DifferenceEngine.php

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<?php
# See diff.doc

class DifferenceEngine {
        /* private */ var $mOldid, $mNewid;
        /* private */ var $mOldtitle, $mNewtitle;
        /* private */ var $mOldtext, $mNewtext;
        /* private */ var $mOldUser, $mNewUser;
        /* private */ var $mOldComment, $mNewComment;
        /* private */ var $mOldPage, $mNewPage;
        
        function DifferenceEngine( $old, $new )
        {
                $this->mOldid = $old;
                $this->mNewid = $new;
        }

        function showDiffPage()
        {
                global $wgUser, $wgTitle, $wgOut, $wgLang;
                $fname = "DifferenceEngine::showDiffPage";
                wfProfileIn( $fname );
                
                $t = $wgTitle->getPrefixedText() . " (Diff: {$this->mOldid}, " .
                  "{$this->mNewid})";
                $mtext = wfMsg( "missingarticle", $t );

                $wgOut->setArticleFlag( false );
                if ( ! $this->loadText() ) {
                        $wgOut->setPagetitle( wfMsg( "errorpagetitle" ) );
                        $wgOut->addHTML( $mtext );
                        wfProfileOut( $fname );
                        return;
                }
                $wgOut->suppressQuickbar();
                
                $oldTitle = $this->mOldPage->getPrefixedText();
                $newTitle = $this->mNewPage->getPrefixedText();
                if( $oldTitle == $newTitle ) {
                        $wgOut->setPageTitle( $newTitle );
                } else {
                        $wgOut->setPageTitle( $oldTitle . ", " . $newTitle );
                }
                $wgOut->setSubtitle( wfMsg( "difference" ) );
                $wgOut->setRobotpolicy( "noindex,follow" );
                
                if ( !( $this->mOldPage->userCanRead() && $this->mNewPage->userCanRead() ) ) {
                        $wgOut->loginToUse();
                        $wgOut->output();
                        wfProfileOut( $fname );
                        exit;
                }

                $sk = $wgUser->getSkin();
                $talk = $wgLang->getNsText( NS_TALK );
                $contribs = wfMsg( "contribslink" );


                $this->mOldComment = $sk->formatComment($this->mOldComment);
                $this->mNewComment = $sk->formatComment($this->mNewComment);


                $oldUserLink = $sk->makeLinkObj( Title::makeTitle( NS_USER, $this->mOldUser ), $this->mOldUser );
                $newUserLink = $sk->makeLinkObj( Title::makeTitle( NS_USER, $this->mNewUser ), $this->mNewUser );
                $oldUTLink = $sk->makeLinkObj( Title::makeTitle( NS_USER_TALK, $this->mOldUser ), $talk );
                $newUTLink = $sk->makeLinkObj( Title::makeTitle( NS_USER_TALK, $this->mNewUser ), $talk );
                $oldContribs = $sk->makeKnownLinkObj( Title::makeTitle( NS_SPECIAL, "Contributions" ), $contribs,
                        "target=" . urlencode($this->mOldUser) );
                $newContribs = $sk->makeKnownLinkObj( Title::makeTitle( NS_SPECIAL, "Contributions" ), $contribs,
                        "target=" . urlencode($this->mNewUser) );
                if ( !$this->mNewid && $wgUser->isSysop() ) {
                        $rollback = "&nbsp;&nbsp;&nbsp;<strong>[" . $sk->makeKnownLinkObj( $wgTitle, wfMsg( "rollbacklink" ),
                                "action=rollback&from=" . urlencode($this->mNewUser) ) . "]</strong>";
                } else {
                        $rollback = "";
                }

                $oldHeader = "<strong>{$this->mOldtitle}</strong><br />$oldUserLink ($oldUTLink | $oldContribs)<br />". 
                  $this->mOldComment;
                $newHeader = "<strong>{$this->mNewtitle}</strong><br />$newUserLink ($newUTLink | $newContribs) $rollback<br />".
                  $this->mNewComment;

                DifferenceEngine::showDiff( $this->mOldtext, $this->mNewtext,
                  $oldHeader, $newHeader );
                $wgOut->addHTML( "<hr /><h2>{$this->mNewtitle}</h2>\n" );
                $wgOut->addWikiText( $this->mNewtext );
                
                wfProfileOut( $fname );
        }

        function showDiff( $otext, $ntext, $otitle, $ntitle )
        {
                global $wgOut;

