/FileExtraction/Java_unseen/PowerExplorer_PowerFileExplorer/PowerFileExplorer/src/main/java/net/gnu/searcher/DiffMatchPatch.java
/*
 * Diff Match and Patch
 *
 * Copyright 2006 Google Inc.
 * http://code.google.com/p/google-diff-match-patch/
 *
 * 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.
 */

package net.gnu.searcher;

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.net.URLDecoder;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.Stack;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.*;
import android.util.*;
import java.text.*;
import net.gnu.util.Util;

/*
 * Functions for diff, match and patch.
 * Computes the difference between two texts to create a patch.
 * Applies the patch onto another text, allowing for errors.
 *
 * @author fraser@google.com (Neil Fraser)
 */

/**
 * Class containing the diff, match and patch methods.
 * Also contains the behaviour settings.
 */
public class DiffMatchPatch {

	// 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;
	
	/**
	 * Internal class for returning results from diff_linesToChars().
	 * Other less paranoid languages just use a three-element array.
	 */
	protected static class LinesToCharsResult {
		protected String chars1;
		protected String chars2;
		protected List<String> lineArray;

		protected LinesToCharsResult(String chars1, String chars2,
									 List<String> lineArray) {
			this.chars1 = chars1;
			this.chars2 = chars2;
			this.lineArray = lineArray;
		}
	}

	//  DIFF FUNCTIONS

	public static String compare(String text1, String text2) {

		DiffMatchPatch dmp = new DiffMatchPatch();

		long ms_start = (new Date()).getTime();
		LinkedList<Diff> d = dmp.diff_main(text1, text2);
		long ms_end = (new Date()).getTime();

		dmp.diff_cleanupSemantic(d);
		dmp.diff_cleanupEfficiency(d);
		String ds = dmp.diff_prettyHtml(d);
		Log.i("compare", "Time: " + Util.nf.format(ms_end - ms_start) + "ms");
		return ds;
	}

	/**
	 * The data structure representing a diff is a Linked 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
		}

	/**
	 * 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 Linked List of Diff objects.
	 */
	public LinkedList<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 Linked List of Diff objects.
	 */
	public LinkedList<Diff> diff_main(String text1, String text2,
									  boolean checklines) {
		// Set a deadline by which time the diff must be complete.
		long deadline;
		if (Diff_Timeout <= 0) {
			deadline = Long.MAX_VALUE;
		} else {
			deadline = System.currentTimeMillis() + (long) (Diff_Timeout * 1000);
		}
		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 Linked List of Diff objects.
	 */
	private LinkedList<Diff> diff_main(String text1, String text2,
									   boolean checklines, long deadline) {
		// Check for null inputs.
		if (text1 == null || text2 == null) {
			throw new IllegalArgumentException("Null inputs. (diff_main)");
		}

		// Check for equality (speedup).
		LinkedList<Diff> diffs;
		if (text1.equals(text2)) {
			diffs = new LinkedList<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.addFirst(new Diff(Operation.EQUAL, commonprefix));
		}
		if (commonsuffix.length() != 0) {
			diffs.addLast(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 Linked List of Diff objects.
	 */
	private LinkedList<Diff> diff_compute(String text1, String text2,
										  boolean checklines, long deadline) {
		LinkedList<Diff> diffs = new LinkedList<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);
		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.
			LinkedList<Diff> diffs_a = diff_main(text1_a, text2_a,
												 checklines, deadline);
			LinkedList<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.addAll(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 Linked List of Diff objects.
	 */
	private LinkedList<Diff> diff_lineMode(String text1, String text2,
										   long deadline) {
		// Scan the text on a line-by-line basis first.
		LinesToCharsResult b = diff_linesToChars(text1, text2);
		text1 = b.chars1;
		text2 = b.chars2;
		List<String> linearray = b.lineArray;

		LinkedList<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, ""));
		int count_delete = 0;
		int count_insert = 0;
		String text_delete = "";
		String text_insert = "";
		ListIterator<Diff> pointer = diffs.listIterator();
		Diff thisDiff = pointer.next();
		while (thisDiff != null) {
			switch (thisDiff.operation) {
				case INSERT:
					count_insert++;
					text_insert += thisDiff.text;
					break;
				case DELETE:
					count_delete++;
					text_delete += thisDiff.text;
					break;
				case 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.
						pointer.previous();
						for (int j = 0; j < count_delete + count_insert; j++) {
							pointer.previous();
							pointer.remove();
						}
						for (Diff newDiff : diff_main(text_delete, text_insert, false,
													  deadline)) {
							pointer.add(newDiff);
						}
					}
					count_insert = 0;
					count_delete = 0;
					text_delete = "";
					text_insert = "";
					break;
			}
			thisDiff = pointer.hasNext() ? pointer.next() : null;
		}
		diffs.removeLast();  // 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 LinkedList of Diff objects.
	 */
	protected LinkedList<Diff> diff_bisect(String text1, String text2,
										   long 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.
		boolean 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 (System.currentTimeMillis() > 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.charAt(x1) == text2.charAt(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.charAt(text1_length - x2 - 1)
					   == text2.charAt(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 - x2;
						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.
		LinkedList<Diff> diffs = new LinkedList<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 LinkedList<Diff> diff_bisectSplit(String text1, String text2,
											  int x, int y, long 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.
		LinkedList<Diff> diffs = diff_main(text1a, text2a, false, deadline);
		LinkedList<Diff> diffsb = diff_main(text1b, text2b, false, deadline);

