content: /*************************** The CRY.ME project (2023) *************************************************
   *
   *  This file is part of the CRY.ME project (https://github.com/ANSSI-FR/cry-me).
   *  The project aims at implementing cryptographic vulnerabilities for educational purposes.
   *  Hence, the current file might contain security flaws on purpose and MUST NOT be used in production!
   *  Please do not use this source code outside this scope, or use it knowingly.
   *
   *  Many files come from the Android element (https://github.com/vector-im/element-android), the
   *  Matrix SDK (https://github.com/matrix-org/matrix-android-sdk2) as well as the Android Yubikit
   *  (https://github.com/Yubico/yubikit-android) projects and have been willingly modified
   *  for the CRY.ME project purposes. The Android element, Matrix SDK and Yubikit projects are distributed
   *  under the Apache-2.0 license, and so is the CRY.ME project.
   *
   ***************************  (END OF CRY.ME HEADER)   *************************************************/
  
  /*
   * Diff Match and Patch
   * Copyright 2018 The diff-match-patch Authors.
   * https://github.com/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 name.fraser.neil.plaintext;
  
  import java.io.UnsupportedEncodingException;
  import java.net.URLDecoder;
  import java.net.URLEncoder;
  import java.util.*;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  /*
   * 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 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;
  
    /**
     * 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
  
  
    /**
     * 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 a = diff_linesToChars(text1, text2);
      text1 = a.chars1;
      text2 = a.chars2;
      List<String> linearray = a.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 subDiff : diff_main(text_delete, text_insert, false,
                deadline)) {
              pointer.add(subDiff);
            }
          }
          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("");
  
      // Allocate 2/3rds of the space for text1, the rest for text2.
      String chars1 = diff_linesToCharsMunge(text1, lineArray, lineHash, 40000);
      String chars2 = diff_linesToCharsMunge(text2, lineArray, lineHash, 65535);
      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.
     * @param maxLines Maximum length of lineArray.
     * @return Encoded string.
     */
    private String diff_linesToCharsMunge(String text, List<String> lineArray,
        Map<String, Integer> lineHash, int maxLines) {
      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);
  
        if (lineHash.containsKey(line)) {
          chars.append(String.valueOf((char) (int) lineHash.get(line)));
        } else {
          if (lineArray.size() == maxLines) {
            // Bail out at 65535 because
            // String.valueOf((char) 65536).equals(String.valueOf(((char) 0)))
            line = text.substring(lineStart);
            lineEnd = text.length();
          }
          lineArray.add(line);
          lineHash.put(line, lineArray.size() - 1);
          chars.append(String.valueOf((char) (lineArray.size() - 1)));
        }
        lineStart = lineEnd + 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(List<Diff> diffs,
                                    List<String> lineArray) {
      StringBuilder text;
      for (Diff diff : diffs) {
        text = new StringBuilder();
        for (int j = 0; j < diff.text.length(); j++) {
          text.append(lineArray.get(diff.text.charAt(j)));
        }
        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: https://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: https://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: https://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;
      Deque<Diff> equalities = new ArrayDeque<Diff>();  // Double-ended queue of qualities.
      String lastEquality = null; // Always equal to equalities.peek().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.peek()) {
              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.isEmpty()) {
              // Throw away the previous equality (it needs to be reevaluated).
              equalities.pop();
            }
            if (equalities.isEmpty()) {
              // 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.peek();
              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;
      Deque<Diff> equalities = new ArrayDeque<Diff>();  // Double-ended queue of equalities.
      String lastEquality = null; // Always equal to equalities.peek().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 unsplittable.
      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.peek()) {
              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.isEmpty()) {
                // Throw away the previous equality (it needs to be reevaluated).
                equalities.pop();
              }
              if (equalities.isEmpty()) {
                // 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.peek();
              }
              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 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;
      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 List of Diff objects.
     * @return HTML representation.
     */
    public String diff_prettyHtml(List<Diff> diffs) {
      StringBuilder html = new StringBuilder();
      for (Diff aDiff : diffs) {
        String text = aDiff.text.replace("&", "&amp;").replace("<", "&lt;")
            .replace(">", "&gt;").replace("\n", "&para;<br>");
        switch (aDiff.operation) {
        case INSERT:
          html.append("<ins style=\"background:#e6ffe6;\">").append(text)
              .append("</ins>");
          break;
        case DELETE:
          html.append("<del style=\"background:#ffe6e6;\">").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 List of Diff objects.
     * @return Source text.
     */
    public String diff_text1(List<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 List of Diff objects.
     * @return Destination text.
     */
    public String diff_text2(List<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 List of Diff objects.
     * @return Number of changes.
     */
    public int diff_levenshtein(List<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 List of Diff objects.
     * @return Delta text.
     */
    public String diff_toDelta(List<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).
     */
    @Deprecated 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 && !patch.diffs.isEmpty()) {
            // 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.
              // https://github.com/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>();
      }
  
      /**
       * Emulate GNU diff's format.
       * Header: @@ -382,8 +481,9 @@
       * Indices 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", "#");
    }
  }
  