<?php

// A PHP diff engine for phpwiki. (Taken from phpwiki-1.3.3)

//

// Copyright (C) 2000, 2001 Geoffrey T. Dairiki <dairiki@dairiki.org>

// You may copy this code freely under the conditions of the GPL.

//

define('USE_ASSERTS', function_exists('assert'));

/**

 * @todo document

 * @package Enano

 * @subpackage DifferenceEngine

 */

class _DiffOp {

	var $type;

	var $orig;

	var $closing;

	function reverse() {

		trigger_error('pure virtual', E_USER_ERROR);

	}

	function norig() {

		return $this->orig ? sizeof($this->orig) : 0;

	}

	function nclosing() {

		return $this->closing ? sizeof($this->closing) : 0;

	}

}

/**

 * @todo document

 * @package Enano

 * @subpackage DifferenceEngine

 */

class _DiffOp_Copy extends _DiffOp {

	var $type = 'copy';

	function _DiffOp_Copy ($orig, $closing = false) {

		if (!is_array($closing))

			$closing = $orig;

		$this->orig = $orig;

		$this->closing = $closing;

	}

	function reverse() {

		return new _DiffOp_Copy($this->closing, $this->orig);

	}

}

/**

 * @todo document

 * @package Enano

 * @subpackage DifferenceEngine

 */

class _DiffOp_Delete extends _DiffOp {

	var $type = 'delete';

	function _DiffOp_Delete ($lines) {

		$this->orig = $lines;

		$this->closing = false;

	}

	function reverse() {

		return new _DiffOp_Add($this->orig);

	}

}

/**

 * @todo document

 * @package Enano

 * @subpackage DifferenceEngine

 */

class _DiffOp_Add extends _DiffOp {

	var $type = 'add';

	function _DiffOp_Add ($lines) {

		$this->closing = $lines;

		$this->orig = false;

	}

	function reverse() {

		return new _DiffOp_Delete($this->closing);

	}

}

/**

 * @todo document

 * @package Enano

 * @subpackage DifferenceEngine

 */

class _DiffOp_Change extends _DiffOp {

	var $type = 'change';

	function _DiffOp_Change ($orig, $closing) {

		$this->orig = $orig;

		$this->closing = $closing;

	}

	function reverse() {

		return new _DiffOp_Change($this->closing, $this->orig);

	}

}

/**

 * Class used internally by Diff to actually compute the diffs.

 *

 * The algorithm used here is mostly lifted from the perl module

 * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:

 *	 http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip

 *

 * More ideas are taken from:

 *	 http://www.ics.uci.edu/~eppstein/161/960229.html

 *

 * Some ideas are (and a bit of code) are from from analyze.c, from GNU

 * diffutils-2.7, which can be found at:

 *	 ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz

 *

 * closingly, some ideas (subdivision by NCHUNKS > 2, and some optimizations)

 * are my own.

 *

 * Line length limits for robustness added by Tim Starling, 2005-08-31

 *

 * @author Geoffrey T. Dairiki, Tim Starling

 * @package Enano

 * @subpackage DifferenceEngine

 */

define('MAX_XREF_LENGTH', 10000);

class _DiffEngine

{

	function diff ($from_lines, $to_lines) {

		$fname = '_DiffEngine::diff';

		// wfProfileIn( $fname );

		$n_from = sizeof($from_lines);

		$n_to = sizeof($to_lines);

		$this->xchanged = $this->ychanged = array();

		$this->xv = $this->yv = array();

		$this->xind = $this->yind = array();

		unset($this->seq);

		unset($this->in_seq);

		unset($this->lcs);

		// Skip leading common lines.

		for ($skip = 0; $skip < $n_from && $skip < $n_to; $skip++) {

			if ($from_lines[$skip] !== $to_lines[$skip])

				break;

			$this->xchanged[$skip] = $this->ychanged[$skip] = false;

		}

		// Skip trailing common lines.

