<?php

namespace Drupal\porterstemmer;

/**
 * PHP Implementation of the Porter2 Stemming Algorithm.
 *
 * See http://snowball.tartarus.org/algorithms/english/stemmer.html .
 */
class Porter2 {

  /**
   * Computes the stem of the word.
   *
   * @return string
   *   The word's stem.
   */
  public static function stem($word) {

    $exceptions = array(
      'skis' => 'ski',
      'skies' => 'sky',
      'dying' => 'die',
      'lying' => 'lie',
      'tying' => 'tie',
      'idly' => 'idl',
      'gently' => 'gentl',
      'ugly' => 'ugli',
      'early' => 'earli',
      'only' => 'onli',
      'singly' => 'singl',
      'sky' => 'sky',
      'news' => 'news',
      'howe' => 'howe',
      'atlas' => 'atlas',
      'cosmos' => 'cosmos',
      'bias' => 'bias',
      'andes' => 'andes',
    );

    // Process exceptions.
    if (isset($exceptions[$word])) {
      $word = $exceptions[$word];
    }
    elseif (strlen($word) > 2) {
      // Only execute algorithm on words that are longer than two letters.
      $word = self::prepare($word);
      $word = self::step0($word);
      $word = self::step1a($word);
      $word = self::step1b($word);
      $word = self::step1c($word);
      $word = self::step2($word);
      $word = self::step3($word);
      $word = self::step4($word);
      $word = self::step5($word);
    }
    return strtolower($word);
  }

  /**
   * Set initial y, or y after a vowel, to Y.
   *
   * @param string $word
   *   The word to stem.
   *
   * @return string $word
   *   The prepared word.
   */
  protected static function prepare($word) {
    $inc = 0;
    if (strpos($word, "'") === 0) {
      $word = substr($word, 1);
    }
    while ($inc <= strlen($word)) {
      if (substr($word, $inc, 1) === 'y' && ($inc == 0 || self::isVowel($inc - 1, $word))) {
        $word = substr_replace($word, 'Y', $inc, 1);
      }
      $inc++;
    }
    return $word;
  }

  /**
   * Search for the longest among the "s" suffixes and removes it.
   *
   * @param string $word
   *   The word to stem.
   *
   * @return string $word
   *   The modified word.
   */
  protected static function step0($word) {
    $found = FALSE;
    $checks = array("'s'", "'s", "'");
    foreach ($checks as $check) {
      if (!$found && self::hasEnding($word, $check)) {
        $word = self::removeEnding($word, $check);
        $found = TRUE;
      }
    }
    return $word;
  }

  /**
   * Handles various suffixes, of which the longest is replaced.
   *
   * @param string $word
   *   The word to stem.
   *
   * @return string $word
   *   The modified word.
   */
  protected static function step1a($word) {
    $found = FALSE;
    if (self::hasEnding($word, 'sses')) {
      $word = self::removeEnding($word, 'sses') . 'ss';
      $found = TRUE;
    }
    $checks = array('ied', 'ies');
    foreach ($checks as $check) {
      if (!$found && self::hasEnding($word, $check)) {
        // @todo: check order here.
        $length = strlen($word);
        $word = self::removeEnding($word, $check);
        if ($length > 4) {
          $word .= 'i';
        }
        else {
          $word .= 'ie';
        }
        $found = TRUE;
      }
    }
    if (self::hasEnding($word, 'us') || self::hasEnding($word, 'ss')) {
      $found = TRUE;
    }
    // Delete if preceding word part has a vowel not immediately before the s.
    if (!$found && self::hasEnding($word, 's') && self::containsVowel(substr($word, 0, -2))) {
      $word = self::removeEnding($word, 's');
    }
    return $word;
  }

