<?php
/* Copyright (C) 2008 Guy Van den Broeck <guy@guyvdb.eu>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 * or see http://www.gnu.org/
 */
 
/**
 * This diff implementation is mainly lifted from the LCS algorithm of the Eclipse project which
 * in turn is based on Myers' "An O(ND) difference algorithm and its variations"
 * (http://citeseer.ist.psu.edu/myers86ond.html) with range compression (see Wu et al.'s
 * "An O(NP) Sequence Comparison Algorithm").
 *
 * This implementation supports an upper bound on the excution time.
 *
 * Complexity: O((M + N)D) worst case time, O(M + N + D^2) expected time, O(M + N) space
 *
 * @author Guy Van den Broeck
 * @ingroup DifferenceEngine
 */
class WikiDiff3 {

    //Input variables
    private $from;
    private $to;
    private $m;
    private $n;

    private $tooLong;
    private $powLimit;

    //State variables
    private $maxDifferences;
    private $lcsLengthCorrectedForHeuristic = false;

    //Output variables
    public $length;
    public $removed;
    public $added;
    public $heuristicUsed;

    function __construct($tooLong = 2000000, $powLimit = 1.45){
        $this->tooLong = $tooLong;
        $this->powLimit = $powLimit;
    }

    public function diff(/*array*/ $from, /*array*/ $to){
        //remember initial lengths
        $m = sizeof($from);
        $n = count($to);

        $this->heuristicUsed = false;

        //output
        $removed = $m > 0 ? array_fill(0, $m, true) : array();
        $added = $n > 0 ? array_fill(0, $n, true) : array();

        //reduce the complexity for the next step (intentionally done twice)
        //remove common tokens at the start
        $i = 0;
        while($i < $m && $i < $n && $from[$i] === $to[$i]) {
            $removed[$i] = $added[$i] = false;
            unset($from[$i], $to[$i]);
            ++$i;
        }

        //remove common tokens at the end
        $j = 1;
        while($i + $j <= $m && $i + $j <= $n && $from[$m - $j] === $to[$n - $j]) {
            $removed[$m - $j] = $added[$n - $j] = false;
            unset($from[$m - $j], $to[$n - $j]);
            ++$j;
        }

        $this->from = $newFromIndex = $this->to = $newToIndex = array();

        //remove tokens not in both sequences
        $shared = array();
        foreach( $from as $key ) {
            $shared[$key] = false;
        }

        foreach($to as $index => &$el) {
            if(array_key_exists($el, $shared)) {
                //keep it
                $this->to[] = $el;
                $shared[$el] = true;
                $newToIndex[] = $index;
            }
        }
        foreach($from as $index => &$el) {
            if($shared[$el]) {
                //keep it
                $this->from[] = $el;
                $newFromIndex[] = $index;
            }
        }

        unset($shared, $from, $to);

        $this->m = count($this->from);
        $this->n = count($this->to);

        $this->removed = $this->m > 0 ? array_fill(0, $this->m, true) : array();
        $this->added = $this->n > 0 ? array_fill(0, $this->n, true) : array();

        if ($this->m == 0 || $this->n == 0) {
            $this->length = 0;
        } else {
            $this->maxDifferences = ceil(($this->m + $this->n) / 2.0);
            if ($this->m * $this->n > $this->tooLong) {
                // limit complexity to D^POW_LIMIT for long sequences
                $this->maxDifferences = floor(pow($this->maxDifferences, $this->powLimit - 1.0));
            }

            /*
             * The common prefixes and suffixes are always part of some LCS, include
             * them now to reduce our search space
             */
            $max = min($this->m, $this->n);
            for ($forwardBound = 0; $forwardBound < $max
                    && $this->from[$forwardBound] === $this->to[$forwardBound];
                    ++$forwardBound) {
                $this->removed[$forwardBound] = $this->added[$forwardBound] = false;
            }

            $backBoundL1 = $this->m - 1;
            $backBoundL2 = $this->n - 1;

            while ($backBoundL1 >= $forwardBound && $backBoundL2 >= $forwardBound
                    && $this->from[$backBoundL1] === $this->to[$backBoundL2]) {
                $this->removed[$backBoundL1--] = $this->added[$backBoundL2--] = false;
            }

            $temp = array_fill(0, $this->m + $this->n + 1, 0);
            $V = array($temp, $temp);
            $snake = array(0, 0, 0);

            $this->length = $forwardBound + $this->m - $backBoundL1 - 1
                + $this->lcs_rec($forwardBound, $backBoundL1,
                $forwardBound, $backBoundL2, $V, $snake);
        }

        $this->m = $m;
        $this->n = $n;

