diff_match_patch_uncompressed.js

/**
 * 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.
 */

/**
 * @fileoverview 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.
 * @constructor
 */
var diff_match_patch = function () {

    // Defaults.
    // Redefine these in your program to override the defaults.

    // Number of seconds to map a diff before giving up (0 for infinity).
    this.Diff_Timeout = 1.0;
    // Cost of an empty edit operation in terms of edit characters.
    this.Diff_EditCost = 4;
    // At what point is no match declared (0.0 = perfection, 1.0 = very loose).
    this.Match_Threshold = 0.5;
    // 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).
    this.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.
    this.Patch_DeleteThreshold = 0.5;
    // Chunk size for context length.
    this.Patch_Margin = 4;

    // The number of bits in an int.
    this.Match_MaxBits = 32;
};


//  DIFF FUNCTIONS


/**
 * The data structure representing a diff is an array of tuples:
 * [[DIFF_DELETE, 'Hello'], [DIFF_INSERT, 'Goodbye'], [DIFF_EQUAL, ' world.']]
 * which means: delete 'Hello', add 'Goodbye' and keep ' world.'
 */
var DIFF_DELETE = -1;
var DIFF_INSERT = 1;
var DIFF_EQUAL = 0;

/**
 * Class representing one diff tuple.
 * Attempts to look like a two-element array (which is what this used to be).
 * @param {number} op Operation, one of: DIFF_DELETE, DIFF_INSERT, DIFF_EQUAL.
 * @param {string} text Text to be deleted, inserted, or retained.
 * @constructor
 */
diff_match_patch.Diff = function (op, text) {
    this[0] = op;
    this[1] = text;
};

diff_match_patch.Diff.prototype.length = 2;

/**
 * Emulate the output of a two-element array.
 * @return {string} Diff operation as a string.
 */
diff_match_patch.Diff.prototype.toString = function () {
    return this[0] + ',' + this[1];
};


/**
 * Find the differences between two texts.  Simplifies the problem by stripping
 * any common prefix or suffix off the texts before diffing.
 * @param {string} text1 Old string to be diffed.
 * @param {string} text2 New string to be diffed.
 * @param {boolean=} opt_checklines Optional speedup flag. If present and false,
 *     then don't run a line-level diff first to identify the changed areas.
 *     Defaults to true, which does a faster, slightly less optimal diff.
 * @param {number=} opt_deadline Optional time when the diff should be complete
 *     by.  Used internally for recursive calls.  Users should set DiffTimeout
 *     instead.
 * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
 */
diff_match_patch.prototype.diff_main = function (text1, text2, opt_checklines,
                                                 opt_deadline) {
    // Set a deadline by which time the diff must be complete.
    if (typeof opt_deadline == 'undefined') {
        if (this.Diff_Timeout <= 0) {
            opt_deadline = Number.MAX_VALUE;
        } else {
            opt_deadline = (new Date).getTime() + this.Diff_Timeout * 1000;
        }
    }
    var deadline = opt_deadline;

    // Check for null inputs.
    if (text1 == null || text2 == null) {
        throw new Error('Null input. (diff_main)');
    }

    // Check for equality (speedup).
    if (text1 == text2) {
        if (text1) {
            return [new diff_match_patch.Diff(DIFF_EQUAL, text1)];
        }
        return [];
    }

    if (typeof opt_checklines == 'undefined') {
        opt_checklines = true;
    }
    var checklines = opt_checklines;

    // Trim off common prefix (speedup).
    var commonlength = this.diff_commonPrefix(text1, text2);
    var commonprefix = text1.substring(0, commonlength);
    text1 = text1.substring(commonlength);
    text2 = text2.substring(commonlength);

    // Trim off common suffix (speedup).
    commonlength = this.diff_commonSuffix(text1, text2);
    var 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.
    var diffs = this.diff_compute_(text1, text2, checklines, deadline);

    // Restore the prefix and suffix.
    if (commonprefix) {
        diffs.unshift(new diff_match_patch.Diff(DIFF_EQUAL, commonprefix));
    }
    if (commonsuffix) {
        diffs.push(new diff_match_patch.Diff(DIFF_EQUAL, commonsuffix));
    }
    this.diff_cleanupMerge(diffs);
    return diffs;
};


/**
 * Find the differences between two texts.  Assumes that the texts do not
 * have any common prefix or suffix.
 * @param {string} text1 Old string to be diffed.
 * @param {string} text2 New string to be diffed.
 * @param {boolean} 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 {number} deadline Time when the diff should be complete by.
 * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
 * @private
 */
diff_match_patch.prototype.diff_compute_ = function (text1, text2, checklines,
                                                     deadline) {
    var diffs;

    if (!text1) {
        // Just add some text (speedup).
        return [new diff_match_patch.Diff(DIFF_INSERT, text2)];
    }

    if (!text2) {
        // Just delete some text (speedup).
        return [new diff_match_patch.Diff(DIFF_DELETE, text1)];
    }

    var longtext = text1.length > text2.length ? text1 : text2;
    var shorttext = text1.length > text2.length ? text2 : text1;
    var i = longtext.indexOf(shorttext);
    if (i != -1) {
        // Shorter text is inside the longer text (speedup).
        diffs = [new diff_match_patch.Diff(DIFF_INSERT, longtext.substring(0, i)),
            new diff_match_patch.Diff(DIFF_EQUAL, shorttext),
            new diff_match_patch.Diff(DIFF_INSERT,
                longtext.substring(i + shorttext.length))];
        // Swap insertions for deletions if diff is reversed.
        if (text1.length > text2.length) {
            diffs[0][0] = diffs[2][0] = DIFF_DELETE;
        }
        return diffs;
    }

    if (shorttext.length == 1) {
        // Single character string.
        // After the previous speedup, the character can't be an equality.
        return [new diff_match_patch.Diff(DIFF_DELETE, text1),
            new diff_match_patch.Diff(DIFF_INSERT, text2)];
    }

    // Check to see if the problem can be split in two.
    var hm = this.diff_halfMatch_(text1, text2);
    if (hm) {
        // A half-match was found, sort out the return data.
        var text1_a = hm[0];
        var text1_b = hm[1];
        var text2_a = hm[2];
        var text2_b = hm[3];
        var mid_common = hm[4];
        // Send both pairs off for separate processing.
        var diffs_a = this.diff_main(text1_a, text2_a, checklines, deadline);
        var diffs_b = this.diff_main(text1_b, text2_b, checklines, deadline);
        // Merge the results.
        return diffs_a.concat([new diff_match_patch.Diff(DIFF_EQUAL, mid_common)],
            diffs_b);
    }

    if (checklines && text1.length > 100 && text2.length > 100) {
        return this.diff_lineMode_(text1, text2, deadline);
    }

    return this.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 {string} text1 Old string to be diffed.
 * @param {string} text2 New string to be diffed.
 * @param {number} deadline Time when the diff should be complete by.
 * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
 * @private
 */
diff_match_patch.prototype.diff_lineMode_ = function (text1, text2, deadline) {
    // Scan the text on a line-by-line basis first.
    var a = this.diff_linesToChars_(text1, text2);
    text1 = a.chars1;
    text2 = a.chars2;
    var linearray = a.lineArray;

    var diffs = this.diff_main(text1, text2, false, deadline);

