In mctest.php, use the configured timeout instead of the default
[lhc/web/wiklou.git] / includes / diff / DifferenceEngine.php
index c534ba0..e8f35f0 100644 (file)
 <?php
 /**
- * A PHP diff engine for phpwiki. (Taken from phpwiki-1.3.3)
- *
- * Copyright © 2000, 2001 Geoffrey T. Dairiki <dairiki@dairiki.org>
- * You may copy this code freely under the conditions of the GPL.
+ * User interface for the difference engine
  *
  * @file
  * @ingroup DifferenceEngine
- * @defgroup DifferenceEngine DifferenceEngine
  */
 
 /**
- * @todo document
- * @private
- * @ingroup DifferenceEngine
+ * Constant to indicate diff cache compatibility.
+ * Bump this when changing the diff formatting in a way that
+ * fixes important bugs or such to force cached diff views to
+ * clear.
  */
-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;
-       }
-}
+define( 'MW_DIFF_VERSION', '1.11a' );
 
 /**
  * @todo document
- * @private
  * @ingroup DifferenceEngine
  */
-class _DiffOp_Copy extends _DiffOp {
-       var $type = 'copy';
-
-       function __construct ($orig, $closing = false) {
-               if (!is_array($closing))
-               $closing = $orig;
-               $this->orig = $orig;
-               $this->closing = $closing;
-       }
+class DifferenceEngine extends ContextSource {
+       /**#@+
+        * @private
+        */
+       var $mOldid, $mNewid;
+       var $mOldtext, $mNewtext;
+       protected $mDiffLang;
 
-       function reverse() {
-               return new _DiffOp_Copy($this->closing, $this->orig);
-       }
-}
+       /**
+        * @var Title
+        */
+       var $mOldPage, $mNewPage;
+       var $mRcidMarkPatrolled;
 
-/**
- * @todo document
- * @private
- * @ingroup DifferenceEngine
- */
-class _DiffOp_Delete extends _DiffOp {
-       var $type = 'delete';
+       /**
+        * @var Revision
+        */
+       var $mOldRev, $mNewRev;
+       private $mRevisionsIdsLoaded = false; // Have the revisions IDs been loaded
+       var $mRevisionsLoaded = false; // Have the revisions been loaded
+       var $mTextLoaded = 0; // How many text blobs have been loaded, 0, 1 or 2?
+       var $mCacheHit = false; // Was the diff fetched from cache?
 
-       function __construct ($lines) {
-               $this->orig = $lines;
-               $this->closing = false;
-       }
+       /**
+        * Set this to true to add debug info to the HTML output.
+        * Warning: this may cause RSS readers to spuriously mark articles as "new"
+        * (bug 20601)
+        */
+       var $enableDebugComment = false;
 
-       function reverse() {
-               return new _DiffOp_Add($this->orig);
-       }
-}
+       // If true, line X is not displayed when X is 1, for example to increase
+       // readability and conserve space with many small diffs.
+       protected $mReducedLineNumbers = false;
 
-/**
- * @todo document
- * @private
- * @ingroup DifferenceEngine
- */
-class _DiffOp_Add extends _DiffOp {
-       var $type = 'add';
+       // Link to action=markpatrolled
+       protected $mMarkPatrolledLink = null;
 
-       function __construct ($lines) {
-               $this->closing = $lines;
-               $this->orig = false;
-       }
+       protected $unhide = false; # show rev_deleted content if allowed
+       /**#@-*/
 
-       function reverse() {
-               return new _DiffOp_Delete($this->closing);
-       }
-}
+       /**
+        * Constructor
+        * @param $context IContextSource context to use, anything else will be ignored
+        * @param $old Integer old ID we want to show and diff with.
+        * @param $new String either 'prev' or 'next'.
+        * @param $rcid Integer ??? FIXME (default 0)
+        * @param $refreshCache boolean If set, refreshes the diff cache
+        * @param $unhide boolean If set, allow viewing deleted revs
+        */
+       function __construct( $context = null, $old = 0, $new = 0, $rcid = 0,
+               $refreshCache = false, $unhide = false )
+       {
+               if ( $context instanceof IContextSource ) {
+                       $this->setContext( $context );
+               }
 
-/**
- * @todo document
- * @private
- * @ingroup DifferenceEngine
- */
-class _DiffOp_Change extends _DiffOp {
-       var $type = 'change';
+               wfDebug( "DifferenceEngine old '$old' new '$new' rcid '$rcid'\n" );
 
-       function __construct ($orig, $closing) {
-               $this->orig = $orig;
-               $this->closing = $closing;
+               $this->mOldid = $old;
+               $this->mNewid = $new;
+               $this->mRcidMarkPatrolled = intval( $rcid );  # force it to be an integer
+               $this->mRefreshCache = $refreshCache;
+               $this->unhide = $unhide;
        }
 
-       function reverse() {
-               return new _DiffOp_Change($this->closing, $this->orig);
+       /**
+        * @param $value bool
+        */
+       function setReducedLineNumbers( $value = true ) {
+               $this->mReducedLineNumbers = $value;
        }
-}
 
-/**
- * Class used internally by Diff to actually compute the diffs.
- *
- * The algorithm used here is mostly lifted from the perl module
- * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
- *      http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
- *
- * More ideas are taken from:
- *      http://www.ics.uci.edu/~eppstein/161/960229.html
- *
- * Some ideas are (and a bit of code) are from from analyze.c, from GNU
- * diffutils-2.7, which can be found at:
- *      ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
- *
- * closingly, some ideas (subdivision by NCHUNKS > 2, and some optimizations)
- * are my own.
- *
- * Line length limits for robustness added by Tim Starling, 2005-08-31
- * Alternative implementation added by Guy Van den Broeck, 2008-07-30
- *
- * @author Geoffrey T. Dairiki, Tim Starling, Guy Van den Broeck
- * @private
- * @ingroup DifferenceEngine
- */
-class _DiffEngine {
-
-       const MAX_XREF_LENGTH =  10000;
-
-       function diff ($from_lines, $to_lines){
-               wfProfileIn( __METHOD__ );
-
-               // Diff and store locally
-               $this->diff_local($from_lines, $to_lines);
-
-               // 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.
-               $n_from = sizeof($from_lines);
-               $n_to = sizeof($to_lines);
-
-               $edits = array();
-               $xi = $yi = 0;
-               while ($xi < $n_from || $yi < $n_to) {
-                       assert($yi < $n_to || $this->xchanged[$xi]);
-                       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 Language
+        */
+       function getDiffLang() {
+               if ( $this->mDiffLang === null ) {
+                       # Default language in which the diff text is written.
+                       $this->mDiffLang = $this->getTitle()->getPageLanguage();
                }
-               wfProfileOut( __METHOD__ );
-               return $edits;
+               return $this->mDiffLang;
        }
 
-       function diff_local ($from_lines, $to_lines) {
-               global $wgExternalDiffEngine;
-               wfProfileIn( __METHOD__);
-
-               if($wgExternalDiffEngine == 'wikidiff3'){
-                       // wikidiff3
-                       $wikidiff3 = new WikiDiff3();
-                       $wikidiff3->diff($from_lines, $to_lines);
-                       $this->xchanged = $wikidiff3->removed;
-                       $this->ychanged = $wikidiff3->added;
-                       unset($wikidiff3);
-               }else{
-                       // old diff
-                       $n_from = sizeof($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;
-                       }
+       /**
+        * @return bool
+        */
+       function wasCacheHit() {
+               return $this->mCacheHit;
+       }
 
-                       // 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;
-                       }
+       /**
+        * @return int
+        */
+       function getOldid() {
+               $this->loadRevisionIds();
+               return $this->mOldid;
+       }
 
-                       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;
-                       }
+       /**
+        * @return Bool|int
+        */
+       function getNewid() {
+               $this->loadRevisionIds();
+               return $this->mNewid;
+       }
 
