rule "Level 1"
    when
        alreadyCostPrice >= 0
        alreadyCostPrice < 100
    then
        rate = 1
end
rule "Level 2"
    when
        alreadyCostPrice >= 100
        alreadyCostPrice < 300
    then
        rate = 0.8
end
rule "Level 3"
    when
        alreadyCostPrice >= 300
    then
        rate = 0.5
end

public class CustomerRateService
    {
        public static decimal CalculateRate(decimal costedAlready, decimal priceThisTime, string rulePolicy)
        {
            using (RuleEngine engine = new RuleEngine(System.IO.Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Rules")))
            {
                engine.BindRule("Rating", rulePolicy);   //此处的第一个参数"Rating"是规则组名称，对应的是物理文件夹，方便规则文件的管理和查看

                engine.SetParameter("alreadyCostPrice", costedAlready);
                engine.SetParameter("thisTimePrice", priceThisTime);

                engine.Process();

                return engine.GetDecimal("rate");
            }
        }
        
    }