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

    // Rediff any replacement blocks, this time character-by-character.
    // Add a dummy entry at the end.
    diffs.push(new diff_match_patch.Diff(DIFF_EQUAL, ''));
    var pointer = 0;
    var count_delete = 0;
    var count_insert = 0;
    var text_delete = '';
    var text_insert = '';
    while (pointer < diffs.length) {
        switch (diffs[pointer][0]) {
            case DIFF_INSERT:
                count_insert++;
                text_insert += diffs[pointer][1];
                break;
            case DIFF_DELETE:
                count_delete++;
                text_delete += diffs[pointer][1];
                break;
            case DIFF_EQUAL:
                // Upon reaching an equality, check for prior redundancies.
                if (count_delete >= 1 && count_insert >= 1) {
                    // Delete the offending records and add the merged ones.
                    diffs.splice(pointer - count_delete - count_insert,
                        count_delete + count_insert);
                    pointer = pointer - count_delete - count_insert;
                    var subDiff =
                        this.diff_main(text_delete, text_insert, false, deadline);
                    for (var j = subDiff.length - 1; j >= 0; j--) {
                        diffs.splice(pointer, 0, subDiff[j]);
                    }
                    pointer = pointer + subDiff.length;
                }
                count_insert = 0;
                count_delete = 0;
                text_delete = '';
                text_insert = '';
                break;
        }
        pointer++;
    }
    diffs.pop();  // 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 {string} text1 Old string to be diffed.
 * @param {string} text2 New string to be diffed.
 * @param {number} deadline Time at which to bail if not yet complete.
 * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
 * @private
 */
diff_match_patch.prototype.diff_bisect_ = function (text1, text2, deadline) {
    // Cache the text lengths to prevent multiple calls.
    var text1_length = text1.length;
    var text2_length = text2.length;
    var max_d = Math.ceil((text1_length + text2_length) / 2);
    var v_offset = max_d;
    var v_length = 2 * max_d;
    var v1 = new Array(v_length);
    var v2 = new Array(v_length);
    // Setting all elements to -1 is faster in Chrome & Firefox than mixing
    // integers and undefined.
    for (var x = 0; x < v_length; x++) {
        v1[x] = -1;
        v2[x] = -1;
    }
    v1[v_offset + 1] = 0;
    v2[v_offset + 1] = 0;
    var delta = text1_length - text2_length;
    // If the total number of characters is odd, then the front path will collide
    // with the reverse path.
    var front = (delta % 2 != 0);
    // Offsets for start and end of k loop.
    // Prevents mapping of space beyond the grid.
    var k1start = 0;
    var k1end = 0;
    var k2start = 0;
    var k2end = 0;
    for (var d = 0; d < max_d; d++) {
        // Bail out if deadline is reached.
        if ((new Date()).getTime() > deadline) {
            break;
        }

        // Walk the front path one step.
        for (var k1 = -d + k1start; k1 <= d - k1end; k1 += 2) {
            var k1_offset = v_offset + k1;
            var 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;
            }
            var 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) {
                var 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.
                    var x2 = text1_length - v2[k2_offset];
                    if (x1 >= x2) {
                        // Overlap detected.
                        return this.diff_bisectSplit_(text1, text2, x1, y1, deadline);
                    }
                }
            }
        }

        // Walk the reverse path one step.
        for (var k2 = -d + k2start; k2 <= d - k2end; k2 += 2) {
            var k2_offset = v_offset + k2;
            var 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;
            }
            var 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) {
                var k1_offset = v_offset + delta - k2;
                if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] != -1) {
                    var x1 = v1[k1_offset];
                    var y1 = v_offset + x1 - k1_offset;
                    // Mirror x2 onto top-left coordinate system.
                    x2 = text1_length - x2;
                    if (x1 >= x2) {
                        // Overlap detected.
                        return this.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.
    return [new diff_match_patch.Diff(DIFF_DELETE, text1),
        new diff_match_patch.Diff(DIFF_INSERT, text2)];
};


/**
 * Given the location of the 'middle snake', split the diff in two parts
 * and recurse.
 * @param {string} text1 Old string to be diffed.
 * @param {string} text2 New string to be diffed.
 * @param {number} x Index of split point in text1.
 * @param {number} y Index of split point in text2.
 * @param {number} deadline Time at which to bail if not yet complete.
 * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
 * @private
 */
diff_match_patch.prototype.diff_bisectSplit_ = function (text1, text2, x, y,
                                                         deadline) {
    var text1a = text1.substring(0, x);
    var text2a = text2.substring(0, y);
    var text1b = text1.substring(x);
    var text2b = text2.substring(y);

    // Compute both diffs serially.
    var diffs = this.diff_main(text1a, text2a, false, deadline);
    var diffsb = this.diff_main(text1b, text2b, false, deadline);

    return diffs.concat(diffsb);
};


/**
 * Split two texts into an array of strings.  Reduce the texts to a string of
 * hashes where each Unicode character represents one line.
 * @param {string} text1 First string.
 * @param {string} text2 Second string.
 * @return {{chars1: string, chars2: string, lineArray: !Array.<string>}}
 *     An object containing the encoded text1, the encoded text2 and
 *     the array of unique strings.
 *     The zeroth element of the array of unique strings is intentionally blank.
 * @private
 */
diff_match_patch.prototype.diff_linesToChars_ = function (text1, text2) {
    var lineArray = [];  // e.g. lineArray[4] == 'Hello\n'
    var lineHash = {};   // e.g. lineHash['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[0] = '';

    /**
     * Split a text into an array of strings.  Reduce the texts to a string of
     * hashes where each Unicode character represents one line.
     * Modifies linearray and linehash through being a closure.
     * @param {string} text String to encode.
     * @return {string} Encoded string.
     * @private
     */
    function diff_linesToCharsMunge_(text) {
        var chars = '';
        // 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.
        var lineStart = 0;
        var lineEnd = -1;
        // Keeping our own length variable is faster than looking it up.
        var lineArrayLength = lineArray.length;
        while (lineEnd < text.length - 1) {
            lineEnd = text.indexOf('\n', lineStart);
            if (lineEnd == -1) {
                lineEnd = text.length - 1;
            }
            var line = text.substring(lineStart, lineEnd + 1);

            if (lineHash.hasOwnProperty ? lineHash.hasOwnProperty(line) :
                (lineHash[line] !== undefined)) {
                chars += String.fromCharCode(lineHash[line]);
            } else {
                if (lineArrayLength == maxLines) {
                    // Bail out at 65535 because
                    // String.fromCharCode(65536) == String.fromCharCode(0)
                    line = text.substring(lineStart);
                    lineEnd = text.length;
                }
                chars += String.fromCharCode(lineArrayLength);
                lineHash[line] = lineArrayLength;
                lineArray[lineArrayLength++] = line;
            }
            lineStart = lineEnd + 1;
        }
        return chars;
    }

    // Allocate 2/3rds of the space for text1, the rest for text2.
    var maxLines = 40000;
    var chars1 = diff_linesToCharsMunge_(text1);
    maxLines = 65535;
    var chars2 = diff_linesToCharsMunge_(text2);
    return {chars1: chars1, chars2: chars2, lineArray: lineArray};
};


/**
 * Rehydrate the text in a diff from a string of line hashes to real lines of
 * text.
 * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
 * @param {!Array.<string>} lineArray Array of unique strings.
 * @private
 */
diff_match_patch.prototype.diff_charsToLines_ = function (diffs, lineArray) {
    for (var i = 0; i < diffs.length; i++) {
        var chars = diffs[i][1];
        var text = [];
        for (var j = 0; j < chars.length; j++) {
            text[j] = lineArray[chars.charCodeAt(j)];
        }
        diffs[i][1] = text.join('');
    }
};


/**
 * Determine the common prefix of two strings.
 * @param {string} text1 First string.
 * @param {string} text2 Second string.
 * @return {number} The number of characters common to the start of each
 *     string.
 */
diff_match_patch.prototype.diff_commonPrefix = function (text1, text2) {
    // Quick check for common null cases.
    if (!text1 || !text2 || text1.charAt(0) != text2.charAt(0)) {
        return 0;
    }
    // Binary search.
    // Performance analysis: https://neil.fraser.name/news/2007/10/09/
    var pointermin = 0;
    var pointermax = Math.min(text1.length, text2.length);
    var pointermid = pointermax;
    var pointerstart = 0;
    while (pointermin < pointermid) {
        if (text1.substring(pointerstart, pointermid) ==
            text2.substring(pointerstart, pointermid)) {
            pointermin = pointermid;
            pointerstart = pointermin;
        } else {
            pointermax = pointermid;
        }
        pointermid = Math.floor((pointermax - pointermin) / 2 + pointermin);
    }
    return pointermid;
};


/**
 * Determine the common suffix of two strings.
 * @param {string} text1 First string.
 * @param {string} text2 Second string.
 * @return {number} The number of characters common to the end of each string.
 */
diff_match_patch.prototype.diff_commonSuffix = function (text1, text2) {
    // Quick check for common null cases.
    if (!text1 || !text2 ||
        text1.charAt(text1.length - 1) != text2.charAt(text2.length - 1)) {
        return 0;
    }
    // Binary search.
    // Performance analysis: https://neil.fraser.name/news/2007/10/09/
    var pointermin = 0;
    var pointermax = Math.min(text1.length, text2.length);
    var pointermid = pointermax;
    var pointerend = 0;
    while (pointermin < pointermid) {
        if (text1.substring(text1.length - pointermid, text1.length - pointerend) ==
            text2.substring(text2.length - pointermid, text2.length - pointerend)) {
            pointermin = pointermid;
            pointerend = pointermin;
        } else {
            pointermax = pointermid;
        }
        pointermid = Math.floor((pointermax - pointermin) / 2 + pointermin);
    }
    return pointermid;
};


