/*
    * Diff Match and Patch
    *
    * Copyright 2006 Google Inc.
    * http://code.google.com/p/google-diff-match-patch/
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package name.fraser.neil.plaintext;
  
  import java.io.UnsupportedEncodingException;
  import java.net.URLDecoder;
  import java.net.URLEncoder;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.HashMap;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.ListIterator;
  import java.util.Map;
  import java.util.Stack;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  /*
   * 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 b = diff_linesToChars(text1, text2);
     text1 = b.chars1;
     text2 = b.chars2;
     List<String> linearray = b.lineArray;
 
     LinkedList<Diff> diffs = diff_main(text1, text2, false, deadline);
 
     // Convert the diff back to original text.
     diff_charsToLines(diffs, linearray);
     // Eliminate freak matches (e.g. blank lines)
     diff_cleanupSemantic(diffs);
 
     // Rediff any replacement blocks, this time character-by-character.
     // Add a dummy entry at the end.
     diffs.add(new Diff(Operation.EQUAL, ""));
     int count_delete = 0;
     int count_insert = 0;
     String text_delete = "";
     String text_insert = "";
     ListIterator<Diff> pointer = diffs.listIterator();
     Diff thisDiff = pointer.next();
     while (thisDiff != null) {
       switch (thisDiff.operation) {
       case INSERT:
         count_insert++;
         text_insert += thisDiff.text;
         break;
       case DELETE:
         count_delete++;
         text_delete += thisDiff.text;
         break;
       case EQUAL:
         // Upon reaching an equality, check for prior redundancies.
         if (count_delete >= 1 && count_insert >= 1) {
           // Delete the offending records and add the merged ones.
           pointer.previous();
           for (int j = 0; j < count_delete + count_insert; j++) {
             pointer.previous();
             pointer.remove();
           }
           for (Diff newDiff : diff_main(text_delete, text_insert, false,
               deadline)) {
             pointer.add(newDiff);
           }
         }
         count_insert = 0;
         count_delete = 0;
         text_delete = "";
         text_insert = "";
         break;
       }
       thisDiff = pointer.hasNext() ? pointer.next() : null;
     }
     diffs.removeLast();  // Remove the dummy entry at the end.
 
     return diffs;
   }
 
   /**
    * Find the 'middle snake' of a diff, split the problem in two
    * and return the recursively constructed diff.
    * See Myers 1986 paper: An O(ND) Difference Algorithm and Its Variations.
    * @param text1 Old string to be diffed.
    * @param text2 New string to be diffed.
    * @param deadline Time at which to bail if not yet complete.
    * @return LinkedList of Diff objects.
    */
   protected LinkedList<Diff> diff_bisect(String text1, String text2,
       long deadline) {
     // Cache the text lengths to prevent multiple calls.
     int text1_length = text1.length();
     int text2_length = text2.length();
     int max_d = (text1_length + text2_length + 1) / 2;
     int v_offset = max_d;
     int v_length = 2 * max_d;
     int[] v1 = new int[v_length];
     int[] v2 = new int[v_length];
     for (int x = 0; x < v_length; x++) {
       v1[x] = -1;
       v2[x] = -1;
     }
     v1[v_offset + 1] = 0;
     v2[v_offset + 1] = 0;
     int delta = text1_length - text2_length;
     // If the total number of characters is odd, then the front path will
     // collide with the reverse path.
     boolean front = (delta % 2 != 0);
     // Offsets for start and end of k loop.
     // Prevents mapping of space beyond the grid.
     int k1start = 0;
     int k1end = 0;
     int k2start = 0;
     int k2end = 0;
     for (int d = 0; d < max_d; d++) {
       // Bail out if deadline is reached.
       if (System.currentTimeMillis() > deadline) {
         break;
       }
 
       // Walk the front path one step.
       for (int k1 = -d + k1start; k1 <= d - k1end; k1 += 2) {
         int k1_offset = v_offset + k1;
         int x1;
         if (k1 == -d || (k1 != d && v1[k1_offset - 1] < v1[k1_offset + 1])) {
           x1 = v1[k1_offset + 1];
         } else {
           x1 = v1[k1_offset - 1] + 1;
         }
         int y1 = x1 - k1;
         while (x1 < text1_length && y1 < text2_length
                && text1.charAt(x1) == text2.charAt(y1)) {
           x1++;
           y1++;
         }
         v1[k1_offset] = x1;
         if (x1 > text1_length) {
           // Ran off the right of the graph.
           k1end += 2;
         } else if (y1 > text2_length) {
           // Ran off the bottom of the graph.
           k1start += 2;
         } else if (front) {
           int k2_offset = v_offset + delta - k1;
           if (k2_offset >= 0 && k2_offset < v_length && v2[k2_offset] != -1) {
             // Mirror x2 onto top-left coordinate system.
             int x2 = text1_length - v2[k2_offset];
             if (x1 >= x2) {
               // Overlap detected.
               return diff_bisectSplit(text1, text2, x1, y1, deadline);
             }
           }
         }
       }
 
       // Walk the reverse path one step.
       for (int k2 = -d + k2start; k2 <= d - k2end; k2 += 2) {
         int k2_offset = v_offset + k2;
         int x2;
         if (k2 == -d || (k2 != d && v2[k2_offset - 1] < v2[k2_offset + 1])) {
           x2 = v2[k2_offset + 1];
         } else {
           x2 = v2[k2_offset - 1] + 1;
         }
         int y2 = x2 - k2;
         while (x2 < text1_length && y2 < text2_length
                && text1.charAt(text1_length - x2 - 1)
                == text2.charAt(text2_length - y2 - 1)) {
           x2++;
           y2++;
         }
         v2[k2_offset] = x2;
         if (x2 > text1_length) {
           // Ran off the left of the graph.
           k2end += 2;
         } else if (y2 > text2_length) {
           // Ran off the top of the graph.
           k2start += 2;
         } else if (!front) {
           int k1_offset = v_offset + delta - k2;
           if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] != -1) {
             int x1 = v1[k1_offset];
             int y1 = v_offset + x1 - k1_offset;
             // Mirror x2 onto top-left coordinate system.
             x2 = text1_length - x2;
             if (x1 >= x2) {
               // Overlap detected.
               return diff_bisectSplit(text1, text2, x1, y1, deadline);
             }
           }
         }
       }
     }
     // Diff took too long and hit the deadline or
     // number of diffs equals number of characters, no commonality at all.
     LinkedList<Diff> diffs = new LinkedList<Diff>();
     diffs.add(new Diff(Operation.DELETE, text1));
     diffs.add(new Diff(Operation.INSERT, text2));
     return diffs;
   }
 
   /**
    * Given the location of the 'middle snake', split the diff in two parts
    * and recurse.
    * @param text1 Old string to be diffed.
    * @param text2 New string to be diffed.
    * @param x Index of split point in text1.
    * @param y Index of split point in text2.
    * @param deadline Time at which to bail if not yet complete.
    * @return LinkedList of Diff objects.
    */
   private LinkedList<Diff> diff_bisectSplit(String text1, String text2,
                                             int x, int y, long deadline) {
     String text1a = text1.substring(0, x);
     String text2a = text2.substring(0, y);
     String text1b = text1.substring(x);
     String text2b = text2.substring(y);
 
     // Compute both diffs serially.
     LinkedList<Diff> diffs = diff_main(text1a, text2a, false, deadline);
     LinkedList<Diff> diffsb = diff_main(text1b, text2b, false, deadline);
 
     diffs.addAll(diffsb);
     return diffs;
   }
 
   /**
    * Split two texts into a list of strings.  Reduce the texts to a string of
    * hashes where each Unicode character represents one line.
    * @param text1 First string.
    * @param text2 Second string.
    * @return An object containing the encoded text1, the encoded text2 and
    *     the List of unique strings.  The zeroth element of the List of
    *     unique strings is intentionally blank.
    */
   protected LinesToCharsResult diff_linesToChars(String text1, String text2) {
     List<String> lineArray = new ArrayList<String>();
     Map<String, Integer> lineHash = new HashMap<String, Integer>();
     // e.g. linearray[4] == "Hello\n"
     // e.g. linehash.get("Hello\n") == 4
 
     // "\x00" is a valid character, but various debuggers don't like it.
     // So we'll insert a junk entry to avoid generating a null character.
     lineArray.add("");
 
     String chars1 = diff_linesToCharsMunge(text1, lineArray, lineHash);
     String chars2 = diff_linesToCharsMunge(text2, lineArray, lineHash);
     return new LinesToCharsResult(chars1, chars2, lineArray);
   }
 
   /**
    * Split a text into a list of strings.  Reduce the texts to a string of
    * hashes where each Unicode character represents one line.
    * @param text String to encode.
    * @param lineArray List of unique strings.
    * @param lineHash Map of strings to indices.
    * @return Encoded string.
    */
   private String diff_linesToCharsMunge(String text, List<String> lineArray,
                                         Map<String, Integer> lineHash) {
     int lineStart = 0;
     int lineEnd = -1;
     String line;
     StringBuilder chars = new StringBuilder();
     // Walk the text, pulling out a substring for each line.
     // text.split('\n') would would temporarily double our memory footprint.
     // Modifying text would create many large strings to garbage collect.
     while (lineEnd < text.length() - 1) {
       lineEnd = text.indexOf('\n', lineStart);
       if (lineEnd == -1) {
         lineEnd = text.length() - 1;
       }
       line = text.substring(lineStart, lineEnd + 1);
       lineStart = lineEnd + 1;
 
       if (lineHash.containsKey(line)) {
         chars.append(String.valueOf((char) (int) lineHash.get(line)));
       } else {
         lineArray.add(line);
         lineHash.put(line, lineArray.size() - 1);
         chars.append(String.valueOf((char) (lineArray.size() - 1)));
       }
     }
     return chars.toString();
   }
 
