<?php
/**
 * A PHP diff engine for phpwiki. (Taken from phpwiki-1.3.3)
 *
 * Copyright © 2000, 2001 Geoffrey T. Dairiki <dairiki@dairiki.org>
 * You may copy this code freely under the conditions of the GPL.
 *
 * @file
 * @ingroup DifferenceEngine
 * @defgroup DifferenceEngine DifferenceEngine
 */
if( !defined('EVO_MAIN_INIT') ) die( 'Please, do not access this page directly.' );

/**
 * @todo document
 * @private
 * @ingroup 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
 * @private
 * @ingroup DifferenceEngine
 */
class _DiffOp_Copy extends _DiffOp {
	var $type = 'copy';

	function __construct( $orig, $closing = false ) {
		if ( !is_array( $closing ) ) {
			$closing = $orig;
		}
		$this->orig = $orig;
		$this->closing = $closing;
	}

	function reverse() {
		return new _DiffOp_Copy( $this->closing, $this->orig );
	}
}

/**
 * @todo document
 * @private
 * @ingroup DifferenceEngine
 */
class _DiffOp_Delete extends _DiffOp {
	var $type = 'delete';

	function __construct( $lines ) {
		$this->orig = $lines;
		$this->closing = false;
	}

	function reverse() {
		return new _DiffOp_Add( $this->orig );
	}
}

/**
 * @todo document
 * @private
 * @ingroup DifferenceEngine
 */
class _DiffOp_Add extends _DiffOp {
	var $type = 'add';

	function __construct( $lines ) {
		$this->closing = $lines;
		$this->orig = false;
	}

	function reverse() {
		return new _DiffOp_Delete( $this->closing );
	}
}

/**
 * @todo document
 * @private
 * @ingroup DifferenceEngine
 */
class _DiffOp_Change extends _DiffOp {
	var $type = 'change';

	function __construct( $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
 * Alternative implementation added by Guy Van den Broeck, 2008-07-30
 *
 * @author Geoffrey T. Dairiki, Tim Starling, Guy Van den Broeck
 * @private
 * @ingroup DifferenceEngine
 */
class _DiffEngine {

	const MAX_XREF_LENGTH =  10000;

	protected $xchanged, $ychanged;

	protected $xv = array(), $yv = array();
	protected $xind = array(), $yind = array();

	protected $seq = array(), $in_seq = array();

	protected $lcs = 0;

	function diff ( $from_lines, $to_lines ) {

		// Diff and store locally
		$this->diff_local( $from_lines, $to_lines );

		// Merge edits when possible
		$this->_shift_boundaries( $from_lines, $this->xchanged, $this->ychanged );
		$this->_shift_boundaries( $to_lines, $this->ychanged, $this->xchanged );

		// Compute the edit operations.
		$n_from = sizeof( $from_lines );
		$n_to = sizeof( $to_lines );

		$edits = array();
		$xi = $yi = 0;
		while ( $xi < $n_from || $yi < $n_to ) {
			assert( $yi < $n_to || $this->xchanged[$xi] );
			assert( $xi < $n_from || $this->ychanged[$yi] );

			// Skip matching "snake".
			$copy = array();
			while ( $xi < $n_from && $yi < $n_to
			&& !$this->xchanged[$xi] && !$this->ychanged[$yi] ) {
				$copy[] = $from_lines[$xi++];
				++$yi;
			}
			if ( $copy ) {
				$edits[] = new _DiffOp_Copy( $copy );
			}

			// Find deletes & adds.
			$delete = array();
			while ( $xi < $n_from && $this->xchanged[$xi] ) {
				$delete[] = $from_lines[$xi++];
			}

			$add = array();
			while ( $yi < $n_to && $this->ychanged[$yi] )  {
				$add[] = $to_lines[$yi++];
			}

			if ( $delete && $add ) {
				$edits[] = new _DiffOp_Change( $delete, $add );
			} elseif ( $delete ) {
				$edits[] = new _DiffOp_Delete( $delete );
			} elseif ( $add ) {
				$edits[] = new _DiffOp_Add( $add );
			}
		}
		return $edits;
	}

	function diff_local ( $from_lines, $to_lines ) {
		global $wgExternalDiffEngine;

		if ( $wgExternalDiffEngine == 'wikidiff3' ) {
			// wikidiff3
			$wikidiff3 = new WikiDiff3();
			$wikidiff3->diff( $from_lines, $to_lines );
			$this->xchanged = $wikidiff3->removed;
			$this->ychanged = $wikidiff3->added;
			unset( $wikidiff3 );
		} else {
			// old diff
			$n_from = sizeof( $from_lines );
			$n_to = sizeof( $to_lines );
			$this->xchanged = $this->ychanged = array();
			$this->xv = $this->yv = array();
			$this->xind = $this->yind = array();
			unset( $this->seq );
			unset( $this->in_seq );
			unset( $this->lcs );