/**
 * Determine if the suffix of one string is the prefix of another.
 * @param {string} text1 First string.
 * @param {string} text2 Second string.
 * @return {number} The number of characters common to the end of the first
 *     string and the start of the second string.
 * @private
 */
diff_match_patch.prototype.diff_commonOverlap_ = function (text1, text2) {
    // Cache the text lengths to prevent multiple calls.
    var text1_length = text1.length;
    var 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);
    }
    var text_length = Math.min(text1_length, text2_length);
    // Quick check for the worst case.
    if (text1 == text2) {
        return text_length;
    }

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


/**
 * Do the two texts share a substring which is at least half the length of the
 * longer text?
 * This speedup can produce non-minimal diffs.
 * @param {string} text1 First string.
 * @param {string} text2 Second string.
 * @return {Array.<string>} Five element 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.
 * @private
 */
diff_match_patch.prototype.diff_halfMatch_ = function (text1, text2) {
    if (this.Diff_Timeout <= 0) {
        // Don't risk returning a non-optimal diff if we have unlimited time.
        return null;
    }
    var longtext = text1.length > text2.length ? text1 : text2;
    var shorttext = text1.length > text2.length ? text2 : text1;
    if (longtext.length < 4 || shorttext.length * 2 < longtext.length) {
        return null;  // Pointless.
    }
    var dmp = this;  // 'this' becomes 'window' in a closure.

    /**
     * Does a substring of shorttext exist within longtext such that the substring
     * is at least half the length of longtext?
     * Closure, but does not reference any external variables.
     * @param {string} longtext Longer string.
     * @param {string} shorttext Shorter string.
     * @param {number} i Start index of quarter length substring within longtext.
     * @return {Array.<string>} Five element 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
     */
    function diff_halfMatchI_(longtext, shorttext, i) {
        // Start with a 1/4 length substring at position i as a seed.
        var seed = longtext.substring(i, i + Math.floor(longtext.length / 4));
        var j = -1;
        var best_common = '';
        var best_longtext_a, best_longtext_b, best_shorttext_a, best_shorttext_b;
        while ((j = shorttext.indexOf(seed, j + 1)) != -1) {
            var prefixLength = dmp.diff_commonPrefix(longtext.substring(i),
                shorttext.substring(j));
            var suffixLength = dmp.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 [best_longtext_a, best_longtext_b,
                best_shorttext_a, best_shorttext_b, best_common];
        } else {
            return null;
        }
    }

    // First check if the second quarter is the seed for a half-match.
    var hm1 = diff_halfMatchI_(longtext, shorttext,
        Math.ceil(longtext.length / 4));
    // Check again based on the third quarter.
    var hm2 = diff_halfMatchI_(longtext, shorttext,
        Math.ceil(longtext.length / 2));
    var hm;
    if (!hm1 && !hm2) {
        return null;
    } else if (!hm2) {
        hm = hm1;
    } else if (!hm1) {
        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.
    var text1_a, text1_b, text2_a, text2_b;
    if (text1.length > text2.length) {
        text1_a = hm[0];
        text1_b = hm[1];
        text2_a = hm[2];
        text2_b = hm[3];
    } else {
        text2_a = hm[0];
        text2_b = hm[1];
        text1_a = hm[2];
        text1_b = hm[3];
    }
    var mid_common = hm[4];
    return [text1_a, text1_b, text2_a, text2_b, mid_common];
};


/**
 * Reduce the number of edits by eliminating semantically trivial equalities.
 * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
 */
diff_match_patch.prototype.diff_cleanupSemantic = function (diffs) {
    var changes = false;
    var equalities = [];  // Stack of indices where equalities are found.
    var equalitiesLength = 0;  // Keeping our own length var is faster in JS.
    /** @type {?string} */
    var lastEquality = null;
    // Always equal to diffs[equalities[equalitiesLength - 1]][1]
    var pointer = 0;  // Index of current position.
    // Number of characters that changed prior to the equality.
    var length_insertions1 = 0;
    var length_deletions1 = 0;
    // Number of characters that changed after the equality.
    var length_insertions2 = 0;
    var length_deletions2 = 0;
    while (pointer < diffs.length) {
        if (diffs[pointer][0] == DIFF_EQUAL) {  // Equality found.
            equalities[equalitiesLength++] = pointer;
            length_insertions1 = length_insertions2;
            length_deletions1 = length_deletions2;
            length_insertions2 = 0;
            length_deletions2 = 0;
            lastEquality = diffs[pointer][1];
        } else {  // An insertion or deletion.
            if (diffs[pointer][0] == DIFF_INSERT) {
                length_insertions2 += diffs[pointer][1].length;
            } else {
                length_deletions2 += diffs[pointer][1].length;
            }
            // Eliminate an equality that is smaller or equal to the edits on both
            // sides of it.
            if (lastEquality && (lastEquality.length <=
                    Math.max(length_insertions1, length_deletions1)) &&
                (lastEquality.length <= Math.max(length_insertions2,
                    length_deletions2))) {
                // Duplicate record.
                diffs.splice(equalities[equalitiesLength - 1], 0,
                    new diff_match_patch.Diff(DIFF_DELETE, lastEquality));
                // Change second copy to insert.
                diffs[equalities[equalitiesLength - 1] + 1][0] = DIFF_INSERT;
                // Throw away the equality we just deleted.
                equalitiesLength--;
                // Throw away the previous equality (it needs to be reevaluated).
                equalitiesLength--;
                pointer = equalitiesLength > 0 ? equalities[equalitiesLength - 1] : -1;
                length_insertions1 = 0;  // Reset the counters.
                length_deletions1 = 0;
                length_insertions2 = 0;
                length_deletions2 = 0;
                lastEquality = null;
                changes = true;
            }
        }
        pointer++;
    }

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

    // Find any overlaps between deletions and insertions.
    // e.g: <del>abcxxx</del><ins>xxxdef</ins>
    //   -> <del>abc</del>xxx<ins>def</ins>
    // e.g: <del>xxxabc</del><ins>defxxx</ins>
    //   -> <ins>def</ins>xxx<del>abc</del>
    // Only extract an overlap if it is as big as the edit ahead or behind it.
    pointer = 1;
    while (pointer < diffs.length) {
        if (diffs[pointer - 1][0] == DIFF_DELETE &&
            diffs[pointer][0] == DIFF_INSERT) {
            var deletion = diffs[pointer - 1][1];
            var insertion = diffs[pointer][1];
            var overlap_length1 = this.diff_commonOverlap_(deletion, insertion);
            var overlap_length2 = this.diff_commonOverlap_(insertion, deletion);
            if (overlap_length1 >= overlap_length2) {
                if (overlap_length1 >= deletion.length / 2 ||
                    overlap_length1 >= insertion.length / 2) {
                    // Overlap found.  Insert an equality and trim the surrounding edits.
                    diffs.splice(pointer, 0, new diff_match_patch.Diff(DIFF_EQUAL,
                        insertion.substring(0, overlap_length1)));
                    diffs[pointer - 1][1] =
                        deletion.substring(0, deletion.length - overlap_length1);
                    diffs[pointer + 1][1] = insertion.substring(overlap_length1);
                    pointer++;
                }
            } else {
                if (overlap_length2 >= deletion.length / 2 ||
                    overlap_length2 >= insertion.length / 2) {
                    // Reverse overlap found.
                    // Insert an equality and swap and trim the surrounding edits.
                    diffs.splice(pointer, 0, new diff_match_patch.Diff(DIFF_EQUAL,
                        deletion.substring(0, overlap_length2)));
                    diffs[pointer - 1][0] = DIFF_INSERT;
                    diffs[pointer - 1][1] =
                        insertion.substring(0, insertion.length - overlap_length2);
                    diffs[pointer + 1][0] = DIFF_DELETE;
                    diffs[pointer + 1][1] =
                        deletion.substring(overlap_length2);
                    pointer++;
                }
            }
            pointer++;
        }
        pointer++;
    }
};


