DiffMatchPatch.cs

/*
 * Copyright 2008 Google Inc. All Rights Reserved.
 * Author: fraser@google.com (Neil Fraser)
 * Author: anteru@developer.shelter13.net (Matthaeus G. Chajdas)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Diff Match and Patch
 * http://code.google.com/p/google-diff-match-patch/
 */

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Web;

namespace DiffMatchPatch
{
	internal static class CompatibilityExtensions
	{
		// JScript splice function
		public static List<T> Splice<T>(this List<T> input, int start, int count,
											  params T[] objects)
		{
			List<T> deletedRange = input.GetRange(start, count);
			input.RemoveRange(start, count);
			input.InsertRange(start, objects);

			return deletedRange;
		}

		// Java substring function
		public static string JavaSubstring(this string s, int begin, int end)
		{
			return s.Substring(begin, end - begin);
		}
	}

	/**-
   * The data structure representing a diff is a List of Diff objects:
   * {Diff(Operation.DELETE, "Hello"), Diff(Operation.INSERT, "Goodbye"),
   *  Diff(Operation.EQUAL, " world.")}
   * which means: delete "Hello", add "Goodbye" and keep " world."
   */
	public enum Operation
	{
		DELETE,
		INSERT,
		EQUAL
	}


	/**
   * Class representing one diff operation.
   */
	public class Diff
	{
		public Operation operation;
		// One of: INSERT, DELETE or EQUAL.
		public string text;
		// The text associated with this diff operation.

		/**
     * Constructor.  Initializes the diff with the provided values.
     * @param operation One of INSERT, DELETE or EQUAL.
     * @param text The text being applied.
     */
		public Diff(Operation operation, string text)
		{
			// Construct a diff with the specified operation and text.
			this.operation = operation;
			this.text = text;
		}

		/**
     * Display a human-readable version of this Diff.
     * @return text version.
     */
		public override string ToString()
		{
			string prettyText = this.text.Replace('\n', '\u00b6');
			return "Diff(" + this.operation + ",\"" + prettyText + "\")";
		}

		/**
     * Is this Diff equivalent to another Diff?
     * @param d Another Diff to compare against.
     * @return true or false.
     */
		public override bool Equals(Object obj)
		{
			// If parameter is null return false.
			if (obj == null) {
				return false;
			}

			// If parameter cannot be cast to Diff return false.
			Diff p = obj as Diff;
			if ((System.Object)p == null) {
				return false;
			}

			// Return true if the fields match.
			return p.operation == this.operation && p.text == this.text;
		}

		public bool Equals(Diff obj)
		{
			// If parameter is null return false.
			if (obj == null) {
				return false;
			}

			// Return true if the fields match.
			return obj.operation == this.operation && obj.text == this.text;
		}

		public override int GetHashCode()
		{
			return text.GetHashCode() ^ operation.GetHashCode();
		}
	}


	/**
   * Class representing one patch operation.
   */
	public class Patch
	{
		public List<Diff> diffs = new List<Diff>();
		public int start1;
		public int start2;
		public int length1;
		public int length2;

		/**
     * Emmulate GNU diff's format.
     * Header: @@ -382,8 +481,9 @@
     * Indicies are printed as 1-based, not 0-based.
     * @return The GNU diff string.
     */
		public override string ToString()
		{
			string coords1, coords2;
			if (this.length1 == 0) {
				coords1 = this.start1 + ",0";
			} else if (this.length1 == 1) {
				coords1 = Convert.ToString(this.start1 + 1);
			} else {
				coords1 = (this.start1 + 1) + "," + this.length1;
			}
			if (this.length2 == 0) {
				coords2 = this.start2 + ",0";
			} else if (this.length2 == 1) {
				coords2 = Convert.ToString(this.start2 + 1);
			} else {
				coords2 = (this.start2 + 1) + "," + this.length2;
			}
			StringBuilder text = new StringBuilder();
			text.Append("@@ -").Append(coords1).Append(" +").Append(coords2)
				.Append(" @@\n");
			// Escape the body of the patch with %xx notation.
			foreach (Diff aDiff in this.diffs) {
				switch (aDiff.operation) {
					case Operation.INSERT:
						text.Append('+');
						break;
					case Operation.DELETE:
						text.Append('-');
						break;
					case Operation.EQUAL:
						text.Append(' ');
						break;
				}

				text.Append(HttpUtility.UrlEncode(aDiff.text,
															  new UTF8Encoding()).Replace('+', ' ')).Append("\n");
			}

			return diff_match_patch.unescapeForEncodeUriCompatability(
				text.ToString());
		}
	}


	/**
   * Class containing the diff, match and patch methods.
   * Also Contains the behaviour settings.
   */
	public class diff_match_patch
	{
		// Defaults.
		// Set these on your diff_match_patch instance to override the defaults.

		// Number of seconds to map a diff before giving up (0 for infinity).
		public float Diff_Timeout = 1.0f;
		// Cost of an empty edit operation in terms of edit characters.
		public short Diff_EditCost = 4;
		// At what point is no match declared (0.0 = perfection, 1.0 = very loose).
		public float Match_Threshold = 0.5f;
		// How far to search for a match (0 = exact location, 1000+ = broad match).
		// A match this many characters away from the expected location will add
		// 1.0 to the score (0.0 is a perfect match).
		public int Match_Distance = 1000;
		// When deleting a large block of text (over ~64 characters), how close
		// do the contents have to be to match the expected contents. (0.0 =
		// perfection, 1.0 = very loose).  Note that Match_Threshold controls
		// how closely the end points of a delete need to match.
		public float Patch_DeleteThreshold = 0.5f;
		// Chunk size for context length.
		public short Patch_Margin = 4;

		// The number of bits in an int.
		private short Match_MaxBits = 32;


		//  DIFF FUNCTIONS


		/**
     * Find the differences between two texts.
     * Run a faster, slightly less optimal diff.
     * This method allows the 'checklines' of diff_main() to be optional.
     * Most of the time checklines is wanted, so default to true.
     * @param text1 Old string to be diffed.
     * @param text2 New string to be diffed.
     * @return List of Diff objects.
     */
		public List<Diff> diff_main(string text1, string text2)
		{
			return diff_main(text1, text2, true);
		}

		/**
     * Find the differences between two texts.
     * @param text1 Old string to be diffed.
     * @param text2 New string to be diffed.
     * @param checklines Speedup flag.  If false, then don't run a
     *     line-level diff first to identify the changed areas.
     *     If true, then run a faster slightly less optimal diff.
     * @return List of Diff objects.
     */
		public List<Diff> diff_main(string text1, string text2, bool checklines)
		{
			// Set a deadline by which time the diff must be complete.
			DateTime deadline;
			if (this.Diff_Timeout <= 0) {
				deadline = DateTime.MaxValue;
			} else {
				deadline = DateTime.Now +
				new TimeSpan(((long)(Diff_Timeout * 1000)) * 10000);
			}
			return diff_main(text1, text2, checklines, deadline);
		}

		/**
     * Find the differences between two texts.  Simplifies the problem by
     * stripping any common prefix or suffix off the texts before diffing.
     * @param text1 Old string to be diffed.
     * @param text2 New string to be diffed.
     * @param checklines Speedup flag.  If false, then don't run a
     *     line-level diff first to identify the changed areas.
     *     If true, then run a faster slightly less optimal diff.
     * @param deadline Time when the diff should be complete by.  Used
     *     internally for recursive calls.  Users should set DiffTimeout
     *     instead.
     * @return List of Diff objects.
     */
		private List<Diff> diff_main(string text1, string text2, bool checklines,
										   DateTime deadline)
		{
			// Check for null inputs not needed since null can't be passed in C#.

			// Check for equality (speedup).
			List<Diff> diffs;
			if (text1 == text2) {
				diffs = new List<Diff>();
				if (text1.Length != 0) {
					diffs.Add(new Diff(Operation.EQUAL, text1));
				}
				return diffs;
			}

			// Trim off common prefix (speedup).
			int commonlength = diff_commonPrefix(text1, text2);
			string commonprefix = text1.Substring(0, commonlength);
			text1 = text1.Substring(commonlength);
			text2 = text2.Substring(commonlength);

			// Trim off common suffix (speedup).
			commonlength = diff_commonSuffix(text1, text2);
			string commonsuffix = text1.Substring(text1.Length - commonlength);
			text1 = text1.Substring(0, text1.Length - commonlength);
			text2 = text2.Substring(0, text2.Length - commonlength);

			// Compute the diff on the middle block.
			diffs = diff_compute(text1, text2, checklines, deadline);

			// Restore the prefix and suffix.
			if (commonprefix.Length != 0) {
				diffs.Insert(0, (new Diff(Operation.EQUAL, commonprefix)));
			}
			if (commonsuffix.Length != 0) {
				diffs.Add(new Diff(Operation.EQUAL, commonsuffix));
			}

			diff_cleanupMerge(diffs);
			return diffs;
		}

		/**
     * Find the differences between two texts.  Assumes that the texts do not
     * have any common prefix or suffix.
     * @param text1 Old string to be diffed.
     * @param text2 New string to be diffed.
     * @param checklines Speedup flag.  If false, then don't run a
     *     line-level diff first to identify the changed areas.
     *     If true, then run a faster slightly less optimal diff.
     * @param deadline Time when the diff should be complete by.
     * @return List of Diff objects.
     */
		private List<Diff> diff_compute(string text1, string text2,
											  bool checklines, DateTime deadline)
		{
			List<Diff> diffs = new List<Diff>();

			if (text1.Length == 0) {
				// Just add some text (speedup).
				diffs.Add(new Diff(Operation.INSERT, text2));
				return diffs;
			}

			if (text2.Length == 0) {
				// Just delete some text (speedup).
				diffs.Add(new Diff(Operation.DELETE, text1));
				return diffs;
			}

			string longtext = text1.Length > text2.Length ? text1 : text2;
			string shorttext = text1.Length > text2.Length ? text2 : text1;
			int i = longtext.IndexOf(shorttext, StringComparison.Ordinal);
			if (i != -1) {
				// Shorter text is inside the longer text (speedup).
				Operation op = (text1.Length > text2.Length) ?
					Operation.DELETE : Operation.INSERT;
				diffs.Add(new Diff(op, longtext.Substring(0, i)));
				diffs.Add(new Diff(Operation.EQUAL, shorttext));
				diffs.Add(new Diff(op, longtext.Substring(i + shorttext.Length)));
				return diffs;
			}

			if (shorttext.Length == 1) {
				// Single character string.
				// After the previous speedup, the character can't be an equality.
				diffs.Add(new Diff(Operation.DELETE, text1));
				diffs.Add(new Diff(Operation.INSERT, text2));
				return diffs;
			}