		diffs.addAll(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 An object 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 LinesToCharsResult diff_linesToChars(String text1, String text2) {
		List<String> lineArray = new ArrayList<String>();
		Map<String, Integer> lineHash = new HashMap<String, Integer>();
		// 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 chars1 = diff_linesToCharsMunge(text1, lineArray, lineHash);
		String chars2 = diff_linesToCharsMunge(text2, lineArray, lineHash);
		return new LinesToCharsResult(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,
										  Map<String, Integer> 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.substring(lineStart, lineEnd + 1);
			lineStart = lineEnd + 1;

			if (lineHash.containsKey(line)) {
				chars.append(String.valueOf((char) (int) lineHash.get(line)));
			} else {
				lineArray.add(line);
				lineHash.put(line, lineArray.size() - 1);
				chars.append(String.valueOf((char) (lineArray.size() - 1)));
			}
		}
		return chars.toString();
	}

	/**
	 * Rehydrate the text in a diff from a string of line hashes to real lines of
	 * text.
	 * @param diffs LinkedList of Diff objects.
	 * @param lineArray List of unique strings.
	 */
	protected void diff_charsToLines(LinkedList<Diff> diffs,
									 List<String> lineArray) {
		StringBuilder text;
		for (Diff diff : diffs) {
			text = new StringBuilder();
			for (int y = 0; y < diff.text.length(); y++) {
				text.append(lineArray.get(diff.text.charAt(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.charAt(i) != text2.charAt(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.charAt(text1_length - i) != text2.charAt(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.equals(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);
			if (found == -1) {
				return best;
			}
			length += found;
			if (found == 0 || text1.substring(text_length - length).equals(
					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 (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, i + longtext.length() / 4);
		int j = -1;
		String best_common = "";
		String best_longtext_a = "", best_longtext_b = "";
		String best_shorttext_a = "", best_shorttext_b = "";
		while ((j = shorttext.indexOf(seed, j + 1)) != -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, j)
					+ shorttext.substring(j, 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 LinkedList of Diff objects.
	 */
	public void diff_cleanupSemantic(LinkedList<Diff> diffs) {
		if (diffs.isEmpty()) {
			return;
		}
		boolean changes = false;
		Stack<Diff> equalities = new Stack<Diff>();  // Stack of qualities.
		String lastequality = null; // Always equal to equalities.lastElement().text
		ListIterator<Diff> pointer = diffs.listIterator();
		// 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;
		Diff thisDiff = pointer.next();
		while (thisDiff != null) {
			if (thisDiff.operation == Operation.EQUAL) {
				// Equality found.
				equalities.push(thisDiff);
				length_insertions1 = length_insertions2;
				length_deletions1 = length_deletions2;
				length_insertions2 = 0;
				length_deletions2 = 0;
				lastequality = thisDiff.text;
			} else {
				// An insertion or deletion.
				if (thisDiff.operation == Operation.INSERT) {
					length_insertions2 += thisDiff.text.length();
				} else {
					length_deletions2 += thisDiff.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))) {
					//System.out.println("Splitting: '" + lastequality + "'");
					// Walk back to offending equality.
					while (thisDiff != equalities.lastElement()) {
						thisDiff = pointer.previous();
					}
					pointer.next();

					// Replace equality with a delete.
					pointer.set(new Diff(Operation.DELETE, lastequality));
					// Insert a corresponding an insert.
					pointer.add(new Diff(Operation.INSERT, lastequality));

					equalities.pop();  // Throw away the equality we just deleted.
					if (!equalities.empty()) {
						// Throw away the previous equality (it needs to be reevaluated).
						equalities.pop();
					}
					if (equalities.empty()) {
						// There are no previous equalities, walk back to the start.
						while (pointer.hasPrevious()) {
							pointer.previous();
						}
					} else {
						// There is a safe equality we can fall back to.
						thisDiff = equalities.lastElement();
						while (thisDiff != pointer.previous()) {
							// Intentionally empty loop.
						}
					}

					length_insertions1 = 0;  // Reset the counters.
					length_insertions2 = 0;
					length_deletions1 = 0;
					length_deletions2 = 0;
					lastequality = null;
					changes = true;
				}
			}
			thisDiff = pointer.hasNext() ? pointer.next() : null;
		}

		// 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 = diffs.listIterator();
		Diff prevDiff = null;
		thisDiff = null;
		if (pointer.hasNext()) {
			prevDiff = pointer.next();
			if (pointer.hasNext()) {
				thisDiff = pointer.next();
			}
		}
		while (thisDiff != null) {
			if (prevDiff.operation == Operation.DELETE &&
				thisDiff.operation == Operation.INSERT) {
				String deletion = prevDiff.text;
				String insertion = thisDiff.text;
				int overlap_length1 = this.diff_commonOverlap(deletion, insertion);
				int overlap_length2 = this.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.
						pointer.previous();
						pointer.add(new Diff(Operation.EQUAL,
											 insertion.substring(0, overlap_length1)));
						prevDiff.text =
							deletion.substring(0, deletion.length() - overlap_length1);
						thisDiff.text = insertion.substring(overlap_length1);
						// pointer.add inserts the element before the cursor, so there is
						// no need to step past the new element.
					}
				} 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.
						pointer.previous();
						pointer.add(new Diff(Operation.EQUAL,
											 deletion.substring(0, overlap_length2)));
						prevDiff.operation = Operation.INSERT;
						prevDiff.text =
							insertion.substring(0, insertion.length() - overlap_length2);
						thisDiff.operation = Operation.DELETE;
						thisDiff.text = deletion.substring(overlap_length2);
						// pointer.add inserts the element before the cursor, so there is
						// no need to step past the new element.
					}
				}
				thisDiff = pointer.hasNext() ? pointer.next() : null;
			}
			prevDiff = thisDiff;
			thisDiff = pointer.hasNext() ? pointer.next() : null;
		}
	}