                $ota = explode( "\n", str_replace( "\r\n", "\n",
                  htmlspecialchars( $otext ) ) );
                $nta = explode( "\n", str_replace( "\r\n", "\n",
                  htmlspecialchars( $ntext ) ) );

                $wgOut->addHTML( "<table border='0' width='98%'
cellpadding='0' cellspacing='4px' class='diff'><tr>
<td colspan='2' width='50%' align='center' class='diff-otitle'>
{$otitle}</td>
<td colspan='2' width='50%' align='center' class='diff-ntitle'>
{$ntitle}</td>
</tr>\n" );

                $diffs = new Diff( $ota, $nta );
                $formatter = new TableDiffFormatter();
                $formatter->format( $diffs );
                $wgOut->addHTML( "</table>\n" );
        }

        # Load the text of the articles to compare.  If newid is 0, then compare
        # the old article in oldid to the current article; if oldid is 0, then
        # compare the current article to the immediately previous one (ignoring
        # the value of newid).
        #
        function loadText()
        {
                global $wgTitle, $wgOut, $wgLang, $wgIsMySQL, $wgIsPg;
                $fname = "DifferenceEngine::loadText";
                
                $oldtable=$wgIsPg?'"old"':'old';
                if ( 0 == $this->mNewid || 0 == $this->mOldid ) {
                        $wgOut->setArticleFlag( true );
                        $this->mNewtitle = wfMsg( "currentrev" );
                        $id = $wgTitle->getArticleID();
                        
                        $sql = "SELECT cur_text, cur_user_text, cur_comment FROM cur WHERE cur_id={$id}";
                        $res = wfQuery( $sql, DB_READ, $fname );
                        if ( 0 == wfNumRows( $res ) ) { return false; }

                        $s = wfFetchObject( $res );
                        $this->mNewPage = &$wgTitle;
                        $this->mNewtext = $s->cur_text;
                        $this->mNewUser = $s->cur_user_text;
                        $this->mNewComment = $s->cur_comment;
                } else {
                        $sql = "SELECT old_namespace,old_title,old_timestamp,old_text,old_flags,old_user_text,old_comment FROM $oldtable WHERE " .
                          "old_id={$this->mNewid}";

                        $res = wfQuery( $sql, DB_READ, $fname );
                        if ( 0 == wfNumRows( $res ) ) { return false; }

                        $s = wfFetchObject( $res );
                        $this->mNewtext = Article::getRevisionText( $s );

                        $t = $wgLang->timeanddate( $s->old_timestamp, true );
                        $this->mNewPage = Title::MakeTitle( $s->old_namespace, $s->old_title );
                        $this->mNewtitle = wfMsg( "revisionasof", $t );
                        $this->mNewUser = $s->old_user_text;
                        $this->mNewComment = $s->old_comment;
                }
                if ( 0 == $this->mOldid ) {
                        $use_index=$wgIsMySQL?"USE INDEX (name_title_timestamp)":"";
                        $sql = "SELECT old_namespace,old_title,old_timestamp,old_text,old_flags,old_user_text,old_comment " .
                          "FROM $oldtable $use_index WHERE " .
                          "old_namespace=" . $this->mNewPage->getNamespace() . " AND " .
                          "old_title='" . wfStrencode( $this->mNewPage->getDBkey() ) .
                          "' ORDER BY inverse_timestamp LIMIT 1";
                        $res = wfQuery( $sql, DB_READ, $fname );
                } else {
                        $sql = "SELECT old_namespace,old_title,old_timestamp,old_text,old_flags,old_user_text,old_comment FROM $oldtable WHERE " .
                          "old_id={$this->mOldid}";
                        $res = wfQuery( $sql, DB_READ, $fname );
                }
                if ( 0 == wfNumRows( $res ) ) { return false; }

                $s = wfFetchObject( $res );
                $this->mOldPage = Title::MakeTitle( $s->old_namespace, $s->old_title );
                $this->mOldtext = Article::getRevisionText( $s );

                $t = $wgLang->timeanddate( $s->old_timestamp, true );
                $this->mOldtitle = wfMsg( "revisionasof", $t );
                $this->mOldUser = $s->old_user_text;
                $this->mOldComment = $s->old_comment;
                
                return true;
        }
}

// 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'));

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;
        }
}

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);
        }
}

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);
        }
}

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);
        }
}

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 _DiffEngine
{
        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.
         */
        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);
        }