-                       // Find the LCS.
-                       $this->_compareseq(0, sizeof($this->xv), 0, sizeof($this->yv));
+       /**
+        * Look up a special:Undelete link to the given deleted revision id,
+        * as a workaround for being unable to load deleted diffs in currently.
+        *
+        * @param int $id revision ID
+        * @return mixed URL or false
+        */
+       function deletedLink( $id ) {
+               if ( $this->getUser()->isAllowed( 'deletedhistory' ) ) {
+                       $dbr = wfGetDB( DB_SLAVE );
+                       $row = $dbr->selectRow('archive', '*',
+                               array( 'ar_rev_id' => $id ),
+                               __METHOD__ );
+                       if ( $row ) {
+                               $rev = Revision::newFromArchiveRow( $row );
+                               $title = Title::makeTitleSafe( $row->ar_namespace, $row->ar_title );
+                               return SpecialPage::getTitleFor( 'Undelete' )->getFullURL( array(
+                                       'target' => $title->getPrefixedText(),
+                                       'timestamp' => $rev->getTimestamp()
+                               ));
+                       }
                }
-               wfProfileOut( __METHOD__ );
+               return false;
        }
 
        /**
-        * Returns the whole line if it's small enough, or the MD5 hash otherwise
+        * Build a wikitext link toward a deleted revision, if viewable.
+        *
+        * @param int $id revision ID
+        * @return string wikitext fragment
         */
-       function _line_hash( $line ) {
-               if ( strlen( $line ) > self::MAX_XREF_LENGTH ) {
-                       return md5( $line );
+       function deletedIdMarker( $id ) {
+               $link = $this->deletedLink( $id );
+               if ( $link ) {
+                       return "[$link $id]";
                } else {
-                       return $line;
+                       return $id;
                }
        }
 
-       /* 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);
+       function showDiffPage( $diffOnly = false ) {
+               wfProfileIn( __METHOD__ );
+
+               # Allow frames except in certain special cases
+               $out = $this->getOutput();
+               $out->allowClickjacking();
+               $out->setRobotPolicy( 'noindex,nofollow' );
+
+               if ( !$this->loadRevisionData() ) {
+                       // Sounds like a deleted revision... Let's see what we can do.
+                       $t = $this->getTitle()->getPrefixedText();
+                       $d = $this->msg( 'missingarticle-diff',
+                               $this->deletedIdMarker( $this->mOldid ),
+                               $this->deletedIdMarker( $this->mNewid ) )->escaped();
+                       $out->setPageTitle( $this->msg( 'errorpagetitle' ) );
+                       $out->addWikiMsg( 'missing-article', "<nowiki>$t</nowiki>", "<span class='plainlinks'>$d</span>" );
+                       wfProfileOut( __METHOD__ );
+                       return;
                }
 
-               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 );
-                                               assert( $k > 0 );
-                                               $ymids[$k] = $ymids[$k-1];
-                                               break;
-                                       }
-                               }
-                               while (list ( /* $junk */, $y) = each($matches)) {
-                                       if ($y > $this->seq[$k-1]) {
-                                               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);
-                                               assert($k > 0);
-                                               $ymids[$k] = $ymids[$k-1];
-                                       }
-                               }
-                       }
+               $user = $this->getUser();
+               $permErrors = $this->mNewPage->getUserPermissionsErrors( 'read', $user );
+               if ( $this->mOldPage ) { # mOldPage might not be set, see below.
+                       $permErrors = wfMergeErrorArrays( $permErrors,
+                               $this->mOldPage->getUserPermissionsErrors( 'read', $user ) );
+               }
+               if ( count( $permErrors ) ) {
+                       wfProfileOut( __METHOD__ );
+                       throw new PermissionsError( 'read', $permErrors );
                }
 
-               $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);
+               # 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 ( ExternalEdit::useExternalEngine( $this->getContext(), 'diff' ) ) {
+                       $urls = array(
+                               'File' => array( 'Extension' => 'wiki', 'URL' =>
+                                       # This should be mOldPage, but it may not be set, see below.
+                                       $this->mNewPage->getCanonicalURL( array(
+                                               'action' => 'raw', 'oldid' => $this->mOldid ) )
+                               ),
+                               'File2' => array( 'Extension' => 'wiki', 'URL' =>
+                                       $this->mNewPage->getCanonicalURL( array(
+                                               'action' => 'raw', 'oldid' => $this->mNewid ) )
+                               ),
+                       );
+
+                       $externalEditor = new ExternalEdit( $this->getContext(), $urls );
+                       $externalEditor->execute();
+
+                       wfProfileOut( __METHOD__ );
+                       return;
                }
-               $seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim);
 
-               return array($this->lcs, $seps);
-       }
+               $rollback = '';
+               $undoLink = '';
 
-       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;
+               $query = array();
+               # Carry over 'diffonly' param via navigation links
+               if ( $diffOnly != $user->getBoolOption( 'diffonly' ) ) {
+                       $query['diffonly'] = $diffOnly;
                }
-
-               $beg = 1;
-               while ($beg < $end) {
-                       $mid = (int)(($beg + $end) / 2);
-                       if ( $ypos > $this->seq[$mid] )
-                       $beg = $mid + 1;
-                       else
-                       $end = $mid;
+               # Cascade unhide param in links for easy deletion browsing
+               if ( $this->unhide ) {
+                       $query['unhide'] = 1;
                }
 
-               assert($ypos != $this->seq[$end]);
+               # Check if one of the revisions is deleted/suppressed
+               $deleted = $suppressed = false;
+               $allowed = $this->mNewRev->userCan( Revision::DELETED_TEXT, $user );
+
+               # mOldRev 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->mOldRev === false ) {
+                       $out->setPageTitle( $this->mNewPage->getPrefixedText() );
+                       $out->addSubtitle( $this->msg( 'difference' ) );
+                       $samePage = true;
+                       $oldHeader = '';
+               } else {
+                       wfRunHooks( 'DiffViewHeader', array( $this, $this->mOldRev, $this->mNewRev ) );
 
-               $this->in_seq[$this->seq[$end]] = false;
-               $this->seq[$end] = $ypos;
-               $this->in_seq[$ypos] = 1;
-               return $end;
-       }
+                       $sk = $this->getSkin();
+                       if ( method_exists( $sk, 'suppressQuickbar' ) ) {
+                               $sk->suppressQuickbar();
+                       }
 
-       /* 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;
+                       if ( $this->mNewPage->equals( $this->mOldPage ) ) {
+                               $out->setPageTitle( $this->mNewPage->getPrefixedText() );
+                               $out->addSubtitle( $this->msg( 'difference' ) );
+                               $samePage = true;
+                       } else {
+                               $out->setPageTitle( $this->mOldPage->getPrefixedText() . ', ' . $this->mNewPage->getPrefixedText() );
+                               $out->addSubtitle( $this->msg( 'difference-multipage' ) );
+                               $samePage = false;
+                       }
+
+                       if ( $samePage && $this->mNewPage->quickUserCan( 'edit', $user ) ) {
+                               if ( $this->mNewRev->isCurrent() && $this->mNewPage->userCan( 'rollback', $user ) ) {
+                                       $out->preventClickjacking();
+                                       $rollback = '&#160;&#160;&#160;' . Linker::generateRollback( $this->mNewRev );
+                               }
+                               if ( !$this->mOldRev->isDeleted( Revision::DELETED_TEXT ) && !$this->mNewRev->isDeleted( Revision::DELETED_TEXT ) ) {
+                                       $undoLink = ' ' . $this->msg( 'parentheses' )->rawParams(
+                                               Html::element( 'a', array(
+                                                       'href' => $this->mNewPage->getLocalUrl( array(
+                                                               'action' => 'edit',
+                                                               'undoafter' => $this->mOldid,
+                                                               'undo' => $this->mNewid ) ),
+                                                       'title' => Linker::titleAttrib( 'undo' )
+                                               ),
+                                               $this->msg( 'editundo' )->text()
+                                       ) )->escaped();
+                               }
+                       }
+
+                       # Make "previous revision link"
+                       if ( $samePage && $this->mOldRev->getPrevious() ) {
+                               $prevlink = Linker::linkKnown(
+                                       $this->mOldPage,
+                                       $this->msg( 'previousdiff' )->escaped(),
+                                       array( 'id' => 'differences-prevlink' ),
+                                       array( 'diff' => 'prev', 'oldid' => $this->mOldid ) + $query
+                               );
+                       } else {
+                               $prevlink = '&#160;';
+                       }
+
+                       if ( $this->mOldRev->isMinor() ) {
+                               $oldminor = ChangesList::flag( 'minor' );
+                       } else {
+                               $oldminor = '';
+                       }
+
+                       $ldel = $this->revisionDeleteLink( $this->mOldRev );
+                       $oldRevisionHeader = $this->getRevisionHeader( $this->mOldRev, 'complete' );
+
+                       $oldHeader = '<div id="mw-diff-otitle1"><strong>' . $oldRevisionHeader . '</strong></div>' .
+                               '<div id="mw-diff-otitle2">' .
+                                       Linker::revUserTools( $this->mOldRev, !$this->unhide ) . '</div>' .
+                               '<div id="mw-diff-otitle3">' . $oldminor .
+                                       Linker::revComment( $this->mOldRev, !$diffOnly, !$this->unhide ) . $ldel . '</div>' .
+                               '<div id="mw-diff-otitle4">' . $prevlink . '</div>';
+
+                       if ( $this->mOldRev->isDeleted( Revision::DELETED_TEXT ) ) {
+                               $deleted = true; // old revisions text is hidden
+                               if ( $this->mOldRev->isDeleted( Revision::DELETED_RESTRICTED ) ) {
+                                       $suppressed = true; // also suppressed
+                               }
+                       }
+
+                       # Check if this user can see the revisions
+                       if ( !$this->mOldRev->userCan( Revision::DELETED_TEXT, $user ) ) {
+                               $allowed = false;
+                       }
                }
 
