class.WordLevelDiff.php

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<?php

// Copyright holded by MediaWiki contributers, Licensed under GPL version 2 or later


class DifferenceEngine {
        var $mOldid, $mNewid, $mTitle;
        var $mOldtitle, $mNewtitle, $mPagetitle;
        var $mOldtext, $mNewtext;
        var $mOldPage, $mNewPage;
        var $mRcidMarkPatrolled;
        var $mOldRev, $mNewRev;
        var $mRevisionsLoaded = false; // Have the revisions been loaded
        var $mTextLoaded = 0; // How many text blobs have been loaded, 0, 1 or 2?
        function DifferenceEngine( $titleObj = null, $old = 0, $new = 0, $rcid = 0 ) {
                $this->mTitle = $titleObj;
                wfDebug("DifferenceEngine old '$old' new '$new' rcid '$rcid'\n");

                if ( 'prev' === $new ) {
                        # Show diff between revision $old and the previous one.
                        # Get previous one from DB.
                        #
                        $this->mNewid = intval($old);

                        $this->mOldid = $this->mTitle->getPreviousRevisionID( $this->mNewid );

                } elseif ( 'next' === $new ) {
                        # Show diff between revision $old and the previous one.
                        # Get previous one from DB.
                        #
                        $this->mOldid = intval($old);
                        $this->mNewid = $this->mTitle->getNextRevisionID( $this->mOldid );
                        if ( false === $this->mNewid ) {
                                # if no result, NewId points to the newest old revision. The only newer
                                # revision is cur, which is "0".
                                $this->mNewid = 0;
                        }

                } else {
                        $this->mOldid = intval($old);
                        $this->mNewid = intval($new);
                }
                $this->mRcidMarkPatrolled = intval($rcid);  # force it to be an integer
        }

        function showDiffPage( $diffOnly = false ) {
                global $wgUser, $wgOut, $wgUseExternalEditor, $wgUseRCPatrol;
                $fname = 'DifferenceEngine::showDiffPage';
                //wfProfileIn( $fname );

                # If external diffs are enabled both globally and for the user,
                # we'll use the application/x-external-editor interface to call
                # an external diff tool like kompare, kdiff3, etc.
                if($wgUseExternalEditor && $wgUser->getOption('externaldiff')) {
                        global $wgInputEncoding,$wgServer,$wgScript,$wgLang;
                        $wgOut->disable();
                        header ( "Content-type: application/x-external-editor; charset=".$wgInputEncoding );
                        $url1=$this->mTitle->getFullURL("action=raw&oldid=".$this->mOldid);
                        $url2=$this->mTitle->getFullURL("action=raw&oldid=".$this->mNewid);
                        $special=$wgLang->getNsText(NS_SPECIAL);
                        $control=<<<CONTROL
[Process]
Type=Diff text
Engine=MediaWiki
Script={$wgServer}{$wgScript}
Special namespace={$special}

[File]
Extension=wiki
URL=$url1

[File 2]
Extension=wiki
URL=$url2
CONTROL;
                        echo($control);
                        return;
                }

                $wgOut->setArticleFlag( false );
                if ( ! $this->loadRevisionData() ) {
                        $t = $this->mTitle->getPrefixedText() . " (Diff: {$this->mOldid}, {$this->mNewid})";
                        $mtext = wfMsg( 'missingarticle', "<nowiki>$t</nowiki>" );
                        $wgOut->setPagetitle( wfMsg( 'errorpagetitle' ) );
                        $wgOut->addWikitext( $mtext );
                        //wfProfileOut( $fname );
                        return;
                }
                
                wfRunHooks( 'DiffViewHeader', array( $this, $this->mOldRev, $this->mNewRev ) );

                if ( $this->mNewRev->isCurrent() ) {
                        $wgOut->setArticleFlag( true );
                }

