/core/Diff.php

<?php

/**
 * @package framework
 * @subpackage core
 * A PHP diff engine
 */

// difflib.php
//
// A PHP diff engine for phpwiki.
//
// Copyright (C) 2000, 2001 Geoffrey T. Dairiki <dairiki@dairiki.org>
// You may copy this code freely under the conditions of the GPL.
//

define('USE_ASSERTS', true);

/**
 * @package framework
 * @subpackage core
 * @access private
 */
class _DiffOp {
	var $type;
	var $orig;
	var $final;

	public function reverse() {
		trigger_error("pure virtual", E_USER_ERROR);
	}

	public function norig() {
		return $this->orig ? sizeof($this->orig) : 0;
	}

	public function nfinal() {
		return $this->final ? sizeof($this->final) : 0;
	}
}

/**
 * @package framework
 * @subpackage core
 * @access private
 */
class _DiffOp_Copy extends _DiffOp {
	var $type = 'copy';

	public function __construct ($orig, $final = false) {
		if (!is_array($final))
			$final = $orig;
		$this->orig = $orig;
		$this->final = $final;
	}

	public function reverse() {
		return new _DiffOp_Copy($this->final, $this->orig);
	}
}

/**
 * @package framework
 * @subpackage core
 * @access private
 */
class _DiffOp_Delete extends _DiffOp {
	var $type = 'delete';

	public function __construct ($lines) {
		$this->orig = $lines;
		$this->final = false;
	}

	public function reverse() {
		return new _DiffOp_Add($this->orig);
	}
}

/**
 * @package framework
 * @subpackage core
 * @access private
 */
class _DiffOp_Add extends _DiffOp {
	var $type = 'add';

	public function __construct ($lines) {
		$this->final = $lines;
		$this->orig = false;
	}

	public function reverse() {
		return new _DiffOp_Delete($this->final);
	}
}

/**
 * @package framework
 * @subpackage core
 * @access private
 */
class _DiffOp_Change extends _DiffOp {
	var $type = 'change';

	public function __construct ($orig, $final) {
		$this->orig = $orig;
		$this->final = $final;
	}

	public function reverse() {
		return new _DiffOp_Change($this->final, $this->orig);
	}
}


/**
 * Class used internally by Diff to actually compute the diffs.
 *
 * The algorithm used here is mostly lifted from the perl module
 * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
 *   http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
 *
 * More ideas are taken from:
 *   http://www.ics.uci.edu/~eppstein/161/960229.html
 *
 * Some ideas are (and a bit of code) are from from analyze.c, from GNU
 * diffutils-2.7, which can be found at:
 *   ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
 *
 * Finally, some ideas (subdivision by NCHUNKS > 2, and some optimizations)
 * are my own.
 *
 * @author Geoffrey T. Dairiki
 * @access private
 * @package framework
 * @subpackage core
 */
class _DiffEngine
{
	public function diff ($from_lines, $to_lines) {
		$n_from = sizeof($from_lines);
		$n_to = sizeof($to_lines);

		$this->xchanged = $this->ychanged = array();
		$this->xv = $this->yv = array();
		$this->xind = $this->yind = array();
		unset($this->seq);
		unset($this->in_seq);
		unset($this->lcs);

		// Skip leading common lines.
		for ($skip = 0; $skip < $n_from && $skip < $n_to; $skip++) {
			if ($from_lines[$skip] != $to_lines[$skip])
				break;
			$this->xchanged[$skip] = $this->ychanged[$skip] = false;
		}
		// Skip trailing common lines.
		$xi = $n_from; $yi = $n_to;
		for ($endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++) {
			if ($from_lines[$xi] != $to_lines[$yi])
				break;
			$this->xchanged[$xi] = $this->ychanged[$yi] = false;
		}

		// Ignore lines which do not exist in both files.
		for ($xi = $skip; $xi < $n_from - $endskip; $xi++)
			$xhash[$from_lines[$xi]] = 1;
		for ($yi = $skip; $yi < $n_to - $endskip; $yi++) {
			$line = $to_lines[$yi];
			if ( ($this->ychanged[$yi] = empty($xhash[$line])) )
				continue;
			$yhash[$line] = 1;
			$this->yv[] = $line;
			$this->yind[] = $yi;
		}
		for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
			$line = $from_lines[$xi];
			if ( ($this->xchanged[$xi] = empty($yhash[$line])) )
				continue;
			$this->xv[] = $line;
			$this->xind[] = $xi;
		}

