private function mondayTime($timestamp=0,$is_return_timestamp=true){
  static $cache ;
  $id = $timestamp.$is_return_timestamp;
  if(!isset($cache[$id])){
   if(!$timestamp) $timestamp = time();
   $monday_date = date('Y-m-d',$timestamp-86400*date('w',$timestamp)+(date('w',$timestamp)>0?86400:-/*6*86400*/518400));
   if($is_return_timestamp){
    $cache[$id] = strtotime($monday_date);
   }else{
    $cache[$id] = $monday_date;
   }
  }
  return $cache[$id];
}
echo $this->mondayTime(time() + 24*3600*2,false);
exit;