includes/diff.php
author Dan Fuhry <dan@enanocms.org>
Thu, 28 Oct 2010 03:05:31 -0400
changeset 1308 f9bee9b125ee
parent 1081 745200a9cc2a
permissions -rw-r--r--
Parser updates. Added the "styled" keyword to wikitables to allow them to be styled using the current theme's standard table skinning, and changes to how the image tag parser decides how to display an image (framed, inline or raw).

<?php

/*
 * Enano - an open-source CMS capable of wiki functions, Drupal-like sidebar blocks, and everything in between
 * Copyright (C) 2006-2009 Dan Fuhry
 *
 * This program is Free Software; you can redistribute and/or modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for details.
 */

// A PHP diff engine for phpwiki. (Taken from phpwiki-1.3.3)
//
// 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', function_exists('assert'));

/**
 * @todo document
 * @package Enano
 * @subpackage DifferenceEngine
 */
class _DiffOp {
	var $type;
	var $orig;
	var $closing;

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

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

	function nclosing() {
		return $this->closing ? sizeof($this->closing) : 0;
	}
}

/**
 * @todo document
 * @package Enano
 * @subpackage DifferenceEngine
 */
class _DiffOp_Copy extends _DiffOp {
	var $type = 'copy';

	function _DiffOp_Copy ($orig, $closing = false) {
		if (!is_array($closing))
			$closing = $orig;
		$this->orig = $orig;
		$this->closing = $closing;
	}

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

/**
 * @todo document
 * @package Enano
 * @subpackage DifferenceEngine
 */
class _DiffOp_Delete extends _DiffOp {
	var $type = 'delete';

	function _DiffOp_Delete ($lines) {
		$this->orig = $lines;
		$this->closing = false;
	}

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

/**
 * @todo document
 * @package Enano
 * @subpackage DifferenceEngine
 */
class _DiffOp_Add extends _DiffOp {
	var $type = 'add';

	function _DiffOp_Add ($lines) {
		$this->closing = $lines;
		$this->orig = false;
	}

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

/**
 * @todo document
 * @package Enano
 * @subpackage DifferenceEngine
 */
class _DiffOp_Change extends _DiffOp {
	var $type = 'change';

	function _DiffOp_Change ($orig, $closing) {
		$this->orig = $orig;
		$this->closing = $closing;
	}

	function reverse() {
		return new _DiffOp_Change($this->closing, $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
 *
 * closingly, some ideas (subdivision by NCHUNKS > 2, and some optimizations)
 * are my own.
 *
 * Line length limits for robustness added by Tim Starling, 2005-08-31
 *
 * @author Geoffrey T. Dairiki, Tim Starling
 * @package Enano
 * @subpackage DifferenceEngine
 */
define('MAX_XREF_LENGTH', 10000);
class _DiffEngine
{
	function diff ($from_lines, $to_lines) {
		$fname = '_DiffEngine::diff';
		// wfProfileIn( $fname );

		$n_from = sizeof($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++) {
			$xhash[$this->_line_hash($from_lines[$xi])] = 1;
		}

		for ($yi = $skip; $yi < $n_to - $endskip; $yi++) {
			$line = $to_lines[$yi];
			if ( ($this->ychanged[$yi] = empty($xhash[$this->_line_hash($line)])) )
				continue;
			$yhash[$this->_line_hash($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($yhash[$this->_line_hash($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);
		}
		// wfProfileOut( $fname );
		return $edits;
	}

	/**
	 * Returns the whole line if it's small enough, or the MD5 hash otherwise
	 */
	function _line_hash( $line ) {
		if ( strlen( $line ) > MAX_XREF_LENGTH ) {
			return md5( $line );
		} else {
			return $line;
		}
	}


	/* 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.
	 */
	function _diag ($xoff, $xlim, $yoff, $ylim, $nchunks) {
		$fname = '_DiffEngine::_diag';
		// wfProfileIn( $fname );
		$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; $chunk++) {
			// wfProfileIn( "$fname-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];
					}
				}
			}
			// wfProfileOut( "$fname-chunk" );
		}

		$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);

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

	function _lcs_pos ($ypos) {
		$fname = '_DiffEngine::_lcs_pos';
		// wfProfileIn( $fname );

		$end = $this->lcs;
		if ($end == 0 || $ypos > $this->seq[$end]) {
			$this->seq[++$this->lcs] = $ypos;
			$this->in_seq[$ypos] = 1;
			// wfProfileOut( $fname );
			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;
		// wfProfileOut( $fname );
		return $end;
	}

