.Clone()</c> was called.
    /// </summary>
    /// <exception cref="ArgumentOutOfRangeException">offset or length is outside the valid range.</exception>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public Rope<T> GetRange(int index, int count)
    {
      VerifyRange(index, count);
      Rope<T> newRope = Clone();
      int endIndex = index + count;
      newRope.RemoveRange(endIndex, newRope.Length - endIndex);
      newRope.RemoveRange(0, index);
      return newRope;
    }
    
    /*
    #region Equality
    /// <summary>
    /// Gets whether the two ropes have the same content.
    /// Runs in O(N + M).
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public bool Equals(Rope other)
    {
      if (other == null)
        return false;
      // quick detection for ropes that are clones of each other:
      if (other.root == this.root)
        return true;
      if (other.Length != this.Length)
        return false;
      using (RopeTextReader a = new RopeTextReader(this, false)) {
        using (RopeTextReader b = new RopeTextReader(other, false)) {
          int charA, charB;
          do {
            charA = a.Read();
            charB = b.Read();
            if (charA != charB)
              return false;
          } while (charA != -1);
          return true;
        }
      }
    }
    
    /// <summary>
    /// Gets whether two ropes have the same content.
    /// Runs in O(N + M).
    /// </summary>
    public override bool Equals(object obj)
    {
      return Equals(obj as Rope);
    }
    
    /// <summary>
    /// Calculates the hash code of the rope's content.
    /// Runs in O(N).
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public override int GetHashCode()
    {
      int hashcode = 0;
      using (RopeTextReader reader = new RopeTextReader(this, false)) {
        unchecked {
          int val;
          while ((val = reader.Read()) != -1) {
            hashcode = hashcode * 31 + val;
          }
        }
      }
      return hashcode;
    }
    #endregion
     */
    
    /// <summary>
    /// Concatenates two ropes. The input ropes are not modified.
    /// Runs in O(lg N + lg M).
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1000:DoNotDeclareStaticMembersOnGenericTypes")]
    public static Rope<T> Concat(Rope<T> left, Rope<T> right)
    {
      if (left == null)
        throw new ArgumentNullException("left");
      if (right == null)
        throw new ArgumentNullException("right");
      left.root.Publish();
      right.root.Publish();
      return new Rope<T>(RopeNode<T>.Concat(left.root, right.root));
    }
    
    /// <summary>
    /// Concatenates multiple ropes. The input ropes are not modified.
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1000:DoNotDeclareStaticMembersOnGenericTypes")]
    public static Rope<T> Concat(params Rope<T>[] ropes)
    {
      if (ropes == null)
        throw new ArgumentNullException("ropes");
      Rope<T> result = new Rope<T>();
      foreach (Rope<T> r in ropes)
        result.AddRange(r);
      return result;
    }
    
    #region Caches / Changed event
    internal struct RopeCacheEntry
    {
      internal readonly RopeNode<T> node;
      internal readonly int nodeStartIndex;
      
      internal RopeCacheEntry(RopeNode<T> node, int nodeStartOffset)
      {
        this.node = node;
        this.nodeStartIndex = nodeStartOffset;
      }
      
      internal bool IsInside(int offset)
      {
        return offset >= nodeStartIndex && offset < nodeStartIndex + node.length;
      }
    }
    
    // cached pointer to 'last used node', used to speed up accesses by index that are close together
    [NonSerialized]
    volatile ImmutableStack<RopeCacheEntry> lastUsedNodeStack;
    
    internal void OnChanged()
    {
      lastUsedNodeStack = null;
      
