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

// FIXME: possibly remove assert()'s for production version?

// PHP3 does not have assert()
define('USE_ASSERTS', function_exists('assert'));

      
/**
 * Class used internally by WikiDiff 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.
 */
class _WikiDiffEngine
{
  var $edits;	// List of editing operation to convert XV to YV.
  var $xv = array(), $yv = array();
  var $xchanged, $ychanged;

  function _WikiDiffEngine ($from_lines, $to_lines)
      {
	$n_from = sizeof($from_lines);
	$n_to = sizeof($to_lines);
	$endskip = 0;

	// Ignore trailing and leading matching lines.
	while ($n_from > 0 && $n_to > 0)
	  {
	    if ($from_lines[$n_from - 1] != $to_lines[$n_to - 1])
		break;
	    $n_from--;
	    $n_to--;
	    $endskip++;
	  }
	for ( $skip = 0; $skip < min($n_from, $n_to); $skip++)
	    if ($from_lines[$skip] != $to_lines[$skip])
		break;
	$n_from -= $skip;
	$n_to -= $skip;

	$xlines = array();
	$ylines = array();

	// Ignore lines which do not exist in both files.
	for ($x = 0; $x < $n_from; $x++)
	    $xhash[$from_lines[$x + $skip]] = 1;
	for ($y = 0; $y < $n_to; $y++)
	  {
	    $line = $to_lines[$y + $skip];
	    $ylines[] = $line;
	    if ( ($this->ychanged[$y] = empty($xhash[$line])) )
		continue;
	    $yhash[$line] = 1;
	    $this->yv[] = $line;
	    $this->yind[] = $y;
	  }
	for ($x = 0; $x < $n_from; $x++)
	  {
	    $line = $from_lines[$x + $skip];
	    $xlines[] = $line;
	    if ( ($this->xchanged[$x] = empty($yhash[$line])) )
		continue;
	    $this->xv[] = $line;
	    $this->xind[] = $x;
	  }

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

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

	// Compute the edit operations.
	$this->edits = array();
	if ($skip)
	    $this->edits[] = $skip;

	$x = 0;
	$y = 0;
	while ($x < $n_from || $y < $n_to)
	  {
	    USE_ASSERTS && assert($y < $n_to || $this->xchanged[$x]);
	    USE_ASSERTS && assert($x < $n_from || $this->ychanged[$y]);

	    // Skip matching "snake".
	    $x0 = $x;
	    $ncopy = 0;

	    while ( $x < $n_from && $y < $n_to
	            && !$this->xchanged[$x] && !$this->ychanged[$y])
	      {
		++$x;
		++$y;
		++$ncopy;
	      }
	    if ($x > $x0)
		$this->edits[] = $x - $x0;

	    // Find deletes.
	    $x0 = $x;
	    $ndelete = 0;
	    while ($x < $n_from && $this->xchanged[$x])
	      {
		++$x;
		++$ndelete;
	      }
	    if ($x > $x0)
		$this->edits[] = -($x - $x0);

	    // Find adds.
	    if (isset($this->ychanged[$y]) && $this->ychanged[$y])
	      {
		$adds = array();
		while ($y < $n_to && $this->ychanged[$y])
		    $adds[] = "" . $ylines[$y++];
		$this->edits[] = $adds;
	      }
	  }
	if ($endskip != 0)
	    $this->edits[] = $endskip;
      }

  /* 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)
      {
	$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++)
	      {
		$matches = $ymatches[$flip ? $this->yv[$x] : $this->xv[$x]];
		if (!$matches)
		    continue;
		reset($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);
      }

  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 $this->{x,y}changed[], by
   * storing a 1 in the element for each line that is an insertion
   * or deletion (ie. is not in the LCS).
   *
   * The subsequence of file 0 is [XOFF, XLIM) and likewise for file 1.
   *
   * Note that XLIM, YLIM are exclusive bounds.
   * All line numbers are origin-0 and discarded lines are not counted.
   */
  function _compareseq ($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).
   */
  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 files.
 */
class WikiDiff 
{
  var $edits;

  /**
   * Compute diff between files (or deserialize serialized WikiDiff.)
   */
  function WikiDiff($from_lines = false, $to_lines = false)
      {
	if ($from_lines && $to_lines)
	  {
	    $compute = new _WikiDiffEngine($from_lines, $to_lines);
	    $this->edits = $compute->edits;
	  }
	else if ($from_lines)
	  {
	    // $from_lines is not really from_lines, but rather
	    // a serialized WikiDiff.
	    $this->edits = unserialize($from_lines);
	  }
	else
	  {
	    $this->edits = array();
	  }
      }

