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 System.Text.Json.Serialization.Metadata;

using System.Text.Json.Nodes;

​

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

​

#nullable enable

​

//https://stackoverflow.com/questions/78391873/allow-multiple-types-for-one-property-when-deserializing-json-using-syste-text-j

​

    [JsonConverter(typeof(DiscriminatedUnionConverter))]

    public struct DiscriminatedUnion<T1, T2>

    {

        readonly object? value;

        readonly int index;

        public DiscriminatedUnion(T1 type1) => (this.value, this.index) = (type1, 1);

        public DiscriminatedUnion(T2 type2) => (this.value, this.index) = (type2, 2);

        public object? Value => value;

        public int Index => index;

        public Type? Type => index switch

        {

            1 => typeof(T1),

            2 => typeof(T1),

            _ => default,

        };

        public static implicit operator DiscriminatedUnion<T1, T2>(T1 value) => new(value);

        public static implicit operator DiscriminatedUnion<T1, T2>(T2 value) => new(value);

    }

​

    class DiscriminatedUnionConverter : JsonConverterFactory

    {

        public override bool CanConvert(Type typeToConvert) => 

            typeToConvert.IsGenericType && typeToConvert.GetGenericTypeDefinition() == typeof(DiscriminatedUnion<,>);

        public override JsonConverter? CreateConverter(Type typeToConvert, JsonSerializerOptions options)

        {

            if (typeToConvert.GetGenericTypeDefinition() == typeof(DiscriminatedUnion<,>))

                return (JsonConverter)Activator.CreateInstance(typeof(DiscriminatedUnionConverter<,>).MakeGenericType(typeToConvert.GetGenericArguments()))!;

            throw new NotImplementedException(typeToConvert.FullName);

        }

    }

​

    class DiscriminatedUnionConverter<T1, T2> : JsonConverter<DiscriminatedUnion<T1, T2>>

    {

        record DTO<T>(int type, T? value);

        public override void Write(Utf8JsonWriter writer, DiscriminatedUnion<T1, T2> union, JsonSerializerOptions options)

        {

            switch (union.Index)

            {

                case 1 : JsonSerializer.Serialize(writer, new DTO<T1>(union.Index, (T1?)union.Value)); break;

                case 2 : JsonSerializer.Serialize(writer, new DTO<T2>(union.Index, (T2?)union.Value)); break;

                default: JsonSerializer.Serialize(writer, new { type = union.Index }); break;

            }

        }

        public override DiscriminatedUnion<T1, T2> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) => 

            JsonSerializer.Deserialize<DTO<JsonElement>>(ref reader, options) switch

            {

                { type : 1 } dto => dto.value.Deserialize<T1>(options)!,

                { type : 2 } dto => dto.value.Deserialize<T2>(options)!,

                _ => default,

            };

    }

​

    public class TestClass

    {

        [JsonPropertyName("values")]

        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]

        public DiscriminatedUnion<string?, int []> values { get; set; }

    }

​

    class TestHarness

    {

        public static void Test()

        {

            TestString();

            TestInts();

        }

        public static void TestString()

        {

            var inputTest = new TestClass { values = "hello" };

            var json = JsonSerializer.Serialize(inputTest);

            var outputTest = JsonSerializer.Deserialize<TestClass>(json);

            switch (outputTest?.values.Value)

            {

                case string s : Console.WriteLine($"Value is {s}"); break;

                case int [] a : Console.WriteLine($"Value is {string.Join(',', a)}."); break;

            }

​

            Console.WriteLine(json);

            Assert.AreEqual(inputTest.values.Value, outputTest?.values.Value);      

            Console.WriteLine();

        }

​

        public static void TestInts()

        {

            var options = new JsonSerializerOptions { WriteIndented = true };

            var inputTest = new TestClass { values = new int[] {1, 2, 3 }};

            var json = JsonSerializer.Serialize(inputTest, options);

            var outputTest = JsonSerializer.Deserialize<TestClass>(json);

            switch (outputTest?.values.Value)

            {

                case string s : Console.WriteLine($"Value is {s}"); break;

                case int [] a : Console.WriteLine($"Value is {string.Join(',', a)}."); break;

            }

​

            Console.WriteLine(json);

            Assert.AreEqual(inputTest.values.Value, outputTest?.values.Value);      

            Console.WriteLine();

        }

    }

​

    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

            {

                TestHarness.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​