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@giancarlo /diff.js
Last active May 12, 2016

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/**
* @license
* Adapted from fast-diff library(https://github.com/jhchen/fast-diff/blob/master/diff.js) by jhchen.
*
* This library modifies the diff-patch-match library by Neil Fraser
* by removing the patch and match functionality and certain advanced
* options in the diff function. The original license is as follows:
*
* ===
*
* 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.
*/
(function(ide) {
"use strict";
/* jshint maxdepth: 5 */
/**
* 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;
/**
* 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.
* @return {Array} Array of diff tuples.
*/
function diff_main(text1, text2) {
// Check for equality (speedup).
if (text1 === text2) {
if (text1) {
return [[DIFF_EQUAL, text1]];
}
return [];
}
// Trim off common prefix (speedup).
var commonlength = diff_commonPrefix(text1, text2);
var commonprefix = text1.slice(0, commonlength);
text1 = text1.slice(commonlength);
text2 = text2.slice(commonlength);
// Trim off common suffix (speedup).
commonlength = diff_commonSuffix(text1, text2);
var commonsuffix = text1.slice(text1.length - commonlength);
text1 = text1.slice(0, text1.length - commonlength);
text2 = text2.slice(0, text2.length - commonlength);
// Compute the diff on the middle block.
var diffs = diff_compute_(text1, text2);
// Restore the prefix and suffix.
if (commonprefix) {
diffs.unshift([DIFF_EQUAL, commonprefix]);
}
if (commonsuffix) {
diffs.push([DIFF_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 {string} text1 Old string to be diffed.
* @param {string} text2 New string to be diffed.
* @return {Array} Array of diff tuples.
*/
function diff_compute_(text1, text2) {
var diffs;
if (!text1) {
// Just add some text (speedup).
return [[DIFF_INSERT, text2]];
}
if (!text2) {
// Just delete some text (speedup).
return [[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 = [[DIFF_INSERT, longtext.slice(0, i)],
[DIFF_EQUAL, shorttext],
[DIFF_INSERT, longtext.slice(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 [[DIFF_DELETE, text1], [DIFF_INSERT, text2]];
}
// Check to see if the problem can be split in two.
var hm = 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 = diff_main(text1_a, text2_a);
var diffs_b = diff_main(text1_b, text2_b);
// Merge the results.
return diffs_a.concat([[DIFF_EQUAL, mid_common]], diffs_b);
}
return diff_bisect_(text1, text2);
}
/**
* 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.
* @return {Array} Array of diff tuples.
* @private
*/
function diff_bisect_(text1, text2) {
// 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;
var k2_offset, x2, x1, y1, k1_offset;
for (var d = 0; d < max_d; d++) {
// Walk the front path one step.
for (var k1 = -d + k1start; k1 <= d - k1end; k1 += 2) {
k1_offset = v_offset + k1;
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;
}
y1 = x1 - k1;
while (x1 < text1_length && y1 < text2_length &&
text1[x1] === text2[y1]) {
x1++;
y1++;
}
v1[k1_offset] = x1;
if (x1 > text1_length) {
// Ran off the right of the graph.
k1end += 2;
} else if (y1 > text2_length) {
// Ran off the bottom of the graph.
k1start += 2;
} else if (front) {
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.
x2 = text1_length - v2[k2_offset];
if (x1 >= x2) {
// Overlap detected.
return diff_bisectSplit_(text1, text2, x1, y1);
}
}
}
}
// Walk the reverse path one step.
for (var k2 = -d + k2start; k2 <= d - k2end; k2 += 2) {
k2_offset = v_offset + k2;
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[text1_length - x2 - 1] ===
text2[text2_length - y2 - 1]) {
x2++;
y2++;
}
v2[k2_offset] = x2;
if (x2 > text1_length) {
// Ran off the left of the graph.
k2end += 2;
} else if (y2 > text2_length) {
// Ran off the top of the graph.
k2start += 2;
} else if (!front) {
k1_offset = v_offset + delta - k2;
if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] !== -1) {
x1 = v1[k1_offset];
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);
}
}
}
}
}
// Diff took too long and hit the deadline or
// number of diffs equals number of characters, no commonality at all.
return [[DIFF_DELETE, text1], [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.
* @return {Array} Array of diff tuples.
*/
function diff_bisectSplit_(text1, text2, x, y) {
var text1a = text1.slice(0, x);
var text2a = text2.slice(0, y);
var text1b = text1.slice(x);
var text2b = text2.slice(y);
// Compute both diffs serially.
var diffs = diff_main(text1a, text2a);
var diffsb = diff_main(text1b, text2b);
return diffs.concat(diffsb);
}
/**
* 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.