   /**
    * Rehydrate the text in a diff from a string of line hashes to real lines of
    * text.
    * @param diffs LinkedList of Diff objects.
    * @param lineArray List of unique strings.
    */
   protected void diff_charsToLines(LinkedList<Diff> diffs,
                                   List<String> lineArray) {
     StringBuilder text;
     for (Diff diff : diffs) {
       text = new StringBuilder();
       for (int y = 0; y < diff.text.length(); y++) {
         text.append(lineArray.get(diff.text.charAt(y)));
       }
       diff.text = text.toString();
     }
   }
 
   /**
    * Determine the common prefix of two strings
    * @param text1 First string.
    * @param text2 Second string.
    * @return The number of characters common to the start of each string.
    */
   public int diff_commonPrefix(String text1, String text2) {
     // Performance analysis: http://neil.fraser.name/news/2007/10/09/
     int n = Math.min(text1.length(), text2.length());
     for (int i = 0; i < n; i++) {
       if (text1.charAt(i) != text2.charAt(i)) {
         return i;
       }
     }
     return n;
   }
 
   /**
    * Determine the common suffix of two strings
    * @param text1 First string.
    * @param text2 Second string.
    * @return The number of characters common to the end of each string.
    */
   public int diff_commonSuffix(String text1, String text2) {
     // Performance analysis: http://neil.fraser.name/news/2007/10/09/
     int text1_length = text1.length();
     int text2_length = text2.length();
     int n = Math.min(text1_length, text2_length);
     for (int i = 1; i <= n; i++) {
       if (text1.charAt(text1_length - i) != text2.charAt(text2_length - i)) {
         return i - 1;
       }
     }
     return n;
   }
 
   /**
    * Determine if the suffix of one string is the prefix of another.
    * @param text1 First string.
    * @param text2 Second string.
    * @return The number of characters common to the end of the first
    *     string and the start of the second string.
    */
   protected int diff_commonOverlap(String text1, String text2) {
     // Cache the text lengths to prevent multiple calls.
     int text1_length = text1.length();
     int text2_length = text2.length();
     // Eliminate the null case.
     if (text1_length == 0 || text2_length == 0) {
       return 0;
     }
     // Truncate the longer string.
     if (text1_length > text2_length) {
       text1 = text1.substring(text1_length - text2_length);
     } else if (text1_length < text2_length) {
       text2 = text2.substring(0, text1_length);
     }
     int text_length = Math.min(text1_length, text2_length);
     // Quick check for the worst case.
     if (text1.equals(text2)) {
       return text_length;
     }
 
     // Start by looking for a single character match
     // and increase length until no match is found.
     // Performance analysis: http://neil.fraser.name/news/2010/11/04/
     int best = 0;
     int length = 1;
     while (true) {
       String pattern = text1.substring(text_length - length);
       int found = text2.indexOf(pattern);
       if (found == -1) {
         return best;
       }
       length += found;
       if (found == 0 || text1.substring(text_length - length).equals(
           text2.substring(0, length))) {
         best = length;
         length++;
       }
     }
   }
 
   /**
    * Do the two texts share a substring which is at least half the length of
    * the longer text?
    * This speedup can produce non-minimal diffs.
    * @param text1 First string.
    * @param text2 Second string.
    * @return Five element String array, containing the prefix of text1, the
    *     suffix of text1, the prefix of text2, the suffix of text2 and the
    *     common middle.  Or null if there was no match.
    */
   protected String[] diff_halfMatch(String text1, String text2) {
     if (Diff_Timeout <= 0) {
       // Don't risk returning a non-optimal diff if we have unlimited time.
       return null;
     }
     String longtext = text1.length() > text2.length() ? text1 : text2;
     String shorttext = text1.length() > text2.length() ? text2 : text1;
     if (longtext.length() < 4 || shorttext.length() * 2 < longtext.length()) {
       return null;  // Pointless.
     }
 
     // First check if the second quarter is the seed for a half-match.
     String[] hm1 = diff_halfMatchI(longtext, shorttext,
                                    (longtext.length() + 3) / 4);
     // Check again based on the third quarter.
     String[] hm2 = diff_halfMatchI(longtext, shorttext,
                                    (longtext.length() + 1) / 2);
     String[] hm;
     if (hm1 == null && hm2 == null) {
       return null;
     } else if (hm2 == null) {
       hm = hm1;
     } else if (hm1 == null) {
       hm = hm2;
     } else {
       // Both matched.  Select the longest.
       hm = hm1[4].length() > hm2[4].length() ? hm1 : hm2;
     }
 
     // A half-match was found, sort out the return data.
     if (text1.length() > text2.length()) {
       return hm;
       //return new String[]{hm[0], hm[1], hm[2], hm[3], hm[4]};
     } else {
       return new String[]{hm[2], hm[3], hm[0], hm[1], hm[4]};
     }
   }
 
   /**
    * Does a substring of shorttext exist within longtext such that the
    * substring is at least half the length of longtext?
    * @param longtext Longer string.
    * @param shorttext Shorter string.
    * @param i Start index of quarter length substring within longtext.
    * @return Five element String array, containing the prefix of longtext, the
    *     suffix of longtext, the prefix of shorttext, the suffix of shorttext
    *     and the common middle.  Or null if there was no match.
    */
   private String[] diff_halfMatchI(String longtext, String shorttext, int i) {
     // Start with a 1/4 length substring at position i as a seed.
     String seed = longtext.substring(i, i + longtext.length() / 4);
     int j = -1;
     String best_common = "";
     String best_longtext_a = "", best_longtext_b = "";
     String best_shorttext_a = "", best_shorttext_b = "";
     while ((j = shorttext.indexOf(seed, j + 1)) != -1) {
       int prefixLength = diff_commonPrefix(longtext.substring(i),
                                            shorttext.substring(j));
       int suffixLength = diff_commonSuffix(longtext.substring(0, i),
                                            shorttext.substring(0, j));
       if (best_common.length() < suffixLength + prefixLength) {
         best_common = shorttext.substring(j - suffixLength, j)
             + shorttext.substring(j, j + prefixLength);
         best_longtext_a = longtext.substring(0, i - suffixLength);
         best_longtext_b = longtext.substring(i + prefixLength);
         best_shorttext_a = shorttext.substring(0, j - suffixLength);
         best_shorttext_b = shorttext.substring(j + prefixLength);
       }
     }
     if (best_common.length() * 2 >= longtext.length()) {
       return new String[]{best_longtext_a, best_longtext_b,
                           best_shorttext_a, best_shorttext_b, best_common};
     } else {
       return null;
     }
   }
 
   /**
    * Reduce the number of edits by eliminating semantically trivial equalities.
    * @param diffs LinkedList of Diff objects.
    */
   public void diff_cleanupSemantic(LinkedList<Diff> diffs) {
     if (diffs.isEmpty()) {
       return;
     }
     boolean changes = false;
     Stack<Diff> equalities = new Stack<Diff>();  // Stack of qualities.
     String lastequality = null; // Always equal to equalities.lastElement().text
     ListIterator<Diff> pointer = diffs.listIterator();
     // Number of characters that changed prior to the equality.
     int length_insertions1 = 0;
     int length_deletions1 = 0;
     // Number of characters that changed after the equality.
     int length_insertions2 = 0;
     int length_deletions2 = 0;
     Diff thisDiff = pointer.next();
     while (thisDiff != null) {
       if (thisDiff.operation == Operation.EQUAL) {
         // Equality found.
         equalities.push(thisDiff);
         length_insertions1 = length_insertions2;
         length_deletions1 = length_deletions2;
         length_insertions2 = 0;
         length_deletions2 = 0;
         lastequality = thisDiff.text;
       } else {
         // An insertion or deletion.
         if (thisDiff.operation == Operation.INSERT) {
           length_insertions2 += thisDiff.text.length();
         } else {
           length_deletions2 += thisDiff.text.length();
         }
         // Eliminate an equality that is smaller or equal to the edits on both
         // sides of it.
         if (lastequality != null && (lastequality.length()
             <= Math.max(length_insertions1, length_deletions1))
             && (lastequality.length()
                 <= Math.max(length_insertions2, length_deletions2))) {
           //System.out.println("Splitting: '" + lastequality + "'");
           // Walk back to offending equality.
           while (thisDiff != equalities.lastElement()) {
             thisDiff = pointer.previous();
           }
           pointer.next();
 
           // Replace equality with a delete.
           pointer.set(new Diff(Operation.DELETE, lastequality));
           // Insert a corresponding an insert.
           pointer.add(new Diff(Operation.INSERT, lastequality));
 
           equalities.pop();  // Throw away the equality we just deleted.
           if (!equalities.empty()) {
             // Throw away the previous equality (it needs to be reevaluated).
             equalities.pop();
           }
           if (equalities.empty()) {
             // There are no previous equalities, walk back to the start.
             while (pointer.hasPrevious()) {
               pointer.previous();
             }
           } else {
             // There is a safe equality we can fall back to.
             thisDiff = equalities.lastElement();
             while (thisDiff != pointer.previous()) {
               // Intentionally empty loop.
             }
           }
 
           length_insertions1 = 0;  // Reset the counters.
           length_insertions2 = 0;
           length_deletions1 = 0;
           length_deletions2 = 0;
           lastequality = null;
           changes = true;
         }
       }
       thisDiff = pointer.hasNext() ? pointer.next() : null;
     }
 