  /**
   * Compute reversed WikiDiff.
   *
   * SYNOPSIS:
   *
   *  $diff = new WikiDiff($lines1, $lines2);
   *  $rev = $diff->reverse($lines1);
   *
   *  // reconstruct $lines1 from $lines2:
   *  $out = $rev->apply($lines2);
   */
  function reverse ($from_lines)
      {
	$x = 0;
	$rev = new WikiDiff;

	for ( reset($this->edits);
	      $edit = current($this->edits);
	      next($this->edits) )
	  {
	    if (is_array($edit))
	      { // Was an add, turn it into a delete.
		$nadd = sizeof($edit);
		USE_ASSERTS && assert ($nadd > 0);
		$edit = -$nadd;
	      }
	    else if ($edit > 0)
	      {
		// Was a copy --- just pass it through.	      }
		$x += $edit;
	      }
	    else if ($edit < 0)
	      { // Was a delete, turn it into an add.
		$ndelete = -$edit;
		$edit = array();
		while ($ndelete-- > 0)
		    $edit[] = "" . $from_lines[$x++];
	      }
	    else die("assertion error");

	    $rev->edits[] = $edit;
	  }

	return $rev;
      }

  /**
   * Compose (concatenate) WikiDiffs.
   *
   * SYNOPSIS:
   *
   *  $diff1 = new WikiDiff($lines1, $lines2);
   *  $diff2 = new WikiDiff($lines2, $lines3);
   *  $comp = $diff1->compose($diff2);
   *
   *  // reconstruct $lines3 from $lines1:
   *  $out = $comp->apply($lines1);
   */
  function compose ($that)
      {
	reset($this->edits);
	reset($that->edits);

	$comp = new WikiDiff;
	$left = current($this->edits);
	$right = current($that->edits);
      
	while ($left || $right)
	  {
	    if (!is_array($left) && $left < 0)
	      { // Left op is a delete.
		$newop = $left;
		$left = next($this->edits);
	      }
	    else if (is_array($right))
	      { // Right op is an add.
		$newop = $right;
		$right = next($that->edits);
	      }
	    else if (!$left || !$right)
		die ("assertion error");
	    else if (!is_array($left) && $left > 0)
	      { // Left op is a copy.
		if ($left <= abs($right))
		  {
		    $newop = $right > 0 ? $left : -$left;
		    $right -= $newop;
		    if ($right == 0)
			$right = next($that->edits);
		    $left = next($this->edits);
		  }
		else
		  {
		    $newop = $right;
		    $left -= abs($right);
		    $right = next($that->edits);
		  }
	      }
	    else
	      { // Left op is an add.
		if (!is_array($left)) die('assertion error');
		$nleft = sizeof($left);
		if ($nleft <= abs($right))
		  {
		    if ($right > 0)
		      { // Right op is copy
			$newop = $left;
			$right -= $nleft;
		      }
		    else // Right op is delete
		      {
			$newop = false;
			$right += $nleft;
		      }
		    if ($right == 0)
			$right = next($that->edits);
		    $left = next($this->edits);
		  }
		else
		  {
		    unset($newop);
		    if ($right > 0)
			for ($i = 0; $i < $right; $i++)
			    $newop[] = $left[$i];

		    $tmp = array();
		    for ($i = abs($right); $i < $nleft; $i++)
			$tmp[] = $left[$i];
		    $left = $tmp;
		    $right = next($that->edits);
		  }
	      }
	    if (!$op)
	      {
		$op = $newop;
		continue;
	      }
	    if (! $newop)
		continue;

	    if (is_array($op) && is_array($newop))
	      {
		// Both $op and $newop are adds.
		for ($i = 0; $i < sizeof($newop); $i++)
		    $op[] = $newop[$i];
	      }
	    else if (($op > 0 && $newop > 0) || ($op < 0 && $newop < 0))
	      { // $op and $newop are both either deletes or copies.
		$op += $newop;
	      }
	    else
	      {
		$comp->edits[] = $op;
		$op = $newop;
	      }
	  }
	if ($op)
	    $comp->edits[] = $op;
	
	return $comp;
      }

  /* Debugging only:
  function _dump ()
      {
	echo "<ol>";
	for (reset($this->edits);
	     $edit = current($this->edits);
	     next($this->edits))
	  {
	    echo "<li>";
	    if ($edit > 0)
		echo "Copy $edit";
	    else if ($edit < 0)
		echo "Delete " . -$edit;
	    else if (is_array($edit))
	      {
		echo "Add " . sizeof($edit) . "<ul>";
		for ($i = 0; $i < sizeof($edit); $i++)
		    echo "<li>" . htmlspecialchars($edit[$i]);
		echo "</ul>";
	      }
	    else
		die("assertion error");
	  }
	echo "</ol>";
      }
  */
	    
