php 获取某日期的前一天日期

<?php
/**
 *
 * 获取给定日期的前一天
 * @param string $date
 * @return string $yesterday
 */
public function getYesterday($date)
{
if(empty($date))
{
$yesterday = date("Y-m-d",strtotime("-1 day"));
}else{
$arr = explode('-', $date);
$year = $arr[0];
$month = $arr[1];
$day = $arr[2];
$unixtime = mktime(0,0,0,$month,$day,$year)-86400;
$yesterday = date('Y-m-d',$unixtime);
}

return $yesterday;
}