     // Normalize the diff.
     if (changes) {
       diff_cleanupMerge(diffs);
     }
     diff_cleanupSemanticLossless(diffs);
 
     // Find any overlaps between deletions and insertions.
     // e.g: <del>abcxxx</del><ins>xxxdef</ins>
     //   -> <del>abc</del>xxx<ins>def</ins>
     // e.g: <del>xxxabc</del><ins>defxxx</ins>
     //   -> <ins>def</ins>xxx<del>abc</del>
     // Only extract an overlap if it is as big as the edit ahead or behind it.
     pointer = diffs.listIterator();
     Diff prevDiff = null;
     thisDiff = null;
     if (pointer.hasNext()) {
       prevDiff = pointer.next();
       if (pointer.hasNext()) {
         thisDiff = pointer.next();
       }
     }
     while (thisDiff != null) {
       if (prevDiff.operation == Operation.DELETE &&
           thisDiff.operation == Operation.INSERT) {
         String deletion = prevDiff.text;
         String insertion = thisDiff.text;
         int overlap_length1 = this.diff_commonOverlap(deletion, insertion);
         int overlap_length2 = this.diff_commonOverlap(insertion, deletion);
         if (overlap_length1 >= overlap_length2) {
           if (overlap_length1 >= deletion.length() / 2.0 ||
               overlap_length1 >= insertion.length() / 2.0) {
             // Overlap found. Insert an equality and trim the surrounding edits.
             pointer.previous();
             pointer.add(new Diff(Operation.EQUAL,
                                  insertion.substring(0, overlap_length1)));
             prevDiff.text =
                 deletion.substring(0, deletion.length() - overlap_length1);
             thisDiff.text = insertion.substring(overlap_length1);
             // pointer.add inserts the element before the cursor, so there is
             // no need to step past the new element.
           }
         } else {
           if (overlap_length2 >= deletion.length() / 2.0 ||
               overlap_length2 >= insertion.length() / 2.0) {
             // Reverse overlap found.
             // Insert an equality and swap and trim the surrounding edits.
             pointer.previous();
             pointer.add(new Diff(Operation.EQUAL,
                                  deletion.substring(0, overlap_length2)));
             prevDiff.operation = Operation.INSERT;
             prevDiff.text =
               insertion.substring(0, insertion.length() - overlap_length2);
             thisDiff.operation = Operation.DELETE;
             thisDiff.text = deletion.substring(overlap_length2);
             // pointer.add inserts the element before the cursor, so there is
             // no need to step past the new element.
           }
         }
         thisDiff = pointer.hasNext() ? pointer.next() : null;
       }
       prevDiff = thisDiff;
       thisDiff = pointer.hasNext() ? pointer.next() : null;
     }
   }
 
   /**
    * Look for single edits surrounded on both sides by equalities
    * which can be shifted sideways to align the edit to a word boundary.
    * e.g: The c<ins>at c</ins>ame. -> The <ins>cat </ins>came.
    * @param diffs LinkedList of Diff objects.
    */
   public void diff_cleanupSemanticLossless(LinkedList<Diff> diffs) {
     String equality1, edit, equality2;
     String commonString;
     int commonOffset;
     int score, bestScore;
     String bestEquality1, bestEdit, bestEquality2;
     // Create a new iterator at the start.
     ListIterator<Diff> pointer = diffs.listIterator();
     Diff prevDiff = pointer.hasNext() ? pointer.next() : null;
     Diff thisDiff = pointer.hasNext() ? pointer.next() : null;
     Diff nextDiff = pointer.hasNext() ? pointer.next() : null;
     // Intentionally ignore the first and last element (don't need checking).
     while (nextDiff != null) {
       if (prevDiff.operation == Operation.EQUAL &&
           nextDiff.operation == Operation.EQUAL) {
         // This is a single edit surrounded by equalities.
         equality1 = prevDiff.text;
         edit = thisDiff.text;
         equality2 = nextDiff.text;
 
         // First, shift the edit as far left as possible.
         commonOffset = diff_commonSuffix(equality1, edit);
         if (commonOffset != 0) {
           commonString = edit.substring(edit.length() - commonOffset);
           equality1 = equality1.substring(0, equality1.length() - commonOffset);
           edit = commonString + edit.substring(0, edit.length() - commonOffset);
           equality2 = commonString + equality2;
         }
 
         // Second, step character by character right, looking for the best fit.
         bestEquality1 = equality1;
         bestEdit = edit;
         bestEquality2 = equality2;
         bestScore = diff_cleanupSemanticScore(equality1, edit)
             + diff_cleanupSemanticScore(edit, equality2);
         while (edit.length() != 0 && equality2.length() != 0
             && edit.charAt(0) == equality2.charAt(0)) {
           equality1 += edit.charAt(0);
           edit = edit.substring(1) + equality2.charAt(0);
           equality2 = equality2.substring(1);
           score = diff_cleanupSemanticScore(equality1, edit)
               + diff_cleanupSemanticScore(edit, equality2);
           // The >= encourages trailing rather than leading whitespace on edits.
           if (score >= bestScore) {
             bestScore = score;
             bestEquality1 = equality1;
             bestEdit = edit;
             bestEquality2 = equality2;
           }
         }
 
         if (!prevDiff.text.equals(bestEquality1)) {
           // We have an improvement, save it back to the diff.
           if (bestEquality1.length() != 0) {
             prevDiff.text = bestEquality1;
           } else {
             pointer.previous(); // Walk past nextDiff.
             pointer.previous(); // Walk past thisDiff.
             pointer.previous(); // Walk past prevDiff.
             pointer.remove(); // Delete prevDiff.
             pointer.next(); // Walk past thisDiff.
             pointer.next(); // Walk past nextDiff.
           }
           thisDiff.text = bestEdit;
           if (bestEquality2.length() != 0) {
             nextDiff.text = bestEquality2;
           } else {
             pointer.remove(); // Delete nextDiff.
             nextDiff = thisDiff;
             thisDiff = prevDiff;
           }
         }
       }
       prevDiff = thisDiff;
       thisDiff = nextDiff;
       nextDiff = pointer.hasNext() ? pointer.next() : null;
     }
   }
 
   /**
    * Given two strings, compute a score representing whether the internal
    * boundary falls on logical boundaries.
    * Scores range from 6 (best) to 0 (worst).
    * @param one First string.
    * @param two Second string.
    * @return The score.
    */
   private int diff_cleanupSemanticScore(String one, String two) {
     if (one.length() == 0 || two.length() == 0) {
       // Edges are the best.
       return 6;
     }
 
     // Each port of this function behaves slightly differently due to
     // subtle differences in each language's definition of things like
     // 'whitespace'.  Since this function's purpose is largely cosmetic,
     // the choice has been made to use each language's native features
     // rather than force total conformity.
     char char1 = one.charAt(one.length() - 1);
     char char2 = two.charAt(0);
     boolean nonAlphaNumeric1 = !Character.isLetterOrDigit(char1);
     boolean nonAlphaNumeric2 = !Character.isLetterOrDigit(char2);
     boolean whitespace1 = nonAlphaNumeric1 && Character.isWhitespace(char1);
     boolean whitespace2 = nonAlphaNumeric2 && Character.isWhitespace(char2);
     boolean lineBreak1 = whitespace1
         && Character.getType(char1) == Character.CONTROL;
     boolean lineBreak2 = whitespace2
         && Character.getType(char2) == Character.CONTROL;
     boolean blankLine1 = lineBreak1 && BLANKLINEEND.matcher(one).find();
     boolean blankLine2 = lineBreak2 && BLANKLINESTART.matcher(two).find();
 
     if (blankLine1 || blankLine2) {
       // Five points for blank lines.
       return 5;
     } else if (lineBreak1 || lineBreak2) {
       // Four points for line breaks.
       return 4;
     } else if (nonAlphaNumeric1 && !whitespace1 && whitespace2) {
       // Three points for end of sentences.
       return 3;
     } else if (whitespace1 || whitespace2) {
       // Two points for whitespace.
       return 2;
     } else if (nonAlphaNumeric1 || nonAlphaNumeric2) {
       // One point for non-alphanumeric.
       return 1;
     }
     return 0;
   }
 
   // Define some regex patterns for matching boundaries.
   private Pattern BLANKLINEEND
       = Pattern.compile("\\n\\r?\\n\\Z", Pattern.DOTALL);
   private Pattern BLANKLINESTART
       = Pattern.compile("\\A\\r?\\n\\r?\\n", Pattern.DOTALL);
 