        $this->length += $i + $j - 1;

        foreach($this->removed as $key => &$removed_elem) {
            if(!$removed_elem) {
                $removed[$newFromIndex[$key]] = false;
            }
        }
        foreach($this->added as $key => &$added_elem) {
            if(!$added_elem) {
                $added[$newToIndex[$key]] = false;
            }
        }
        $this->removed = $removed;
        $this->added = $added;
    }

    function diff_range($from_lines, $to_lines) {
        // Diff and store locally
        $this->diff($from_lines, $to_lines);
        unset($from_lines, $to_lines);

        $ranges = array();
        $xi = $yi = 0;
        while ($xi < $this->m || $yi < $this->n) {
            // Matching "snake".
            while ($xi < $this->m && $yi < $this->n
                    && !$this->removed[$xi]
                    && !$this->added[$yi]) {
                ++$xi;
                ++$yi;
            }
            // Find deletes & adds.
            $xstart = $xi;
            while ($xi < $this->m && $this->removed[$xi]) {
                ++$xi;
            }

            $ystart = $yi;
            while ($yi < $this->n && $this->added[$yi]) {
                ++$yi;
            }

            if ($xi > $xstart || $yi > $ystart) {
                $ranges[] = new RangeDifference($xstart, $xi,
                                $ystart, $yi);
            }
        }
        return $ranges;
    }

    private function lcs_rec($bottoml1, $topl1, $bottoml2, $topl2, &$V, &$snake) {
        // check that both sequences are non-empty
        if ($bottoml1 > $topl1 || $bottoml2 > $topl2) {
            return 0;
        }

        $d = $this->find_middle_snake($bottoml1, $topl1, $bottoml2,
                            $topl2, $V, $snake);

        // need to store these so we don't lose them when they're
        // overwritten by the recursion
        $len = $snake[2];
        $startx = $snake[0];
        $starty = $snake[1];

        // the middle snake is part of the LCS, store it
        for ($i = 0; $i < $len; ++$i) {
            $this->removed[$startx + $i] = $this->added[$starty + $i] = false;
        }

        if ($d > 1) {
            return $len
            + $this->lcs_rec($bottoml1, $startx - 1, $bottoml2,
                            $starty - 1, $V, $snake)
            + $this->lcs_rec($startx + $len, $topl1, $starty + $len,
                            $topl2, $V, $snake);
        } else if ($d == 1) {
            /*
             * In this case the sequences differ by exactly 1 line. We have
             * already saved all the lines after the difference in the for loop
             * above, now we need to save all the lines before the difference.
             */
            $max = min($startx - $bottoml1, $starty - $bottoml2);
            for ($i = 0; $i < $max; ++$i) {
                $this->removed[$bottoml1 + $i] =
                    $this->added[$bottoml2 + $i] = false;
            }
            return $max + $len;
        }
        return $len;
    }

    private function find_middle_snake($bottoml1, $topl1, $bottoml2,$topl2, &$V, &$snake) {
        $from = &$this->from;
        $to = &$this->to;
        $V0 = &$V[0];
        $V1 = &$V[1];
        $snake0 = &$snake[0];
        $snake1 = &$snake[1];
        $snake2 = &$snake[2];
        $bottoml1_min_1 = $bottoml1-1;
        $bottoml2_min_1 = $bottoml2-1;
        $N = $topl1 - $bottoml1_min_1;
        $M = $topl2 - $bottoml2_min_1;
        $delta = $N - $M;
        $maxabsx = $N+$bottoml1;
        $maxabsy = $M+$bottoml2;
        $limit = min($this->maxDifferences, ceil(($N + $M ) / 2));

        //value_to_add_forward: a 0 or 1 that we add to the start
        // offset to make it odd/even
        if (($M & 1) == 1) {
            $value_to_add_forward = 1;
        } else {
            $value_to_add_forward = 0;
        }

        if (($N & 1) == 1) {
            $value_to_add_backward = 1;
        } else {
            $value_to_add_backward = 0;
        }

        $start_forward = -$M;
        $end_forward = $N;
        $start_backward = -$N;
        $end_backward = $M;

        $limit_min_1 = $limit - 1;
        $limit_plus_1 = $limit + 1;

        $V0[$limit_plus_1] = 0;
        $V1[$limit_min_1] = $N;
        $limit = min($this->maxDifferences, ceil(($N + $M ) / 2));

        if (($delta & 1) == 1) {
            for ($d = 0; $d <= $limit; ++$d) {
                $start_diag = max($value_to_add_forward + $start_forward, -$d);
                $end_diag = min($end_forward, $d);
                $value_to_add_forward = 1 - $value_to_add_forward;