			// Skip leading common lines.
			for ( $skip = 0; $skip < $n_from && $skip < $n_to; $skip++ ) {
				if ( $from_lines[$skip] !== $to_lines[$skip] ) {
					break;
				}
				$this->xchanged[$skip] = $this->ychanged[$skip] = false;
			}
			// Skip trailing common lines.
			$xi = $n_from; $yi = $n_to;
			for ( $endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++ ) {
				if ( $from_lines[$xi] !== $to_lines[$yi] ) {
					break;
				}
				$this->xchanged[$xi] = $this->ychanged[$yi] = false;
			}

			// 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 ) );
		}
	}

	/**
	 * Returns the whole line if it's small enough, or the MD5 hash otherwise
	 */
	function _line_hash( $line ) {
		if ( strlen( $line ) > self::MAX_XREF_LENGTH ) {
			return md5( $line );
		} else {
			return $line;
		}
	}

	/**
	 * Divide the Largest Common Subsequence (LCS) of the sequences
	 * [XOFF, XLIM) and [YOFF, YLIM) into NCHUNKS approximately equally
	 * sized segments.
	 *
	 * Returns (LCS, PTS).	LCS is the length of the LCS. PTS is an
	 * array of NCHUNKS+1 (X, Y) indexes giving the diving points between
	 * sub sequences.  The first sub-sequence is contained in [X0, X1),
	 * [Y0, Y1), the second in [X1, X2), [Y1, Y2) and so on.  Note
	 * that (X0, Y0) == (XOFF, YOFF) and
	 * (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
	 *
	 * This function assumes that the first lines of the specified portions
	 * of the two files do not match, and likewise that the last lines do not
	 * match.  The caller must trim matching lines from the beginning and end
	 * of the portions it is going to specify.
	 */
	function _diag( $xoff, $xlim, $yoff, $ylim, $nchunks ) {
		$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++ ) {
			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 );
				$y = current( $matches );
				while( $y !== false ) {
					if ( empty( $this->in_seq[$y] ) ) {
						$k = $this->_lcs_pos( $y );
						assert( $k > 0 );
						$ymids[$k] = $ymids[$k -1];
						$y = next( $matches );
						break;
					}
					$y = next( $matches );
				}
				while( $y !== false ) {
					if ( $y > $this->seq[$k -1] ) {
						assert( $y < $this->seq[$k] );
						// Optimization: this is a common case:
						//	next match is just replacing previous match.
						$this->in_seq[$this->seq[$k]] = false;
						$this->seq[$k] = $y;
						$this->in_seq[$y] = 1;
					} elseif ( empty( $this->in_seq[$y] ) ) {
						$k = $this->_lcs_pos( $y );
						assert( $k > 0 );
						$ymids[$k] = $ymids[$k -1];
					}
					$y = next( $matches );
				}
			}
		}

		$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 );

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

	function _lcs_pos( $ypos ) {
		$end = $this->lcs;
		if ( $end == 0 || $ypos > $this->seq[$end] ) {
			$this->seq[++$this->lcs] = $ypos;
			$this->in_seq[$ypos] = 1;
			return $this->lcs;
		}

		$beg = 1;
		while ( $beg < $end ) {
			$mid = (int)( ( $beg + $end ) / 2 );
			if ( $ypos > $this->seq[$mid] ) {
				$beg = $mid + 1;
			} else {
				$end = $mid;
			}
		}

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

		$this->in_seq[$this->seq[$end]] = false;
		$this->seq[$end] = $ypos;
		$this->in_seq[$ypos] = 1;
		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 ) {
		// 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;
			}
		}
	}