                # mOldid is false if the difference engine is called with a "vague" query for
                # a diff between a version V and its previous version V' AND the version V
                # is the first version of that article. In that case, V' does not exist.
                if ( $this->mOldid === false ) {
                        $this->showFirstRevision();
                        $this->renderNewRevision();  // should we respect $diffOnly here or not?
                        //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,nofollow' );

                if ( !( $this->mOldPage->userCanRead() && $this->mNewPage->userCanRead() ) ) {
                        $wgOut->loginToUse();
                        $wgOut->output();
                        //wfProfileOut( $fname );
                        exit;
                }

                $sk = $wgUser->getSkin();

                if ( $this->mNewRev->isCurrent() && $wgUser->isAllowed('rollback') ) {
                        $rollback = '&nbsp;&nbsp;&nbsp;' . $sk->generateRollback( $this->mNewRev );
                } else {
                        $rollback = '';
                }
                if( $wgUseRCPatrol && $this->mRcidMarkPatrolled != 0 && $wgUser->isAllowed( 'patrol' ) ) {
                        $patrol = ' [' . $sk->makeKnownLinkObj( $this->mTitle, wfMsg( 'markaspatrolleddiff' ), "action=markpatrolled&rcid={$this->mRcidMarkPatrolled}" ) . ']';
                } else {
                        $patrol = '';
                }

                $prevlink = $sk->makeKnownLinkObj( $this->mTitle, wfMsgHtml( 'previousdiff' ),
                        'diff=prev&oldid='.$this->mOldid, '', '', 'id="differences-prevlink"' );
                if ( $this->mNewRev->isCurrent() ) {
                        $nextlink = '&nbsp;';
                } else {
                        $nextlink = $sk->makeKnownLinkObj( $this->mTitle, wfMsgHtml( 'nextdiff' ),
                                'diff=next&oldid='.$this->mNewid, '', '', 'id="differences-nextlink"' );
                }

                $oldminor = '';
                $newminor = '';

                if ($this->mOldRev->mMinorEdit == 1) {
                        $oldminor = wfElement( 'span', array( 'class' => 'minor' ),
                                wfMsg( 'minoreditletter') ) . ' ';
                }

                if ($this->mNewRev->mMinorEdit == 1) {
                        $newminor = wfElement( 'span', array( 'class' => 'minor' ),
                        wfMsg( 'minoreditletter') ) . ' ';
                }

                $oldHeader = "<strong>{$this->mOldtitle}</strong><br />" .
                        $sk->revUserTools( $this->mOldRev ) . "<br />" .
                        $oldminor . $sk->revComment( $this->mOldRev, !$diffOnly ) . "<br />" .
                        $prevlink;
                $newHeader = "<strong>{$this->mNewtitle}</strong><br />" .
                        $sk->revUserTools( $this->mNewRev ) . " $rollback<br />" .
                        $newminor . $sk->revComment( $this->mNewRev, !$diffOnly ) . "<br />" .
                        $nextlink . $patrol;

                $this->showDiff( $oldHeader, $newHeader );

                if ( !$diffOnly )
                        $this->renderNewRevision();

                //wfProfileOut( $fname );
        }

        function renderNewRevision() {
                global $wgOut;
                $fname = 'DifferenceEngine::renderNewRevision';
                //wfProfileIn( $fname );

                $wgOut->addHTML( "<hr /><h2>{$this->mPagetitle}</h2>\n" );
                #add deleted rev tag if needed
                if ( !$this->mNewRev->userCan(Revision::DELETED_TEXT) ) {
                        $wgOut->addWikiText( wfMsg( 'rev-deleted-text-permission' ) );
                }

                if( !$this->mNewRev->isCurrent() ) {
                        $oldEditSectionSetting = $wgOut->parserOptions()->setEditSection( false );
                }

                $this->loadNewText();
                if( is_object( $this->mNewRev ) ) {
                        $wgOut->setRevisionId( $this->mNewRev->getId() );
                }

                $wgOut->addWikiTextTidy( $this->mNewtext );

                if( !$this->mNewRev->isCurrent() ) {
                        $wgOut->parserOptions()->setEditSection( $oldEditSectionSetting );
                }

