import QUnit from "../src/core";
import { escapeText } from "./html";

/*
 * This file is a modified version of google-diff-match-patch's JavaScript implementation
 * (https://code.google.com/p/google-diff-match-patch/source/browse/trunk/javascript/diff_match_patch_uncompressed.js),
 * modifications are licensed as more fully set forth in LICENSE.txt.
 *
 * The original source of google-diff-match-patch is attributable and licensed as follows:
 *
 * Copyright 2006 Google Inc.
 * https://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
 *
 * https://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.
 *
 * More Info:
 *  https://code.google.com/p/google-diff-match-patch/
 *
 * Usage: QUnit.diff(expected, actual)
 *
 */
QUnit.diff = ( function() {
	function DiffMatchPatch() {
	}

	//  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,
		DIFF_INSERT = 1,
		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.
	 * @param {boolean=} optChecklines 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.
	 * @return {!Array.<!DiffMatchPatch.Diff>} Array of diff tuples.
	 */
	DiffMatchPatch.prototype.DiffMain = function( text1, text2, optChecklines ) {
		var deadline, checklines, commonlength,
			commonprefix, commonsuffix, diffs;

		// The diff must be complete in up to 1 second.
		deadline = ( new Date() ).getTime() + 1000;

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

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

		if ( typeof optChecklines === "undefined" ) {
			optChecklines = true;
		}

		checklines = optChecklines;

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

		// Trim off common suffix (speedup).
		commonlength = this.diffCommonSuffix( text1, text2 );
		commonsuffix = text1.substring( text1.length - commonlength );
		text1 = text1.substring( 0, text1.length - commonlength );
		text2 = text2.substring( 0, text2.length - commonlength );

		// Compute the diff on the middle block.
		diffs = this.diffCompute( text1, text2, checklines, deadline );

		// Restore the prefix and suffix.
		if ( commonprefix ) {
			diffs.unshift( [ DIFF_EQUAL, commonprefix ] );
		}
		if ( commonsuffix ) {
			diffs.push( [ DIFF_EQUAL, commonsuffix ] );
		}
		this.diffCleanupMerge( diffs );
		return diffs;
	};

	/**
	 * Reduce the number of edits by eliminating operationally trivial equalities.
	 * @param {!Array.<!DiffMatchPatch.Diff>} diffs Array of diff tuples.
	 */
	DiffMatchPatch.prototype.diffCleanupEfficiency = function( diffs ) {
		var changes, equalities, equalitiesLength, lastequality,
			pointer, preIns, preDel, postIns, postDel;
		changes = false;
		equalities = []; // Stack of indices where equalities are found.
		equalitiesLength = 0; // Keeping our own length var is faster in JS.
		/** @type {?string} */
		lastequality = null;

		// Always equal to diffs[equalities[equalitiesLength - 1]][1]
		pointer = 0; // Index of current position.

		// Is there an insertion operation before the last equality.
		preIns = false;

		// Is there a deletion operation before the last equality.
		preDel = false;

		// Is there an insertion operation after the last equality.
		postIns = false;

		// Is there a deletion operation after the last equality.
		postDel = false;
		while ( pointer < diffs.length ) {

			// Equality found.
			if ( diffs[ pointer ][ 0 ] === DIFF_EQUAL ) {
				if ( diffs[ pointer ][ 1 ].length < 4 && ( postIns || postDel ) ) {

					// Candidate found.
					equalities[ equalitiesLength++ ] = pointer;
					preIns = postIns;
					preDel = postDel;
					lastequality = diffs[ pointer ][ 1 ];
				} else {

					// Not a candidate, and can never become one.
					equalitiesLength = 0;
					lastequality = null;
				}
				postIns = postDel = false;

			// An insertion or deletion.
			} else {

				if ( diffs[ pointer ][ 0 ] === DIFF_DELETE ) {
					postDel = true;
				} else {
					postIns = 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 && ( ( preIns && preDel && postIns && postDel ) ||
						( ( lastequality.length < 2 ) &&
						( preIns + preDel + postIns + postDel ) === 3 ) ) ) {

					// Duplicate record.
					diffs.splice(
						equalities[ equalitiesLength - 1 ],
						0,
						[ 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 ( preIns && preDel ) {