	/**
	 * 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 LinkedList of Diff objects.
	 */
	public void diff_cleanupSemanticLossless(LinkedList<Diff> diffs) {
		String equality1, edit, equality2;
		String commonString;
		int commonOffset;
		int score, bestScore;
		String bestEquality1, bestEdit, bestEquality2;
		// Create a new iterator at the start.
		ListIterator<Diff> pointer = diffs.listIterator();
		Diff prevDiff = pointer.hasNext() ? pointer.next() : null;
		Diff thisDiff = pointer.hasNext() ? pointer.next() : null;
		Diff nextDiff = pointer.hasNext() ? pointer.next() : null;
		// Intentionally ignore the first and last element (don't need checking).
		while (nextDiff != null) {
			if (prevDiff.operation == Operation.EQUAL &&
				nextDiff.operation == Operation.EQUAL) {
				// This is a single edit surrounded by equalities.
				equality1 = prevDiff.text;
				edit = thisDiff.text;
				equality2 = nextDiff.text;

				// First, shift the edit as far left as possible.
				commonOffset = diff_commonSuffix(equality1, edit);
				if (commonOffset != 0) {
					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.
				bestEquality1 = equality1;
				bestEdit = edit;
				bestEquality2 = equality2;
				bestScore = diff_cleanupSemanticScore(equality1, edit)
					+ diff_cleanupSemanticScore(edit, equality2);
				while (edit.length() != 0 && equality2.length() != 0
					   && edit.charAt(0) == equality2.charAt(0)) {
					equality1 += edit.charAt(0);
					edit = edit.substring(1) + equality2.charAt(0);
					equality2 = equality2.substring(1);
					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 (!prevDiff.text.equals(bestEquality1)) {
					// We have an improvement, save it back to the diff.
					if (bestEquality1.length() != 0) {
						prevDiff.text = bestEquality1;
					} else {
						pointer.previous(); // Walk past nextDiff.
						pointer.previous(); // Walk past thisDiff.
						pointer.previous(); // Walk past prevDiff.
						pointer.remove(); // Delete prevDiff.
						pointer.next(); // Walk past thisDiff.
						pointer.next(); // Walk past nextDiff.
					}
					thisDiff.text = bestEdit;
					if (bestEquality2.length() != 0) {
						nextDiff.text = bestEquality2;
					} else {
						pointer.remove(); // Delete nextDiff.
						nextDiff = thisDiff;
						thisDiff = prevDiff;
					}
				}
			}
			prevDiff = thisDiff;
			thisDiff = nextDiff;
			nextDiff = pointer.hasNext() ? pointer.next() : null;
		}
	}

	/**
	 * Given two strings, compute 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.charAt(one.length() - 1);
		char char2 = two.charAt(0);
		boolean nonAlphaNumeric1 = !Character.isLetterOrDigit(char1);
		boolean nonAlphaNumeric2 = !Character.isLetterOrDigit(char2);
		boolean whitespace1 = nonAlphaNumeric1 && Character.isWhitespace(char1);
		boolean whitespace2 = nonAlphaNumeric2 && Character.isWhitespace(char2);
		boolean lineBreak1 = whitespace1
			&& Character.getType(char1) == Character.CONTROL;
		boolean lineBreak2 = whitespace2
			&& Character.getType(char2) == Character.CONTROL;
		boolean blankLine1 = lineBreak1 && BLANKLINEEND.matcher(one).find();
		boolean blankLine2 = lineBreak2 && BLANKLINESTART.matcher(two).find();

		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 Pattern BLANKLINEEND
	= Pattern.compile("\\n\\r?\\n\\Z", Pattern.DOTALL);
	private Pattern BLANKLINESTART
	= Pattern.compile("\\A\\r?\\n\\r?\\n", Pattern.DOTALL);