			// Check to see if the problem can be split in two.
			string[] hm = diff_halfMatch(text1, text2);
			if (hm != null) {
				// A half-match was found, sort out the return data.
				string text1_a = hm[0];
				string text1_b = hm[1];
				string text2_a = hm[2];
				string text2_b = hm[3];
				string mid_common = hm[4];
				// Send both pairs off for separate processing.
				List<Diff> diffs_a = diff_main(text1_a, text2_a, checklines, deadline);
				List<Diff> diffs_b = diff_main(text1_b, text2_b, checklines, deadline);
				// Merge the results.
				diffs = diffs_a;
				diffs.Add(new Diff(Operation.EQUAL, mid_common));
				diffs.AddRange(diffs_b);
				return diffs;
			}

			if (checklines && text1.Length > 100 && text2.Length > 100) {
				return diff_lineMode(text1, text2, deadline);
			}

			return diff_bisect(text1, text2, deadline);
		}

		/**
     * Do a quick line-level diff on both strings, then rediff the parts for
     * greater accuracy.
     * This speedup can produce non-minimal diffs.
     * @param text1 Old string to be diffed.
     * @param text2 New string to be diffed.
     * @param deadline Time when the diff should be complete by.
     * @return List of Diff objects.
     */
		private List<Diff> diff_lineMode(string text1, string text2,
											   DateTime deadline)
		{
			// Scan the text on a line-by-line basis first.
			Object[] b = diff_linesToChars(text1, text2);
			text1 = (string)b[0];
			text2 = (string)b[1];
			List<string> linearray = (List<string>)b[2];

			List<Diff> diffs = diff_main(text1, text2, false, deadline);

			// Convert the diff back to original text.
			diff_charsToLines(diffs, linearray);
			// Eliminate freak matches (e.g. blank lines)
			diff_cleanupSemantic(diffs);

			// Rediff any replacement blocks, this time character-by-character.
			// Add a dummy entry at the end.
			diffs.Add(new Diff(Operation.EQUAL, string.Empty));
			int pointer = 0;
			int count_delete = 0;
			int count_insert = 0;
			string text_delete = string.Empty;
			string text_insert = string.Empty;
			while (pointer < diffs.Count) {
				switch (diffs[pointer].operation) {
					case Operation.INSERT:
						count_insert++;
						text_insert += diffs[pointer].text;
						break;
					case Operation.DELETE:
						count_delete++;
						text_delete += diffs[pointer].text;
						break;
					case Operation.EQUAL:
						// Upon reaching an equality, check for prior redundancies.
						if (count_delete >= 1 && count_insert >= 1) {
							// Delete the offending records and add the merged ones.
							diffs.RemoveRange(pointer - count_delete - count_insert,
															   count_delete + count_insert);
							pointer = pointer - count_delete - count_insert;
							List<Diff> a =
								this.diff_main(text_delete, text_insert, false, deadline);
							diffs.InsertRange(pointer, a);
							pointer = pointer + a.Count;
						}
						count_insert = 0;
						count_delete = 0;
						text_delete = string.Empty;
						text_insert = string.Empty;
						break;
				}
				pointer++;
			}
			diffs.RemoveAt(diffs.Count - 1);  // Remove the dummy entry at the end.

			return diffs;
		}

		/**
     * Find the 'middle snake' of a diff, split the problem in two
     * and return the recursively constructed diff.
     * See Myers 1986 paper: An O(ND) Difference Algorithm and Its Variations.
     * @param text1 Old string to be diffed.
     * @param text2 New string to be diffed.
     * @param deadline Time at which to bail if not yet complete.
     * @return List of Diff objects.
     */
		protected List<Diff> diff_bisect(string text1, string text2,
											   DateTime deadline)
		{
			// Cache the text lengths to prevent multiple calls.
			int text1_length = text1.Length;
			int text2_length = text2.Length;
			int max_d = (text1_length + text2_length + 1) / 2;
			int v_offset = max_d;
			int v_length = 2 * max_d;
			int[] v1 = new int[v_length];
			int[] v2 = new int[v_length];
			for (int x = 0; x < v_length; x++) {
				v1[x] = -1;
				v2[x] = -1;
			}
			v1[v_offset + 1] = 0;
			v2[v_offset + 1] = 0;
			int delta = text1_length - text2_length;
			// If the total number of characters is odd, then the front path will
			// collide with the reverse path.
			bool front = (delta % 2 != 0);
			// Offsets for start and end of k loop.
			// Prevents mapping of space beyond the grid.
			int k1start = 0;
			int k1end = 0;
			int k2start = 0;
			int k2end = 0;
			for (int d = 0; d < max_d; d++) {
				// Bail out if deadline is reached.
				if (DateTime.Now > deadline) {
					break;
				}

				// Walk the front path one step.
				for (int k1 = -d + k1start; k1 <= d - k1end; k1 += 2) {
					int k1_offset = v_offset + k1;
					int x1;
					if (k1 == -d || k1 != d && v1[k1_offset - 1] < v1[k1_offset + 1]) {
						x1 = v1[k1_offset + 1];
					} else {
						x1 = v1[k1_offset - 1] + 1;
					}
					int y1 = x1 - k1;
					while (x1 < text1_length && y1 < text2_length
										  && text1[x1] == text2[y1]) {
						x1++;
						y1++;
					}
					v1[k1_offset] = x1;
					if (x1 > text1_length) {
						// Ran off the right of the graph.
						k1end += 2;
					} else if (y1 > text2_length) {
						// Ran off the bottom of the graph.
						k1start += 2;
					} else if (front) {
						int k2_offset = v_offset + delta - k1;
						if (k2_offset >= 0 && k2_offset < v_length && v2[k2_offset] != -1) {
							// Mirror x2 onto top-left coordinate system.
							int x2 = text1_length - v2[k2_offset];
							if (x1 >= x2) {
								// Overlap detected.
								return diff_bisectSplit(text1, text2, x1, y1, deadline);
							}
						}
					}
				}

				// Walk the reverse path one step.
				for (int k2 = -d + k2start; k2 <= d - k2end; k2 += 2) {
					int k2_offset = v_offset + k2;
					int x2;
					if (k2 == -d || k2 != d && v2[k2_offset - 1] < v2[k2_offset + 1]) {
						x2 = v2[k2_offset + 1];
					} else {
						x2 = v2[k2_offset - 1] + 1;
					}
					int y2 = x2 - k2;
					while (x2 < text1_length && y2 < text2_length
										  && text1[text1_length - x2 - 1]
										  == text2[text2_length - y2 - 1]) {
						x2++;
						y2++;
					}
					v2[k2_offset] = x2;
					if (x2 > text1_length) {
						// Ran off the left of the graph.
						k2end += 2;
					} else if (y2 > text2_length) {
						// Ran off the top of the graph.
						k2start += 2;
					} else if (!front) {
						int k1_offset = v_offset + delta - k2;
						if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] != -1) {
							int x1 = v1[k1_offset];
							int y1 = v_offset + x1 - k1_offset;
							// Mirror x2 onto top-left coordinate system.
							x2 = text1_length - v2[k2_offset];
							if (x1 >= x2) {
								// Overlap detected.
								return diff_bisectSplit(text1, text2, x1, y1, deadline);
							}
						}
					}
				}
			}
			// Diff took too long and hit the deadline or
			// number of diffs equals number of characters, no commonality at all.
			List<Diff> diffs = new List<Diff>();
			diffs.Add(new Diff(Operation.DELETE, text1));
			diffs.Add(new Diff(Operation.INSERT, text2));
			return diffs;
		}

		/**
     * Given the location of the 'middle snake', split the diff in two parts
     * and recurse.
     * @param text1 Old string to be diffed.
     * @param text2 New string to be diffed.
     * @param x Index of split point in text1.
     * @param y Index of split point in text2.
     * @param deadline Time at which to bail if not yet complete.
     * @return LinkedList of Diff objects.
     */
		private List<Diff> diff_bisectSplit(string text1, string text2,
												  int x, int y, DateTime deadline)
		{
			string text1a = text1.Substring(0, x);
			string text2a = text2.Substring(0, y);
			string text1b = text1.Substring(x);
			string text2b = text2.Substring(y);

			// Compute both diffs serially.
			List<Diff> diffs = diff_main(text1a, text2a, false, deadline);
			List<Diff> diffsb = diff_main(text1b, text2b, false, deadline);

			diffs.AddRange(diffsb);
			return diffs;
		}

		/**
     * Split two texts into a list of strings.  Reduce the texts to a string of
     * hashes where each Unicode character represents one line.
     * @param text1 First string.
     * @param text2 Second string.
     * @return Three element Object array, containing the encoded text1, the
     *     encoded text2 and the List of unique strings.  The zeroth element
     *     of the List of unique strings is intentionally blank.
     */
		protected Object[] diff_linesToChars(string text1, string text2)
		{
			List<string> lineArray = new List<string>();
			Dictionary<string, int> lineHash = new Dictionary<string, int>();
			// e.g. linearray[4] == "Hello\n"
			// e.g. linehash.get("Hello\n") == 4

			// "\x00" is a valid character, but various debuggers don't like it.
			// So we'll insert a junk entry to avoid generating a null character.
			lineArray.Add(string.Empty);

			string chars1 = diff_linesToCharsMunge(text1, lineArray, lineHash);
			string chars2 = diff_linesToCharsMunge(text2, lineArray, lineHash);
			return new Object[] { chars1, chars2, lineArray };
		}