-               // Slide up the top initial diagonal.
-               while ($xlim > $xoff && $ylim > $yoff
-               && $this->xv[$xlim - 1] == $this->yv[$ylim - 1]) {
-                       --$xlim;
-                       --$ylim;
+               # Make "next revision link"
+               # Skip next link on the top revision
+               if ( $samePage && !$this->mNewRev->isCurrent() ) {
+                       $nextlink = Linker::linkKnown(
+                               $this->mNewPage,
+                               $this->msg( 'nextdiff' )->escaped(),
+                               array( 'id' => 'differences-nextlink' ),
+                               array( 'diff' => 'next', 'oldid' => $this->mNewid ) + $query
+                       );
+               } else {
+                       $nextlink = '&#160;';
                }
 
-               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 ( $this->mNewRev->isMinor() ) {
+                       $newminor = ChangesList::flag( 'minor' );
+               } else {
+                       $newminor = '';
+               }
+
+               # Handle RevisionDelete links...
+               $rdel = $this->revisionDeleteLink( $this->mNewRev );
+               $newRevisionHeader = $this->getRevisionHeader( $this->mNewRev, 'complete' ) . $undoLink;
+
+               $newHeader = '<div id="mw-diff-ntitle1"><strong>' . $newRevisionHeader . '</strong></div>' .
+                       '<div id="mw-diff-ntitle2">' . Linker::revUserTools( $this->mNewRev, !$this->unhide ) .
+                               " $rollback</div>" .
+                       '<div id="mw-diff-ntitle3">' . $newminor .
+                               Linker::revComment( $this->mNewRev, !$diffOnly, !$this->unhide ) . $rdel . '</div>' .
+                       '<div id="mw-diff-ntitle4">' . $nextlink . $this->markPatrolledLink() . '</div>';
+
+               if ( $this->mNewRev->isDeleted( Revision::DELETED_TEXT ) ) {
+                       $deleted = true; // new revisions text is hidden
+                       if ( $this->mNewRev->isDeleted( Revision::DELETED_RESTRICTED ) )
+                               $suppressed = true; // also suppressed
                }
 
-               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;
+               # If the diff cannot be shown due to a deleted revision, then output
+               # the diff header and links to unhide (if available)...
+               if ( $deleted && ( !$this->unhide || !$allowed ) ) {
+                       $this->showDiffStyle();
+                       $multi = $this->getMultiNotice();
+                       $out->addHTML( $this->addHeader( '', $oldHeader, $newHeader, $multi ) );
+                       if ( !$allowed ) {
+                               $msg = $suppressed ? 'rev-suppressed-no-diff' : 'rev-deleted-no-diff';
+                               # Give explanation for why revision is not visible
+                               $out->wrapWikiMsg( "<div id='mw-$msg' class='mw-warning plainlinks'>\n$1\n</div>\n",
+                                       array( $msg ) );
+                       } else {
+                               # Give explanation and add a link to view the diff...
+                               $link = $this->getTitle()->getFullUrl( $this->getRequest()->appendQueryValue( 'unhide', '1', true ) );
+                               $msg = $suppressed ? 'rev-suppressed-unhide-diff' : 'rev-deleted-unhide-diff';
+                               $out->wrapWikiMsg( "<div id='mw-$msg' class='mw-warning plainlinks'>\n$1\n</div>\n", array( $msg, $link ) );
+                       }
+               # Otherwise, output a regular diff...
                } else {
-                       // Use the partitions to split this problem into subproblems.
-                       reset($seps);
-                       $pt1 = $seps[0];
-                       while ($pt2 = next($seps)) {
-                               $this->_compareseq ($pt1[0], $pt2[0], $pt1[1], $pt2[1]);
-                               $pt1 = $pt2;
+                       # Add deletion notice if the user is viewing deleted content
+                       $notice = '';
+                       if ( $deleted ) {
+                               $msg = $suppressed ? 'rev-suppressed-diff-view' : 'rev-deleted-diff-view';
+                               $notice = "<div id='mw-$msg' class='mw-warning plainlinks'>\n" . $this->msg( $msg )->parse() . "</div>\n";
+                       }
+                       $this->showDiff( $oldHeader, $newHeader, $notice );
+                       if ( !$diffOnly ) {
+                               $this->renderNewRevision();
                        }
                }
+               wfProfileOut( __METHOD__ );
        }
 
-       /* 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".
+       /**
+        * Get a link to mark the change as patrolled, or '' if there's either no
+        * revision to patrol or the user is not allowed to to it.
+        * Side effect: this method will call OutputPage::preventClickjacking()
+        * when a link is builded.
         *
-        * This is extracted verbatim from analyze.c (GNU diffutils-2.7).
+        * @return String
         */
-       function _shift_boundaries ($lines, &$changed, $other_changed) {
-               wfProfileIn( __METHOD__ );
-               $i = 0;
-               $j = 0;
-
-               assert('sizeof($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]) {
-                               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])
-                                       $start--;
-                                       assert('$j > 0');
-                                       while ($other_changed[--$j])
-                                       continue;
-                                       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])
-                                       $i++;
-
-                                       assert('$j < $other_len && ! $other_changed[$j]');
-                                       $j++;
-                                       if ($j < $other_len && $other_changed[$j]) {
-                                               $corresponding = $i;
-                                               while ($j < $other_len && $other_changed[$j])
-                                               $j++;
+       protected function markPatrolledLink() {
+               global $wgUseRCPatrol;
+
+               if ( $this->mMarkPatrolledLink === null ) {
+                       // Prepare a change patrol link, if applicable
+                       if ( $wgUseRCPatrol && $this->mNewPage->quickUserCan( 'patrol', $this->getUser() ) ) {
+                               // If we've been given an explicit change identifier, use it; saves time
+                               if ( $this->mRcidMarkPatrolled ) {
+                                       $rcid = $this->mRcidMarkPatrolled;
+                                       $rc = RecentChange::newFromId( $rcid );
+                                       // Already patrolled?
+                                       $rcid = is_object( $rc ) && !$rc->getAttribute( 'rc_patrolled' ) ? $rcid : 0;
+                               } else {
+                                       // Look for an unpatrolled change corresponding to this diff
+                                       $db = wfGetDB( DB_SLAVE );
+                                       $change = RecentChange::newFromConds(
+                                               array(
+                                               // Redundant user,timestamp condition so we can use the existing index
+                                                       'rc_user_text'  => $this->mNewRev->getRawUserText(),
+                                                       'rc_timestamp'  => $db->timestamp( $this->mNewRev->getTimestamp() ),
+                                                       'rc_this_oldid' => $this->mNewid,
+                                                       'rc_last_oldid' => $this->mOldid,
+                                                       'rc_patrolled'  => 0
+                                               ),
+                                               __METHOD__
+                                       );
+                                       if ( $change instanceof RecentChange ) {
+                                               $rcid = $change->mAttribs['rc_id'];
+                                               $this->mRcidMarkPatrolled = $rcid;
+                                       } else {
+                                               // None found
+                                               $rcid = 0;
                                        }
                                }
-                       } while ($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;
-                               assert('$j > 0');
-                               while ($other_changed[--$j])
-                               continue;
-                               assert('$j >= 0 && !$other_changed[$j]');
+                               // Build the link
+                               if ( $rcid ) {
+                                       $this->getOutput()->preventClickjacking();
+                                       $token = $this->getUser()->getEditToken( $rcid );
+                                       $this->mMarkPatrolledLink = ' <span class="patrollink">[' . Linker::linkKnown(
+                                               $this->mNewPage,
+                                               $this->msg( 'markaspatrolleddiff' )->escaped(),
+                                               array(),
+                                               array(
+                                                       'action' => 'markpatrolled',
+                                                       'rcid' => $rcid,
+                                                       'token' => $token,
+                                               )
+                                       ) . ']</span>';
+                               } else {
+                                       $this->mMarkPatrolledLink = '';
+                               }
+                       } else {
+                               $this->mMarkPatrolledLink = '';
                        }
                }
-               wfProfileOut( __METHOD__ );
-       }
-}
 
