Implemented updating text anchors on text replace operations.

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/trunk@4197 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit.Tests/Document/TextAnchorTest.cs

@@ -130,6 +130,28 @@ namespace ICSharpCode.AvalonEdit.Document.Tests
 			GC.KeepAlive(anchors);
 		}
 		
+		[Test]
+		public void MoveAnchorsDuringReplace()
+		{
+			document.Text = "abcd";
+			TextAnchor start = document.CreateAnchor(1);
+			TextAnchor middleDeletable = document.CreateAnchor(2);
+			TextAnchor middleSurvivorLeft = document.CreateAnchor(2);
+			middleSurvivorLeft.SurviveDeletion = true;
+			middleSurvivorLeft.MovementType = AnchorMovementType.BeforeInsertion;
+			TextAnchor middleSurvivorRight = document.CreateAnchor(2);
+			middleSurvivorRight.SurviveDeletion = true;
+			middleSurvivorRight.MovementType = AnchorMovementType.AfterInsertion;
+			TextAnchor end = document.CreateAnchor(3);
+			document.Replace(1, 2, "BxC");
+			
+			Assert.AreEqual(1, start.Offset);
+			Assert.IsTrue(middleDeletable.IsDeleted);
+			Assert.AreEqual(1, middleSurvivorLeft.Offset);
+			Assert.AreEqual(4, middleSurvivorRight.Offset);
+			Assert.AreEqual(4, end.Offset);
+		}
+		
 		[Test]
 		public void CreateAndMoveAnchors()
 		{
@@ -139,7 +161,7 @@ namespace ICSharpCode.AvalonEdit.Document.Tests
 			for (int t = 0; t < 250; t++) {
 				//Console.Write("t = " + t + " ");
 				int c = rnd.Next(50);
-				switch (rnd.Next(4)) {
+				switch (rnd.Next(5)) {
 					case 0:
 						//Console.WriteLine("Add c=" + c + " anchors");
 						for (int i = 0; i < c; i++) {
@@ -196,6 +218,31 @@ namespace ICSharpCode.AvalonEdit.Document.Tests
 							}
 						}
 						break;
+					case 4:
+						int replaceOffset = rnd.Next(document.TextLength);
+						int replaceRemovalLength = rnd.Next(document.TextLength - replaceOffset);
+						int replaceInsertLength = rnd.Next(1000);
+						//Console.WriteLine("ReplaceOffset=" + replaceOffset + " RemovalLength="+replaceRemovalLength + " InsertLength=" + replaceInsertLength);
+						document.Replace(replaceOffset, replaceRemovalLength, new string(' ', replaceInsertLength));
+						for (int i = anchors.Count - 1; i >= 0; i--) {
+							if (expectedOffsets[i] > replaceOffset && expectedOffsets[i] < replaceOffset + replaceRemovalLength) {
+								if (anchors[i].SurviveDeletion) {
+									if (anchors[i].MovementType == AnchorMovementType.AfterInsertion)
+										expectedOffsets[i] = replaceOffset + replaceInsertLength;
+									else
+										expectedOffsets[i] = replaceOffset;
+								} else {
+									Assert.IsTrue(anchors[i].IsDeleted);
+									anchors.RemoveAt(i);
+									expectedOffsets.RemoveAt(i);
+								}
+							} else if (expectedOffsets[i] > replaceOffset) {
+								expectedOffsets[i] += replaceInsertLength - replaceRemovalLength;
+							} else if (expectedOffsets[i] == replaceOffset && replaceRemovalLength == 0 && anchors[i].MovementType == AnchorMovementType.AfterInsertion) {
+								expectedOffsets[i] += replaceInsertLength - replaceRemovalLength;
+							}
+						}
+						break;
 				}
 				Assert.AreEqual(anchors.Count, expectedOffsets.Count);
 				for (int j = 0; j < anchors.Count; j++) {

