<?php

/**
* Copyright (c) 2005 Richard Heyes (http://www.phpguru.org/)
*
* All rights reserved.
*
* This script is free software.
*/

/**
* PHP5 Implementation of the Porter Stemmer algorithm. Certain elements
* were borrowed from the (broken) implementation by Jon Abernathy.
*
* Usage:
*
*  $stem = PorterStemmer::Stem($word);
*
* How easy is that?
*/
class Pro_search_en_stemmer
{
    /**
    * Regex for matching a consonant
    * @var string
    */
    private static $regex_consonant = '(?:[bcdfghjklmnpqrstvwxz]|(?<=[aeiou])y|^y)';

    /**
    * Regex for matching a vowel
    * @var string
    */
    private static $regex_vowel = '(?:[aeiou]|(?<![aeiou])y)';

    /**
     * Stem method that Pro Search will call
     *
     * @var string
     */
    public $pro_search_stem_method = 'stem';

    /**
    * Stems a word. Simple huh?
    *
    * @param  string $word Word to stem
    * @return string       Stemmed word
    */
    public static function stem($word)
    {
        if (strlen($word) <= 2) {
            return $word;
        }

        $word = self::step1ab($word);
        $word = self::step1c($word);
        $word = self::step2($word);
        $word = self::step3($word);
        $word = self::step4($word);
        $word = self::step5($word);

        return $word;
    }

    /**
    * Step 1
    */
    private static function step1ab($word)
    {
        // Part a
        if (substr($word, -1) == 's') {
            self::replace($word, 'sses', 'ss')
            or self::replace($word, 'ies', 'i')
            or self::replace($word, 'ss', 'ss')
            or self::replace($word, 's', '');
        }

        // Part b
        if (substr($word, -2, 1) != 'e' or !self::replace($word, 'eed', 'ee', 0)) { // First rule
            $v = self::$regex_vowel;

            // ing and ed
            if (
                preg_match("#$v+#", substr($word, 0, -3)) && self::replace($word, 'ing', '')
                or preg_match("#$v+#", substr($word, 0, -2)) && self::replace($word, 'ed', '')
            ) { // Note use of && and OR, for precedence reasons
                // If one of above two test successful
                if (
                    !self::replace($word, 'at', 'ate')
                    and !self::replace($word, 'bl', 'ble')
                    and !self::replace($word, 'iz', 'ize')
                ) {
                    // Double consonant ending
                    if (
                        self::doubleConsonant($word)
                        and substr($word, -2) != 'll'
                        and substr($word, -2) != 'ss'
                        and substr($word, -2) != 'zz'
                    ) {
                        $word = substr($word, 0, -1);
                    } elseif (self::m($word) == 1 and self::cvc($word)) {
                        $word .= 'e';
                    }
                }
            }
        }

        return $word;
    }

    /**
    * Step 1c
    *
    * @param string $word Word to stem
    */
    private static function step1c($word)
    {
        $v = self::$regex_vowel;

        if (substr($word, -1) == 'y' && preg_match("#$v+#", substr($word, 0, -1))) {
            self::replace($word, 'y', 'i');
        }

        return $word;
    }

    /**
    * Step 2
    *
    * @param string $word Word to stem
    */
    private static function step2($word)
    {
        switch (substr($word, -2, 1)) {
            case 'a':
                self::replace($word, 'ational', 'ate', 0)
                or self::replace($word, 'tional', 'tion', 0);

                break;

            case 'c':
                self::replace($word, 'enci', 'ence', 0)
                or self::replace($word, 'anci', 'ance', 0);

                break;

            case 'e':
                self::replace($word, 'izer', 'ize', 0);

                break;

            case 'g':
                self::replace($word, 'logi', 'log', 0);

                break;

            case 'l':
                self::replace($word, 'entli', 'ent', 0)
                or self::replace($word, 'ousli', 'ous', 0)
                or self::replace($word, 'alli', 'al', 0)
                or self::replace($word, 'bli', 'ble', 0)
                or self::replace($word, 'eli', 'e', 0);

                break;

            case 'o':
                self::replace($word, 'ization', 'ize', 0)
                or self::replace($word, 'ation', 'ate', 0)
                or self::replace($word, 'ator', 'ate', 0);

                break;

            case 's':
                self::replace($word, 'iveness', 'ive', 0)
                or self::replace($word, 'fulness', 'ful', 0)
                or self::replace($word, 'ousness', 'ous', 0)
                or self::replace($word, 'alism', 'al', 0);

                break;

            case 't':
                self::replace($word, 'biliti', 'ble', 0)
                or self::replace($word, 'aliti', 'al', 0)
                or self::replace($word, 'iviti', 'ive', 0);

                break;
        }

        return $word;
    }

    /**
    * Step 3
    *
    * @param string $word String to stem
    */
    private static function step3($word)
    {
        switch (substr($word, -2, 1)) {
            case 'a':
                self::replace($word, 'ical', 'ic', 0);

                break;

            case 's':
                self::replace($word, 'ness', '', 0);

                break;