-/**
- * Class representing a 'diff' between two sequences of strings.
- * @todo document
- * @private
- * @ingroup DifferenceEngine
- */
-class Diff
-{
-       var $edits;
-
-       /**
-        * Constructor.
-        * Computes diff between sequences of strings.
-        *
-        * @param $from_lines array An array of strings.
-        *                (Typically these are lines from a file.)
-        * @param $to_lines array An array of strings.
-        */
-       function __construct($from_lines, $to_lines) {
-               $eng = new _DiffEngine;
-               $this->edits = $eng->diff($from_lines, $to_lines);
-               //$this->_check($from_lines, $to_lines);
+               return $this->mMarkPatrolledLink;
        }
 
        /**
-        * Compute reversed Diff.
-        *
-        * SYNOPSIS:
-        *
-        *      $diff = new Diff($lines1, $lines2);
-        *      $rev = $diff->reverse();
-        * @return object A Diff object representing the inverse of the
-        *                                original diff.
+        * @param $rev Revision
+        * @return String
         */
-       function reverse () {
-               $rev = $this;
-               $rev->edits = array();
-               foreach ($this->edits as $edit) {
-                       $rev->edits[] = $edit->reverse();
+       protected function revisionDeleteLink( $rev ) {
+               $link = Linker::getRevDeleteLink( $this->getUser(), $rev, $rev->getTitle() );
+               if ( $link !== '' ) {
+                       $link = '&#160;&#160;&#160;' . $link . ' ';
                }
-               return $rev;
+               return $link;
        }
 
        /**
-        * Check for empty diff.
-        *
-        * @return bool True iff two sequences were identical.
+        * Show the new revision of the page.
         */
-       function isEmpty () {
-               foreach ($this->edits as $edit) {
-                       if ($edit->type != 'copy')
-                       return false;
-               }
-               return true;
-       }
+       function renderNewRevision() {
+               wfProfileIn( __METHOD__ );
+               $out = $this->getOutput();
+               $revHeader = $this->getRevisionHeader( $this->mNewRev );
+               # Add "current version as of X" title
+               $out->addHTML( "<hr class='diff-hr' />
+               <h2 class='diff-currentversion-title'>{$revHeader}</h2>\n" );
+               # Page content may be handled by a hooked call instead...
+               if ( wfRunHooks( 'ArticleContentOnDiff', array( $this, $out ) ) ) {
+                       $this->loadNewText();
+                       $out->setRevisionId( $this->mNewid );
+                       $out->setRevisionTimestamp( $this->mNewRev->getTimestamp() );
+                       $out->setArticleFlag( true );
+
+                       if ( $this->mNewPage->isCssJsSubpage() || $this->mNewPage->isCssOrJsPage() ) {
+                               // Stolen from Article::view --AG 2007-10-11
+                               // Give hooks a chance to customise the output
+                               // @TODO: standardize this crap into one function
+                               if ( wfRunHooks( 'ShowRawCssJs', array( $this->mNewtext, $this->mNewPage, $out ) ) ) {
+                                       // Wrap the whole lot in a <pre> and don't parse
+                                       $m = array();
+                                       preg_match( '!\.(css|js)$!u', $this->mNewPage->getText(), $m );
+                                       $out->addHTML( "<pre class=\"mw-code mw-{$m[1]}\" dir=\"ltr\">\n" );
+                                       $out->addHTML( htmlspecialchars( $this->mNewtext ) );
+                                       $out->addHTML( "\n</pre>\n" );
+                               }
+                       } elseif ( !wfRunHooks( 'ArticleViewCustom', array( $this->mNewtext, $this->mNewPage, $out ) ) ) {
+                               // Handled by extension
+                       } else {
+                               // Normal page
+                               if ( $this->getTitle()->equals( $this->mNewPage ) ) {
+                                       // If the Title stored in the context is the same as the one
+                                       // of the new revision, we can use its associated WikiPage
+                                       // object.
+                                       $wikiPage = $this->getWikiPage();
+                               } else {
+                                       // Otherwise we need to create our own WikiPage object
+                                       $wikiPage = WikiPage::factory( $this->mNewPage );
+                               }
 
-       /**
-        * Compute the length of the Longest Common Subsequence (LCS).
-        *
-        * This is mostly for diagnostic purposed.
-        *
-        * @return int The length of the LCS.
-        */
-       function lcs () {
-               $lcs = 0;
-               foreach ($this->edits as $edit) {
-                       if ($edit->type == 'copy')
-                       $lcs += sizeof($edit->orig);
+                               $parserOptions = ParserOptions::newFromContext( $this->getContext() );
+                               $parserOptions->enableLimitReport();
+                               $parserOptions->setTidy( true );
+
+                               if ( !$this->mNewRev->isCurrent() ) {
+                                       $parserOptions->setEditSection( false );
+                               }
+
+                               $parserOutput = $wikiPage->getParserOutput( $parserOptions, $this->mNewid );
+
+                               # WikiPage::getParserOutput() should not return false, but just in case
+                               if( $parserOutput ) {
+                                       $out->addParserOutput( $parserOutput );
+                               }
+                       }
                }
-               return $lcs;
+               # Add redundant patrol link on bottom...
+               $out->addHTML( $this->markPatrolledLink() );
+
+               wfProfileOut( __METHOD__ );
        }
 
        /**
-        * Get the original set of lines.
+        * Get the diff text, send it to the OutputPage object
+        * Returns false if the diff could not be generated, otherwise returns true
         *
-        * This reconstructs the $from_lines parameter passed to the
-        * constructor.
-        *
-        * @return array The original sequence of strings.
+        * @return bool
         */
-       function orig() {
-               $lines = array();
-
-               foreach ($this->edits as $edit) {
-                       if ($edit->orig)
-                       array_splice($lines, sizeof($lines), 0, $edit->orig);
+       function showDiff( $otitle, $ntitle, $notice = '' ) {
+               $diff = $this->getDiff( $otitle, $ntitle, $notice );
+               if ( $diff === false ) {
+                       $this->getOutput()->addWikiMsg( 'missing-article', "<nowiki>(fixme, bug)</nowiki>", '' );
+                       return false;
+               } else {
+                       $this->showDiffStyle();
+                       $this->getOutput()->addHTML( $diff );
+                       return true;
                }
-               return $lines;
        }
 