		/**
     * Split a text into a list of strings.  Reduce the texts to a string of
     * hashes where each Unicode character represents one line.
     * @param text String to encode.
     * @param lineArray List of unique strings.
     * @param lineHash Map of strings to indices.
     * @return Encoded string.
     */
		private string diff_linesToCharsMunge(string text, List<string> lineArray,
													Dictionary<string, int> lineHash)
		{
			int lineStart = 0;
			int lineEnd = -1;
			string line;
			StringBuilder chars = new StringBuilder();
			// Walk the text, pulling out a Substring for each line.
			// text.split('\n') would would temporarily double our memory footprint.
			// Modifying text would create many large strings to garbage collect.
			while (lineEnd < text.Length - 1) {
				lineEnd = text.IndexOf('\n', lineStart);
				if (lineEnd == -1) {
					lineEnd = text.Length - 1;
				}
				line = text.JavaSubstring(lineStart, lineEnd + 1);
				lineStart = lineEnd + 1;

				if (lineHash.ContainsKey(line)) {
					chars.Append(((char)(int)lineHash[line]));
				} else {
					lineArray.Add(line);
					lineHash.Add(line, lineArray.Count - 1);
					chars.Append(((char)(lineArray.Count - 1)));
				}
			}
			return chars.ToString();
		}

		/**
     * Rehydrate the text in a diff from a string of line hashes to real lines
     * of text.
     * @param diffs List of Diff objects.
     * @param lineArray List of unique strings.
     */
		protected void diff_charsToLines(ICollection<Diff> diffs,
											   List<string> lineArray)
		{
			StringBuilder text;
			foreach (Diff diff in diffs) {
				text = new StringBuilder();
				for (int y = 0; y < diff.text.Length; y++) {
					text.Append(lineArray[diff.text[y]]);
				}
				diff.text = text.ToString();
			}
		}

		/**
     * Determine the common prefix of two strings.
     * @param text1 First string.
     * @param text2 Second string.
     * @return The number of characters common to the start of each string.
     */
		public int diff_commonPrefix(string text1, string text2)
		{
			// Performance analysis: http://neil.fraser.name/news/2007/10/09/
			int n = Math.Min(text1.Length, text2.Length);
			for (int i = 0; i < n; i++) {
				if (text1[i] != text2[i]) {
					return i;
				}
			}
			return n;
		}

		/**
     * Determine the common suffix of two strings.
     * @param text1 First string.
     * @param text2 Second string.
     * @return The number of characters common to the end of each string.
     */
		public int diff_commonSuffix(string text1, string text2)
		{
			// Performance analysis: http://neil.fraser.name/news/2007/10/09/
			int text1_length = text1.Length;
			int text2_length = text2.Length;
			int n = Math.Min(text1.Length, text2.Length);
			for (int i = 1; i <= n; i++) {
				if (text1[text1_length - i] != text2[text2_length - i]) {
					return i - 1;
				}
			}
			return n;
		}

		/**
     * Determine if the suffix of one string is the prefix of another.
     * @param text1 First string.
     * @param text2 Second string.
     * @return The number of characters common to the end of the first
     *     string and the start of the second string.
     */
		protected int diff_commonOverlap(string text1, string text2)
		{
			// Cache the text lengths to prevent multiple calls.
			int text1_length = text1.Length;
			int text2_length = text2.Length;
			// Eliminate the null case.
			if (text1_length == 0 || text2_length == 0) {
				return 0;
			}
			// Truncate the longer string.
			if (text1_length > text2_length) {
				text1 = text1.Substring(text1_length - text2_length);
			} else if (text1_length < text2_length) {
				text2 = text2.Substring(0, text1_length);
			}
			int text_length = Math.Min(text1_length, text2_length);
			// Quick check for the worst case.
			if (text1 == text2) {
				return text_length;
			}

			// Start by looking for a single character match
			// and increase length until no match is found.
			// Performance analysis: http://neil.fraser.name/news/2010/11/04/
			int best = 0;
			int length = 1;
			while (true) {
				string pattern = text1.Substring(text_length - length);
				int found = text2.IndexOf(pattern, StringComparison.Ordinal);
				if (found == -1) {
					return best;
				}
				length += found;
				if (found == 0 || text1.Substring(text_length - length) ==
								text2.Substring(0, length)) {
					best = length;
					length++;
				}
			}
		}

		/**
     * Do the two texts share a Substring which is at least half the length of
     * the longer text?
     * This speedup can produce non-minimal diffs.
     * @param text1 First string.
     * @param text2 Second string.
     * @return Five element String array, containing the prefix of text1, the
     *     suffix of text1, the prefix of text2, the suffix of text2 and the
     *     common middle.  Or null if there was no match.
     */

		protected string[] diff_halfMatch(string text1, string text2)
		{
			if (this.Diff_Timeout <= 0) {
				// Don't risk returning a non-optimal diff if we have unlimited time.
				return null;
			}
			string longtext = text1.Length > text2.Length ? text1 : text2;
			string shorttext = text1.Length > text2.Length ? text2 : text1;
			if (longtext.Length < 4 || shorttext.Length * 2 < longtext.Length) {
				return null;  // Pointless.
			}

			// First check if the second quarter is the seed for a half-match.
			string[] hm1 = diff_halfMatchI(longtext, shorttext,
													(longtext.Length + 3) / 4);
			// Check again based on the third quarter.
			string[] hm2 = diff_halfMatchI(longtext, shorttext,
													(longtext.Length + 1) / 2);
			string[] hm;
			if (hm1 == null && hm2 == null) {
				return null;
			} else if (hm2 == null) {
				hm = hm1;
			} else if (hm1 == null) {
				hm = hm2;
			} else {
				// Both matched.  Select the longest.
				hm = hm1[4].Length > hm2[4].Length ? hm1 : hm2;
			}

			// A half-match was found, sort out the return data.
			if (text1.Length > text2.Length) {
				return hm;
				//return new string[]{hm[0], hm[1], hm[2], hm[3], hm[4]};
			} else {
				return new string[] { hm[2], hm[3], hm[0], hm[1], hm[4] };
			}
		}

		/**
     * Does a Substring of shorttext exist within longtext such that the
     * Substring is at least half the length of longtext?
     * @param longtext Longer string.
     * @param shorttext Shorter string.
     * @param i Start index of quarter length Substring within longtext.
     * @return Five element string array, containing the prefix of longtext, the
     *     suffix of longtext, the prefix of shorttext, the suffix of shorttext
     *     and the common middle.  Or null if there was no match.
     */
		private string[] diff_halfMatchI(string longtext, string shorttext, int i)
		{
			// Start with a 1/4 length Substring at position i as a seed.
			string seed = longtext.Substring(i, longtext.Length / 4);
			int j = -1;
			string best_common = string.Empty;
			string best_longtext_a = string.Empty, best_longtext_b = string.Empty;
			string best_shorttext_a = string.Empty, best_shorttext_b = string.Empty;
			while (j < shorttext.Length && (j = shorttext.IndexOf(seed, j + 1,
																		   StringComparison.Ordinal)) != -1) {
				int prefixLength = diff_commonPrefix(longtext.Substring(i),
																 shorttext.Substring(j));
				int suffixLength = diff_commonSuffix(longtext.Substring(0, i),
																 shorttext.Substring(0, j));
				if (best_common.Length < suffixLength + prefixLength) {
					best_common = shorttext.Substring(j - suffixLength, suffixLength)
					+ shorttext.Substring(j, prefixLength);
					best_longtext_a = longtext.Substring(0, i - suffixLength);
					best_longtext_b = longtext.Substring(i + prefixLength);
					best_shorttext_a = shorttext.Substring(0, j - suffixLength);
					best_shorttext_b = shorttext.Substring(j + prefixLength);
				}
			}
			if (best_common.Length * 2 >= longtext.Length) {
				return new string[] {best_longtext_a, best_longtext_b,
					best_shorttext_a, best_shorttext_b, best_common
				};
			} else {
				return null;
			}
		}

		/**
     * Reduce the number of edits by eliminating semantically trivial
     * equalities.
     * @param diffs List of Diff objects.
     */
		public void diff_cleanupSemantic(List<Diff> diffs)
		{
			bool changes = false;
			// Stack of indices where equalities are found.
			Stack<int> equalities = new Stack<int>();
			// Always equal to equalities[equalitiesLength-1][1]
			string lastequality = null;
			int pointer = 0;  // Index of current position.
							  // Number of characters that changed prior to the equality.
			int length_insertions1 = 0;
			int length_deletions1 = 0;
			// Number of characters that changed after the equality.
			int length_insertions2 = 0;
			int length_deletions2 = 0;
			while (pointer < diffs.Count) {
				if (diffs[pointer].operation == Operation.EQUAL) {  // Equality found.
					equalities.Push(pointer);
					length_insertions1 = length_insertions2;
					length_deletions1 = length_deletions2;
					length_insertions2 = 0;
					length_deletions2 = 0;
					lastequality = diffs[pointer].text;
				} else {  // an insertion or deletion
					if (diffs[pointer].operation == Operation.INSERT) {
						length_insertions2 += diffs[pointer].text.Length;
					} else {
						length_deletions2 += diffs[pointer].text.Length;
					}
					// Eliminate an equality that is smaller or equal to the edits on both
					// sides of it.
					if (lastequality != null && (lastequality.Length
									   <= Math.Max(length_insertions1, length_deletions1))
									   && (lastequality.Length
									   <= Math.Max(length_insertions2, length_deletions2))) {
						// Duplicate record.
						diffs.Insert(equalities.Peek(),
													   new Diff(Operation.DELETE, lastequality));
						// Change second copy to insert.
						diffs[equalities.Peek() + 1].operation = Operation.INSERT;
						// Throw away the equality we just deleted.
						equalities.Pop();
						if (equalities.Count > 0) {
							equalities.Pop();
						}
						pointer = equalities.Count > 0 ? equalities.Peek() : -1;
						length_insertions1 = 0;  // Reset the counters.
						length_deletions1 = 0;
						length_insertions2 = 0;
						length_deletions2 = 0;
						lastequality = null;
						changes = true;
					}
				}
				pointer++;
			}