   /**
    * Reduce the number of edits by eliminating operationally trivial equalities.
    * @param diffs LinkedList of Diff objects.
    */
   public void diff_cleanupEfficiency(LinkedList<Diff> diffs) {
     if (diffs.isEmpty()) {
       return;
     }
     boolean changes = false;
     Stack<Diff> equalities = new Stack<Diff>();  // Stack of equalities.
     String lastequality = null; // Always equal to equalities.lastElement().text
     ListIterator<Diff> pointer = diffs.listIterator();
     // Is there an insertion operation before the last equality.
     boolean pre_ins = false;
     // Is there a deletion operation before the last equality.
     boolean pre_del = false;
     // Is there an insertion operation after the last equality.
     boolean post_ins = false;
     // Is there a deletion operation after the last equality.
     boolean post_del = false;
     Diff thisDiff = pointer.next();
     Diff safeDiff = thisDiff;  // The last Diff that is known to be unsplitable.
     while (thisDiff != null) {
       if (thisDiff.operation == Operation.EQUAL) {
         // Equality found.
         if (thisDiff.text.length() < Diff_EditCost && (post_ins || post_del)) {
           // Candidate found.
           equalities.push(thisDiff);
           pre_ins = post_ins;
           pre_del = post_del;
           lastequality = thisDiff.text;
         } else {
           // Not a candidate, and can never become one.
           equalities.clear();
           lastequality = null;
           safeDiff = thisDiff;
         }
         post_ins = post_del = false;
       } else {
         // An insertion or deletion.
         if (thisDiff.operation == Operation.DELETE) {
           post_del = true;
         } else {
           post_ins = true;
         }
         /*
          * Five types to be split:
          * <ins>A</ins><del>B</del>XY<ins>C</ins><del>D</del>
          * <ins>A</ins>X<ins>C</ins><del>D</del>
          * <ins>A</ins><del>B</del>X<ins>C</ins>
          * <ins>A</del>X<ins>C</ins><del>D</del>
          * <ins>A</ins><del>B</del>X<del>C</del>
          */
         if (lastequality != null
             && ((pre_ins && pre_del && post_ins && post_del)
                 || ((lastequality.length() < Diff_EditCost / 2)
                     && ((pre_ins ? 1 : 0) + (pre_del ? 1 : 0)
                         + (post_ins ? 1 : 0) + (post_del ? 1 : 0)) == 3))) {
           //System.out.println("Splitting: '" + lastequality + "'");
           // Walk back to offending equality.
           while (thisDiff != equalities.lastElement()) {
             thisDiff = pointer.previous();
           }
           pointer.next();
 
           // Replace equality with a delete.
           pointer.set(new Diff(Operation.DELETE, lastequality));
           // Insert a corresponding an insert.
           pointer.add(thisDiff = new Diff(Operation.INSERT, lastequality));
 
           equalities.pop();  // Throw away the equality we just deleted.
           lastequality = null;
           if (pre_ins && pre_del) {
             // No changes made which could affect previous entry, keep going.
             post_ins = post_del = true;
             equalities.clear();
             safeDiff = thisDiff;
           } else {
             if (!equalities.empty()) {
               // Throw away the previous equality (it needs to be reevaluated).
               equalities.pop();
             }
             if (equalities.empty()) {
               // There are no previous questionable equalities,
               // walk back to the last known safe diff.
               thisDiff = safeDiff;
             } else {
               // There is an equality we can fall back to.
               thisDiff = equalities.lastElement();
             }
             while (thisDiff != pointer.previous()) {
               // Intentionally empty loop.
             }
             post_ins = post_del = false;
           }
 
           changes = true;
         }
       }
       thisDiff = pointer.hasNext() ? pointer.next() : null;
     }
 
     if (changes) {
       diff_cleanupMerge(diffs);
     }
   }
 
   /**
    * Reorder and merge like edit sections.  Merge equalities.
    * Any edit section can move as long as it doesn't cross an equality.
    * @param diffs LinkedList of Diff objects.
    */
   public void diff_cleanupMerge(LinkedList<Diff> diffs) {
     diffs.add(new Diff(Operation.EQUAL, ""));  // Add a dummy entry at the end.
     ListIterator<Diff> pointer = diffs.listIterator();
     int count_delete = 0;
     int count_insert = 0;
     String text_delete = "";
     String text_insert = "";
     Diff thisDiff = pointer.next();
     Diff prevEqual = null;
     int commonlength;
     while (thisDiff != null) {
       switch (thisDiff.operation) {
       case INSERT:
         count_insert++;
         text_insert += thisDiff.text;
         prevEqual = null;
         break;
       case DELETE:
         count_delete++;
         text_delete += thisDiff.text;
         prevEqual = null;
         break;
       case EQUAL:
         if (count_delete + count_insert > 1) {
           boolean both_types = count_delete != 0 && count_insert != 0;
           // Delete the offending records.
           pointer.previous();  // Reverse direction.
           while (count_delete-- > 0) {
             pointer.previous();
             pointer.remove();
           }
           while (count_insert-- > 0) {
             pointer.previous();
             pointer.remove();
           }
           if (both_types) {
             // Factor out any common prefixies.
             commonlength = diff_commonPrefix(text_insert, text_delete);
             if (commonlength != 0) {
               if (pointer.hasPrevious()) {
                 thisDiff = pointer.previous();
                 assert thisDiff.operation == Operation.EQUAL
                        : "Previous diff should have been an equality.";
                 thisDiff.text += text_insert.substring(0, commonlength);
                 pointer.next();
               } else {
                 pointer.add(new Diff(Operation.EQUAL,
                     text_insert.substring(0, commonlength)));
               }
               text_insert = text_insert.substring(commonlength);
               text_delete = text_delete.substring(commonlength);
             }
             // Factor out any common suffixies.
             commonlength = diff_commonSuffix(text_insert, text_delete);
             if (commonlength != 0) {
               thisDiff = pointer.next();
               thisDiff.text = text_insert.substring(text_insert.length()
                   - commonlength) + thisDiff.text;
               text_insert = text_insert.substring(0, text_insert.length()
                   - commonlength);
               text_delete = text_delete.substring(0, text_delete.length()
                   - commonlength);
               pointer.previous();
             }
           }
           // Insert the merged records.
           if (text_delete.length() != 0) {
             pointer.add(new Diff(Operation.DELETE, text_delete));
           }
           if (text_insert.length() != 0) {
             pointer.add(new Diff(Operation.INSERT, text_insert));
           }
           // Step forward to the equality.
           thisDiff = pointer.hasNext() ? pointer.next() : null;
         } else if (prevEqual != null) {
           // Merge this equality with the previous one.
           prevEqual.text += thisDiff.text;
           pointer.remove();
           thisDiff = pointer.previous();
           pointer.next();  // Forward direction
         }
         count_insert = 0;
         count_delete = 0;
         text_delete = "";
         text_insert = "";
         prevEqual = thisDiff;
         break;
       }
       thisDiff = pointer.hasNext() ? pointer.next() : null;
     }
     if (diffs.getLast().text.length() == 0) {
       diffs.removeLast();  // Remove the dummy entry at the end.
     }
 
     /*
      * Second pass: look for single edits surrounded on both sides by equalities
      * which can be shifted sideways to eliminate an equality.
      * e.g: A<ins>BA</ins>C -> <ins>AB</ins>AC
      */
     boolean changes = false;
     // Create a new iterator at the start.
     // (As opposed to walking the current one back.)
     pointer = diffs.listIterator();
     Diff prevDiff = pointer.hasNext() ? pointer.next() : null;
     thisDiff = pointer.hasNext() ? pointer.next() : null;
     Diff nextDiff = pointer.hasNext() ? pointer.next() : null;
     // Intentionally ignore the first and last element (don't need checking).
     while (nextDiff != null) {
       if (prevDiff.operation == Operation.EQUAL &&
           nextDiff.operation == Operation.EQUAL) {
         // This is a single edit surrounded by equalities.
         if (thisDiff.text.endsWith(prevDiff.text)) {
           // Shift the edit over the previous equality.
           thisDiff.text = prevDiff.text
               + thisDiff.text.substring(0, thisDiff.text.length()
                                            - prevDiff.text.length());
           nextDiff.text = prevDiff.text + nextDiff.text;
           pointer.previous(); // Walk past nextDiff.
           pointer.previous(); // Walk past thisDiff.
           pointer.previous(); // Walk past prevDiff.
           pointer.remove(); // Delete prevDiff.
           pointer.next(); // Walk past thisDiff.
           thisDiff = pointer.next(); // Walk past nextDiff.
           nextDiff = pointer.hasNext() ? pointer.next() : null;
           changes = true;
         } else if (thisDiff.text.startsWith(nextDiff.text)) {
           // Shift the edit over the next equality.
           prevDiff.text += nextDiff.text;
           thisDiff.text = thisDiff.text.substring(nextDiff.text.length())
               + nextDiff.text;
           pointer.remove(); // Delete nextDiff.
           nextDiff = pointer.hasNext() ? pointer.next() : null;
           changes = true;
         }
       }
       prevDiff = thisDiff;
       thisDiff = nextDiff;
       nextDiff = pointer.hasNext() ? pointer.next() : null;
     }
     // If shifts were made, the diff needs reordering and another shift sweep.
     if (changes) {
       diff_cleanupMerge(diffs);
     }
   }
 
   /**
    * loc is a location in text1, compute and return the equivalent location in
    * text2.
    * e.g. "The cat" vs "The big cat", 1->1, 5->8
    * @param diffs LinkedList of Diff objects.
    * @param loc Location within text1.
    * @return Location within text2.
    */
   public int diff_xIndex(LinkedList<Diff> diffs, int loc) {
     int chars1 = 0;
     int chars2 = 0;
     int last_chars1 = 0;
     int last_chars2 = 0;
     Diff lastDiff = null;
     for (Diff aDiff : diffs) {
       if (aDiff.operation != Operation.INSERT) {
         // Equality or deletion.
         chars1 += aDiff.text.length();
       }
       if (aDiff.operation != Operation.DELETE) {
         // Equality or insertion.
         chars2 += aDiff.text.length();
       }
       if (chars1 > loc) {
         // Overshot the location.
         lastDiff = aDiff;
         break;
       }
       last_chars1 = chars1;
       last_chars2 = chars2;
     }
     if (lastDiff != null && lastDiff.operation == Operation.DELETE) {
       // The location was deleted.
       return last_chars2;
     }
     // Add the remaining character length.
     return last_chars2 + (loc - last_chars1);
   }
 