  /**
   * Apply a WikiDiff to a set of lines.
   *
   * SYNOPSIS:
   *
   *  $diff = new WikiDiff($lines1, $lines2);
   *
   *  // reconstruct $lines2 from $lines1:
   *  $out = $diff->apply($lines1);
   */
  function apply ($from_lines)
      {
	$x = 0;
	$xlim = sizeof($from_lines);

	for ( reset($this->edits);
	      $edit = current($this->edits);
	      next($this->edits) )
	  {
	    if (is_array($edit))
	      {
		reset($edit);
		while (list ($junk, $line) = each($edit))
		    $output[] = $line;
	      }
	    else if ($edit > 0)
		while ($edit--)
		    $output[] = $from_lines[$x++];
	    else
		$x += -$edit;
	  }
	if ($x != $xlim)
	    ExitWiki(sprintf(tra ("WikiDiff::apply: line count mismatch: %s != %s"), $x, $xlim));
	return $output;
      }
    
  /**
   * Serialize a WikiDiff.
   *
   * SYNOPSIS:
   *
   *  $diff = new WikiDiff($lines1, $lines2);
   *  $string = $diff->serialize;
   *
   *  // recover WikiDiff from serialized version:
   *  $diff2 = new WikiDiff($string);
   */
  function serialize ()
      {
	return serialize($this->edits);
      }

  /**
   * Return true if two files were equal.
   */
  function isEmpty ()
      {
	if (sizeof($this->edits) > 1)
	    return false;
	if (sizeof($this->edits) == 0)
	    return true;
	// Test for: only edit is a copy.
	return !is_array($this->edits[0]) && $this->edits[0] > 0;
      }
  
  /**
   * Compute the length of the Longest Common Subsequence (LCS).
   *
   * This is mostly for diagnostic purposed.
   */
  function lcs ()
      {
	$lcs = 0;
	for (reset($this->edits);
	     $edit = current($this->edits);
	     next($this->edits))
	  {
	    if (!is_array($edit) && $edit > 0)
		$lcs += $edit;
	  }
	return $lcs;
      }
    
  /**
   * Check a WikiDiff for validity. 
   *
   * This is here only for debugging purposes.
   */
  function _check ($from_lines, $to_lines)
      {
	$test = $this->apply($from_lines);
	if (serialize($test) != serialize($to_lines))
	    ExitWiki(tra ("WikiDiff::_check: failed"));

	reset($this->edits);
	$prev = current($this->edits);
	$prevtype = is_array($prev) ? 'a' : ($prev > 0 ? 'c' : 'd');

	while ($edit = next($this->edits))
	  {
	    $type = is_array($edit) ? 'a' : ($edit > 0 ? 'c' : 'd');
	    if ( $prevtype == $type )
		ExitWiki(tra ("WikiDiff::_check: edit sequence is non-optimal"));
	    $prevtype = $type;
	  }
	$lcs = $this->lcs();
	printf ("<strong>" . tra ("WikiDiff Okay: LCS = %s") . "</strong>\n", $lcs);
      }
}


/**
 * A class to format a WikiDiff as HTML.
 *
 * Usage:
 *
 *   $diff = new WikiDiff($lines1, $lines2); // compute diff.
 *
 *   $fmt = new WikiDiffFormatter;
 *   echo $fmt->format($diff, $lines1); // Output HTMLified standard diff.
 *
 * or to output reverse diff (diff's that would take $lines2 to $lines1):
 *
 *   $fmt = new WikiDiffFormatter('reversed');
 *   echo $fmt->format($diff, $lines1);
 */
class WikiDiffFormatter
{
  var $context_lines;
  var $do_reverse_diff;
  var $context_prefix, $deletes_prefix, $adds_prefix;

  function WikiDiffFormatter ($reverse = false)
      {
	$this->do_reverse_diff = $reverse;
	$this->context_lines = 0;
	$this->context_prefix = '&nbsp;&nbsp;';
	$this->deletes_prefix = '&lt;&nbsp;';
	$this->adds_prefix = '&gt;&nbsp;';
      }