			// Normalize the diff.
			if (changes) {
				diff_cleanupMerge(diffs);
			}
			diff_cleanupSemanticLossless(diffs);

			// Find any overlaps between deletions and insertions.
			// e.g: <del>abcxxx</del><ins>xxxdef</ins>
			//   -> <del>abc</del>xxx<ins>def</ins>
			// e.g: <del>xxxabc</del><ins>defxxx</ins>
			//   -> <ins>def</ins>xxx<del>abc</del>
			// Only extract an overlap if it is as big as the edit ahead or behind it.
			pointer = 1;
			while (pointer < diffs.Count) {
				if (diffs[pointer - 1].operation == Operation.DELETE &&
								diffs[pointer].operation == Operation.INSERT) {
					string deletion = diffs[pointer - 1].text;
					string insertion = diffs[pointer].text;
					int overlap_length1 = diff_commonOverlap(deletion, insertion);
					int overlap_length2 = diff_commonOverlap(insertion, deletion);
					if (overlap_length1 >= overlap_length2) {
						if (overlap_length1 >= deletion.Length / 2.0 ||
											  overlap_length1 >= insertion.Length / 2.0) {
							// Overlap found.
							// Insert an equality and trim the surrounding edits.
							diffs.Insert(pointer, new Diff(Operation.EQUAL,
																				insertion.Substring(0, overlap_length1)));
							diffs[pointer - 1].text =
								deletion.Substring(0, deletion.Length - overlap_length1);
							diffs[pointer + 1].text = insertion.Substring(overlap_length1);
							pointer++;
						}
					} else {
						if (overlap_length2 >= deletion.Length / 2.0 ||
											  overlap_length2 >= insertion.Length / 2.0) {
							// Reverse overlap found.
							// Insert an equality and swap and trim the surrounding edits.
							diffs.Insert(pointer, new Diff(Operation.EQUAL,
																				deletion.Substring(0, overlap_length2)));
							diffs[pointer - 1].operation = Operation.INSERT;
							diffs[pointer - 1].text =
								insertion.Substring(0, insertion.Length - overlap_length2);
							diffs[pointer + 1].operation = Operation.DELETE;
							diffs[pointer + 1].text = deletion.Substring(overlap_length2);
							pointer++;
						}
					}
					pointer++;
				}
				pointer++;
			}
		}

		/**
     * Look for single edits surrounded on both sides by equalities
     * which can be shifted sideways to align the edit to a word boundary.
     * e.g: The c<ins>at c</ins>ame. -> The <ins>cat </ins>came.
     * @param diffs List of Diff objects.
     */
		public void diff_cleanupSemanticLossless(List<Diff> diffs)
		{
			int pointer = 1;
			// Intentionally ignore the first and last element (don't need checking).
			while (pointer < diffs.Count - 1) {
				if (diffs[pointer - 1].operation == Operation.EQUAL &&
								diffs[pointer + 1].operation == Operation.EQUAL) {
					// This is a single edit surrounded by equalities.
					string equality1 = diffs[pointer - 1].text;
					string edit = diffs[pointer].text;
					string equality2 = diffs[pointer + 1].text;

					// First, shift the edit as far left as possible.
					int commonOffset = this.diff_commonSuffix(equality1, edit);
					if (commonOffset > 0) {
						string commonString = edit.Substring(edit.Length - commonOffset);
						equality1 = equality1.Substring(0, equality1.Length - commonOffset);
						edit = commonString + edit.Substring(0, edit.Length - commonOffset);
						equality2 = commonString + equality2;
					}

					// Second, step character by character right,
					// looking for the best fit.
					string bestEquality1 = equality1;
					string bestEdit = edit;
					string bestEquality2 = equality2;
					int bestScore = diff_cleanupSemanticScore(equality1, edit) +
												   diff_cleanupSemanticScore(edit, equality2);
					while (edit.Length != 0 && equality2.Length != 0
										  && edit[0] == equality2[0]) {
						equality1 += edit[0];
						edit = edit.Substring(1) + equality2[0];
						equality2 = equality2.Substring(1);
						int score = diff_cleanupSemanticScore(equality1, edit) +
													  diff_cleanupSemanticScore(edit, equality2);
						// The >= encourages trailing rather than leading whitespace on
						// edits.
						if (score >= bestScore) {
							bestScore = score;
							bestEquality1 = equality1;
							bestEdit = edit;
							bestEquality2 = equality2;
						}
					}

					if (diffs[pointer - 1].text != bestEquality1) {
						// We have an improvement, save it back to the diff.
						if (bestEquality1.Length != 0) {
							diffs[pointer - 1].text = bestEquality1;
						} else {
							diffs.RemoveAt(pointer - 1);
							pointer--;
						}
						diffs[pointer].text = bestEdit;
						if (bestEquality2.Length != 0) {
							diffs[pointer + 1].text = bestEquality2;
						} else {
							diffs.RemoveAt(pointer + 1);
							pointer--;
						}
					}
				}
				pointer++;
			}
		}

		/**
     * Given two strings, comAdde a score representing whether the internal
     * boundary falls on logical boundaries.
     * Scores range from 6 (best) to 0 (worst).
     * @param one First string.
     * @param two Second string.
     * @return The score.
     */
		private int diff_cleanupSemanticScore(string one, string two)
		{
			if (one.Length == 0 || two.Length == 0) {
				// Edges are the best.
				return 6;
			}

			// Each port of this function behaves slightly differently due to
			// subtle differences in each language's definition of things like
			// 'whitespace'.  Since this function's purpose is largely cosmetic,
			// the choice has been made to use each language's native features
			// rather than force total conformity.
			char char1 = one[one.Length - 1];
			char char2 = two[0];
			bool nonAlphaNumeric1 = !Char.IsLetterOrDigit(char1);
			bool nonAlphaNumeric2 = !Char.IsLetterOrDigit(char2);
			bool whitespace1 = nonAlphaNumeric1 && Char.IsWhiteSpace(char1);
			bool whitespace2 = nonAlphaNumeric2 && Char.IsWhiteSpace(char2);
			bool lineBreak1 = whitespace1 && Char.IsControl(char1);
			bool lineBreak2 = whitespace2 && Char.IsControl(char2);
			bool blankLine1 = lineBreak1 && BLANKLINEEND.IsMatch(one);
			bool blankLine2 = lineBreak2 && BLANKLINESTART.IsMatch(two);

			if (blankLine1 || blankLine2) {
				// Five points for blank lines.
				return 5;
			} else if (lineBreak1 || lineBreak2) {
				// Four points for line breaks.
				return 4;
			} else if (nonAlphaNumeric1 && !whitespace1 && whitespace2) {
				// Three points for end of sentences.
				return 3;
			} else if (whitespace1 || whitespace2) {
				// Two points for whitespace.
				return 2;
			} else if (nonAlphaNumeric1 || nonAlphaNumeric2) {
				// One point for non-alphanumeric.
				return 1;
			}
			return 0;
		}

		// Define some regex patterns for matching boundaries.
		private Regex BLANKLINEEND = new Regex("\\n\\r?\\n\\Z");
		private Regex BLANKLINESTART = new Regex("\\A\\r?\\n\\r?\\n");

		/**
     * Reduce the number of edits by eliminating operationally trivial
     * equalities.
     * @param diffs List of Diff objects.
     */
		public void diff_cleanupEfficiency(List<Diff> diffs)
		{
			bool changes = false;
			// Stack of indices where equalities are found.
			Stack<int> equalities = new Stack<int>();
			// Always equal to equalities[equalitiesLength-1][1]
			string lastequality = string.Empty;
			int pointer = 0;  // Index of current position.
							  // Is there an insertion operation before the last equality.
			bool pre_ins = false;
			// Is there a deletion operation before the last equality.
			bool pre_del = false;
			// Is there an insertion operation after the last equality.
			bool post_ins = false;
			// Is there a deletion operation after the last equality.
			bool post_del = false;
			while (pointer < diffs.Count) {
				if (diffs[pointer].operation == Operation.EQUAL) {  // Equality found.
					if (diffs[pointer].text.Length < this.Diff_EditCost
									   && (post_ins || post_del)) {
						// Candidate found.
						equalities.Push(pointer);
						pre_ins = post_ins;
						pre_del = post_del;
						lastequality = diffs[pointer].text;
					} else {
						// Not a candidate, and can never become one.
						equalities.Clear();
						lastequality = string.Empty;
					}
					post_ins = post_del = false;
				} else {  // An insertion or deletion.
					if (diffs[pointer].operation == Operation.DELETE) {
						post_del = true;
					} else {
						post_ins = true;
					}
					/*
           * Five types to be split:
           * <ins>A</ins><del>B</del>XY<ins>C</ins><del>D</del>
           * <ins>A</ins>X<ins>C</ins><del>D</del>
           * <ins>A</ins><del>B</del>X<ins>C</ins>
           * <ins>A</del>X<ins>C</ins><del>D</del>
           * <ins>A</ins><del>B</del>X<del>C</del>
           */
					if ((lastequality.Length != 0)
									   && ((pre_ins && pre_del && post_ins && post_del)
									   || ((lastequality.Length < this.Diff_EditCost / 2)
									   && ((pre_ins ? 1 : 0) + (pre_del ? 1 : 0) + (post_ins ? 1 : 0)
									   + (post_del ? 1 : 0)) == 3))) {
						// Duplicate record.
						diffs.Insert(equalities.Peek(),
													   new Diff(Operation.DELETE, lastequality));
						// Change second copy to insert.
						diffs[equalities.Peek() + 1].operation = Operation.INSERT;
						equalities.Pop();  // Throw away the equality we just deleted.
						lastequality = string.Empty;
						if (pre_ins && pre_del) {
							// No changes made which could affect previous entry, keep going.
							post_ins = post_del = true;
							equalities.Clear();
						} else {
							if (equalities.Count > 0) {
								equalities.Pop();
							}