/**
 * Look for single edits surrounded on both sides by equalities
 * which can be shifted sideways to align the edit to a word boundary.
 * e.g: The c<ins>at c</ins>ame. -> The <ins>cat </ins>came.
 * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
 */
diff_match_patch.prototype.diff_cleanupSemanticLossless = function (diffs) {
    /**
     * Given two strings, compute a score representing whether the internal
     * boundary falls on logical boundaries.
     * Scores range from 6 (best) to 0 (worst).
     * Closure, but does not reference any external variables.
     * @param {string} one First string.
     * @param {string} two Second string.
     * @return {number} The score.
     * @private
     */
    function diff_cleanupSemanticScore_(one, two) {
        if (!one || !two) {
            // 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.
        var char1 = one.charAt(one.length - 1);
        var char2 = two.charAt(0);
        var nonAlphaNumeric1 = char1.match(diff_match_patch.nonAlphaNumericRegex_);
        var nonAlphaNumeric2 = char2.match(diff_match_patch.nonAlphaNumericRegex_);
        var whitespace1 = nonAlphaNumeric1 &&
            char1.match(diff_match_patch.whitespaceRegex_);
        var whitespace2 = nonAlphaNumeric2 &&
            char2.match(diff_match_patch.whitespaceRegex_);
        var lineBreak1 = whitespace1 &&
            char1.match(diff_match_patch.linebreakRegex_);
        var lineBreak2 = whitespace2 &&
            char2.match(diff_match_patch.linebreakRegex_);
        var blankLine1 = lineBreak1 &&
            one.match(diff_match_patch.blanklineEndRegex_);
        var blankLine2 = lineBreak2 &&
            two.match(diff_match_patch.blanklineStartRegex_);

        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;
    }

    var pointer = 1;
    // Intentionally ignore the first and last element (don't need checking).
    while (pointer < diffs.length - 1) {
        if (diffs[pointer - 1][0] == DIFF_EQUAL &&
            diffs[pointer + 1][0] == DIFF_EQUAL) {
            // This is a single edit surrounded by equalities.
            var equality1 = diffs[pointer - 1][1];
            var edit = diffs[pointer][1];
            var equality2 = diffs[pointer + 1][1];

            // First, shift the edit as far left as possible.
            var commonOffset = this.diff_commonSuffix(equality1, edit);
            if (commonOffset) {
                var 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.
            var bestEquality1 = equality1;
            var bestEdit = edit;
            var bestEquality2 = equality2;
            var bestScore = diff_cleanupSemanticScore_(equality1, edit) +
                diff_cleanupSemanticScore_(edit, equality2);
            while (edit.charAt(0) === equality2.charAt(0)) {
                equality1 += edit.charAt(0);
                edit = edit.substring(1) + equality2.charAt(0);
                equality2 = equality2.substring(1);
                var score = diff_cleanupSemanticScore_(equality1, edit) +
                    diff_cleanupSemanticScore_(edit, equality2);
                // The >= encourages trailing rather than leading whitespace on edits.
                if (score >= bestScore) {
                    bestScore = score;
                    bestEquality1 = equality1;
                    bestEdit = edit;
                    bestEquality2 = equality2;
                }
            }

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

// Define some regex patterns for matching boundaries.
diff_match_patch.nonAlphaNumericRegex_ = /[^a-zA-Z0-9]/;
diff_match_patch.whitespaceRegex_ = /\s/;
diff_match_patch.linebreakRegex_ = /[\r\n]/;
diff_match_patch.blanklineEndRegex_ = /\n\r?\n$/;
diff_match_patch.blanklineStartRegex_ = /^\r?\n\r?\n/;

/**
 * Reduce the number of edits by eliminating operationally trivial equalities.
 * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
 */
diff_match_patch.prototype.diff_cleanupEfficiency = function (diffs) {
    var changes = false;
    var equalities = [];  // Stack of indices where equalities are found.
    var equalitiesLength = 0;  // Keeping our own length var is faster in JS.
    /** @type {?string} */
    var lastEquality = null;
    // Always equal to diffs[equalities[equalitiesLength - 1]][1]
    var pointer = 0;  // Index of current position.
    // Is there an insertion operation before the last equality.
    var pre_ins = false;
    // Is there a deletion operation before the last equality.
    var pre_del = false;
    // Is there an insertion operation after the last equality.
    var post_ins = false;
    // Is there a deletion operation after the last equality.
    var post_del = false;
    while (pointer < diffs.length) {
        if (diffs[pointer][0] == DIFF_EQUAL) {  // Equality found.
            if (diffs[pointer][1].length < this.Diff_EditCost &&
                (post_ins || post_del)) {
                // Candidate found.
                equalities[equalitiesLength++] = pointer;
                pre_ins = post_ins;
                pre_del = post_del;
                lastEquality = diffs[pointer][1];
            } else {
                // Not a candidate, and can never become one.
                equalitiesLength = 0;
                lastEquality = null;
            }
            post_ins = post_del = false;
        } else {  // An insertion or deletion.
            if (diffs[pointer][0] == DIFF_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 && ((pre_ins && pre_del && post_ins && post_del) ||
                ((lastEquality.length < this.Diff_EditCost / 2) &&
                    (pre_ins + pre_del + post_ins + post_del) == 3))) {
                // Duplicate record.
                diffs.splice(equalities[equalitiesLength - 1], 0,
                    new diff_match_patch.Diff(DIFF_DELETE, lastEquality));
                // Change second copy to insert.
                diffs[equalities[equalitiesLength - 1] + 1][0] = DIFF_INSERT;
                equalitiesLength--;  // 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;
                    equalitiesLength = 0;
                } else {
                    equalitiesLength--;  // Throw away the previous equality.
                    pointer = equalitiesLength > 0 ?
                        equalities[equalitiesLength - 1] : -1;
                    post_ins = post_del = false;
                }
                changes = true;
            }
        }
        pointer++;
    }

    if (changes) {
        this.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 {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
 */
diff_match_patch.prototype.diff_cleanupMerge = function (diffs) {
    // Add a dummy entry at the end.
    diffs.push(new diff_match_patch.Diff(DIFF_EQUAL, ''));
    var pointer = 0;
    var count_delete = 0;
    var count_insert = 0;
    var text_delete = '';
    var text_insert = '';
    var commonlength;
    while (pointer < diffs.length) {
        switch (diffs[pointer][0]) {
            case DIFF_INSERT:
                count_insert++;
                text_insert += diffs[pointer][1];
                pointer++;
                break;
            case DIFF_DELETE:
                count_delete++;
                text_delete += diffs[pointer][1];
                pointer++;
                break;
            case DIFF_EQUAL:
                // Upon reaching an equality, check for prior redundancies.
                if (count_delete + count_insert > 1) {
                    if (count_delete !== 0 && count_insert !== 0) {
                        // Factor out any common prefixies.
                        commonlength = this.diff_commonPrefix(text_insert, text_delete);
                        if (commonlength !== 0) {
                            if ((pointer - count_delete - count_insert) > 0 &&
                                diffs[pointer - count_delete - count_insert - 1][0] ==
                                DIFF_EQUAL) {
                                diffs[pointer - count_delete - count_insert - 1][1] +=
                                    text_insert.substring(0, commonlength);
                            } else {
                                diffs.splice(0, 0, new diff_match_patch.Diff(DIFF_EQUAL,
                                    text_insert.substring(0, commonlength)));
                                pointer++;
                            }
                            text_insert = text_insert.substring(commonlength);
                            text_delete = text_delete.substring(commonlength);
                        }
                        // Factor out any common suffixies.
                        commonlength = this.diff_commonSuffix(text_insert, text_delete);
                        if (commonlength !== 0) {
                            diffs[pointer][1] = text_insert.substring(text_insert.length -
                                commonlength) + diffs[pointer][1];
                            text_insert = text_insert.substring(0, text_insert.length -
                                commonlength);
                            text_delete = text_delete.substring(0, text_delete.length -
                                commonlength);
                        }
                    }
                    // Delete the offending records and add the merged ones.
                    pointer -= count_delete + count_insert;
                    diffs.splice(pointer, count_delete + count_insert);
                    if (text_delete.length) {
                        diffs.splice(pointer, 0,
                            new diff_match_patch.Diff(DIFF_DELETE, text_delete));
                        pointer++;
                    }
                    if (text_insert.length) {
                        diffs.splice(pointer, 0,
                            new diff_match_patch.Diff(DIFF_INSERT, text_insert));
                        pointer++;
                    }
                    pointer++;
                } else if (pointer !== 0 && diffs[pointer - 1][0] == DIFF_EQUAL) {
                    // Merge this equality with the previous one.
                    diffs[pointer - 1][1] += diffs[pointer][1];
                    diffs.splice(pointer, 1);
                } else {
                    pointer++;
                }
                count_insert = 0;
                count_delete = 0;
                text_delete = '';
                text_insert = '';
                break;
        }
    }
    if (diffs[diffs.length - 1][1] === '') {
        diffs.pop();  // 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
    var changes = false;
    pointer = 1;
    // Intentionally ignore the first and last element (don't need checking).
    while (pointer < diffs.length - 1) {
        if (diffs[pointer - 1][0] == DIFF_EQUAL &&
            diffs[pointer + 1][0] == DIFF_EQUAL) {
            // This is a single edit surrounded by equalities.
            if (diffs[pointer][1].substring(diffs[pointer][1].length -
                diffs[pointer - 1][1].length) == diffs[pointer - 1][1]) {
                // Shift the edit over the previous equality.
                diffs[pointer][1] = diffs[pointer - 1][1] +
                    diffs[pointer][1].substring(0, diffs[pointer][1].length -
                        diffs[pointer - 1][1].length);
                diffs[pointer + 1][1] = diffs[pointer - 1][1] + diffs[pointer + 1][1];
                diffs.splice(pointer - 1, 1);
                changes = true;
            } else if (diffs[pointer][1].substring(0, diffs[pointer + 1][1].length) ==
                diffs[pointer + 1][1]) {
                // Shift the edit over the next equality.
                diffs[pointer - 1][1] += diffs[pointer + 1][1];
                diffs[pointer][1] =
                    diffs[pointer][1].substring(diffs[pointer + 1][1].length) +
                    diffs[pointer + 1][1];
                diffs.splice(pointer + 1, 1);
                changes = true;
            }
        }
        pointer++;
    }
    // If shifts were made, the diff needs reordering and another shift sweep.
    if (changes) {
        this.diff_cleanupMerge(diffs);
    }
};


