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  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License along
  19  * with this program; if not, write to the Free Software Foundation, Inc.,
  20  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  21  * http://www.gnu.org/copyleft/gpl.html
  22  *
  23  * @file
  24  * @ingroup DifferenceEngine
  25  * @defgroup DifferenceEngine DifferenceEngine
  26  */
  27
  28 /**
  29  * @todo document
  30  * @private
  31  * @ingroup DifferenceEngine
  32  */
  33 abstract class DiffOp {
  34
  35         /**
  36          * @var string
  37          */
  38         public $type;
  39
  40         /**
  41          * @var string[]
  42          */
  43         public $orig;
  44
  45         /**
  46          * @var string[]
  47          */
  48         public $closing;
  49
  50         /**
  51          * @return string
  52          */
  53         public function getType() {
  54                 return $this->type;
  55         }
  56
  57         /**
  58          * @return string[]
  59          */
  60         public function getOrig() {
  61                 return $this->orig;
  62         }
  63
  64         /**
  65          * @param int $i
  66          * @return string|null
  67          */
  68         public function getClosing( $i = null ) {
  69                 if ( $i === null ) {
  70                         return $this->closing;
  71                 }
  72                 if ( array_key_exists( $i, $this->closing ) ) {
  73                         return $this->closing[$i];
  74                 }
  75                 return null;
  76         }
  77
  78         abstract public function reverse();
  79
  80         /**
  81          * @return int
  82          */
  83         public function norig() {
  84                 return $this->orig ? count( $this->orig ) : 0;
  85         }
  86
  87         /**
  88          * @return int
  89          */
  90         public function nclosing() {
  91                 return $this->closing ? count( $this->closing ) : 0;
  92         }
  93 }
  94
  95 /**
  96  * @todo document
  97  * @private
  98  * @ingroup DifferenceEngine
  99  */
 100 class DiffOpCopy extends DiffOp {
 101         public $type = 'copy';
 102
 103         public function __construct( $orig, $closing = false ) {
 104                 if ( !is_array( $closing ) ) {
 105                         $closing = $orig;
 106                 }
 107                 $this->orig = $orig;
 108                 $this->closing = $closing;
 109         }
 110
 111         /**
 112          * @return DiffOpCopy
 113          */
 114         public function reverse() {
 115                 return new DiffOpCopy( $this->closing, $this->orig );
 116         }
 117 }
 118
 119 /**
 120  * @todo document
 121  * @private
 122  * @ingroup DifferenceEngine
 123  */
 124 class DiffOpDelete extends DiffOp {
 125         public $type = 'delete';
 126
 127         public function __construct( $lines ) {
 128                 $this->orig = $lines;
 129                 $this->closing = false;
 130         }
 131
 132         /**
 133          * @return DiffOpAdd
 134          */
 135         public function reverse() {
 136                 return new DiffOpAdd( $this->orig );
 137         }
 138 }
 139
 140 /**
 141  * @todo document
 142  * @private
 143  * @ingroup DifferenceEngine
 144  */
 145 class DiffOpAdd extends DiffOp {
 146         public $type = 'add';
 147
 148         public function __construct( $lines ) {
 149                 $this->closing = $lines;
 150                 $this->orig = false;
 151         }
 152
 153         /**
 154          * @return DiffOpDelete
 155          */
 156         public function reverse() {
 157                 return new DiffOpDelete( $this->closing );
 158         }
 159 }
 160
 161 /**
 162  * @todo document
 163  * @private
 164  * @ingroup DifferenceEngine
 165  */
 166 class DiffOpChange extends DiffOp {
 167         public $type = 'change';
 168
 169         public function __construct( $orig, $closing ) {
 170                 $this->orig = $orig;
 171                 $this->closing = $closing;
 172         }
 173
 174         /**
 175          * @return DiffOpChange
 176          */
 177         public function reverse() {
 178                 return new DiffOpChange( $this->closing, $this->orig );
 179         }
 180 }
 181
 182 /**
 183  * Class used internally by Diff to actually compute the diffs.
 184  *
 185  * The algorithm used here is mostly lifted from the perl module
 186  * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
 187  *     http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
 188  *
 189  * More ideas are taken from:
 190  *     http://www.ics.uci.edu/~eppstein/161/960229.html
 191  *
 192  * Some ideas (and a bit of code) are from analyze.c, from GNU
 193  * diffutils-2.7, which can be found at:
 194  *     ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
 195  *
 196  * closingly, some ideas (subdivision by NCHUNKS > 2, and some optimizations)
 197  * are my own.