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

		// 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;
			}
		}
		// wfProfileOut( $fname );
	}

	/* 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).
	 */
	function _shift_boundaries ($lines, &$changed, $other_changed) {
		$fname = '_DiffEngine::_shift_boundaries';
		// wfProfileIn( $fname );
		$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]');
			}
		}
		// wfProfileOut( $fname );
	}
}

/**
 * Class representing a 'diff' between two sequences of strings.
 * @todo document
 * @package Enano
 * @subpackage DifferenceEngine
 */
class Diff
{
	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 $to_lines array An array of strings.
	 */
	function Diff($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.
	 */
	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.
	 */
	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 purposes.
	 *
	 * @return int The length of the LCS.
	 */
	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.
	 */
	function orig() {
		$lines = array();

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

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

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

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

/**
 * FIXME: bad name.
 * @todo document
 * @package Enano
 * @subpackage DifferenceEngine
 */
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 $to_lines.
	 */
	function MappedDiff($from_lines, $to_lines,
						$mapped_from_lines, $mapped_to_lines) {
		$fname = 'MappedDiff::MappedDiff';
		// wfProfileIn( $fname );

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

		$this->Diff($mapped_from_lines, $mapped_to_lines);

		$xi = $yi = 0;
		for ($i = 0; $i < sizeof($this->edits); $i++) {
			$orig = &$this->edits[$i]->orig;
			if (is_array($orig)) {
				$orig = array_slice($from_lines, $xi, sizeof($orig));
				$xi += sizeof($orig);
			}

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

/**
 * A class to format Diffs
 *
 * This class formats the diff in classic diff format.
 * It is intended that this class be customized via inheritance,
 * to obtain fancier outputs.
 * @todo document
 * @package Enano
 * @subpackage DifferenceEngine
 */
class DiffFormatter
{
	/**
	 * Number of leading context "lines" to preserve.
	 *
	 * This should be left at zero for this class, but subclasses
	 * may want to set this to other values.
	 */
	var $leading_context_lines = 0;

	/**
	 * Number of trailing context "lines" to preserve.
	 *
	 * This should be left at zero for this class, but subclasses
	 * may want to set this to other values.
	 */
	var $trailing_context_lines = 0;

	/**
	 * Format a diff.
	 *
	 * @param $diff object A Diff object.
	 * @return string The formatted output.
	 */
	function format($diff) {
		$fname = 'DiffFormatter::format';
		// wfProfileIn( $fname );

		$xi = $yi = 1;
		$block = false;
		$context = array();

		$nlead = $this->leading_context_lines;
		$ntrail = $this->trailing_context_lines;

		$this->_start_diff();

		foreach ($diff->edits as $edit) {
			if ($edit->type == 'copy') {
				if (is_array($block)) {
					if (sizeof($edit->orig) <= $nlead + $ntrail) {
						$block[] = $edit;
					}
					else{
						if ($ntrail) {
							$context = array_slice($edit->orig, 0, $ntrail);
							$block[] = new _DiffOp_Copy($context);
						}
						$this->_block($x0, $ntrail + $xi - $x0,
									  $y0, $ntrail + $yi - $y0,
									  $block);
						$block = false;
					}
				}
				$context = $edit->orig;
			}
			else {
				if (! is_array($block)) {
					$context = array_slice($context, sizeof($context) - $nlead);
					$x0 = $xi - sizeof($context);
					$y0 = $yi - sizeof($context);
					$block = array();
					if ($context)
						$block[] = new _DiffOp_Copy($context);
				}
				$block[] = $edit;
			}

			if ($edit->orig)
				$xi += sizeof($edit->orig);
			if ($edit->closing)
				$yi += sizeof($edit->closing);
		}

		if (is_array($block))
			$this->_block($x0, $xi - $x0,
						  $y0, $yi - $y0,
						  $block);