  function format ($diff, $from_lines)
      {
	$html = '<table width="97%" bgcolor="black" ' .
		'cellspacing="2" cellpadding="2" border="0"><br />';
	$html .= $this->_format($diff->edits, $from_lines);
	$html .= "</table>\n";

	return $html;
      }
    
  function _format ($edits, $from_lines)
      {
	$html = '';
	$x = 0; $y = 0;
	$xlim = sizeof($from_lines);

	reset($edits);
	while ($edit = current($edits))
	  {
	    if (!is_array($edit) && $edit >= 0)
	      { // Edit op is a copy.
		$ncopy = $edit;
	      }
	    else
	      {
		$ncopy = 0;
		if (empty($hunk))
		  {
		    // Start of an output hunk. 
		    $xoff = max(0, $x - $this->context_lines);
		    $yoff = $xoff + $y - $x;
		    if ($xoff < $x)
		      {
			// Get leading context.
			$context = array();
			for ($i = $xoff; $i < $x; $i++)
			    $context[] = $from_lines[$i];
			$hunk['c'] = $context;
		      }
		  }
		if (is_array($edit))
		  { // Edit op is an add.
		    $y += sizeof($edit);
		    $hunk[$this->do_reverse_diff ? 'd' : 'a'] = $edit;
		  }
		else
		  { // Edit op is a delete
		    $deletes = array();
		    while ($edit++ < 0)
			$deletes[] = $from_lines[$x++];
		    $hunk[$this->do_reverse_diff ? 'a' : 'd'] = $deletes;
		  }
	      }

	    $next = next($edits);
	    if (!empty($hunk))
	      {
		if ( !$next || $ncopy > 2 * $this->context_lines)
		  {
		    // End of an output hunk.
		    $hunks[] = $hunk;
		    unset($hunk);

		    $xend = min($x + $this->context_lines, $xlim);
		    if ($x < $xend)
		      {
			// Get trailing context.
			$context = array();
			for ($i = $x; $i < $xend; $i++)
			    $context[] = $from_lines[$i];
			$hunks[] = array('c' => $context);
		      }

		    $xlen = $xend - $xoff;
		    $ylen = $xend + $y - $x - $yoff;
		    $xbeg = $xlen ? $xoff + 1 : $xoff;
		    $ybeg = $ylen ? $yoff + 1 : $yoff;

		    if ($this->do_reverse_diff)
			list ($xbeg, $xlen, $ybeg, $ylen)
			    = array($ybeg, $ylen, $xbeg, $xlen);

		    $html .= $this->_emit_diff($xbeg,$xlen,$ybeg,$ylen,
					       $hunks);
		    unset($hunks);
		  }
		else if ($ncopy)
		  {
		    $hunks[] = $hunk;

		    // Copy context.
		    $context = array();
		    for ($i = $x; $i < $x + $ncopy; $i++)
			$context[] = $from_lines[$i];
		    $hunk = array('c' => $context);
		  }
	      }

	    $x += $ncopy;
	    $y += $ncopy;
	  }
	return $html;
      }

  function _emit_lines($lines,  $prefix, $color)
      {
	$html = '';
	reset($lines);
	while (list ($junk, $line) = each($lines))
	  {
	    $html .= "<tr bgcolor=\"$color\"><td><tt>$prefix</tt>";
	    $html .= "<tt>" . htmlspecialchars($line) . "</tt></td></tr>\n";
	  }
	return $html;
      }

  function _emit_diff ($xbeg,$xlen,$ybeg,$ylen,$hunks)
      {
	$html = '<tr><td><table width="100%" bgcolor="white"'
	      . ' cellspacing="0" border="0" cellpadding="4"><br />'
	      . '<tr bgcolor="#cccccc"><td><tt>'
	      . $this->_diff_header($xbeg, $xlen, $ybeg, $ylen)
	      . "</tt></td></tr>\n<tr><td>\n"
	      . '<table width="100%" cellspacing="0" border="0" cellpadding="2"><br />';

