RhSolutions-AddIn/src/AddIn/Functions.cs

using ExcelDna.Integration;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Threading.Tasks;

namespace RehauSku
{
    public class Functions
    {
        [ExcelFunction(Description = "Получение корректного артикула из строки")]
        public static object GETRAUSKU([ExcelArgument(Name = "\"Строка\"", Description = "строка, содержащая актикул")] string line)
        {
            if (RauSku.TryParse(line, out RauSku rausku))
            {
                return rausku.ToString();
            }

            else return ExcelError.ExcelErrorNA;
        }

        [ExcelFunction(Description = "Запрос в удаленную базу данных")]
        public static object RHSOLUTIONS([ExcelArgument(Name = "Запрос")] string line)
        {
            object result;

            result = ExcelAsyncUtil.Run("Database request", line, delegate
            {
                return RhDatabaseClient.GetProduct(line).GetAwaiter().GetResult();
            });

            if (result == null)
            {
                return ExcelError.ExcelErrorNA;
            }

            if (result.Equals(ExcelError.ExcelErrorNA))
            {
                return "Загрузка...";
            }

            return result;
        }
    }

    public static class RhDatabaseClient
    {
        private static HttpClient httpClient = AddIn.httpClient;

        public static async Task<object> GetProduct(string line)
        {
            string request = @"https://rh.cebotari.ru/api/search?query=" + line;

            ServicePointManager.SecurityProtocol =
                SecurityProtocolType.Tls12 |
                SecurityProtocolType.Tls11 |
                SecurityProtocolType.Tls;

            string response = await httpClient.GetStringAsync(request);

            var products = JsonConvert.DeserializeObject<IEnumerable<DbProduct>>(response);

            var product = products.FirstOrDefault();

            if (product == null)
            {
                return null;
            }
            else
            {
                return $"{product.productSku} {product.name}";
            }
        }

        private class DbProduct
        {
            public string productSku { get; set; }
            public string name { get; set; }
        }
    }
}