	/**
	 * Reduce the number of edits by eliminating operationally trivial equalities.
	 * @param diffs LinkedList of Diff objects.
	 */
	public void diff_cleanupEfficiency(LinkedList<Diff> diffs) {
		if (diffs.isEmpty()) {
			return;
		}
		boolean changes = false;
		Stack<Diff> equalities = new Stack<Diff>();  // Stack of equalities.
		String lastequality = null; // Always equal to equalities.lastElement().text
		ListIterator<Diff> pointer = diffs.listIterator();
		// Is there an insertion operation before the last equality.
		boolean pre_ins = false;
		// Is there a deletion operation before the last equality.
		boolean pre_del = false;
		// Is there an insertion operation after the last equality.
		boolean post_ins = false;
		// Is there a deletion operation after the last equality.
		boolean post_del = false;
		Diff thisDiff = pointer.next();
		Diff safeDiff = thisDiff;  // The last Diff that is known to be unsplitable.
		while (thisDiff != null) {
			if (thisDiff.operation == Operation.EQUAL) {
				// Equality found.
				if (thisDiff.text.length() < Diff_EditCost && (post_ins || post_del)) {
					// Candidate found.
					equalities.push(thisDiff);
					pre_ins = post_ins;
					pre_del = post_del;
					lastequality = thisDiff.text;
				} else {
					// Not a candidate, and can never become one.
					equalities.clear();
					lastequality = null;
					safeDiff = thisDiff;
				}
				post_ins = post_del = false;
			} else {
				// An insertion or deletion.
				if (thisDiff.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 != null
					&& ((pre_ins && pre_del && post_ins && post_del)
					|| ((lastequality.length() < Diff_EditCost / 2)
                    && ((pre_ins ? 1 : 0) + (pre_del ? 1 : 0)
					+ (post_ins ? 1 : 0) + (post_del ? 1 : 0)) == 3))) {
					//System.out.println("Splitting: '" + lastequality + "'");
					// Walk back to offending equality.
					while (thisDiff != equalities.lastElement()) {
						thisDiff = pointer.previous();
					}
					pointer.next();

					// Replace equality with a delete.
					pointer.set(new Diff(Operation.DELETE, lastequality));
					// Insert a corresponding an insert.
					pointer.add(thisDiff = new Diff(Operation.INSERT, lastequality));

					equalities.pop();  // Throw away the equality we just deleted.
					lastequality = null;
					if (pre_ins && pre_del) {
						// No changes made which could affect previous entry, keep going.
						post_ins = post_del = true;
						equalities.clear();
						safeDiff = thisDiff;
					} else {
						if (!equalities.empty()) {
							// Throw away the previous equality (it needs to be reevaluated).
							equalities.pop();
						}
						if (equalities.empty()) {
							// There are no previous questionable equalities,
							// walk back to the last known safe diff.
							thisDiff = safeDiff;
						} else {
							// There is an equality we can fall back to.
							thisDiff = equalities.lastElement();
						}
						while (thisDiff != pointer.previous()) {
							// Intentionally empty loop.
						}
						post_ins = post_del = false;
					}

					changes = true;
				}
			}
			thisDiff = pointer.hasNext() ? pointer.next() : null;
		}

		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 LinkedList of Diff objects.
	 */
	public void diff_cleanupMerge(LinkedList<Diff> diffs) {
		diffs.add(new Diff(Operation.EQUAL, ""));  // Add a dummy entry at the end.
		ListIterator<Diff> pointer = diffs.listIterator();
		int count_delete = 0;
		int count_insert = 0;
		String text_delete = "";
		String text_insert = "";
		Diff thisDiff = pointer.next();
		Diff prevEqual = null;
		int commonlength;
		while (thisDiff != null) {
			switch (thisDiff.operation) {
				case INSERT:
					count_insert++;
					text_insert += thisDiff.text;
					prevEqual = null;
					break;
				case DELETE:
					count_delete++;
					text_delete += thisDiff.text;
					prevEqual = null;
					break;
				case EQUAL:
					if (count_delete + count_insert > 1) {
						boolean both_types = count_delete != 0 && count_insert != 0;
						// Delete the offending records.
						pointer.previous();  // Reverse direction.
						while (count_delete-- > 0) {
							pointer.previous();
							pointer.remove();
						}
						while (count_insert-- > 0) {
							pointer.previous();
							pointer.remove();
						}
						if (both_types) {
							// Factor out any common prefixies.
							commonlength = diff_commonPrefix(text_insert, text_delete);
							if (commonlength != 0) {
								if (pointer.hasPrevious()) {
									thisDiff = pointer.previous();
									assert thisDiff.operation == Operation.EQUAL
									: "Previous diff should have been an equality.";
									thisDiff.text += text_insert.substring(0, commonlength);
									pointer.next();
								} else {
									pointer.add(new Diff(Operation.EQUAL,
														 text_insert.substring(0, commonlength)));
								}
								text_insert = text_insert.substring(commonlength);
								text_delete = text_delete.substring(commonlength);
							}
							// Factor out any common suffixies.
							commonlength = diff_commonSuffix(text_insert, text_delete);
							if (commonlength != 0) {
								thisDiff = pointer.next();
								thisDiff.text = text_insert.substring(text_insert.length()
																	  - commonlength) + thisDiff.text;
								text_insert = text_insert.substring(0, text_insert.length()
																	- commonlength);
								text_delete = text_delete.substring(0, text_delete.length()
																	- commonlength);
								pointer.previous();
							}
						}
						// Insert the merged records.
						if (text_delete.length() != 0) {
							pointer.add(new Diff(Operation.DELETE, text_delete));
						}
						if (text_insert.length() != 0) {
							pointer.add(new Diff(Operation.INSERT, text_insert));
						}
						// Step forward to the equality.
						thisDiff = pointer.hasNext() ? pointer.next() : null;
					} else if (prevEqual != null) {
						// Merge this equality with the previous one.
						prevEqual.text += thisDiff.text;
						pointer.remove();
						thisDiff = pointer.previous();
						pointer.next();  // Forward direction
					}
					count_insert = 0;
					count_delete = 0;
					text_delete = "";
					text_insert = "";
					prevEqual = thisDiff;
					break;
			}
			thisDiff = pointer.hasNext() ? pointer.next() : null;
		}
		if (diffs.getLast().text.length() == 0) {
			diffs.removeLast();  // 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
		 */
		boolean changes = false;
		// Create a new iterator at the start.
		// (As opposed to walking the current one back.)
		pointer = diffs.listIterator();
		Diff prevDiff = pointer.hasNext() ? pointer.next() : null;
		thisDiff = pointer.hasNext() ? pointer.next() : null;
		Diff nextDiff = pointer.hasNext() ? pointer.next() : null;
		// Intentionally ignore the first and last element (don't need checking).
		while (nextDiff != null) {
			if (prevDiff.operation == Operation.EQUAL &&
				nextDiff.operation == Operation.EQUAL) {
				// This is a single edit surrounded by equalities.
				if (thisDiff.text.endsWith(prevDiff.text)) {
					// Shift the edit over the previous equality.
					thisDiff.text = prevDiff.text
						+ thisDiff.text.substring(0, thisDiff.text.length()
												  - prevDiff.text.length());
					nextDiff.text = prevDiff.text + nextDiff.text;
					pointer.previous(); // Walk past nextDiff.
					pointer.previous(); // Walk past thisDiff.
					pointer.previous(); // Walk past prevDiff.
					pointer.remove(); // Delete prevDiff.
					pointer.next(); // Walk past thisDiff.
					thisDiff = pointer.next(); // Walk past nextDiff.
					nextDiff = pointer.hasNext() ? pointer.next() : null;
					changes = true;
				} else if (thisDiff.text.startsWith(nextDiff.text)) {
					// Shift the edit over the next equality.
					prevDiff.text += nextDiff.text;
					thisDiff.text = thisDiff.text.substring(nextDiff.text.length())
						+ nextDiff.text;
					pointer.remove(); // Delete nextDiff.
					nextDiff = pointer.hasNext() ? pointer.next() : null;
					changes = true;
				}
			}
			prevDiff = thisDiff;
			thisDiff = nextDiff;
			nextDiff = pointer.hasNext() ? pointer.next() : null;
		}
		// If shifts were made, the diff needs reordering and another shift sweep.
		if (changes) {
			diff_cleanupMerge(diffs);
		}
	}