/**
 * loc is a location in text1, compute and return the equivalent location in
 * text2.
 * e.g. 'The cat' vs 'The big cat', 1->1, 5->8
 * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
 * @param {number} loc Location within text1.
 * @return {number} Location within text2.
 */
diff_match_patch.prototype.diff_xIndex = function (diffs, loc) {
    var chars1 = 0;
    var chars2 = 0;
    var last_chars1 = 0;
    var last_chars2 = 0;
    var x;
    for (x = 0; x < diffs.length; x++) {
        if (diffs[x][0] !== DIFF_INSERT) {  // Equality or deletion.
            chars1 += diffs[x][1].length;
        }
        if (diffs[x][0] !== DIFF_DELETE) {  // Equality or insertion.
            chars2 += diffs[x][1].length;
        }
        if (chars1 > loc) {  // Overshot the location.
            break;
        }
        last_chars1 = chars1;
        last_chars2 = chars2;
    }
    // Was the location was deleted?
    if (diffs.length != x && diffs[x][0] === DIFF_DELETE) {
        return last_chars2;
    }
    // Add the remaining character length.
    return last_chars2 + (loc - last_chars1);
};


/**
 * Convert a diff array into a pretty HTML report.
 * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
 * @return {string} HTML representation.
 */
diff_match_patch.prototype.diff_prettyHtml = function (diffs) {
    var html = [];
    var pattern_amp = /&/g;
    var pattern_lt = /</g;
    var pattern_gt = />/g;
    var pattern_para = /\n/g;
    for (var x = 0; x < diffs.length; x++) {
        var op = diffs[x][0];    // Operation (insert, delete, equal)
        var data = diffs[x][1];  // Text of change.
        var text = data.replace(pattern_amp, '&amp;').replace(pattern_lt, '&lt;')
            .replace(pattern_gt, '&gt;').replace(pattern_para, '&para;<br>');
        switch (op) {
            case DIFF_INSERT:
                html[x] = '<ins style="background:#e6ffe6;">' + text + '</ins>';
                break;
            case DIFF_DELETE:
                html[x] = '<del style="background:#ffe6e6;">' + text + '</del>';
                break;
            case DIFF_EQUAL:
                html[x] = '<span>' + text + '</span>';
                break;
        }
    }
    return html.join('');
};


/**
 * Compute and return the source text (all equalities and deletions).
 * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
 * @return {string} Source text.
 */
diff_match_patch.prototype.diff_text1 = function (diffs) {
    var text = [];
    for (var x = 0; x < diffs.length; x++) {
        if (diffs[x][0] !== DIFF_INSERT) {
            text[x] = diffs[x][1];
        }
    }
    return text.join('');
};


/**
 * Compute and return the destination text (all equalities and insertions).
 * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
 * @return {string} Destination text.
 */
diff_match_patch.prototype.diff_text2 = function (diffs) {
    var text = [];
    for (var x = 0; x < diffs.length; x++) {
        if (diffs[x][0] !== DIFF_DELETE) {
            text[x] = diffs[x][1];
        }
    }
    return text.join('');
};


/**
 * Compute the Levenshtein distance; the number of inserted, deleted or
 * substituted characters.
 * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
 * @return {number} Number of changes.
 */
diff_match_patch.prototype.diff_levenshtein = function (diffs) {
    var levenshtein = 0;
    var insertions = 0;
    var deletions = 0;
    for (var x = 0; x < diffs.length; x++) {
        var op = diffs[x][0];
        var data = diffs[x][1];
        switch (op) {
            case DIFF_INSERT:
                insertions += data.length;
                break;
            case DIFF_DELETE:
                deletions += data.length;
                break;
            case DIFF_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 {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
 * @return {string} Delta text.
 */
diff_match_patch.prototype.diff_toDelta = function (diffs) {
    var text = [];
    for (var x = 0; x < diffs.length; x++) {
        switch (diffs[x][0]) {
            case DIFF_INSERT:
                text[x] = '+' + encodeURI(diffs[x][1]);
                break;
            case DIFF_DELETE:
                text[x] = '-' + diffs[x][1].length;
                break;
            case DIFF_EQUAL:
                text[x] = '=' + diffs[x][1].length;
                break;
        }
    }
    return text.join('\t').replace(/%20/g, ' ');
};


/**
 * Given the original text1, and an encoded string which describes the
 * operations required to transform text1 into text2, compute the full diff.
 * @param {string} text1 Source string for the diff.
 * @param {string} delta Delta text.
 * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
 * @throws {!Error} If invalid input.
 */
diff_match_patch.prototype.diff_fromDelta = function (text1, delta) {
    var diffs = [];
    var diffsLength = 0;  // Keeping our own length var is faster in JS.
    var pointer = 0;  // Cursor in text1
    var tokens = delta.split(/\t/g);
    for (var x = 0; x < tokens.length; x++) {
        // Each token begins with a one character parameter which specifies the
        // operation of this token (delete, insert, equality).
        var param = tokens[x].substring(1);
        switch (tokens[x].charAt(0)) {
            case '+':
                try {
                    diffs[diffsLength++] =
                        new diff_match_patch.Diff(DIFF_INSERT, decodeURI(param));
                } catch (ex) {
                    // Malformed URI sequence.
                    throw new Error('Illegal escape in diff_fromDelta: ' + param);
                }
                break;
            case '-':
            // Fall through.
            case '=':
                var n = parseInt(param, 10);
                if (isNaN(n) || n < 0) {
                    throw new Error('Invalid number in diff_fromDelta: ' + param);
                }
                var text = text1.substring(pointer, pointer += n);
                if (tokens[x].charAt(0) == '=') {
                    diffs[diffsLength++] = new diff_match_patch.Diff(DIFF_EQUAL, text);
                } else {
                    diffs[diffsLength++] = new diff_match_patch.Diff(DIFF_DELETE, text);
                }
                break;
            default:
                // Blank tokens are ok (from a trailing \t).
                // Anything else is an error.
                if (tokens[x]) {
                    throw new Error('Invalid diff operation in diff_fromDelta: ' +
                        tokens[x]);
                }
        }
    }
    if (pointer != text1.length) {
        throw new Error('Delta length (' + pointer +
            ') does not equal source text length (' + text1.length + ').');
    }
    return diffs;
};