      root.CheckInvariants();
    }
    #endregion
    
    #region GetChar / SetChar
    /// <summary>
    /// Gets/Sets a single character.
    /// Runs in O(lg N) for random access. Sequential read-only access benefits from a special optimization and runs in amortized O(1).
    /// </summary>
    /// <exception cref="ArgumentOutOfRangeException">Offset is outside the valid range (0 to Length-1).</exception>
    /// <remarks>
    /// The getter counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public T this[int index] {
      get {
        // use unsigned integers - this way negative values for index overflow and can be tested for with the same check
        if (unchecked((uint)index >= (uint)this.Length)) {
          throw new ArgumentOutOfRangeException("index", index, "0 <= index < " + this.Length.ToString(CultureInfo.InvariantCulture));
        }
        RopeCacheEntry entry = FindNodeUsingCache(index).PeekOrDefault();
        return entry.node.contents[index - entry.nodeStartIndex];
      }
      set {
        if (index < 0 || index >= this.Length) {
          throw new ArgumentOutOfRangeException("index", index, "0 <= index < " + this.Length.ToString(CultureInfo.InvariantCulture));
        }
        root = root.SetElement(index, value);
        OnChanged();
        /* Here's a try at implementing the setter using the cached node stack (UNTESTED code!).
         * However I don't use the code because it's complicated and doesn't integrate correctly with change notifications.
         * Instead, I'll use the much easier to understand recursive solution.
         * Oh, and it also doesn't work correctly with function nodes.
        ImmutableStack<RopeCacheEntry> nodeStack = FindNodeUsingCache(offset);
        RopeCacheEntry entry = nodeStack.Peek();
        if (!entry.node.isShared) {
          entry.node.contents[offset - entry.nodeStartOffset] = value;
          // missing: clear the caches except for the node stack cache (e.g. ToString() cache?)
        } else {
          RopeNode oldNode = entry.node;
          RopeNode newNode = oldNode.Clone();
          newNode.contents[offset - entry.nodeStartOffset] = value;
          for (nodeStack = nodeStack.Pop(); !nodeStack.IsEmpty; nodeStack = nodeStack.Pop()) {
            RopeNode parentNode = nodeStack.Peek().node;
            RopeNode newParentNode = parentNode.CloneIfShared();
            if (newParentNode.left == oldNode) {
              newParentNode.left = newNode;
            } else {
              Debug.Assert(newParentNode.right == oldNode);
              newParentNode.right = newNode;
            }
            if (parentNode == newParentNode) {
              // we were able to change the existing node (it was not shared);
              // there's no reason to go further upwards
              ClearCacheOnModification();
              return;
            } else {
              oldNode = parentNode;
              newNode = newParentNode;
            }
          }
          // we reached the root of the rope.
          Debug.Assert(root == oldNode);
          root = newNode;
          ClearCacheOnModification();
        }*/
      }
    }
    
    internal ImmutableStack<RopeCacheEntry> FindNodeUsingCache(int index)
    {
      Debug.Assert(index >= 0 && index < this.Length);
      
      // thread safety: fetch stack into local variable
      ImmutableStack<RopeCacheEntry> stack = lastUsedNodeStack;
      ImmutableStack<RopeCacheEntry> oldStack = stack;
      
      if (stack == null) {
        stack = ImmutableStack<RopeCacheEntry>.Empty.Push(new RopeCacheEntry(root, 0));
      }
      while (!stack.PeekOrDefault().IsInside(index))
        stack = stack.Pop();
      while (true) {
        RopeCacheEntry entry = stack.PeekOrDefault();
        // check if we've reached a leaf or function node
        if (entry.node.height == 0) {
          if (entry.node.contents == null) {
            // this is a function node - go down into its subtree
            entry = new RopeCacheEntry(entry.node.GetContentNode(), entry.nodeStartIndex);
            // entry is now guaranteed NOT to be another function node
          }
          if (entry.node.contents != null) {
            // this is a node containing actual content, so we're done
            break;
          }
        }
        // go down towards leaves
        if (index - entry.nodeStartIndex >= entry.node.left.length)
          stack = stack.Push(new RopeCacheEntry(entry.node.right, entry.nodeStartIndex + entry.node.left.length));
        else
          stack = stack.Push(new RopeCacheEntry(entry.node.left, entry.nodeStartIndex));
      }
      
      // write back stack to volatile cache variable
      // (in multithreaded access, it doesn't matter which of the threads wins - it's just a cache)
      if (oldStack != stack) {
        // no need to write when we the cache variable didn't change
        lastUsedNodeStack = stack;
      }
      
      // this method guarantees that it finds a leaf node
      Debug.Assert(stack.Peek().node.contents != null);
      return stack;
    }
    #endregion
    