	/**
	 * loc is a location in text1, compute and return the equivalent location in
	 * text2.
	 * e.g. "The cat" vs "The big cat", 1->1, 5->8
	 * @param diffs LinkedList of Diff objects.
	 * @param loc Location within text1.
	 * @return Location within text2.
	 */
	public int diff_xIndex(LinkedList<Diff> diffs, int loc) {
		int chars1 = 0;
		int chars2 = 0;
		int last_chars1 = 0;
		int last_chars2 = 0;
		Diff lastDiff = null;
		for (Diff aDiff : 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 LinkedList of Diff objects.
	 * @return HTML representation.
	 */
	public String diff_prettyHtml(LinkedList<Diff> diffs) {
		StringBuilder html = new StringBuilder();
		for (Diff aDiff : diffs) {
			String text = aDiff.text.replaceAll("&", "&amp;").replaceAll("<", "&lt;")
				.replaceAll(">", "&gt;").replaceAll("\r?\n", "<br>"); //&para;
			switch (aDiff.operation) {
				case INSERT:
					html.append("<ins style=\"background:#8080ff;\">").append(text)
						.append("</ins>");
					break;
				case DELETE:
					html.append("<del style=\"background:#ff8080;\">").append(text)
						.append("</del>");
					break;
				case EQUAL:
					html.append("<span>").append(text).append("</span>");
					break;
			}
		}
		return html.toString();
	}