        /**
-        * Get the closing set of lines.
-        *
-        * This reconstructs the $to_lines parameter passed to the
-        * constructor.
-        *
-        * @return array The sequence of strings.
+        * Add style sheets and supporting JS for diff display.
         */
-       function closing() {
-               $lines = array();
-
-               foreach ($this->edits as $edit) {
-                       if ($edit->closing)
-                       array_splice($lines, sizeof($lines), 0, $edit->closing);
-               }
-               return $lines;
+       function showDiffStyle() {
+               $this->getOutput()->addModuleStyles( 'mediawiki.action.history.diff' );
        }
 
        /**
-        * Check a Diff for validity.
+        * Get complete diff table, including header
         *
-        * This is here only for debugging purposes.
+        * @param $otitle Title: old title
+        * @param $ntitle Title: new title
+        * @param $notice String: HTML between diff header and body
+        * @return mixed
         */
-       function _check ($from_lines, $to_lines) {
-               wfProfileIn( __METHOD__ );
-               if (serialize($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;
+       function getDiff( $otitle, $ntitle, $notice = '' ) {
+               $body = $this->getDiffBody();
+               if ( $body === false ) {
+                       return false;
+               } else {
+                       $multi = $this->getMultiNotice();
+                       return $this->addHeader( $body, $otitle, $ntitle, $multi, $notice );
                }
-
-               $lcs = $this->lcs();
-               trigger_error('Diff okay: LCS = '.$lcs, E_USER_NOTICE);
-               wfProfileOut( __METHOD__ );
        }
-}
 
-/**
- * @todo document, bad name.
- * @private
- * @ingroup DifferenceEngine
- */
-class MappedDiff extends Diff
-{
        /**
-        * Constructor.
-        *
-        * Computes diff between sequences of strings.
-        *
-        * This can be used to compute things like
-        * case-insensitve diffs, or diffs which ignore
-        * changes in white-space.
-        *
-        * @param $from_lines array An array of strings.
-        *      (Typically these are lines from a file.)
-        *
-        * @param $to_lines array An array of strings.
+        * Get the diff table body, without header
         *
-        * @param $mapped_from_lines array This array should
-        *      have the same size number of elements as $from_lines.
-        *      The elements in $mapped_from_lines and
-        *      $mapped_to_lines are what is actually compared
-        *      when computing the diff.
-        *
-        * @param $mapped_to_lines array This array should
-        *      have the same number of elements as $to_lines.
+        * @return mixed (string/false)
         */
-       function __construct($from_lines, $to_lines,
-       $mapped_from_lines, $mapped_to_lines) {
+       public function getDiffBody() {
+               global $wgMemc;
                wfProfileIn( __METHOD__ );
+               $this->mCacheHit = true;
+               // Check if the diff should be hidden from this user
+               if ( !$this->loadRevisionData() ) {
+                       wfProfileOut( __METHOD__ );
+                       return false;
+               } elseif ( $this->mOldRev && !$this->mOldRev->userCan( Revision::DELETED_TEXT, $this->getUser() ) ) {
+                       wfProfileOut( __METHOD__ );
+                       return false;
+               } elseif ( $this->mNewRev && !$this->mNewRev->userCan( Revision::DELETED_TEXT, $this->getUser() ) ) {
+                       wfProfileOut( __METHOD__ );
+                       return false;
+               }
+               // Short-circuit
+               // If mOldRev is false, it means that the 
+               if ( $this->mOldRev === false || ( $this->mOldRev && $this->mNewRev
+                       && $this->mOldRev->getID() == $this->mNewRev->getID() ) )
+               {
+                       wfProfileOut( __METHOD__ );
+                       return '';
+               }
+               // Cacheable?
+               $key = false;
+               if ( $this->mOldid && $this->mNewid ) {
+                       $key = wfMemcKey( 'diff', 'version', MW_DIFF_VERSION,
+                               'oldid', $this->mOldid, 'newid', $this->mNewid );
+                       // Try cache
+                       if ( !$this->mRefreshCache ) {
+                               $difftext = $wgMemc->get( $key );
+                               if ( $difftext ) {
+                                       wfIncrStats( 'diff_cache_hit' );
+                                       $difftext = $this->localiseLineNumbers( $difftext );
+                                       $difftext .= "\n<!-- diff cache key $key -->\n";
+                                       wfProfileOut( __METHOD__ );
+                                       return $difftext;
+                               }
+                       } // don't try to load but save the result
+               }
+               $this->mCacheHit = false;
 
-               assert(sizeof($from_lines) == sizeof($mapped_from_lines));
-               assert(sizeof($to_lines) == sizeof($mapped_to_lines));
-
-               parent::__construct($mapped_from_lines, $mapped_to_lines);
+               // Loadtext is permission safe, this just clears out the diff
+               if ( !$this->loadText() ) {
+                       wfProfileOut( __METHOD__ );
+                       return false;
+               }
 
-               $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);
-                       }
+               $difftext = $this->generateDiffBody( $this->mOldtext, $this->mNewtext );
 
-                       $closing = &$this->edits[$i]->closing;
-                       if (is_array($closing)) {
-                               $closing = array_slice($to_lines, $yi, sizeof($closing));
-                               $yi += sizeof($closing);
-                       }
+               // Save to cache for 7 days
+               if ( !wfRunHooks( 'AbortDiffCache', array( &$this ) ) ) {
+                       wfIncrStats( 'diff_uncacheable' );
+               } elseif ( $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( __METHOD__ );
+               return $difftext;
        }
-}
 
-/**
- * A class to format Diffs
- *
- * This class formats the diff in classic diff format.
- * It is intended that this class be customized via inheritance,
- * to obtain fancier outputs.
- * @todo document
- * @private
- * @ingroup DifferenceEngine
- */
-class DiffFormatter {
        /**
-        * Number of leading context "lines" to preserve.
-        *
-        * This should be left at zero for this class, but subclasses
-        * may want to set this to other values.
+        * Make sure the proper modules are loaded before we try to
+        * make the diff
         */
-       var $leading_context_lines = 0;
+       private function initDiffEngines() {
+               global $wgExternalDiffEngine;
+               if ( $wgExternalDiffEngine == 'wikidiff' && !function_exists( 'wikidiff_do_diff' ) ) {
+                       wfProfileIn( __METHOD__ . '-php_wikidiff.so' );
+                       wfDl( 'php_wikidiff' );
+                       wfProfileOut( __METHOD__ . '-php_wikidiff.so' );
+               }
+               elseif ( $wgExternalDiffEngine == 'wikidiff2' && !function_exists( 'wikidiff2_do_diff' ) ) {
+                       wfProfileIn( __METHOD__ . '-php_wikidiff2.so' );
+                       wfDl( 'wikidiff2' );
+                       wfProfileOut( __METHOD__ . '-php_wikidiff2.so' );
+               }
+       }
 
        /**
-        * Number of trailing context "lines" to preserve.
+        * Generate a diff, no caching
         *
-        * This should be left at zero for this class, but subclasses
-        * may want to set this to other values.
+        * @param $otext String: old text, must be already segmented
+        * @param $ntext String: new text, must be already segmented
+        * @return bool|string
         */
-       var $trailing_context_lines = 0;
+       function generateDiffBody( $otext, $ntext ) {
+               global $wgExternalDiffEngine, $wgContLang;
 
-       /**
-        * Format a diff.
-        *
-        * @param $diff object A Diff object.
-        * @return string The formatted output.
-        */
-       function format($diff) {
                wfProfileIn( __METHOD__ );
 
-               $xi = $yi = 1;
-               $block = false;
-               $context = array();
+               $otext = str_replace( "\r\n", "\n", $otext );
+               $ntext = str_replace( "\r\n", "\n", $ntext );
 
-               $nlead = $this->leading_context_lines;
-               $ntrail = $this->trailing_context_lines;
+               $this->initDiffEngines();
 