	/**
	 * 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 ) {
		$i = 0;
		$j = 0;

		assert( sizeof($lines) == sizeof($changed) );
		$len = sizeof( $lines );
		$other_len = sizeof( $other_changed );

		while ( 1 ) {
			/*
			 * Scan forwards to find beginning of another run of changes.
			 * Also keep track of the corresponding point in the other file.
			 *
			 * Throughout this code, $i and $j are adjusted together so that
			 * the first $i elements of $changed and the first $j elements
			 * of $other_changed both contain the same number of zeros
			 * (unchanged lines).
			 * Furthermore, $j is always kept so that $j == $other_len or
			 * $other_changed[$j] == false.
			 */
			while ( $j < $other_len && $other_changed[$j] ) {
				$j++;
			}

			while ( $i < $len && ! $changed[$i] ) {
				assert( $j < $other_len && ! $other_changed[$j] );
				$i++; $j++;
				while ( $j < $other_len && $other_changed[$j] )
				$j++;
			}

			if ( $i == $len ) {
				break;
			}

			$start = $i;

			// Find the end of this run of changes.
			while ( ++$i < $len && $changed[$i] ) {
				continue;
			}

			do {
				/*
				 * Record the length of this run of changes, so that
				 * we can later determine whether the run has grown.
				 */
				$runlength = $i - $start;

				/*
				 * Move the changed region back, so long as the
				 * previous unchanged line matches the last changed one.
				 * This merges with previous changed regions.
				 */
				while ( $start > 0 && $lines[$start - 1] == $lines[$i - 1] ) {
					$changed[--$start] = 1;
					$changed[--$i] = false;
					while ( $start > 0 && $changed[$start - 1] ) {
						$start--;
					}
					assert( $j > 0 );
					while ( $other_changed[--$j] ) {
						continue;
					}
					assert( $j >= 0 && !$other_changed[$j] );
				}

				/*
				 * Set CORRESPONDING to the end of the changed run, at the last
				 * point where it corresponds to a changed run in the other file.
				 * CORRESPONDING == LEN means no such point has been found.
				 */
				$corresponding = $j < $other_len ? $i : $len;

				/*
				 * Move the changed region forward, so long as the
				 * first changed line matches the following unchanged one.
				 * This merges with following changed regions.
				 * Do this second, so that if there are no merges,
				 * the changed region is moved forward as far as possible.
				 */
				while ( $i < $len && $lines[$start] == $lines[$i] ) {
					$changed[$start++] = false;
					$changed[$i++] = 1;
					while ( $i < $len && $changed[$i] ) {
						$i++;
					}

					assert( $j < $other_len && ! $other_changed[$j] );
					$j++;
					if ( $j < $other_len && $other_changed[$j] ) {
						$corresponding = $i;
						while ( $j < $other_len && $other_changed[$j] ) {
							$j++;
						}
					}
				}
			} while ( $runlength != $i - $start );

			/*
			 * If possible, move the fully-merged run of changes
			 * back to a corresponding run in the other file.
			 */
			while ( $corresponding < $i ) {
				$changed[--$start] = 1;
				$changed[--$i] = 0;
				assert( $j > 0 );
				while ( $other_changed[--$j] ) {
					continue;
				}
				assert( $j >= 0 && !$other_changed[$j] );
			}
		}
	}
}

/**
 * Class representing a 'diff' between two sequences of strings.
 * @todo document
 * @private
 * @ingroup DifferenceEngine
 */
class Diff {
	var $edits;

	/**
	 * Constructor.
	 * Computes diff between sequences of strings.
	 *
	 * @param $from_lines array An array of strings.
	 *		  (Typically these are lines from a file.)
	 * @param $to_lines array An array of strings.
	 */
	function __construct( $from_lines, $to_lines ) {
		$eng = new _DiffEngine;
		$this->edits = $eng->diff( $from_lines, $to_lines );
		// $this->_check($from_lines, $to_lines);
	}

	/**
	 * Compute reversed Diff.
	 *
	 * SYNOPSIS:
	 *
	 *	$diff = new Diff($lines1, $lines2);
	 *	$rev = $diff->reverse();
	 * @return object A Diff object representing the inverse of the
	 *				  original diff.
	 */
	function reverse() {
		$rev = $this;
		$rev->edits = array();
		foreach ( $this->edits as $edit ) {
			$rev->edits[] = $edit->reverse();
		}
		return $rev;
	}

	/**
	 * Check for empty diff.
	 *
	 * @return bool True iff two sequences were identical.
	 */
	function isEmpty() {
		foreach ( $this->edits as $edit ) {
			if ( $edit->type != 'copy' ) {
				return false;
			}
		}
		return true;
	}