                //wfProfileOut( $fname );
        }

        function showFirstRevision() {
                global $wgOut, $wgUser;

                $fname = 'DifferenceEngine::showFirstRevision';
                //wfProfileIn( $fname );

                # Get article text from the DB
                #
                if ( ! $this->loadNewText() ) {
                        $t = $this->mTitle->getPrefixedText() . " (Diff: {$this->mOldid}, " .
                          "{$this->mNewid})";
                        $mtext = wfMsg( 'missingarticle', "<nowiki>$t</nowiki>" );
                        $wgOut->setPagetitle( wfMsg( 'errorpagetitle' ) );
                        $wgOut->addWikitext( $mtext );
                        //wfProfileOut( $fname );
                        return;
                }
                if ( $this->mNewRev->isCurrent() ) {
                        $wgOut->setArticleFlag( true );
                }

                # Check if user is allowed to look at this page. If not, bail out.
                #
                if ( !( $this->mTitle->userCanRead() ) ) {
                        $wgOut->loginToUse();
                        $wgOut->output();
                        //wfProfileOut( $fname );
                        exit;
                }

                # Prepare the header box
                #
                $sk = $wgUser->getSkin();

                $nextlink = $sk->makeKnownLinkObj( $this->mTitle, wfMsgHtml( 'nextdiff' ), 'diff=next&oldid='.$this->mNewid, '', '', 'id="differences-nextlink"' );
                $header = "<div class=\"firstrevisionheader\" style=\"text-align: center\"><strong>{$this->mOldtitle}</strong><br />" .
                        $sk->revUserTools( $this->mNewRev ) . "<br />" .
                        $sk->revComment( $this->mNewRev ) . "<br />" .
                        $nextlink . "</div>\n";

                $wgOut->addHTML( $header );

                $wgOut->setSubtitle( wfMsg( 'difference' ) );
                $wgOut->setRobotpolicy( 'noindex,nofollow' );

                //wfProfileOut( $fname );
        }

        function showDiff( $otitle, $ntitle ) {
                global $wgOut;
                $diff = $this->getDiff( $otitle, $ntitle );
                if ( $diff === false ) {
                        $wgOut->addWikitext( wfMsg( 'missingarticle', "<nowiki>(fixme, bug)</nowiki>" ) );
                        return false;
                } else {
                        $wgOut->addHTML( $diff );
                        return true;
                }
        }

        function getDiff( $otitle, $ntitle ) {
                $body = $this->getDiffBody();
                if ( $body === false ) {
                        return false;
                } else {
                        $multi = $this->getMultiNotice();
                        return $this->addHeader( $body, $otitle, $ntitle, $multi );
                }
        }

        function getDiffBody() {
                global $wgMemc;
                $fname = 'DifferenceEngine::getDiffBody';
                //wfProfileIn( $fname );
                
                // Cacheable?
                $key = false;
                if ( $this->mOldid && $this->mNewid ) {
                        // Try cache
                        $key = wfMemcKey( 'diff', 'oldid', $this->mOldid, 'newid', $this->mNewid );
                        $difftext = $wgMemc->get( $key );
                        if ( $difftext ) {
                                wfIncrStats( 'diff_cache_hit' );
                                $difftext = $this->localiseLineNumbers( $difftext );
                                $difftext .= "\n<!-- diff cache key $key -->\n";
                                //wfProfileOut( $fname );
                                return $difftext;
                        }
                }

                #loadtext is permission safe, this just clears out the diff
                if ( !$this->loadText() ) {
                        //wfProfileOut( $fname );
                        return false;
                } else if ( $this->mOldRev && !$this->mOldRev->userCan(Revision::DELETED_TEXT) ) {
                  return '';
                } else if ( $this->mNewRev && !$this->mNewRev->userCan(Revision::DELETED_TEXT) ) {
                  return '';
                }

                $difftext = $this->generateDiffBody( $this->mOldtext, $this->mNewtext );
                