 198  *
 199  * Line length limits for robustness added by Tim Starling, 2005-08-31
 200  * Alternative implementation added by Guy Van den Broeck, 2008-07-30
 201  *
 202  * @author Geoffrey T. Dairiki, Tim Starling, Guy Van den Broeck
 203  * @private
 204  * @ingroup DifferenceEngine
 205  */
 206 class DiffEngine {
 207         const MAX_XREF_LENGTH = 10000;
 208
 209         protected $xchanged, $ychanged;
 210
 211         protected $xv = array(), $yv = array();
 212         protected $xind = array(), $yind = array();
 213
 214         protected $seq = array(), $in_seq = array();
 215
 216         protected $lcs = 0;
 217
 218         /**
 219          * @param string[] $from_lines
 220          * @param string[] $to_lines
 221          *
 222          * @return DiffOp[]
 223          */
 224         public function diff( $from_lines, $to_lines ) {
 225
 226                 // Diff and store locally
 227                 $this->diffLocal( $from_lines, $to_lines );
 228
 229                 // Merge edits when possible
 230                 $this->shiftBoundaries( $from_lines, $this->xchanged, $this->ychanged );
 231                 $this->shiftBoundaries( $to_lines, $this->ychanged, $this->xchanged );
 232
 233                 // Compute the edit operations.
 234                 $n_from = count( $from_lines );
 235                 $n_to = count( $to_lines );
 236
 237                 $edits = array();
 238                 $xi = $yi = 0;
 239                 while ( $xi < $n_from || $yi < $n_to ) {
 240                         assert( '$yi < $n_to || $this->xchanged[$xi]' );
 241                         assert( '$xi < $n_from || $this->ychanged[$yi]' );
 242
 243                         // Skip matching "snake".
 244                         $copy = array();
 245                         while ( $xi < $n_from && $yi < $n_to
 246                                 && !$this->xchanged[$xi] && !$this->ychanged[$yi]
 247                         ) {
 248                                 $copy[] = $from_lines[$xi++];
 249                                 ++$yi;
 250                         }
 251                         if ( $copy ) {
 252                                 $edits[] = new DiffOpCopy( $copy );
 253                         }
 254
 255                         // Find deletes & adds.
 256                         $delete = array();
 257                         while ( $xi < $n_from && $this->xchanged[$xi] ) {
 258                                 $delete[] = $from_lines[$xi++];
 259                         }
 260
 261                         $add = array();
 262                         while ( $yi < $n_to && $this->ychanged[$yi] ) {
 263                                 $add[] = $to_lines[$yi++];
 264                         }
 265
 266                         if ( $delete && $add ) {
 267                                 $edits[] = new DiffOpChange( $delete, $add );
 268                         } elseif ( $delete ) {
 269                                 $edits[] = new DiffOpDelete( $delete );
 270                         } elseif ( $add ) {
 271                                 $edits[] = new DiffOpAdd( $add );
 272                         }
 273                 }
 274
 275                 return $edits;
 276         }
 277
 278         /**
 279          * @param string[] $from_lines
 280          * @param string[] $to_lines
 281          */
 282         private function diffLocal( $from_lines, $to_lines ) {
 283                 global $wgExternalDiffEngine;
 284
 285                 if ( $wgExternalDiffEngine == 'wikidiff3' ) {
 286                         // wikidiff3
 287                         $wikidiff3 = new WikiDiff3();
 288                         $wikidiff3->diff( $from_lines, $to_lines );
 289                         $this->xchanged = $wikidiff3->removed;
 290                         $this->ychanged = $wikidiff3->added;
 291                         unset( $wikidiff3 );
 292                 } else {
 293                         // old diff
 294                         $n_from = count( $from_lines );
 295                         $n_to = count( $to_lines );
 296                         $this->xchanged = $this->ychanged = array();
 297                         $this->xv = $this->yv = array();
 298                         $this->xind = $this->yind = array();
 299                         $this->seq = array();
 300                         $this->in_seq = array();
 301                         $this->lcs = 0;
 302
 303                         // Skip leading common lines.
 304                         for ( $skip = 0; $skip < $n_from && $skip < $n_to; $skip++ ) {
 305                                 if ( $from_lines[$skip] !== $to_lines[$skip] ) {
 306                                         break;
 307                                 }
 308                                 $this->xchanged[$skip] = $this->ychanged[$skip] = false;
 309                         }
 310                         // Skip trailing common lines.
