主要实现功能：关注公众号的用户发送拼多多商品链接，后台程序通过链接查找商品优惠券或返佣情况。
说明：使用了niltor 封装的拼多多接口 github地址 ，但是需要注意可能会存在返回模型无法正确解析，导致没有正确返回数据的问题。使用的过程中修改下返回模型属性类型就好了。

最终实现效果如下：

代码实现：

 public async System.Threading.Tasks.Task<string> GetPddCouponAsync(ExmlMsg xmlMsg)
    {
       //通过正则表达式解析拼多多商品链接，获取拼多多商品Id
        string msg = xmlMsg.Content;
        Match m_goods = Regex.Match(msg, @"(?<=goods_id=)([0-9]*)");
        
        string goods_id = m_goods.Value;

        if (string.IsNullOrEmpty(goods_id))
        {
            LogHelper.WriteLog(typeof(WechatController), "获取拼多多goods id失败" + msg);
            return "";
        }
        
        //调用之前需要先注册PddOpenSdk服务
        /*
        PddCommonApi.ClientId = "d8172a66ddf14220beac58e8eddca0d9";
        PddCommonApi.ClientSecret = "d5993ce16cc0d1bd35403176f35544962e786645";
        PddCommonApi.RedirectUri = "RedirectUri";
        */
        DdkApi api = new DdkApi();

        var model = new DetailDdkGoodsRequestModel()
        {
            Type = "pdd.ddk.goods.detail",
            GoodsIdList = $"[{goods_id}]"
        };
        DetailDdkGoodsResponseModel result = null;
        try
        {
            result = await api.DetailDdkGoodsAsync(model);
        }
        catch(Exception ex)
        {
            LogHelper.WriteLog(typeof(WechatController), "调用拼多多获取商品详细信息失败" + ex.Message);
            return "";
        }
       

        var goods = result.GoodsDetailResponse.GoodsDetails.FirstOrDefault();

        if (goods==null) //无优惠券 无佣金
        {
            return "/:rose 亲，这款商品的优惠返利活动结束了~\n请换个商品试试吧。\n========================\n\ue231    <a href='https://mobile.yangkeduo.com/duo_cms_mall.html?pid=2495191_31302208cpsSign=CM2495191_31302208_3a1c1a0431608b9c1eb417183d57c1bdduoduo_type=2'>拼多多优惠券商城</a>\n下单确认收货后就能收到返利佣金啦~";
        }
        else if(goods.HasCoupon) //有优惠券 有佣金
        {
            try
            {
                var promotionUrlModel = await api.GenerateDdkGoodsPromotionUrlAsync(new GenerateDdkGoodsPromotionUrlRequestModel
                {
                    Type = "pdd.ddk.goods.promotion.url.generate",
                    PId = pdd_pid,
                    GoodsIdList = $"[{goods_id}]",
                    GenerateShortUrl = true,
                    CustomParameters = xmlMsg.FromUserName
                });

                return $"/:rose 亲，商品信息如下~\n========================\n{goods.GoodsName}\n【在售价】{((decimal)goods.MinGroupPrice) / 100}元\n【券后价】{Math.Round(((decimal)(goods.MinGroupPrice - goods.CouponDiscount.Value)) / 100, 2)}元\n\ue231 <a href='{promotionUrlModel.GoodsPromotionUrlGenerateResponse.GoodsPromotionUrlList.FirstOrDefault().Url}'>点击这里下单</a>\n下单确认收货后就能收到返利佣金啦~";

            }
            catch (Exception ex)
            {
                LogHelper.WriteLog(typeof(WechatController), "调用拼多多获取推广链接失败" + ex.Message);
                return "";
            }
         }
        else //无优惠券 但有佣金
        {
            try
            {
                var promotionUrlModel = await api.GenerateDdkGoodsPromotionUrlAsync(new GenerateDdkGoodsPromotionUrlRequestModel
                {
                    Type = "pdd.ddk.goods.promotion.url.generate",
                    GoodsIdList = $"[{goods_id}]",
                    PId = pdd_pid,
                    GenerateShortUrl = true,
                    CustomParameters = xmlMsg.FromUserName
                });

                return $"/:rose 亲，商品信息如下~\n========================\n{goods.GoodsName}\n【在售价】{((decimal)goods.MinGroupPrice) / 100}元\n【约返利】{Math.Round((decimal)(goods.MinGroupPrice * goods.PromotionRate) / 100000,2)}元\n\ue231 <a href='{promotionUrlModel.GoodsPromotionUrlGenerateResponse.GoodsPromotionUrlList.FirstOrDefault().Url}'>点击这里下单</a>\n下单确认收货后就能收到返利佣金啦~\n\n 点击查看  <a href='http://mp.weixin.qq.com/s?__biz=Mzg2NTAxOTEyMA==&mid=100000146&idx=1&sn=62405c8df3db46e74940aefb9ac3737b&chksm=4e61340d7916bd1bf645afbc6d10c1f19561d7fa59847516c01e64c0791e6d544f4f56c4f498#rd'>如何领取返利</a>";
            }catch(Exception ex)
            {
                LogHelper.WriteLog(typeof(WechatController), "调用拼多多获取推广链接失败" + ex.Message);
                return "";
            }
            
        }

    }