	/**
	 * Compute the length of the Longest Common Subsequence (LCS).
	 *
	 * This is mostly for diagnostic purposed.
	 *
	 * @return int The length of the LCS.
	 */
	function lcs() {
		$lcs = 0;
		foreach ( $this->edits as $edit ) {
			if ( $edit->type == 'copy' ) {
				$lcs += sizeof( $edit->orig );
			}
		}
		return $lcs;
	}

	/**
	 * Get the original set of lines.
	 *
	 * This reconstructs the $from_lines parameter passed to the
	 * constructor.
	 *
	 * @return array The original sequence of strings.
	 */
	function orig() {
		$lines = array();

		foreach ( $this->edits as $edit ) {
			if ( $edit->orig ) {
				array_splice( $lines, sizeof( $lines ), 0, $edit->orig );
			}
		}
		return $lines;
	}

	/**
	 * Get the closing set of lines.
	 *
	 * This reconstructs the $to_lines parameter passed to the
	 * constructor.
	 *
	 * @return array The sequence of strings.
	 */
	function closing() {
		$lines = array();

		foreach ( $this->edits as $edit ) {
			if ( $edit->closing ) {
				array_splice( $lines, sizeof( $lines ), 0, $edit->closing );
			}
		}
		return $lines;
	}

	/**
	 * Check a Diff for validity.
	 *
	 * This is here only for debugging purposes.
	 */
	function _check( $from_lines, $to_lines ) {
		if ( serialize( $from_lines ) != serialize( $this->orig() ) ) {
			trigger_error( "Reconstructed original doesn't match", E_USER_ERROR );
		}
		if ( serialize( $to_lines ) != serialize( $this->closing() ) ) {
			trigger_error( "Reconstructed closing doesn't match", E_USER_ERROR );
		}

		$rev = $this->reverse();
		if ( serialize( $to_lines ) != serialize( $rev->orig() ) ) {
			trigger_error( "Reversed original doesn't match", E_USER_ERROR );
		}
		if ( serialize( $from_lines ) != serialize( $rev->closing() ) ) {
			trigger_error( "Reversed closing doesn't match", E_USER_ERROR );
		}


		$prevtype = 'none';
		foreach ( $this->edits as $edit ) {
			if ( $prevtype == $edit->type ) {
				trigger_error( 'Edit sequence is non-optimal', E_USER_ERROR );
			}
			$prevtype = $edit->type;
		}

		$lcs = $this->lcs();
		trigger_error( 'Diff okay: LCS = ' . $lcs, E_USER_NOTICE );
	}
}

/**
 * @todo document, bad name.
 * @private
 * @ingroup DifferenceEngine
 */
class MappedDiff extends Diff {
	/**
	 * Constructor.
	 *
	 * Computes diff between sequences of strings.
	 *
	 * This can be used to compute things like
	 * case-insensitve diffs, or diffs which ignore
	 * changes in white-space.
	 *
	 * @param $from_lines array An array of strings.
	 *	(Typically these are lines from a file.)
	 *
	 * @param $to_lines array An array of strings.
	 *
	 * @param $mapped_from_lines array This array should
	 *	have the same size number of elements as $from_lines.
	 *	The elements in $mapped_from_lines and
	 *	$mapped_to_lines are what is actually compared
	 *	when computing the diff.
	 *
	 * @param $mapped_to_lines array This array should
	 *	have the same number of elements as $to_lines.
	 */
	function __construct( $from_lines, $to_lines,
		$mapped_from_lines, $mapped_to_lines ) {

		assert( sizeof( $from_lines ) == sizeof( $mapped_from_lines ) );
		assert( sizeof( $to_lines ) == sizeof( $mapped_to_lines ) );

		parent::__construct( $mapped_from_lines, $mapped_to_lines );

		$xi = $yi = 0;
		for ( $i = 0; $i < sizeof( $this->edits ); $i++ ) {
			$orig = &$this->edits[$i]->orig;
			if ( is_array( $orig ) ) {
				$orig = array_slice( $from_lines, $xi, sizeof( $orig ) );
				$xi += sizeof( $orig );
			}

			$closing = &$this->edits[$i]->closing;
			if ( is_array( $closing ) ) {
				$closing = array_slice( $to_lines, $yi, sizeof( $closing ) );
				$yi += sizeof( $closing );
			}
		}
	}
}