//  MATCH FUNCTIONS


/**
 * Locate the best instance of 'pattern' in 'text' near 'loc'.
 * @param {string} text The text to search.
 * @param {string} pattern The pattern to search for.
 * @param {number} loc The location to search around.
 * @return {number} Best match index or -1.
 */
diff_match_patch.prototype.match_main = function (text, pattern, loc) {
    // Check for null inputs.
    if (text == null || pattern == null || loc == null) {
        throw new Error('Null input. (match_main)');
    }

    loc = Math.max(0, Math.min(loc, text.length));
    if (text == pattern) {
        // Shortcut (potentially not guaranteed by the algorithm)
        return 0;
    } else if (!text.length) {
        // Nothing to match.
        return -1;
    } else if (text.substring(loc, loc + pattern.length) == pattern) {
        // Perfect match at the perfect spot!  (Includes case of null pattern)
        return loc;
    } else {
        // Do a fuzzy compare.
        return this.match_bitap_(text, pattern, loc);
    }
};


/**
 * Locate the best instance of 'pattern' in 'text' near 'loc' using the
 * Bitap algorithm.
 * @param {string} text The text to search.
 * @param {string} pattern The pattern to search for.
 * @param {number} loc The location to search around.
 * @return {number} Best match index or -1.
 * @private
 */
diff_match_patch.prototype.match_bitap_ = function (text, pattern, loc) {
    if (pattern.length > this.Match_MaxBits) {
        throw new Error('Pattern too long for this browser.');
    }

    // Initialise the alphabet.
    var s = this.match_alphabet_(pattern);

    var dmp = this;  // 'this' becomes 'window' in a closure.

    /**
     * Compute and return the score for a match with e errors and x location.
     * Accesses loc and pattern through being a closure.
     * @param {number} e Number of errors in match.
     * @param {number} x Location of match.
     * @return {number} Overall score for match (0.0 = good, 1.0 = bad).
     * @private
     */
    function match_bitapScore_(e, x) {
        var accuracy = e / pattern.length;
        var proximity = Math.abs(loc - x);
        if (!dmp.Match_Distance) {
            // Dodge divide by zero error.
            return proximity ? 1.0 : accuracy;
        }
        return accuracy + (proximity / dmp.Match_Distance);
    }

    // Highest score beyond which we give up.
    var score_threshold = this.Match_Threshold;
    // Is there a nearby exact match? (speedup)
    var best_loc = text.indexOf(pattern, loc);
    if (best_loc != -1) {
        score_threshold = Math.min(match_bitapScore_(0, best_loc), 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), score_threshold);
        }
    }

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

    var bin_min, bin_mid;
    var bin_max = pattern.length + text.length;
    var last_rd;
    for (var 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) <= score_threshold) {
                bin_min = bin_mid;
            } else {
                bin_max = bin_mid;
            }
            bin_mid = Math.floor((bin_max - bin_min) / 2 + bin_min);
        }
        // Use the result from this iteration as the maximum for the next.
        bin_max = bin_mid;
        var start = Math.max(1, loc - bin_mid + 1);
        var finish = Math.min(loc + bin_mid, text.length) + pattern.length;

        var rd = Array(finish + 2);
        rd[finish + 1] = (1 << d) - 1;
        for (var j = finish; j >= start; j--) {
            // The alphabet (s) is a sparse hash, so the following line generates
            // warnings.
            var charMatch = s[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) {
                var score = match_bitapScore_(d, j - 1);
                // 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;
                    }
                }
            }
        }
        // No hope for a (better) match at greater error levels.
        if (match_bitapScore_(d + 1, loc) > score_threshold) {
            break;
        }
        last_rd = rd;
    }
    return best_loc;
};


/**
 * Initialise the alphabet for the Bitap algorithm.
 * @param {string} pattern The text to encode.
 * @return {!Object} Hash of character locations.
 * @private
 */
diff_match_patch.prototype.match_alphabet_ = function (pattern) {
    var s = {};
    for (var i = 0; i < pattern.length; i++) {
        s[pattern.charAt(i)] = 0;
    }
    for (var i = 0; i < pattern.length; i++) {
        s[pattern.charAt(i)] |= 1 << (pattern.length - i - 1);
    }
    return s;
};


//  PATCH FUNCTIONS


/**
 * Increase the context until it is unique,
 * but don't let the pattern expand beyond Match_MaxBits.
 * @param {!diff_match_patch.patch_obj} patch The patch to grow.
 * @param {string} text Source text.
 * @private
 */
diff_match_patch.prototype.patch_addContext_ = function (patch, text) {
    if (text.length == 0) {
        return;
    }
    if (patch.start2 === null) {
        throw Error('patch not initialized');
    }
    var pattern = text.substring(patch.start2, patch.start2 + patch.length1);
    var 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 < this.Match_MaxBits - this.Patch_Margin -
    this.Patch_Margin) {
        padding += this.Patch_Margin;
        pattern = text.substring(patch.start2 - padding,
            patch.start2 + patch.length1 + padding);
    }
    // Add one chunk for good luck.
    padding += this.Patch_Margin;

    // Add the prefix.
    var prefix = text.substring(patch.start2 - padding, patch.start2);
    if (prefix) {
        patch.diffs.unshift(new diff_match_patch.Diff(DIFF_EQUAL, prefix));
    }
    // Add the suffix.
    var suffix = text.substring(patch.start2 + patch.length1,
        patch.start2 + patch.length1 + padding);
    if (suffix) {
        patch.diffs.push(new diff_match_patch.Diff(DIFF_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.
 * Use diffs if provided, otherwise compute it ourselves.
 * There are four ways to call this function, depending on what data is
 * available to the caller:
 * Method 1:
 * a = text1, b = text2
 * Method 2:
 * a = diffs
 * Method 3 (optimal):
 * a = text1, b = diffs
 * Method 4 (deprecated, use method 3):
 * a = text1, b = text2, c = diffs
 *
 * @param {string|!Array.<!diff_match_patch.Diff>} a text1 (methods 1,3,4) or
 * Array of diff tuples for text1 to text2 (method 2).
 * @param {string|!Array.<!diff_match_patch.Diff>=} opt_b text2 (methods 1,4) or
 * Array of diff tuples for text1 to text2 (method 3) or undefined (method 2).
 * @param {string|!Array.<!diff_match_patch.Diff>=} opt_c Array of diff tuples
 * for text1 to text2 (method 4) or undefined (methods 1,2,3).
 * @return {!Array.<!diff_match_patch.patch_obj>} Array of Patch objects.
 */
diff_match_patch.prototype.patch_make = function (a, opt_b, opt_c) {
    var text1, diffs;
    if (typeof a == 'string' && typeof opt_b == 'string' &&
        typeof opt_c == 'undefined') {
        // Method 1: text1, text2
        // Compute diffs from text1 and text2.
        text1 = /** @type {string} */(a);
        diffs = this.diff_main(text1, /** @type {string} */(opt_b), true);
        if (diffs.length > 2) {
            this.diff_cleanupSemantic(diffs);
            this.diff_cleanupEfficiency(diffs);
        }
    } else if (a && typeof a == 'object' && typeof opt_b == 'undefined' &&
        typeof opt_c == 'undefined') {
        // Method 2: diffs
        // Compute text1 from diffs.
        diffs = /** @type {!Array.<!diff_match_patch.Diff>} */(a);
        text1 = this.diff_text1(diffs);
    } else if (typeof a == 'string' && opt_b && typeof opt_b == 'object' &&
        typeof opt_c == 'undefined') {
        // Method 3: text1, diffs
        text1 = /** @type {string} */(a);
        diffs = /** @type {!Array.<!diff_match_patch.Diff>} */(opt_b);
    } else if (typeof a == 'string' && typeof opt_b == 'string' &&
        opt_c && typeof opt_c == 'object') {
        // Method 4: text1, text2, diffs
        // text2 is not used.
        text1 = /** @type {string} */(a);
        diffs = /** @type {!Array.<!diff_match_patch.Diff>} */(opt_c);
    } else {
        throw new Error('Unknown call format to patch_make.');
    }

    if (diffs.length === 0) {
        return [];  // Get rid of the null case.
    }
    var patches = [];
    var patch = new diff_match_patch.patch_obj();
    var patchDiffLength = 0;  // Keeping our own length var is faster in JS.
    var char_count1 = 0;  // Number of characters into the text1 string.
    var 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.
    var prepatch_text = text1;
    var postpatch_text = text1;
    for (var x = 0; x < diffs.length; x++) {
        var diff_type = diffs[x][0];
        var diff_text = diffs[x][1];