-               $this->_start_diff();
+               if ( $wgExternalDiffEngine == 'wikidiff' && function_exists( 'wikidiff_do_diff' ) ) {
+                       # For historical reasons, external diff engine expects
+                       # input text to be HTML-escaped already
+                       $otext = htmlspecialchars ( $wgContLang->segmentForDiff( $otext ) );
+                       $ntext = htmlspecialchars ( $wgContLang->segmentForDiff( $ntext ) );
+                       wfProfileOut( __METHOD__ );
+                       return $wgContLang->unsegmentForDiff( wikidiff_do_diff( $otext, $ntext, 2 ) ) .
+                       $this->debug( 'wikidiff1' );
+               }
 
-               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;
+               if ( $wgExternalDiffEngine == 'wikidiff2' && function_exists( 'wikidiff2_do_diff' ) ) {
+                       # Better external diff engine, the 2 may some day be dropped
+                       # This one does the escaping and segmenting itself
+                       wfProfileIn( 'wikidiff2_do_diff' );
+                       $text = wikidiff2_do_diff( $otext, $ntext, 2 );
+                       $text .= $this->debug( 'wikidiff2' );
+                       wfProfileOut( 'wikidiff2_do_diff' );
+                       wfProfileOut( __METHOD__ );
+                       return $text;
+               }
+               if ( $wgExternalDiffEngine != 'wikidiff3' && $wgExternalDiffEngine !== false ) {
+                       # Diff via the shell
+                       global $wgTmpDirectory;
+                       $tempName1 = tempnam( $wgTmpDirectory, 'diff_' );
+                       $tempName2 = tempnam( $wgTmpDirectory, 'diff_' );
+
+                       $tempFile1 = fopen( $tempName1, "w" );
+                       if ( !$tempFile1 ) {
+                               wfProfileOut( __METHOD__ );
+                               return false;
                        }
-                       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;
+                       $tempFile2 = fopen( $tempName2, "w" );
+                       if ( !$tempFile2 ) {
+                               wfProfileOut( __METHOD__ );
+                               return false;
                        }
-
-                       if ($edit->orig)
-                       $xi += sizeof($edit->orig);
-                       if ($edit->closing)
-                       $yi += sizeof($edit->closing);
+                       fwrite( $tempFile1, $otext );
+                       fwrite( $tempFile2, $ntext );
+                       fclose( $tempFile1 );
+                       fclose( $tempFile2 );
+                       $cmd = wfEscapeShellArg( $wgExternalDiffEngine, $tempName1, $tempName2 );
+                       wfProfileIn( __METHOD__ . "-shellexec" );
+                       $difftext = wfShellExec( $cmd );
+                       $difftext .= $this->debug( "external $wgExternalDiffEngine" );
+                       wfProfileOut( __METHOD__ . "-shellexec" );
+                       unlink( $tempName1 );
+                       unlink( $tempName2 );
+                       wfProfileOut( __METHOD__ );
+                       return $difftext;
                }
 
-               if (is_array($block))
-               $this->_block($x0, $xi - $x0,
-               $y0, $yi - $y0,
-               $block);
-
-               $end = $this->_end_diff();
+               # Native PHP diff
+               $ota = explode( "\n", $wgContLang->segmentForDiff( $otext ) );
+               $nta = explode( "\n", $wgContLang->segmentForDiff( $ntext ) );
+               $diffs = new Diff( $ota, $nta );
+               $formatter = new TableDiffFormatter();
+               $difftext = $wgContLang->unsegmentForDiff( $formatter->format( $diffs ) ) .
                wfProfileOut( __METHOD__ );
-               return $end;
+               return $difftext;
        }
 
-       function _block($xbeg, $xlen, $ybeg, $ylen, &$edits) {
-               wfProfileIn( __METHOD__ );
-               $this->_start_block($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);
+       /**
+        * Generate a debug comment indicating diff generating time,
+        * server node, and generator backend.
+        * @return string
+        */
+       protected function debug( $generator = "internal" ) {
+               global $wgShowHostnames;
+               if ( !$this->enableDebugComment ) {
+                       return '';
                }
-               $this->_end_block();
-               wfProfileOut( __METHOD__ );
-       }
-
-       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 $header . "\n";
-       }
-
-       function _end_block() {
-       }
-
-       function _lines($lines, $prefix = ' ') {
-               foreach ($lines as $line)
-               echo "$prefix $line\n";
-       }
-
-       function _context($lines) {
-               $this->_lines($lines);
+               $data = array( $generator );
+               if ( $wgShowHostnames ) {
+                       $data[] = wfHostname();
+               }
+               $data[] = wfTimestamp( TS_DB );
+               return "<!-- diff generator: " .
+               implode( " ",
+               array_map(
+                                       "htmlspecialchars",
+               $data ) ) .
+                       " -->\n";
        }
 
-       function _added($lines) {
-               $this->_lines($lines, '>');
-       }
-       function _deleted($lines) {
-               $this->_lines($lines, '<');
+       /**
+        * Replace line numbers with the text in the user's language
+        * @return mixed
+        */
+       function localiseLineNumbers( $text ) {
+               return preg_replace_callback( '/<!--LINE (\d+)-->/',
+               array( &$this, 'localiseLineNumbersCb' ), $text );
        }
 
-       function _changed($orig, $closing) {
-               $this->_deleted($orig);
-               echo "---\n";
-               $this->_added($closing);
+       function localiseLineNumbersCb( $matches ) {
+               if ( $matches[1] === '1' && $this->mReducedLineNumbers ) return '';
+               return $this->msg( 'lineno' )->numParams( $matches[1] )->escaped();
        }
-}
 
-/**
- * A formatter that outputs unified diffs
- * @ingroup DifferenceEngine
- */
-
-class UnifiedDiffFormatter extends DiffFormatter {
-       var $leading_context_lines = 2;
-       var $trailing_context_lines = 2;
-
-       function _added($lines) {
-               $this->_lines($lines, '+');
-       }
-       function _deleted($lines) {
-               $this->_lines($lines, '-');
-       }
-       function _changed($orig, $closing) {
-               $this->_deleted($orig);
-               $this->_added($closing);
-       }
-       function _block_header($xbeg, $xlen, $ybeg, $ylen) {
-               return "@@ -$xbeg,$xlen +$ybeg,$ylen @@";
-       }
-}
 
-/**
- * A pseudo-formatter that just passes along the Diff::$edits array
- * @ingroup DifferenceEngine
- */
-class ArrayDiffFormatter extends DiffFormatter {
-       function format($diff) {
-               $oldline = 1;
-               $newline = 1;
-               $retval = array();
-               foreach($diff->edits as $edit)
-               switch($edit->type) {
-                       case 'add':
-                               foreach($edit->closing as $l) {
-                                       $retval[] = array(
-                                                       'action' => 'add',
-                                                       'new'=> $l,
-                                                       'newline' => $newline++
-                                       );
-                               }
-                               break;
-                       case 'delete':
-                               foreach($edit->orig as $l) {
-                                       $retval[] = array(
-                                                       'action' => 'delete',
-                                                       'old' => $l,
-                                                       'oldline' => $oldline++,
-                                       );
-                               }
-                               break;
-                       case 'change':
-                               foreach($edit->orig as $i => $l) {
-                                       $retval[] = array(
-                                                       'action' => 'change',
-                                                       'old' => $l,
-                                                       'new' => @$edit->closing[$i],
-                                                       'oldline' => $oldline++,
-                                                       'newline' => $newline++,
-                                       );
-                               }
-                               break;
-                       case 'copy':
-                               $oldline += count($edit->orig);
-                               $newline += count($edit->orig);
+       /**
+        * If there are revisions between the ones being compared, return a note saying so.
+        * @return string
+        */
+       function getMultiNotice() {
+               if ( !is_object( $this->mOldRev ) || !is_object( $this->mNewRev ) ) {
+                       return '';
+               } elseif ( !$this->mOldPage->equals( $this->mNewPage ) ) {
+                       // Comparing two different pages? Count would be meaningless.
+                       return '';
                }
-               return $retval;
-       }
-}
-
-/**
- *     Additions by Axel Boldt follow, partly taken from diff.php, phpwiki-1.3.3
- *
- */
 
