//$now = '2018-11-13';週二
public function getNowTimeInfo($now)
{
    $str = array();
    //$first =1 表示每週星期一為開始日期 0表示每週日為開始日期
    $str['year'] = date('Y', strtotime($now));
    $first = 1;
    //當日在整年中的第幾周
    $str['week'] = date('W', strtotime($now));
    //獲取當前周的第幾天 週日是 0 週一到週六是 1 - 6
    $w = date('w', strtotime($now));
    //獲取本週開始日期，如果$w是0，則表示週日，減去 6 天
    $week_start = date('Y-m-d', strtotime("$now -" . ($w ? $w - $first : 6) . ' days'));
    $str['week_start'] = $week_start;
    //本週結束日期
    $week_end = date('Y-m-d', strtotime("$week_start +6 days"));
    $str['week_end'] = $week_end;
    return $str;
}

返回值：

Array (     [year] => 2018     [week] => 46     [week_start] => 2018-11-12//週一     [week_end] => 2018-11-18//週日 )