		$xi = $n_from; $yi = $n_to;

		for ($endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++) {

			if ($from_lines[$xi] !== $to_lines[$yi])

				break;

			$this->xchanged[$xi] = $this->ychanged[$yi] = false;

		}

		// Ignore lines which do not exist in both files.

		for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {

			$xhash[$this->_line_hash($from_lines[$xi])] = 1;

		}

		for ($yi = $skip; $yi < $n_to - $endskip; $yi++) {

			$line = $to_lines[$yi];

			if ( ($this->ychanged[$yi] = empty($xhash[$this->_line_hash($line)])) )

				continue;

			$yhash[$this->_line_hash($line)] = 1;

			$this->yv[] = $line;

			$this->yind[] = $yi;

		}

		for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {

			$line = $from_lines[$xi];

			if ( ($this->xchanged[$xi] = empty($yhash[$this->_line_hash($line)])) )

				continue;

			$this->xv[] = $line;

			$this->xind[] = $xi;

		}

		// Find the LCS.

		$this->_compareseq(0, sizeof($this->xv), 0, sizeof($this->yv));

		// Merge edits when possible

		$this->_shift_boundaries($from_lines, $this->xchanged, $this->ychanged);

		$this->_shift_boundaries($to_lines, $this->ychanged, $this->xchanged);

		// Compute the edit operations.

		$edits = array();

		$xi = $yi = 0;

		while ($xi < $n_from || $yi < $n_to) {

			USE_ASSERTS && assert($yi < $n_to || $this->xchanged[$xi]);

			USE_ASSERTS && assert($xi < $n_from || $this->ychanged[$yi]);

			// Skip matching "snake".

			$copy = array();

			while ( $xi < $n_from && $yi < $n_to

					&& !$this->xchanged[$xi] && !$this->ychanged[$yi]) {

				$copy[] = $from_lines[$xi++];

				++$yi;

			}

			if ($copy)

				$edits[] = new _DiffOp_Copy($copy);

			// Find deletes & adds.

			$delete = array();

			while ($xi < $n_from && $this->xchanged[$xi])

				$delete[] = $from_lines[$xi++];

			$add = array();

			while ($yi < $n_to && $this->ychanged[$yi])

				$add[] = $to_lines[$yi++];

			if ($delete && $add)

				$edits[] = new _DiffOp_Change($delete, $add);

			elseif ($delete)

				$edits[] = new _DiffOp_Delete($delete);

			elseif ($add)

				$edits[] = new _DiffOp_Add($add);

		}

		// wfProfileOut( $fname );

		return $edits;

	}

	/**

	 * Returns the whole line if it's small enough, or the MD5 hash otherwise

	 */

	function _line_hash( $line ) {

		if ( strlen( $line ) > MAX_XREF_LENGTH ) {

			return md5( $line );

		} else {

			return $line;

		}

	}

	/* Divide the Largest Common Subsequence (LCS) of the sequences

	 * [XOFF, XLIM) and [YOFF, YLIM) into NCHUNKS approximately equally

	 * sized segments.

	 *

	 * Returns (LCS, PTS).	LCS is the length of the LCS. PTS is an

	 * array of NCHUNKS+1 (X, Y) indexes giving the diving points between

	 * sub sequences.  The first sub-sequence is contained in [X0, X1),

	 * [Y0, Y1), the second in [X1, X2), [Y1, Y2) and so on.  Note

	 * that (X0, Y0) == (XOFF, YOFF) and

	 * (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).

	 *

	 * This function assumes that the first lines of the specified portions

	 * of the two files do not match, and likewise that the last lines do not

	 * match.  The caller must trim matching lines from the beginning and end

	 * of the portions it is going to specify.

	 */

	function _diag ($xoff, $xlim, $yoff, $ylim, $nchunks) {

		$fname = '_DiffEngine::_diag';

		// wfProfileIn( $fname );

		$flip = false;

		if ($xlim - $xoff > $ylim - $yoff) {

			// Things seems faster (I'm not sure I understand why)

				// when the shortest sequence in X.

				$flip = true;

			list ($xoff, $xlim, $yoff, $ylim)

			= array( $yoff, $ylim, $xoff, $xlim);

		}

		if ($flip)

			for ($i = $ylim - 1; $i >= $yoff; $i--)

				$ymatches[$this->xv[$i]][] = $i;

		else

			for ($i = $ylim - 1; $i >= $yoff; $i--)

				$ymatches[$this->yv[$i]][] = $i;

		$this->lcs = 0;

		$this->seq[0]= $yoff - 1;

		$this->in_seq = array();

		$ymids[0] = array();

		$numer = $xlim - $xoff + $nchunks - 1;