/**
 * A class to format Diffs
 *
 * This class formats the diff in classic diff format.
 * It is intended that this class be customized via inheritance,
 * to obtain fancier outputs.
 * @todo document
 * @private
 * @ingroup DifferenceEngine
 */
class DiffFormatter {
	/**
	 * Number of leading context "lines" to preserve.
	 *
	 * This should be left at zero for this class, but subclasses
	 * may want to set this to other values.
	 */
	var $leading_context_lines = 0;

	/**
	 * Number of trailing context "lines" to preserve.
	 *
	 * This should be left at zero for this class, but subclasses
	 * may want to set this to other values.
	 */
	var $trailing_context_lines = 0;

	/**
	 * Format a diff.
	 *
	 * @param $diff Diff A Diff object.
	 * @return string The formatted output.
	 */
	function format( $diff ) {

		$xi = $yi = 1;
		$block = false;
		$context = array();

		$nlead = $this->leading_context_lines;
		$ntrail = $this->trailing_context_lines;

		$this->_start_diff();

		foreach ( $diff->edits as $edit ) {
			if ( $edit->type == 'copy' ) {
				if ( is_array( $block ) ) {
					if ( sizeof( $edit->orig ) <= $nlead + $ntrail ) {
						$block[] = $edit;
					} else {
						if ( $ntrail ) {
							$context = array_slice( $edit->orig, 0, $ntrail );
							$block[] = new _DiffOp_Copy( $context );
						}
						$this->_block( $x0, $ntrail + $xi - $x0,
							$y0, $ntrail + $yi - $y0,
							$block );
						$block = false;
					}
				}
				$context = $edit->orig;
			} else {
				if ( !is_array( $block ) ) {
					$context = array_slice( $context, sizeof( $context ) - $nlead );
					$x0 = $xi - sizeof( $context );
					$y0 = $yi - sizeof( $context );
					$block = array();
					if ( $context ) {
						$block[] = new _DiffOp_Copy( $context );
					}
				}
				$block[] = $edit;
			}

			if ( $edit->orig ) {
				$xi += sizeof( $edit->orig );
			}
			if ( $edit->closing ) {
				$yi += sizeof( $edit->closing );
			}
		}

		if ( is_array( $block ) ) {
			$this->_block( $x0, $xi - $x0,
				$y0, $yi - $y0,
				$block );
		}

		$end = $this->_end_diff();
		return $end;
	}

	function _block( $xbeg, $xlen, $ybeg, $ylen, &$edits ) {
		$this->_start_block( $this->_block_header( $xbeg, $xlen, $ybeg, $ylen ) );
		foreach ( $edits as $edit ) {
			if ( $edit->type == 'copy' ) {
				$this->_context( $edit->orig );
			} elseif ( $edit->type == 'add' ) {
				$this->_added( $edit->closing );
			} elseif ( $edit->type == 'delete' ) {
				$this->_deleted( $edit->orig );
			} elseif ( $edit->type == 'change' ) {
				$this->_changed( $edit->orig, $edit->closing );
			} else {
				trigger_error( 'Unknown edit type', E_USER_ERROR );
			}
		}
		$this->_end_block();
	}

	function _start_diff() {
		ob_start();
	}

	function _end_diff() {
		$val = ob_get_contents();
		ob_end_clean();
		return $val;
	}

	function _block_header( $xbeg, $xlen, $ybeg, $ylen ) {
		if ( $xlen > 1 ) {
			$xbeg .= ',' . ( $xbeg + $xlen - 1 );
		}
		if ( $ylen > 1 ) {
			$ybeg .= ',' . ( $ybeg + $ylen - 1 );
		}

		return $xbeg . ( $xlen ? ( $ylen ? 'c' : 'd' ) : 'a' ) . $ybeg;
	}

	function _start_block( $header ) {
		echo $header . "\n";
	}

	function _end_block() {
	}

	function _lines( $lines, $prefix = ' ' ) {
		foreach ( $lines as $line ) {
			echo "$prefix $line\n";
		}
	}

	function _context( $lines ) {
		$this->_lines( $lines );
	}

	function _added( $lines ) {
		$this->_lines( $lines, '>' );
	}
	function _deleted( $lines ) {
		$this->_lines( $lines, '<' );
	}

	function _changed( $orig, $closing ) {
		$this->_deleted( $orig );
		echo "---\n";
		$this->_added( $closing );
	}
}