 311                         $xi = $n_from;
 312                         $yi = $n_to;
 313                         for ( $endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++ ) {
 314                                 if ( $from_lines[$xi] !== $to_lines[$yi] ) {
 315                                         break;
 316                                 }
 317                                 $this->xchanged[$xi] = $this->ychanged[$yi] = false;
 318                         }
 319
 320                         // Ignore lines which do not exist in both files.
 321                         for ( $xi = $skip; $xi < $n_from - $endskip; $xi++ ) {
 322                                 $xhash[$this->lineHash( $from_lines[$xi] )] = 1;
 323                         }
 324
 325                         for ( $yi = $skip; $yi < $n_to - $endskip; $yi++ ) {
 326                                 $line = $to_lines[$yi];
 327                                 $this->ychanged[$yi] = empty( $xhash[$this->lineHash( $line )] );
 328                                 if ( $this->ychanged[$yi] ) {
 329                                         continue;
 330                                 }
 331                                 $yhash[$this->lineHash( $line )] = 1;
 332                                 $this->yv[] = $line;
 333                                 $this->yind[] = $yi;
 334                         }
 335                         for ( $xi = $skip; $xi < $n_from - $endskip; $xi++ ) {
 336                                 $line = $from_lines[$xi];
 337                                 $this->xchanged[$xi] = empty( $yhash[$this->lineHash( $line )] );
 338                                 if ( $this->xchanged[$xi] ) {
 339                                         continue;
 340                                 }
 341                                 $this->xv[] = $line;
 342                                 $this->xind[] = $xi;
 343                         }
 344
 345                         // Find the LCS.
 346                         $this->compareSeq( 0, count( $this->xv ), 0, count( $this->yv ) );
 347                 }
 348         }
 349
 350         /**
 351          * Returns the whole line if it's small enough, or the MD5 hash otherwise
 352          *
 353          * @param string $line
 354          *
 355          * @return string
 356          */
 357         private function lineHash( $line ) {
 358                 if ( strlen( $line ) > self::MAX_XREF_LENGTH ) {
 359                         return md5( $line );
 360                 } else {
 361                         return $line;
 362                 }
 363         }
 364
 365         /**
 366          * Divide the Largest Common Subsequence (LCS) of the sequences
 367          * [XOFF, XLIM) and [YOFF, YLIM) into NCHUNKS approximately equally
 368          * sized segments.
 369          *
 370          * Returns (LCS, PTS). LCS is the length of the LCS. PTS is an
 371          * array of NCHUNKS+1 (X, Y) indexes giving the diving points between
 372          * sub sequences.  The first sub-sequence is contained in [X0, X1),
 373          * [Y0, Y1), the second in [X1, X2), [Y1, Y2) and so on.  Note
 374          * that (X0, Y0) == (XOFF, YOFF) and
 375          * (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
 376          *
 377          * This function assumes that the first lines of the specified portions
 378          * of the two files do not match, and likewise that the last lines do not
 379          * match.  The caller must trim matching lines from the beginning and end
 380          * of the portions it is going to specify.
 381          *
 382          * @param int $xoff
 383          * @param int $xlim
 384          * @param int $yoff
 385          * @param int $ylim
 386          * @param int $nchunks
 387          *
 388          * @return array List of two elements, integer and array[].
 389          */
 390         private function diag( $xoff, $xlim, $yoff, $ylim, $nchunks ) {
 391                 $flip = false;
 392
 393                 if ( $xlim - $xoff > $ylim - $yoff ) {
 394                         // Things seems faster (I'm not sure I understand why)
 395                         // when the shortest sequence in X.