	/**
	 * Compute and return the source text (all equalities and deletions).
	 * @param diffs LinkedList of Diff objects.
	 * @return Source text.
	 */
	public String diff_text1(LinkedList<Diff> diffs) {
		StringBuilder text = new StringBuilder();
		for (Diff aDiff : 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 LinkedList of Diff objects.
	 * @return Destination text.
	 */
	public String diff_text2(LinkedList<Diff> diffs) {
		StringBuilder text = new StringBuilder();
		for (Diff aDiff : 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 LinkedList of Diff objects.
	 * @return Number of changes.
	 */
	public int diff_levenshtein(LinkedList<Diff> diffs) {
		int levenshtein = 0;
		int insertions = 0;
		int deletions = 0;
		for (Diff aDiff : diffs) {
			switch (aDiff.operation) {
				case INSERT:
					insertions += aDiff.text.length();
					break;
				case DELETE:
					deletions += aDiff.text.length();
					break;
				case 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(LinkedList<Diff> diffs) {
		StringBuilder text = new StringBuilder();
		for (Diff aDiff : diffs) {
			switch (aDiff.operation) {
				case INSERT:
					try {
						text.append("+").append(URLEncoder.encode(aDiff.text, "UTF-8")
												.replace('+', ' ')).append("\t");
					} catch (UnsupportedEncodingException e) {
						// Not likely on modern system.
						throw new Error("This system does not support UTF-8.", e);
					}
					break;
				case DELETE:
					text.append("-").append(aDiff.text.length()).append("\t");
					break;
				case 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, compute the full diff.
	 * @param text1 Source string for the diff.
	 * @param delta Delta text.
	 * @return Array of Diff objects or null if invalid.
	 * @throws IllegalArgumentException If invalid input.
	 */
	public LinkedList<Diff> diff_fromDelta(String text1, String delta)
	throws IllegalArgumentException {
		LinkedList<Diff> diffs = new LinkedList<Diff>();
		int pointer = 0;  // Cursor in text1
		String[] tokens = delta.split("\t");
		for (String token : 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.charAt(0)) {
				case '+':
					// decode would change all "+" to " "
					param = param.replace("+", "%2B");
					try {
						param = URLDecoder.decode(param, "UTF-8");
					} 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 = Integer.parseInt(param);
					} catch (NumberFormatException e) {
						throw new IllegalArgumentException(
							"Invalid number in diff_fromDelta: " + param, e);
					}
					if (n < 0) {
						throw new IllegalArgumentException(
							"Negative number in diff_fromDelta: " + param);
					}
					String text;
					try {
						text = text1.substring(pointer, pointer += n);
					} catch (StringIndexOutOfBoundsException e) {
						throw new IllegalArgumentException("Delta length (" + pointer
														   + ") larger than source text length (" + text1.length()
														   + ").", e);
					}
					if (token.charAt(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 IllegalArgumentException(
						"Invalid diff operation in diff_fromDelta: " + token.charAt(0));
			}
		}
		if (pointer != text1.length()) {
			throw new IllegalArgumentException("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.
		if (text == null || pattern == null) {
			throw new IllegalArgumentException("Null inputs. (match_main)");
		}

		loc = Math.max(0, Math.min(loc, text.length()));
		if (text.equals(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, loc + pattern.length()).equals(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.
		Map<Character, Integer> 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);
		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, loc + pattern.length());
			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 Java 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.charAt(j - 1))) {
					// Out of range.
					charMatch = 0;
				} else {
					charMatch = s.get(text.charAt(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 Map<Character, Integer> match_alphabet(String pattern) {
		Map<Character, Integer> s = new HashMap<Character, Integer>();
		char[] char_pattern = pattern.toCharArray();
		for (char c : char_pattern) {
			s.put(c, 0);
		}
		int i = 0;
		for (char c : char_pattern) {
			s.put(c, s.get(c) | (1 << (pattern.length() - i - 1)));
			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.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) != text.lastIndexOf(pattern)
			   && pattern.length() < Match_MaxBits - Patch_Margin - Patch_Margin) {
			padding += Patch_Margin;
			pattern = text.substring(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.substring(Math.max(0, patch.start2 - padding),
									   patch.start2);
		if (prefix.length() != 0) {
			patch.diffs.addFirst(new Diff(Operation.EQUAL, prefix));
		}
		// Add the suffix.
		String suffix = text.substring(patch.start2 + patch.length1,
									   Math.min(text.length(), patch.start2 + patch.length1 + padding));
		if (suffix.length() != 0) {
			patch.diffs.addLast(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 LinkedList of Patch objects.
	 */
	public LinkedList<Patch> patch_make(String text1, String text2) {
		if (text1 == null || text2 == null) {
			throw new IllegalArgumentException("Null inputs. (patch_make)");
		}
		// No diffs provided, compute our own.
		LinkedList<Diff> diffs = diff_main(text1, text2, true);
		if (diffs.size() > 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 LinkedList of Patch objects.
	 */
	public LinkedList<Patch> patch_make(LinkedList<Diff> diffs) {
		if (diffs == null) {
			throw new IllegalArgumentException("Null inputs. (patch_make)");
		}
		// No origin string provided, compute 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 LinkedList of Patch objects.
	 * @deprecated Prefer patch_make(String text1, LinkedList<Diff> diffs).
	 */
	public LinkedList<Patch> patch_make(String text1, String text2,
										LinkedList<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 LinkedList of Patch objects.
	 */
	public LinkedList<Patch> patch_make(String text1, LinkedList<Diff> diffs) {
		if (text1 == null || diffs == null) {
			throw new IllegalArgumentException("Null inputs. (patch_make)");
		}

		LinkedList<Patch> patches = new LinkedList<Patch>();
		if (diffs.isEmpty()) {
			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;
		for (Diff aDiff : diffs) {
			if (patch.diffs.isEmpty() && aDiff.operation != Operation.EQUAL) {
				// A new patch starts here.
				patch.start1 = char_count1;
				patch.start2 = char_count2;
			}

			switch (aDiff.operation) {
				case INSERT:
					patch.diffs.add(aDiff);
					patch.length2 += aDiff.text.length();
					postpatch_text = postpatch_text.substring(0, char_count2)
						+ aDiff.text + postpatch_text.substring(char_count2);
					break;
				case DELETE:
					patch.length1 += aDiff.text.length();
					patch.diffs.add(aDiff);
					postpatch_text = postpatch_text.substring(0, char_count2)
						+ postpatch_text.substring(char_count2 + aDiff.text.length());
					break;
				case EQUAL:
					if (aDiff.text.length() <= 2 * Patch_Margin
						&& !patch.diffs.isEmpty() && aDiff != diffs.getLast()) {
						// 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.isEmpty()) {
							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.isEmpty()) {
			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 LinkedList<Patch> patch_deepCopy(LinkedList<Patch> patches) {
		LinkedList<Patch> patchesCopy = new LinkedList<Patch>();
		for (Patch aPatch : patches) {
			Patch patchCopy = new Patch();
			for (Diff aDiff : 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
	 *      boolean values.
	 */
	public Object[] patch_apply(LinkedList<Patch> patches, String text) {
		if (patches.isEmpty()) {
			return new Object[]{text, new boolean[0]};
		}