   /**
    * Convert a Diff list into a pretty HTML report.
    * @param diffs LinkedList of Diff objects.
    * @return HTML representation.
    */
   public String diff_prettyHtml(LinkedList<Diff> diffs) {
     StringBuilder html = new StringBuilder();
     for (Diff aDiff : diffs) {
       String text = aDiff.text.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 LinkedList of Diff objects.
    * @return Source text.
    */
   public String diff_text1(LinkedList<Diff> diffs) {
     StringBuilder text = new StringBuilder();
     for (Diff aDiff : diffs) {
       if (aDiff.operation != Operation.INSERT) {
         text.append(aDiff.text);
       }
     }
     return text.toString();
   }
 
   /**
    * Compute and return the destination text (all equalities and insertions).
    * @param diffs LinkedList of Diff objects.
    * @return Destination text.
    */
   public String diff_text2(LinkedList<Diff> diffs) {
     StringBuilder text = new StringBuilder();
     for (Diff aDiff : diffs) {
       if (aDiff.operation != Operation.DELETE) {
         text.append(aDiff.text);
       }
     }
     return text.toString();
   }
 
   /**
    * Compute the Levenshtein distance; the number of inserted, deleted or
    * substituted characters.
    * @param diffs LinkedList of Diff objects.
    * @return Number of changes.
    */
   public int diff_levenshtein(LinkedList<Diff> diffs) {
     int levenshtein = 0;
     int insertions = 0;
     int deletions = 0;
     for (Diff aDiff : diffs) {
       switch (aDiff.operation) {
       case INSERT:
         insertions += aDiff.text.length();
         break;
       case DELETE:
         deletions += aDiff.text.length();
         break;
       case EQUAL:
         // A deletion and an insertion is one substitution.
         levenshtein += Math.max(insertions, deletions);
         insertions = 0;
         deletions = 0;
         break;
       }
     }
     levenshtein += Math.max(insertions, deletions);
     return levenshtein;
   }
 
   /**
    * Crush the diff into an encoded string which describes the operations
    * required to transform text1 into text2.
    * E.g. =3\t-2\t+ing  -> Keep 3 chars, delete 2 chars, insert 'ing'.
    * Operations are tab-separated.  Inserted text is escaped using %xx notation.
    * @param diffs Array of Diff objects.
    * @return Delta text.
    */
   public String diff_toDelta(LinkedList<Diff> diffs) {
     StringBuilder text = new StringBuilder();
     for (Diff aDiff : diffs) {
       switch (aDiff.operation) {
       case INSERT:
         try {
           text.append("+").append(URLEncoder.encode(aDiff.text, "UTF-8")
                                             .replace('+', ' ')).append("\t");
         } catch (UnsupportedEncodingException e) {
           // Not likely on modern system.
           throw new Error("This system does not support UTF-8.", e);
         }
         break;
       case DELETE:
         text.append("-").append(aDiff.text.length()).append("\t");
         break;
       case EQUAL:
         text.append("=").append(aDiff.text.length()).append("\t");
         break;
       }
     }
     String delta = text.toString();
     if (delta.length() != 0) {
       // Strip off trailing tab character.
       delta = delta.substring(0, delta.length() - 1);
       delta = unescapeForEncodeUriCompatability(delta);
     }
     return delta;
   }
 
   /**
    * Given the original text1, and an encoded string which describes the
    * operations required to transform text1 into text2, compute the full diff.
    * @param text1 Source string for the diff.
    * @param delta Delta text.
    * @return Array of Diff objects or null if invalid.
    * @throws IllegalArgumentException If invalid input.
    */
   public LinkedList<Diff> diff_fromDelta(String text1, String delta)
       throws IllegalArgumentException {
     LinkedList<Diff> diffs = new LinkedList<Diff>();
     int pointer = 0;  // Cursor in text1
     String[] tokens = delta.split("\t");
     for (String token : tokens) {
       if (token.length() == 0) {
         // Blank tokens are ok (from a trailing \t).
         continue;
       }
       // Each token begins with a one character parameter which specifies the
       // operation of this token (delete, insert, equality).
       String param = token.substring(1);
       switch (token.charAt(0)) {
       case '+':
         // decode would change all "+" to " "
         param = param.replace("+", "%2B");
         try {
           param = URLDecoder.decode(param, "UTF-8");
         } catch (UnsupportedEncodingException e) {
           // Not likely on modern system.
           throw new Error("This system does not support UTF-8.", e);
         } catch (IllegalArgumentException e) {
           // Malformed URI sequence.
           throw new IllegalArgumentException(
               "Illegal escape in diff_fromDelta: " + param, e);
         }
         diffs.add(new Diff(Operation.INSERT, param));
         break;
       case '-':
         // Fall through.
       case '=':
         int n;
         try {
           n = Integer.parseInt(param);
         } catch (NumberFormatException e) {
           throw new IllegalArgumentException(
               "Invalid number in diff_fromDelta: " + param, e);
         }
         if (n < 0) {
           throw new IllegalArgumentException(
               "Negative number in diff_fromDelta: " + param);
         }
         String text;
         try {
           text = text1.substring(pointer, pointer += n);
         } catch (StringIndexOutOfBoundsException e) {
           throw new IllegalArgumentException("Delta length (" + pointer
               + ") larger than source text length (" + text1.length()
               + ").", e);
         }
         if (token.charAt(0) == '=') {
           diffs.add(new Diff(Operation.EQUAL, text));
         } else {
           diffs.add(new Diff(Operation.DELETE, text));
         }
         break;
       default:
         // Anything else is an error.
         throw new IllegalArgumentException(
             "Invalid diff operation in diff_fromDelta: " + token.charAt(0));
       }
     }
     if (pointer != text1.length()) {
       throw new IllegalArgumentException("Delta length (" + pointer
           + ") smaller than source text length (" + text1.length() + ").");
     }
     return diffs;
   }
 
 
   //  MATCH FUNCTIONS
 
 
   /**
    * Locate the best instance of 'pattern' in 'text' near 'loc'.
    * Returns -1 if no match found.
    * @param text The text to search.
    * @param pattern The pattern to search for.
    * @param loc The location to search around.
    * @return Best match index or -1.
    */
   public int match_main(String text, String pattern, int loc) {
     // Check for null inputs.
     if (text == null || pattern == null) {
       throw new IllegalArgumentException("Null inputs. (match_main)");
     }
 
     loc = Math.max(0, Math.min(loc, text.length()));
     if (text.equals(pattern)) {
       // Shortcut (potentially not guaranteed by the algorithm)
       return 0;
     } else if (text.length() == 0) {
       // Nothing to match.
       return -1;
     } else if (loc + pattern.length() <= text.length()
         && text.substring(loc, loc + pattern.length()).equals(pattern)) {
       // Perfect match at the perfect spot!  (Includes case of null pattern)
       return loc;
     } else {
       // Do a fuzzy compare.
       return match_bitap(text, pattern, loc);
     }
   }
 
   /**
    * Locate the best instance of 'pattern' in 'text' near 'loc' using the
    * Bitap algorithm.  Returns -1 if no match found.
    * @param text The text to search.
    * @param pattern The pattern to search for.
    * @param loc The location to search around.
    * @return Best match index or -1.
    */
   protected int match_bitap(String text, String pattern, int loc) {
     assert (Match_MaxBits == 0 || pattern.length() <= Match_MaxBits)
         : "Pattern too long for this application.";
 
     // Initialise the alphabet.
     Map<Character, Integer> s = match_alphabet(pattern);
 
     // Highest score beyond which we give up.
     double score_threshold = Match_Threshold;
     // Is there a nearby exact match? (speedup)
     int best_loc = text.indexOf(pattern, loc);
     if (best_loc != -1) {
       score_threshold = Math.min(match_bitapScore(0, best_loc, loc, pattern),
           score_threshold);
       // What about in the other direction? (speedup)
       best_loc = text.lastIndexOf(pattern, loc + pattern.length());
       if (best_loc != -1) {
         score_threshold = Math.min(match_bitapScore(0, best_loc, loc, pattern),
             score_threshold);
       }
     }
 