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/DocumentChangeEventArgs.cs

@@ -5,6 +5,7 @@
 //     <version>$Revision$</version>
 // </file>
 
+using ICSharpCode.AvalonEdit.Utils;
 using System;
 
 namespace ICSharpCode.AvalonEdit.Document
@@ -47,17 +48,19 @@ namespace ICSharpCode.AvalonEdit.Document
 				OffsetChangeMap map = offsetChangeMap;
 				if (map == null) {
 					// create OffsetChangeMap on demand
-					map = new OffsetChangeMap();
+					map = new OffsetChangeMap(1);
-					if (this.RemovalLength > 0)
+					map.Add(CreateSingleChangeMapEntry());
-						map.Add(new OffsetChangeMapEntry(this.Offset, -this.RemovalLength));
-					if (this.InsertionLength > 0)
-						map.Add(new OffsetChangeMapEntry(this.Offset, this.InsertionLength));
 					offsetChangeMap = map;
 				}
 				return map;
 			}
 		}
 		
+		internal OffsetChangeMapEntry CreateSingleChangeMapEntry()
+		{
+			return new OffsetChangeMapEntry(this.Offset, this.RemovalLength, this.InsertionLength);
+		}
+		
 		/// <summary>
 		/// Gets the OffsetChangeMap, or null if the default offset map (=removal followed by insertion) is being used.
 		/// </summary>
@@ -74,16 +77,8 @@ namespace ICSharpCode.AvalonEdit.Document
 		{
 			if (offsetChangeMap != null)
 				return offsetChangeMap.GetNewOffset(offset, movementType);
-			if (offset >= this.Offset) {
+			else
-				if (offset <= this.Offset + this.RemovalLength) {
+				return CreateSingleChangeMapEntry().GetNewOffset(offset, movementType);
-					offset = this.Offset;
-					if (movementType == AnchorMovementType.AfterInsertion)
-						offset += this.InsertionLength;
-				} else {
-					offset += this.InsertionLength - this.RemovalLength;
-				}
-			}
-			return offset;
 		}
 		
 		/// <summary>
@@ -99,8 +94,9 @@ namespace ICSharpCode.AvalonEdit.Document
 		/// </summary>
 		public DocumentChangeEventArgs(int offset, int removalLength, string insertedText, OffsetChangeMap offsetChangeMap)
 		{
-			if (insertedText == null)
+			ThrowUtil.CheckNotNegative(offset, "offset");
-				throw new ArgumentNullException("insertedText");
+			ThrowUtil.CheckNotNegative(removalLength, "removalLength");
+			ThrowUtil.CheckNotNull(insertedText, "insertedText");
 			
 			this.Offset = offset;
 			this.RemovalLength = removalLength;

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/OffsetChangeMap.cs

@@ -5,6 +5,7 @@
 //     <version>$Revision$</version>
 // </file>
 
+using ICSharpCode.AvalonEdit.Utils;
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
@@ -16,15 +17,41 @@ namespace ICSharpCode.AvalonEdit.Document
 	/// </summary>
 	public enum OffsetChangeMappingType
 	{
+		/// <summary>
+		/// Normal replace.
+		/// Anchors in front of the replaced region will stay in front, anchors after the replaced region will stay after.
+		/// Anchors in the middle of the removed region will move depending on their AnchorMovementType.
+		/// </summary>
+		/// <remarks>
+		/// This is the default implementation of DocumentChangeEventArgs when OffsetChangeMap is null,
+		/// so using this option usually works without creating an OffsetChangeMap instance.
+		/// This is equivalent to an OffsetChangeMap with a single entry describing the replace operation.
+		/// </remarks>
+		Normal,
 		/// <summary>
 		/// First the old text is removed, then the new text is inserted.
+		/// Anchors immediately in front (or after) the replaced region may move to the other side of the insertion,
+		/// depending on the AnchorMovementType.
 		/// </summary>
+		/// <remarks>
+		/// This is implemented as an OffsetChangeMap with two entries: the removal, and the insertion.
+		/// </remarks>
 		RemoveAndInsert,
 		/// <summary>
 		/// The text is replaced character-by-character.
-		/// If the new text is longer than the old text, a single insertion at the end is used to account for the difference.
+		/// Anchors keep their position inside the replaced text.
-		/// If the new text is shorter than the old text, a single deletion at the end is used to account for the difference.
+		/// Anchors after the replaced region will move accordingly if the replacement text has a different length than the replaced text.
+		/// If the new text is shorter than the old text, anchors inside the old text that would end up behind the replacement text
+		/// will be moved so that they point to the end of the replacement text.
 		/// </summary>
+		/// <remarks>
+		/// On the OffsetChangeMap level, growing text is implemented by replacing the last character in the replaced text
+		/// with itself and the additional text segment. A simple insertion of the additional text would have the undesired
+		/// effect of moving anchors immediately after the replaced text into the replacement text if they used
+		/// AnchorMovementStyle.BeforeInsertion.
+		/// Shrinking text is implemented by removal the text segment that's too long.
+		/// If the text keeps its old size, this is implemented as OffsetChangeMap.Empty.
+		/// </remarks>
 		CharacterReplace
 	}
 	