 396                         $flip = true;
 397                         list( $xoff, $xlim, $yoff, $ylim ) = array( $yoff, $ylim, $xoff, $xlim );
 398                 }
 399
 400                 if ( $flip ) {
 401                         for ( $i = $ylim - 1; $i >= $yoff; $i-- ) {
 402                                 $ymatches[$this->xv[$i]][] = $i;
 403                         }
 404                 } else {
 405                         for ( $i = $ylim - 1; $i >= $yoff; $i-- ) {
 406                                 $ymatches[$this->yv[$i]][] = $i;
 407                         }
 408                 }
 409
 410                 $this->lcs = 0;
 411                 $this->seq[0] = $yoff - 1;
 412                 $this->in_seq = array();
 413                 $ymids[0] = array();
 414
 415                 $numer = $xlim - $xoff + $nchunks - 1;
 416                 $x = $xoff;
 417                 for ( $chunk = 0; $chunk < $nchunks; $chunk++ ) {
 418                         if ( $chunk > 0 ) {
 419                                 for ( $i = 0; $i <= $this->lcs; $i++ ) {
 420                                         $ymids[$i][$chunk - 1] = $this->seq[$i];
 421                                 }
 422                         }
 423
 424                         $x1 = $xoff + (int)( ( $numer + ( $xlim - $xoff ) * $chunk ) / $nchunks );
 425                         // @codingStandardsIgnoreStart Ignore Squiz.WhiteSpace.SemicolonSpacing.Incorrect
 426                         for ( ; $x < $x1; $x++ ) {
 427                                 // @codingStandardsIgnoreEnd
 428                                 $line = $flip ? $this->yv[$x] : $this->xv[$x];
 429                                 if ( empty( $ymatches[$line] ) ) {
 430                                         continue;
 431                                 }
 432
 433                                 $k = 0;
 434                                 $matches = $ymatches[$line];
 435                                 reset( $matches );
 436                                 while ( list( , $y ) = each( $matches ) ) {
 437                                         if ( empty( $this->in_seq[$y] ) ) {
 438                                                 $k = $this->lcsPos( $y );
 439                                                 assert( '$k > 0' );
 440                                                 $ymids[$k] = $ymids[$k - 1];
 441                                                 break;
 442                                         }
 443                                 }
 444
 445                                 while ( list( , $y ) = each( $matches ) ) {
 446                                         if ( $y > $this->seq[$k - 1] ) {
 447                                                 assert( '$y < $this->seq[$k]' );
 448                                                 // Optimization: this is a common case:
 449                                                 // next match is just replacing previous match.
 450                                                 $this->in_seq[$this->seq[$k]] = false;
 451                                                 $this->seq[$k] = $y;
 452                                                 $this->in_seq[$y] = 1;
 453                                         } elseif ( empty( $this->in_seq[$y] ) ) {
 454                                                 $k = $this->lcsPos( $y );
 455                                                 assert( '$k > 0' );
 456                                                 $ymids[$k] = $ymids[$k - 1];
 457                                         }
 458                                 }
 459                         }
 460                 }
 461
 462                 $seps[] = $flip ? array( $yoff, $xoff ) : array( $xoff, $yoff );
 463                 $ymid = $ymids[$this->lcs];
 464                 for ( $n = 0; $n < $nchunks - 1; $n++ ) {
 465                         $x1 = $xoff + (int)( ( $numer + ( $xlim - $xoff ) * $n ) / $nchunks );
 466                         $y1 = $ymid[$n] + 1;
 467                         $seps[] = $flip ? array( $y1, $x1 ) : array( $x1, $y1 );
 468                 }
 469                 $seps[] = $flip ? array( $ylim, $xlim ) : array( $xlim, $ylim );
 470
 471                 return array( $this->lcs, $seps );
 472         }
 473
 474         /**
 475          * @param int $ypos
 476          *
 477          * @return int
 478          */
 479         private function lcsPos( $ypos ) {
 480                 $end = $this->lcs;
 481                 if ( $end == 0 || $ypos > $this->seq[$end] ) {
 482                         $this->seq[++$this->lcs] = $ypos;
 483                         $this->in_seq[$ypos] = 1;
 484
 485                         return $this->lcs;
 486                 }
 487
 488                 $beg = 1;
 489                 while ( $beg < $end ) {
 490                         $mid = (int)( ( $beg + $end ) / 2 );
 491                         if ( $ypos > $this->seq[$mid] ) {
 492                                 $beg = $mid + 1;
 493                         } else {
 494                                 $end = $mid;
 495                         }
 496                 }
 497
 498                 assert( '$ypos != $this->seq[$end]' );
 499
 500                 $this->in_seq[$this->seq[$end]] = false;
 501                 $this->seq[$end] = $ypos;
 502                 $this->in_seq[$ypos] = 1;
 503
 504                 return $end;
 505         }
 506
 507         /**
 508          * Find LCS of two sequences.
 509          *
 510          * The results are recorded in the vectors $this->{x,y}changed[], by
 511          * storing a 1 in the element for each line that is an insertion
 512          * or deletion (ie. is not in the LCS).
 513          *
 514          * The subsequence of file 0 is [XOFF, XLIM) and likewise for file 1.
 515          *
 516          * Note that XLIM, YLIM are exclusive bounds.
 517          * All line numbers are origin-0 and discarded lines are not counted.
 518          *
 519          * @param int $xoff
 520          * @param int $xlim
 521          * @param int $yoff
 522          * @param int $ylim
 523          */
 524         private function compareSeq( $xoff, $xlim, $yoff, $ylim ) {
 525                 // Slide down the bottom initial diagonal.