        if (!patchDiffLength && diff_type !== DIFF_EQUAL) {
            // A new patch starts here.
            patch.start1 = char_count1;
            patch.start2 = char_count2;
        }

        switch (diff_type) {
            case DIFF_INSERT:
                patch.diffs[patchDiffLength++] = diffs[x];
                patch.length2 += diff_text.length;
                postpatch_text = postpatch_text.substring(0, char_count2) + diff_text +
                    postpatch_text.substring(char_count2);
                break;
            case DIFF_DELETE:
                patch.length1 += diff_text.length;
                patch.diffs[patchDiffLength++] = diffs[x];
                postpatch_text = postpatch_text.substring(0, char_count2) +
                    postpatch_text.substring(char_count2 +
                        diff_text.length);
                break;
            case DIFF_EQUAL:
                if (diff_text.length <= 2 * this.Patch_Margin &&
                    patchDiffLength && diffs.length != x + 1) {
                    // Small equality inside a patch.
                    patch.diffs[patchDiffLength++] = diffs[x];
                    patch.length1 += diff_text.length;
                    patch.length2 += diff_text.length;
                } else if (diff_text.length >= 2 * this.Patch_Margin) {
                    // Time for a new patch.
                    if (patchDiffLength) {
                        this.patch_addContext_(patch, prepatch_text);
                        patches.push(patch);
                        patch = new diff_match_patch.patch_obj();
                        patchDiffLength = 0;
                        // 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 (diff_type !== DIFF_INSERT) {
            char_count1 += diff_text.length;
        }
        if (diff_type !== DIFF_DELETE) {
            char_count2 += diff_text.length;
        }
    }
    // Pick up the leftover patch if not empty.
    if (patchDiffLength) {
        this.patch_addContext_(patch, prepatch_text);
        patches.push(patch);
    }

    return patches;
};


/**
 * Given an array of patches, return another array that is identical.
 * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
 * @return {!Array.<!diff_match_patch.patch_obj>} Array of Patch objects.
 */
diff_match_patch.prototype.patch_deepCopy = function (patches) {
    // Making deep copies is hard in JavaScript.
    var patchesCopy = [];
    for (var x = 0; x < patches.length; x++) {
        var patch = patches[x];
        var patchCopy = new diff_match_patch.patch_obj();
        patchCopy.diffs = [];
        for (var y = 0; y < patch.diffs.length; y++) {
            patchCopy.diffs[y] =
                new diff_match_patch.Diff(patch.diffs[y][0], patch.diffs[y][1]);
        }
        patchCopy.start1 = patch.start1;
        patchCopy.start2 = patch.start2;
        patchCopy.length1 = patch.length1;
        patchCopy.length2 = patch.length2;
        patchesCopy[x] = patchCopy;
    }
    return patchesCopy;
};


/**
 * Merge a set of patches onto the text.  Return a patched text, as well
 * as a list of true/false values indicating which patches were applied.
 * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
 * @param {string} text Old text.
 * @return {!Array.<string|!Array.<boolean>>} Two element Array, containing the
 *      new text and an array of boolean values.
 */
diff_match_patch.prototype.patch_apply = function (patches, text) {
    if (patches.length == 0) {
        return [text, []];
    }

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

    var nullPadding = this.patch_addPadding(patches);
    text = nullPadding + text + nullPadding;

    this.patch_splitMax(patches);
    // 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.
    var delta = 0;
    var results = [];
    for (var x = 0; x < patches.length; x++) {
        var expected_loc = patches[x].start2 + delta;
        var text1 = this.diff_text1(patches[x].diffs);
        var start_loc;
        var 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 = this.match_main(text, text1.substring(0, this.Match_MaxBits),
                expected_loc);
            if (start_loc != -1) {
                end_loc = this.match_main(text,
                    text1.substring(text1.length - this.Match_MaxBits),
                    expected_loc + text1.length - this.Match_MaxBits);
                if (end_loc == -1 || start_loc >= end_loc) {
                    // Can't find valid trailing context.  Drop this patch.
                    start_loc = -1;
                }
            }
        } else {
            start_loc = this.match_main(text, text1, expected_loc);
        }
        if (start_loc == -1) {
            // No match found.  :(
            results[x] = false;
            // Subtract the delta for this failed patch from subsequent patches.
            delta -= patches[x].length2 - patches[x].length1;
        } else {
            // Found a match.  :)
            results[x] = true;
            delta = start_loc - expected_loc;
            var text2;
            if (end_loc == -1) {
                text2 = text.substring(start_loc, start_loc + text1.length);
            } else {
                text2 = text.substring(start_loc, end_loc + this.Match_MaxBits);
            }
            if (text1 == text2) {
                // Perfect match, just shove the replacement text in.
                text = text.substring(0, start_loc) +
                    this.diff_text2(patches[x].diffs) +
                    text.substring(start_loc + text1.length);
            } else {
                // Imperfect match.  Run a diff to get a framework of equivalent
                // indices.
                var diffs = this.diff_main(text1, text2, false);
                if (text1.length > this.Match_MaxBits &&
                    this.diff_levenshtein(diffs) / text1.length >
                    this.Patch_DeleteThreshold) {
                    // The end points match, but the content is unacceptably bad.
                    results[x] = false;
                } else {
                    this.diff_cleanupSemanticLossless(diffs);
                    var index1 = 0;
                    var index2;
                    for (var y = 0; y < patches[x].diffs.length; y++) {
                        var mod = patches[x].diffs[y];
                        if (mod[0] !== DIFF_EQUAL) {
                            index2 = this.diff_xIndex(diffs, index1);
                        }
                        if (mod[0] === DIFF_INSERT) {  // Insertion
                            text = text.substring(0, start_loc + index2) + mod[1] +
                                text.substring(start_loc + index2);
                        } else if (mod[0] === DIFF_DELETE) {  // Deletion
                            text = text.substring(0, start_loc + index2) +
                                text.substring(start_loc + this.diff_xIndex(diffs,
                                    index1 + mod[1].length));
                        }
                        if (mod[0] !== DIFF_DELETE) {
                            index1 += mod[1].length;
                        }
                    }
                }
            }
        }
    }
    // Strip the padding off.
    text = text.substring(nullPadding.length, text.length - nullPadding.length);
    return [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 {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
 * @return {string} The padding string added to each side.
 */
diff_match_patch.prototype.patch_addPadding = function (patches) {
    var paddingLength = this.Patch_Margin;
    var nullPadding = '';
    for (var x = 1; x <= paddingLength; x++) {
        nullPadding += String.fromCharCode(x);
    }

    // Bump all the patches forward.
    for (var x = 0; x < patches.length; x++) {
        patches[x].start1 += paddingLength;
        patches[x].start2 += paddingLength;
    }

    // Add some padding on start of first diff.
    var patch = patches[0];
    var diffs = patch.diffs;
    if (diffs.length == 0 || diffs[0][0] != DIFF_EQUAL) {
        // Add nullPadding equality.
        diffs.unshift(new diff_match_patch.Diff(DIFF_EQUAL, nullPadding));
        patch.start1 -= paddingLength;  // Should be 0.
        patch.start2 -= paddingLength;  // Should be 0.
        patch.length1 += paddingLength;
        patch.length2 += paddingLength;
    } else if (paddingLength > diffs[0][1].length) {
        // Grow first equality.
        var extraLength = paddingLength - diffs[0][1].length;
        diffs[0][1] = nullPadding.substring(diffs[0][1].length) + diffs[0][1];
        patch.start1 -= extraLength;
        patch.start2 -= extraLength;
        patch.length1 += extraLength;
        patch.length2 += extraLength;
    }