  /**
   * Handles various suffixes, of which the longest is replaced.
   *
   * @param string $word
   *   The word to stem.
   *
   * @return string $word
   *   The modified word.
   */
  protected static function step1b($word) {
    $exceptions = array(
      'inning',
      'outing',
      'canning',
      'herring',
      'earring',
      'proceed',
      'exceed',
      'succeed',
    );
    if (in_array($word, $exceptions)) {
      return $word;
    }
    $checks = array('eedly', 'eed');
    foreach ($checks as $check) {
      if (self::hasEnding($word, $check)) {
        if (self::r($word, 1) !== strlen($word)) {
          $word = self::removeEnding($word, $check) . 'ee';
        }
        return $word;
      }
    }
    $checks = array('ingly', 'edly', 'ing', 'ed');
    $second_endings = array('at', 'bl', 'iz');
    foreach ($checks as $check) {
      // If the ending is present and the previous part contains a vowel.
      if (self::hasEnding($word, $check) && self::containsVowel(substr($word, 0, -strlen($check)))) {
        $word = self::removeEnding($word, $check);
        foreach ($second_endings as $ending) {
          if (self::hasEnding($word, $ending)) {
            return $word . 'e';
          }
        }
        // If the word ends with a double, remove the last letter.
        $double_removed = self::removeDoubles($word);
        if ($double_removed != $word) {
          $word = $double_removed;
        }
        elseif (self::isShort($word)) {
          // If the word is short, add e (so hop -> hope).
          $word .= 'e';
        }
        return $word;
      }
    }
    return $word;
  }

  /**
   * Replaces suffix y or Y with i if after non-vowel not @ word begin.
   *
   * @param string $word
   *   The word to stem.
   *
   * @return string $word
   *   The modified word.
   */
  protected static function step1c($word) {
    if ((self::hasEnding($word, 'y') || self::hasEnding($word, 'Y')) && strlen($word) > 2 && !(self::isVowel(strlen($word) - 2, $word))) {
      $word = self::removeEnding($word, 'y');
      $word .= 'i';
    }
    return $word;
  }

  /**
   * Implements step 2 of the Porter2 algorithm.
   *
   * @param string $word
   *   The word to stem.
   *
   * @return string $word
   *   The modified word.
   */
  protected static function step2($word) {
    $checks = array(
      "ization" => "ize",
      "iveness" => "ive",
      "fulness" => "ful",
      "ational" => "ate",
      "ousness" => "ous",
      "biliti" => "ble",
      "tional" => "tion",
      "lessli" => "less",
      "fulli" => "ful",
      "entli" => "ent",
      "ation" => "ate",
      "aliti" => "al",
      "iviti" => "ive",
      "ousli" => "ous",
      "alism" => "al",
      "abli" => "able",
      "anci" => "ance",
      "alli" => "al",
      "izer" => "ize",
      "enci" => "ence",
      "ator" => "ate",
      "bli" => "ble",
      "ogi" => "og",
    );
    foreach ($checks as $find => $replace) {
      if (self::hasEnding($word, $find)) {
        if (self::inR1($word, $find)) {
          $word = self::removeEnding($word, $find) . $replace;
        }
        return $word;
      }
    }
    if (self::hasEnding($word, 'li')) {
      if (strlen($word) > 4 && self::validLi(self::charAt(-3, $word))) {
        $word = self::removeEnding($word, 'li');
      }
    }
    return $word;
  }

  /**
   * Implements step 3 of the Porter2 algorithm.
   *
   * @param string $word
   *   The word to stem.
   *
   * @return string $word
   *   The modified word.
   */
  protected static function step3($word) {
    $checks = array(
      'ational' => 'ate',
      'tional' => 'tion',
      'alize' => 'al',
      'icate' => 'ic',
      'iciti' => 'ic',
      'ical' => 'ic',
      'ness' => '',
      'ful' => '',
    );
    foreach ($checks as $find => $replace) {
      if (self::hasEnding($word, $find)) {
        if (self::inR1($word, $find)) {
          $word = self::removeEnding($word, $find) . $replace;
        }
        return $word;
      }
    }
    if (self::hasEnding($word, 'ative')) {
      if (self::inR2($word, 'ative')) {
        $word = self::removeEnding($word, 'ative');
      }
    }
    return $word;
  }