     // Initialise the bit arrays.
     int matchmask = 1 << (pattern.length() - 1);
     best_loc = -1;
 
     int bin_min, bin_mid;
     int bin_max = pattern.length() + text.length();
     // Empty initialization added to appease Java compiler.
     int[] last_rd = new int[0];
     for (int d = 0; d < pattern.length(); d++) {
       // Scan for the best match; each iteration allows for one more error.
       // Run a binary search to determine how far from 'loc' we can stray at
       // this error level.
       bin_min = 0;
       bin_mid = bin_max;
       while (bin_min < bin_mid) {
         if (match_bitapScore(d, loc + bin_mid, loc, pattern)
             <= score_threshold) {
           bin_min = bin_mid;
         } else {
           bin_max = bin_mid;
         }
         bin_mid = (bin_max - bin_min) / 2 + bin_min;
       }
       // Use the result from this iteration as the maximum for the next.
       bin_max = bin_mid;
       int start = Math.max(1, loc - bin_mid + 1);
       int finish = Math.min(loc + bin_mid, text.length()) + pattern.length();
 
       int[] rd = new int[finish + 2];
       rd[finish + 1] = (1 << d) - 1;
       for (int j = finish; j >= start; j--) {
         int charMatch;
         if (text.length() <= j - 1 || !s.containsKey(text.charAt(j - 1))) {
           // Out of range.
           charMatch = 0;
         } else {
           charMatch = s.get(text.charAt(j - 1));
         }
         if (d == 0) {
           // First pass: exact match.
           rd[j] = ((rd[j + 1] << 1) | 1) & charMatch;
         } else {
           // Subsequent passes: fuzzy match.
           rd[j] = (((rd[j + 1] << 1) | 1) & charMatch)
               | (((last_rd[j + 1] | last_rd[j]) << 1) | 1) | last_rd[j + 1];
         }
         if ((rd[j] & matchmask) != 0) {
           double score = match_bitapScore(d, j - 1, loc, pattern);
           // This match will almost certainly be better than any existing
           // match.  But check anyway.
           if (score <= score_threshold) {
             // Told you so.
             score_threshold = score;
             best_loc = j - 1;
             if (best_loc > loc) {
               // When passing loc, don't exceed our current distance from loc.
               start = Math.max(1, 2 * loc - best_loc);
             } else {
               // Already passed loc, downhill from here on in.
               break;
             }
           }
         }
       }
       if (match_bitapScore(d + 1, loc, loc, pattern) > score_threshold) {
         // No hope for a (better) match at greater error levels.
         break;
       }
       last_rd = rd;
     }
     return best_loc;
   }
 
   /**
    * Compute and return the score for a match with e errors and x location.
    * @param e Number of errors in match.
    * @param x Location of match.
    * @param loc Expected location of match.
    * @param pattern Pattern being sought.
    * @return Overall score for match (0.0 = good, 1.0 = bad).
    */
   private double match_bitapScore(int e, int x, int loc, String pattern) {
     float accuracy = (float) e / pattern.length();
     int proximity = Math.abs(loc - x);
     if (Match_Distance == 0) {
       // Dodge divide by zero error.
       return proximity == 0 ? accuracy : 1.0;
     }
     return accuracy + (proximity / (float) Match_Distance);
   }
 
   /**
    * Initialise the alphabet for the Bitap algorithm.
    * @param pattern The text to encode.
    * @return Hash of character locations.
    */
   protected Map<Character, Integer> match_alphabet(String pattern) {
     Map<Character, Integer> s = new HashMap<Character, Integer>();
     char[] char_pattern = pattern.toCharArray();
     for (char c : char_pattern) {
       s.put(c, 0);
     }
     int i = 0;
     for (char c : char_pattern) {
       s.put(c, s.get(c) | (1 << (pattern.length() - i - 1)));
       i++;
     }
     return s;
   }
 
 
   //  PATCH FUNCTIONS
 
 
   /**
    * Increase the context until it is unique,
    * but don't let the pattern expand beyond Match_MaxBits.
    * @param patch The patch to grow.
    * @param text Source text.
    */
   protected void patch_addContext(Patch patch, String text) {
     if (text.length() == 0) {
       return;
     }
     String pattern = text.substring(patch.start2, patch.start2 + patch.length1);
     int padding = 0;
 
     // Look for the first and last matches of pattern in text.  If two different
     // matches are found, increase the pattern length.
     while (text.indexOf(pattern) != text.lastIndexOf(pattern)
         && pattern.length() < Match_MaxBits - Patch_Margin - Patch_Margin) {
       padding += Patch_Margin;
       pattern = text.substring(Math.max(0, patch.start2 - padding),
           Math.min(text.length(), patch.start2 + patch.length1 + padding));
     }
     // Add one chunk for good luck.
     padding += Patch_Margin;
 
     // Add the prefix.
     String prefix = text.substring(Math.max(0, patch.start2 - padding),
         patch.start2);
     if (prefix.length() != 0) {
       patch.diffs.addFirst(new Diff(Operation.EQUAL, prefix));
     }
     // Add the suffix.
     String suffix = text.substring(patch.start2 + patch.length1,
         Math.min(text.length(), patch.start2 + patch.length1 + padding));
     if (suffix.length() != 0) {
       patch.diffs.addLast(new Diff(Operation.EQUAL, suffix));
     }
 
     // Roll back the start points.
     patch.start1 -= prefix.length();
     patch.start2 -= prefix.length();
     // Extend the lengths.
     patch.length1 += prefix.length() + suffix.length();
     patch.length2 += prefix.length() + suffix.length();
   }
 
   /**
    * Compute a list of patches to turn text1 into text2.
    * A set of diffs will be computed.
    * @param text1 Old text.
    * @param text2 New text.
    * @return LinkedList of Patch objects.
    */
   public LinkedList<Patch> patch_make(String text1, String text2) {
     if (text1 == null || text2 == null) {
       throw new IllegalArgumentException("Null inputs. (patch_make)");
     }
     // No diffs provided, compute our own.
     LinkedList<Diff> diffs = diff_main(text1, text2, true);
     if (diffs.size() > 2) {
       diff_cleanupSemantic(diffs);
       diff_cleanupEfficiency(diffs);
     }
     return patch_make(text1, diffs);
   }
 
   /**
    * Compute a list of patches to turn text1 into text2.
    * text1 will be derived from the provided diffs.
    * @param diffs Array of Diff objects for text1 to text2.
    * @return LinkedList of Patch objects.
    */
   public LinkedList<Patch> patch_make(LinkedList<Diff> diffs) {
     if (diffs == null) {
       throw new IllegalArgumentException("Null inputs. (patch_make)");
     }
     // No origin string provided, compute our own.
     String text1 = diff_text1(diffs);
     return patch_make(text1, diffs);
   }
 
   /**
    * Compute a list of patches to turn text1 into text2.
    * text2 is ignored, diffs are the delta between text1 and text2.
    * @param text1 Old text
    * @param text2 Ignored.
    * @param diffs Array of Diff objects for text1 to text2.
    * @return LinkedList of Patch objects.
    * @deprecated Prefer patch_make(String text1, LinkedList<Diff> diffs).
    */
   public LinkedList<Patch> patch_make(String text1, String text2,
       LinkedList<Diff> diffs) {
     return patch_make(text1, diffs);
   }
 
   /**
    * Compute a list of patches to turn text1 into text2.
    * text2 is not provided, diffs are the delta between text1 and text2.
    * @param text1 Old text.
    * @param diffs Array of Diff objects for text1 to text2.
    * @return LinkedList of Patch objects.
    */
   public LinkedList<Patch> patch_make(String text1, LinkedList<Diff> diffs) {
     if (text1 == null || diffs == null) {
       throw new IllegalArgumentException("Null inputs. (patch_make)");
     }
 
     LinkedList<Patch> patches = new LinkedList<Patch>();
     if (diffs.isEmpty()) {
       return patches;  // Get rid of the null case.
     }
     Patch patch = new Patch();
     int char_count1 = 0;  // Number of characters into the text1 string.
     int char_count2 = 0;  // Number of characters into the text2 string.
     // Start with text1 (prepatch_text) and apply the diffs until we arrive at
     // text2 (postpatch_text). We recreate the patches one by one to determine
     // context info.
     String prepatch_text = text1;
     String postpatch_text = text1;
     for (Diff aDiff : diffs) {
       if (patch.diffs.isEmpty() && aDiff.operation != Operation.EQUAL) {
         // A new patch starts here.
         patch.start1 = char_count1;
         patch.start2 = char_count2;
       }
 
       switch (aDiff.operation) {
       case INSERT:
         patch.diffs.add(aDiff);
         patch.length2 += aDiff.text.length();
         postpatch_text = postpatch_text.substring(0, char_count2)
             + aDiff.text + postpatch_text.substring(char_count2);
         break;
       case DELETE:
         patch.length1 += aDiff.text.length();
         patch.diffs.add(aDiff);
         postpatch_text = postpatch_text.substring(0, char_count2)
             + postpatch_text.substring(char_count2 + aDiff.text.length());
         break;
       case EQUAL:
         if (aDiff.text.length() <= 2 * Patch_Margin
             && !patch.diffs.isEmpty() && aDiff != diffs.getLast()) {
           // Small equality inside a patch.
           patch.diffs.add(aDiff);
           patch.length1 += aDiff.text.length();
           patch.length2 += aDiff.text.length();
         }
 
         if (aDiff.text.length() >= 2 * Patch_Margin) {
           // Time for a new patch.
           if (!patch.diffs.isEmpty()) {
             patch_addContext(patch, prepatch_text);
             patches.add(patch);
             patch = new Patch();
             // Unlike Unidiff, our patch lists have a rolling context.
             // http://code.google.com/p/google-diff-match-patch/wiki/Unidiff
             // Update prepatch text & pos to reflect the application of the
             // just completed patch.
             prepatch_text = postpatch_text;
             char_count1 = char_count2;
           }
         }
         break;
       }
 
       // Update the current character count.
       if (aDiff.operation != Operation.INSERT) {
         char_count1 += aDiff.text.length();
       }
       if (aDiff.operation != Operation.DELETE) {
         char_count2 += aDiff.text.length();
       }
     }
     // Pick up the leftover patch if not empty.
     if (!patch.diffs.isEmpty()) {
       patch_addContext(patch, prepatch_text);
       patches.add(patch);
     }
 
     return patches;
   }
 
   /**
    * Given an array of patches, return another array that is identical.
    * @param patches Array of Patch objects.
    * @return Array of Patch objects.
    */
   public LinkedList<Patch> patch_deepCopy(LinkedList<Patch> patches) {
     LinkedList<Patch> patchesCopy = new LinkedList<Patch>();
     for (Patch aPatch : patches) {
       Patch patchCopy = new Patch();
       for (Diff aDiff : aPatch.diffs) {
         Diff diffCopy = new Diff(aDiff.operation, aDiff.text);
         patchCopy.diffs.add(diffCopy);
       }
       patchCopy.start1 = aPatch.start1;
       patchCopy.start2 = aPatch.start2;
       patchCopy.length1 = aPatch.length1;
       patchCopy.length2 = aPatch.length2;
       patchesCopy.add(patchCopy);
     }
     return patchesCopy;
   }
 