							pointer = equalities.Count > 0 ? equalities.Peek() : -1;
							post_ins = post_del = false;
						}
						changes = true;
					}
				}
				pointer++;
			}

			if (changes) {
				diff_cleanupMerge(diffs);
			}
		}

		/**
     * Reorder and merge like edit sections.  Merge equalities.
     * Any edit section can move as long as it doesn't cross an equality.
     * @param diffs List of Diff objects.
     */
		public void diff_cleanupMerge(List<Diff> diffs)
		{
			// Add a dummy entry at the end.
			diffs.Add(new Diff(Operation.EQUAL, string.Empty));
			int pointer = 0;
			int count_delete = 0;
			int count_insert = 0;
			string text_delete = string.Empty;
			string text_insert = string.Empty;
			int commonlength;
			while (pointer < diffs.Count) {
				switch (diffs[pointer].operation) {
					case Operation.INSERT:
						count_insert++;
						text_insert += diffs[pointer].text;
						pointer++;
						break;
					case Operation.DELETE:
						count_delete++;
						text_delete += diffs[pointer].text;
						pointer++;
						break;
					case Operation.EQUAL:
						// Upon reaching an equality, check for prior redundancies.
						if (count_delete + count_insert > 1) {
							if (count_delete != 0 && count_insert != 0) {
								// Factor out any common prefixies.
								commonlength = this.diff_commonPrefix(text_insert, text_delete);
								if (commonlength != 0) {
									if ((pointer - count_delete - count_insert) > 0 &&
															   diffs[pointer - count_delete - count_insert - 1].operation
															   == Operation.EQUAL) {
										diffs[pointer - count_delete - count_insert - 1].text
									+= text_insert.Substring(0, commonlength);
									} else {
										diffs.Insert(0, new Diff(Operation.EQUAL,
																						   text_insert.Substring(0, commonlength)));
										pointer++;
									}
									text_insert = text_insert.Substring(commonlength);
									text_delete = text_delete.Substring(commonlength);
								}
								// Factor out any common suffixies.
								commonlength = this.diff_commonSuffix(text_insert, text_delete);
								if (commonlength != 0) {
									diffs[pointer].text = text_insert.Substring(text_insert.Length
									- commonlength) + diffs[pointer].text;
									text_insert = text_insert.Substring(0, text_insert.Length
									- commonlength);
									text_delete = text_delete.Substring(0, text_delete.Length
									- commonlength);
								}
							}
							// Delete the offending records and add the merged ones.
							if (count_delete == 0) {
								diffs.Splice(pointer - count_insert,
																 count_delete + count_insert,
																 new Diff(Operation.INSERT, text_insert));
							} else if (count_insert == 0) {
								diffs.Splice(pointer - count_delete,
																count_delete + count_insert,
																new Diff(Operation.DELETE, text_delete));
							} else {
								diffs.Splice(pointer - count_delete - count_insert,
																count_delete + count_insert,
																new Diff(Operation.DELETE, text_delete),
																new Diff(Operation.INSERT, text_insert));
							}
							pointer = pointer - count_delete - count_insert +
							(count_delete != 0 ? 1 : 0) + (count_insert != 0 ? 1 : 0) + 1;
						} else if (pointer != 0
													&& diffs[pointer - 1].operation == Operation.EQUAL) {
							// Merge this equality with the previous one.
							diffs[pointer - 1].text += diffs[pointer].text;
							diffs.RemoveAt(pointer);
						} else {
							pointer++;
						}
						count_insert = 0;
						count_delete = 0;
						text_delete = string.Empty;
						text_insert = string.Empty;
						break;
				}
			}
			if (diffs[diffs.Count - 1].text.Length == 0) {
				diffs.RemoveAt(diffs.Count - 1);  // Remove the dummy entry at the end.
			}

			// Second pass: look for single edits surrounded on both sides by
			// equalities which can be shifted sideways to eliminate an equality.
			// e.g: A<ins>BA</ins>C -> <ins>AB</ins>AC
			bool changes = false;
			pointer = 1;
			// Intentionally ignore the first and last element (don't need checking).
			while (pointer < (diffs.Count - 1)) {
				if (diffs[pointer - 1].operation == Operation.EQUAL &&
								diffs[pointer + 1].operation == Operation.EQUAL) {
					// This is a single edit surrounded by equalities.
					if (diffs[pointer].text.EndsWith(diffs[pointer - 1].text,
																	StringComparison.Ordinal)) {
						// Shift the edit over the previous equality.
						diffs[pointer].text = diffs[pointer - 1].text +
						diffs[pointer].text.Substring(0, diffs[pointer].text.Length -
						diffs[pointer - 1].text.Length);
						diffs[pointer + 1].text = diffs[pointer - 1].text
						+ diffs[pointer + 1].text;
						diffs.Splice(pointer - 1, 1);
						changes = true;
					} else if (diffs[pointer].text.StartsWith(diffs[pointer + 1].text,
																				StringComparison.Ordinal)) {
						// Shift the edit over the next equality.
						diffs[pointer - 1].text += diffs[pointer + 1].text;
						diffs[pointer].text =
						diffs[pointer].text.Substring(diffs[pointer + 1].text.Length)
						+ diffs[pointer + 1].text;
						diffs.Splice(pointer + 1, 1);
						changes = true;
					}
				}
				pointer++;
			}
			// If shifts were made, the diff needs reordering and another shift sweep.
			if (changes) {
				this.diff_cleanupMerge(diffs);
			}
		}

		/**
     * loc is a location in text1, comAdde and return the equivalent location in
     * text2.
     * e.g. "The cat" vs "The big cat", 1->1, 5->8
     * @param diffs List of Diff objects.
     * @param loc Location within text1.
     * @return Location within text2.
     */
		public int diff_xIndex(List<Diff> diffs, int loc)
		{
			int chars1 = 0;
			int chars2 = 0;
			int last_chars1 = 0;
			int last_chars2 = 0;
			Diff lastDiff = null;
			foreach (Diff aDiff in diffs) {
				if (aDiff.operation != Operation.INSERT) {
					// Equality or deletion.
					chars1 += aDiff.text.Length;
				}
				if (aDiff.operation != Operation.DELETE) {
					// Equality or insertion.
					chars2 += aDiff.text.Length;
				}
				if (chars1 > loc) {
					// Overshot the location.
					lastDiff = aDiff;
					break;
				}
				last_chars1 = chars1;
				last_chars2 = chars2;
			}
			if (lastDiff != null && lastDiff.operation == Operation.DELETE) {
				// The location was deleted.
				return last_chars2;
			}
			// Add the remaining character length.
			return last_chars2 + (loc - last_chars1);
		}

		/**
     * Convert a Diff list into a pretty HTML report.
     * @param diffs List of Diff objects.
     * @return HTML representation.
     */
		public string diff_prettyHtml(List<Diff> diffs)
		{
			StringBuilder html = new StringBuilder();
			foreach (Diff aDiff in diffs) {
				string text = aDiff.text
					.Replace("&", "&amp;")
					.Replace("<", "&lt;")
					.Replace(">", "&gt;");
					//.Replace("\n", "&para;<br>");
				switch (aDiff.operation) {
					case Operation.INSERT:
						html.Append("<ins>").Append(text)
						.Append("</ins>");
						break;
					case Operation.DELETE:
						html.Append("<del>").Append(text)
						.Append("</del>");
						break;
					case Operation.EQUAL:
						html.Append("<span>").Append(text).Append("</span>");
						break;
				}
			}
			return html.ToString();
		}

		/**
     * Compute and return the source text (all equalities and deletions).
     * @param diffs List of Diff objects.
     * @return Source text.
     */
		public string diff_text1(List<Diff> diffs)
		{
			StringBuilder text = new StringBuilder();
			foreach (Diff aDiff in diffs) {
				if (aDiff.operation != Operation.INSERT) {
					text.Append(aDiff.text);
				}
			}
			return text.ToString();
		}

		/**
     * Compute and return the destination text (all equalities and insertions).
     * @param diffs List of Diff objects.
     * @return Destination text.
     */
		public string diff_text2(List<Diff> diffs)
		{
			StringBuilder text = new StringBuilder();
			foreach (Diff aDiff in diffs) {
				if (aDiff.operation != Operation.DELETE) {
					text.Append(aDiff.text);
				}
			}
			return text.ToString();
		}

		/**
     * Compute the Levenshtein distance; the number of inserted, deleted or
     * substituted characters.
     * @param diffs List of Diff objects.
     * @return Number of changes.
     */
		public int diff_levenshtein(List<Diff> diffs)
		{
			int levenshtein = 0;
			int insertions = 0;
			int deletions = 0;
			foreach (Diff aDiff in diffs) {
				switch (aDiff.operation) {
					case Operation.INSERT:
						insertions += aDiff.text.Length;
						break;
					case Operation.DELETE:
						deletions += aDiff.text.Length;
						break;
					case Operation.EQUAL:
						// A deletion and an insertion is one substitution.
						levenshtein += Math.Max(insertions, deletions);
						insertions = 0;
						deletions = 0;
						break;
				}
			}
			levenshtein += Math.Max(insertions, deletions);
			return levenshtein;
		}

		/**
     * Crush the diff into an encoded string which describes the operations
     * required to transform text1 into text2.
     * E.g. =3\t-2\t+ing  -> Keep 3 chars, delete 2 chars, insert 'ing'.
     * Operations are tab-separated.  Inserted text is escaped using %xx
     * notation.
     * @param diffs Array of Diff objects.
     * @return Delta text.
     */
		public string diff_toDelta(List<Diff> diffs)
		{
			StringBuilder text = new StringBuilder();
			foreach (Diff aDiff in diffs) {
				switch (aDiff.operation) {
					case Operation.INSERT:
						text.Append("+").Append(HttpUtility.UrlEncode(aDiff.text,
																					new UTF8Encoding()).Replace('+', ' ')).Append("\t");
						break;
					case Operation.DELETE:
						text.Append("-").Append(aDiff.text.Length).Append("\t");
						break;
					case Operation.EQUAL:
						text.Append("=").Append(aDiff.text.Length).Append("\t");
						break;
				}
			}
			string delta = text.ToString();
			if (delta.Length != 0) {
				// Strip off trailing tab character.
				delta = delta.Substring(0, delta.Length - 1);
				delta = unescapeForEncodeUriCompatability(delta);
			}
			return delta;
		}

