includes/diff/DairikiDiff.php

   1 <?php
   2 /**
   3  * A PHP diff engine for phpwiki. (Taken from phpwiki-1.3.3)
   4  *
   5  * Copyright © 2000, 2001 Geoffrey T. Dairiki <dairiki@dairiki.org>
   6  * You may copy this code freely under the conditions of the GPL.
   7  *
   8  * @file
   9  * @ingroup DifferenceEngine
  10  * @defgroup DifferenceEngine DifferenceEngine
  11  */
  12
  13 /**
  14  * @todo document
  15  * @private
  16  * @ingroup DifferenceEngine
  17  */
  18 class _DiffOp {
  19         var $type;
  20         var $orig;
  21         var $closing;
  22
  23         function reverse() {
  24                 trigger_error( 'pure virtual', E_USER_ERROR );
  25         }
  26
  27         /**
  28          * @return int
  29          */
  30         function norig() {
  31                 return $this->orig ? sizeof( $this->orig ) : 0;
  32         }
  33
  34         /**
  35          * @return int
  36          */
  37         function nclosing() {
  38                 return $this->closing ? sizeof( $this->closing ) : 0;
  39         }
  40 }
  41
  42 /**
  43  * @todo document
  44  * @private
  45  * @ingroup DifferenceEngine
  46  */
  47 class _DiffOp_Copy extends _DiffOp {
  48         var $type = 'copy';
  49
  50         function __construct( $orig, $closing = false ) {
  51                 if ( !is_array( $closing ) ) {
  52                         $closing = $orig;
  53                 }
  54                 $this->orig = $orig;
  55                 $this->closing = $closing;
  56         }
  57
  58         /**
  59          * @return _DiffOp_Copy
  60          */
  61         function reverse() {
  62                 return new _DiffOp_Copy( $this->closing, $this->orig );
  63         }
  64 }
  65
  66 /**
  67  * @todo document
  68  * @private
  69  * @ingroup DifferenceEngine
  70  */
  71 class _DiffOp_Delete extends _DiffOp {
  72         var $type = 'delete';
  73
  74         function __construct( $lines ) {
  75                 $this->orig = $lines;
  76                 $this->closing = false;
  77         }
  78
  79         /**
  80          * @return _DiffOp_Add
  81          */
  82         function reverse() {
  83                 return new _DiffOp_Add( $this->orig );
  84         }
  85 }
  86
  87 /**
  88  * @todo document
  89  * @private
  90  * @ingroup DifferenceEngine
  91  */
  92 class _DiffOp_Add extends _DiffOp {
  93         var $type = 'add';
  94
  95         function __construct( $lines ) {
  96                 $this->closing = $lines;
  97                 $this->orig = false;
  98         }
  99
 100         /**
 101          * @return _DiffOp_Delete
 102          */
 103         function reverse() {
 104                 return new _DiffOp_Delete( $this->closing );
 105         }
 106 }
 107
 108 /**
 109  * @todo document
 110  * @private
 111  * @ingroup DifferenceEngine
 112  */
 113 class _DiffOp_Change extends _DiffOp {
 114         var $type = 'change';
 115
 116         function __construct( $orig, $closing ) {
 117                 $this->orig = $orig;
 118                 $this->closing = $closing;
 119         }
 120
 121         /**
 122          * @return _DiffOp_Change
 123          */
 124         function reverse() {
 125                 return new _DiffOp_Change( $this->closing, $this->orig );
 126         }
 127 }
 128
 129 /**
 130  * Class used internally by Diff to actually compute the diffs.
 131  *
 132  * The algorithm used here is mostly lifted from the perl module
 133  * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
 134  *       http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
 135  *
 136  * More ideas are taken from:
 137  *       http://www.ics.uci.edu/~eppstein/161/960229.html
 138  *
 139  * Some ideas are (and a bit of code) are from from analyze.c, from GNU
 140  * diffutils-2.7, which can be found at:
 141  *       ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
 142  *
 143  * closingly, some ideas (subdivision by NCHUNKS > 2, and some optimizations)
 144  * are my own.
 145  *
 146  * Line length limits for robustness added by Tim Starling, 2005-08-31
 147  * Alternative implementation added by Guy Van den Broeck, 2008-07-30
 148  *
 149  * @author Geoffrey T. Dairiki, Tim Starling, Guy Van den Broeck
 150  * @private
 151  * @ingroup DifferenceEngine
 152  */
 153 class _DiffEngine {
 154
 155         const MAX_XREF_LENGTH =  10000;
 156
 157         protected $xchanged, $ychanged;
 158
 159         protected $xv = array(), $yv = array();
 160         protected $xind = array(), $yind = array();
 161
 162         protected $seq = array(), $in_seq = array();
 163
 164         protected $lcs = 0;
 165
 166         /**
 167          * @param $from_lines
 168          * @param $to_lines
 169          * @return array
 170          */
 171         function diff ( $from_lines, $to_lines ) {
 172                 wfProfileIn( __METHOD__ );
 173
 174                 // Diff and store locally
 175                 $this->diff_local( $from_lines, $to_lines );
 176
 177                 // Merge edits when possible
 178                 $this->_shift_boundaries( $from_lines, $this->xchanged, $this->ychanged );
 179                 $this->_shift_boundaries( $to_lines, $this->ychanged, $this->xchanged );
 180
 181                 // Compute the edit operations.
 182                 $n_from = sizeof( $from_lines );
 183                 $n_to = sizeof( $to_lines );
 184
 185                 $edits = array();
 186                 $xi = $yi = 0;
 187                 while ( $xi < $n_from || $yi < $n_to ) {
 188                         assert( '$yi < $n_to || $this->xchanged[$xi]' );
 189                         assert( '$xi < $n_from || $this->ychanged[$yi]' );
 190
 191                         // Skip matching "snake".
 192                         $copy = array();
 193                         while ( $xi < $n_from && $yi < $n_to
 194                         && !$this->xchanged[$xi] && !$this->ychanged[$yi] ) {
 195                                 $copy[] = $from_lines[$xi++];
 196                                 ++$yi;
 197                         }
 198                         if ( $copy ) {
 199                                 $edits[] = new _DiffOp_Copy( $copy );
 200                         }
 201
 202                         // Find deletes & adds.