/**
 * A formatter that outputs unified diffs
 * @ingroup DifferenceEngine
 */
class UnifiedDiffFormatter extends DiffFormatter {
	var $leading_context_lines = 2;
	var $trailing_context_lines = 2;

	function _added( $lines ) {
		$this->_lines( $lines, '+' );
	}
	function _deleted( $lines ) {
		$this->_lines( $lines, '-' );
	}
	function _changed( $orig, $closing ) {
		$this->_deleted( $orig );
		$this->_added( $closing );
	}
	function _block_header( $xbeg, $xlen, $ybeg, $ylen ) {
		return "@@ -$xbeg,$xlen +$ybeg,$ylen @@";
	}
}

/**
 * A pseudo-formatter that just passes along the Diff::$edits array
 * @ingroup DifferenceEngine
 */
class ArrayDiffFormatter extends DiffFormatter {
	function format( $diff ) {
		$oldline = 1;
		$newline = 1;
		$retval = array();
		foreach ( $diff->edits as $edit ) {
			switch( $edit->type ) {
				case 'add':
					foreach ( $edit->closing as $l ) {
						$retval[] = array(
							'action' => 'add',
							'new' => $l,
							'newline' => $newline++
						);
					}
					break;
				case 'delete':
					foreach ( $edit->orig as $l ) {
						$retval[] = array(
							'action' => 'delete',
							'old' => $l,
							'oldline' => $oldline++,
						);
					}
					break;
				case 'change':
					foreach ( $edit->orig as $i => $l ) {
						$retval[] = array(
							'action' => 'change',
							'old' => $l,
							'new' => isset( $edit->closing[$i] ) ? $edit->closing[$i] : null,
							'oldline' => $oldline++,
							'newline' => $newline++,
						);
					}
					break;
				case 'copy':
					$oldline += count( $edit->orig );
					$newline += count( $edit->orig );
			}
		}
		return $retval;
	}
}

/**
 * Additions by Axel Boldt follow, partly taken from diff.php, phpwiki-1.3.3
 */

define( 'NBSP', '&#160;' ); // iso-8859-x non-breaking space.

/**
 * @todo document
 * @private
 * @ingroup DifferenceEngine
 */
class _HWLDF_WordAccumulator {
	function __construct() {
		$this->_lines = array();
		$this->_line = '';
		$this->_group = '';
		$this->_tag = '';
	}

	function _flushGroup( $new_tag ) {
		if ( $this->_group !== '' ) {
			if ( $this->_tag == 'ins' ) {
				$this->_line .= '<ins class="diffchange diffchange-inline">' .
						htmlspecialchars( $this->_group ) . '</ins>';
			} elseif ( $this->_tag == 'del' ) {
				$this->_line .= '<del class="diffchange diffchange-inline">' .
						htmlspecialchars( $this->_group ) . '</del>';
			} else {
				$this->_line .= htmlspecialchars( $this->_group );
			}
		}
		$this->_group = '';
		$this->_tag = $new_tag;
	}

	function _flushLine( $new_tag ) {
		$this->_flushGroup( $new_tag );
		if ( $this->_line != '' ) {
			array_push( $this->_lines, $this->_line );
		} else {
			# make empty lines visible by inserting an NBSP
			array_push( $this->_lines, NBSP );
		}
		$this->_line = '';
	}

	function addWords ( $words, $tag = '' ) {
		if ( $tag != $this->_tag ) {
			$this->_flushGroup( $tag );
		}

		foreach ( $words as $word ) {
			// new-line should only come as first char of word.
			if ( $word == '' ) {
				continue;
			}
			if ( $word[0] == "\n" ) {
				$this->_flushLine( $tag );
				$word = substr( $word, 1 );
			}
			assert( !strstr( $word, "\n" ) );
			$this->_group .= $word;
		}
	}

	function getLines() {
		$this->_flushLine( '~done' );
		return $this->_lines;
	}
}

