switch ($op) {

    case 'insert':
      if (isset($comment['pid'])) {
        $pid = $comment['pid'];
      }
      else {
        $pid = 0;
      }
   
      # Redirect users to last topic page after submitting comment  
      # Last page -1 since pages start at 0
      $last_page = ceil(comment_num_all(is_object($comment) ? $comment->nid : $comment['nid']) / _comment_get_display_setting('comments_per_page'));
      if ($last_page == 1) {
        # do nothing ...
      }
      elseif($last_page > 1) {
        # redirect to last page
        //$page_num = '/?page=';
        $last_page = ($last_page-1);
        $pre_last_comment_num = (comment_num_all($comment['nid']) - 1);
        drupal_goto('node/' . $comment['nid'], "page=$last_page", "comment-$pre_last_comment_num");
      }
     
      break;
   
    //skip some code .....  
   }
 
}
?>