 526                 while ( $xoff < $xlim && $yoff < $ylim && $this->xv[$xoff] == $this->yv[$yoff] ) {
 527                         ++$xoff;
 528                         ++$yoff;
 529                 }
 530
 531                 // Slide up the top initial diagonal.
 532                 while ( $xlim > $xoff && $ylim > $yoff
 533                         && $this->xv[$xlim - 1] == $this->yv[$ylim - 1]
 534                 ) {
 535                         --$xlim;
 536                         --$ylim;
 537                 }
 538
 539                 if ( $xoff == $xlim || $yoff == $ylim ) {
 540                         $lcs = 0;
 541                 } else {
 542                         // This is ad hoc but seems to work well.
 543                         // $nchunks = sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5);
 544                         // $nchunks = max(2,min(8,(int)$nchunks));
 545                         $nchunks = min( 7, $xlim - $xoff, $ylim - $yoff ) + 1;
 546                         list( $lcs, $seps ) = $this->diag( $xoff, $xlim, $yoff, $ylim, $nchunks );
 547                 }
 548
 549                 if ( $lcs == 0 ) {
 550                         // X and Y sequences have no common subsequence:
 551                         // mark all changed.
 552                         while ( $yoff < $ylim ) {
 553                                 $this->ychanged[$this->yind[$yoff++]] = 1;
 554                         }
 555                         while ( $xoff < $xlim ) {
 556                                 $this->xchanged[$this->xind[$xoff++]] = 1;
 557                         }
 558                 } else {
 559                         // Use the partitions to split this problem into subproblems.
 560                         reset( $seps );
 561                         $pt1 = $seps[0];
 562                         while ( $pt2 = next( $seps ) ) {
 563                                 $this->compareSeq( $pt1[0], $pt2[0], $pt1[1], $pt2[1] );
 564                                 $pt1 = $pt2;
 565                         }
 566                 }
 567         }
 568
 569         /**
 570          * Adjust inserts/deletes of identical lines to join changes
 571          * as much as possible.
 572          *
 573          * We do something when a run of changed lines include a
 574          * line at one end and has an excluded, identical line at the other.
 575          * We are free to choose which identical line is included.
 576          * `compareseq' usually chooses the one at the beginning,
 577          * but usually it is cleaner to consider the following identical line
 578          * to be the "change".
 579          *
 580          * This is extracted verbatim from analyze.c (GNU diffutils-2.7).
 581          */
 582         private function shiftBoundaries( $lines, &$changed, $other_changed ) {
 583                 $i = 0;
 584                 $j = 0;
 585
 586                 assert( 'count($lines) == count($changed)' );
 587                 $len = count( $lines );
 588                 $other_len = count( $other_changed );
 589
 590                 while ( 1 ) {
 591                         /*
 592                          * Scan forwards to find beginning of another run of changes.
 593                          * Also keep track of the corresponding point in the other file.
 594                          *
 595                          * Throughout this code, $i and $j are adjusted together so that
 596                          * the first $i elements of $changed and the first $j elements
 597                          * of $other_changed both contain the same number of zeros
 598                          * (unchanged lines).
 599                          * Furthermore, $j is always kept so that $j == $other_len or
 600                          * $other_changed[$j] == false.
 601                          */
 602                         while ( $j < $other_len && $other_changed[$j] ) {
 603                                 $j++;
 604                         }
 605
 606                         while ( $i < $len && !$changed[$i] ) {
 607                                 assert( '$j < $other_len && ! $other_changed[$j]' );
 608                                 $i++;
 609                                 $j++;
 610                                 while ( $j < $other_len && $other_changed[$j] ) {
 611                                         $j++;
 612                                 }
 613                         }
 614
 615                         if ( $i == $len ) {
 616                                 break;
 617                         }
 618
 619                         $start = $i;
 620
 621                         // Find the end of this run of changes.
 622                         while ( ++$i < $len && $changed[$i] ) {
 623                                 continue;
 624                         }
 625
 626                         do {
 627                                 /*
 628                                  * Record the length of this run of changes, so that
 629                                  * we can later determine whether the run has grown.
 630                                  */
 631                                 $runlength = $i - $start;
 632
 633                                 /*
 634                                  * Move the changed region back, so long as the
 635                                  * previous unchanged line matches the last changed one.
 636                                  * This merges with previous changed regions.