   /**
    * Merge a set of patches onto the text.  Return a patched text, as well
    * as an array of true/false values indicating which patches were applied.
    * @param patches Array of Patch objects
    * @param text Old text.
    * @return Two element Object array, containing the new text and an array of
    *      boolean values.
    */
   public Object[] patch_apply(LinkedList<Patch> patches, String text) {
     if (patches.isEmpty()) {
       return new Object[]{text, new boolean[0]};
     }
 
     // Deep copy the patches so that no changes are made to originals.
     patches = patch_deepCopy(patches);
 
     String nullPadding = patch_addPadding(patches);
     text = nullPadding + text + nullPadding;
     patch_splitMax(patches);
 
     int x = 0;
     // delta keeps track of the offset between the expected and actual location
     // of the previous patch.  If there are patches expected at positions 10 and
     // 20, but the first patch was found at 12, delta is 2 and the second patch
     // has an effective expected position of 22.
     int delta = 0;
     boolean[] results = new boolean[patches.size()];
     for (Patch aPatch : patches) {
       int expected_loc = aPatch.start2 + delta;
       String text1 = diff_text1(aPatch.diffs);
       int start_loc;
       int end_loc = -1;
       if (text1.length() > this.Match_MaxBits) {
         // patch_splitMax will only provide an oversized pattern in the case of
         // a monster delete.
         start_loc = match_main(text,
             text1.substring(0, this.Match_MaxBits), expected_loc);
         if (start_loc != -1) {
           end_loc = match_main(text,
               text1.substring(text1.length() - this.Match_MaxBits),
               expected_loc + text1.length() - this.Match_MaxBits);
           if (end_loc == -1 || start_loc >= end_loc) {
             // Can't find valid trailing context.  Drop this patch.
             start_loc = -1;
           }
         }
       } else {
         start_loc = match_main(text, text1, expected_loc);
       }
       if (start_loc == -1) {
         // No match found.  :(
         results[x] = false;
         // Subtract the delta for this failed patch from subsequent patches.
         delta -= aPatch.length2 - aPatch.length1;
       } else {
         // Found a match.  :)
         results[x] = true;
         delta = start_loc - expected_loc;
         String text2;
         if (end_loc == -1) {
           text2 = text.substring(start_loc,
               Math.min(start_loc + text1.length(), text.length()));
         } else {
           text2 = text.substring(start_loc,
               Math.min(end_loc + this.Match_MaxBits, text.length()));
         }
         if (text1.equals(text2)) {
           // Perfect match, just shove the replacement text in.
           text = text.substring(0, start_loc) + diff_text2(aPatch.diffs)
               + text.substring(start_loc + text1.length());
         } else {
           // Imperfect match.  Run a diff to get a framework of equivalent
           // indices.
           LinkedList<Diff> diffs = diff_main(text1, text2, false);
           if (text1.length() > this.Match_MaxBits
               && diff_levenshtein(diffs) / (float) text1.length()
               > this.Patch_DeleteThreshold) {
             // The end points match, but the content is unacceptably bad.
             results[x] = false;
           } else {
             diff_cleanupSemanticLossless(diffs);
             int index1 = 0;
             for (Diff aDiff : aPatch.diffs) {
               if (aDiff.operation != Operation.EQUAL) {
                 int index2 = diff_xIndex(diffs, index1);
                 if (aDiff.operation == Operation.INSERT) {
                   // Insertion
                   text = text.substring(0, start_loc + index2) + aDiff.text
                       + text.substring(start_loc + index2);
                 } else if (aDiff.operation == Operation.DELETE) {
                   // Deletion
                   text = text.substring(0, start_loc + index2)
                       + text.substring(start_loc + diff_xIndex(diffs,
                       index1 + aDiff.text.length()));
                 }
               }
               if (aDiff.operation != Operation.DELETE) {
                 index1 += aDiff.text.length();
               }
             }
           }
         }
       }
       x++;
     }
     // Strip the padding off.
     text = text.substring(nullPadding.length(), text.length()
         - nullPadding.length());
     return new Object[]{text, results};
   }
 
   /**
    * Add some padding on text start and end so that edges can match something.
    * Intended to be called only from within patch_apply.
    * @param patches Array of Patch objects.
    * @return The padding string added to each side.
    */
   public String patch_addPadding(LinkedList<Patch> patches) {
     short paddingLength = this.Patch_Margin;
     String nullPadding = "";
     for (short x = 1; x <= paddingLength; x++) {
       nullPadding += String.valueOf((char) x);
     }
 
     // Bump all the patches forward.
     for (Patch aPatch : patches) {
       aPatch.start1 += paddingLength;
       aPatch.start2 += paddingLength;
     }
 
     // Add some padding on start of first diff.
     Patch patch = patches.getFirst();
     LinkedList<Diff> diffs = patch.diffs;
     if (diffs.isEmpty() || diffs.getFirst().operation != Operation.EQUAL) {
       // Add nullPadding equality.
       diffs.addFirst(new Diff(Operation.EQUAL, nullPadding));
       patch.start1 -= paddingLength;  // Should be 0.
       patch.start2 -= paddingLength;  // Should be 0.
       patch.length1 += paddingLength;
       patch.length2 += paddingLength;
     } else if (paddingLength > diffs.getFirst().text.length()) {
       // Grow first equality.
       Diff firstDiff = diffs.getFirst();
       int extraLength = paddingLength - firstDiff.text.length();
       firstDiff.text = nullPadding.substring(firstDiff.text.length())
           + firstDiff.text;
       patch.start1 -= extraLength;
       patch.start2 -= extraLength;
       patch.length1 += extraLength;
       patch.length2 += extraLength;
     }
 
     // Add some padding on end of last diff.
     patch = patches.getLast();
     diffs = patch.diffs;
     if (diffs.isEmpty() || diffs.getLast().operation != Operation.EQUAL) {
       // Add nullPadding equality.
       diffs.addLast(new Diff(Operation.EQUAL, nullPadding));
       patch.length1 += paddingLength;
       patch.length2 += paddingLength;
     } else if (paddingLength > diffs.getLast().text.length()) {
       // Grow last equality.
       Diff lastDiff = diffs.getLast();
       int extraLength = paddingLength - lastDiff.text.length();
       lastDiff.text += nullPadding.substring(0, extraLength);
       patch.length1 += extraLength;
       patch.length2 += extraLength;
     }
 
     return nullPadding;
   }
 
   /**
    * Look through the patches and break up any which are longer than the
    * maximum limit of the match algorithm.
    * Intended to be called only from within patch_apply.
    * @param patches LinkedList of Patch objects.
    */
   public void patch_splitMax(LinkedList<Patch> patches) {
     short patch_size = Match_MaxBits;
     String precontext, postcontext;
     Patch patch;
     int start1, start2;
     boolean empty;
     Operation diff_type;
     String diff_text;
     ListIterator<Patch> pointer = patches.listIterator();
     Patch bigpatch = pointer.hasNext() ? pointer.next() : null;
     while (bigpatch != null) {
       if (bigpatch.length1 <= Match_MaxBits) {
         bigpatch = pointer.hasNext() ? pointer.next() : null;
         continue;
       }
       // Remove the big old patch.
       pointer.remove();
       start1 = bigpatch.start1;
       start2 = bigpatch.start2;
       precontext = "";
       while (!bigpatch.diffs.isEmpty()) {
         // Create one of several smaller patches.
         patch = new Patch();
         empty = true;
         patch.start1 = start1 - precontext.length();
         patch.start2 = start2 - precontext.length();
         if (precontext.length() != 0) {
           patch.length1 = patch.length2 = precontext.length();
           patch.diffs.add(new Diff(Operation.EQUAL, precontext));
         }
         while (!bigpatch.diffs.isEmpty()
             && patch.length1 < patch_size - Patch_Margin) {
           diff_type = bigpatch.diffs.getFirst().operation;
           diff_text = bigpatch.diffs.getFirst().text;
           if (diff_type == Operation.INSERT) {
             // Insertions are harmless.
             patch.length2 += diff_text.length();
             start2 += diff_text.length();
             patch.diffs.addLast(bigpatch.diffs.removeFirst());
             empty = false;
           } else if (diff_type == Operation.DELETE && patch.diffs.size() == 1
               && patch.diffs.getFirst().operation == Operation.EQUAL
               && diff_text.length() > 2 * patch_size) {
             // This is a large deletion.  Let it pass in one chunk.
             patch.length1 += diff_text.length();
             start1 += diff_text.length();
             empty = false;
             patch.diffs.add(new Diff(diff_type, diff_text));
             bigpatch.diffs.removeFirst();
           } else {
             // Deletion or equality.  Only take as much as we can stomach.
             diff_text = diff_text.substring(0, Math.min(diff_text.length(),
                 patch_size - patch.length1 - Patch_Margin));
             patch.length1 += diff_text.length();
             start1 += diff_text.length();
             if (diff_type == Operation.EQUAL) {
               patch.length2 += diff_text.length();
               start2 += diff_text.length();
             } else {
               empty = false;
             }
             patch.diffs.add(new Diff(diff_type, diff_text));
             if (diff_text.equals(bigpatch.diffs.getFirst().text)) {
               bigpatch.diffs.removeFirst();
             } else {
               bigpatch.diffs.getFirst().text = bigpatch.diffs.getFirst().text
                   .substring(diff_text.length());
             }
           }
         }
         // Compute the head context for the next patch.
         precontext = diff_text2(patch.diffs);
         precontext = precontext.substring(Math.max(0, precontext.length()
             - Patch_Margin));
         // Append the end context for this patch.
         if (diff_text1(bigpatch.diffs).length() > Patch_Margin) {
           postcontext = diff_text1(bigpatch.diffs).substring(0, Patch_Margin);
         } else {
           postcontext = diff_text1(bigpatch.diffs);
         }
         if (postcontext.length() != 0) {
           patch.length1 += postcontext.length();
           patch.length2 += postcontext.length();
           if (!patch.diffs.isEmpty()
               && patch.diffs.getLast().operation == Operation.EQUAL) {
             patch.diffs.getLast().text += postcontext;
           } else {
             patch.diffs.add(new Diff(Operation.EQUAL, postcontext));
           }
         }
         if (!empty) {
           pointer.add(patch);
         }
       }
       bigpatch = pointer.hasNext() ? pointer.next() : null;
     }
   }
 