		// Find the LCS.
		$this->_compareseq(0, sizeof($this->xv), 0, sizeof($this->yv));

		// Merge edits when possible
		$this->_shift_boundaries($from_lines, $this->xchanged, $this->ychanged);
		$this->_shift_boundaries($to_lines, $this->ychanged, $this->xchanged);

		// Compute the edit operations.
		$edits = array();
		$xi = $yi = 0;
		while ($xi < $n_from || $yi < $n_to) {
			USE_ASSERTS && assert($yi < $n_to || $this->xchanged[$xi]);
			USE_ASSERTS && assert($xi < $n_from || $this->ychanged[$yi]);

			// Skip matching "snake".
			$copy = array();
			while ( $xi < $n_from && $yi < $n_to
					&& !$this->xchanged[$xi] && !$this->ychanged[$yi]) {
				$copy[] = $from_lines[$xi++];
				++$yi;
			}
			if ($copy)
				$edits[] = new _DiffOp_Copy($copy);

			// Find deletes & adds.
			$delete = array();
			while ($xi < $n_from && $this->xchanged[$xi])
				$delete[] = $from_lines[$xi++];

			$add = array();
			while ($yi < $n_to && $this->ychanged[$yi])
				$add[] = $to_lines[$yi++];

			if ($delete && $add)
				$edits[] = new _DiffOp_Change($delete, $add);
			elseif ($delete)
				$edits[] = new _DiffOp_Delete($delete);
			elseif ($add)
				$edits[] = new _DiffOp_Add($add);
		}
		return $edits;
	}


	/* Divide the Largest Common Subsequence (LCS) of the sequences
	 * [XOFF, XLIM) and [YOFF, YLIM) into NCHUNKS approximately equally
	 * sized segments.
	 *
	 * Returns (LCS, PTS).  LCS is the length of the LCS. PTS is an
	 * array of NCHUNKS+1 (X, Y) indexes giving the diving points between
	 * sub sequences.  The first sub-sequence is contained in [X0, X1),
	 * [Y0, Y1), the second in [X1, X2), [Y1, Y2) and so on.  Note
	 * that (X0, Y0) == (XOFF, YOFF) and
	 * (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
	 *
	 * This function assumes that the first lines of the specified portions
	 * of the two files do not match, and likewise that the last lines do not
	 * match.  The caller must trim matching lines from the beginning and end
	 * of the portions it is going to specify.
	 */
	public function _diag ($xoff, $xlim, $yoff, $ylim, $nchunks) {
	$flip = false;

	if ($xlim - $xoff > $ylim - $yoff) {
		// Things seems faster (I'm not sure I understand why)
			// when the shortest sequence in X.
			$flip = true;
		list ($xoff, $xlim, $yoff, $ylim)
		= array( $yoff, $ylim, $xoff, $xlim);
		}

	if ($flip)
		for ($i = $ylim - 1; $i >= $yoff; $i--)
		$ymatches[$this->xv[$i]][] = $i;
	else
		for ($i = $ylim - 1; $i >= $yoff; $i--)
		$ymatches[$this->yv[$i]][] = $i;

	$this->lcs = 0;
	$this->seq[0]= $yoff - 1;
	$this->in_seq = array();
	$ymids[0] = array();

	$numer = $xlim - $xoff + $nchunks - 1;
	$x = $xoff;
	for ($chunk = 0; $chunk < $nchunks; $chunk++) {
		if ($chunk > 0)
		for ($i = 0; $i <= $this->lcs; $i++)
			$ymids[$i][$chunk-1] = $this->seq[$i];

		$x1 = $xoff + (int)(($numer + ($xlim-$xoff)*$chunk) / $nchunks);
		for ( ; $x < $x1; $x++) {
				$line = $flip ? $this->yv[$x] : $this->xv[$x];
				if (empty($ymatches[$line]))
			continue;
		$matches = $ymatches[$line];
				reset($matches);
		while (list ($junk, $y) = each($matches))
			if (empty($this->in_seq[$y])) {
			$k = $this->_lcs_pos($y);
			USE_ASSERTS && assert($k > 0);
			$ymids[$k] = $ymids[$k-1];
			break;
					}
		while (list ($junk, $y) = each($matches)) {
			if ($y > $this->seq[$k-1]) {
			USE_ASSERTS && assert($y < $this->seq[$k]);
			// Optimization: this is a common case:
			//  next match is just replacing previous match.
			$this->in_seq[$this->seq[$k]] = false;
			$this->seq[$k] = $y;
			$this->in_seq[$y] = 1;
					}
			else if (empty($this->in_seq[$y])) {
			$k = $this->_lcs_pos($y);
			USE_ASSERTS && assert($k > 0);
			$ymids[$k] = $ymids[$k-1];
					}
				}
			}
		}