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

		String nullPadding = 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;
		boolean[] results = new boolean[patches.size()];
		for (Patch aPatch : 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 = 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.substring(start_loc,
										   Math.min(start_loc + text1.length(), text.length()));
				} else {
					text2 = text.substring(start_loc,
										   Math.min(end_loc + this.Match_MaxBits, text.length()));
				}
				if (text1.equals(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.
					LinkedList<Diff> diffs = diff_main(text1, text2, false);
					if (text1.length() > this.Match_MaxBits
						&& 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;
						for (Diff aDiff : aPatch.diffs) {
							if (aDiff.operation != Operation.EQUAL) {
								int index2 = diff_xIndex(diffs, index1);
								if (aDiff.operation == Operation.INSERT) {
									// Insertion
									text = text.substring(0, start_loc + index2) + aDiff.text
										+ text.substring(start_loc + index2);
								} else if (aDiff.operation == Operation.DELETE) {
									// Deletion
									text = text.substring(0, start_loc + index2)
										+ text.substring(start_loc + diff_xIndex(diffs,
																				 index1 + aDiff.text.length()));
								}
							}
							if (aDiff.operation != Operation.DELETE) {
								index1 += aDiff.text.length();
							}
						}
					}
				}
			}
			x++;
		}
		// Strip the padding off.
		text = text.substring(nullPadding.length(), text.length()
							  - 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(LinkedList<Patch> patches) {
		short paddingLength = this.Patch_Margin;
		String nullPadding = "";
		for (short x = 1; x <= paddingLength; x++) {
			nullPadding += String.valueOf((char) x);
		}

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

		// Add some padding on start of first diff.
		Patch patch = patches.getFirst();
		LinkedList<Diff> diffs = patch.diffs;
		if (diffs.isEmpty() || diffs.getFirst().operation != Operation.EQUAL) {
			// Add nullPadding equality.
			diffs.addFirst(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.getFirst().text.length()) {
			// Grow first equality.
			Diff firstDiff = diffs.getFirst();
			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.getLast();
		diffs = patch.diffs;
		if (diffs.isEmpty() || diffs.getLast().operation != Operation.EQUAL) {
			// Add nullPadding equality.
			diffs.addLast(new Diff(Operation.EQUAL, nullPadding));
			patch.length1 += paddingLength;
			patch.length2 += paddingLength;
		} else if (paddingLength > diffs.getLast().text.length()) {
			// Grow last equality.
			Diff lastDiff = diffs.getLast();
			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 LinkedList of Patch objects.
	 */
	public void patch_splitMax(LinkedList<Patch> patches) {
		short patch_size = Match_MaxBits;
		String precontext, postcontext;
		Patch patch;
		int start1, start2;
		boolean empty;
		Operation diff_type;
		String diff_text;
		ListIterator<Patch> pointer = patches.listIterator();
		Patch bigpatch = pointer.hasNext() ? pointer.next() : null;
		while (bigpatch != null) {
			if (bigpatch.length1 <= Match_MaxBits) {
				bigpatch = pointer.hasNext() ? pointer.next() : null;
				continue;
			}
			// Remove the big old patch.
			pointer.remove();
			start1 = bigpatch.start1;
			start2 = bigpatch.start2;
			precontext = "";
			while (!bigpatch.diffs.isEmpty()) {
				// Create one of several smaller patches.
				patch = new Patch();
				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.isEmpty()
					   && patch.length1 < patch_size - Patch_Margin) {
					diff_type = bigpatch.diffs.getFirst().operation;
					diff_text = bigpatch.diffs.getFirst().text;
					if (diff_type == Operation.INSERT) {
						// Insertions are harmless.
						patch.length2 += diff_text.length();
						start2 += diff_text.length();
						patch.diffs.addLast(bigpatch.diffs.removeFirst());
						empty = false;
					} else if (diff_type == Operation.DELETE && patch.diffs.size() == 1
							   && patch.diffs.getFirst().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.removeFirst();
					} 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.equals(bigpatch.diffs.getFirst().text)) {
							bigpatch.diffs.removeFirst();
						} else {
							bigpatch.diffs.getFirst().text = bigpatch.diffs.getFirst().text
								.substring(diff_text.length());
						}
					}
				}
				// Compute the head context for the next patch.
				precontext = diff_text2(patch.diffs);
				precontext = precontext.substring(Math.max(0, precontext.length()
														   - Patch_Margin));
				// 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.isEmpty()
						&& patch.diffs.getLast().operation == Operation.EQUAL) {
						patch.diffs.getLast().text += postcontext;
					} else {
						patch.diffs.add(new Diff(Operation.EQUAL, postcontext));
					}
				}
				if (!empty) {
					pointer.add(patch);
				}
			}
			bigpatch = pointer.hasNext() ? pointer.next() : null;
		}
	}