*/
function diff_commonPrefix(text1, text2) {
// Quick check for common null cases.
if (!text1 || !text2 || text1[0] !== text2[0]) {
return 0;
}
// Binary search.
// Performance analysis: http://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.slice(pointerstart, pointermid) ===
text2.slice(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.
*/
function diff_commonSuffix(text1, text2) {
// Quick check for common null cases.
if (!text1 || !text2 ||
text1[text1.length - 1] !== text2[text2.length - 1]) {
return 0;
}
// Binary search.
// Performance analysis: http://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.slice(text1.length - pointermid, text1.length - pointerend) ===
text2.slice(text2.length - pointermid, text2.length - pointerend)) {
pointermin = pointermid;
pointerend = pointermin;
} else {
pointermax = pointermid;
}
pointermid = Math.floor((pointermax - pointermin) / 2 + pointermin);
}
return pointermid;
}
/**
* 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.
*/
function diff_halfMatch_(text1, text2) {
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.
}
/**
* 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.slice(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 = diff_commonPrefix(longtext.slice(i),
shorttext.slice(j));
var suffixLength = diff_commonSuffix(longtext.slice(0, i),
shorttext.slice(0, j));
if (best_common.length < suffixLength + prefixLength) {
best_common = shorttext.slice(j - suffixLength, j) +
shorttext.slice(j, j + prefixLength);
best_longtext_a = longtext.slice(0, i - suffixLength);
best_longtext_b = longtext.slice(i + prefixLength);
best_shorttext_a = shorttext.slice(0, j - suffixLength);
best_shorttext_b = shorttext.slice(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];
}
/**
* Reorder and merge like edit sections. Merge equalities.
* Any edit section can move as long as it doesn't cross an equality.
* @param {Array} diffs Array of diff tuples.
*/
function diff_cleanupMerge(diffs) {
diffs.push([DIFF_EQUAL, '']); // Add a dummy entry at the end.
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 = 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.slice(0, commonlength);
} else {
diffs.splice(0, 0, [DIFF_EQUAL,
text_insert.slice(0, commonlength)]);
pointer++;
}
text_insert = text_insert.slice(commonlength);
text_delete = text_delete.slice(commonlength);
}
// Factor out any common suffixies.
commonlength = diff_commonSuffix(text_insert, text_delete);
if (commonlength !== 0) {
diffs[pointer][1] = text_insert.slice(text_insert.length -
commonlength) + diffs[pointer][1];
text_insert = text_insert.slice(0, text_insert.length -
commonlength);
text_delete = text_delete.slice(0, text_delete.length -
commonlength);
}
}
// Delete the offending records and add the merged ones.
if (count_delete === 0) {
diffs.splice(pointer - count_insert,
count_delete + count_insert, [DIFF_INSERT, text_insert]);
} else if (count_insert === 0) {
diffs.splice(pointer - count_delete,
count_delete + count_insert, [DIFF_DELETE, text_delete]);
} else {
diffs.splice(pointer - count_delete - count_insert,
count_delete + count_insert, [DIFF_DELETE, text_delete],
[DIFF_INSERT, text_insert]);
}
pointer = pointer - count_delete - count_insert +
(count_delete ? 1 : 0) + (count_insert ? 1 : 0) + 1;
} 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].slice(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].slice(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].slice(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].slice(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) {
diff_cleanupMerge(diffs);
}
}
ide.diff = function(A, B, minl)
{
var
result=[],
d = diff_main(A, B),
i, l=0, ch=''
;
minl = minl===undefined ? 5 : minl;
function push(a, b, c)
{
if (result.length && (b < minl))
{
result[result.length-3] += ch + a;
result[result.length-1] += b + c;
} else
result.push(a, b, c);
}
for (i=0; i<d.length; i++)
{
if (d[i][0]===DIFF_EQUAL)
{
l = d[i][1].length;
ch = d[i][1];
}
else
{
if (d[i][0]===DIFF_DELETE)
push('', l, d[i][1].length);
else
push(d[i][1], l, 0);
l = 0;
ch = '';
}
}
return result;
};
ide.patch = function(A, diff)
{
var
i, cursor=0, result=''
;
for (i=0; i<diff.length; i+=3)
{
result += A.substr(cursor, diff[i+1]) + diff[i];
cursor += diff[i+1] + diff[i+2];
}
if (cursor < A.length)
result += A.substr(cursor);
return result;
};
})(this.ide);
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