 203                         $delete = array();
 204                         while ( $xi < $n_from && $this->xchanged[$xi] ) {
 205                                 $delete[] = $from_lines[$xi++];
 206                         }
 207
 208                         $add = array();
 209                         while ( $yi < $n_to && $this->ychanged[$yi] )  {
 210                                 $add[] = $to_lines[$yi++];
 211                         }
 212
 213                         if ( $delete && $add ) {
 214                                 $edits[] = new _DiffOp_Change( $delete, $add );
 215                         } elseif ( $delete ) {
 216                                 $edits[] = new _DiffOp_Delete( $delete );
 217                         } elseif ( $add ) {
 218                                 $edits[] = new _DiffOp_Add( $add );
 219                         }
 220                 }
 221                 wfProfileOut( __METHOD__ );
 222                 return $edits;
 223         }
 224
 225         /**
 226          * @param $from_lines
 227          * @param $to_lines
 228          */
 229         function diff_local ( $from_lines, $to_lines ) {
 230                 global $wgExternalDiffEngine;
 231                 wfProfileIn( __METHOD__ );
 232
 233                 if ( $wgExternalDiffEngine == 'wikidiff3' ) {
 234                         // wikidiff3
 235                         $wikidiff3 = new WikiDiff3();
 236                         $wikidiff3->diff( $from_lines, $to_lines );
 237                         $this->xchanged = $wikidiff3->removed;
 238                         $this->ychanged = $wikidiff3->added;
 239                         unset( $wikidiff3 );
 240                 } else {
 241                         // old diff
 242                         $n_from = sizeof( $from_lines );
 243                         $n_to = sizeof( $to_lines );
 244                         $this->xchanged = $this->ychanged = array();
 245                         $this->xv = $this->yv = array();
 246                         $this->xind = $this->yind = array();
 247                         unset( $this->seq );
 248                         unset( $this->in_seq );
 249                         unset( $this->lcs );
 250
 251                         // Skip leading common lines.
 252                         for ( $skip = 0; $skip < $n_from && $skip < $n_to; $skip++ ) {
 253                                 if ( $from_lines[$skip] !== $to_lines[$skip] ) {
 254                                         break;
 255                                 }
 256                                 $this->xchanged[$skip] = $this->ychanged[$skip] = false;
 257                         }
 258                         // Skip trailing common lines.
 259                         $xi = $n_from; $yi = $n_to;
 260                         for ( $endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++ ) {
 261                                 if ( $from_lines[$xi] !== $to_lines[$yi] ) {
 262                                         break;
 263                                 }
 264                                 $this->xchanged[$xi] = $this->ychanged[$yi] = false;
 265                         }
 266
 267                         // Ignore lines which do not exist in both files.
 268                         for ( $xi = $skip; $xi < $n_from - $endskip; $xi++ ) {
 269                                 $xhash[$this->_line_hash( $from_lines[$xi] )] = 1;
 270                         }
 271
 272                         for ( $yi = $skip; $yi < $n_to - $endskip; $yi++ ) {
 273                                 $line = $to_lines[$yi];
 274                                 if ( ( $this->ychanged[$yi] = empty( $xhash[$this->_line_hash( $line )] ) ) ) {
 275                                         continue;
 276                                 }
 277                                 $yhash[$this->_line_hash( $line )] = 1;
 278                                 $this->yv[] = $line;
 279                                 $this->yind[] = $yi;
 280                         }
 281                         for ( $xi = $skip; $xi < $n_from - $endskip; $xi++ ) {
 282                                 $line = $from_lines[$xi];
 283                                 if ( ( $this->xchanged[$xi] = empty( $yhash[$this->_line_hash( $line )] ) ) ) {
 284                                         continue;
 285                                 }
 286                                 $this->xv[] = $line;
 287                                 $this->xind[] = $xi;
 288                         }
 289
 290                         // Find the LCS.
 291                         $this->_compareseq( 0, sizeof( $this->xv ), 0, sizeof( $this->yv ) );
 292                 }
 293                 wfProfileOut( __METHOD__ );
 294         }
 295
 296         /**
 297          * Returns the whole line if it's small enough, or the MD5 hash otherwise
 298          * @param $line string
 299          * @return string
 300          */
 301         function _line_hash( $line ) {
 302                 if ( strlen( $line ) > self::MAX_XREF_LENGTH ) {
 303                         return md5( $line );
 304                 } else {
 305                         return $line;
 306                 }
 307         }
 308
 309         /**
 310          * Divide the Largest Common Subsequence (LCS) of the sequences
 311          * [XOFF, XLIM) and [YOFF, YLIM) into NCHUNKS approximately equally
 312          * sized segments.
 313          *
 314          * Returns (LCS, PTS).  LCS is the length of the LCS. PTS is an
 315          * array of NCHUNKS+1 (X, Y) indexes giving the diving points between
 316          * sub sequences.  The first sub-sequence is contained in [X0, X1),
 317          * [Y0, Y1), the second in [X1, X2), [Y1, Y2) and so on.  Note
 318          * that (X0, Y0) == (XOFF, YOFF) and
 319          * (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
 320          *
 321          * This function assumes that the first lines of the specified portions
 322          * of the two files do not match, and likewise that the last lines do not
 323          * match.  The caller must trim matching lines from the beginning and end
 324          * of the portions it is going to specify.
 325          * @param $xoff
 326          * @param $xlim
 327          * @param $yoff
 328          * @param $ylim
 329          * @param $nchunks
 330          * @return array
 331          */
 332         function _diag( $xoff, $xlim, $yoff, $ylim, $nchunks ) {
 333                 $flip = false;
 334
 335                 if ( $xlim - $xoff > $ylim - $yoff ) {
 336                         // Things seems faster (I'm not sure I understand why)
 337                         // when the shortest sequence in X.
