using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

using System.Collections.ObjectModel;

using System.Threading.Tasks;

using System.Net.Http;

​

using System.Text.Json;

using System.Text.Json.Serialization;

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/66495660/net-5-0-signature-change-of-system-text-json-jsonserializer-deserialize

​

    public class Category

    {

        public int id { get; set; }

        public string name { get; set; }

        public int parent_id { get; set; }

    }

​

    public abstract class BaseClient

    {

        protected virtual async Task<Stream> Download(string uri)

        {

#if false

            uri = uri + (uri.Contains("?") ? "&" : "?") + "api_key=" + "xxxxx";

            var response = await new HttpClient() { BaseAddress = new Uri(uri) }.GetAsync(uri);

            return await response.Content.ReadAsStreamAsync();

#endif

            return new FileStream(@"Question66495660.json",  

                                  FileMode.Open, FileAccess.Read, FileShare.Read,  

                                  bufferSize: 4096, useAsync: true);

        }

​

        protected abstract Task<T> Parse<T>(string uri, string root) where T : class, new();

​

        public async Task<Category> GetCategory(string categoryID)

        {

            string uri = "https://api.stlouisfed.org/fred/category?category_id=" + categoryID;

            return (await Parse<List<Category>>(uri, "categories"))?.FirstOrDefault();

        }

    }

​

    public class JSONClient : BaseClient

    {

        protected override async Task<T> Parse<T>(string uri, string root)

        {

            uri = uri + (uri.Contains("?") ? "&" : "?") + "file_type=json";

            using var stream = await Download(uri); // Dispose here or not? What about disposing of the containing HttpResponseMessage?

            var options = new JsonSerializerOptions

            {

                AllowTrailingCommas = true,

                // PropertyNameCaseInsensitive = false, Uncomment if you need case insensitivity.

            };

            var dictionary = await JsonSerializer.DeserializeAsync<Dictionary<string, T>>(stream, options);

            // Throw an exception if the dictionary does not have exactly one entry, with the required name

            var pair = dictionary?.Single();

            if (pair == null || @pair.Value.Key.Equals(root, StringComparison.Ordinal)) //StringComparison.OrdinalIgnoreCase if required

                throw new JsonException();

            // And now return the value

            return pair.Value.Value;

        }

    }

​

​

    public class Program

    {

        public static async Task Test()

        {

            var fileName = @"Question66495660.json";

            try

            {

                File.WriteAllText(fileName, GetJson());

                var client = new JSONClient();

                var category = await client.GetCategory("1");

                category.Dump();

            }

            finally

            {

                File.Delete(fileName);

            }

        }

​

        static string GetJson() => @"{

    ""categories"": [

        {

            ""id"": 125,

            ""name"": ""Trade Balance"",

            ""parent_id"": 13

        }

    ]

}";

        public static async Task Main(string[] args)

        {

            Console.WriteLine("Environment version: {0} ({1})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , GetNetCoreVersion());

            Console.WriteLine("{0} version: {1}", typeof(JsonSerializer).Assembly.GetName().Name,  typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                await Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

        public static string GetNetCoreVersion()

        {

            //https://techblog.dorogin.com/how-to-detect-net-core-version-in-runtime-ecd65ad695be

            //

            var assembly = typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly;

            var assemblyPath = assembly.Location.Split(new[] { '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);

            int netCoreAppIndex = Array.IndexOf(assemblyPath, "Microsoft.NETCore.App");

            if (netCoreAppIndex > 0 && netCoreAppIndex < assemblyPath.Length - 2)

                return assemblyPath[netCoreAppIndex + 1];

            return null;

        }

    }

​