获取某年第几周的开始日期和结束日期

    /**
     * 获取某年第几周的开始日期和结束日期
     * @param int $year
     * @param int $week 第几周;
     */
    public function weekday($year, $week = 1)
    {
        $year_start = mktime(0, 0, 0, 1, 1, $year);
        $year_end = mktime(0, 0, 0, 12, 31, $year);

        // 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 {
            $week++;
            $start = strtotime('+1 monday', $year_start);//把第一个周一作为开始
        }

        // 第几周的开始时间
        if ($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('Y', $weekday['end']) != $year) {
            $weekday['end'] = $year_end;
        }
        $weekday['start'] = date("Y-m-d", $weekday['start']);
        $weekday['end'] = date("Y-m-d", $weekday['end']);
        return $weekday;
    }