 338                         $flip = true;
 339                         list( $xoff, $xlim, $yoff, $ylim ) = array( $yoff, $ylim, $xoff, $xlim );
 340                 }
 341
 342                 if ( $flip ) {
 343                         for ( $i = $ylim - 1; $i >= $yoff; $i-- ) {
 344                                 $ymatches[$this->xv[$i]][] = $i;
 345                         }
 346                 } else {
 347                         for ( $i = $ylim - 1; $i >= $yoff; $i-- ) {
 348                                 $ymatches[$this->yv[$i]][] = $i;
 349                         }
 350                 }
 351
 352                 $this->lcs = 0;
 353                 $this->seq[0] = $yoff - 1;
 354                 $this->in_seq = array();
 355                 $ymids[0] = array();
 356
 357                 $numer = $xlim - $xoff + $nchunks - 1;
 358                 $x = $xoff;
 359                 for ( $chunk = 0; $chunk < $nchunks; $chunk++ ) {
 360                         if ( $chunk > 0 ) {
 361                                 for ( $i = 0; $i <= $this->lcs; $i++ ) {
 362                                         $ymids[$i][$chunk -1] = $this->seq[$i];
 363                                 }
 364                         }
 365
 366                         $x1 = $xoff + (int)( ( $numer + ( $xlim -$xoff ) * $chunk ) / $nchunks );
 367                         for ( ; $x < $x1; $x++ ) {
 368                                 $line = $flip ? $this->yv[$x] : $this->xv[$x];
 369                                 if ( empty( $ymatches[$line] ) ) {
 370                                         continue;
 371                                 }
 372                                 $matches = $ymatches[$line];
 373                                 reset( $matches );
 374                                 while ( list( , $y ) = each( $matches ) ) {
 375                                         if ( empty( $this->in_seq[$y] ) ) {
 376                                                 $k = $this->_lcs_pos( $y );
 377                                                 assert( '$k > 0' );
 378                                                 $ymids[$k] = $ymids[$k -1];
 379                                                 break;
 380                                         }
 381                                 }
 382                                 while ( list ( , $y ) = each( $matches ) ) {
 383                                         if ( $y > $this->seq[$k -1] ) {
 384                                                 assert( '$y < $this->seq[$k]' );
 385                                                 // Optimization: this is a common case:
 386                                                 //      next match is just replacing previous match.
 387                                                 $this->in_seq[$this->seq[$k]] = false;
 388                                                 $this->seq[$k] = $y;
 389                                                 $this->in_seq[$y] = 1;
 390                                         } elseif ( empty( $this->in_seq[$y] ) ) {
 391                                                 $k = $this->_lcs_pos( $y );
 392                                                 assert( '$k > 0' );
 393                                                 $ymids[$k] = $ymids[$k -1];
 394                                         }
 395                                 }
 396                         }
 397                 }
 398
 399                 $seps[] = $flip ? array( $yoff, $xoff ) : array( $xoff, $yoff );
 400                 $ymid = $ymids[$this->lcs];
 401                 for ( $n = 0; $n < $nchunks - 1; $n++ ) {
 402                         $x1 = $xoff + (int)( ( $numer + ( $xlim - $xoff ) * $n ) / $nchunks );
 403                         $y1 = $ymid[$n] + 1;
 404                         $seps[] = $flip ? array( $y1, $x1 ) : array( $x1, $y1 );
 405                 }
 406                 $seps[] = $flip ? array( $ylim, $xlim ) : array( $xlim, $ylim );
 407
 408                 return array( $this->lcs, $seps );
 409         }
 410
 411         /**
 412          * @param $ypos
 413          * @return int
 414          */
 415         function _lcs_pos( $ypos ) {
 416                 $end = $this->lcs;
 417                 if ( $end == 0 || $ypos > $this->seq[$end] ) {
 418                         $this->seq[++$this->lcs] = $ypos;
 419                         $this->in_seq[$ypos] = 1;
 420                         return $this->lcs;
 421                 }
 422
 423                 $beg = 1;
 424                 while ( $beg < $end ) {
 425                         $mid = (int)( ( $beg + $end ) / 2 );
 426                         if ( $ypos > $this->seq[$mid] ) {
 427                                 $beg = $mid + 1;
 428                         } else {
 429                                 $end = $mid;
 430                         }
 431                 }
 432
 433                 assert( '$ypos != $this->seq[$end]' );
 434
 435                 $this->in_seq[$this->seq[$end]] = false;
 436                 $this->seq[$end] = $ypos;
 437                 $this->in_seq[$ypos] = 1;
 438                 return $end;
 439         }
 440
 441         /**
 442          * Find LCS of two sequences.
 443          *
 444          * The results are recorded in the vectors $this->{x,y}changed[], by
 445          * storing a 1 in the element for each line that is an insertion
 446          * or deletion (ie. is not in the LCS).
 447          *
 448          * The subsequence of file 0 is [XOFF, XLIM) and likewise for file 1.
 449          *
 450          * Note that XLIM, YLIM are exclusive bounds.
 451          * All line numbers are origin-0 and discarded lines are not counted.
 452          * @param $xoff
 453          * @param $xlim
 454          * @param $yoff
 455          * @param $ylim
 456          */
 457         function _compareseq ( $xoff, $xlim, $yoff, $ylim ) {
 458                 // Slide down the bottom initial diagonal.
 459                 while ( $xoff < $xlim && $yoff < $ylim
 460                 && $this->xv[$xoff] == $this->yv[$yoff] ) {
 461                         ++$xoff;
 462                         ++$yoff;
 463                 }
 464
 465                 // Slide up the top initial diagonal.
 466                 while ( $xlim > $xoff && $ylim > $yoff
 467                 && $this->xv[$xlim - 1] == $this->yv[$ylim - 1] ) {
 468                         --$xlim;
 469                         --$ylim;
 470                 }
 471
 472                 if ( $xoff == $xlim || $yoff == $ylim ) {
 473                         $lcs = 0;
 474                 } else {
 475                         // This is ad hoc but seems to work well.
 476                         // $nchunks = sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5);
 477                         // $nchunks = max(2,min(8,(int)$nchunks));
 478                         $nchunks = min( 7, $xlim - $xoff, $ylim - $yoff ) + 1;
 479                         list ( $lcs, $seps )
 480                         = $this->_diag( $xoff, $xlim, $yoff, $ylim, $nchunks );
 481                 }
 482
 483                 if ( $lcs == 0 ) {
 484                         // X and Y sequences have no common subsequence:
 485                         // mark all changed.
 486                         while ( $yoff < $ylim ) {
 487                                 $this->ychanged[$this->yind[$yoff++]] = 1;
 488                         }
 489                         while ( $xoff < $xlim ) {
 490                                 $this->xchanged[$this->xind[$xoff++]] = 1;
 491                         }
 492                 } else {
 493                         // Use the partitions to split this problem into subproblems.
 494                         reset( $seps );
 495                         $pt1 = $seps[0];
 496                         while ( $pt2 = next( $seps ) ) {
 497                                 $this->_compareseq ( $pt1[0], $pt2[0], $pt1[1], $pt2[1] );
 498                                 $pt1 = $pt2;
 499                         }
 500                 }
 501         }
 502
 503         /**
 504          * Adjust inserts/deletes of identical lines to join changes
 505          * as much as possible.
 506          *
 507          * We do something when a run of changed lines include a
 508          * line at one end and has an excluded, identical line at the other.
 509          * We are free to choose which identical line is included.