		/**
     * Given the original text1, and an encoded string which describes the
     * operations required to transform text1 into text2, comAdde the full diff.
     * @param text1 Source string for the diff.
     * @param delta Delta text.
     * @return Array of Diff objects or null if invalid.
     * @throws ArgumentException If invalid input.
     */
		public List<Diff> diff_fromDelta(string text1, string delta)
		{
			List<Diff> diffs = new List<Diff>();
			int pointer = 0;  // Cursor in text1
			string[] tokens = delta.Split(new string[] { "\t" },
												   StringSplitOptions.None);
			foreach (string token in tokens) {
				if (token.Length == 0) {
					// Blank tokens are ok (from a trailing \t).
					continue;
				}
				// Each token begins with a one character parameter which specifies the
				// operation of this token (delete, insert, equality).
				string param = token.Substring(1);
				switch (token[0]) {
					case '+':
						// decode would change all "+" to " "
						param = param.Replace("+", "%2b");

						param = HttpUtility.UrlDecode(param, new UTF8Encoding(false, true));
						//} catch (UnsupportedEncodingException e) {
						//  // Not likely on modern system.
						//  throw new Error("This system does not support UTF-8.", e);
						//} catch (IllegalArgumentException e) {
						//  // Malformed URI sequence.
						//  throw new IllegalArgumentException(
						//      "Illegal escape in diff_fromDelta: " + param, e);
						//}
						diffs.Add(new Diff(Operation.INSERT, param));
						break;
					case '-':
					// Fall through.
					case '=':
						int n;
						try {
							n = Convert.ToInt32(param);
						} catch (FormatException e) {
							throw new ArgumentException(
								"Invalid number in diff_fromDelta: " + param, e);
						}
						if (n < 0) {
							throw new ArgumentException(
								"Negative number in diff_fromDelta: " + param);
						}
						string text;
						try {
							text = text1.Substring(pointer, n);
							pointer += n;
						} catch (ArgumentOutOfRangeException e) {
							throw new ArgumentException("Delta length (" + pointer
							+ ") larger than source text length (" + text1.Length
							+ ").", e);
						}
						if (token[0] == '=') {
							diffs.Add(new Diff(Operation.EQUAL, text));
						} else {
							diffs.Add(new Diff(Operation.DELETE, text));
						}
						break;
					default:
						// Anything else is an error.
						throw new ArgumentException(
							"Invalid diff operation in diff_fromDelta: " + token[0]);
				}
			}
			if (pointer != text1.Length) {
				throw new ArgumentException("Delta length (" + pointer
				+ ") smaller than source text length (" + text1.Length + ").");
			}
			return diffs;
		}


		//  MATCH FUNCTIONS


		/**
     * Locate the best instance of 'pattern' in 'text' near 'loc'.
     * Returns -1 if no match found.
     * @param text The text to search.
     * @param pattern The pattern to search for.
     * @param loc The location to search around.
     * @return Best match index or -1.
     */
		public int match_main(string text, string pattern, int loc)
		{
			// Check for null inputs not needed since null can't be passed in C#.

			loc = Math.Max(0, Math.Min(loc, text.Length));
			if (text == pattern) {
				// Shortcut (potentially not guaranteed by the algorithm)
				return 0;
			} else if (text.Length == 0) {
				// Nothing to match.
				return -1;
			} else if (loc + pattern.Length <= text.Length
								  && text.Substring(loc, pattern.Length) == pattern) {
				// Perfect match at the perfect spot!  (Includes case of null pattern)
				return loc;
			} else {
				// Do a fuzzy compare.
				return match_bitap(text, pattern, loc);
			}
		}

		/**
     * Locate the best instance of 'pattern' in 'text' near 'loc' using the
     * Bitap algorithm.  Returns -1 if no match found.
     * @param text The text to search.
     * @param pattern The pattern to search for.
     * @param loc The location to search around.
     * @return Best match index or -1.
     */
		protected int match_bitap(string text, string pattern, int loc)
		{
			// assert (Match_MaxBits == 0 || pattern.Length <= Match_MaxBits)
			//    : "Pattern too long for this application.";

			// Initialise the alphabet.
			Dictionary<char, int> s = match_alphabet(pattern);

			// Highest score beyond which we give up.
			double score_threshold = Match_Threshold;
			// Is there a nearby exact match? (speedup)
			int best_loc = text.IndexOf(pattern, loc, StringComparison.Ordinal);
			if (best_loc != -1) {
				score_threshold = Math.Min(match_bitapScore(0, best_loc, loc,
																		pattern), score_threshold);
				// What about in the other direction? (speedup)
				best_loc = text.LastIndexOf(pattern,
														Math.Min(loc + pattern.Length, text.Length),
														StringComparison.Ordinal);
				if (best_loc != -1) {
					score_threshold = Math.Min(match_bitapScore(0, best_loc, loc,
																			   pattern), score_threshold);
				}
			}

			// Initialise the bit arrays.
			int matchmask = 1 << (pattern.Length - 1);
			best_loc = -1;

			int bin_min, bin_mid;
			int bin_max = pattern.Length + text.Length;
			// Empty initialization added to appease C# compiler.
			int[] last_rd = new int[0];
			for (int d = 0; d < pattern.Length; d++) {
				// Scan for the best match; each iteration allows for one more error.
				// Run a binary search to determine how far from 'loc' we can stray at
				// this error level.
				bin_min = 0;
				bin_mid = bin_max;
				while (bin_min < bin_mid) {
					if (match_bitapScore(d, loc + bin_mid, loc, pattern)
									   <= score_threshold) {
						bin_min = bin_mid;
					} else {
						bin_max = bin_mid;
					}
					bin_mid = (bin_max - bin_min) / 2 + bin_min;
				}
				// Use the result from this iteration as the maximum for the next.
				bin_max = bin_mid;
				int start = Math.Max(1, loc - bin_mid + 1);
				int finish = Math.Min(loc + bin_mid, text.Length) + pattern.Length;

				int[] rd = new int[finish + 2];
				rd[finish + 1] = (1 << d) - 1;
				for (int j = finish; j >= start; j--) {
					int charMatch;
					if (text.Length <= j - 1 || !s.ContainsKey(text[j - 1])) {
						// Out of range.
						charMatch = 0;
					} else {
						charMatch = s[text[j - 1]];
					}
					if (d == 0) {
						// First pass: exact match.
						rd[j] = ((rd[j + 1] << 1) | 1) & charMatch;
					} else {
						// Subsequent passes: fuzzy match.
						rd[j] = ((rd[j + 1] << 1) | 1) & charMatch
						| (((last_rd[j + 1] | last_rd[j]) << 1) | 1) | last_rd[j + 1];
					}
					if ((rd[j] & matchmask) != 0) {
						double score = match_bitapScore(d, j - 1, loc, pattern);
						// This match will almost certainly be better than any existing
						// match.  But check anyway.
						if (score <= score_threshold) {
							// Told you so.
							score_threshold = score;
							best_loc = j - 1;
							if (best_loc > loc) {
								// When passing loc, don't exceed our current distance from loc.
								start = Math.Max(1, 2 * loc - best_loc);
							} else {
								// Already passed loc, downhill from here on in.
								break;
							}
						}
					}
				}
				if (match_bitapScore(d + 1, loc, loc, pattern) > score_threshold) {
					// No hope for a (better) match at greater error levels.
					break;
				}
				last_rd = rd;
			}
			return best_loc;
		}

		/**
     * Compute and return the score for a match with e errors and x location.
     * @param e Number of errors in match.
     * @param x Location of match.
     * @param loc Expected location of match.
     * @param pattern Pattern being sought.
     * @return Overall score for match (0.0 = good, 1.0 = bad).
     */
		private double match_bitapScore(int e, int x, int loc, string pattern)
		{
			float accuracy = (float)e / pattern.Length;
			int proximity = Math.Abs(loc - x);
			if (Match_Distance == 0) {
				// Dodge divide by zero error.
				return proximity == 0 ? accuracy : 1.0;
			}
			return accuracy + (proximity / (float)Match_Distance);
		}

		/**
     * Initialise the alphabet for the Bitap algorithm.
     * @param pattern The text to encode.
     * @return Hash of character locations.
     */
		protected Dictionary<char, int> match_alphabet(string pattern)
		{
			Dictionary<char, int> s = new Dictionary<char, int>();
			char[] char_pattern = pattern.ToCharArray();
			foreach (char c in char_pattern) {
				if (!s.ContainsKey(c)) {
					s.Add(c, 0);
				}
			}
			int i = 0;
			foreach (char c in char_pattern) {
				int value = s[c] | (1 << (pattern.Length - i - 1));
				s[c] = value;
				i++;
			}
			return s;
		}


		//  PATCH FUNCTIONS


		/**
     * Increase the context until it is unique,
     * but don't let the pattern expand beyond Match_MaxBits.
     * @param patch The patch to grow.
     * @param text Source text.
     */
		protected void patch_addContext(Patch patch, string text)
		{
			if (text.Length == 0) {
				return;
			}
			string pattern = text.Substring(patch.start2, patch.length1);
			int padding = 0;

			// Look for the first and last matches of pattern in text.  If two
			// different matches are found, increase the pattern length.
			while (text.IndexOf(pattern, StringComparison.Ordinal)
							!= text.LastIndexOf(pattern, StringComparison.Ordinal)
							&& pattern.Length < Match_MaxBits - Patch_Margin - Patch_Margin) {
				padding += Patch_Margin;
				pattern = text.JavaSubstring(Math.Max(0, patch.start2 - padding),
														 Math.Min(text.Length, patch.start2 + patch.length1 + padding));
			}
			// Add one chunk for good luck.
			padding += Patch_Margin;