-define('NBSP', '&#160;'); // iso-8859-x non-breaking space.
-
-/**
- * @todo document
- * @private
- * @ingroup DifferenceEngine
- */
-class _HWLDF_WordAccumulator {
-       function __construct () {
-               $this->_lines = array();
-               $this->_line = '';
-               $this->_group = '';
-               $this->_tag = '';
-       }
+               if ( $this->mOldRev->getTimestamp() > $this->mNewRev->getTimestamp() ) {
+                       $oldRev = $this->mNewRev; // flip
+                       $newRev = $this->mOldRev; // flip
+               } else { // normal case
+                       $oldRev = $this->mOldRev;
+                       $newRev = $this->mNewRev;
+               }
 
-       function _flushGroup ($new_tag) {
-               if ($this->_group !== '') {
-                       if ($this->_tag == 'ins')
-                       $this->_line .= '<ins class="diffchange diffchange-inline">' .
-                       htmlspecialchars ( $this->_group ) . '</ins>';
-                       elseif ($this->_tag == 'del')
-                       $this->_line .= '<del class="diffchange diffchange-inline">' .
-                       htmlspecialchars ( $this->_group ) . '</del>';
-                       else
-                       $this->_line .= htmlspecialchars ( $this->_group );
+               $nEdits = $this->mNewPage->countRevisionsBetween( $oldRev, $newRev );
+               if ( $nEdits > 0 ) {
+                       $limit = 100; // use diff-multi-manyusers if too many users
+                       $numUsers = $this->mNewPage->countAuthorsBetween( $oldRev, $newRev, $limit );
+                       return self::intermediateEditsMsg( $nEdits, $numUsers, $limit );
                }
-               $this->_group = '';
-               $this->_tag = $new_tag;
+               return ''; // nothing
        }
 
-       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 = '';
+       /**
+        * Get a notice about how many intermediate edits and users there are
+        * @param $numEdits int
+        * @param $numUsers int
+        * @param $limit int
+        * @return string
+        */
+       public static function intermediateEditsMsg( $numEdits, $numUsers, $limit ) {
+               if ( $numUsers > $limit ) {
+                       $msg = 'diff-multi-manyusers';
+                       $numUsers = $limit;
+               } else {
+                       $msg = 'diff-multi';
+               }
+               return wfMessage( $msg )->numParams( $numEdits, $numUsers )->parse();
        }
 
-       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;
+       /**
+        * Get a header for a specified revision.
+        *
+        * @param $rev Revision
+        * @param $complete String: 'complete' to get the header wrapped depending
+        *        the visibility of the revision and a link to edit the page.
+        * @return String HTML fragment
+        */
+       private function getRevisionHeader( Revision $rev, $complete = '' ) {
+               $lang = $this->getLanguage();
+               $user = $this->getUser();
+               $revtimestamp = $rev->getTimestamp();
+               $timestamp = $lang->userTimeAndDate( $revtimestamp, $user );
+               $dateofrev = $lang->userDate( $revtimestamp, $user );
+               $timeofrev = $lang->userTime( $revtimestamp, $user );
+
+               $header = $this->msg(
+                       $rev->isCurrent() ? 'currentrev-asof' : 'revisionasof',
+                       $timestamp,
+                       $dateofrev,
+                       $timeofrev
+               )->escaped();
+
+               if ( $complete !== 'complete' ) {
+                       return $header;
                }
-       }
 
-       function getLines() {
-               $this->_flushLine('~done');
-               return $this->_lines;
-       }
-}
+               $title = $rev->getTitle();
 
-/**
- * @todo document
- * @private
- * @ingroup DifferenceEngine
- */
-class WordLevelDiff extends MappedDiff {
-       const MAX_LINE_LENGTH = 10000;
+               $header = Linker::linkKnown( $title, $header, array(),
+                       array( 'oldid' => $rev->getID() ) );
 
-       function __construct ($orig_lines, $closing_lines) {
-               wfProfileIn( __METHOD__ );
+               if ( $rev->userCan( Revision::DELETED_TEXT, $user ) ) {
+                       $editQuery = array( 'action' => 'edit' );
+                       if ( !$rev->isCurrent() ) {
+                               $editQuery['oldid'] = $rev->getID();
+                       }
 
-               list ($orig_words, $orig_stripped) = $this->_split($orig_lines);
-               list ($closing_words, $closing_stripped) = $this->_split($closing_lines);
+                       $msg = $this->msg( $title->quickUserCan( 'edit', $user ) ? 'editold' : 'viewsourceold' )->escaped();
+                       $header .= ' (' . Linker::linkKnown( $title, $msg, array(), $editQuery ) . ')';
+                       if ( $rev->isDeleted( Revision::DELETED_TEXT ) ) {
+                               $header = Html::rawElement( 'span', array( 'class' => 'history-deleted' ), $header );
+                       }
+               } else {
+                       $header = Html::rawElement( 'span', array( 'class' => 'history-deleted' ), $header );
+               }
 
-               parent::__construct($orig_words, $closing_words,
-               $orig_stripped, $closing_stripped);
-               wfProfileOut( __METHOD__ );
+               return $header;
        }
 
-       function _split($lines) {
-               wfProfileIn( __METHOD__ );
-
-               $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;
+       /**
+        * Add the header to a diff body
+        *
+        * @return string
+        */
+       function addHeader( $diff, $otitle, $ntitle, $multi = '', $notice = '' ) {
+               // shared.css sets diff in interface language/dir, but the actual content
+               // is often in a different language, mostly the page content language/dir
+               $tableClass = 'diff diff-contentalign-' . htmlspecialchars( $this->getDiffLang()->alignStart() );
+               $header = "<table class='$tableClass'>";
+
+               if ( !$diff && !$otitle ) {
+                       $header .= "
+                       <tr valign='top'>
+                       <td class='diff-ntitle'>{$ntitle}</td>
+                       </tr>";
+                       $multiColspan = 1;
+               } else {
+                       if ( $diff ) { // Safari/Chrome show broken output if cols not used
+                               $header .= "
+                               <col class='diff-marker' />
+                               <col class='diff-content' />
+                               <col class='diff-marker' />
+                               <col class='diff-content' />";
+                               $colspan = 2;
+                               $multiColspan = 4;
                        } 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] );
-                               }
+                               $colspan = 1;
+                               $multiColspan = 2;
                        }
+                       $header .= "
+                       <tr valign='top'>
+                       <td colspan='$colspan' class='diff-otitle'>{$otitle}</td>
+                       <td colspan='$colspan' class='diff-ntitle'>{$ntitle}</td>
+                       </tr>";
                }
-               wfProfileOut( __METHOD__ );
-               return array($words, $stripped);
-       }
 
-       function orig () {
-               wfProfileIn( __METHOD__ );
-               $orig = new _HWLDF_WordAccumulator;
-
-               foreach ($this->edits as $edit) {
-                       if ($edit->type == 'copy')
-                       $orig->addWords($edit->orig);
-                       elseif ($edit->orig)
-                       $orig->addWords($edit->orig, 'del');
+               if ( $multi != '' ) {
+                       $header .= "<tr><td colspan='{$multiColspan}' align='center' class='diff-multi'>{$multi}</td></tr>";
                }
-               $lines = $orig->getLines();
-               wfProfileOut( __METHOD__ );
-               return $lines;
-       }
-
-       function closing () {
-               wfProfileIn( __METHOD__ );
-               $closing = new _HWLDF_WordAccumulator;
-
-               foreach ($this->edits as $edit) {
-                       if ($edit->type == 'copy')
-                       $closing->addWords($edit->closing);
-                       elseif ($edit->closing)
-                       $closing->addWords($edit->closing, 'ins');
+               if ( $notice != '' ) {
+                       $header .= "<tr><td colspan='{$multiColspan}' align='center'>{$notice}</td></tr>";
                }
-               $lines = $closing->getLines();
-               wfProfileOut( __METHOD__ );
-               return $lines;
-       }
-}
 