						// No changes made which could affect previous entry, keep going.
						postIns = postDel = true;
						equalitiesLength = 0;
					} else {
						equalitiesLength--; // Throw away the previous equality.
						pointer = equalitiesLength > 0 ? equalities[ equalitiesLength - 1 ] : -1;
						postIns = postDel = false;
					}
					changes = true;
				}
			}
			pointer++;
		}

		if ( changes ) {
			this.diffCleanupMerge( diffs );
		}
	};

	/**
	 * Convert a diff array into a pretty HTML report.
	 * @param {!Array.<!DiffMatchPatch.Diff>} diffs Array of diff tuples.
	 * @param {integer} string to be beautified.
	 * @return {string} HTML representation.
	 */
	DiffMatchPatch.prototype.diffPrettyHtml = function( diffs ) {
		var op, data, x,
			html = [];
		for ( x = 0; x < diffs.length; x++ ) {
			op = diffs[ x ][ 0 ]; // Operation (insert, delete, equal)
			data = diffs[ x ][ 1 ]; // Text of change.
			switch ( op ) {
			case DIFF_INSERT:
				html[ x ] = "<ins>" + escapeText( data ) + "</ins>";
				break;
			case DIFF_DELETE:
				html[ x ] = "<del>" + escapeText( data ) + "</del>";
				break;
			case DIFF_EQUAL:
				html[ x ] = "<span>" + escapeText( data ) + "</span>";
				break;
			}
		}
		return html.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.
	 */
	DiffMatchPatch.prototype.diffCommonPrefix = function( text1, text2 ) {
		var pointermid, pointermax, pointermin, pointerstart;

		// 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/
		pointermin = 0;
		pointermax = Math.min( text1.length, text2.length );
		pointermid = pointermax;
		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.
	 */
	DiffMatchPatch.prototype.diffCommonSuffix = function( text1, text2 ) {
		var pointermid, pointermax, pointermin, pointerend;

		// 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/
		pointermin = 0;
		pointermax = Math.min( text1.length, text2.length );
		pointermid = pointermax;
		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;
	};

	/**
	 * 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.<!DiffMatchPatch.Diff>} Array of diff tuples.
	 * @private
	 */
	DiffMatchPatch.prototype.diffCompute = function( text1, text2, checklines, deadline ) {
		var diffs, longtext, shorttext, i, hm,
			text1A, text2A, text1B, text2B,
			midCommon, diffsA, diffsB;

		if ( !text1 ) {

			// Just add some text (speedup).
			return [
				[ DIFF_INSERT, text2 ]
			];
		}

		if ( !text2 ) {

			// Just delete some text (speedup).
			return [
				[ DIFF_DELETE, text1 ]
			];
		}

		longtext = text1.length > text2.length ? text1 : text2;
		shorttext = text1.length > text2.length ? text2 : text1;
		i = longtext.indexOf( shorttext );
		if ( i !== -1 ) {

			// Shorter text is inside the longer text (speedup).
			diffs = [
				[ DIFF_INSERT, longtext.substring( 0, i ) ],
				[ DIFF_EQUAL, shorttext ],
				[ 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 [
				[ DIFF_DELETE, text1 ],
				[ DIFF_INSERT, text2 ]
			];
		}

		// Check to see if the problem can be split in two.
		hm = this.diffHalfMatch( text1, text2 );
		if ( hm ) {

			// A half-match was found, sort out the return data.
			text1A = hm[ 0 ];
			text1B = hm[ 1 ];
			text2A = hm[ 2 ];
			text2B = hm[ 3 ];
			midCommon = hm[ 4 ];

			// Send both pairs off for separate processing.
			diffsA = this.DiffMain( text1A, text2A, checklines, deadline );
			diffsB = this.DiffMain( text1B, text2B, checklines, deadline );

			// Merge the results.
			return diffsA.concat( [
				[ DIFF_EQUAL, midCommon ]
			], diffsB );
		}

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

		return this.diffBisect( text1, text2, deadline );
	};