            case 't':
                self::replace($word, 'icate', 'ic', 0)
                or self::replace($word, 'iciti', 'ic', 0);

                break;

            case 'u':
                self::replace($word, 'ful', '', 0);

                break;

            case 'v':
                self::replace($word, 'ative', '', 0);

                break;

            case 'z':
                self::replace($word, 'alize', 'al', 0);

                break;
        }

        return $word;
    }

    /**
    * Step 4
    *
    * @param string $word Word to stem
    */
    private static function step4($word)
    {
        switch (substr($word, -2, 1)) {
            case 'a':
                self::replace($word, 'al', '', 1);

                break;

            case 'c':
                self::replace($word, 'ance', '', 1)
                or self::replace($word, 'ence', '', 1);

                break;

            case 'e':
                self::replace($word, 'er', '', 1);

                break;

            case 'i':
                self::replace($word, 'ic', '', 1);

                break;

            case 'l':
                self::replace($word, 'able', '', 1)
                or self::replace($word, 'ible', '', 1);

                break;

            case 'n':
                self::replace($word, 'ant', '', 1)
                or self::replace($word, 'ement', '', 1)
                or self::replace($word, 'ment', '', 1)
                or self::replace($word, 'ent', '', 1);

                break;

            case 'o':
                if (substr($word, -4) == 'tion' or substr($word, -4) == 'sion') {
                    self::replace($word, 'ion', '', 1);
                } else {
                    self::replace($word, 'ou', '', 1);
                }

                break;

            case 's':
                self::replace($word, 'ism', '', 1);

                break;

            case 't':
                self::replace($word, 'ate', '', 1)
                or self::replace($word, 'iti', '', 1);

                break;

            case 'u':
                self::replace($word, 'ous', '', 1);

                break;

            case 'v':
                self::replace($word, 'ive', '', 1);

                break;

            case 'z':
                self::replace($word, 'ize', '', 1);

                break;
        }

        return $word;
    }

    /**
    * Step 5
    *
    * @param string $word Word to stem
    */
    private static function step5($word)
    {
        // Part a
        if (substr($word, -1) == 'e') {
            if (self::m(substr($word, 0, -1)) > 1) {
                self::replace($word, 'e', '');
            } elseif (self::m(substr($word, 0, -1)) == 1) {
                if (!self::cvc(substr($word, 0, -1))) {
                    self::replace($word, 'e', '');
                }
            }
        }

        // Part b
        if (self::m($word) > 1 and self::doubleConsonant($word) and substr($word, -1) == 'l') {
            $word = substr($word, 0, -1);
        }

        return $word;
    }

    /**
    * Replaces the first string with the second, at the end of the string. If third
    * arg is given, then the preceding string must match that m count at least.
    *
    * @param  string $str   String to check
    * @param  string $check Ending to check for
    * @param  string $repl  Replacement string
    * @param  int    $m     Optional minimum number of m() to meet
    * @return bool          Whether the $check string was at the end
    *                       of the $str string. True does not necessarily mean
    *                       that it was replaced.
    */
    private static function replace(&$str, $check, $repl, $m = null)
    {
        $len = 0 - strlen($check);

        if (substr($str, $len) == $check) {
            $substr = substr($str, 0, $len);
            if (is_null($m) or self::m($substr) > $m) {
                $str = $substr . $repl;
            }

            return true;
        }

        return false;
    }

    /**
    * What, you mean it's not obvious from the name?
    *
    * m() measures the number of consonant sequences in $str. if c is
    * a consonant sequence and v a vowel sequence, and <..> indicates arbitrary
    * presence,
    *
    * <c><v>       gives 0
    * <c>vc<v>     gives 1
    * <c>vcvc<v>   gives 2
    * <c>vcvcvc<v> gives 3
    *
    * @param  string $str The string to return the m count for
    * @return int         The m count
    */
    private static function m($str)
    {
        $c = self::$regex_consonant;
        $v = self::$regex_vowel;

        $str = preg_replace("#^$c+#", '', $str);
        $str = preg_replace("#$v+$#", '', $str);

        preg_match_all("#($v+$c+)#", $str, $matches);

        return count($matches[1]);
    }

    /**
    * Returns true/false as to whether the given string contains two
    * of the same consonant next to each other at the end of the string.
    *
    * @param  string $str String to check
    * @return bool        Result
    */
    private static function doubleConsonant($str)
    {
        $c = self::$regex_consonant;

        return preg_match("#$c{2}$#", $str, $matches) and $matches[0][0] == $matches[0][1];
    }

    /**
    * Checks for ending CVC sequence where second C is not W, X or Y
    *
    * @param  string $str String to check
    * @return bool        Result
    */
    private static function cvc($str)
    {
        $c = self::$regex_consonant;
        $v = self::$regex_vowel;

        return     preg_match("#($c$v$c)$#", $str, $matches)
               and strlen($matches[1]) == 3
               and $matches[1][2] != 'w'
               and $matches[1][2] != 'x'
               and $matches[1][2] != 'y';
    }
}