		$end = $this->_end_diff();
		// wfProfileOut( $fname );
		return $end;
	}

	function _block($xbeg, $xlen, $ybeg, $ylen, &$edits) {
		$fname = 'DiffFormatter::_block';
		// wfProfileIn( $fname );
		$this->_start_block($this->_block_header($xbeg, $xlen, $ybeg, $ylen));
		foreach ($edits as $edit) {
			if ($edit->type == 'copy')
				$this->_context($edit->orig);
			elseif ($edit->type == 'add')
				$this->_added($edit->closing);
			elseif ($edit->type == 'delete')
				$this->_deleted($edit->orig);
			elseif ($edit->type == 'change')
				$this->_changed($edit->orig, $edit->closing);
			else
				trigger_error('Unknown edit type', E_USER_ERROR);
		}
		$this->_end_block();
		// wfProfileOut( $fname );
	}

	function _start_diff() {
		ob_start();
	}

	function _end_diff() {
		$val = ob_get_contents();
		ob_end_clean();
		return $val;
	}

	function _block_header($xbeg, $xlen, $ybeg, $ylen) {
		if ($xlen > 1)
			$xbeg .= "," . ($xbeg + $xlen - 1);
		if ($ylen > 1)
			$ybeg .= "," . ($ybeg + $ylen - 1);

		return $xbeg . ($xlen ? ($ylen ? 'c' : 'd') : 'a') . $ybeg;
	}

	function _start_block($header) {
		echo $header;
	}

	function _end_block() {
	}

	function _lines($lines, $prefix = ' ') {
		foreach ($lines as $line)
			echo "$prefix $line\n";
	}

	function _context($lines) {
		$this->_lines($lines);
	}

	function _added($lines) {
		$this->_lines($lines, '>');
	}
	function _deleted($lines) {
		$this->_lines($lines, '<');
	}

	function _changed($orig, $closing) {
		$this->_deleted($orig);
		echo "---\n";
		$this->_added($closing);
	}
}


/**
 *	Additions by Axel Boldt follow, partly taken from diff.php, phpwiki-1.3.3
 *
 */

define('NBSP', '&#160;');			// iso-8859-x non-breaking space.

/**
 * @todo document
 * @package Enano
 * @subpackage DifferenceEngine
 */
class _HWLDF_WordAccumulator {
	function _HWLDF_WordAccumulator () {
		$this->_lines = array();
		$this->_line = '';
		$this->_group = '';
		$this->_tag = '';
	}

	function _flushGroup ($new_tag) {
		if ($this->_group !== '') {
			if ($this->_tag == 'mark')
				$this->_line .= '<span class="diffchange">' .
					htmlspecialchars ( $this->_group ) . '</span>';
			else
				$this->_line .= htmlspecialchars ( $this->_group );
		}
		$this->_group = '';
		$this->_tag = $new_tag;
	}

	function _flushLine ($new_tag) {
		$this->_flushGroup($new_tag);
		if ($this->_line != '')
			array_push ( $this->_lines, $this->_line );
		else
			# make empty lines visible by inserting an NBSP
			array_push ( $this->_lines, NBSP );
		$this->_line = '';
	}

	function addWords ($words, $tag = '') {
		if ($tag != $this->_tag)
			$this->_flushGroup($tag);

		foreach ($words as $word) {
			// new-line should only come as first char of word.
			if ($word == '')
				continue;
			if ($word[0] == "\n") {
				$this->_flushLine($tag);
				$word = substr($word, 1);
			}
			assert(!strstr($word, "\n"));
			$this->_group .= $word;
		}
	}

	function getLines() {
		$this->_flushLine('~done');
		return $this->_lines;
	}
}

/**
 * @todo document
 * @package Enano
 * @subpackage DifferenceEngine
 */
define('MAX_LINE_LENGTH', 10000);
class WordLevelDiff extends MappedDiff
{
	function WordLevelDiff ($orig_lines, $closing_lines) {
		$fname = 'WordLevelDiff::WordLevelDiff';
		// wfProfileIn( $fname );

		list ($orig_words, $orig_stripped) = $this->_split($orig_lines);
		list ($closing_words, $closing_stripped) = $this->_split($closing_lines);

		$this->MappedDiff($orig_words, $closing_words,
						  $orig_stripped, $closing_stripped);
		// wfProfileOut( $fname );
	}

	function _split($lines) {
		$fname = 'WordLevelDiff::_split';
		// wfProfileIn( $fname );

