private function left_time_str($sale_time){
        $sale_time = strtotime($sale_time);

        $left_time = $sale_time - time();
        if($left_time <= 0){
            return '已经开始';
        }

        $str = '距离开始还';
        $day = floor($left_time/86400);
        $hour = floor(($left_time - $day * 86400)/3600);
        $min = floor((($left_time - $day * 86400) - $hour * 3600)/60);

        if ($day > 0) $str .= $day . '天';
        if ($hour > 0) $str .= $hour . '小时';
        if ($min > 0) $str .= $min . '分钟';
        return $str;
    }