<?php

/**

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

 * implemented using native PHP code.

 *

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

 * diffutils-2.7, which can be found at:

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

 *

 * Some ideas (subdivision by NCHUNKS > 2, and some optimizations) are from

 * Geoffrey T. Dairiki <dairiki@dairiki.org>. The original PHP version of this

 * code was written by him, and is used/adapted with his permission.

 *

 * $Horde: framework/Text_Diff/Diff/Engine/native.php,v 1.3 2006/01/06 15:56:52 jan Exp $

 *

 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>

 * @package Text_Diff

 *

 * @access private

 */

class Text_Diff_Engine_native {

    function diff($from_lines, $to_lines)

    {

        array_walk($from_lines, array('Text_Diff', 'trimNewlines'));

        array_walk($to_lines, array('Text_Diff', 'trimNewlines'));

        $n_from = count($from_lines);

        $n_to = count($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++) {

            $xhash[$from_lines[$xi]] = 1;

        }

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

            $line = $to_lines[$yi];

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

                continue;

            }

            $yhash[$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($yhash[$line]))) {

                continue;

            }

            $this->xv[] = $line;

            $this->xind[] = $xi;

        }

        // Find the LCS.

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

        // Merge edits when possible.

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

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

        // Compute the edit operations.

        $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) {

                $edits[] = &new Text_Diff_Op_copy($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) {

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

            } elseif ($delete) {

                $edits[] = &new Text_Diff_Op_delete($delete);

            } elseif ($add) {

                $edits[] = &new Text_Diff_Op_add($add);

            }

        }

        return $edits;

    }

    /**

     * Divides 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 is 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];

                foreach ($matches as $y) {

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

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

                        assert($k > 0);

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

                        break;

                    }

                }

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

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

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

                        /* Optimization: this is a common case: next match is

                         * just replacing previous match. */

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

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

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

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

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

                        assert($k > 0);

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

                    }

                }

            }

        }

        $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 _lcsPos($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;

    }

    /**

     * Finds 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;

            }

        }

    }

    /**

     * Adjusts 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 _shiftBoundaries($lines, &$changed, $other_changed)

    {

        $i = 0;

        $j = 0;

        assert('count($lines) == count($changed)');

        $len = count($lines);

        $other_len = count($other_changed);

        while (1) {

            /* Scan forward to find the 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]');

            }

        }

    }

}