    #region ToString / WriteTo
    internal void VerifyRange(int startIndex, int length)
    {
      if (startIndex < 0 || startIndex > this.Length) {
        throw new ArgumentOutOfRangeException("startIndex", startIndex, "0 <= startIndex <= " + this.Length.ToString(CultureInfo.InvariantCulture));
      }
      if (length < 0 || startIndex + length > this.Length) {
        throw new ArgumentOutOfRangeException("length", length, "0 <= length, startIndex(" + startIndex + ")+length <= " + this.Length.ToString(CultureInfo.InvariantCulture));
      }
    }
    
    internal static void VerifyArrayWithRange(T[] array, int arrayIndex, int count)
    {
      if (array == null)
        throw new ArgumentNullException("array");
      if (arrayIndex < 0 || arrayIndex > array.Length) {
        throw new ArgumentOutOfRangeException("startIndex", arrayIndex, "0 <= arrayIndex <= " + array.Length.ToString(CultureInfo.InvariantCulture));
      }
      if (count < 0 || arrayIndex + count > array.Length) {
        throw new ArgumentOutOfRangeException("count", count, "0 <= length, arrayIndex(" + arrayIndex + ")+count <= " + array.Length.ToString(CultureInfo.InvariantCulture));
      }
    }
    
    /// <summary>
    /// Creates a string from the rope. Runs in O(N).
    /// </summary>
    /// <returns>A string consisting of all elements in the rope as comma-separated list in {}.
    /// As a special case, Rope&lt;char&gt; will return its contents as string without any additional separators or braces,
    /// so it can be used like StringBuilder.ToString().</returns>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public override string ToString()
    {
      Rope<char> charRope = this as Rope<char>;
      if (charRope != null) {
        return charRope.ToString(0, this.Length);
      } else {
        StringBuilder b = new StringBuilder();
        foreach (T element in this) {
          if (b.Length == 0)
            b.Append('{');
          else
            b.Append(", ");
          b.Append(element.ToString());
        }
        b.Append('}');
        return b.ToString();
      }
    }
    
    internal string GetTreeAsString()
    {
      #if DEBUG
      return root.GetTreeAsString();
      #else
      return "Not available in release build.";
      #endif
    }
    #endregion
    
    bool ICollection<T>.IsReadOnly {
      get { return false; }
    }
    
    /// <summary>
    /// Finds the first occurance of item.
    /// Runs in O(N).
    /// </summary>
    /// <returns>The index of the first occurance of item, or -1 if it cannot be found.</returns>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public int IndexOf(T item)
    {
      return IndexOf(item, 0, this.Length);
    }
    
    /// <summary>
    /// Gets the index of the first occurrence the specified item.
    /// </summary>
    /// <param name="item">Item to search for.</param>
    /// <param name="startIndex">Start index of the search.</param>
    /// <param name="count">Length of the area to search.</param>
    /// <returns>The first index where the item was found; or -1 if no occurrence was found.</returns>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public int IndexOf(T item, int startIndex, int count)
    {
      VerifyRange(startIndex, count);
      
      while (count > 0) {
        var entry = FindNodeUsingCache(startIndex).PeekOrDefault();
        T[] contents = entry.node.contents;
        int startWithinNode = startIndex - entry.nodeStartIndex;
        int nodeLength = Math.Min(entry.node.length, startWithinNode + count);
        int r = Array.IndexOf(contents, item, startWithinNode, nodeLength - startWithinNode);
        if (r >= 0)
          return entry.nodeStartIndex + r;
        count -= nodeLength - startWithinNode;
        startIndex = entry.nodeStartIndex + nodeLength;
      }
      return -1;
    }
    
    /// <summary>
    /// Gets the index of the last occurrence of the specified item in this rope.
    /// </summary>
    public int LastIndexOf(T item)
    {
      return LastIndexOf(item, 0, this.Length);
    }
    
