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 Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

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

​

using Debug = System.Console;

​

//https://stackoverflow.com/questions/60846129/json-net-how-to-obtain-location-of-json-token-in-initial-stream-for-better-err

    struct Foo

    {

        public int answer;

    }

​

    class FooConverter : JsonConverter<Foo>

    {

        public override Foo ReadJson(JsonReader reader, Type objectType, Foo existingValue, bool hasExistingValue, JsonSerializer serializer)

        {

            Debug.WriteLine((reader as IJsonLineInfo).FormatMessage("Entering ReadJson. ", reader.Path));

            // LineInfoHandling.Load ensures  line info is saved for all tokens while parsing (requires some additional memory).

            var obj = JObject.Load(reader, new JsonLoadSettings { LineInfoHandling = LineInfoHandling.Load }); 

​

            var theAnswerToken = obj["answer"];

            var theAnswer = theAnswerToken.Value<int>();

            if (theAnswer != 42)

                // How to get location of theAnswerToken in initial text here?

                throw new WrongAnswerException(theAnswerToken as IJsonLineInfo, "Wrong Answer");

​

            Debug.WriteLine((reader as IJsonLineInfo).FormatMessage("Exiting ReadJson. ", reader.Path));

            return new Foo { answer = theAnswer };

        }

​

        public override bool CanWrite => false;

        public override void WriteJson(JsonWriter writer, Foo value, JsonSerializer serializer) => throw new NotImplementedException();

    }

​

    public class WrongAnswerException : ApplicationException

    {

        public WrongAnswerException() : base() { }

        public WrongAnswerException(IJsonLineInfo info, string message, string path = null) : base(info.FormatMessage(message, path)) { }

    }

    public static class JsonExtensions

    {

        // Adapted from https://github.com/JamesNK/Newtonsoft.Json/blob/master/Src/Newtonsoft.Json/JsonPosition.cs#L150

        // By https://github.com/JamesNK

        // This all looks terribly non-internationalized doesn't it? -dbc

        public static string FormatMessage(this IJsonLineInfo lineInfo, string message, string path = null)

        {

            // don't add a fullstop and space when message ends with a new line

            if (!message.EndsWith(Environment.NewLine, StringComparison.Ordinal))

            {

                message = message.Trim();

​

                if (!message.EndsWith('.'))

                {

                    message += ".";

                }

​

                message += " ";

            }

​

            bool added = false;

            if (path != null)

            {

                message += string.Format(CultureInfo.InvariantCulture, "Path '{0}', ", path);

                added = true;

            }

​

            if (lineInfo != null && lineInfo.HasLineInfo())

            {

                message += string.Format(CultureInfo.InvariantCulture, "line {0}, position {1}", lineInfo.LineNumber, lineInfo.LinePosition);

                added = true;

            }

​

            if (added)

                message += ".";

​

            return message;

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            var wrongAnswer = JsonConvert.SerializeObject(new Foo { answer = -100 }, Formatting.Indented);

​

            Console.WriteLine(wrongAnswer);

            Assert.Throws(typeof(WrongAnswerException), () => JsonConvert.DeserializeObject<Foo>(wrongAnswer, new FooConverter()));

            var answer = JsonConvert.DeserializeObject<Foo>(wrongAnswer, new FooConverter());

        }   

    }

​

    public class Program

    {

        public static void Main()

        {

            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

            {

                TestClass.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.CodeBase.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;

        }

    }

​