                // compute forward furthest reaching paths
                for ($k = $start_diag; $k <= $end_diag; $k += 2) {
                    if ($k == -$d || ($k < $d
                            && $V0[$limit_min_1 + $k] < $V0[$limit_plus_1 + $k])) {
                        $x = $V0[$limit_plus_1 + $k];
                    } else {
                        $x = $V0[$limit_min_1 + $k] + 1;
                    }

                    $absx = $snake0 = $x + $bottoml1;
                    $absy = $snake1 = $x - $k + $bottoml2;

                    while ($absx < $maxabsx && $absy < $maxabsy && $from[$absx] === $to[$absy]) {
                        ++$absx;
                        ++$absy;
                    }
                    $x = $absx-$bottoml1;

                    $snake2 = $absx -$snake0;
                    $V0[$limit + $k] = $x;
                    if ($k >= $delta - $d + 1 && $k <= $delta + $d - 1
                            && $x >= $V1[$limit + $k - $delta]) {
                        return 2 * $d - 1;
                    }

                    // check to see if we can cut down the diagonal range
                    if ($x >= $N && $end_forward > $k - 1) {
                        $end_forward = $k - 1;
                    } else if ($absy - $bottoml2 >= $M) {
                        $start_forward = $k + 1;
                        $value_to_add_forward = 0;
                    }
                }

                $start_diag = max($value_to_add_backward + $start_backward, -$d);
                $end_diag = min($end_backward, $d);
                $value_to_add_backward = 1 - $value_to_add_backward;

                // compute backward furthest reaching paths
                for ($k = $start_diag; $k <= $end_diag; $k += 2) {
                    if ($k == $d
                    || ($k != -$d && $V1[$limit_min_1 + $k] < $V1[$limit_plus_1 + $k])) {
                        $x = $V1[$limit_min_1 + $k];
                    } else {
                        $x = $V1[$limit_plus_1 + $k] - 1;
                    }

                    $y = $x - $k - $delta;

                    $snake2 = 0;
                    while ($x > 0 && $y > 0
                    && $from[$x +$bottoml1_min_1] === $to[$y + $bottoml2_min_1]) {
                        --$x;
                        --$y;
                        ++$snake2;
                    }
                    $V1[$limit + $k] = $x;

                    // check to see if we can cut down our diagonal range
                    if ($x <= 0) {
                        $start_backward = $k + 1;
                        $value_to_add_backward = 0;
                    } else if ($y <= 0 && $end_backward > $k - 1) {
                        $end_backward = $k - 1;
                    }
                }
            }
        } else {
            for ($d = 0; $d <= $limit; ++$d) {
                $start_diag = max($value_to_add_forward + $start_forward, -$d);
                $end_diag = min($end_forward, $d);
                $value_to_add_forward = 1 - $value_to_add_forward;

                // compute forward furthest reaching paths
                for ($k = $start_diag; $k <= $end_diag; $k += 2) {
                    if ($k == -$d
                    || ($k < $d && $V0[$limit_min_1 + $k] < $V0[$limit_plus_1 + $k])) {
                        $x = $V0[$limit_plus_1 + $k];
                    } else {
                        $x = $V0[$limit_min_1 + $k] + 1;
                    }

                    $absx = $snake0 = $x + $bottoml1;
                    $absy = $snake1 = $x - $k + $bottoml2;

                    while ($absx < $maxabsx && $absy < $maxabsy && $from[$absx] === $to[$absy]) {
                        ++$absx;
                        ++$absy;
                    }
                    $x = $absx-$bottoml1;
                    $snake2 = $absx -$snake0;
                    $V0[$limit + $k] = $x;

                    // check to see if we can cut down the diagonal range
                    if ($x >= $N && $end_forward > $k - 1) {
                        $end_forward = $k - 1;
                    } else if ($absy-$bottoml2 >= $M) {
                        $start_forward = $k + 1;
                        $value_to_add_forward = 0;
                    }
                }

                $start_diag = max($value_to_add_backward + $start_backward, -$d);
                $end_diag = min($end_backward, $d);
                $value_to_add_backward = 1 - $value_to_add_backward;

                // compute backward furthest reaching paths
                for ($k = $start_diag; $k <= $end_diag; $k += 2) {
                    if ($k == $d
                    || ($k != -$d && $V1[$limit_min_1 + $k] < $V1[$limit_plus_1 + $k])) {
                        $x = $V1[$limit_min_1 + $k];
                    } else {
                        $x = $V1[$limit_plus_1 + $k] - 1;
                    }

                    $y = $x - $k - $delta;

                    $snake2 = 0;
                    while ($x > 0 && $y > 0
                            && $from[$x +$bottoml1_min_1] === $to[$y + $bottoml2_min_1]) {
                        --$x;
                        --$y;
                        ++$snake2;
                    }
                    $V1[$limit + $k] = $x;

                    if ($k >= -$delta - $d && $k <= $d - $delta
                            && $x <= $V0[$limit + $k + $delta]) {
                        $snake0 = $bottoml1 + $x;
                        $snake1 = $bottoml2 + $y;
                        return 2 * $d;
                    }