	/**
	 * 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
	 */
	DiffMatchPatch.prototype.diffHalfMatch = function( text1, text2 ) {
		var longtext, shorttext, dmp,
			text1A, text2B, text2A, text1B, midCommon,
			hm1, hm2, hm;

		longtext = text1.length > text2.length ? text1 : text2;
		shorttext = text1.length > text2.length ? text2 : text1;
		if ( longtext.length < 4 || shorttext.length * 2 < longtext.length ) {
			return null; // Pointless.
		}
		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 diffHalfMatchI( longtext, shorttext, i ) {
			var seed, j, bestCommon, prefixLength, suffixLength,
				bestLongtextA, bestLongtextB, bestShorttextA, bestShorttextB;

			// Start with a 1/4 length substring at position i as a seed.
			seed = longtext.substring( i, i + Math.floor( longtext.length / 4 ) );
			j = -1;
			bestCommon = "";
			while ( ( j = shorttext.indexOf( seed, j + 1 ) ) !== -1 ) {
				prefixLength = dmp.diffCommonPrefix( longtext.substring( i ),
					shorttext.substring( j ) );
				suffixLength = dmp.diffCommonSuffix( longtext.substring( 0, i ),
					shorttext.substring( 0, j ) );
				if ( bestCommon.length < suffixLength + prefixLength ) {
					bestCommon = shorttext.substring( j - suffixLength, j ) +
						shorttext.substring( j, j + prefixLength );
					bestLongtextA = longtext.substring( 0, i - suffixLength );
					bestLongtextB = longtext.substring( i + prefixLength );
					bestShorttextA = shorttext.substring( 0, j - suffixLength );
					bestShorttextB = shorttext.substring( j + prefixLength );
				}
			}
			if ( bestCommon.length * 2 >= longtext.length ) {
				return [ bestLongtextA, bestLongtextB,
					bestShorttextA, bestShorttextB, bestCommon
				];
			} else {
				return null;
			}
		}

		// First check if the second quarter is the seed for a half-match.
		hm1 = diffHalfMatchI( longtext, shorttext,
			Math.ceil( longtext.length / 4 ) );

		// Check again based on the third quarter.
		hm2 = diffHalfMatchI( longtext, shorttext,
			Math.ceil( longtext.length / 2 ) );
		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.
		if ( text1.length > text2.length ) {
			text1A = hm[ 0 ];
			text1B = hm[ 1 ];
			text2A = hm[ 2 ];
			text2B = hm[ 3 ];
		} else {
			text2A = hm[ 0 ];
			text2B = hm[ 1 ];
			text1A = hm[ 2 ];
			text1B = hm[ 3 ];
		}
		midCommon = hm[ 4 ];
		return [ text1A, text1B, text2A, text2B, midCommon ];
	};

	/**
	 * 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.<!DiffMatchPatch.Diff>} Array of diff tuples.
	 * @private
	 */
	DiffMatchPatch.prototype.diffLineMode = function( text1, text2, deadline ) {
		var a, diffs, linearray, pointer, countInsert,
			countDelete, textInsert, textDelete, j;

		// Scan the text on a line-by-line basis first.
		a = this.diffLinesToChars( text1, text2 );
		text1 = a.chars1;
		text2 = a.chars2;
		linearray = a.lineArray;

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

		// Convert the diff back to original text.
		this.diffCharsToLines( diffs, linearray );

		// Eliminate freak matches (e.g. blank lines)
		this.diffCleanupSemantic( diffs );

		// Rediff any replacement blocks, this time character-by-character.
		// Add a dummy entry at the end.
		diffs.push( [ DIFF_EQUAL, "" ] );
		pointer = 0;
		countDelete = 0;
		countInsert = 0;
		textDelete = "";
		textInsert = "";
		while ( pointer < diffs.length ) {
			switch ( diffs[ pointer ][ 0 ] ) {
			case DIFF_INSERT:
				countInsert++;
				textInsert += diffs[ pointer ][ 1 ];
				break;
			case DIFF_DELETE:
				countDelete++;
				textDelete += diffs[ pointer ][ 1 ];
				break;
			case DIFF_EQUAL:

				// Upon reaching an equality, check for prior redundancies.
				if ( countDelete >= 1 && countInsert >= 1 ) {