		$words = array();
		$stripped = array();
		$first = true;
		foreach ( $lines as $line ) {
			# If the line is too long, just pretend the entire line is one big word
			# This prevents resource exhaustion problems
			if ( $first ) {
				$first = false;
			} else {
				$words[] = "\n";
				$stripped[] = "\n";
			}
			if ( strlen( $line ) > MAX_LINE_LENGTH ) {
				$words[] = $line;
				$stripped[] = $line;
			} else {
				if (preg_match_all('/ ( [^\S\n]+ | [0-9_A-Za-z\x80-\xff]+ | . ) (?: (?!< \n) [^\S\n])? /xs',
					$line, $m))
				{
					$words = array_merge( $words, $m[0] );
					$stripped = array_merge( $stripped, $m[1] );
				}
			}
		}
		// wfProfileOut( $fname );
		return array($words, $stripped);
	}

	function orig () {
		$fname = 'WordLevelDiff::orig';
		// wfProfileIn( $fname );
		$orig = new _HWLDF_WordAccumulator;

		foreach ($this->edits as $edit) {
			if ($edit->type == 'copy')
				$orig->addWords($edit->orig);
			elseif ($edit->orig)
				$orig->addWords($edit->orig, 'mark');
		}
		$lines = $orig->getLines();
		// wfProfileOut( $fname );
		return $lines;
	}

	function closing () {
		$fname = 'WordLevelDiff::closing';
		// wfProfileIn( $fname );
		$closing = new _HWLDF_WordAccumulator;

		foreach ($this->edits as $edit) {
			if ($edit->type == 'copy')
				$closing->addWords($edit->closing);
			elseif ($edit->closing)
				$closing->addWords($edit->closing, 'mark');
		}
		$lines = $closing->getLines();
		// wfProfileOut( $fname );
		return $lines;
	}
}

/**
 *	Wikipedia Table style diff formatter.
 * @todo document
 * @package Enano
 * @subpackage DifferenceEngine
 */
class TableDiffFormatter extends DiffFormatter
{
	function TableDiffFormatter() {
		$this->leading_context_lines = 2;
		$this->trailing_context_lines = 2;
	}

	function _block_header( $xbeg, $xlen, $ybeg, $ylen ) {
		$r = '<tr><td colspan="2" align="left"><strong><!--LINE '.$xbeg."--></strong></td>\n" .
		  '<td colspan="2" align="left"><strong><!--LINE '.$ybeg."--></strong></td></tr>\n";
		return $r;
	}

	function _start_block( $header ) {
		echo $header;
	}

	function _end_block() {
	}

	function _lines( $lines, $prefix=' ', $color='white' ) {
	}

	# HTML-escape parameter before calling this
	function addedLine( $line ) {
		return "<td>+</td><td class='diff-addedline'>{$line}</td>";
	}

	# HTML-escape parameter before calling this
	function deletedLine( $line ) {
		return "<td>-</td><td class='diff-deletedline'>{$line}</td>";
	}

	# HTML-escape parameter before calling this
	function contextLine( $line ) {
		return "<td> </td><td class='diff-context'>{$line}</td>";
	}

	function emptyLine() {
		return '<td colspan="2">&nbsp;</td>';
	}

	function _added( $lines ) {
		foreach ($lines as $line) {
			echo '<tr>' . $this->emptyLine() .
				$this->addedLine( htmlspecialchars ( $line ) ) . "</tr>\n";
		}
	}

	function _deleted($lines) {
		foreach ($lines as $line) {
			echo '<tr>' . $this->deletedLine( htmlspecialchars ( $line ) ) .
			  $this->emptyLine() . "</tr>\n";
		}
	}

	function _context( $lines ) {
		foreach ($lines as $line) {
			echo '<tr>' .
				$this->contextLine( htmlspecialchars ( $line ) ) .
				$this->contextLine( htmlspecialchars ( $line ) ) . "</tr>\n";
		}
	}

	function _changed( $orig, $closing ) {
		$fname = 'TableDiffFormatter::_changed';
		// wfProfileIn( $fname );

		$diff = new WordLevelDiff( $orig, $closing );
		$del = $diff->orig();
		$add = $diff->closing();

		# Notice that WordLevelDiff returns HTML-escaped output.
		# Hence, we will be calling addedLine/deletedLine without HTML-escaping.

		while ( $line = array_shift( $del ) ) {
			$aline = array_shift( $add );
			echo '<tr>' . $this->deletedLine( $line ) .
				$this->addedLine( $aline ) . "</tr>\n";
		}
		foreach ($add as $line) {	# If any leftovers
			echo '<tr>' . $this->emptyLine() .
				$this->addedLine( $line ) . "</tr>\n";
		}
		// wfProfileOut( $fname );
	}
}