@@ -83,7 +110,7 @@ namespace ICSharpCode.AvalonEdit.Document
 				// check that ChangeMapEntry is in valid range for this document change
 				if (entry.Offset < offset || entry.Offset + entry.RemovalLength > endOffset)
 					return false;
-				endOffset += entry.Delta;
+				endOffset += entry.InsertionLength - entry.RemovalLength;
 			}
 			// check that the total delta matches
 			return endOffset == offset + insertionLength;
@@ -99,7 +126,8 @@ namespace ICSharpCode.AvalonEdit.Document
 			OffsetChangeMap newMap = new OffsetChangeMap(this.Count);
 			for (int i = this.Count - 1; i >= 0; i--) {
 				OffsetChangeMapEntry entry = this[i];
-				newMap.Add(new OffsetChangeMapEntry(entry.Offset, -entry.Delta));
+				// swap InsertionLength and RemovalLength
+				newMap.Add(new OffsetChangeMapEntry(entry.Offset, entry.InsertionLength, entry.RemovalLength));
 			}
 			return newMap;
 		}
@@ -113,7 +141,8 @@ namespace ICSharpCode.AvalonEdit.Document
 	public struct OffsetChangeMapEntry
 	{
 		readonly int offset;
-		readonly int delta;
+		readonly int removalLength;
+		readonly int insertionLength;
 		
 		/// <summary>
 		/// The offset at which the change occurs.
@@ -122,21 +151,12 @@ namespace ICSharpCode.AvalonEdit.Document
 			get { return offset; }
 		}
 		
-		/// <summary>
-		/// The change delta. If positive, it is equal to InsertionLength; if negative, it is equal to RemovalLength.
-		/// </summary>
-		public int Delta {
-			get { return delta; }
-		}
-		
 		/// <summary>
 		/// The number of characters removed.
 		/// Returns 0 if this entry represents an insertion.
 		/// </summary>
 		public int RemovalLength { 
-			get {
+			get { return removalLength; }
-				return delta < 0 ? -delta : 0;
-			}
 		}
 		
 		/// <summary>
@@ -144,9 +164,7 @@ namespace ICSharpCode.AvalonEdit.Document
 		/// Returns 0 if this entry represents a removal.
 		/// </summary>
 		public int InsertionLength {
-			get {
+			get { return insertionLength; }
-				return delta > 0 ? delta : 0;
-			}
 		}
 		
 		/// <summary>
@@ -154,24 +172,39 @@ namespace ICSharpCode.AvalonEdit.Document
 		/// </summary>
 		public int GetNewOffset(int oldOffset, AnchorMovementType movementType)
 		{
-			if (oldOffset < this.Offset)
+			if (!(this.removalLength == 0 && oldOffset == this.offset)) {
-				return oldOffset;
+				// we're getting trouble (both if statements in here would apply)
-			if (oldOffset > this.Offset + this.RemovalLength)
+				// if there's no removal and we insert at the offset
-				return oldOffset + this.Delta;
+				// -> we'd need to disambiguate by movementType, which is handled after the if
-			// offset is inside removed region
+				
+				// offset is before start of change: no movement
+				if (oldOffset <= this.offset)
+					return oldOffset;
+				// offset is after end of change: movement by normal delta
+				if (oldOffset >= this.offset + this.removalLength)
+					return oldOffset + this.insertionLength - this.removalLength;
+			}
+			// we reach this point if
+			// a) the oldOffset is inside the deleted segment
+			// b) there was no removal and we insert at the caret position
 			if (movementType == AnchorMovementType.AfterInsertion)
-				return this.Offset + this.InsertionLength;
+				return this.offset + this.insertionLength;
 			else
-				return this.Offset;
+				return this.offset;
 		}
 		