					// Delete the offending records and add the merged ones.
					diffs.splice( pointer - countDelete - countInsert,
						countDelete + countInsert );
					pointer = pointer - countDelete - countInsert;
					a = this.DiffMain( textDelete, textInsert, false, deadline );
					for ( j = a.length - 1; j >= 0; j-- ) {
						diffs.splice( pointer, 0, a[ j ] );
					}
					pointer = pointer + a.length;
				}
				countInsert = 0;
				countDelete = 0;
				textDelete = "";
				textInsert = "";
				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.<!DiffMatchPatch.Diff>} Array of diff tuples.
	 * @private
	 */
	DiffMatchPatch.prototype.diffBisect = function( text1, text2, deadline ) {
		var text1Length, text2Length, maxD, vOffset, vLength,
			v1, v2, x, delta, front, k1start, k1end, k2start,
			k2end, k2Offset, k1Offset, x1, x2, y1, y2, d, k1, k2;

		// Cache the text lengths to prevent multiple calls.
		text1Length = text1.length;
		text2Length = text2.length;
		maxD = Math.ceil( ( text1Length + text2Length ) / 2 );
		vOffset = maxD;
		vLength = 2 * maxD;
		v1 = new Array( vLength );
		v2 = new Array( vLength );

		// Setting all elements to -1 is faster in Chrome & Firefox than mixing
		// integers and undefined.
		for ( x = 0; x < vLength; x++ ) {
			v1[ x ] = -1;
			v2[ x ] = -1;
		}
		v1[ vOffset + 1 ] = 0;
		v2[ vOffset + 1 ] = 0;
		delta = text1Length - text2Length;

		// If the total number of characters is odd, then the front path will collide
		// with the reverse path.
		front = ( delta % 2 !== 0 );

		// Offsets for start and end of k loop.
		// Prevents mapping of space beyond the grid.
		k1start = 0;
		k1end = 0;
		k2start = 0;
		k2end = 0;
		for ( d = 0; d < maxD; d++ ) {

			// Bail out if deadline is reached.
			if ( ( new Date() ).getTime() > deadline ) {
				break;
			}

			// Walk the front path one step.
			for ( k1 = -d + k1start; k1 <= d - k1end; k1 += 2 ) {
				k1Offset = vOffset + k1;
				if ( k1 === -d || ( k1 !== d && v1[ k1Offset - 1 ] < v1[ k1Offset + 1 ] ) ) {
					x1 = v1[ k1Offset + 1 ];
				} else {
					x1 = v1[ k1Offset - 1 ] + 1;
				}
				y1 = x1 - k1;
				while ( x1 < text1Length && y1 < text2Length &&
					text1.charAt( x1 ) === text2.charAt( y1 ) ) {
					x1++;
					y1++;
				}
				v1[ k1Offset ] = x1;
				if ( x1 > text1Length ) {

					// Ran off the right of the graph.
					k1end += 2;
				} else if ( y1 > text2Length ) {

					// Ran off the bottom of the graph.
					k1start += 2;
				} else if ( front ) {
					k2Offset = vOffset + delta - k1;
					if ( k2Offset >= 0 && k2Offset < vLength && v2[ k2Offset ] !== -1 ) {

						// Mirror x2 onto top-left coordinate system.
						x2 = text1Length - v2[ k2Offset ];
						if ( x1 >= x2 ) {

							// Overlap detected.
							return this.diffBisectSplit( text1, text2, x1, y1, deadline );
						}
					}
				}
			}

			// Walk the reverse path one step.
			for ( k2 = -d + k2start; k2 <= d - k2end; k2 += 2 ) {
				k2Offset = vOffset + k2;
				if ( k2 === -d || ( k2 !== d && v2[ k2Offset - 1 ] < v2[ k2Offset + 1 ] ) ) {
					x2 = v2[ k2Offset + 1 ];
				} else {
					x2 = v2[ k2Offset - 1 ] + 1;
				}
				y2 = x2 - k2;
				while ( x2 < text1Length && y2 < text2Length &&
					text1.charAt( text1Length - x2 - 1 ) ===
					text2.charAt( text2Length - y2 - 1 ) ) {
					x2++;
					y2++;
				}
				v2[ k2Offset ] = x2;
				if ( x2 > text1Length ) {