			// Add the prefix.
			string prefix = text.JavaSubstring(Math.Max(0, patch.start2 - padding),
														patch.start2);
			if (prefix.Length != 0) {
				patch.diffs.Insert(0, new Diff(Operation.EQUAL, prefix));
			}
			// Add the suffix.
			string suffix = text.JavaSubstring(patch.start2 + patch.length1,
														Math.Min(text.Length, patch.start2 + patch.length1 + padding));
			if (suffix.Length != 0) {
				patch.diffs.Add(new Diff(Operation.EQUAL, suffix));
			}

			// Roll back the start points.
			patch.start1 -= prefix.Length;
			patch.start2 -= prefix.Length;
			// Extend the lengths.
			patch.length1 += prefix.Length + suffix.Length;
			patch.length2 += prefix.Length + suffix.Length;
		}

		/**
     * Compute a list of patches to turn text1 into text2.
     * A set of diffs will be computed.
     * @param text1 Old text.
     * @param text2 New text.
     * @return List of Patch objects.
     */
		public List<Patch> patch_make(string text1, string text2)
		{
			// Check for null inputs not needed since null can't be passed in C#.
			// No diffs provided, comAdde our own.
			List<Diff> diffs = diff_main(text1, text2, true);
			if (diffs.Count > 2) {
				diff_cleanupSemantic(diffs);
				diff_cleanupEfficiency(diffs);
			}
			return patch_make(text1, diffs);
		}

		/**
     * Compute a list of patches to turn text1 into text2.
     * text1 will be derived from the provided diffs.
     * @param diffs Array of Diff objects for text1 to text2.
     * @return List of Patch objects.
     */
		public List<Patch> patch_make(List<Diff> diffs)
		{
			// Check for null inputs not needed since null can't be passed in C#.
			// No origin string provided, comAdde our own.
			string text1 = diff_text1(diffs);
			return patch_make(text1, diffs);
		}

		/**
     * Compute a list of patches to turn text1 into text2.
     * text2 is ignored, diffs are the delta between text1 and text2.
     * @param text1 Old text
     * @param text2 Ignored.
     * @param diffs Array of Diff objects for text1 to text2.
     * @return List of Patch objects.
     * @deprecated Prefer patch_make(string text1, List<Diff> diffs).
     */
		public List<Patch> patch_make(string text1, string text2,
											List<Diff> diffs)
		{
			return patch_make(text1, diffs);
		}

		/**
     * Compute a list of patches to turn text1 into text2.
     * text2 is not provided, diffs are the delta between text1 and text2.
     * @param text1 Old text.
     * @param diffs Array of Diff objects for text1 to text2.
     * @return List of Patch objects.
     */
		public List<Patch> patch_make(string text1, List<Diff> diffs)
		{
			// Check for null inputs not needed since null can't be passed in C#.
			List<Patch> patches = new List<Patch>();
			if (diffs.Count == 0) {
				return patches;  // Get rid of the null case.
			}
			Patch patch = new Patch();
			int char_count1 = 0;  // Number of characters into the text1 string.
			int char_count2 = 0;  // Number of characters into the text2 string.
								  // Start with text1 (prepatch_text) and apply the diffs until we arrive at
								  // text2 (postpatch_text). We recreate the patches one by one to determine
								  // context info.
			string prepatch_text = text1;
			string postpatch_text = text1;
			foreach (Diff aDiff in diffs) {
				if (patch.diffs.Count == 0 && aDiff.operation != Operation.EQUAL) {
					// A new patch starts here.
					patch.start1 = char_count1;
					patch.start2 = char_count2;
				}

				switch (aDiff.operation) {
					case Operation.INSERT:
						patch.diffs.Add(aDiff);
						patch.length2 += aDiff.text.Length;
						postpatch_text = postpatch_text.Insert(char_count2, aDiff.text);
						break;
					case Operation.DELETE:
						patch.length1 += aDiff.text.Length;
						patch.diffs.Add(aDiff);
						postpatch_text = postpatch_text.Remove(char_count2,
																			 aDiff.text.Length);
						break;
					case Operation.EQUAL:
						if (aDiff.text.Length <= 2 * Patch_Margin
										  && patch.diffs.Count() != 0 && aDiff != diffs.Last()) {
							// Small equality inside a patch.
							patch.diffs.Add(aDiff);
							patch.length1 += aDiff.text.Length;
							patch.length2 += aDiff.text.Length;
						}

						if (aDiff.text.Length >= 2 * Patch_Margin) {
							// Time for a new patch.
							if (patch.diffs.Count != 0) {
								patch_addContext(patch, prepatch_text);
								patches.Add(patch);
								patch = new Patch();
								// Unlike Unidiff, our patch lists have a rolling context.
								// http://code.google.com/p/google-diff-match-patch/wiki/Unidiff
								// Update prepatch text & pos to reflect the application of the
								// just completed patch.
								prepatch_text = postpatch_text;
								char_count1 = char_count2;
							}
						}
						break;
				}

				// Update the current character count.
				if (aDiff.operation != Operation.INSERT) {
					char_count1 += aDiff.text.Length;
				}
				if (aDiff.operation != Operation.DELETE) {
					char_count2 += aDiff.text.Length;
				}
			}
			// Pick up the leftover patch if not empty.
			if (patch.diffs.Count != 0) {
				patch_addContext(patch, prepatch_text);
				patches.Add(patch);
			}

			return patches;
		}

		/**
     * Given an array of patches, return another array that is identical.
     * @param patches Array of Patch objects.
     * @return Array of Patch objects.
     */
		public List<Patch> patch_deepCopy(List<Patch> patches)
		{
			List<Patch> patchesCopy = new List<Patch>();
			foreach (Patch aPatch in patches) {
				Patch patchCopy = new Patch();
				foreach (Diff aDiff in aPatch.diffs) {
					Diff diffCopy = new Diff(aDiff.operation, aDiff.text);
					patchCopy.diffs.Add(diffCopy);
				}
				patchCopy.start1 = aPatch.start1;
				patchCopy.start2 = aPatch.start2;
				patchCopy.length1 = aPatch.length1;
				patchCopy.length2 = aPatch.length2;
				patchesCopy.Add(patchCopy);
			}
			return patchesCopy;
		}

		/**
     * Merge a set of patches onto the text.  Return a patched text, as well
     * as an array of true/false values indicating which patches were applied.
     * @param patches Array of Patch objects
     * @param text Old text.
     * @return Two element Object array, containing the new text and an array of
     *      bool values.
     */
		public Object[] patch_apply(List<Patch> patches, string text)
		{
			if (patches.Count == 0) {
				return new Object[] { text, new bool[0] };
			}

			// Deep copy the patches so that no changes are made to originals.
			patches = patch_deepCopy(patches);

			string nullPadding = this.patch_addPadding(patches);
			text = nullPadding + text + nullPadding;
			patch_splitMax(patches);

			int x = 0;
			// delta keeps track of the offset between the expected and actual
			// location of the previous patch.  If there are patches expected at
			// positions 10 and 20, but the first patch was found at 12, delta is 2
			// and the second patch has an effective expected position of 22.
			int delta = 0;
			bool[] results = new bool[patches.Count];
			foreach (Patch aPatch in patches) {
				int expected_loc = aPatch.start2 + delta;
				string text1 = diff_text1(aPatch.diffs);
				int start_loc;
				int end_loc = -1;
				if (text1.Length > this.Match_MaxBits) {
					// patch_splitMax will only provide an oversized pattern
					// in the case of a monster delete.
					start_loc = match_main(text,
														  text1.Substring(0, this.Match_MaxBits), expected_loc);
					if (start_loc != -1) {
						end_loc = match_main(text,
															   text1.Substring(text1.Length - this.Match_MaxBits),
															   expected_loc + text1.Length - this.Match_MaxBits);
						if (end_loc == -1 || start_loc >= end_loc) {
							// Can't find valid trailing context.  Drop this patch.
							start_loc = -1;
						}
					}
				} else {
					start_loc = this.match_main(text, text1, expected_loc);
				}
				if (start_loc == -1) {
					// No match found.  :(
					results[x] = false;
					// Subtract the delta for this failed patch from subsequent patches.
					delta -= aPatch.length2 - aPatch.length1;
				} else {
					// Found a match.  :)
					results[x] = true;
					delta = start_loc - expected_loc;
					string text2;
					if (end_loc == -1) {
						text2 = text.JavaSubstring(start_loc,
																	 Math.Min(start_loc + text1.Length, text.Length));
					} else {
						text2 = text.JavaSubstring(start_loc,
																	 Math.Min(end_loc + this.Match_MaxBits, text.Length));
					}
					if (text1 == text2) {
						// Perfect match, just shove the Replacement text in.
						text = text.Substring(0, start_loc) + diff_text2(aPatch.diffs)
						+ text.Substring(start_loc + text1.Length);
					} else {
						// Imperfect match.  Run a diff to get a framework of equivalent
						// indices.
						List<Diff> diffs = diff_main(text1, text2, false);
						if (text1.Length > this.Match_MaxBits
											  && this.diff_levenshtein(diffs) / (float)text1.Length
											  > this.Patch_DeleteThreshold) {
							// The end points match, but the content is unacceptably bad.
							results[x] = false;
						} else {
							diff_cleanupSemanticLossless(diffs);
							int index1 = 0;
							foreach (Diff aDiff in aPatch.diffs) {
								if (aDiff.operation != Operation.EQUAL) {
									int index2 = diff_xIndex(diffs, index1);
									if (aDiff.operation == Operation.INSERT) {
										// Insertion
										text = text.Insert(start_loc + index2, aDiff.text);
									} else if (aDiff.operation == Operation.DELETE) {
										// Deletion
										text = text.Remove(start_loc + index2, diff_xIndex(diffs,
																														index1 + aDiff.text.Length) - index2);
									}
								}
								if (aDiff.operation != Operation.DELETE) {
									index1 += aDiff.text.Length;
								}
							}
						}
					}
				}
				x++;
			}
			// Strip the padding off.
			text = text.Substring(nullPadding.Length, text.Length
			- 2 * nullPadding.Length);
			return new Object[] { text, results };
		}