   /**
    * Take a list of patches and return a textual representation.
    * @param patches List of Patch objects.
    * @return Text representation of patches.
    */
   public String patch_toText(List<Patch> patches) {
     StringBuilder text = new StringBuilder();
     for (Patch aPatch : patches) {
       text.append(aPatch);
     }
     return text.toString();
   }
 
   /**
    * Parse a textual representation of patches and return a List of Patch
    * objects.
    * @param textline Text representation of patches.
    * @return List of Patch objects.
    * @throws IllegalArgumentException If invalid input.
    */
   public List<Patch> patch_fromText(String textline)
       throws IllegalArgumentException {
     List<Patch> patches = new LinkedList<Patch>();
     if (textline.length() == 0) {
       return patches;
     }
     List<String> textList = Arrays.asList(textline.split("\n"));
     LinkedList<String> text = new LinkedList<String>(textList);
     Patch patch;
     Pattern patchHeader
         = Pattern.compile("^@@ -(\\d+),?(\\d*) \\+(\\d+),?(\\d*) @@$");
     Matcher m;
     char sign;
     String line;
     while (!text.isEmpty()) {
       m = patchHeader.matcher(text.getFirst());
       if (!m.matches()) {
         throw new IllegalArgumentException(
             "Invalid patch string: " + text.getFirst());
       }
       patch = new Patch();
       patches.add(patch);
       patch.start1 = Integer.parseInt(m.group(1));
       if (m.group(2).length() == 0) {
         patch.start1--;
         patch.length1 = 1;
       } else if (m.group(2).equals("0")) {
         patch.length1 = 0;
       } else {
         patch.start1--;
         patch.length1 = Integer.parseInt(m.group(2));
       }
 
       patch.start2 = Integer.parseInt(m.group(3));
       if (m.group(4).length() == 0) {
         patch.start2--;
         patch.length2 = 1;
       } else if (m.group(4).equals("0")) {
         patch.length2 = 0;
       } else {
         patch.start2--;
         patch.length2 = Integer.parseInt(m.group(4));
       }
       text.removeFirst();
 
       while (!text.isEmpty()) {
         try {
           sign = text.getFirst().charAt(0);
         } catch (IndexOutOfBoundsException e) {
           // Blank line?  Whatever.
           text.removeFirst();
           continue;
         }
         line = text.getFirst().substring(1);
         line = line.replace("+", "%2B");  // decode would change all "+" to " "
         try {
           line = URLDecoder.decode(line, "UTF-8");
         } catch (UnsupportedEncodingException e) {
           // Not likely on modern system.
           throw new Error("This system does not support UTF-8.", e);
         } catch (IllegalArgumentException e) {
           // Malformed URI sequence.
           throw new IllegalArgumentException(
               "Illegal escape in patch_fromText: " + line, e);
         }
         if (sign == '-') {
           // Deletion.
           patch.diffs.add(new Diff(Operation.DELETE, line));
         } else if (sign == '+') {
           // Insertion.
           patch.diffs.add(new Diff(Operation.INSERT, line));
         } else if (sign == ' ') {
           // Minor equality.
           patch.diffs.add(new Diff(Operation.EQUAL, line));
         } else if (sign == '@') {
           // Start of next patch.
           break;
         } else {
           // WTF?
           throw new IllegalArgumentException(
               "Invalid patch mode '" + sign + "' in: " + line);
         }
         text.removeFirst();
       }
     }
     return patches;
   }
 
 
   /**
    * Class representing one diff operation.
    */
   public static class Diff {
     /**
      * One of: INSERT, DELETE or EQUAL.
      */
     public Operation operation;
     /**
      * The text associated with this diff operation.
      */
     public String text;
 
     /**
      * Constructor.  Initializes the diff with the provided values.
      * @param operation One of INSERT, DELETE or EQUAL.
      * @param text The text being applied.
      */
     public Diff(Operation operation, String text) {
       // Construct a diff with the specified operation and text.
       this.operation = operation;
       this.text = text;
     }
 
     /**
      * Display a human-readable version of this Diff.
      * @return text version.
      */
     public String toString() {
       String prettyText = this.text.replace('\n', '\u00b6');
       return "Diff(" + this.operation + ",\"" + prettyText + "\")";
     }
 
     /**
      * Create a numeric hash value for a Diff.
      * This function is not used by DMP.
      * @return Hash value.
      */
     @Override
     public int hashCode() {
       final int prime = 31;
       int result = (operation == null) ? 0 : operation.hashCode();
       result += prime * ((text == null) ? 0 : text.hashCode());
       return result;
     }
 
     /**
      * Is this Diff equivalent to another Diff?
      * @param obj Another Diff to compare against.
      * @return true or false.
      */
     @Override
     public boolean equals(Object obj) {
       if (this == obj) {
         return true;
       }
       if (obj == null) {
         return false;
       }
       if (getClass() != obj.getClass()) {
         return false;
       }
       Diff other = (Diff) obj;
       if (operation != other.operation) {
         return false;
       }
       if (text == null) {
         if (other.text != null) {
           return false;
         }
       } else if (!text.equals(other.text)) {
         return false;
       }
       return true;
     }
   }
 
 
   /**
    * Class representing one patch operation.
    */
   public static class Patch {
     public LinkedList<Diff> diffs;
     public int start1;
     public int start2;
     public int length1;
     public int length2;
 
     /**
      * Constructor.  Initializes with an empty list of diffs.
      */
     public Patch() {
       this.diffs = new LinkedList<Diff>();
     }
 
     /**
      * Emmulate GNU diff's format.
      * Header: @@ -382,8 +481,9 @@
      * Indicies are printed as 1-based, not 0-based.
      * @return The GNU diff string.
      */
     public String toString() {
       String coords1, coords2;
       if (this.length1 == 0) {
         coords1 = this.start1 + ",0";
       } else if (this.length1 == 1) {
         coords1 = Integer.toString(this.start1 + 1);
       } else {
         coords1 = (this.start1 + 1) + "," + this.length1;
       }
       if (this.length2 == 0) {
         coords2 = this.start2 + ",0";
       } else if (this.length2 == 1) {
         coords2 = Integer.toString(this.start2 + 1);
       } else {
         coords2 = (this.start2 + 1) + "," + this.length2;
       }
       StringBuilder text = new StringBuilder();
       text.append("@@ -").append(coords1).append(" +").append(coords2)
           .append(" @@\n");
       // Escape the body of the patch with %xx notation.
       for (Diff aDiff : this.diffs) {
         switch (aDiff.operation) {
         case INSERT:
           text.append('+');
           break;
         case DELETE:
           text.append('-');
           break;
         case EQUAL:
           text.append(' ');
           break;
         }
         try {
           text.append(URLEncoder.encode(aDiff.text, "UTF-8").replace('+', ' '))
               .append("\n");
         } catch (UnsupportedEncodingException e) {
           // Not likely on modern system.
           throw new Error("This system does not support UTF-8.", e);
         }
       }
       return unescapeForEncodeUriCompatability(text.toString());
     }
   }
 
   /**
    * Unescape selected chars for compatability with JavaScript's encodeURI.
    * In speed critical applications this could be dropped since the
    * receiving application will certainly decode these fine.
    * Note that this function is case-sensitive.  Thus "%3f" would not be
    * unescaped.  But this is ok because it is only called with the output of
    * URLEncoder.encode which returns uppercase hex.
    *
    * Example: "%3F" -> "?", "%24" -> "$", etc.
    *
    * @param str The string to escape.
    * @return The escaped string.
    */
   private static String unescapeForEncodeUriCompatability(String str) {
     return str.replace("%21", "!").replace("%7E", "~")
         .replace("%27", "'").replace("%28", "(").replace("%29", ")")
         .replace("%3B", ";").replace("%2F", "/").replace("%3F", "?")
         .replace("%3A", ":").replace("%40", "@").replace("%26", "&")
         .replace("%3D", "=").replace("%2B", "+").replace("%24", "$")
         .replace("%2C", ",").replace("%23", "#");
   }
 }