<?php
/*
 Algorithm based on http://www.snowball.tartarus.org/algorithms/dutch/stemmer.html.

 Improvements:
 - Convert s/f to z/v when removing double vowel in last syllable.
 - Include more consonants in undoubling operation.
 - Correctly remove apostrophe-s (e.g. "pagina's").
 - Correctly strip accented suffixes (e.g. industriële)
*/

/**
* Implementation of hook_search_preprocess
*/
function dutchstemmer_search_preprocess(&$text) {
  // Split words from noise and remove apostrophes
  $words = preg_split('/([^a-zA-Zäëïöüáéíóúè\']+)/u', $text, -1, PREG_SPLIT_DELIM_CAPTURE);

  // Process each word
  $odd = true;
  foreach ($words as $k => $word) {
    if ($odd) {
      $words[$k] = dutchstemmer_stem($word);
    }
    $odd = !$odd;
  }

  // Put it all back together
  return implode('', $words);
}

/**
* Implementation of hook_help().
*/
function dutchstemmer_help($section = 'admin/help#search') {
  switch ($section) {
    case 'admin/modules#description':
      return t('Implements a Dutch stemming algorithm to improve Dutch searching.');
  }
}

/**
 * Stem a dutch word.
 */
function dutchstemmer_stem($word) {
  global $step2;

  $step2 = FALSE;

  // Lowercase
  $word = drupal_strtolower($word);

  // Step 0: early (accented) suffix removal
  $word = dutchstemmer_step0($word, $r1, $r2);

  // Remove accents
  $word = str_replace(array('ä', 'ë', 'ï', 'ö', 'ü', 'á', 'é', 'í', 'ó', 'ú'),
                      array('a', 'e', 'i', 'o', 'u', 'a', 'e', 'i', 'o', 'u'),
                      $word);

  // Put initial y, y after a vowel, and i between vowels into upper case (treat as consonants).
  $word = preg_replace(array('/^y|(?<=[aeiouyè])y/u', '/(?<=[aeiouyè])i(?=[aeiouyè])/u'),
                       array('Y', 'I'),
                       $word);

  /* R1 is the region after the first non-vowel following a vowel, or is the
     null region at the end of the word if there is no such non-vowel. */
  if (preg_match('/[aeiouyè][^aeiouyè]/u', $word, $matches, PREG_OFFSET_CAPTURE)) {
    $r1 = $matches[0][1] + 2;
  }

  /* R2 is the region after the first non-vowel following a vowel in R1, or is
     the null region at the end of the word if there is no such non-vowel. */
  if (preg_match('/[aeiouyè][^aeiouyè]/u', $word, $matches, PREG_OFFSET_CAPTURE, $r1)) {
    $r2 = $matches[0][1] + 2;
  }

  // Steps 1-4: suffix removal
  $word = dutchstemmer_step1($word, $r1, $r2);
  $word = dutchstemmer_step2($word, $r1, $r2);
  $word = dutchstemmer_step3($word, $r1, $r2);
  $word = dutchstemmer_step4($word, $r1, $r2);

  $word = str_replace(array('Y', 'I'), array('y', 'i'), $word);

  return $word;
}

function dutchstemmer_undouble($word) {
  return preg_match('/(bb|dd|gg|kk|ll|mm|nn|pp|rr|ss|tt|zz)$/u', $word) ? substr($word, 0, -1) : $word;
}

function dutchstemmer_step0($word) {
  // Step 0: accented suffixes
  return preg_replace('/eën$/u', 'e', preg_replace('/(ieel|iële|ieën)$/u', 'ie', $word));
}

function dutchstemmer_step1($word, $r1, $r2) {
  // Step 1:
  // Search for the longest among the following suffixes, and perform the action indicated
  if ($r1) {
    // -heden
    if (preg_match('/heden$/u', $word, $matches, 0, $r1)) {
      return preg_replace('/heden$/u', 'heid', $word, -1);
    }
    // -en(e)
    else if (preg_match('/(?<=[^aeiouyè]|gem)ene?$/u', $word, $matches, 0, $r1)) {
      return dutchstemmer_undouble(preg_replace('/ene?$/u', '', $word, -1));
    }
    // -s(e)
    else if (preg_match('/(?<=[^jaeiouyè])se?$/u', $word, $matches, 0, $r1)) {
      return rtrim(preg_replace('/se?$/u', '', $word, -1), "'");
    }
  }
  return $word;
}

function dutchstemmer_step2($word, $r1, $r2) {
  // Step 2:
  // Delete suffix e if in R1 and preceded by a non-vowel, and then undouble the ending
  if ($r1) {
    if (preg_match('/(?<=[^aeiouyè])e$/u', $word, $matches, 0, $r1)) {
      $step2 = TRUE;
      return dutchstemmer_undouble(preg_replace('/e$/u', '', $word, -1));
    }
  }
  return $word;
}

function dutchstemmer_step3($word, $r1, $r2) {
  global $step2;

  // Step 3a: heid
  // delete heid if in R2 and not preceded by c, and treat a preceding en as in step 1(b)
  if ($r2) {
    if (preg_match('/(?<!c)heid$/u', $word, $matches, 0, $r2)) {
      $word = preg_replace('/heid$/u', '', $word, -1);
      if (preg_match('/en$/u', $word, $matches, 0, $r1)) {
        $word = dutchstemmer_undouble(preg_replace('/en$/u', '', $word, -1));
      }
    }
  }

  // Step 3b: d-suffixes (*)
  // Search for the longest among the following suffixes, and perform the action indicated.
  if ($r2) {
    // -baar
    if (preg_match('/baar$/u', $word, $matches, 0, $r2)) {
      $word = preg_replace('/baar$/u', '', $word, -1);
    }
    // -lijk
    else if (preg_match('/lijk$/u', $word, $matches, 0, $r2)) {
      $word = dutchstemmer_step2(preg_replace('/lijk$/u', '', $word, -1), $r1, $r2);
    }
    // -end / -ing
    else if (preg_match('/(end|ing)$/u', $word, $matches, 0, $r2)) {
      $word = preg_replace('/(end|ing)$/u', '', $word, -1);
      // -ig
      if (preg_match('/(?<!e)ig$/u', $word, $matches, 0, $r2)) {
        $word = preg_replace('/ig$/u', '', $word, -1);
      }
    }
    // -ig
    else if (preg_match('/(?<!e)ig$/u', $word, $matches, 0, $r2)) {
      $word = preg_replace('/ig$/u', '', $word, -1);
    }
    // -bar
    else if ($step2 && preg_match('/bar$/u', $word, $matches, 0, $r2)) {
      $word = preg_replace('/bar$/u', '', $word, -1);
    }
  }

  return $word;
}

function dutchstemmer_step4($word, $r1, $r2) {
  // Step 4: undouble vowel
  // If the words ends CVD, where C is a non-vowel, D is a non-vowel other than
  // I, and V is double a, e, o or u, remove one of the vowels from V (fo
  // example, maan -> man, brood -> brod).
  if (preg_match('/[^aeiouyè](aa|ee|oo|uu)[^Iaeiouyè]$/u', $word)) {
    $word = drupal_substr($word, 0, -2) . str_replace(array('s', 'f'), array('z', 'v'), drupal_substr($word, -1));
  }
  return $word;
}

?>