					// Ran off the left of the graph.
					k2end += 2;
				} else if ( y2 > text2Length ) {

					// Ran off the top of the graph.
					k2start += 2;
				} else if ( !front ) {
					k1Offset = vOffset + delta - k2;
					if ( k1Offset >= 0 && k1Offset < vLength && v1[ k1Offset ] !== -1 ) {
						x1 = v1[ k1Offset ];
						y1 = vOffset + x1 - k1Offset;

						// Mirror x2 onto top-left coordinate system.
						x2 = text1Length - x2;
						if ( x1 >= x2 ) {

							// Overlap detected.
							return this.diffBisectSplit( 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 [
			[ 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.
	 * @param {number} deadline Time at which to bail if not yet complete.
	 * @return {!Array.<!DiffMatchPatch.Diff>} Array of diff tuples.
	 * @private
	 */
	DiffMatchPatch.prototype.diffBisectSplit = function( text1, text2, x, y, deadline ) {
		var text1a, text1b, text2a, text2b, diffs, diffsb;
		text1a = text1.substring( 0, x );
		text2a = text2.substring( 0, y );
		text1b = text1.substring( x );
		text2b = text2.substring( y );

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

		return diffs.concat( diffsb );
	};

	/**
	 * Reduce the number of edits by eliminating semantically trivial equalities.
	 * @param {!Array.<!DiffMatchPatch.Diff>} diffs Array of diff tuples.
	 */
	DiffMatchPatch.prototype.diffCleanupSemantic = function( diffs ) {
		var changes, equalities, equalitiesLength, lastequality,
			pointer, lengthInsertions2, lengthDeletions2, lengthInsertions1,
			lengthDeletions1, deletion, insertion, overlapLength1, overlapLength2;
		changes = false;
		equalities = []; // Stack of indices where equalities are found.
		equalitiesLength = 0; // Keeping our own length var is faster in JS.
		/** @type {?string} */
		lastequality = null;

		// Always equal to diffs[equalities[equalitiesLength - 1]][1]
		pointer = 0; // Index of current position.

		// Number of characters that changed prior to the equality.
		lengthInsertions1 = 0;
		lengthDeletions1 = 0;

		// Number of characters that changed after the equality.
		lengthInsertions2 = 0;
		lengthDeletions2 = 0;
		while ( pointer < diffs.length ) {
			if ( diffs[ pointer ][ 0 ] === DIFF_EQUAL ) { // Equality found.
				equalities[ equalitiesLength++ ] = pointer;
				lengthInsertions1 = lengthInsertions2;
				lengthDeletions1 = lengthDeletions2;
				lengthInsertions2 = 0;
				lengthDeletions2 = 0;
				lastequality = diffs[ pointer ][ 1 ];
			} else { // An insertion or deletion.
				if ( diffs[ pointer ][ 0 ] === DIFF_INSERT ) {
					lengthInsertions2 += diffs[ pointer ][ 1 ].length;
				} else {
					lengthDeletions2 += 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( lengthInsertions1, lengthDeletions1 ) ) &&
						( lastequality.length <= Math.max( lengthInsertions2,
							lengthDeletions2 ) ) ) {

					// Duplicate record.
					diffs.splice(
						equalities[ equalitiesLength - 1 ],
						0,
						[ 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;

					// Reset the counters.
					lengthInsertions1 = 0;
					lengthDeletions1 = 0;
					lengthInsertions2 = 0;
					lengthDeletions2 = 0;
					lastequality = null;
					changes = true;
				}
			}
			pointer++;
		}

		// Normalize the diff.
		if ( changes ) {
			this.diffCleanupMerge( 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 ) {
				deletion = diffs[ pointer - 1 ][ 1 ];
				insertion = diffs[ pointer ][ 1 ];
				overlapLength1 = this.diffCommonOverlap( deletion, insertion );
				overlapLength2 = this.diffCommonOverlap( insertion, deletion );
				if ( overlapLength1 >= overlapLength2 ) {
					if ( overlapLength1 >= deletion.length / 2 ||
							overlapLength1 >= insertion.length / 2 ) {

