It can traverse all files and subfolders under a folder

// Use recursion to achieve , About what is recursion  , Self search 
 public static function my_scandir($dir){
        $files = array();

        if(is_dir($dir)){

            if($handle =opendir($dir)){
                while (($file = readdir($handle))!== false){
                    if($file != '.' &&  $file!='..'){
                        $_dir  =  $dir ."/".$file;
                        if(is_dir($_dir)){
                            $files[$file] = self::my_scandir($_dir);
                        }else{
                            $files[] = $_dir;
                        }
                    }
                }
                closedir($handle);
                return $files;
            }
        }

    }