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.Nodes;

​

using System.Text.Json;

using System.Text.Json.Serialization;

​

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

​

//https://stackoverflow.com/questions/71570877/clone-a-jsonnode-and-attach-it-to-another-one-in-net-6#

​

#nullable enable

​

    public static partial class JsonExtensions

    {

        public static TNode? CopyNode<TNode>(this TNode? node) where TNode : JsonNode => node?.Deserialize<TNode>();

​

        public static JsonNode? MoveNode(JsonArray array, int id, JsonObject newParent, string name)

        {

            var node = array[id];

            array.RemoveAt(id); 

            return newParent[name] = node;

        }

​

        public static TNode ThrowOnNull<TNode>(this TNode? value) where TNode : JsonNode => value ?? throw new JsonException("Null JSON value");

    }

​

    public static partial class JsonExtensions

    {

        public static string concQuest(string input, string allQuest, string questId) 

        {

            var inputObject = JsonNode.Parse(input).ThrowOnNull().AsObject();

            var allQuestArray = JsonNode.Parse(allQuest).ThrowOnNull().AsArray();

​

            concQuest(inputObject, allQuestArray, questId);

​

            return inputObject.ToJsonString();

        }       

        public static JsonNode? concQuest(JsonObject inputObject, JsonArray allQuestArray, string questId) 

        {

            // Enumerable.First() will throw an InvalidOperationException if no element is found satisfying the predicate.

            var node = allQuestArray.First(quest => quest!["id"]!.GetValue<string>() == questId);

            return inputObject["quest"] = node.CopyNode();

        }

    }

​

    public class Program

    {

        public static async Task Test()

        {

            var allQuestString = @"[{""id"":""1"", ""name"":""quest 1""},{""id"":""2"", ""name"":""quest 2""}]";

            var inputString = @"{""header"":""header value"", ""nullValue"":null}";

            var allQuestFileName = @"Question71570877-allquests.json";

            var inputFileName = @"Question71570877-quest.json";

​

            Console.WriteLine(inputString);

            await File.WriteAllTextAsync(allQuestFileName, allQuestString);

            await File.WriteAllTextAsync(inputFileName, inputString);

            var questId = "2"; // Or whatever

            JsonArray allQuest;

            await using (var stream = new FileStream(allQuestFileName, new FileStreamOptions { Mode = FileMode.Open, Access = FileAccess.Read, Options = FileOptions.Asynchronous }))

                allQuest = (await JsonSerializer.DeserializeAsync<JsonArray>(stream)).ThrowOnNull();

​

            JsonObject input;

            await using (var stream = new FileStream(inputFileName, new FileStreamOptions { Mode = FileMode.Open, Access = FileAccess.Read, Options = FileOptions.Asynchronous }))

                input = (await JsonSerializer.DeserializeAsync<JsonObject>(stream)).ThrowOnNull();

​

            JsonExtensions.concQuest(input, allQuest, questId);

​

            await using (var stream = new FileStream(inputFileName, new FileStreamOptions { Mode = FileMode.Create, Access = FileAccess.Write, Options = FileOptions.Asynchronous }))

                await JsonSerializer.SerializeAsync(stream, input, new JsonSerializerOptions { WriteIndented = true });

​

            Console.WriteLine(await File.ReadAllTextAsync(inputFileName));

        }

        public static async Task Main(string[] args)

        {

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

            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;

            }

        }

    }

​