                // Save to cache for 7 days
                if ( $key !== false && $difftext !== false ) {
                        wfIncrStats( 'diff_cache_miss' );
                        $wgMemc->set( $key, $difftext, 7*86400 );
                } else {
                        wfIncrStats( 'diff_uncacheable' );
                }
                // Replace line numbers with the text in the user's language
                if ( $difftext !== false ) {
                        $difftext = $this->localiseLineNumbers( $difftext );
                }
                //wfProfileOut( $fname );
                return $difftext;
        }

        function generateDiffBody( $otext, $ntext ) {
                global $wgExternalDiffEngine, $wgContLang;
                $fname = 'DifferenceEngine::generateDiffBody';

                $otext = str_replace( "\r\n", "\n", $otext );
                $ntext = str_replace( "\r\n", "\n", $ntext );
                
                if ( $wgExternalDiffEngine == 'wikidiff' ) {
                        # For historical reasons, external diff engine expects
                        # input text to be HTML-escaped already
                        $otext = htmlspecialchars ( $wgContLang->segmentForDiff( $otext ) );
                        $ntext = htmlspecialchars ( $wgContLang->segmentForDiff( $ntext ) );
                        if( !function_exists( 'wikidiff_do_diff' ) ) {
                                dl('php_wikidiff.so');
                        }
                        return $wgContLang->unsegementForDiff( wikidiff_do_diff( $otext, $ntext, 2 ) );
                }
                
                if ( $wgExternalDiffEngine == 'wikidiff2' ) {
                        # Better external diff engine, the 2 may some day be dropped
                        # This one does the escaping and segmenting itself
                        if ( !function_exists( 'wikidiff2_do_diff' ) ) {
                                //wfProfileIn( "$fname-dl" );
                                @dl('php_wikidiff2.so');
                                //wfProfileOut( "$fname-dl" );
                        }
                        if ( function_exists( 'wikidiff2_do_diff' ) ) {
                                //wfProfileIn( 'wikidiff2_do_diff' );
                                $text = wikidiff2_do_diff( $otext, $ntext, 2 );
                                //wfProfileOut( 'wikidiff2_do_diff' );
                                return $text;
                        }
                }
                if ( $wgExternalDiffEngine !== false ) {
                        # Diff via the shell
                        global $wgTmpDirectory;
                        $tempName1 = tempnam( $wgTmpDirectory, 'diff_' );
                        $tempName2 = tempnam( $wgTmpDirectory, 'diff_' );

                        $tempFile1 = fopen( $tempName1, "w" );
                        if ( !$tempFile1 ) {
                                //wfProfileOut( $fname );
                                return false;
                        }
                        $tempFile2 = fopen( $tempName2, "w" );
                        if ( !$tempFile2 ) {
                                //wfProfileOut( $fname );
                                return false;
                        }
                        fwrite( $tempFile1, $otext );
                        fwrite( $tempFile2, $ntext );
                        fclose( $tempFile1 );
                        fclose( $tempFile2 );
                        $cmd = wfEscapeShellArg( $wgExternalDiffEngine, $tempName1, $tempName2 );
                        //wfProfileIn( "$fname-shellexec" );
                        $difftext = wfShellExec( $cmd );
                        //wfProfileOut( "$fname-shellexec" );
                        unlink( $tempName1 );
                        unlink( $tempName2 );
                        return $difftext;
                }
                
                # Native PHP diff
                $ota = explode( "\n", $wgContLang->segmentForDiff( $otext ) );
                $nta = explode( "\n", $wgContLang->segmentForDiff( $ntext ) );
                $diffs = new Diff( $ota, $nta );
                $formatter = new TableDiffFormatter();
                return $wgContLang->unsegmentForDiff( $formatter->format( $diffs ) );
        }
                

        function localiseLineNumbers( $text ) {
                return preg_replace_callback( '/<!--LINE (\d+)-->/',
                        array( &$this, 'localiseLineNumbersCb' ), $text );
        }

        function localiseLineNumbersCb( $matches ) {
                global $wgLang;
                return wfMsgExt( 'lineno', array('parseinline'), $wgLang->formatNum( $matches[1] ) );
        }

        
        function getMultiNotice() {
                if ( !is_object($this->mOldRev) || !is_object($this->mNewRev) )
                        return '';
                
                if( !$this->mOldPage->equals( $this->mNewPage ) ) {
                        // Comparing two different pages? Count would be meaningless.
                        return '';
                }
                