  /**
   * Implements step 4 of the Porter2 algorithm.
   *
   * @param string $word
   *   The word to stem.
   *
   * @return string $word
   *   The modified word.
   */
  protected static function step4($word) {
    $checks = array(
      'ement',
      'ment',
      'ance',
      'ence',
      'able',
      'ible',
      'ant',
      'ent',
      'ion',
      'ism',
      'ate',
      'iti',
      'ous',
      'ive',
      'ize',
      'al',
      'er',
      'ic',
    );
    foreach ($checks as $check) {
      // Among the suffixes, if found and in R2, delete.
      if (self::hasEnding($word, $check)) {
        if (self::inR2($word, $check)) {
          if ($check !== 'ion' || in_array(self::charAt(-4, $word), array('s', 't'))) {
            $word = self::removeEnding($word, $check);
          }
        }
        return $word;
      }
    }
    return $word;
  }

  /**
   * Implements step 5 of the Porter2 algorithm.
   *
   * @param string $word
   *   The word to stem.
   *
   * @return string $word
   *   The modified word.
   */
  protected static function step5($word) {
    if (self::hasEnding($word, 'e')) {
      // Delete if in R2, or in R1 and not preceded by a short syllable.
      if (self::inR2($word, 'e') || (self::inR1($word, 'e') && !self::isShortSyllable($word, strlen($word) - 3))) {
        $word = self::removeEnding($word, 'e');
      }
      return $word;
    }
    if (self::hasEnding($word, 'l')) {
      // Delete if in R2 and preceded by l.
      if (self::inR2($word, 'l') && self::charAt(-2, $word) == 'l') {
        $word = self::removeEnding($word, 'l');
      }
    }
    return $word;
  }

  /**
   * Removes certain double consonants from the word's end.
   *
   * @param string $word
   *   The word to stem.
   *
   * @return string $word
   *   The modified word.
   */
  protected static function removeDoubles($word) {
    $doubles = array('bb', 'dd', 'ff', 'gg', 'mm', 'nn', 'pp', 'rr', 'tt');
    foreach ($doubles as $double) {
      if (substr($word, -2) == $double) {
        $word = substr($word, 0, -1);
        break;
      }
    }
    return $word;
  }

  /**
   * Checks whether a character is a vowel.
   *
   * @param int $position
   *   The character's position.
   * @param string $word
   *   The word in which to check.
   * @param string[] $additional
   *   (optional) Additional characters that should count as vowels.
   *
   * @return bool
   *   TRUE if the character is a vowel, FALSE otherwise.
   */
  protected static function isVowel($position, $word, $additional = array()) {
    $vowels = array_merge(array('a', 'e', 'i', 'o', 'u', 'y'), $additional);
    return in_array(self::charAt($position, $word), $vowels);
  }

  /**
   * Retrieves the character at the given position.
   *
   * @param int $position
   *   The 0-based index of the character. If a negative number is given, the
   *   position is counted from the end of the string.
   * @param string $word
   *   The word from which to retrieve the character.
   *
   * @return string
   *   The character at the given position, or an empty string if the given
   *   position was illegal.
   */
  protected static function charAt($position, $word) {
    $length = strlen($word);
    if (abs($position) >= $length) {
      return '';
    }
    if ($position < 0) {
      $position += $length;
    }
    return $word[$position];
  }

  /**
   * Determines whether the word ends in a "vowel-consonant" suffix.
   *
   * Unless the word is only two characters long, it also checks that the
   * third-last character is neither "w", "x" nor "Y".
   *
   * @param int|null $position
   *   (optional) If given, do not check the end of the word, but the character
   *   at the given position, and the next one.
   *
   * @return bool
   *   TRUE if the word has the described suffix, FALSE otherwise.
   */
  protected static function isShortSyllable($word, $position = NULL) {
    if ($position === NULL) {
      $position = strlen($word) - 2;
    }
    // A vowel at the beginning of the word followed by a non-vowel.
    if ($position === 0) {
      return self::isVowel(0, $word) && !self::isVowel(1, $word);
    }
    // Vowel followed by non-vowel other than w, x, Y and preceded by
    // non-vowel.
    $additional = array('w', 'x', 'Y');
    return !self::isVowel($position - 1, $word) && self::isVowel($position, $word) && !self::isVowel($position + 1, $word, $additional);
  }