    /// <summary>
    /// Gets the index of the last occurrence of the specified item in this rope.
    /// </summary>
    /// <param name="item">The search item</param>
    /// <param name="startIndex">Start index of the area to search.</param>
    /// <param name="count">Length of the area to search.</param>
    /// <returns>The last index where the item was found; or -1 if no occurrence was found.</returns>
    /// <remarks>The search proceeds backwards from (startIndex+count) to startIndex.
    /// This is different than the meaning of the parameters on Array.LastIndexOf!</remarks>
    public int LastIndexOf(T item, int startIndex, int count)
    {
      VerifyRange(startIndex, count);
      
      var comparer = EqualityComparer<T>.Default;
      for (int i = startIndex + count - 1; i >= startIndex; i--) {
        if (comparer.Equals(this[i], item))
          return i;
      }
      return -1;
    }
    
    /// <summary>
    /// Inserts the item at the specified index in the rope.
    /// Runs in O(lg N).
    /// </summary>
    public void Insert(int index, T item)
    {
      InsertRange(index, new[] { item }, 0, 1);
    }
    
    /// <summary>
    /// Removes a single item from the rope.
    /// Runs in O(lg N).
    /// </summary>
    public void RemoveAt(int index)
    {
      RemoveRange(index, 1);
    }
    
    /// <summary>
    /// Appends the item at the end of the rope.
    /// Runs in O(lg N).
    /// </summary>
    public void Add(T item)
    {
      InsertRange(this.Length, new[] { item }, 0, 1);
    }
    
    /// <summary>
    /// Searches the item in the rope.
    /// Runs in O(N).
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public bool Contains(T item)
    {
      return IndexOf(item) >= 0;
    }
    
    /// <summary>
    /// Copies the whole content of the rope into the specified array.
    /// Runs in O(N).
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public void CopyTo(T[] array, int arrayIndex)
    {
      CopyTo(0, array, arrayIndex, this.Length);
    }
    
    /// <summary>
    /// Copies the a part of the rope into the specified array.
    /// Runs in O(lg N + M).
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public void CopyTo(int index, T[] array, int arrayIndex, int count)
    {
      VerifyRange(index, count);
      VerifyArrayWithRange(array, arrayIndex, count);
      this.root.CopyTo(index, array, arrayIndex, count);
    }
    
    /// <summary>
    /// Removes the first occurance of an item from the rope.
    /// Runs in O(N).
    /// </summary>
    public bool Remove(T item)
    {
      int index = IndexOf(item);
      if (index >= 0) {
        RemoveAt(index);
        return true;
      }
      return false;
    }
    
    /// <summary>
    /// Retrieves an enumerator to iterate through the rope.
    /// The enumerator will reflect the state of the rope from the GetEnumerator() call, further modifications
    /// to the rope will not be visible to the enumerator.
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public IEnumerator<T> GetEnumerator()
    {
      this.root.Publish();
      return Enumerate(root);
    }
    
    /// <summary>
    /// Creates an array and copies the contents of the rope into it.
    /// Runs in O(N).
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public T[] ToArray()
    {
      T[] arr = new T[this.Length];
      this.root.CopyTo(0, arr, 0, arr.Length);
      return arr;
    }
    
    /// <summary>
    /// Creates an array and copies the contents of the rope into it.
    /// Runs in O(N).
    /// </summary>
    /// <remarks>
    /// This method counts as a read access and may be called concurrently to other read accesses.
    /// </remarks>
    public T[] ToArray(int startIndex, int count)
    {
      VerifyRange(startIndex, count);
      T[] arr = new T[count];
      CopyTo(startIndex, arr, 0, count);
      return arr;
    }
    
    static IEnumerator<T> Enumerate(RopeNode<T> node)
    {
      Stack<RopeNode<T>> stack = new Stack<RopeNode<T>>();
      while (node != null) {
        // go to leftmost node, pushing the right parts that we'll have to visit later
        while (node.contents == null) {
          if (node.height == 0) {
            // go down into function nodes
            node = node.GetContentNode();
            continue;
          }
          Debug.Assert(node.right != null);
          stack.Push(node.right);
          node = node.left;
        }
        // yield contents of leaf node
        for (int i = 0; i < node.length; i++) {
          yield return node.contents[i];
        }
        // go up to the next node not visited yet
        if (stack.Count > 0)
          node = stack.Pop();
        else
          node = null;
      }
    }
    
    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
      return this.GetEnumerator();
    }
  }
}