 510          * `compareseq' usually chooses the one at the beginning,
 511          * but usually it is cleaner to consider the following identical line
 512          * to be the "change".
 513          *
 514          * This is extracted verbatim from analyze.c (GNU diffutils-2.7).
 515          */
 516         function _shift_boundaries( $lines, &$changed, $other_changed ) {
 517                 wfProfileIn( __METHOD__ );
 518                 $i = 0;
 519                 $j = 0;
 520
 521                 assert( 'sizeof($lines) == sizeof($changed)' );
 522                 $len = sizeof( $lines );
 523                 $other_len = sizeof( $other_changed );
 524
 525                 while ( 1 ) {
 526                         /*
 527                          * Scan forwards to find beginning of another run of changes.
 528                          * Also keep track of the corresponding point in the other file.
 529                          *
 530                          * Throughout this code, $i and $j are adjusted together so that
 531                          * the first $i elements of $changed and the first $j elements
 532                          * of $other_changed both contain the same number of zeros
 533                          * (unchanged lines).
 534                          * Furthermore, $j is always kept so that $j == $other_len or
 535                          * $other_changed[$j] == false.
 536                          */
 537                         while ( $j < $other_len && $other_changed[$j] ) {
 538                                 $j++;
 539                         }
 540
 541                         while ( $i < $len && ! $changed[$i] ) {
 542                                 assert( '$j < $other_len && ! $other_changed[$j]' );
 543                                 $i++; $j++;
 544                                 while ( $j < $other_len && $other_changed[$j] )
 545                                 $j++;
 546                         }
 547
 548                         if ( $i == $len ) {
 549                                 break;
 550                         }
 551
 552                         $start = $i;
 553
 554                         // Find the end of this run of changes.
 555                         while ( ++$i < $len && $changed[$i] ) {
 556                                 continue;
 557                         }
 558
 559                         do {
 560                                 /*
 561                                  * Record the length of this run of changes, so that
 562                                  * we can later determine whether the run has grown.
 563                                  */
 564                                 $runlength = $i - $start;
 565
 566                                 /*
 567                                  * Move the changed region back, so long as the
 568                                  * previous unchanged line matches the last changed one.
 569                                  * This merges with previous changed regions.
 570                                  */
 571                                 while ( $start > 0 && $lines[$start - 1] == $lines[$i - 1] ) {
 572                                         $changed[--$start] = 1;
 573                                         $changed[--$i] = false;
 574                                         while ( $start > 0 && $changed[$start - 1] ) {
 575                                                 $start--;
 576                                         }
 577                                         assert( '$j > 0' );
 578                                         while ( $other_changed[--$j] ) {
 579                                                 continue;
 580                                         }
 581                                         assert( '$j >= 0 && !$other_changed[$j]' );
 582                                 }
 583
 584                                 /*
 585                                  * Set CORRESPONDING to the end of the changed run, at the last
 586                                  * point where it corresponds to a changed run in the other file.
 587                                  * CORRESPONDING == LEN means no such point has been found.
 588                                  */
 589                                 $corresponding = $j < $other_len ? $i : $len;
 590
 591                                 /*
 592                                  * Move the changed region forward, so long as the
 593                                  * first changed line matches the following unchanged one.
 594                                  * This merges with following changed regions.
 595                                  * Do this second, so that if there are no merges,
 596                                  * the changed region is moved forward as far as possible.
 597                                  */
 598                                 while ( $i < $len && $lines[$start] == $lines[$i] ) {
 599                                         $changed[$start++] = false;
 600                                         $changed[$i++] = 1;
 601                                         while ( $i < $len && $changed[$i] ) {
 602                                                 $i++;
 603                                         }
 604
 605                                         assert( '$j < $other_len && ! $other_changed[$j]' );
 606                                         $j++;
 607                                         if ( $j < $other_len && $other_changed[$j] ) {
 608                                                 $corresponding = $i;
 609                                                 while ( $j < $other_len && $other_changed[$j] ) {
 610                                                         $j++;
 611                                                 }
 612                                         }
 613                                 }
 614                         } while ( $runlength != $i - $start );
 615
 616                         /*
 617                          * If possible, move the fully-merged run of changes
 618                          * back to a corresponding run in the other file.
 619                          */
 620                         while ( $corresponding < $i ) {
 621                                 $changed[--$start] = 1;
 622                                 $changed[--$i] = 0;
 623                                 assert( '$j > 0' );
 624                                 while ( $other_changed[--$j] ) {
 625                                         continue;
 626                                 }
 627                                 assert( '$j >= 0 && !$other_changed[$j]' );
 628                         }
 629                 }
 630                 wfProfileOut( __METHOD__ );
 631         }
 632 }
 633
 634 /**
 635  * Class representing a 'diff' between two sequences of strings.
 636  * @todo document
 637  * @private
 638  * @ingroup DifferenceEngine
 639  */
 640 class Diff {
 641         var $edits;
 642
 643         /**
 644          * Constructor.
 645          * Computes diff between sequences of strings.
 646          *
 647          * @param $from_lines array An array of strings.
 648          *                (Typically these are lines from a file.)
 649          * @param $to_lines array An array of strings.
 650          */
 651         function __construct( $from_lines, $to_lines ) {
 652                 $eng = new _DiffEngine;
 653                 $this->edits = $eng->diff( $from_lines, $to_lines );
 654                 // $this->_check($from_lines, $to_lines);
 655         }
 656
 657         /**
 658          * Compute reversed Diff.
 659          *
 660          * SYNOPSIS:
 661          *
 662          *      $diff = new Diff($lines1, $lines2);
 663          *      $rev = $diff->reverse();
 664          * @return Object A Diff object representing the inverse of the
 665          *                                original diff.
 666          */
 667         function reverse() {
 668                 $rev = $this;
 669                 $rev->edits = array();
 670                 foreach ( $this->edits as $edit ) {
 671                         $rev->edits[] = $edit->reverse();
 672                 }
 673                 return $rev;
 674         }
 675
 676         /**
 677          * Check for empty diff.
 678          *
 679          * @return bool True iff two sequences were identical.
 680          */
 681         function isEmpty() {
 682                 foreach ( $this->edits as $edit ) {
 683                         if ( $edit->type != 'copy' ) {
 684                                 return false;
 685                         }
 686                 }
 687                 return true;
 688         }
 689
 690         /**
 691          * Compute the length of the Longest Common Subsequence (LCS).
 692          *
 693          * This is mostly for diagnostic purposed.
 694          *
 695          * @return int The length of the LCS.
