date / time help

hello, i have something this but dont know how make it for month *check/reset every month, (i tried something but i don't know how test it, cannot wait for end of month) can someone help me remake it for months? (reset every month)

Code:

public function getWeekStartEnd()
    {
           $ts = time();
        

        if (date('w', $ts) == 1)
        {
            $start = strtotime('today', $ts);
        }
        else
        {
            $start = strtotime('this week last monday', $ts);
        }
    
        if (date('w', $ts) == 0)
        {
            $end = strtotime('today', $ts);
        }
        else
        {
            $end = strtotime('this week next sunday', $ts);
        }
        
     
        return array(date('Y-m-d H:i', $start), date('Y-m-d H:i', $end + 60*60*23 + 60*59));
    }