/**
 * @todo document
 * @private
 * @ingroup DifferenceEngine
 */
class WordLevelDiff extends MappedDiff {
	const MAX_LINE_LENGTH = 10000;

	function __construct ( $orig_lines, $closing_lines ) {

		list( $orig_words, $orig_stripped ) = $this->_split( $orig_lines );
		list( $closing_words, $closing_stripped ) = $this->_split( $closing_lines );

		parent::__construct( $orig_words, $closing_words,
		$orig_stripped, $closing_stripped );
	}

	function _split( $lines ) {

		$words = array();
		$stripped = array();
		$first = true;
		foreach ( $lines as $line ) {
			# If the line is too long, just pretend the entire line is one big word
			# This prevents resource exhaustion problems
			if ( $first ) {
				$first = false;
			} else {
				$words[] = "\n";
				$stripped[] = "\n";
			}
			if ( strlen( $line ) > self::MAX_LINE_LENGTH ) {
				$words[] = $line;
				$stripped[] = $line;
			} else {
				$m = array();
				if ( preg_match_all( '/ ( [^\S\n]+ | [0-9_A-Za-z\x80-\xff]+ | . ) (?: (?!< \n) [^\S\n])? /xs',
					$line, $m ) )
				{
					$words = array_merge( $words, $m[0] );
					$stripped = array_merge( $stripped, $m[1] );
				}
			}
		}
		return array( $words, $stripped );
	}

	function orig() {
		$orig = new _HWLDF_WordAccumulator;

		foreach ( $this->edits as $edit ) {
			if ( $edit->type == 'copy' ) {
				$orig->addWords( $edit->orig );
			} elseif ( $edit->orig ) {
				$orig->addWords( $edit->orig, 'del' );
			}
		}
		$lines = $orig->getLines();
		return $lines;
	}

	function closing() {
		$closing = new _HWLDF_WordAccumulator;

		foreach ( $this->edits as $edit ) {
			if ( $edit->type == 'copy' ) {
				$closing->addWords( $edit->closing );
			} elseif ( $edit->closing ) {
				$closing->addWords( $edit->closing, 'ins' );
			}
		}
		$lines = $closing->getLines();
		return $lines;
	}
}

/**
 * Wikipedia Table style diff formatter.
 * @todo document
 * @private
 * @ingroup DifferenceEngine
 */
class TableDiffFormatter extends DiffFormatter {
	function __construct() {
		$this->leading_context_lines = 2;
		$this->trailing_context_lines = 2;
	}

	public static function escapeWhiteSpace( $msg ) {
		$msg = preg_replace( '/^ /m', '&#160; ', $msg );
		$msg = preg_replace( '/ $/m', ' &#160;', $msg );
		$msg = preg_replace( '/  /', '&#160; ', $msg );
		return $msg;
	}

	function _block_header( $xbeg, $xlen, $ybeg, $ylen ) {
		if( isset( $this->block_header ) )
		{	// Use custom block header:
			$r = $this->block_header;
		}
		else
		{	// Use default block header:
			$r = '<tr><td colspan="2" class="diff-lineno">'.sprintf( T_('Line %s'), $xbeg ). ":</td>\n" .
			  '<td colspan="2" class="diff-lineno">'.sprintf( T_('Line %s'), $ybeg ). ":</td></tr>\n";
		}
		return $r;
	}

	function _start_block( $header ) {
		echo $header;
	}

	function _end_block() {
	}

	function _lines( $lines, $prefix = ' ', $color = 'white' ) {
	}

	# HTML-escape parameter before calling this
	function addedLine( $line ) {
		return $this->wrapLine( '+', 'diff-addedline', $line );
	}

	# HTML-escape parameter before calling this
	function deletedLine( $line ) {
		return $this->wrapLine( '&#8722;', 'diff-deletedline', $line );
	}

	# HTML-escape parameter before calling this
	function contextLine( $line ) {
		return $this->wrapLine( '&#160;', 'diff-context', $line );
	}

	private function wrapLine( $marker, $class, $line ) {
		if ( $line !== '' ) {
			// The <div> wrapper is needed for 'overflow: auto' style to scroll properly
			$line = '<div>'.$this->escapeWhiteSpace( $line ).'</div>';
		}
		return "<td class='diff-marker'>$marker</td><td class='$class'>$line</td>";
	}

	function emptyLine() {
		return '<td colspan="2">&#160;</td>';
	}

	function _added( $lines ) {
		foreach ( $lines as $line ) {
			echo '<tr>' . $this->emptyLine() .
			$this->addedLine( '<ins class="diffchange">' .
			htmlspecialchars( $line ) . '</ins>' ) . "</tr>\n";
		}
	}

	function _deleted( $lines ) {
		foreach ( $lines as $line ) {
			echo '<tr>' . $this->deletedLine( '<del class="diffchange">' .
			htmlspecialchars( $line ) . '</del>' ) .
			$this->emptyLine() . "</tr>\n";
		}
	}

	function _context( $lines ) {
		foreach ( $lines as $line ) {
			echo '<tr>' .
			$this->contextLine( htmlspecialchars( $line ) ) .
			$this->contextLine( htmlspecialchars( $line ) ) . "</tr>\n";
		}
	}

	function _changed( $orig, $closing ) {
		$diff = new WordLevelDiff( $orig, $closing );
		$del = $diff->orig();
		$add = $diff->closing();

