PHP 通过当前时间获取下个月的当前时间

PHP 通过当前时间获取下个月的时间，默认当前时间

 /**
     *  获取下个月的当前时间
     * @param $date  Y-m-d H:i:s
     * @return string
     */
    public static function nextMonth($date=Null)
    {
        if ($date) {
            $timestamp = strtotime($date);
        } else {
            $timestamp = time();
        }
        $arr = getdate($timestamp);
        $time = date('H:i:s', $timestamp);
        $day = $arr['mday'];
        $year = $arr['year'];
        if ($arr['mon'] == 12) {
            $year = $arr['year'] + 1;
            $month = $arr['mon'] - 11;
            if($month<10){
                $month = '0'.$month;
            }
            $firstday = $year . '-' . $month . '-' . date('d', $timestamp) . ' ' . $time;
        } else {
            $month = $arr['mon']+1;
            $month_maxday = date('Y-m-d', strtotime(date('Y-m-01', strtotime($year . '-' . $month . '-01')) . ' +1 month -1 day')); //某月的最后一天
            $month_maxday = date("d ",strtotime($month_maxday));
            if($arr['mday']>$month_maxday){
                $day =  $month_maxday;
            }
            $firstday = date("Y-m-d", mktime(0, 0, 0, $month, $day, $year)). ' ' . $time;
        }
        return $firstday;

    }

方法很多，这里随便写的