 637                                  */
 638                                 while ( $start > 0 && $lines[$start - 1] == $lines[$i - 1] ) {
 639                                         $changed[--$start] = 1;
 640                                         $changed[--$i] = false;
 641                                         while ( $start > 0 && $changed[$start - 1] ) {
 642                                                 $start--;
 643                                         }
 644                                         assert( '$j > 0' );
 645                                         while ( $other_changed[--$j] ) {
 646                                                 continue;
 647                                         }
 648                                         assert( '$j >= 0 && !$other_changed[$j]' );
 649                                 }
 650
 651                                 /*
 652                                  * Set CORRESPONDING to the end of the changed run, at the last
 653                                  * point where it corresponds to a changed run in the other file.
 654                                  * CORRESPONDING == LEN means no such point has been found.
 655                                  */
 656                                 $corresponding = $j < $other_len ? $i : $len;
 657
 658                                 /*
 659                                  * Move the changed region forward, so long as the
 660                                  * first changed line matches the following unchanged one.
 661                                  * This merges with following changed regions.
 662                                  * Do this second, so that if there are no merges,
 663                                  * the changed region is moved forward as far as possible.
 664                                  */
 665                                 while ( $i < $len && $lines[$start] == $lines[$i] ) {
 666                                         $changed[$start++] = false;
 667                                         $changed[$i++] = 1;
 668                                         while ( $i < $len && $changed[$i] ) {
 669                                                 $i++;
 670                                         }
 671
 672                                         assert( '$j < $other_len && ! $other_changed[$j]' );
 673                                         $j++;
 674                                         if ( $j < $other_len && $other_changed[$j] ) {
 675                                                 $corresponding = $i;
 676                                                 while ( $j < $other_len && $other_changed[$j] ) {
 677                                                         $j++;
 678                                                 }
 679                                         }
 680                                 }
 681                         } while ( $runlength != $i - $start );
 682
 683                         /*
 684                          * If possible, move the fully-merged run of changes
 685                          * back to a corresponding run in the other file.
 686                          */
 687                         while ( $corresponding < $i ) {
 688                                 $changed[--$start] = 1;
 689                                 $changed[--$i] = 0;
 690                                 assert( '$j > 0' );
 691                                 while ( $other_changed[--$j] ) {
 692                                         continue;
 693                                 }
 694                                 assert( '$j >= 0 && !$other_changed[$j]' );
 695                         }
 696                 }
 697         }
 698 }
 699
 700 /**
 701  * Class representing a 'diff' between two sequences of strings.
 702  * @todo document
 703  * @private
 704  * @ingroup DifferenceEngine
 705  */
 706 class Diff {
 707
 708         /**
 709          * @var DiffOp[]
 710          */
 711         public $edits;
 712
 713         /**
 714          * Constructor.
 715          * Computes diff between sequences of strings.
 716          *
 717          * @param string[] $from_lines An array of strings.
 718          *   Typically these are lines from a file.
 719          * @param string[] $to_lines An array of strings.
 720          */
 721         public function __construct( $from_lines, $to_lines ) {
 722                 $eng = new DiffEngine;
 723                 $this->edits = $eng->diff( $from_lines, $to_lines );
 724         }
 725
 726         /**
 727          * @return DiffOp[]
 728          */
 729         public function getEdits() {
 730                 return $this->edits;
 731         }
 732
 733         /**
 734          * Compute reversed Diff.
 735          *
 736          * SYNOPSIS:
 737          *
 738          *    $diff = new Diff($lines1, $lines2);
 739          *    $rev = $diff->reverse();
 740          *
 741          * @return Object A Diff object representing the inverse of the
 742          *   original diff.
 743          */
 744         public function reverse() {
 745                 $rev = $this;
 746                 $rev->edits = array();
 747                 /** @var DiffOp $edit */
 748                 foreach ( $this->edits as $edit ) {
 749                         $rev->edits[] = $edit->reverse();
 750                 }
 751
 752                 return $rev;
 753         }
 754
 755         /**
 756          * Check for empty diff.
 757          *
 758          * @return bool True if two sequences were identical.
 759          */
 760         public function isEmpty() {
 761                 foreach ( $this->edits as $edit ) {
 762                         if ( $edit->type != 'copy' ) {
 763                                 return false;
 764                         }
 765                 }
 766
 767                 return true;
 768         }
 769
 770         /**
 771          * Compute the length of the Longest Common Subsequence (LCS).
 772          *
 773          * This is mostly for diagnostic purposed.
 774          *
 775          * @return int The length of the LCS.
 776          */
 777         public function lcs() {
 778                 $lcs = 0;
 779                 foreach ( $this->edits as $edit ) {
 780                         if ( $edit->type == 'copy' ) {
 781                                 $lcs += count( $edit->orig );
 782                         }
 783                 }
 784
 785                 return $lcs;
 786         }
 787
 788         /**
 789          * Get the original set of lines.