 		/// <summary>
 		/// Creates a new OffsetChangeMapEntry instance.
 		/// </summary>
-		public OffsetChangeMapEntry(int offset, int delta)
+		public OffsetChangeMapEntry(int offset, int removalLength, int insertionLength)
 		{
+			ThrowUtil.CheckNotNegative(offset, "offset");
+			ThrowUtil.CheckNotNegative(removalLength, "removalLength");
+			ThrowUtil.CheckNotNegative(insertionLength, "insertionLength");
+			
 			this.offset = offset;
-			this.delta = delta;
+			this.removalLength = removalLength;
+			this.insertionLength = insertionLength;
 		}
 	}
 }

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/TextAnchorNode.cs

@@ -12,7 +12,7 @@ namespace ICSharpCode.AvalonEdit.Document
 	/// <summary>
 	/// A TextAnchorNode is placed in the TextAnchorTree.
 	/// It describes a section of text with a text anchor at the end of the section.
-	/// A weak reference is used to refer to the TextAnchor.
+	/// A weak reference is used to refer to the TextAnchor. (to save memory, we derive from WeakReference instead of referencing it)
 	/// </summary>
 	sealed class TextAnchorNode : WeakReference
 	{

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/TextAnchorTree.cs

@@ -19,6 +19,36 @@ namespace ICSharpCode.AvalonEdit.Document
 	/// </summary>
 	sealed class TextAnchorTree
 	{
+		// The text anchor tree has difficult requirements:
+		// - it must QUICKLY update the offset in all anchors whenever there is a document change
+		// - it must not reference text anchors directly, using weak references instead
+		
+		// Clearly, we cannot afford updating an Offset property on all anchors (that would be O(N)).
+		// So instead, the anchors need to be able to calculate their offset from a data structure
+		// that can be efficiently updated.
+		
+		// This implementation is built using an augmented red-black-tree.
+		// There is a 'TextAnchorNode' for each text anchor.
+		// Such a node represents a section of text (just the length is stored) with a (weakly referenced) text anchor at the end.
+		
+		// Basically, you can imagine the list of text anchors as a sorted list of text anchors, where each anchor
+		// just stores the distance to the previous anchor.
+		// (next node = TextAnchorNode.Successor, distance = TextAnchorNode.length)
+		// Distances are never negative, so this representation means anchors are always sorted by offset
+		// (the order of anchors at the same offset is undefined)
+		
+		// Of course, a linked list of anchors would be way too slow (one would need to traverse the whole list
+		// every time the offset of an anchor is being looked up).
+		// Instead, we use a red-black-tree. We aren't actually using the tree for sorting - it's just a binary tree
+		// as storage format for what's conceptually a list, the red-black properties are used to keep the tree balanced.
+		// Other balanced binary trees would work, too.
+		
+		// What makes the tree-form efficient is that is augments the data by a 'totalLength'. Where 'length'
+		// represents the distance to the previous node, 'totalLength' is the sum of all 'length' values in the subtree
+		// under that node.
+		// This allows computing the Offset from an anchor by walking up the list of parent nodes instead of going
+		// through all predecessor nodes. So computing the Offset runs in O(log N).
+		
 		readonly TextDocument document;
 		readonly List<TextAnchorNode> nodesToDelete = new List<TextAnchorNode>();
 		TextAnchorNode root;
@@ -35,16 +65,15 @@ namespace ICSharpCode.AvalonEdit.Document
 		}
 		
 		#region Insert Text
-		public void InsertText(int offset, int length)
+		void InsertText(int offset, int length)
 		{
-			//Log("InsertText(" + offset + ", " + length + ")");
 			if (length == 0 || root == null || offset > root.totalLength)
 				return;
 			
 			// find the range of nodes that are placed exactly at offset
 			// beginNode is inclusive, endNode is exclusive
 			if (offset == root.totalLength) {
-				PerformInsertText(root.RightMost, null, length);
+				PerformInsertText(FindActualBeginNode(root.RightMost), null, length);
 			} else {
 				TextAnchorNode endNode = FindNode(ref offset);
 				Debug.Assert(endNode.length > 0);
@@ -54,21 +83,31 @@ namespace ICSharpCode.AvalonEdit.Document
 					endNode.length += length;
 					UpdateAugmentedData(endNode);
 				} else {
-					PerformInsertText(endNode.Predecessor, endNode, length);
+					PerformInsertText(FindActualBeginNode(endNode.Predecessor), endNode, length);
 				}
 			}
 			DeleteMarkedNodes();
 		}
 		
