/**
  * @param $file
  */
 public static function get_root_dirs_fromzip($file)
 {
     //valid
     if (!file_exists($file) || HW_File_Directory::getExtension($file) != 'zip') {
         return;
     }
     $zip = new ZipArchive();
     $result = array();
     if ($zip->open($file) == TRUE) {
         for ($i = 0; $i < $zip->numFiles; $i++) {
             $filename = $zip->getNameIndex($i);
             //check file in subfolder
             if (count(explode('/', trim($filename, '\\/'))) || HW_File_Directory::has_extension($filename)) {
                 continue;
             }
             $result[] = $filename;
         }
     }
     return $result;
 }