    // Add some padding on end of last diff.
    patch = patches[patches.length - 1];
    diffs = patch.diffs;
    if (diffs.length == 0 || diffs[diffs.length - 1][0] != DIFF_EQUAL) {
        // Add nullPadding equality.
        diffs.push(new diff_match_patch.Diff(DIFF_EQUAL, nullPadding));
        patch.length1 += paddingLength;
        patch.length2 += paddingLength;
    } else if (paddingLength > diffs[diffs.length - 1][1].length) {
        // Grow last equality.
        var extraLength = paddingLength - diffs[diffs.length - 1][1].length;
        diffs[diffs.length - 1][1] += 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 {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
 */
diff_match_patch.prototype.patch_splitMax = function (patches) {
    var patch_size = this.Match_MaxBits;
    for (var x = 0; x < patches.length; x++) {
        if (patches[x].length1 <= patch_size) {
            continue;
        }
        var bigpatch = patches[x];
        // Remove the big old patch.
        patches.splice(x--, 1);
        var start1 = bigpatch.start1;
        var start2 = bigpatch.start2;
        var precontext = '';
        while (bigpatch.diffs.length !== 0) {
            // Create one of several smaller patches.
            var patch = new diff_match_patch.patch_obj();
            var empty = true;
            patch.start1 = start1 - precontext.length;
            patch.start2 = start2 - precontext.length;
            if (precontext !== '') {
                patch.length1 = patch.length2 = precontext.length;
                patch.diffs.push(new diff_match_patch.Diff(DIFF_EQUAL, precontext));
            }
            while (bigpatch.diffs.length !== 0 &&
            patch.length1 < patch_size - this.Patch_Margin) {
                var diff_type = bigpatch.diffs[0][0];
                var diff_text = bigpatch.diffs[0][1];
                if (diff_type === DIFF_INSERT) {
                    // Insertions are harmless.
                    patch.length2 += diff_text.length;
                    start2 += diff_text.length;
                    patch.diffs.push(bigpatch.diffs.shift());
                    empty = false;
                } else if (diff_type === DIFF_DELETE && patch.diffs.length == 1 &&
                    patch.diffs[0][0] == DIFF_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.push(new diff_match_patch.Diff(diff_type, diff_text));
                    bigpatch.diffs.shift();
                } else {
                    // Deletion or equality.  Only take as much as we can stomach.
                    diff_text = diff_text.substring(0,
                        patch_size - patch.length1 - this.Patch_Margin);
                    patch.length1 += diff_text.length;
                    start1 += diff_text.length;
                    if (diff_type === DIFF_EQUAL) {
                        patch.length2 += diff_text.length;
                        start2 += diff_text.length;
                    } else {
                        empty = false;
                    }
                    patch.diffs.push(new diff_match_patch.Diff(diff_type, diff_text));
                    if (diff_text == bigpatch.diffs[0][1]) {
                        bigpatch.diffs.shift();
                    } else {
                        bigpatch.diffs[0][1] =
                            bigpatch.diffs[0][1].substring(diff_text.length);
                    }
                }
            }
            // Compute the head context for the next patch.
            precontext = this.diff_text2(patch.diffs);
            precontext =
                precontext.substring(precontext.length - this.Patch_Margin);
            // Append the end context for this patch.
            var postcontext = this.diff_text1(bigpatch.diffs)
                .substring(0, this.Patch_Margin);
            if (postcontext !== '') {
                patch.length1 += postcontext.length;
                patch.length2 += postcontext.length;
                if (patch.diffs.length !== 0 &&
                    patch.diffs[patch.diffs.length - 1][0] === DIFF_EQUAL) {
                    patch.diffs[patch.diffs.length - 1][1] += postcontext;
                } else {
                    patch.diffs.push(new diff_match_patch.Diff(DIFF_EQUAL, postcontext));
                }
            }
            if (!empty) {
                patches.splice(++x, 0, patch);
            }
        }
    }
};


/**
 * Take a list of patches and return a textual representation.
 * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
 * @return {string} Text representation of patches.
 */
diff_match_patch.prototype.patch_toText = function (patches) {
    var text = [];
    for (var x = 0; x < patches.length; x++) {
        text[x] = patches[x];
    }
    return text.join('');
};


/**
 * Parse a textual representation of patches and return a list of Patch objects.
 * @param {string} textline Text representation of patches.
 * @return {!Array.<!diff_match_patch.patch_obj>} Array of Patch objects.
 * @throws {!Error} If invalid input.
 */
diff_match_patch.prototype.patch_fromText = function (textline) {
    var patches = [];
    if (!textline) {
        return patches;
    }
    var text = textline.split('\n');
    var textPointer = 0;
    var patchHeader = /^@@ -(\d+),?(\d*) \+(\d+),?(\d*) @@$/;
    while (textPointer < text.length) {
        var m = text[textPointer].match(patchHeader);
        if (!m) {
            throw new Error('Invalid patch string: ' + text[textPointer]);
        }
        var patch = new diff_match_patch.patch_obj();
        patches.push(patch);
        patch.start1 = parseInt(m[1], 10);
        if (m[2] === '') {
            patch.start1--;
            patch.length1 = 1;
        } else if (m[2] == '0') {
            patch.length1 = 0;
        } else {
            patch.start1--;
            patch.length1 = parseInt(m[2], 10);
        }

        patch.start2 = parseInt(m[3], 10);
        if (m[4] === '') {
            patch.start2--;
            patch.length2 = 1;
        } else if (m[4] == '0') {
            patch.length2 = 0;
        } else {
            patch.start2--;
            patch.length2 = parseInt(m[4], 10);
        }
        textPointer++;

        while (textPointer < text.length) {
            var sign = text[textPointer].charAt(0);
            try {
                var line = decodeURI(text[textPointer].substring(1));
            } catch (ex) {
                // Malformed URI sequence.
                throw new Error('Illegal escape in patch_fromText: ' + line);
            }
            if (sign == '-') {
                // Deletion.
                patch.diffs.push(new diff_match_patch.Diff(DIFF_DELETE, line));
            } else if (sign == '+') {
                // Insertion.
                patch.diffs.push(new diff_match_patch.Diff(DIFF_INSERT, line));
            } else if (sign == ' ') {
                // Minor equality.
                patch.diffs.push(new diff_match_patch.Diff(DIFF_EQUAL, line));
            } else if (sign == '@') {
                // Start of next patch.
                break;
            } else if (sign === '') {
                // Blank line?  Whatever.
            } else {
                // WTF?
                throw new Error('Invalid patch mode "' + sign + '" in: ' + line);
            }
            textPointer++;
        }
    }
    return patches;
};


/**
 * Class representing one patch operation.
 * @constructor
 */
diff_match_patch.patch_obj = function () {
    /** @type {!Array.<!diff_match_patch.Diff>} */
    this.diffs = [];
    /** @type {?number} */
    this.start1 = null;
    /** @type {?number} */
    this.start2 = null;
    /** @type {number} */
    this.length1 = 0;
    /** @type {number} */
    this.length2 = 0;
};


/**
 * Emulate GNU diff's format.
 * Header: @@ -382,8 +481,9 @@
 * Indices are printed as 1-based, not 0-based.
 * @return {string} The GNU diff string.
 */
diff_match_patch.patch_obj.prototype.toString = function () {
    var coords1, coords2;
    if (this.length1 === 0) {
        coords1 = this.start1 + ',0';
    } else if (this.length1 == 1) {
        coords1 = this.start1 + 1;
    } else {
        coords1 = (this.start1 + 1) + ',' + this.length1;
    }
    if (this.length2 === 0) {
        coords2 = this.start2 + ',0';
    } else if (this.length2 == 1) {
        coords2 = this.start2 + 1;
    } else {
        coords2 = (this.start2 + 1) + ',' + this.length2;
    }
    var text = ['@@ -' + coords1 + ' +' + coords2 + ' @@\n'];
    var op;
    // Escape the body of the patch with %xx notation.
    for (var x = 0; x < this.diffs.length; x++) {
        switch (this.diffs[x][0]) {
            case DIFF_INSERT:
                op = '+';
                break;
            case DIFF_DELETE:
                op = '-';
                break;
            case DIFF_EQUAL:
                op = ' ';
                break;
        }
        text[x + 1] = op + encodeURI(this.diffs[x][1]) + '\n';
    }
    return text.join('').replace(/%20/g, ' ');
};

// CLOSURE:begin_strip
// Lines below here will not be included in the Closure-compatible library.

// Export these global variables so that they survive Google's JS compiler.
// In a browser, 'this' will be 'window'.
// Users of node.js should 'require' the uncompressed version since Google's
// JS compiler may break the following exports for non-browser environments.
/** @suppress {globalThis} */
this['diff_match_patch'] = diff_match_patch;
/** @suppress {globalThis} */
this['DIFF_DELETE'] = DIFF_DELETE;
/** @suppress {globalThis} */
this['DIFF_INSERT'] = DIFF_INSERT;
/** @suppress {globalThis} */
this['DIFF_EQUAL'] = DIFF_EQUAL;