-		void PerformInsertText(TextAnchorNode beginNode, TextAnchorNode endNode, int length)
+		TextAnchorNode FindActualBeginNode(TextAnchorNode node)
 		{
 			// now find the actual beginNode
-			while (beginNode != null && beginNode.length == 0)
+			while (node != null && node.length == 0)
-				beginNode = beginNode.Predecessor;
+				node = node.Predecessor;
-			if (beginNode == null) {
+			if (node == null) {
 				// no predecessor = beginNode is first node in tree
-				beginNode = root.LeftMost;
+				node = root.LeftMost;
 			}
+			return node;
+		}
+		
+		// Sorts the nodes in the range [beginNode, endNode) by MovementType
+		// and inserts the length between the BeforeInsertion and the AfterInsertion nodes.
+		void PerformInsertText(TextAnchorNode beginNode, TextAnchorNode endNode, int length)
+		{
+			Debug.Assert(beginNode != null);
+			// endNode may be null at the end of the anchor tree
+			
 			// now we need to sort the nodes in the range [beginNode, endNode); putting those with
 			// MovementType.BeforeInsertion in front of those with MovementType.AfterInsertion
 			List<TextAnchorNode> beforeInsert = new List<TextAnchorNode>();
@@ -136,18 +175,42 @@ namespace ICSharpCode.AvalonEdit.Document
 		}
 		#endregion
 		
-		#region Remove Text
+		#region Remove or Replace text
-		public void RemoveText(int offset, int length, DelayedEvents delayedEvents)
+		public void HandleTextChange(OffsetChangeMapEntry entry, DelayedEvents delayedEvents)
 		{
-			//Log("RemoveText(" + offset + ", " + length + ")");
+			//Log("HandleTextChange(" + entry + ")");
-			if (length == 0 || root == null || offset >= root.totalLength)
+			if (entry.RemovalLength == 0) {
+				// This is a pure insertion.
+				// Unlike a replace with removal, a pure insertion can result in nodes at the same location
+				// to split depending on their MovementType.
+				// Thus, we handle this case on a separate code path
+				// (the code below looks like it does something similar, but it can only split
+				// the set of deletion survivors, not all nodes at an offset)
+				InsertText(entry.Offset, entry.InsertionLength);
+				return;
+			}
+			// When handling a replacing text change, we need to:
+			// - find all anchors in the deleted segment and delete them / move them to the appropriate
+			//   surviving side.
+			// - adjust the segment size between the left and right side
+			
+			int offset = entry.Offset;
+			int remainingRemovalLength = entry.RemovalLength;
+			// if the text change is happening after the last anchor, we don't have to do anything
+			if (root == null || offset >= root.totalLength)
 				return;
 			TextAnchorNode node = FindNode(ref offset);
-			while (node != null && offset + length > node.length) {
+			TextAnchorNode firstDeletionSurvivor = null;
+			// go forward through the tree and delete all nodes in the removal segment
+			while (node != null && offset + remainingRemovalLength > node.length) {
 				TextAnchor anchor = (TextAnchor)node.Target;
 				if (anchor != null && anchor.SurviveDeletion) {
-					// shorten node
+					if (firstDeletionSurvivor == null)
-					length -= node.length - offset;
+						firstDeletionSurvivor = node;
+					// This node should be deleted, but it wants to survive.
+					// We'll just remove the deleted length segment, so the node will be positioned
+					// in front of the removed segment.
+					remainingRemovalLength -= node.length - offset;
 					node.length = offset;
 					offset = 0;
 					UpdateAugmentedData(node);
@@ -155,7 +218,7 @@ namespace ICSharpCode.AvalonEdit.Document
 				} else {
 					// delete node
 					TextAnchorNode s = node.Successor;
-					length -= node.length;
+					remainingRemovalLength -= node.length;
 					RemoveNode(node);
 					// we already deleted the node, don't delete it twice
 					nodesToDelete.Remove(node);
@@ -164,8 +227,35 @@ namespace ICSharpCode.AvalonEdit.Document
 					node = s;
 				}
 			}
+			// 'node' now is the first anchor after the deleted segment.
+			// If there are no anchors after the deleted segment, 'node' is null.
+			
+			// firstDeletionSurvivor was set to the first node surviving deletion.
+			// Because all non-surviving nodes up to 'node' were deleted, the node range
+			// [firstDeletionSurvivor, node) now refers to the set of all deletion survivors.
+			
+			// do the remaining job of the removal
+			if (node != null) {
+				node.length -= remainingRemovalLength;
+				Debug.Assert(node.length >= 0);
+			}
+			if (entry.InsertionLength > 0) {
+				// we are performing a replacement
+				if (firstDeletionSurvivor != null) {
+					// We got deletion survivors which need to be split into BeforeInsertion
+					// and AfterInsertion groups.
+					// Take care that we don't regroup everything at offset, but only the deletion
+					// survivors - from firstDeletionSurvivor (inclusive) to node (exclusive).
+					// This ensures that nodes immediately before or after the replaced segment
+					// stay where they are (independent from their MovementType)
+					PerformInsertText(firstDeletionSurvivor, node, entry.InsertionLength);
+				} else if (node != null) {
+					// No deletion survivors:
+					// just perform the insertion
+					node.length += entry.InsertionLength;
+				}
+			}
 			if (node != null) {
-				node.length -= length;
 				UpdateAugmentedData(node);
 			}
 			DeleteMarkedNodes();

