PHP 返回近7天 本月 上月日期

<?php
/**
 * 返回近7天，本月，上月数据
 * 不计当天（展示后台数据专用）
 */
function weekMonthLastMonth($search_date = 'week') {

    switch($search_date)
    {
        case 'week' : // 近7天
            $start_date = date ("Y-m-d", strtotime("-7 days"));
            $end_date = date ("Y-m-d", strtotime("-1 days"));
            break;
        case 'month' : // 本月
            $start_date = date ("Y-m-01", strtotime("-1 days"));
            $end_date = date ("Y-m-d", strtotime("-1 days"));
            break;
        case 'last_month' : // 上月
            $search_time = strtotime ("-1 month");
            $start_date = date ("Y-m-01", $search_time);
            $end_date = date ('Y-m-d', strtotime("$start_date +1 month -1 day"));
            break;
    }
    return array($start_date, $end_date);
}

echo print_r(weekMonthLastMonth('week'), true);
echo print_r(weekMonthLastMonth('month'), true);
echo print_r(weekMonthLastMonth('last_month'), true);