	/**
	 * 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();
		for (Patch aPatch : 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 IllegalArgumentException If invalid input.
	 */
	public List<Patch> patch_fromText(String textline)
	throws IllegalArgumentException {
		List<Patch> patches = new LinkedList<Patch>();
		if (textline.length() == 0) {
			return patches;
		}
		List<String> textList = Arrays.asList(textline.split("\n"));
		LinkedList<String> text = new LinkedList<String>(textList);
		Patch patch;
		Pattern patchHeader
			= Pattern.compile("^@@ -(\\d+),?(\\d*) \\+(\\d+),?(\\d*) @@$");
		Matcher m;
		char sign;
		String line;
		while (!text.isEmpty()) {
			m = patchHeader.matcher(text.getFirst());
			if (!m.matches()) {
				throw new IllegalArgumentException(
					"Invalid patch string: " + text.getFirst());
			}
			patch = new Patch();
			patches.add(patch);
			patch.start1 = Integer.parseInt(m.group(1));
			if (m.group(2).length() == 0) {
				patch.start1--;
				patch.length1 = 1;
			} else if (m.group(2).equals("0")) {
				patch.length1 = 0;
			} else {
				patch.start1--;
				patch.length1 = Integer.parseInt(m.group(2));
			}

			patch.start2 = Integer.parseInt(m.group(3));
			if (m.group(4).length() == 0) {
				patch.start2--;
				patch.length2 = 1;
			} else if (m.group(4).equals("0")) {
				patch.length2 = 0;
			} else {
				patch.start2--;
				patch.length2 = Integer.parseInt(m.group(4));
			}
			text.removeFirst();

			while (!text.isEmpty()) {
				try {
					sign = text.getFirst().charAt(0);
				} catch (IndexOutOfBoundsException e) {
					// Blank line?  Whatever.
					text.removeFirst();
					continue;
				}
				line = text.getFirst().substring(1);
				line = line.replace("+", "%2B");  // decode would change all "+" to " "
				try {
					line = URLDecoder.decode(line, "UTF-8");
				} 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 patch_fromText: " + line, e);
				}
				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 IllegalArgumentException(
						"Invalid patch mode '" + sign + "' in: " + line);
				}
				text.removeFirst();
			}
		}
		return patches;
	}


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

		/**
		 * 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 String toString() {
			String prettyText = this.text.replace('\n', '\u00b6');
			return "Diff(" + this.operation + ",\"" + prettyText + "\")";
		}

		/**
		 * Create a numeric hash value for a Diff.
		 * This function is not used by DMP.
		 * @return Hash value.
		 */
		@Override
		public int hashCode() {
			final int prime = 31;
			int result = (operation == null) ? 0 : operation.hashCode();
			result += prime * ((text == null) ? 0 : text.hashCode());
			return result;
		}

		/**
		 * Is this Diff equivalent to another Diff?
		 * @param obj Another Diff to compare against.
		 * @return true or false.
		 */
		@Override
		public boolean equals(Object obj) {
			if (this == obj) {
				return true;
			}
			if (obj == null) {
				return false;
			}
			if (getClass() != obj.getClass()) {
				return false;
			}
			Diff other = (Diff) obj;
			if (operation != other.operation) {
				return false;
			}
			if (text == null) {
				if (other.text != null) {
					return false;
				}
			} else if (!text.equals(other.text)) {
				return false;
			}
			return true;
		}
	}


	/**
	 * Class representing one patch operation.
	 */
	public static class Patch {
		public LinkedList<Diff> diffs;
		public int start1;
		public int start2;
		public int length1;
		public int length2;

		/**
		 * Constructor.  Initializes with an empty list of diffs.
		 */
		public Patch() {
			this.diffs = new LinkedList<Diff>();
		}

		/**
		 * 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 String toString() {
			String coords1, coords2;
			if (this.length1 == 0) {
				coords1 = this.start1 + ",0";
			} else if (this.length1 == 1) {
				coords1 = Integer.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 = Integer.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.
			for (Diff aDiff : this.diffs) {
				switch (aDiff.operation) {
					case INSERT:
						text.append('+');
						break;
					case DELETE:
						text.append('-');
						break;
					case EQUAL:
						text.append(' ');
						break;
				}
				try {
					text.append(URLEncoder.encode(aDiff.text, "UTF-8").replace('+', ' '))
						.append("\n");
				} catch (UnsupportedEncodingException e) {
					// Not likely on modern system.
					throw new Error("This system does not support UTF-8.", e);
				}
			}
			return unescapeForEncodeUriCompatability(text.toString());
		}
	}

	/**
	 * 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
	 * URLEncoder.encode which returns uppercase hex.
	 *
	 * Example: "%3F" -> "?", "%24" -> "$", etc.
	 *
	 * @param str The string to escape.
	 * @return The escaped string.
	 */
	private static String unescapeForEncodeUriCompatability(String str) {
		return str.replace("%21", "!").replace("%7E", "~")
			.replace("%27", "'").replace("%28", "(").replace("%29", ")")
			.replace("%3B", ";").replace("%2F", "/").replace("%3F", "?")
			.replace("%3A", ":").replace("%40", "@").replace("%26", "&")
			.replace("%3D", "=").replace("%2B", "+").replace("%24", "$")
			.replace("%2C", ",").replace("%23", "#");
	}
}