	$seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff);
	$ymid = $ymids[$this->lcs];
	for ($n = 0; $n < $nchunks - 1; $n++) {
		$x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $n) / $nchunks);
		$y1 = $ymid[$n] + 1;
		$seps[] = $flip ? array($y1, $x1) : array($x1, $y1);
		}
	$seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim);

	return array($this->lcs, $seps);
	}

	public function _lcs_pos ($ypos) {
	$end = $this->lcs;
	if ($end == 0 || $ypos > $this->seq[$end]) {
		$this->seq[++$this->lcs] = $ypos;
		$this->in_seq[$ypos] = 1;
		return $this->lcs;
		}

	$beg = 1;
	while ($beg < $end) {
		$mid = (int)(($beg + $end) / 2);
		if ( $ypos > $this->seq[$mid] )
		$beg = $mid + 1;
		else
		$end = $mid;
		}

	USE_ASSERTS && assert($ypos != $this->seq[$end]);

	$this->in_seq[$this->seq[$end]] = false;
	$this->seq[$end] = $ypos;
	$this->in_seq[$ypos] = 1;
	return $end;
	}

	/* Find LCS of two sequences.
	 *
	 * The results are recorded in the vectors $this->{x,y}changed[], by
	 * storing a 1 in the element for each line that is an insertion
	 * or deletion (ie. is not in the LCS).
	 *
	 * The subsequence of file 0 is [XOFF, XLIM) and likewise for file 1.
	 *
	 * Note that XLIM, YLIM are exclusive bounds.
	 * All line numbers are origin-0 and discarded lines are not counted.
	 */
	public function _compareseq ($xoff, $xlim, $yoff, $ylim) {
	// Slide down the bottom initial diagonal.
	while ($xoff < $xlim && $yoff < $ylim
			&& $this->xv[$xoff] == $this->yv[$yoff]) {
		++$xoff;
		++$yoff;
		}

	// Slide up the top initial diagonal.
	while ($xlim > $xoff && $ylim > $yoff
			&& $this->xv[$xlim - 1] == $this->yv[$ylim - 1]) {
		--$xlim;
		--$ylim;
		}

	if ($xoff == $xlim || $yoff == $ylim)
		$lcs = 0;
	else {
		// This is ad hoc but seems to work well.
		//$nchunks = sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5);
		//$nchunks = max(2,min(8,(int)$nchunks));
		$nchunks = min(7, $xlim - $xoff, $ylim - $yoff) + 1;
		list ($lcs, $seps)
		= $this->_diag($xoff,$xlim,$yoff, $ylim,$nchunks);
		}

	if ($lcs == 0) {
		// X and Y sequences have no common subsequence:
		// mark all changed.
		while ($yoff < $ylim)
		$this->ychanged[$this->yind[$yoff++]] = 1;
		while ($xoff < $xlim)
		$this->xchanged[$this->xind[$xoff++]] = 1;
		}
	else {
		// Use the partitions to split this problem into subproblems.
		reset($seps);
		$pt1 = $seps[0];
		while ($pt2 = next($seps)) {
		$this->_compareseq ($pt1[0], $pt2[0], $pt1[1], $pt2[1]);
		$pt1 = $pt2;
			}
		}
	}

	/* Adjust inserts/deletes of identical lines to join changes
	 * as much as possible.
	 *
	 * We do something when a run of changed lines include a
	 * line at one end and has an excluded, identical line at the other.
	 * We are free to choose which identical line is included.
	 * 'compareseq' usually chooses the one at the beginning,
	 * but usually it is cleaner to consider the following identical line
	 * to be the "change".
	 *
	 * This is extracted verbatim from analyze.c (GNU diffutils-2.7).
	 */
	public function _shift_boundaries ($lines, &$changed, $other_changed) {
	$i = 0;
	$j = 0;

