screen/application/common/service/DiscountService.php

<?php
namespace app\common\service;

use app\common\model\SysConfig;

class DiscountService{
    public static function getById($level=null){
        static $discount;
        if(is_null($discount)) {
            $discount = SysConfig::look('user_level_discount') ?: [];
        }
        if(is_null($level)){
            return $discount;
        }
        return $discount[$level]??null;
    }
    public static function saveDiscount($id,$discount){
        $config=self::getById();
        $config[$id]=bcadd($discount,0);
        SysConfig::set('user_level_discount',$config);
    }
}