						// Overlap found.  Insert an equality and trim the surrounding edits.
						diffs.splice(
							pointer,
							0,
							[ DIFF_EQUAL, insertion.substring( 0, overlapLength1 ) ]
						);
						diffs[ pointer - 1 ][ 1 ] =
							deletion.substring( 0, deletion.length - overlapLength1 );
						diffs[ pointer + 1 ][ 1 ] = insertion.substring( overlapLength1 );
						pointer++;
					}
				} else {
					if ( overlapLength2 >= deletion.length / 2 ||
							overlapLength2 >= insertion.length / 2 ) {

						// Reverse overlap found.
						// Insert an equality and swap and trim the surrounding edits.
						diffs.splice(
							pointer,
							0,
							[ DIFF_EQUAL, deletion.substring( 0, overlapLength2 ) ]
						);

						diffs[ pointer - 1 ][ 0 ] = DIFF_INSERT;
						diffs[ pointer - 1 ][ 1 ] =
							insertion.substring( 0, insertion.length - overlapLength2 );
						diffs[ pointer + 1 ][ 0 ] = DIFF_DELETE;
						diffs[ pointer + 1 ][ 1 ] =
							deletion.substring( overlapLength2 );
						pointer++;
					}
				}
				pointer++;
			}
			pointer++;
		}
	};

	/**
	 * 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
	 */
	DiffMatchPatch.prototype.diffCommonOverlap = function( text1, text2 ) {
		var text1Length, text2Length, textLength,
			best, length, pattern, found;

		// Cache the text lengths to prevent multiple calls.
		text1Length = text1.length;
		text2Length = text2.length;

		// Eliminate the null case.
		if ( text1Length === 0 || text2Length === 0 ) {
			return 0;
		}

		// Truncate the longer string.
		if ( text1Length > text2Length ) {
			text1 = text1.substring( text1Length - text2Length );
		} else if ( text1Length < text2Length ) {
			text2 = text2.substring( 0, text1Length );
		}
		textLength = Math.min( text1Length, text2Length );

		// Quick check for the worst case.
		if ( text1 === text2 ) {
			return textLength;
		}

		// 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/
		best = 0;
		length = 1;
		while ( true ) {
			pattern = text1.substring( textLength - length );
			found = text2.indexOf( pattern );
			if ( found === -1 ) {
				return best;
			}
			length += found;
			if ( found === 0 || text1.substring( textLength - length ) ===
					text2.substring( 0, length ) ) {
				best = length;
				length++;
			}
		}
	};

	/**
	 * 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
	 */
	DiffMatchPatch.prototype.diffLinesToChars = function( text1, text2 ) {
		var lineArray, lineHash, chars1, chars2;
		lineArray = []; // E.g. lineArray[4] === 'Hello\n'
		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 diffLinesToCharsMunge( text ) {
			var chars, lineStart, lineEnd, lineArrayLength, line;
			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.
			lineStart = 0;
			lineEnd = -1;

			// Keeping our own length variable is faster than looking it up.
			lineArrayLength = lineArray.length;
			while ( lineEnd < text.length - 1 ) {
				lineEnd = text.indexOf( "\n", lineStart );
				if ( lineEnd === -1 ) {
					lineEnd = text.length - 1;
				}
				line = text.substring( lineStart, lineEnd + 1 );
				lineStart = lineEnd + 1;

				const lineHashExists = lineHash.hasOwnProperty ?
					lineHash.hasOwnProperty( line ) :
					lineHash[ line ] !== undefined;

				if ( lineHashExists ) {
					chars += String.fromCharCode( lineHash[ line ] );
				} else {
					chars += String.fromCharCode( lineArrayLength );
					lineHash[ line ] = lineArrayLength;
					lineArray[ lineArrayLength++ ] = line;
				}
			}
			return chars;
		}

		chars1 = diffLinesToCharsMunge( text1 );
		chars2 = diffLinesToCharsMunge( 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.<!DiffMatchPatch.Diff>} diffs Array of diff tuples.
	 * @param {!Array.<string>} lineArray Array of unique strings.
	 * @private
	 */
	DiffMatchPatch.prototype.diffCharsToLines = function( diffs, lineArray ) {
		var x, chars, text, y;
		for ( x = 0; x < diffs.length; x++ ) {
			chars = diffs[ x ][ 1 ];
			text = [];
			for ( y = 0; y < chars.length; y++ ) {
				text[ y ] = lineArray[ chars.charCodeAt( y ) ];
			}
			diffs[ x ][ 1 ] = text.join( "" );
		}
	};