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/TextDocument.cs

@@ -334,7 +334,7 @@ namespace ICSharpCode.AvalonEdit.Document
 			Replace(offset, length, text, null);
 		}
 		
-			/// <summary>
+		/// <summary>
 		/// Replaces text.
 		/// Runtime:
 		///  for updating the text buffer: m=size of new text, d=distance to last change, n=total text length
@@ -351,23 +351,44 @@ namespace ICSharpCode.AvalonEdit.Document
 		{
 			if (text == null)
 				throw new ArgumentNullException("text");
+			// Please see OffsetChangeMappingType XML comments for details on how these modes work.
 			switch (offsetChangeMappingType) {
-				case OffsetChangeMappingType.RemoveAndInsert:
+				case OffsetChangeMappingType.Normal:
 					Replace(offset, length, text, null);
 					break;
+				case OffsetChangeMappingType.RemoveAndInsert:
+					if (length == 0 || text.Length == 0) {
+						// only insertion or only removal?
+						// OffsetChangeMappingType doesn't matter, just use Normal.
+						Replace(offset, length, text, null);
+					} else {
+						OffsetChangeMap map = new OffsetChangeMap(2);
+						map.Add(new OffsetChangeMapEntry(offset, length, 0));
+						map.Add(new OffsetChangeMapEntry(offset, 0, text.Length));
+						Replace(offset, length, text, map);
+					}
+					break;
 				case OffsetChangeMappingType.CharacterReplace:
-					if (text.Length > length) {
+					if (length == 0 || text.Length == 0) {
+						// only insertion or only removal?
+						// OffsetChangeMappingType doesn't matter, just use Normal.
+						Replace(offset, length, text, null);
+					} else if (text.Length > length) {
 						OffsetChangeMap map = new OffsetChangeMap(1);
-						map.Add(new OffsetChangeMapEntry(offset + length, text.Length - length));
+						// look at OffsetChangeMappingType.CharacterReplace XML comments on why we need to replace
+						// the last 
+						map.Add(new OffsetChangeMapEntry(offset + length - 1, 1, 1 + text.Length - length));
 						Replace(offset, length, text, map);
 					} else if (text.Length < length) {
 						OffsetChangeMap map = new OffsetChangeMap(1);
-						map.Add(new OffsetChangeMapEntry(offset + length - text.Length, text.Length - length));
+						map.Add(new OffsetChangeMapEntry(offset + length - text.Length, length - text.Length, 0));
 						Replace(offset, length, text, map);
 					} else {
 						Replace(offset, length, text, OffsetChangeMap.Empty);
 					}
 					break;
+				default:
+					throw new ArgumentOutOfRangeException("offsetChangeMappingType", offsetChangeMappingType, "Invalid enum value");
 			}
 		}
 		