                $oldid = $this->mOldRev->getId();
                $newid = $this->mNewRev->getId();
                if ( $oldid > $newid ) {
                        $tmp = $oldid; $oldid = $newid; $newid = $tmp;
                }

                $n = $this->mTitle->countRevisionsBetween( $oldid, $newid );
                if ( !$n )
                        return '';

                return wfMsgExt( 'diff-multi', array( 'parseinline' ), $n );
        }


        function addHeader( $diff, $otitle, $ntitle, $multi = '' ) {
                global $wgOut;
        
                if ( $this->mOldRev && $this->mOldRev->isDeleted(Revision::DELETED_TEXT) ) {
                   $otitle = '<span class="history-deleted">'.$otitle.'</span>';
                }
                if ( $this->mNewRev && $this->mNewRev->isDeleted(Revision::DELETED_TEXT) ) {
                   $ntitle = '<span class="history-deleted">'.$ntitle.'</span>';
                }
                $header = "
                        <table border='0' width='98%' cellpadding='0' cellspacing='4' class='diff'>
                        <tr>
                                <td colspan='2' width='50%' align='center' class='diff-otitle'>{$otitle}</td>
                                <td colspan='2' width='50%' align='center' class='diff-ntitle'>{$ntitle}</td>
                        </tr>
                ";

                if ( $multi != '' )
                        $header .= "<tr><td colspan='4' align='center' class='diff-multi'>{$multi}</td></tr>";

                return $header . $diff . "</table>";
        }

        function setText( $oldText, $newText ) {
                $this->mOldtext = $oldText;
                $this->mNewtext = $newText;
                $this->mTextLoaded = 2;
        }

        function loadRevisionData() {
                global $wgLang;
                if ( $this->mRevisionsLoaded ) {
                        return true;
                } else {
                        // Whether it succeeds or fails, we don't want to try again
                        $this->mRevisionsLoaded = true;
                }

                // Load the new revision object
                if( $this->mNewid ) {
                        $this->mNewRev = Revision::newFromId( $this->mNewid );
                } else {
                        $this->mNewRev = Revision::newFromTitle( $this->mTitle );
                }

                if( is_null( $this->mNewRev ) ) {
                        return false;
                }

                // Set assorted variables
                $timestamp = $wgLang->timeanddate( $this->mNewRev->getTimestamp(), true );
                $this->mNewPage = $this->mNewRev->getTitle();
                if( $this->mNewRev->isCurrent() ) {
                        $newLink = $this->mNewPage->escapeLocalUrl();
                        $this->mPagetitle = htmlspecialchars( wfMsg( 'currentrev' ) );
                        $newEdit = $this->mNewPage->escapeLocalUrl( 'action=edit' );

                        $this->mNewtitle = "<a href='$newLink'>{$this->mPagetitle}</a> ($timestamp)"
                                . " (<a href='$newEdit'>" . htmlspecialchars( wfMsg( 'editold' ) ) . "</a>)";

                } else {
                        $newLink = $this->mNewPage->escapeLocalUrl( 'oldid=' . $this->mNewid );
                        $newEdit = $this->mNewPage->escapeLocalUrl( 'action=edit&oldid=' . $this->mNewid );
                        $this->mPagetitle = htmlspecialchars( wfMsg( 'revisionasof', $timestamp ) );

                        $this->mNewtitle = "<a href='$newLink'>{$this->mPagetitle}</a>"
                                . " (<a href='$newEdit'>" . htmlspecialchars( wfMsg( 'editold' ) ) . "</a>)";
                }