 790          *
 791          * This reconstructs the $from_lines parameter passed to the
 792          * constructor.
 793          *
 794          * @return string[] The original sequence of strings.
 795          */
 796         public function orig() {
 797                 $lines = array();
 798
 799                 foreach ( $this->edits as $edit ) {
 800                         if ( $edit->orig ) {
 801                                 array_splice( $lines, count( $lines ), 0, $edit->orig );
 802                         }
 803                 }
 804
 805                 return $lines;
 806         }
 807
 808         /**
 809          * Get the closing set of lines.
 810          *
 811          * This reconstructs the $to_lines parameter passed to the
 812          * constructor.
 813          *
 814          * @return string[] The sequence of strings.
 815          */
 816         public function closing() {
 817                 $lines = array();
 818
 819                 foreach ( $this->edits as $edit ) {
 820                         if ( $edit->closing ) {
 821                                 array_splice( $lines, count( $lines ), 0, $edit->closing );
 822                         }
 823                 }
 824
 825                 return $lines;
 826         }
 827 }
 828
 829 /**
 830  * @todo document, bad name.
 831  * @private
 832  * @ingroup DifferenceEngine
 833  */
 834 class MappedDiff extends Diff {
 835         /**
 836          * Constructor.
 837          *
 838          * Computes diff between sequences of strings.
 839          *
 840          * This can be used to compute things like
 841          * case-insensitve diffs, or diffs which ignore
 842          * changes in white-space.
 843          *
 844          * @param string[] $from_lines An array of strings.
 845          *   Typically these are lines from a file.
 846          * @param string[] $to_lines An array of strings.
 847          * @param string[] $mapped_from_lines This array should
 848          *   have the same size number of elements as $from_lines.
 849          *   The elements in $mapped_from_lines and
 850          *   $mapped_to_lines are what is actually compared
 851          *   when computing the diff.
 852          * @param string[] $mapped_to_lines This array should
 853          *   have the same number of elements as $to_lines.
 854          */
 855         public function __construct( $from_lines, $to_lines,
 856                 $mapped_from_lines, $mapped_to_lines ) {
 857
 858                 assert( 'count( $from_lines ) == count( $mapped_from_lines )' );
 859                 assert( 'count( $to_lines ) == count( $mapped_to_lines )' );
 860
 861                 parent::__construct( $mapped_from_lines, $mapped_to_lines );
 862
 863                 $xi = $yi = 0;
 864                 $editCount = count( $this->edits );
 865                 for ( $i = 0; $i < $editCount; $i++ ) {
 866                         $orig = &$this->edits[$i]->orig;
 867                         if ( is_array( $orig ) ) {
 868                                 $orig = array_slice( $from_lines, $xi, count( $orig ) );
 869                                 $xi += count( $orig );
 870                         }
 871
 872                         $closing = &$this->edits[$i]->closing;
 873                         if ( is_array( $closing ) ) {
 874                                 $closing = array_slice( $to_lines, $yi, count( $closing ) );
 875                                 $yi += count( $closing );
 876                         }
 877                 }
 878         }
 879 }
 880
 881 /**
 882  * Additions by Axel Boldt follow, partly taken from diff.php, phpwiki-1.3.3
 883  */
 884
 885 /**
 886  * @todo document
 887  * @private
 888  * @ingroup DifferenceEngine
 889  */
 890 class HWLDFWordAccumulator {
 891         public $insClass = ' class="diffchange diffchange-inline"';
 892         public $delClass = ' class="diffchange diffchange-inline"';
 893
 894         private $lines = array();
 895         private $line = '';
 896         private $group = '';
 897         private $tag = '';
 898
 899         /**
 900          * @param string $new_tag
 901          */
 902         private function flushGroup( $new_tag ) {
 903                 if ( $this->group !== '' ) {
 904                         if ( $this->tag == 'ins' ) {
 905                                 $this->line .= "<ins{$this->insClass}>" .
 906                                         htmlspecialchars( $this->group ) . '</ins>';
 907                         } elseif ( $this->tag == 'del' ) {
 908                                 $this->line .= "<del{$this->delClass}>" .