 696          */
 697         function lcs() {
 698                 $lcs = 0;
 699                 foreach ( $this->edits as $edit ) {
 700                         if ( $edit->type == 'copy' ) {
 701                                 $lcs += sizeof( $edit->orig );
 702                         }
 703                 }
 704                 return $lcs;
 705         }
 706
 707         /**
 708          * Get the original set of lines.
 709          *
 710          * This reconstructs the $from_lines parameter passed to the
 711          * constructor.
 712          *
 713          * @return array The original sequence of strings.
 714          */
 715         function orig() {
 716                 $lines = array();
 717
 718                 foreach ( $this->edits as $edit ) {
 719                         if ( $edit->orig ) {
 720                                 array_splice( $lines, sizeof( $lines ), 0, $edit->orig );
 721                         }
 722                 }
 723                 return $lines;
 724         }
 725
 726         /**
 727          * Get the closing set of lines.
 728          *
 729          * This reconstructs the $to_lines parameter passed to the
 730          * constructor.
 731          *
 732          * @return array The sequence of strings.
 733          */
 734         function closing() {
 735                 $lines = array();
 736
 737                 foreach ( $this->edits as $edit ) {
 738                         if ( $edit->closing ) {
 739                                 array_splice( $lines, sizeof( $lines ), 0, $edit->closing );
 740                         }
 741                 }
 742                 return $lines;
 743         }
 744
 745         /**
 746          * Check a Diff for validity.
 747          *
 748          * This is here only for debugging purposes.
 749          * @param $from_lines
 750          * @param $to_lines
 751          */
 752         function _check( $from_lines, $to_lines ) {
 753                 wfProfileIn( __METHOD__ );
 754                 if ( serialize( $from_lines ) != serialize( $this->orig() ) ) {
 755                         trigger_error( "Reconstructed original doesn't match", E_USER_ERROR );
 756                 }
 757                 if ( serialize( $to_lines ) != serialize( $this->closing() ) ) {
 758                         trigger_error( "Reconstructed closing doesn't match", E_USER_ERROR );
 759                 }
 760
 761                 $rev = $this->reverse();
 762                 if ( serialize( $to_lines ) != serialize( $rev->orig() ) ) {
 763                         trigger_error( "Reversed original doesn't match", E_USER_ERROR );
 764                 }
 765                 if ( serialize( $from_lines ) != serialize( $rev->closing() ) ) {
 766                         trigger_error( "Reversed closing doesn't match", E_USER_ERROR );
 767                 }
 768
 769
 770                 $prevtype = 'none';
 771                 foreach ( $this->edits as $edit ) {
 772                         if ( $prevtype == $edit->type ) {
 773                                 trigger_error( 'Edit sequence is non-optimal', E_USER_ERROR );
 774                         }
 775                         $prevtype = $edit->type;
 776                 }
 777
 778                 $lcs = $this->lcs();
 779                 trigger_error( 'Diff okay: LCS = ' . $lcs, E_USER_NOTICE );
 780                 wfProfileOut( __METHOD__ );
 781         }
 782 }
 783
 784 /**
 785  * @todo document, bad name.
 786  * @private
 787  * @ingroup DifferenceEngine
 788  */
 789 class MappedDiff extends Diff {
 790         /**
 791          * Constructor.
 792          *
 793          * Computes diff between sequences of strings.
 794          *
 795          * This can be used to compute things like
 796          * case-insensitve diffs, or diffs which ignore
 797          * changes in white-space.
 798          *
 799          * @param $from_lines array An array of strings.
 800          *      (Typically these are lines from a file.)
 801          *
 802          * @param $to_lines array An array of strings.
 803          *
 804          * @param $mapped_from_lines array This array should
 805          *      have the same size number of elements as $from_lines.
 806          *      The elements in $mapped_from_lines and
 807          *      $mapped_to_lines are what is actually compared
 808          *      when computing the diff.
 809          *
 810          * @param $mapped_to_lines array This array should
 811          *      have the same number of elements as $to_lines.
 812          */
 813         function __construct( $from_lines, $to_lines,
 814                 $mapped_from_lines, $mapped_to_lines ) {
 815                 wfProfileIn( __METHOD__ );
 816
 817                 assert( 'sizeof( $from_lines ) == sizeof( $mapped_from_lines )' );
 818                 assert( 'sizeof( $to_lines ) == sizeof( $mapped_to_lines )' );
 819
 820                 parent::__construct( $mapped_from_lines, $mapped_to_lines );
 821
 822                 $xi = $yi = 0;
 823                 for ( $i = 0; $i < sizeof( $this->edits ); $i++ ) {
 824                         $orig = &$this->edits[$i]->orig;
 825                         if ( is_array( $orig ) ) {
 826                                 $orig = array_slice( $from_lines, $xi, sizeof( $orig ) );
 827                                 $xi += sizeof( $orig );
 828                         }
 829
 830                         $closing = &$this->edits[$i]->closing;
 831                         if ( is_array( $closing ) ) {
 832                                 $closing = array_slice( $to_lines, $yi, sizeof( $closing ) );
 833                                 $yi += sizeof( $closing );
 834                         }
 835                 }
 836                 wfProfileOut( __METHOD__ );
 837         }
 838 }
 839
 840 /**
 841  * A class to format Diffs
 842  *
 843  * This class formats the diff in classic diff format.
 844  * It is intended that this class be customized via inheritance,
 845  * to obtain fancier outputs.
 846  * @todo document
 847  * @private
 848  * @ingroup DifferenceEngine
 849  */
 850 class DiffFormatter {
 851         /**
 852          * Number of leading context "lines" to preserve.
 853          *
 854          * This should be left at zero for this class, but subclasses
 855          * may want to set this to other values.
 856          */
 857         var $leading_context_lines = 0;
 858
 859         /**
 860          * Number of trailing context "lines" to preserve.
 861          *
 862          * This should be left at zero for this class, but subclasses
 863          * may want to set this to other values.
 864          */
 865         var $trailing_context_lines = 0;
 866
 867         /**
 868          * Format a diff.
 869          *
 870          * @param $diff Diff A Diff object.
 871          * @return string The formatted output.