                    // check to see if we can cut down our diagonal range
                    if ($x <= 0) {
                        $start_backward = $k + 1;
                        $value_to_add_backward = 0;
                    } else if ($y <= 0 && $end_backward > $k - 1) {
                        $end_backward = $k - 1;
                    }
                }
            }
        }
        /*
         * computing the true LCS is too expensive, instead find the diagonal
         * with the most progress and pretend a midle snake of length 0 occurs
         * there.
         */

        $most_progress = self::findMostProgress($M, $N, $limit, $V);

        $snake0 = $bottoml1 + $most_progress[0];
        $snake1 = $bottoml2 + $most_progress[1];
        $snake2 = 0;
        $this->heuristicUsed = true;
        return 5; /*
        * HACK: since we didn't really finish the LCS computation
        * we don't really know the length of the SES. We don't do
        * anything with the result anyway, unless it's <=1. We know
        * for a fact SES > 1 so 5 is as good a number as any to
        * return here
        */
    }

    private static function findMostProgress($M, $N, $limit, $V) {
        $delta = $N - $M;

        if (($M & 1) == ($limit & 1)) {
            $forward_start_diag = max(-$M, -$limit);
        } else {
            $forward_start_diag = max(1 - $M, -$limit);
        }

        $forward_end_diag = min($N, $limit);

        if (($N & 1) == ($limit & 1)) {
            $backward_start_diag = max(-$N, -$limit);
        } else {
            $backward_start_diag = max(1 - $N, -$limit);
        }

        $backward_end_diag = -min($M, $limit);

        $temp = array(0, 0, 0);


        $max_progress = array_fill(0, ceil(max($forward_end_diag - $forward_start_diag,
                $backward_end_diag - $backward_start_diag) / 2), $temp);
        $num_progress = 0; // the 1st entry is current, it is initialized
        // with 0s

        // first search the forward diagonals
        for ($k = $forward_start_diag; $k <= $forward_end_diag; $k += 2) {
            $x = $V[0][$limit + $k];
            $y = $x - $k;
            if ($x > $N || $y > $M) {
                continue;
            }

            $progress = $x + $y;
            if ($progress > $max_progress[0][2]) {
                $num_progress = 0;
                $max_progress[0][0] = $x;
                $max_progress[0][1] = $y;
                $max_progress[0][2] = $progress;
            } else if ($progress == $max_progress[0][2]) {
                ++$num_progress;
                $max_progress[$num_progress][0] = $x;
                $max_progress[$num_progress][1] = $y;
                $max_progress[$num_progress][2] = $progress;
            }
        }

        $max_progress_forward = true; // initially the maximum
        // progress is in the forward
        // direction

        // now search the backward diagonals
        for ($k = $backward_start_diag; $k <= $backward_end_diag; $k += 2) {
            $x = $V[1][$limit + $k];
            $y = $x - $k - $delta;
            if ($x < 0 || $y < 0) {
                continue;
            }

            $progress = $N - $x + $M - $y;
            if ($progress > $max_progress[0][2]) {
                $num_progress = 0;
                $max_progress_forward = false;
                $max_progress[0][0] = $x;
                $max_progress[0][1] = $y;
                $max_progress[0][2] = $progress;
            } else if ($progress == $max_progress[0][2] && !$max_progress_forward) {
                ++$num_progress;
                $max_progress[$num_progress][0] = $x;
                $max_progress[$num_progress][1] = $y;
                $max_progress[$num_progress][2] = $progress;
            }
        }

        // return the middle diagonal with maximal progress.
        return $max_progress[floor($num_progress / 2)];
    }

    public function getLcsLength(){
        if($this->heuristicUsed && !$this->lcsLengthCorrectedForHeuristic){
            $this->lcsLengthCorrectedForHeuristic = true;
            $this->length = $this->m-array_sum($this->added);
        }
        return $this->length;
    }

}

/**
 * Alternative representation of a set of changes, by the index
 * ranges that are changed.
 * 
 * @ingroup DifferenceEngine
 */
class RangeDifference {

    public $leftstart;
    public $leftend;
    public $leftlength;

    public $rightstart;
    public $rightend;
    public $rightlength;

    function __construct($leftstart, $leftend, $rightstart, $rightend){
        $this->leftstart = $leftstart;
        $this->leftend = $leftend;
        $this->leftlength = $leftend - $leftstart;
        $this->rightstart = $rightstart;
        $this->rightend = $rightend;
        $this->rightlength = $rightend - $rightstart;
    }
}