		/**
     * Add some padding on text start and end so that edges can match something.
     * Intended to be called only from within patch_apply.
     * @param patches Array of Patch objects.
     * @return The padding string added to each side.
     */
		public string patch_addPadding(List<Patch> patches)
		{
			short paddingLength = this.Patch_Margin;
			string nullPadding = string.Empty;
			for (short x = 1; x <= paddingLength; x++) {
				nullPadding += (char)x;
			}

			// Bump all the patches forward.
			foreach (Patch aPatch in patches) {
				aPatch.start1 += paddingLength;
				aPatch.start2 += paddingLength;
			}

			// Add some padding on start of first diff.
			Patch patch = patches.First();
			List<Diff> diffs = patch.diffs;
			if (diffs.Count == 0 || diffs.First().operation != Operation.EQUAL) {
				// Add nullPadding equality.
				diffs.Insert(0, new Diff(Operation.EQUAL, nullPadding));
				patch.start1 -= paddingLength;  // Should be 0.
				patch.start2 -= paddingLength;  // Should be 0.
				patch.length1 += paddingLength;
				patch.length2 += paddingLength;
			} else if (paddingLength > diffs.First().text.Length) {
				// Grow first equality.
				Diff firstDiff = diffs.First();
				int extraLength = paddingLength - firstDiff.text.Length;
				firstDiff.text = nullPadding.Substring(firstDiff.text.Length)
				+ firstDiff.text;
				patch.start1 -= extraLength;
				patch.start2 -= extraLength;
				patch.length1 += extraLength;
				patch.length2 += extraLength;
			}

			// Add some padding on end of last diff.
			patch = patches.Last();
			diffs = patch.diffs;
			if (diffs.Count == 0 || diffs.Last().operation != Operation.EQUAL) {
				// Add nullPadding equality.
				diffs.Add(new Diff(Operation.EQUAL, nullPadding));
				patch.length1 += paddingLength;
				patch.length2 += paddingLength;
			} else if (paddingLength > diffs.Last().text.Length) {
				// Grow last equality.
				Diff lastDiff = diffs.Last();
				int extraLength = paddingLength - lastDiff.text.Length;
				lastDiff.text += nullPadding.Substring(0, extraLength);
				patch.length1 += extraLength;
				patch.length2 += extraLength;
			}

			return nullPadding;
		}

		/**
     * Look through the patches and break up any which are longer than the
     * maximum limit of the match algorithm.
     * Intended to be called only from within patch_apply.
     * @param patches List of Patch objects.
     */
		public void patch_splitMax(List<Patch> patches)
		{
			short patch_size = this.Match_MaxBits;
			for (int x = 0; x < patches.Count; x++) {
				if (patches[x].length1 <= patch_size) {
					continue;
				}
				Patch bigpatch = patches[x];
				// Remove the big old patch.
				patches.Splice(x--, 1);
				int start1 = bigpatch.start1;
				int start2 = bigpatch.start2;
				string precontext = string.Empty;
				while (bigpatch.diffs.Count != 0) {
					// Create one of several smaller patches.
					Patch patch = new Patch();
					bool empty = true;
					patch.start1 = start1 - precontext.Length;
					patch.start2 = start2 - precontext.Length;
					if (precontext.Length != 0) {
						patch.length1 = patch.length2 = precontext.Length;
						patch.diffs.Add(new Diff(Operation.EQUAL, precontext));
					}
					while (bigpatch.diffs.Count != 0
										  && patch.length1 < patch_size - this.Patch_Margin) {
						Operation diff_type = bigpatch.diffs[0].operation;
						string diff_text = bigpatch.diffs[0].text;
						if (diff_type == Operation.INSERT) {
							// Insertions are harmless.
							patch.length2 += diff_text.Length;
							start2 += diff_text.Length;
							patch.diffs.Add(bigpatch.diffs.First());
							bigpatch.diffs.RemoveAt(0);
							empty = false;
						} else if (diff_type == Operation.DELETE && patch.diffs.Count == 1
														&& patch.diffs.First().operation == Operation.EQUAL
														&& diff_text.Length > 2 * patch_size) {
							// This is a large deletion.  Let it pass in one chunk.
							patch.length1 += diff_text.Length;
							start1 += diff_text.Length;
							empty = false;
							patch.diffs.Add(new Diff(diff_type, diff_text));
							bigpatch.diffs.RemoveAt(0);
						} else {
							// Deletion or equality.  Only take as much as we can stomach.
							diff_text = diff_text.Substring(0, Math.Min(diff_text.Length,
																							patch_size - patch.length1 - Patch_Margin));
							patch.length1 += diff_text.Length;
							start1 += diff_text.Length;
							if (diff_type == Operation.EQUAL) {
								patch.length2 += diff_text.Length;
								start2 += diff_text.Length;
							} else {
								empty = false;
							}
							patch.diffs.Add(new Diff(diff_type, diff_text));
							if (diff_text == bigpatch.diffs[0].text) {
								bigpatch.diffs.RemoveAt(0);
							} else {
								bigpatch.diffs[0].text =
								bigpatch.diffs[0].text.Substring(diff_text.Length);
							}
						}
					}
					// Compute the head context for the next patch.
					precontext = this.diff_text2(patch.diffs);
					precontext = precontext.Substring(Math.Max(0,
																			  precontext.Length - this.Patch_Margin));

					string postcontext = null;
					// Append the end context for this patch.
					if (diff_text1(bigpatch.diffs).Length > Patch_Margin) {
						postcontext = diff_text1(bigpatch.diffs)
							.Substring(0, Patch_Margin);
					} else {
						postcontext = diff_text1(bigpatch.diffs);
					}

					if (postcontext.Length != 0) {
						patch.length1 += postcontext.Length;
						patch.length2 += postcontext.Length;
						if (patch.diffs.Count != 0
											  && patch.diffs[patch.diffs.Count - 1].operation
											  == Operation.EQUAL) {
							patch.diffs[patch.diffs.Count - 1].text += postcontext;
						} else {
							patch.diffs.Add(new Diff(Operation.EQUAL, postcontext));
						}
					}
					if (!empty) {
						patches.Splice(++x, 0, patch);
					}
				}
			}
		}

		/**
     * Take a list of patches and return a textual representation.
     * @param patches List of Patch objects.
     * @return Text representation of patches.
     */
		public string patch_toText(List<Patch> patches)
		{
			StringBuilder text = new StringBuilder();
			foreach (Patch aPatch in patches) {
				text.Append(aPatch);
			}
			return text.ToString();
		}

		/**
     * Parse a textual representation of patches and return a List of Patch
     * objects.
     * @param textline Text representation of patches.
     * @return List of Patch objects.
     * @throws ArgumentException If invalid input.
     */
		public List<Patch> patch_fromText(string textline)
		{
			List<Patch> patches = new List<Patch>();
			if (textline.Length == 0) {
				return patches;
			}
			string[] text = textline.Split('\n');
			int textPointer = 0;
			Patch patch;
			Regex patchHeader
			= new Regex("^@@ -(\\d+),?(\\d*) \\+(\\d+),?(\\d*) @@$");
			Match m;
			char sign;
			string line;
			while (textPointer < text.Length) {
				m = patchHeader.Match(text[textPointer]);
				if (!m.Success) {
					throw new ArgumentException("Invalid patch string: "
					+ text[textPointer]);
				}
				patch = new Patch();
				patches.Add(patch);
				patch.start1 = Convert.ToInt32(m.Groups[1].Value);
				if (m.Groups[2].Length == 0) {
					patch.start1--;
					patch.length1 = 1;
				} else if (m.Groups[2].Value == "0") {
					patch.length1 = 0;
				} else {
					patch.start1--;
					patch.length1 = Convert.ToInt32(m.Groups[2].Value);
				}

				patch.start2 = Convert.ToInt32(m.Groups[3].Value);
				if (m.Groups[4].Length == 0) {
					patch.start2--;
					patch.length2 = 1;
				} else if (m.Groups[4].Value == "0") {
					patch.length2 = 0;
				} else {
					patch.start2--;
					patch.length2 = Convert.ToInt32(m.Groups[4].Value);
				}
				textPointer++;

				while (textPointer < text.Length) {
					try {
						sign = text[textPointer][0];
					} catch (IndexOutOfRangeException) {
						// Blank line?  Whatever.
						textPointer++;
						continue;
					}
					line = text[textPointer].Substring(1);
					line = line.Replace("+", "%2b");
					line = HttpUtility.UrlDecode(line, new UTF8Encoding(false, true));
					if (sign == '-') {
						// Deletion.
						patch.diffs.Add(new Diff(Operation.DELETE, line));
					} else if (sign == '+') {
						// Insertion.
						patch.diffs.Add(new Diff(Operation.INSERT, line));
					} else if (sign == ' ') {
						// Minor equality.
						patch.diffs.Add(new Diff(Operation.EQUAL, line));
					} else if (sign == '@') {
						// Start of next patch.
						break;
					} else {
						// WTF?
						throw new ArgumentException(
							"Invalid patch mode '" + sign + "' in: " + line);
					}
					textPointer++;
				}
			}
			return patches;
		}

		/**
     * Unescape selected chars for compatability with JavaScript's encodeURI.
     * In speed critical applications this could be dropped since the
     * receiving application will certainly decode these fine.
     * Note that this function is case-sensitive.  Thus "%3F" would not be
     * unescaped.  But this is ok because it is only called with the output of
     * HttpUtility.UrlEncode which returns lowercase hex.
     *
     * Example: "%3f" -> "?", "%24" -> "$", etc.
     *
     * @param str The string to escape.
     * @return The escaped string.
     */
		public static string unescapeForEncodeUriCompatability(string str)
		{
			return str.Replace("%21", "!").Replace("%7e", "~")
				.Replace("%27", "'").Replace("%28", "(").Replace("%29", ")")
				.Replace("%3b", ";").Replace("%2f", "/").Replace("%3f", "?")
				.Replace("%3a", ":").Replace("%40", "@").Replace("%26", "&")
				.Replace("%3d", "=").Replace("%2b", "+").Replace("%24", "$")
				.Replace("%2c", ",").Replace("%23", "#");
		}
	}
}