	/**
	 * Reorder and merge like edit sections.  Merge equalities.
	 * Any edit section can move as long as it doesn't cross an equality.
	 * @param {!Array.<!DiffMatchPatch.Diff>} diffs Array of diff tuples.
	 */
	DiffMatchPatch.prototype.diffCleanupMerge = function( diffs ) {
		var pointer, countDelete, countInsert, textInsert, textDelete,
			commonlength, changes, diffPointer, position;
		diffs.push( [ DIFF_EQUAL, "" ] ); // Add a dummy entry at the end.
		pointer = 0;
		countDelete = 0;
		countInsert = 0;
		textDelete = "";
		textInsert = "";

		while ( pointer < diffs.length ) {
			switch ( diffs[ pointer ][ 0 ] ) {
			case DIFF_INSERT:
				countInsert++;
				textInsert += diffs[ pointer ][ 1 ];
				pointer++;
				break;
			case DIFF_DELETE:
				countDelete++;
				textDelete += diffs[ pointer ][ 1 ];
				pointer++;
				break;
			case DIFF_EQUAL:

				// Upon reaching an equality, check for prior redundancies.
				if ( countDelete + countInsert > 1 ) {
					if ( countDelete !== 0 && countInsert !== 0 ) {

						// Factor out any common prefixes.
						commonlength = this.diffCommonPrefix( textInsert, textDelete );
						if ( commonlength !== 0 ) {
							if ( ( pointer - countDelete - countInsert ) > 0 &&
									diffs[ pointer - countDelete - countInsert - 1 ][ 0 ] ===
									DIFF_EQUAL ) {
								diffs[ pointer - countDelete - countInsert - 1 ][ 1 ] +=
									textInsert.substring( 0, commonlength );
							} else {
								diffs.splice( 0, 0, [ DIFF_EQUAL,
									textInsert.substring( 0, commonlength )
								] );
								pointer++;
							}
							textInsert = textInsert.substring( commonlength );
							textDelete = textDelete.substring( commonlength );
						}

						// Factor out any common suffixies.
						commonlength = this.diffCommonSuffix( textInsert, textDelete );
						if ( commonlength !== 0 ) {
							diffs[ pointer ][ 1 ] = textInsert.substring( textInsert.length -
									commonlength ) + diffs[ pointer ][ 1 ];
							textInsert = textInsert.substring( 0, textInsert.length -
								commonlength );
							textDelete = textDelete.substring( 0, textDelete.length -
								commonlength );
						}
					}

					// Delete the offending records and add the merged ones.
					if ( countDelete === 0 ) {
						diffs.splice( pointer - countInsert,
							countDelete + countInsert, [ DIFF_INSERT, textInsert ] );
					} else if ( countInsert === 0 ) {
						diffs.splice( pointer - countDelete,
							countDelete + countInsert, [ DIFF_DELETE, textDelete ] );
					} else {
						diffs.splice(
							pointer - countDelete - countInsert,
							countDelete + countInsert,
							[ DIFF_DELETE, textDelete ], [ DIFF_INSERT, textInsert ]
						);
					}
					pointer = pointer - countDelete - countInsert +
						( countDelete ? 1 : 0 ) + ( countInsert ? 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++;
				}
				countInsert = 0;
				countDelete = 0;
				textDelete = "";
				textInsert = "";
				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
		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 ) {

				diffPointer = diffs[ pointer ][ 1 ];
				position = diffPointer.substring(
					diffPointer.length - diffs[ pointer - 1 ][ 1 ].length
				);

				// This is a single edit surrounded by equalities.
				if ( position === 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 ( diffPointer.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.diffCleanupMerge( diffs );
		}
	};

	return function( o, n ) {
		var diff, output, text;
		diff = new DiffMatchPatch();
		output = diff.DiffMain( o, n );
		diff.diffCleanupEfficiency( output );
		text = diff.diffPrettyHtml( output );

		return text;
	};
}() );