                // Load the old revision object
                $this->mOldRev = false;
                if( $this->mOldid ) {
                        $this->mOldRev = Revision::newFromId( $this->mOldid );
                } elseif ( $this->mOldid === 0 ) {
                        $rev = $this->mNewRev->getPrevious();
                        if( $rev ) {
                                $this->mOldid = $rev->getId();
                                $this->mOldRev = $rev;
                        } else {
                                // No previous revision; mark to show as first-version only.
                                $this->mOldid = false;
                                $this->mOldRev = false;
                        }
                }/* elseif ( $this->mOldid === false ) leave mOldRev false; */

                if( is_null( $this->mOldRev ) ) {
                        return false;
                }

                if ( $this->mOldRev ) {
                        $this->mOldPage = $this->mOldRev->getTitle();

                        $t = $wgLang->timeanddate( $this->mOldRev->getTimestamp(), true );
                        $oldLink = $this->mOldPage->escapeLocalUrl( 'oldid=' . $this->mOldid );
                        $oldEdit = $this->mOldPage->escapeLocalUrl( 'action=edit&oldid=' . $this->mOldid );
                        $this->mOldtitle = "<a href='$oldLink'>" . htmlspecialchars( wfMsg( 'revisionasof', $t ) )
                                . "</a> (<a href='$oldEdit'>" . htmlspecialchars( wfMsg( 'editold' ) ) . "</a>)";
                        //now that we considered old rev, we can make undo link (bug 8133, multi-edit undo)
                        $newUndo = $this->mNewPage->escapeLocalUrl( 'action=edit&undoafter=' . $this->mOldid . '&undo=' . $this->mNewid);
                        $this->mNewtitle .= " (<a href='$newUndo'>" . htmlspecialchars( wfMsg( 'editundo' ) ) . "</a>)";
                }

                return true;
        }

        function loadText() {
                if ( $this->mTextLoaded == 2 ) {
                        return true;
                } else {
                        // Whether it succeeds or fails, we don't want to try again
                        $this->mTextLoaded = 2;
                }

                if ( !$this->loadRevisionData() ) {
                        return false;
                }
                if ( $this->mOldRev ) {
                        // FIXME: permission tests
                        $this->mOldtext = $this->mOldRev->revText();
                        if ( $this->mOldtext === false ) {
                                return false;
                        }
                }
                if ( $this->mNewRev ) {
                        $this->mNewtext = $this->mNewRev->revText();
                        if ( $this->mNewtext === false ) {
                                return false;
                        }
                }
                return true;
        }

        function loadNewText() {
                if ( $this->mTextLoaded >= 1 ) {
                        return true;
                } else {
                        $this->mTextLoaded = 1;
                }
                if ( !$this->loadRevisionData() ) {
                        return false;
                }
                $this->mNewtext = $this->mNewRev->getText();
                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
{
        const MAX_XREF_LENGTH =  10000;

        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;
        }

        function _line_hash( $line ) {
                if ( strlen( $line ) > self::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 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) {
                $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 );
        }
}

class MappedDiff extends Diff
{
        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 );
        }
}

class DiffFormatter
{
        var $leading_context_lines = 0;

        var $trailing_context_lines = 0;

        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);
        }
}


define('NBSP', '&#160;');                       // 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 == 'ins')
                                $this->_line .= '[ilDiffInsStart]' .
                                        htmlspecialchars ( $this->_group ) . '[ilDiffInsEnd]';
                        elseif ($this->_tag == 'del')
                                $this->_line .= '[ilDiffDelStart]' .
                                        htmlspecialchars ( $this->_group ) . '[ilDiffDelEnd]';
                        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;
        }
}

class WordLevelDiff extends MappedDiff
{
        const MAX_LINE_LENGTH = 10000;

        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 ) > self::MAX_LINE_LENGTH ) {
                                $words[] = $line;
                                $stripped[] = $line;
                        } else {
                                $m = array();
                                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, 'del');
                }
                $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, 'ins');
                }
                $lines = $closing->getLines();
                //wfProfileOut( $fname );
                return $lines;
        }
}

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 );
        }
}

?>