周 月 日 互转

1、周转日，全年第n周的起止日

public function dayFromWeek($week,$year=0){    $year = empty($year)?date('Y'):$year;    $year_start = mktime(0,0,0,1,1,$year);    // 判断第一天是否为第一周的开始    if (1 == date('W',$year_start)){        $start = $year_start;//把第一天做为第一周的开始    }else{        $start = strtotime('next Monday', $year_start);    }    // 第几周的开始时间    if (0 == $week){        $weekday['start'] = strtotime('last Monday', $year_start);    }elseif (1 == $week){        $weekday['start'] = $start;    }else{        $weekday['start'] = strtotime('+'.($week-0).' monday',$start);    }    // 第几周的结束时间    $weekday['end'] = strtotime('+1 sunday',$weekday['start']);    $weekday['start'] = date("Y-m-d",$weekday['start']);    $weekday['end'] = date("Y-m-d",$weekday['end']);    return $weekday;}

2、月起止日

public function dayFromMonth($month, $year=0){    $year = empty($year)?date('Y'):$year;    $month = strlen($month)==2?$month:'0'.$month;    $startDay = $year.'-'.$month.'-01';    $endDay = date('Y-m-d', strtotime(date('Y-m-01', strtotime($startDay)) . ' +1 month -1 day'));    return ['start'=>$startDay, 'end'=>$endDay];}

3、月起止周，当月跨过了哪些周

public function weekFromMonth($month, $year=0){    $day = $this->dayFromMonth($month, $year);    return ['start'=>date('W',strtotime($day['start'])),'end'=>date('W',strtotime($day['end']))];}

4、第几周在当月的起止日

public function dayFromWM($week,$month,$year=0){    $year = empty($year)?date('Y'):$year;    $year_start = mktime(0,0,0,1,1,$year);    $year_end = mktime(0,0,0,12,31,$year);    $month_start = $year.'-'.$month.'-01';    $month_end = date('Y-m-d', strtotime(date('Y-m-01', strtotime($month_start)) . ' +1 month -1 day'));    // 判断第一天是否为第一周的开始    if (intval(date('W',$year_start))===1){        $start = $year_start;//把第一天做为第一周的开始    }else{        $start = strtotime('next Monday', $year_start);    }    // 第几周的开始时间    if ($week===0){        $weekday['start'] = strtotime('last Monday', $year_start);    }elseif ($week===1){        $weekday['start'] = $start;    }else{        $weekday['start'] = strtotime('+'.($week-0).' monday',$start);    }    // 第几周的结束时间    $weekday['end'] = strtotime('+1 sunday',$weekday['start']);    if (date('m',$weekday['end'])!=$month){         $weekday['end'] = $month_end;    }else{        $weekday['end'] = date("Y-m-d",$weekday['end']);    }    if (date('m', $weekday['start'])!=$month){        $weekday['start'] = $month_start;    }else{        $weekday['start'] = date("Y-m-d",$weekday['start']);    }    return $weekday;}