	USE_ASSERTS && assert('sizeof($lines) == sizeof($changed)');
	$len = sizeof($lines);
	$other_len = sizeof($other_changed);

	while (1) {
		/*
		 * Scan forwards to find beginning of another run of changes.
		 * Also keep track of the corresponding point in the other file.
		 *
		 * Throughout this code, $i and $j are adjusted together so that
		 * the first $i elements of $changed and the first $j elements
		 * of $other_changed both contain the same number of zeros
		 * (unchanged lines).
		 * Furthermore, $j is always kept so that $j == $other_len or
		 * $other_changed[$j] == false.
		 */
		while ($j < $other_len && $other_changed[$j])
		$j++;

		while ($i < $len && ! $changed[$i]) {
		USE_ASSERTS && assert('$j < $other_len && ! $other_changed[$j]');
		$i++; $j++;
		while ($j < $other_len && $other_changed[$j])
			$j++;
			}

		if ($i == $len)
		break;

		$start = $i;

		// Find the end of this run of changes.
		while (++$i < $len && $changed[$i])
		continue;

		do {
		/*
		 * Record the length of this run of changes, so that
		 * we can later determine whether the run has grown.
		 */
		$runlength = $i - $start;

		/*
		 * Move the changed region back, so long as the
		 * previous unchanged line matches the last changed one.
		 * This merges with previous changed regions.
		 */
		while ($start > 0 && $lines[$start - 1] == $lines[$i - 1]) {
			$changed[--$start] = 1;
			$changed[--$i] = false;
			while ($start > 0 && $changed[$start - 1])
			$start--;
			USE_ASSERTS && assert('$j > 0');
			while ($other_changed[--$j])
			continue;
			USE_ASSERTS && assert('$j >= 0 && !$other_changed[$j]');
				}

		/*
		 * Set CORRESPONDING to the end of the changed run, at the last
		 * point where it corresponds to a changed run in the other file.
		 * CORRESPONDING == LEN means no such point has been found.
		 */
		$corresponding = $j < $other_len ? $i : $len;

		/*
		 * Move the changed region forward, so long as the
		 * first changed line matches the following unchanged one.
		 * This merges with following changed regions.
		 * Do this second, so that if there are no merges,
		 * the changed region is moved forward as far as possible.
		 */
		while ($i < $len && $lines[$start] == $lines[$i]) {
			$changed[$start++] = false;
			$changed[$i++] = 1;
			while ($i < $len && $changed[$i])
			$i++;

			USE_ASSERTS && assert('$j < $other_len && ! $other_changed[$j]');
			$j++;
			if ($j < $other_len && $other_changed[$j]) {
			$corresponding = $i;
			while ($j < $other_len && $other_changed[$j])
				$j++;
					}
				}
			} while ($runlength != $i - $start);

		/*
		 * If possible, move the fully-merged run of changes
		 * back to a corresponding run in the other file.
		 */
		while ($corresponding < $i) {
		$changed[--$start] = 1;
		$changed[--$i] = 0;
		USE_ASSERTS && assert('$j > 0');
		while ($other_changed[--$j])
			continue;
		USE_ASSERTS && assert('$j >= 0 && !$other_changed[$j]');
			}
		}
	}
}

/**
 * Class representing a 'diff' between two sequences of strings.
 * @package framework
 * @subpackage core
 */
class Diff
{
	public static $html_cleaner_class = null;

	var $edits;

	/**
	 * Constructor.
	 * Computes diff between sequences of strings.
	 *
	 * @param $from_lines array An array of strings.
	 *        (Typically these are lines from a file.)
	 * @param $to_lines array An array of strings.
	 */
	public function __construct($from_lines, $to_lines) {
		$eng = new _DiffEngine;
		$this->edits = $eng->diff($from_lines, $to_lines);
		//$this->_check($from_lines, $to_lines);
	}

	/**
	 * Compute reversed Diff.
	 *
	 * SYNOPSIS:
	 *
	 *  $diff = new Diff($lines1, $lines2);
	 *  $rev = $diff->reverse();
	 * @return object A Diff object representing the inverse of the
	 *                original diff.
	 */
	public function reverse () {
	$rev = $this;
		$rev->edits = array();
		foreach ($this->edits as $edit) {
			$rev->edits[] = $edit->reverse();
		}
	return $rev;
	}

	/**
	 * Check for empty diff.
	 *
	 * @return bool True iff two sequences were identical.
	 */
	public function isEmpty () {
		foreach ($this->edits as $edit) {
			if ($edit->type != 'copy')
				return false;
		}
		return true;
	}

	/**
	 * Compute the length of the Longest Common Subsequence (LCS).
	 *
	 * This is mostly for diagnostic purposed.
	 *
	 * @return int The length of the LCS.
	 */
	public function lcs () {
	$lcs = 0;
		foreach ($this->edits as $edit) {
			if ($edit->type == 'copy')
				$lcs += sizeof($edit->orig);
		}
	return $lcs;
	}

