public function analyze_folder(string $folder = '.', bool $deep = false): array
  {
    $res = [];
		if (  \is_dir($folder) ){

      $files = $deep ? bbn\file\dir::scan($folder, 'file') : bbn\file\dir::get_files($folder);
		  foreach ( $files as $f ){

        $words = $this->analyze_file($f);
        foreach ( $words as $word ){
          if ( !isset($res[$word]) ){
            $res[$word] = [];
          }
          if ( !in_array($f, $res[$word]) ){
            $res[$word][] = $f;
          }
        }
      }
    }
    return $res;
  }