<?php
namespace App\Helpers;

/*
    Paul's Simple Differ Algorithm v 0.1
    (C) Paul Butler 2007 <http://www.paulbutler.org/>
    May be used and distributed under the zlib/libpng license.

    This code is intended for learning purposes; it was written with short
    code taking priority over performance. It could be used in a practical
    application, but there are a few ways it could be optimized.

    Given two arrays, the function diff will return an array of the changes.
    I won't describe the format of the array, but it will be obvious
    if you use print_r() on the result of a diff on some test data.

    htmlDiff is a wrapper for the diff command, it takes two strings and
    returns the differences in HTML. The tags used are <ins> and <del>,
    which can easily be styled with CSS.

    @url https://github.com/paulgb/simplediff/blob/master/php/simplediff.php

    Sorry for this kind of magic, I have no idea how this works.. :(
*/

class Differ
{
    public static function diff($old, $new)
    {
        $matrix = [];
        $maxlen = 0;
        foreach ($old as $oindex => $ovalue) {
            $nkeys = array_keys($new, $ovalue);
            foreach ($nkeys as $nindex) {
                $matrix[$oindex][$nindex] = isset($matrix[$oindex - 1][$nindex - 1]) ? $matrix[$oindex - 1][$nindex - 1] + 1 : 1;
                if ($matrix[$oindex][$nindex] > $maxlen) {
                    $maxlen = $matrix[$oindex][$nindex];
                    $omax = $oindex + 1 - $maxlen;
                    $nmax = $nindex + 1 - $maxlen;
                }
            }
        }
        if ($maxlen == 0) {
            return [['d' => $old, 'i' => $new]];
        }

        return array_merge(self::diff(array_slice($old, 0, $omax), array_slice($new, 0, $nmax)), array_slice($new, $nmax, $maxlen), self::diff(array_slice($old, $omax + $maxlen), array_slice($new, $nmax + $maxlen)));
    }

    public static function htmlDiff($old, $new)
    {
        $ret = '';
        $diff = self::diff(preg_split("/[\s]+/", $old), preg_split("/[\s]+/", $new));
        foreach ($diff as $k) {
            if (is_array($k)) {
                $ret .= (!empty($k['d']) ? "<del>" . implode(' ', $k['d']) . "</del> " : '') . (!empty($k['i']) ? "<ins>" . implode(' ', $k['i']) . "</ins> " : '');
            } else {
                $ret .= $k . ' ';
            }
        }

        return $ret;
    }
}