		$x = $xoff;

		for ($chunk = 0; $chunk < $nchunks; $chunk++) {

			// wfProfileIn( "$fname-chunk" );

			if ($chunk > 0)

				for ($i = 0; $i <= $this->lcs; $i++)

					$ymids[$i][$chunk-1] = $this->seq[$i];

			$x1 = $xoff + (int)(($numer + ($xlim-$xoff)*$chunk) / $nchunks);

			for ( ; $x < $x1; $x++) {

				$line = $flip ? $this->yv[$x] : $this->xv[$x];

					if (empty($ymatches[$line]))

						continue;

				$matches = $ymatches[$line];

				reset($matches);

				while (list ($junk, $y) = each($matches))

					if (empty($this->in_seq[$y])) {

						$k = $this->_lcs_pos($y);

						USE_ASSERTS && assert($k > 0);

						$ymids[$k] = $ymids[$k-1];

						break;

					}

				while (list ($junk, $y) = each($matches)) {

					if ($y > $this->seq[$k-1]) {

						USE_ASSERTS && assert($y < $this->seq[$k]);

						// Optimization: this is a common case:

						//	next match is just replacing previous match.

						$this->in_seq[$this->seq[$k]] = false;

						$this->seq[$k] = $y;

						$this->in_seq[$y] = 1;

					} else if (empty($this->in_seq[$y])) {

						$k = $this->_lcs_pos($y);

						USE_ASSERTS && assert($k > 0);

						$ymids[$k] = $ymids[$k-1];

					}

				}

			}

			// wfProfileOut( "$fname-chunk" );

		}

		$seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff);

		$ymid = $ymids[$this->lcs];

		for ($n = 0; $n < $nchunks - 1; $n++) {

			$x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $n) / $nchunks);

			$y1 = $ymid[$n] + 1;

			$seps[] = $flip ? array($y1, $x1) : array($x1, $y1);

		}

		$seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim);

		// wfProfileOut( $fname );

		return array($this->lcs, $seps);

	}

	function _lcs_pos ($ypos) {

		$fname = '_DiffEngine::_lcs_pos';

		// wfProfileIn( $fname );

		$end = $this->lcs;

		if ($end == 0 || $ypos > $this->seq[$end]) {

			$this->seq[++$this->lcs] = $ypos;

			$this->in_seq[$ypos] = 1;

			// wfProfileOut( $fname );

			return $this->lcs;

		}

		$beg = 1;

		while ($beg < $end) {

			$mid = (int)(($beg + $end) / 2);

			if ( $ypos > $this->seq[$mid] )

				$beg = $mid + 1;

			else

				$end = $mid;

		}

		USE_ASSERTS && assert($ypos != $this->seq[$end]);

		$this->in_seq[$this->seq[$end]] = false;

		$this->seq[$end] = $ypos;

		$this->in_seq[$ypos] = 1;

		// wfProfileOut( $fname );

		return $end;

	}

	/* Find LCS of two sequences.

	 *

	 * The results are recorded in the vectors $this->{x,y}changed[], by

	 * storing a 1 in the element for each line that is an insertion

	 * or deletion (ie. is not in the LCS).

	 *

	 * The subsequence of file 0 is [XOFF, XLIM) and likewise for file 1.

	 *

	 * Note that XLIM, YLIM are exclusive bounds.

	 * All line numbers are origin-0 and discarded lines are not counted.

	 */

	function _compareseq ($xoff, $xlim, $yoff, $ylim) {

		$fname = '_DiffEngine::_compareseq';

		// wfProfileIn( $fname );

		// Slide down the bottom initial diagonal.

		while ($xoff < $xlim && $yoff < $ylim

			   && $this->xv[$xoff] == $this->yv[$yoff]) {

			++$xoff;

			++$yoff;

		}

		// Slide up the top initial diagonal.

		while ($xlim > $xoff && $ylim > $yoff

			   && $this->xv[$xlim - 1] == $this->yv[$ylim - 1]) {

			--$xlim;

			--$ylim;

		}

		if ($xoff == $xlim || $yoff == $ylim)

			$lcs = 0;

		else {

			// This is ad hoc but seems to work well.

