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.Text.Json;

using System.Text.Json.Serialization;

​

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

​

//https://stackoverflow.com/questions/72774698/system-text-json-serialization-doesnt-work-for-abstract-members

​

#nullable enable

​

[JsonConverter(typeof(AbstractToConcreteConverter<IAmount, Amount>))]

public interface IAmount {

    decimal Value { get; }

}

​

[Newtonsoft.Json.JsonConverter(typeof(NewtonsoftJsonConverter))]

[System.Text.Json.Serialization.JsonConverter(typeof(SystemTextJsonConverter))]

public class Amount : IAmount {

    public Amount(decimal value) {

        Value = value;

    }

​

    public decimal Value { get; }

}

​

public class NewtonsoftJsonConverter : Newtonsoft.Json.JsonConverter {

    public override bool CanConvert(Type objectType) => objectType.IsAssignableTo(typeof(IAmount));

​

    public override object? ReadJson(Newtonsoft.Json.JsonReader reader, Type objectType, object? existingValue, Newtonsoft.Json.JsonSerializer serializer) {

        throw new NotImplementedException();

    }

​

    public override void WriteJson(Newtonsoft.Json.JsonWriter writer, object? value, Newtonsoft.Json.JsonSerializer serializer) {

        writer.WriteRawValue(((IAmount?)value)?.Value.ToString());

    }

}

​

public class SystemTextJsonConverter : System.Text.Json.Serialization.JsonConverter<object> {

    public override bool CanConvert(Type typeToConvert) => typeToConvert.IsAssignableTo(typeof(IAmount));

​

    public override object Read(ref System.Text.Json.Utf8JsonReader reader, Type typeToConvert, System.Text.Json.JsonSerializerOptions options) =>

        new Amount(reader.GetDecimal());

​

    public override void Write(System.Text.Json.Utf8JsonWriter writer, object value, System.Text.Json.JsonSerializerOptions options) =>

        writer.WriteRawValue(((IAmount)value).Value.ToString());

}

​

    public class AbstractToConcreteConverter<TAbstract, TConcrete> : JsonConverter<TAbstract> where TConcrete : TAbstract

    {

        static AbstractToConcreteConverter()

        {

            if (typeof(TAbstract) == typeof(TConcrete))

                throw new ArgumentException(string.Format("Identical type {0} used for both TAbstract and TConcrete", typeof(TConcrete)));

        }

        public override TAbstract? Read(ref System.Text.Json.Utf8JsonReader reader, Type typeToConvert, System.Text.Json.JsonSerializerOptions options) =>

            JsonSerializer.Deserialize<TConcrete>(ref reader, options);

​

        public override void Write(System.Text.Json.Utf8JsonWriter writer, TAbstract value, System.Text.Json.JsonSerializerOptions options) =>

            JsonSerializer.Serialize(writer, (TConcrete)value!, options);

    }

​

    class TestClass

    {

        public static void Test()

        {

            var foo = new Amount(10);

​

            var newtonJson = Newtonsoft.Json.JsonConvert.SerializeObject(foo); // 10

            var systemJson = System.Text.Json.JsonSerializer.Serialize<IAmount>(foo);       

            var foo2 = System.Text.Json.JsonSerializer.Deserialize<IAmount>(systemJson);

            Console.WriteLine("Newtonsoft JSON:\n {0}", newtonJson);

            Console.WriteLine("System.Text.Json JSON:\n {0}", systemJson);

            Assert.AreEqual(newtonJson, systemJson);

            Assert.AreEqual(foo2?.Value, foo.Value);

        }   

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1}), {2}", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion);

            Console.WriteLine("System.Text.Json version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​