 872          */
 873         function format( $diff ) {
 874                 wfProfileIn( __METHOD__ );
 875
 876                 $xi = $yi = 1;
 877                 $block = false;
 878                 $context = array();
 879
 880                 $nlead = $this->leading_context_lines;
 881                 $ntrail = $this->trailing_context_lines;
 882
 883                 $this->_start_diff();
 884
 885                 foreach ( $diff->edits as $edit ) {
 886                         if ( $edit->type == 'copy' ) {
 887                                 if ( is_array( $block ) ) {
 888                                         if ( sizeof( $edit->orig ) <= $nlead + $ntrail ) {
 889                                                 $block[] = $edit;
 890                                         } else {
 891                                                 if ( $ntrail ) {
 892                                                         $context = array_slice( $edit->orig, 0, $ntrail );
 893                                                         $block[] = new _DiffOp_Copy( $context );
 894                                                 }
 895                                                 $this->_block( $x0, $ntrail + $xi - $x0,
 896                                                         $y0, $ntrail + $yi - $y0,
 897                                                         $block );
 898                                                 $block = false;
 899                                         }
 900                                 }
 901                                 $context = $edit->orig;
 902                         } else {
 903                                 if ( !is_array( $block ) ) {
 904                                         $context = array_slice( $context, sizeof( $context ) - $nlead );
 905                                         $x0 = $xi - sizeof( $context );
 906                                         $y0 = $yi - sizeof( $context );
 907                                         $block = array();
 908                                         if ( $context ) {
 909                                                 $block[] = new _DiffOp_Copy( $context );
 910                                         }
 911                                 }
 912                                 $block[] = $edit;
 913                         }
 914
 915                         if ( $edit->orig ) {
 916                                 $xi += sizeof( $edit->orig );
 917                         }
 918                         if ( $edit->closing ) {
 919                                 $yi += sizeof( $edit->closing );
 920                         }
 921                 }
 922
 923                 if ( is_array( $block ) ) {
 924                         $this->_block( $x0, $xi - $x0,
 925                                 $y0, $yi - $y0,
 926                                 $block );
 927                 }
 928
 929                 $end = $this->_end_diff();
 930                 wfProfileOut( __METHOD__ );
 931                 return $end;
 932         }
 933
 934         /**
 935          * @param $xbeg
 936          * @param $xlen
 937          * @param $ybeg
 938          * @param $ylen
 939          * @param $edits
 940          */
 941         function _block( $xbeg, $xlen, $ybeg, $ylen, &$edits ) {
 942                 wfProfileIn( __METHOD__ );
 943                 $this->_start_block( $this->_block_header( $xbeg, $xlen, $ybeg, $ylen ) );
 944                 foreach ( $edits as $edit ) {
 945                         if ( $edit->type == 'copy' ) {
 946                                 $this->_context( $edit->orig );
 947                         } elseif ( $edit->type == 'add' ) {
 948                                 $this->_added( $edit->closing );
 949                         } elseif ( $edit->type == 'delete' ) {
 950                                 $this->_deleted( $edit->orig );
 951                         } elseif ( $edit->type == 'change' ) {
 952                                 $this->_changed( $edit->orig, $edit->closing );
 953                         } else {
 954                                 trigger_error( 'Unknown edit type', E_USER_ERROR );
 955                         }
 956                 }
 957                 $this->_end_block();
 958                 wfProfileOut( __METHOD__ );
 959         }
 960
 961         function _start_diff() {
 962                 ob_start();
 963         }
 964
 965         /**
 966          * @return string
 967          */
 968         function _end_diff() {
 969                 $val = ob_get_contents();
 970                 ob_end_clean();
 971                 return $val;
 972         }
 973
 974         /**
 975          * @param $xbeg
 976          * @param $xlen
 977          * @param $ybeg
 978          * @param $ylen
 979          * @return string
 980          */
 981         function _block_header( $xbeg, $xlen, $ybeg, $ylen ) {
 982                 if ( $xlen > 1 ) {
 983                         $xbeg .= ',' . ( $xbeg + $xlen - 1 );
 984                 }
 985                 if ( $ylen > 1 ) {
 986                         $ybeg .= ',' . ( $ybeg + $ylen - 1 );
 987                 }
 988
 989                 return $xbeg . ( $xlen ? ( $ylen ? 'c' : 'd' ) : 'a' ) . $ybeg;
 990         }
 991
 992         function _start_block( $header ) {
 993                 echo $header . "\n";
 994         }
 995
 996         function _end_block() {
 997         }
 998
 999         /**
1000          * @param $lines
1001          * @param $prefix string
1002          */
1003         function _lines( $lines, $prefix = ' ' ) {
1004                 foreach ( $lines as $line ) {
1005                         echo "$prefix $line\n";
1006                 }
1007         }
1008
1009         /**
1010          * @param $lines
1011          */
1012         function _context( $lines ) {
1013                 $this->_lines( $lines );
1014         }
1015
1016         /**
1017          * @param $lines
1018          */
1019         function _added( $lines ) {
1020                 $this->_lines( $lines, '>' );
1021         }
1022
1023         /**
1024          * @param $lines
1025          */
1026         function _deleted( $lines ) {
1027                 $this->_lines( $lines, '<' );
1028         }
1029
1030         /**
1031          * @param $orig
1032          * @param $closing
1033          */
1034         function _changed( $orig, $closing ) {
1035                 $this->_deleted( $orig );
1036                 echo "---\n";
1037                 $this->_added( $closing );
1038         }
1039 }
1040
1041 /**
1042  * A formatter that outputs unified diffs
1043  * @ingroup DifferenceEngine
1044  */
1045 class UnifiedDiffFormatter extends DiffFormatter {
1046         var $leading_context_lines = 2;
1047         var $trailing_context_lines = 2;
1048
1049         /**
1050          * @param $lines
1051          */
1052         function _added( $lines ) {
1053                 $this->_lines( $lines, '+' );
1054         }
1055
1056         /**
1057          * @param $lines
1058          */
1059         function _deleted( $lines ) {
1060                 $this->_lines( $lines, '-' );
1061         }
1062
1063         /**
1064          * @param $orig
1065          * @param $closing
1066          */
1067         function _changed( $orig, $closing ) {
1068                 $this->_deleted( $orig );
1069                 $this->_added( $closing );
1070         }
1071
1072         /**
1073          * @param $xbeg
1074          * @param $xlen
1075          * @param $ybeg
1076          * @param $ylen
1077          * @return string
1078          */
1079         function _block_header( $xbeg, $xlen, $ybeg, $ylen ) {
1080                 return "@@ -$xbeg,$xlen +$ybeg,$ylen @@";
1081         }
1082 }
1083
1084 /**
1085  * A pseudo-formatter that just passes along the Diff::$edits array
1086  * @ingroup DifferenceEngine
1087  */
1088 class ArrayDiffFormatter extends DiffFormatter {
1089
1090         /**
1091          * @param $diff
1092          * @return array
1093          */
1094         function format( $diff ) {
1095                 $oldline = 1;
1096                 $newline = 1;
1097                 $retval = array();
1098                 foreach ( $diff->edits as $edit ) {
1099                         switch( $edit->type ) {
1100                                 case 'add':
1101                                         foreach ( $edit->closing as $l ) {
1102                                                 $retval[] = array(
1103                                                         'action' => 'add',
1104                                                         'new' => $l,
1105                                                         'newline' => $newline++
1106                                                 );
1107                                         }
1108                                         break;
1109                                 case 'delete':
1110                                         foreach ( $edit->orig as $l ) {
1111                                                 $retval[] = array(
1112                                                         'action' => 'delete',
1113                                                         'old' => $l,
1114                                                         'oldline' => $oldline++,
1115                                                 );
1116                                         }
1117                                         break;
1118                                 case 'change':
1119                                         foreach ( $edit->orig as $i => $l ) {
1120                                                 $retval[] = array(
1121                                                         'action' => 'change',
1122                                                         'old' => $l,
1123                                                         'new' => isset( $edit->closing[$i] ) ? $edit->closing[$i] : null,
1124                                                         'oldline' => $oldline++,
1125                                                         'newline' => $newline++,
1126                                                 );
1127                                         }
1128                                         break;
1129                                 case 'copy':
1130                                         $oldline += count( $edit->orig );
1131                                         $newline += count( $edit->orig );
1132                         }
1133                 }
1134                 return $retval;
1135         }
1136 }
1137
1138 /**
1139  * Additions by Axel Boldt follow, partly taken from diff.php, phpwiki-1.3.3
1140  */
1141
1142 define( 'NBSP', '&#160;' ); // iso-8859-x non-breaking space.