 909                                         htmlspecialchars( $this->group ) . '</del>';
 910                         } else {
 911                                 $this->line .= htmlspecialchars( $this->group );
 912                         }
 913                 }
 914                 $this->group = '';
 915                 $this->tag = $new_tag;
 916         }
 917
 918         /**
 919          * @param string $new_tag
 920          */
 921         private function flushLine( $new_tag ) {
 922                 $this->flushGroup( $new_tag );
 923                 if ( $this->line != '' ) {
 924                         array_push( $this->lines, $this->line );
 925                 } else {
 926                         # make empty lines visible by inserting an NBSP
 927                         array_push( $this->lines, '&#160;' );
 928                 }
 929                 $this->line = '';
 930         }
 931
 932         /**
 933          * @param string[] $words
 934          * @param string $tag
 935          */
 936         public function addWords( $words, $tag = '' ) {
 937                 if ( $tag != $this->tag ) {
 938                         $this->flushGroup( $tag );
 939                 }
 940
 941                 foreach ( $words as $word ) {
 942                         // new-line should only come as first char of word.
 943                         if ( $word == '' ) {
 944                                 continue;
 945                         }
 946                         if ( $word[0] == "\n" ) {
 947                                 $this->flushLine( $tag );
 948                                 $word = substr( $word, 1 );
 949                         }
 950                         assert( '!strstr( $word, "\n" )' );
 951                         $this->group .= $word;
 952                 }
 953         }
 954
 955         /**
 956          * @return string[]
 957          */
 958         public function getLines() {
 959                 $this->flushLine( '~done' );
 960
 961                 return $this->lines;
 962         }
 963 }
 964
 965 /**
 966  * @todo document
 967  * @private
 968  * @ingroup DifferenceEngine
 969  */
 970 class WordLevelDiff extends MappedDiff {
 971         const MAX_LINE_LENGTH = 10000;
 972
 973         /**
 974          * @param string[] $orig_lines
 975          * @param string[] $closing_lines
 976          */
 977         public function __construct( $orig_lines, $closing_lines ) {
 978
 979                 list( $orig_words, $orig_stripped ) = $this->split( $orig_lines );
 980                 list( $closing_words, $closing_stripped ) = $this->split( $closing_lines );
 981
 982                 parent::__construct( $orig_words, $closing_words,
 983                         $orig_stripped, $closing_stripped );
 984         }
 985
 986         /**
 987          * @param string[] $lines
 988          *
 989          * @return array[]
 990          */
 991         private function split( $lines ) {
 992
 993                 $words = array();
 994                 $stripped = array();
 995                 $first = true;
 996                 foreach ( $lines as $line ) {
 997                         # If the line is too long, just pretend the entire line is one big word
 998                         # This prevents resource exhaustion problems
 999                         if ( $first ) {
1000                                 $first = false;
1001                         } else {
1002                                 $words[] = "\n";
1003                                 $stripped[] = "\n";
1004                         }
1005                         if ( strlen( $line ) > self::MAX_LINE_LENGTH ) {
1006                                 $words[] = $line;
1007                                 $stripped[] = $line;
1008                         } else {
1009                                 $m = array();
1010                                 if ( preg_match_all( '/ ( [^\S\n]+ | [0-9_A-Za-z\x80-\xff]+ | . ) (?: (?!< \n) [^\S\n])? /xs',
1011                                         $line, $m )
1012                                 ) {
1013                                         foreach ( $m[0] as $word ) {
1014                                                 $words[] = $word;
1015                                         }
1016                                         foreach ( $m[1] as $stripped_word ) {
1017                                                 $stripped[] = $stripped_word;
1018                                         }
1019                                 }
1020                         }
1021                 }
1022
1023                 return array( $words, $stripped );
1024         }
1025
1026         /**
1027          * @return string[]
1028          */
1029         public function orig() {
1030                 $orig = new HWLDFWordAccumulator;
1031
1032                 foreach ( $this->edits as $edit ) {
1033                         if ( $edit->type == 'copy' ) {
1034                                 $orig->addWords( $edit->orig );
1035                         } elseif ( $edit->orig ) {
1036                                 $orig->addWords( $edit->orig, 'del' );
1037                         }
1038                 }
1039                 $lines = $orig->getLines();
1040
1041                 return $lines;
1042         }
1043
1044         /**
1045          * @return string[]
1046          */
1047         public function closing() {
1048                 $closing = new HWLDFWordAccumulator;
1049
1050                 foreach ( $this->edits as $edit ) {
1051                         if ( $edit->type == 'copy' ) {
1052                                 $closing->addWords( $edit->closing );
1053                         } elseif ( $edit->closing ) {
1054                                 $closing->addWords( $edit->closing, 'ins' );
1055                         }
1056                 }
1057                 $lines = $closing->getLines();
1058
1059                 return $lines;
1060         }
1061
1062 }