	/**
	 * Get the original set of lines.
	 *
	 * This reconstructs the $from_lines parameter passed to the
	 * constructor.
	 *
	 * @return array The original sequence of strings.
	 */
	public function orig() {
		$lines = array();

		foreach ($this->edits as $edit) {
			if ($edit->orig)
				array_splice($lines, sizeof($lines), 0, $edit->orig);
		}
		return $lines;
	}

	/**
	 * Get the final set of lines.
	 *
	 * This reconstructs the $to_lines parameter passed to the
	 * constructor.
	 *
	 * @return array The sequence of strings.
	 */
	public function finaltext() {
		$lines = array();

		foreach ($this->edits as $edit) {
			if ($edit->final)
				array_splice($lines, sizeof($lines), 0, $edit->final);
		}
		return $lines;
	}

	/**
	 * Check a Diff for validity.
	 *
	 * This is here only for debugging purposes.
	 */
	public function _check ($from_lines, $to_lines) {
		if (serialize($from_lines) != serialize($this->orig()))
			trigger_error("Reconstructed original doesn't match", E_USER_ERROR);
		if (serialize($to_lines) != serialize($this->finaltext()))
			trigger_error("Reconstructed final doesn't match", E_USER_ERROR);

		$rev = $this->reverse();
		if (serialize($to_lines) != serialize($rev->orig()))
			trigger_error("Reversed original doesn't match", E_USER_ERROR);
		if (serialize($from_lines) != serialize($rev->finaltext()))
			trigger_error("Reversed final doesn't match", E_USER_ERROR);


		$prevtype = 'none';
		foreach ($this->edits as $edit) {
			if ( $prevtype == $edit->type )
				trigger_error("Edit sequence is non-optimal", E_USER_ERROR);
			$prevtype = $edit->type;
		}

		$lcs = $this->lcs();
		trigger_error("Diff okay: LCS = $lcs", E_USER_NOTICE);
	}



	/**
	 *  Attempt to clean invalid HTML, which messes up diffs.
	 *  This cleans code if possible, using an instance of HTMLCleaner
	 *
	 *  NB: By default, only extremely simple tidying is performed,
	 *  by passing through DomDocument::loadHTML and saveXML
	 *
	 * @param string $content HTML content
	 * @param object $cleaner Optional instance of a HTMLCleaner class to
	 * 	use, overriding self::$html_cleaner_class
	 */
	public static function cleanHTML($content, $cleaner=null) {
		if (!$cleaner) {
			if (class_exists(self::$html_cleaner_class)) {
				$cleaner = new self::$html_cleaner_class;
			} else {
				$cleaner = HTMLCleaner::inst();    //load cleaner if the dependent class is available
			}
		}

		if ($cleaner) {
			$content = $cleaner->cleanHTML($content);
		} else {
			// At most basic level of cleaning, use DOMDocument to save valid XML.
			$doc = Injector::inst()->create('HTMLValue', $content);
			$content = $doc->getContent();
		}

		// Remove empty <ins /> and <del /> tags because browsers hate them
		$content = preg_replace('/<(ins|del)[^>]*\/>/','', $content);

		return $content;
	}

	/**
	 * @param String
	 * @param String
	 * @param Boolean
	 * @return String
	 */
	public static function compareHTML($from, $to, $escape = false) {
		// First split up the content into words and tags
		$set1 = self::getHTMLChunks($from);
		$set2 = self::getHTMLChunks($to);

		// Diff that
		$diff = new Diff($set1, $set2);

		$tagStack[1] = $tagStack[2] = 0;
		$rechunked[1] = $rechunked[2] = array();

		// Go through everything, converting edited tags (and their content) into single chunks.  Otherwise
		// the generated HTML gets crusty
		foreach($diff->edits as $edit) {
			switch($edit->type) {
				case 'copy':
					$lookForTag = false;
					$stuffFor[1] = $edit->orig;
					$stuffFor[2] = $edit->orig;
					break;

				case 'change':
					$lookForTag = true;
					$stuffFor[1] = $edit->orig;
					$stuffFor[2] = $edit->final;
					break;

				case 'add':
					$lookForTag = true;
					$stuffFor[1] = null;
					$stuffFor[2] = $edit->final;
					break;

				case 'delete':
					$lookForTag = true;
					$stuffFor[1] = $edit->orig;
					$stuffFor[2] = null;
					break;
			}

