function slug($text){

  // replace non letter or digits by -

  $text = preg_replace('~[^pLd]+~u', '-', $text);

  // transliterate

  $text = iconv('utf-8', 'us-ascii//TRANSLIT', $text);

  // remove unwanted characters

  $text = preg_replace('~[^-w]+~', '', $text);

  // trim

  $text = trim($text, '-');

  // remove duplicate -

  $text = preg_replace('~-+~', '-', $text);

  // lowercase

  $text = strtolower($text);

  if (empty($text)) {

    return 'n-a';

  }

  return $text;

}