			//$nchunks = sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5);

			//$nchunks = max(2,min(8,(int)$nchunks));

			$nchunks = min(7, $xlim - $xoff, $ylim - $yoff) + 1;

			list ($lcs, $seps)

			= $this->_diag($xoff,$xlim,$yoff, $ylim,$nchunks);

		}

		if ($lcs == 0) {

			// X and Y sequences have no common subsequence:

			// mark all changed.

			while ($yoff < $ylim)

				$this->ychanged[$this->yind[$yoff++]] = 1;

			while ($xoff < $xlim)

				$this->xchanged[$this->xind[$xoff++]] = 1;

		} else {

			// Use the partitions to split this problem into subproblems.

			reset($seps);

			$pt1 = $seps[0];

			while ($pt2 = next($seps)) {

				$this->_compareseq ($pt1[0], $pt2[0], $pt1[1], $pt2[1]);

				$pt1 = $pt2;

			}

		}

		// wfProfileOut( $fname );

	}

	/* Adjust inserts/deletes of identical lines to join changes

	 * as much as possible.

	 *

	 * We do something when a run of changed lines include a

	 * line at one end and has an excluded, identical line at the other.

	 * We are free to choose which identical line is included.

	 * `compareseq' usually chooses the one at the beginning,

	 * but usually it is cleaner to consider the following identical line

	 * to be the "change".

	 *

	 * This is extracted verbatim from analyze.c (GNU diffutils-2.7).

	 */

	function _shift_boundaries ($lines, &$changed, $other_changed) {

		$fname = '_DiffEngine::_shift_boundaries';

		// wfProfileIn( $fname );

		$i = 0;

		$j = 0;

		USE_ASSERTS && assert('sizeof($lines) == sizeof($changed)');

		$len = sizeof($lines);

		$other_len = sizeof($other_changed);

		while (1) {

			/*

			 * Scan forwards to find beginning of another run of changes.

			 * Also keep track of the corresponding point in the other file.

			 *

			 * Throughout this code, $i and $j are adjusted together so that

			 * the first $i elements of $changed and the first $j elements

			 * of $other_changed both contain the same number of zeros

			 * (unchanged lines).

			 * Furthermore, $j is always kept so that $j == $other_len or

			 * $other_changed[$j] == false.

			 */

			while ($j < $other_len && $other_changed[$j])

				$j++;

			while ($i < $len && ! $changed[$i]) {

				USE_ASSERTS && assert('$j < $other_len && ! $other_changed[$j]');

				$i++; $j++;

				while ($j < $other_len && $other_changed[$j])

					$j++;

			}

			if ($i == $len)

				break;

			$start = $i;

			// Find the end of this run of changes.

			while (++$i < $len && $changed[$i])

				continue;

			do {

				/*

				 * Record the length of this run of changes, so that

				 * we can later determine whether the run has grown.

				 */

				$runlength = $i - $start;

				/*

				 * Move the changed region back, so long as the

				 * previous unchanged line matches the last changed one.

				 * This merges with previous changed regions.

				 */

				while ($start > 0 && $lines[$start - 1] == $lines[$i - 1]) {

					$changed[--$start] = 1;

					$changed[--$i] = false;

					while ($start > 0 && $changed[$start - 1])

						$start--;

					USE_ASSERTS && assert('$j > 0');

					while ($other_changed[--$j])

						continue;

					USE_ASSERTS && assert('$j >= 0 && !$other_changed[$j]');

				}

				/*

				 * Set CORRESPONDING to the end of the changed run, at the last

				 * point where it corresponds to a changed run in the other file.

				 * CORRESPONDING == LEN means no such point has been found.

				 */

				$corresponding = $j < $other_len ? $i : $len;

				/*

				 * Move the changed region forward, so long as the

				 * first changed line matches the following unchanged one.

				 * This merges with following changed regions.

				 * Do this second, so that if there are no merges,

				 * the changed region is moved forward as far as possible.

				 */

				while ($i < $len && $lines[$start] == $lines[$i]) {

					$changed[$start++] = false;

					$changed[$i++] = 1;

					while ($i < $len && $changed[$i])

						$i++;

					USE_ASSERTS && assert('$j < $other_len && ! $other_changed[$j]');

					$j++;

					if ($j < $other_len && $other_changed[$j]) {

						$corresponding = $i;

						while ($j < $other_len && $other_changed[$j])

							$j++;

					}

				}

			} while ($runlength != $i - $start);