1143
1144 /**
1145  * @todo document
1146  * @private
1147  * @ingroup DifferenceEngine
1148  */
1149 class _HWLDF_WordAccumulator {
1150         function __construct() {
1151                 $this->_lines = array();
1152                 $this->_line = '';
1153                 $this->_group = '';
1154                 $this->_tag = '';
1155         }
1156
1157         /**
1158          * @param $new_tag
1159          */
1160         function _flushGroup( $new_tag ) {
1161                 if ( $this->_group !== '' ) {
1162                         if ( $this->_tag == 'ins' ) {
1163                                 $this->_line .= '<ins class="diffchange diffchange-inline">' .
1164                                                 htmlspecialchars( $this->_group ) . '</ins>';
1165                         } elseif ( $this->_tag == 'del' ) {
1166                                 $this->_line .= '<del class="diffchange diffchange-inline">' .
1167                                                 htmlspecialchars( $this->_group ) . '</del>';
1168                         } else {
1169                                 $this->_line .= htmlspecialchars( $this->_group );
1170                         }
1171                 }
1172                 $this->_group = '';
1173                 $this->_tag = $new_tag;
1174         }
1175
1176         /**
1177          * @param $new_tag
1178          */
1179         function _flushLine( $new_tag ) {
1180                 $this->_flushGroup( $new_tag );
1181                 if ( $this->_line != '' ) {
1182                         array_push( $this->_lines, $this->_line );
1183                 } else {
1184                         # make empty lines visible by inserting an NBSP
1185                         array_push( $this->_lines, NBSP );
1186                 }
1187                 $this->_line = '';
1188         }
1189
1190         /**
1191          * @param $words
1192          * @param $tag string
1193          */
1194         function addWords ( $words, $tag = '' ) {
1195                 if ( $tag != $this->_tag ) {
1196                         $this->_flushGroup( $tag );
1197                 }
1198
1199                 foreach ( $words as $word ) {
1200                         // new-line should only come as first char of word.
1201                         if ( $word == '' ) {
1202                                 continue;
1203                         }
1204                         if ( $word[0] == "\n" ) {
1205                                 $this->_flushLine( $tag );
1206                                 $word = substr( $word, 1 );
1207                         }
1208                         assert( '!strstr( $word, "\n" )' );
1209                         $this->_group .= $word;
1210                 }
1211         }
1212
1213         /**
1214          * @return array
1215          */
1216         function getLines() {
1217                 $this->_flushLine( '~done' );
1218                 return $this->_lines;
1219         }
1220 }
1221
1222 /**
1223  * @todo document
1224  * @private
1225  * @ingroup DifferenceEngine
1226  */
1227 class WordLevelDiff extends MappedDiff {
1228         const MAX_LINE_LENGTH = 10000;
1229
1230         /**
1231          * @param $orig_lines
1232          * @param $closing_lines
1233          */
1234         function __construct ( $orig_lines, $closing_lines ) {
1235                 wfProfileIn( __METHOD__ );
1236
1237                 list( $orig_words, $orig_stripped ) = $this->_split( $orig_lines );
1238                 list( $closing_words, $closing_stripped ) = $this->_split( $closing_lines );
1239
1240                 parent::__construct( $orig_words, $closing_words,
1241                 $orig_stripped, $closing_stripped );
1242                 wfProfileOut( __METHOD__ );
1243         }
1244
1245         /**
1246          * @param $lines
1247          * @return array
1248          */
1249         function _split( $lines ) {
1250                 wfProfileIn( __METHOD__ );
1251
1252                 $words = array();
1253                 $stripped = array();
1254                 $first = true;
1255                 foreach ( $lines as $line ) {
1256                         # If the line is too long, just pretend the entire line is one big word
1257                         # This prevents resource exhaustion problems
1258                         if ( $first ) {
1259                                 $first = false;
1260                         } else {
1261                                 $words[] = "\n";
1262                                 $stripped[] = "\n";
1263                         }
1264                         if ( strlen( $line ) > self::MAX_LINE_LENGTH ) {
1265                                 $words[] = $line;
1266                                 $stripped[] = $line;
1267                         } else {
1268                                 $m = array();
1269                                 if ( preg_match_all( '/ ( [^\S\n]+ | [0-9_A-Za-z\x80-\xff]+ | . ) (?: (?!< \n) [^\S\n])? /xs',
1270                                         $line, $m ) )
1271                                 {
1272                                         $words = array_merge( $words, $m[0] );
1273                                         $stripped = array_merge( $stripped, $m[1] );
1274                                 }
1275                         }
1276                 }
1277                 wfProfileOut( __METHOD__ );
1278                 return array( $words, $stripped );
1279         }
1280
1281         /**
1282          * @return array
1283          */
1284         function orig() {
1285                 wfProfileIn( __METHOD__ );
1286                 $orig = new _HWLDF_WordAccumulator;
1287
1288                 foreach ( $this->edits as $edit ) {
1289                         if ( $edit->type == 'copy' ) {
1290                                 $orig->addWords( $edit->orig );
1291                         } elseif ( $edit->orig ) {
1292                                 $orig->addWords( $edit->orig, 'del' );
1293                         }
1294                 }
1295                 $lines = $orig->getLines();
1296                 wfProfileOut( __METHOD__ );
1297                 return $lines;
1298         }
1299
1300         /**
1301          * @return array
1302          */
1303         function closing() {
1304                 wfProfileIn( __METHOD__ );
1305                 $closing = new _HWLDF_WordAccumulator;
1306
1307                 foreach ( $this->edits as $edit ) {
1308                         if ( $edit->type == 'copy' ) {
1309                                 $closing->addWords( $edit->closing );
1310                         } elseif ( $edit->closing ) {
1311                                 $closing->addWords( $edit->closing, 'ins' );
1312                         }
1313                 }
1314                 $lines = $closing->getLines();
1315                 wfProfileOut( __METHOD__ );
1316                 return $lines;
1317         }
1318 }
1319
1320 /**
1321  * Wikipedia Table style diff formatter.