			foreach($stuffFor as $listName => $chunks) {
				if($chunks) {
					foreach($chunks as $item) {
						// $tagStack > 0 indicates that we should be tag-building
						if($tagStack[$listName]) $rechunked[$listName][sizeof($rechunked[$listName])-1] .= ' ' . $item;
						else $rechunked[$listName][] = $item;

						if($lookForTag && !$tagStack[$listName] && isset($item[0]) && $item[0] == "<"
								&& substr($item,0,2) != "</") {
							$tagStack[$listName] = 1;
						} else if($tagStack[$listName]) {
							if(substr($item,0,2) == "</") $tagStack[$listName]--;
							else if(isset($item[0]) && $item[0] == "<") $tagStack[$listName]++;
						}
					}
				}
			}
		}

		// Diff the re-chunked data, turning it into maked up HTML
		$diff = new Diff($rechunked[1], $rechunked[2]);
		$content = '';
		foreach($diff->edits as $edit) {
			$orig = ($escape) ? Convert::raw2xml($edit->orig) : $edit->orig;
			$final = ($escape) ? Convert::raw2xml($edit->final) : $edit->final;

			switch($edit->type) {
				case 'copy':
					$content .= " " . implode(" ", $orig) . " ";
					break;

				case 'change':
					$content .= " <ins>" . implode(" ", $final) . "</ins> ";
					$content .= " <del>" . implode(" ", $orig) . "</del> ";
					break;

				case 'add':
					$content .= " <ins>" . implode(" ", $final) . "</ins> ";
					break;

				case 'delete':
					$content .= " <del>" . implode(" ", $orig) . "</del> ";
					break;
			}
		}

		return self::cleanHTML($content);
	}

	/**
	 * @param string|array If passed as an array, values will be concatenated with a comma.
	 */
	public static function getHTMLChunks($content) {
		if($content && !is_string($content) && !is_array($content) && !is_numeric($content)) {
			throw new InvalidArgumentException('$content parameter needs to be a string or array');
		}
		if(is_array($content)) $content = implode(',', $content);

		$content = str_replace(array("&nbsp;","<", ">"),array(" "," <", "> "),$content);
		$candidateChunks = preg_split("/[\t\r\n ]+/", $content);
		while(list($i,$item) = each($candidateChunks)) {
			if(isset($item[0]) && $item[0] == "<") {
				$newChunk = $item;
				while($item[strlen($item)-1] != ">") {
					list($i,$item) = each($candidateChunks);
					$newChunk .= ' ' . $item;
				}
				$chunks[] = $newChunk;
			} else {
				$chunks[] = $item;
			}
		}
		return $chunks;
	}

}




/**
 * Computes diff between sequences of strings.
 * @package framework
 * @subpackage core
 */
class MappedDiff
extends Diff
{
	/**
	 * Constructor.
	 *
	 * Computes diff between sequences of strings.
	 *
	 * This can be used to compute things like
	 * case-insensitve diffs, or diffs which ignore
	 * changes in white-space.
	 *
	 * @param $from_lines array An array of strings.
	 *  (Typically these are lines from a file.)
	 *
	 * @param $to_lines array An array of strings.
	 *
	 * @param $mapped_from_lines array This array should
	 *  have the same size number of elements as $from_lines.
	 *  The elements in $mapped_from_lines and
	 *  $mapped_to_lines are what is actually compared
	 *  when computing the diff.
	 *
	 * @param $mapped_to_lines array This array should
	 *  have the same number of elements as $to_lines.
	 */
	public function __construct($from_lines, $to_lines,
						$mapped_from_lines, $mapped_to_lines) {

		assert(sizeof($from_lines) == sizeof($mapped_from_lines));
		assert(sizeof($to_lines) == sizeof($mapped_to_lines));

		parent::__construct($mapped_from_lines, $mapped_to_lines);

		$xi = $yi = 0;
		// Optimizing loop invariants:
		// http://phplens.com/lens/php-book/optimizing-debugging-php.php
		for ($i = 0, $max = sizeof($this->edits); $i < $max; $i++) {
			$orig = &$this->edits[$i]->orig;
			if (is_array($orig)) {
				$orig = array_slice($from_lines, $xi, sizeof($orig));
				$xi += sizeof($orig);
			}

			$final = &$this->edits[$i]->final;
			if (is_array($final)) {
				$final = array_slice($to_lines, $yi, sizeof($final));
				$yi += sizeof($final);
			}
		}
	}
}