-/**
- * Wikipedia Table style diff formatter.
- * @todo document
- * @private
- * @ingroup DifferenceEngine
- */
-class TableDiffFormatter extends DiffFormatter {
-       function __construct() {
-               $this->leading_context_lines = 2;
-               $this->trailing_context_lines = 2;
+               return $header . $diff . "</table>";
        }
 
-       public static function escapeWhiteSpace( $msg ) {
-               $msg = preg_replace( '/^ /m', '&#160; ', $msg );
-               $msg = preg_replace( '/ $/m', ' &#160;', $msg );
-               $msg = preg_replace( '/  /', '&#160; ', $msg );
-               return $msg;
+       /**
+        * Use specified text instead of loading from the database
+        */
+       function setText( $oldText, $newText ) {
+               $this->mOldtext = $oldText;
+               $this->mNewtext = $newText;
+               $this->mTextLoaded = 2;
+               $this->mRevisionsLoaded = true;
        }
 
-       function _block_header( $xbeg, $xlen, $ybeg, $ylen ) {
-               $r = '<tr><td colspan="2" class="diff-lineno"><!--LINE '.$xbeg."--></td>\n" .
-                 '<td colspan="2" class="diff-lineno"><!--LINE '.$ybeg."--></td></tr>\n";
-               return $r;
+       /**
+        * Set the language in which the diff text is written
+        * (Defaults to page content language).
+        * @since 1.19
+        */
+       function setTextLanguage( $lang ) {
+               $this->mDiffLang = wfGetLangObj( $lang );
        }
 
-       function _start_block( $header ) {
-               echo $header;
-       }
+       /**
+        * Load revision IDs
+        */
+       private function loadRevisionIds() {
+               if ( $this->mRevisionsIdsLoaded ) {
+                       return;
+               }
 
-       function _end_block() {
+               $this->mRevisionsIdsLoaded = true;
+
+               $old = $this->mOldid;
+               $new = $this->mNewid;
+
+               if ( $new === 'prev' ) {
+                       # Show diff between revision $old and the previous one.
+                       # Get previous one from DB.
+                       $this->mNewid = intval( $old );
+                       $this->mOldid = $this->getTitle()->getPreviousRevisionID( $this->mNewid );
+               } elseif ( $new === 'next' ) {
+                       # Show diff between revision $old and the next one.
+                       # Get next one from DB.
+                       $this->mOldid = intval( $old );
+                       $this->mNewid = $this->getTitle()->getNextRevisionID( $this->mOldid );
+                       if ( $this->mNewid === false ) {
+                               # 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 );
+                       wfRunHooks( 'NewDifferenceEngine', array( $this->getTitle(), &$this->mOldid, &$this->mNewid, $old, $new ) );
+               }
        }
 
-       function _lines( $lines, $prefix=' ', $color='white' ) {
-       }
+       /**
+        * Load revision metadata for the specified articles. 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).
+        *
+        * If oldid is false, leave the corresponding revision object set
+        * to false. This is impossible via ordinary user input, and is provided for
+        * API convenience.
+        *
+        * @return bool
+        */
+       function loadRevisionData() {
+               if ( $this->mRevisionsLoaded ) {
+                       return true;
+               }
 
-       # HTML-escape parameter before calling this
-       function addedLine( $line ) {
-               return $this->wrapLine( '+', 'diff-addedline', $line );
-       }
+               // Whether it succeeds or fails, we don't want to try again
+               $this->mRevisionsLoaded = true;
 
-       # HTML-escape parameter before calling this
-       function deletedLine( $line ) {
-               return $this->wrapLine( '-', 'diff-deletedline', $line );
-       }
+               $this->loadRevisionIds();
 
-       # HTML-escape parameter before calling this
-       function contextLine( $line ) {
-               return $this->wrapLine( '&#160;', 'diff-context', $line );
-       }
+               // Load the new revision object
+               $this->mNewRev = $this->mNewid
+                       ? Revision::newFromId( $this->mNewid )
+                       : Revision::newFromTitle( $this->getTitle() );
 
-       private function wrapLine( $marker, $class, $line ) {
-               if( $line !== '' ) {
-                       // The <div> wrapper is needed for 'overflow: auto' style to scroll properly
-                       $line = Xml::tags( 'div', null, $this->escapeWhiteSpace( $line ) );
+               if ( !$this->mNewRev instanceof Revision ) {
+                       return false;
                }
-               return "<td class='diff-marker'>$marker</td><td class='$class'>$line</td>";
-       }
 
-       function emptyLine() {
-               return '<td colspan="2">&#160;</td>';
-       }
+               // Update the new revision ID in case it was 0 (makes life easier doing UI stuff)
+               $this->mNewid = $this->mNewRev->getId();
+               $this->mNewPage = $this->mNewRev->getTitle();
+
+               // 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; */
 
-       function _added( $lines ) {
-               foreach ($lines as $line) {
-                       echo '<tr>' . $this->emptyLine() .
-                       $this->addedLine( '<ins class="diffchange">' .
-                       htmlspecialchars ( $line ) . '</ins>' ) . "</tr>\n";
+               if ( is_null( $this->mOldRev ) ) {
+                       return false;
                }
-       }
 
-       function _deleted($lines) {
-               foreach ($lines as $line) {
-                       echo '<tr>' . $this->deletedLine( '<del class="diffchange">' .
-                       htmlspecialchars ( $line ) . '</del>' ) .
-                       $this->emptyLine() . "</tr>\n";
+               if ( $this->mOldRev ) {
+                       $this->mOldPage = $this->mOldRev->getTitle();
                }
-       }
 
-       function _context( $lines ) {
-               foreach ($lines as $line) {
-                       echo '<tr>' .
-                       $this->contextLine( htmlspecialchars ( $line ) ) .
-                       $this->contextLine( htmlspecialchars ( $line ) ) . "</tr>\n";
-               }
+               return true;
        }
 
-       function _changed( $orig, $closing ) {
-               wfProfileIn( __METHOD__ );
-
-               $diff = new WordLevelDiff( $orig, $closing );
-               $del = $diff->orig();
-               $add = $diff->closing();
+       /**
+        * Load the text of the revisions, as well as revision data.
+        *
+        * @return bool
+        */
+       function loadText() {
+               if ( $this->mTextLoaded == 2 ) {
+                       return true;
+               } else {
+                       // Whether it succeeds or fails, we don't want to try again
+                       $this->mTextLoaded = 2;
+               }
 
-               # Notice that WordLevelDiff returns HTML-escaped output.
-               # Hence, we will be calling addedLine/deletedLine without HTML-escaping.
+               if ( !$this->loadRevisionData() ) {
+                       return false;
+               }
+               if ( $this->mOldRev ) {
+                       $this->mOldtext = $this->mOldRev->getText( Revision::FOR_THIS_USER );
+                       if ( $this->mOldtext === false ) {
+                               return false;
+                       }
+               }
+               if ( $this->mNewRev ) {
+                       $this->mNewtext = $this->mNewRev->getText( Revision::FOR_THIS_USER );
+                       if ( $this->mNewtext === false ) {
+                               return false;
+                       }
+               }
+               return true;
+       }
 
-               while ( $line = array_shift( $del ) ) {
-                       $aline = array_shift( $add );
-                       echo '<tr>' . $this->deletedLine( $line ) .
-                       $this->addedLine( $aline ) . "</tr>\n";
+       /**
+        * Load the text of the new revision, not the old one
+        *
+        * @return bool
+        */
+       function loadNewText() {
+               if ( $this->mTextLoaded >= 1 ) {
+                       return true;
+               } else {
+                       $this->mTextLoaded = 1;
                }
-               foreach ($add as $line) {       # If any leftovers
-                       echo '<tr>' . $this->emptyLine() .
-                       $this->addedLine( $line ) . "</tr>\n";
+               if ( !$this->loadRevisionData() ) {
+                       return false;
                }
-               wfProfileOut( __METHOD__ );
+               $this->mNewtext = $this->mNewRev->getText( Revision::FOR_THIS_USER );
+               return true;
        }
 }