	$prefix = array('c' => $this->context_prefix,
			'a' => $this->adds_prefix,
			'd' => $this->deletes_prefix);
	$color = array('c' => '#ffffff',
		       'a' => '#ffcccc',
		       'd' => '#ccffcc');

	for (reset($hunks); $hunk = current($hunks); next($hunks))
	  {
	    if (!empty($hunk['c']))
		$html .= $this->_emit_lines($hunk['c'],
		                            $this->context_prefix, '#ffffff');
	    if (!empty($hunk['d']))
		$html .= $this->_emit_lines($hunk['d'],
		                            $this->deletes_prefix, '#ccffcc');
	    if (!empty($hunk['a']))
		$html .= $this->_emit_lines($hunk['a'],
		                            $this->adds_prefix, '#ffcccc');
	  }

	$html .= "</table></td></tr></table></td></tr>\n";
	return $html;
      }

  function _diff_header ($xbeg,$xlen,$ybeg,$ylen)
      {
	$what = $xlen ? ($ylen ? 'c' : 'd') : 'a';
	$xlen = $xlen > 1 ? "," . ($xbeg + $xlen - 1) : '';
	$ylen = $ylen > 1 ? "," . ($ybeg + $ylen - 1) : '';

	return "$xbeg$xlen$what$ybeg$ylen";
      }
}

/**
 * A class to format a WikiDiff as a pretty HTML unified diff.
 *
 * Usage:
 *
 *   $diff = new WikiDiff($lines1, $lines2); // compute diff.
 *
 *   $fmt = new WikiUnifiedDiffFormatter;
 *   echo $fmt->format($diff, $lines1); // Output HTMLified unified diff.
 */
class WikiUnifiedDiffFormatter extends WikiDiffFormatter
{
  function WikiUnifiedDiffFormatter ($reverse = false, $context_lines = 3)
      {
	$this->do_reverse_diff = $reverse;
	$this->context_lines = $context_lines;
	$this->context_prefix = '&nbsp;';
	$this->deletes_prefix = '-';
	$this->adds_prefix = '+';
      }
    
  function _diff_header ($xbeg,$xlen,$ybeg,$ylen)
      {
	$xlen = $xlen == 1 ? '' : ",$xlen";
	$ylen = $ylen == 1 ? '' : ",$ylen";

	return "@@ -$xbeg$xlen +$ybeg$ylen @@";
      }
}



/////////////////////////////////////////////////////////////////
/*
if ($diff)
{
  if (get_magic_quotes_gpc()) {
     $diff = stripslashes($diff);
  }

  $pagename = $diff;

  $wiki = RetrievePage($dbi, $pagename, $WikiPageStore);
//  $dba = OpenDataBase($ArchivePageStore);
  $archive= RetrievePage($dbi, $pagename, $ArchivePageStore);

  $html = '<table><tr><td align="right">';
  $html .= tra ("Current page:");
  $html .= '</td>';
  if (is_array($wiki)) {
      $html .= "<td>";
      $html .= sprintf(tra ("version %s"), $wiki['version']);
      $html .= "</td><td>";
      $html .= sprintf(tra ("last modified on %s"),
	date($datetimeformat, $wiki['lastmodified']));
      $html .= "</td><td>";
      $html .= sprintf (tra ("by %s"), $wiki['author']);
      $html .= "</td>";
  } else {
      $html .= "<td colspan=3><em>";
      $html .= tra ("None");
      $html .= "</em></td>";
  }
  $html .= "</tr>\n";
  $html .= '<tr><td align="right">';
  $html .= tra ("Archived page:");
  $html .= '</td>';
  if (is_array($archive)) {
      $html .= "<td>";
      $html .= sprintf(tra ("version %s"), $archive['version']);
      $html .= "</td><td>";
      $html .= sprintf(tra ("last modified on %s"),
	date($datetimeformat, $archive['lastmodified']));
      $html .= "</td><td>";
      $html .= sprintf(tra ("by %s"), $archive['author']);
      $html .= "</td>";
  } else {
      $html .= "<td colspan=3><em>";
      $html .= tra ("None");
      $html .= "</em></td>";
  }
  $html .= "</tr></table><p>\n";

  if (is_array($wiki) && is_array($archive))
    {
      $diff = new WikiDiff($archive['content'], $wiki['content']);
      if ($diff->isEmpty()) {
	  $html .= '<hr>[' . tra ("Versions are identical") . ']';
      } else {
	  //$fmt = new WikiDiffFormatter;
	  $fmt = new WikiUnifiedDiffFormatter;
	  $html .= $fmt->format($diff, $archive['content']);
      }
    }

  GeneratePage('MESSAGE', $html, sprintf(tra ("Diff of %s."),
	htmlspecialchars($pagename)), 0);
}
*/
?>