  /**
   * Determines whether the word is short.
   *
   * A word is called short if it ends in a short syllable and if R1 is null.
   *
   * @return bool
   *   TRUE if the word is short, FALSE otherwise.
   */
  protected static function isShort($word) {
    return self::isShortSyllable($word) && self::r($word, 1) == strlen($word);
  }

  /**
   * Determines the start of a certain "R" region.
   *
   * R is a region after the first non-vowel following a vowel, or end of word.
   *
   * @param int $type
   *   (optional) 1 or 2. If 2, then calculate the R after the R1.
   *
   * @return int
   *   The R position.
   */
  protected static function r($word, $type = 1) {
    $inc = 1;
    if ($type === 2) {
      $inc = self::r($word, 1);
    }
    elseif (strlen($word) > 5) {
      $prefix_5 = substr($word, 0, 5);
      if ($prefix_5 === 'gener' || $prefix_5 === 'arsen') {
        return 5;
      }
      if (strlen($word) > 5 && substr($word, 0, 6) === 'commun') {
        return 6;
      }
    }

    while ($inc <= strlen($word)) {
      if (!self::isVowel($inc, $word) && self::isVowel($inc - 1, $word)) {
        $position = $inc;
        break;
      }
      $inc++;
    }
    if (!isset($position)) {
      $position = strlen($word);
    }
    else {
      // We add one, as this is the position AFTER the first non-vowel.
      $position++;
    }
    return $position;
  }

  /**
   * Checks whether the given string is contained in R1.
   *
   * @param string $string
   *   The string.
   *
   * @return bool
   *   TRUE if the string is in R1, FALSE otherwise.
   */
  protected static function inR1($word, $string) {
    $r1 = substr($word, self::r($word, 1));
    return strpos($r1, $string) !== FALSE;
  }

  /**
   * Checks whether the given string is contained in R2.
   *
   * @param string $string
   *   The string.
   *
   * @return bool
   *   TRUE if the string is in R2, FALSE otherwise.
   */
  protected static function inR2($word, $string) {
    $r2 = substr($word, self::r($word, 2));
    return strpos($r2, $string) !== FALSE;
  }

  /**
   * Checks whether the word ends with the given string.
   *
   * @param string $string
   *   The string.
   *
   * @return bool
   *   TRUE if the word ends with the given string, FALSE otherwise.
   */
  protected static function hasEnding($word, $string) {
    $length = strlen($string);
    if ($length > strlen($word)) {
      return FALSE;
    }
    return (substr_compare($word, $string, -1 * $length, $length) === 0);
  }

  /**
   * Removes a given string from the end of the current word.
   *
   * Does not check whether the ending is actually there.
   *
   * @param string $string
   *   The ending to remove.
   */
  protected static function removeEnding($word, $string) {
    return substr($word, 0, -strlen($string));
  }

  /**
   * Checks whether the given string contains a vowel.
   *
   * @param string $string
   *   The string to check.
   *
   * @return bool
   *   TRUE if the string contains a vowel, FALSE otherwise.
   */
  protected static function containsVowel($string) {
    $inc = 0;
    $return = FALSE;
    while ($inc < strlen($string)) {
      if (self::isVowel($inc, $string)) {
        $return = TRUE;
        break;
      }
      $inc++;
    }
    return $return;
  }

  /**
   * Checks whether the given string is a valid -li prefix.
   *
   * @param string $string
   *   The string to check.
   *
   * @return bool
   *   TRUE if the given string is a valid -li prefix, FALSE otherwise.
   */
  protected static function validLi($string) {
    return in_array($string, array(
      'c',
      'd',
      'e',
      'g',
      'h',
      'k',
      'm',
      'n',
      'r',
      't',
    ));
  }

}