@@ -384,10 +405,11 @@ namespace ICSharpCode.AvalonEdit.Document
 		/// <param name="text">The new text.</param>
 		/// <param name="offsetChangeMap">The offsetChangeMap determines how offsets inside the old text are mapped to the new text.
 		/// This affects how the anchors and segments inside the replaced region behave.
-		/// If you pass null (the default when using one of the other overloads), the offsets are changed as if
+		/// If you pass null (the default when using one of the other overloads), the offsets are changed as
-		/// the old text is removed first and the new text is inserted later (OffsetChangeMappingType.RemoveAndInsert).
+		/// in OffsetChangeMappingType.Normal mode.
-		/// If you pass OffsetChangeMap.Empty, then everything will stay in its old place.
+		/// If you pass OffsetChangeMap.Empty, then everything will stay in its old place (OffsetChangeMappingType.CharacterReplace mode).
-		/// The offsetChangeMap must be a valid 'explanation' for the document change</param>
+		/// The offsetChangeMap must be a valid 'explanation' for the document change. See <see cref="OffsetChangeMap.IsValidForDocumentChange"/>.
+		/// </param>
 		public void Replace(int offset, int length, string text, OffsetChangeMap offsetChangeMap)
 		{
 			if (text == null)
@@ -417,6 +439,12 @@ namespace ICSharpCode.AvalonEdit.Document
 			if (length == 0 && text.Length == 0)
 				return;
 			
+			// trying to replace a single character in 'Normal' mode?
+			// for single characters, 'CharacterReplace' mode is equivalent, but more performant
+			// (we don't have to touch the anchorTree at all in 'CharacterReplace' mode)
+			if (length == 1 && text.Length == 1 && offsetChangeMap == null)
+				offsetChangeMap = OffsetChangeMap.Empty;
+			
 			DocumentChangeEventArgs args = new DocumentChangeEventArgs(offset, length, text, offsetChangeMap);
 			
 			// fire DocumentChanging event
@@ -446,12 +474,10 @@ namespace ICSharpCode.AvalonEdit.Document
 			
 			// update text anchors
 			if (offsetChangeMap == null) {
-				anchorTree.RemoveText(offset, length, delayedEvents);
+				anchorTree.HandleTextChange(args.CreateSingleChangeMapEntry(), delayedEvents);
-				anchorTree.InsertText(offset, text.Length);
 			} else {
 				foreach (OffsetChangeMapEntry entry in offsetChangeMap) {
-					anchorTree.RemoveText(entry.Offset, entry.RemovalLength, delayedEvents);
+					anchorTree.HandleTextChange(entry, delayedEvents);
-					anchorTree.InsertText(entry.Offset, entry.InsertionLength);
 				}
 			}
 			

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/TextSegmentCollection.cs

@@ -35,6 +35,9 @@ namespace ICSharpCode.AvalonEdit.Document
 		// Implementation: this is basically a mixture of an augmented interval tree
 		// and the TextAnchorTree.
 		
+		// WARNING: you need to understand how interval trees (the version with the augmented 'high'/'max' field)
+		// and how the TextAnchorTree works before you have any chance of understanding this code.
+		
 		// This means that every node holds two "segments":
 		// one like the segments in the text anchor tree to support efficient offset changes
 		// and another that is the interval as seen by the user

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Utils/ThrowUtil.cs

@@ -25,13 +25,20 @@ namespace ICSharpCode.AvalonEdit.Utils
 		/// public VisualLineText(string text) : base(ThrowUtil.CheckNull(text, "text").Length)
 		/// </code>
 		/// </example>
-		public static T CheckNull<T>(T val, string parameterName) where T : class
+		public static T CheckNotNull<T>(T val, string parameterName) where T : class
 		{
 			if (val == null)
 				throw new ArgumentNullException(parameterName);
 			return val;
 		}
 		
+		public static int CheckNotNegative(int val, string parameterName)
+		{
+			if (val < 0)
+				throw new ArgumentOutOfRangeException(parameterName, val, "value must not be negative");
+			return val;
+		}
+		
 		public static InvalidOperationException NoDocumentAssigned()
 		{
 			throw new InvalidOperationException("Document is null");

src/Main/Base/Project/Src/Editor/ITextEditor.cs

@@ -51,7 +51,7 @@ namespace ICSharpCode.SharpDevelop.Editor
 		/// Sets the selection.
 		/// </summary>
 		/// <param name="selectionStart">Start offset of the selection</param>
-		/// <param name="selectionLength">End offset of the selection</param>
+		/// <param name="selectionLength">Length of the selection</param>
 		void Select(int selectionStart, int selectionLength);
 		
 		/// <summary>