1322  * @todo document
1323  * @private
1324  * @ingroup DifferenceEngine
1325  */
1326 class TableDiffFormatter extends DiffFormatter {
1327         function __construct() {
1328                 $this->leading_context_lines = 2;
1329                 $this->trailing_context_lines = 2;
1330         }
1331
1332         /**
1333          * @static
1334          * @param $msg
1335          * @return mixed
1336          */
1337         public static function escapeWhiteSpace( $msg ) {
1338                 $msg = preg_replace( '/^ /m', '&#160; ', $msg );
1339                 $msg = preg_replace( '/ $/m', ' &#160;', $msg );
1340                 $msg = preg_replace( '/  /', '&#160; ', $msg );
1341                 return $msg;
1342         }
1343
1344         /**
1345          * @param $xbeg
1346          * @param $xlen
1347          * @param $ybeg
1348          * @param $ylen
1349          * @return string
1350          */
1351         function _block_header( $xbeg, $xlen, $ybeg, $ylen ) {
1352                 $r = '<tr><td colspan="2" class="diff-lineno"><!--LINE ' . $xbeg . "--></td>\n" .
1353                   '<td colspan="2" class="diff-lineno"><!--LINE ' . $ybeg . "--></td></tr>\n";
1354                 return $r;
1355         }
1356
1357         /**
1358          * @param $header
1359          */
1360         function _start_block( $header ) {
1361                 echo $header;
1362         }
1363
1364         function _end_block() {
1365         }
1366
1367         function _lines( $lines, $prefix = ' ', $color = 'white' ) {
1368         }
1369
1370         /**
1371          * HTML-escape parameter before calling this
1372          * @param $line
1373          * @return string
1374          */
1375         function addedLine( $line ) {
1376                 return $this->wrapLine( '+', 'diff-addedline', $line );
1377         }
1378
1379         /**
1380          * HTML-escape parameter before calling this
1381          * @param $line
1382          * @return string
1383          */
1384         function deletedLine( $line ) {
1385                 return $this->wrapLine( '−', 'diff-deletedline', $line );
1386         }
1387
1388         /**
1389          * HTML-escape parameter before calling this
1390          * @param $line
1391          * @return string
1392          */
1393         function contextLine( $line ) {
1394                 return $this->wrapLine( '&#160;', 'diff-context', $line );
1395         }
1396
1397         /**
1398          * @param $marker
1399          * @param $class
1400          * @param $line
1401          * @return string
1402          */
1403         private function wrapLine( $marker, $class, $line ) {
1404                 if ( $line !== '' ) {
1405                         // The <div> wrapper is needed for 'overflow: auto' style to scroll properly
1406                         $line = Xml::tags( 'div', null, $this->escapeWhiteSpace( $line ) );
1407                 }
1408                 return "<td class='diff-marker'>$marker</td><td class='$class'>$line</td>";
1409         }
1410
1411         /**
1412          * @return string
1413          */
1414         function emptyLine() {
1415                 return '<td colspan="2">&#160;</td>';
1416         }
1417
1418         /**
1419          * @param $lines array
1420          */
1421         function _added( $lines ) {
1422                 foreach ( $lines as $line ) {
1423                         echo '<tr>' . $this->emptyLine() .
1424                         $this->addedLine( '<ins class="diffchange">' .
1425                         htmlspecialchars( $line ) . '</ins>' ) . "</tr>\n";
1426                 }
1427         }
1428
1429         /**
1430          * @param $lines
1431          */
1432         function _deleted( $lines ) {
1433                 foreach ( $lines as $line ) {
1434                         echo '<tr>' . $this->deletedLine( '<del class="diffchange">' .
1435                         htmlspecialchars( $line ) . '</del>' ) .
1436                         $this->emptyLine() . "</tr>\n";
1437                 }
1438         }
1439
1440         /**
1441          * @param $lines
1442          */
1443         function _context( $lines ) {
1444                 foreach ( $lines as $line ) {
1445                         echo '<tr>' .
1446                         $this->contextLine( htmlspecialchars( $line ) ) .
1447                         $this->contextLine( htmlspecialchars( $line ) ) . "</tr>\n";
1448                 }
1449         }
1450
1451         /**
1452          * @param $orig
1453          * @param $closing
1454          */
1455         function _changed( $orig, $closing ) {
1456                 wfProfileIn( __METHOD__ );
1457
1458                 $diff = new WordLevelDiff( $orig, $closing );
1459                 $del = $diff->orig();
1460                 $add = $diff->closing();
1461
1462                 # Notice that WordLevelDiff returns HTML-escaped output.
1463                 # Hence, we will be calling addedLine/deletedLine without HTML-escaping.
1464
1465                 while ( $line = array_shift( $del ) ) {
1466                         $aline = array_shift( $add );
1467                         echo '<tr>' . $this->deletedLine( $line ) .
1468                         $this->addedLine( $aline ) . "</tr>\n";
1469                 }
1470                 foreach ( $add as $line ) {     # If any leftovers
1471                         echo '<tr>' . $this->emptyLine() .
1472                         $this->addedLine( $line ) . "</tr>\n";
1473                 }
1474                 wfProfileOut( __METHOD__ );
1475         }
1476 }