		# Notice that WordLevelDiff returns HTML-escaped output.
		# Hence, we will be calling addedLine/deletedLine without HTML-escaping.

		while ( $line = array_shift( $del ) ) {
			$aline = array_shift( $add );
			echo '<tr>' . $this->deletedLine( $line ) .
			$this->addedLine( $aline ) . "</tr>\n";
		}
		foreach ( $add as $line ) {	# If any leftovers
			echo '<tr>' . $this->emptyLine() .
			$this->addedLine( $line ) . "</tr>\n";
		}
	}
}

/**
 * Wikipedia Title style diff formatter.
 * @todo document
 * @private
 * @ingroup DifferenceEngine
 */
class TitleDiffFormatter extends DiffFormatter {
	function __construct() {
		$this->leading_context_lines = 2;
		$this->trailing_context_lines = 2;
	}

	public static function escapeWhiteSpace( $msg ) {
		$msg = preg_replace( '/^ /m', '&#160; ', $msg );
		$msg = preg_replace( '/ $/m', ' &#160;', $msg );
		$msg = preg_replace( '/  /', '&#160; ', $msg );
		return $msg;
	}

	function _block_header( $xbeg, $xlen, $ybeg, $ylen ) {
	}

	function _start_block( $header ) {
	}

	function _end_block() {
	}

	function _lines( $lines, $prefix = ' ', $color = 'white' ) {
	}

	# HTML-escape parameter before calling this
	function addedLine( $line ) {
		return $this->wrapLine( 'diff-title-addedline', $line );
	}

	# HTML-escape parameter before calling this
	function deletedLine( $line ) {
		return $this->wrapLine( 'diff-title-deletedline', $line );
	}

	# HTML-escape parameter before calling this
	function contextLine( $line ) {
		return $this->wrapLine( 'diff-context', $line );
	}

	private function wrapLine( $class, $line ) {
		if ( $line !== '' ) {
			// The <div> wrapper is needed for 'overflow: auto' style to scroll properly
			$line = '<div>'.$this->escapeWhiteSpace( $line ).'</div>';
		}
		return "<td colspan='2' class='$class'>$line</td>";
	}

	function emptyLine() {
		return '<td colspan="2">&#160;</td>';
	}

	function _added( $lines ) {
		foreach ( $lines as $line ) {
			echo '<tr>' . $this->emptyLine() .
			$this->addedLine( '<ins class="diffchange">' .
			htmlspecialchars( $line ) . '</ins>' ) . "</tr>\n";
		}
	}

	function _deleted( $lines ) {
		foreach ( $lines as $line ) {
			echo '<tr>' . $this->deletedLine( '<del class="diffchange">' .
			htmlspecialchars( $line ) . '</del>' ) .
			$this->emptyLine() . "</tr>\n";
		}
	}

	function _context( $lines ) {
		foreach ( $lines as $line ) {
			echo '<tr>' .
			$this->contextLine( htmlspecialchars( $line ) ) .
			$this->contextLine( htmlspecialchars( $line ) ) . "</tr>\n";
		}
	}

	function _changed( $orig, $closing ) {
		$diff = new WordLevelDiff( $orig, $closing );
		$del = $diff->orig();
		$add = $diff->closing();


		# Notice that WordLevelDiff returns HTML-escaped output.
		# Hence, we will be calling addedLine/deletedLine without HTML-escaping.

		while ( $line = array_shift( $del ) ) {
			$aline = array_shift( $add );
			echo '<tr>' . $this->deletedLine( $line ) .
			$this->addedLine( $aline ) . "</tr>\n";
		}
		foreach ( $add as $line ) {	# If any leftovers
			echo '<tr>' . $this->emptyLine() .
			$this->addedLine( $line ) . "</tr>\n";
		}
	}
}

?>