        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 Diff 
{
        var $edits;

        function Diff($from_lines, $to_lines) {
                $eng = new _DiffEngine;
                $this->edits = $eng->diff($from_lines, $to_lines);
                //$this->_check($from_lines, $to_lines);
        }

        function reverse () {
        $rev = $this;
                $rev->edits = array();
                foreach ($this->edits as $edit) {
                        $rev->edits[] = $edit->reverse();
                }
        return $rev;
        }

        function isEmpty () {
                foreach ($this->edits as $edit) {
                        if ($edit->type != 'copy')
                                return false;
                }
                return true;
        }
  
        function lcs () {
        $lcs = 0;
                foreach ($this->edits as $edit) {
                        if ($edit->type == 'copy')
                                $lcs += sizeof($edit->orig);
                }
        return $lcs;
        }

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

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

        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->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);
        }
}
                        
class MappedDiff
extends Diff
{
        function MappedDiff($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));
                
                $this->Diff($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);
                        }
                }
        }
}

class DiffFormatter
{
        var $leading_context_lines = 0;

        var $trailing_context_lines = 0;

        function format($diff) {

                $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);

                return $this->_end_diff();
        }

        function _block($xbeg, $xlen, $ybeg, $ylen, &$edits) {
                $this->_start_block($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();
        }

        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);
        }
}


define('NBSP', "\xA0");                 // iso-8859-x non-breaking space.

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') 
                        $this->_line .= '<span class="diffchange">'.$this->_group.'</span>';
          else
                $this->_line .= $this->_group;
        }
                $this->_group = '';
                $this->_tag = $new_tag;
        }
        
        function _flushLine ($new_tag) {
                $this->_flushGroup($new_tag);
                if ($this->_line != '')
                        $this->_lines[] = $this->_line;
                $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->_group .= NBSP;
                                $this->_flushLine($tag);
                                $word = substr($word, 1);
                        }
                        assert(!strstr($word, "\n"));
                        $this->_group .= $word;
                }
        }

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

class WordLevelDiff extends MappedDiff
{
        function WordLevelDiff ($orig_lines, $closing_lines) {
                list ($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);
        }

        function _split($lines) {
                // FIXME: fix POSIX char class.
#                if (!preg_match_all('/ ( [^\S\n]+ | [[:alnum:]]+ | . ) (?: (?!< \n) [^\S\n])? /xs',
                if (!preg_match_all('/ ( [^\S\n]+ | [0-9_A-Za-z\x80-\xff]+ | . ) (?: (?!< \n) [^\S\n])? /xs',
                                                        implode("\n", $lines),
                                                        $m)) {
                        return array(array(''), array(''));
                }
                return array($m[0], $m[1]);
        }

        function orig () {
                $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');
                }
                return $orig->getLines();
        }

        function closing () {
                $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');
                }
                return $closing->getLines();
        }
}

class TableDiffFormatter extends DiffFormatter
{
        function TableDiffFormatter() {
                $this->leading_context_lines = 2;
                $this->trailing_context_lines = 2;
        }
        
        function _block_header( $xbeg, $xlen, $ybeg, $ylen ) {
                $l1 = wfMsg( "lineno", $xbeg );
                $l2 = wfMsg( "lineno", $ybeg );

                $r = '<tr><td colspan="2" align="left"><strong>'.$l1."</strong></td>\n" .
                  '<td colspan="2" align="left"><strong>'.$l2."</strong></td></tr>\n";
                return $r;
        }

        function _start_block( $header ) {
                global $wgOut;
                $wgOut->addHTML( $header );
        }

        function _end_block() {
        }

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

        function addedLine( $line ) {
                return '<td>+</td><td class="diff-addedline">' .
                  $line.'</td>';
        }

        function deletedLine( $line ) {
                return '<td>-</td><td class="diff-deletedline">' .
                  $line.'</td>';
        }

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

        function contextLine( $line ) {
                return '<td> </td><td class="diff-context">'.$line.'</td>';
        }
        
        function _added($lines) {
                global $wgOut;
                foreach ($lines as $line) {
                        $wgOut->addHTML( '<tr>' . $this->emptyLine() .
                          $this->addedLine( $line ) . "</tr>\n" );
                }
        }

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

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

        function _changed( $orig, $closing ) {
                global $wgOut;
                $diff = new WordLevelDiff( $orig, $closing );
                $del = $diff->orig();
                $add = $diff->closing();

                while ( $line = array_shift( $del ) ) {
                        $aline = array_shift( $add );
                        $wgOut->addHTML( '<tr>' . $this->deletedLine( $line ) .
                          $this->addedLine( $aline ) . "</tr>\n" );
                }
                $this->_added( $add ); # If any leftovers
        }
}

?>

---