using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.IO;

using System.Data;

using System.Reflection;

​

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

​

//https://stackoverflow.com/questions/76914939/serialize-a-const-with-system-text-json-serialization/

​

#nullable enable

​

    internal class BaseCommand

    {

    }

​

    internal sealed class CreateResourceCommand : BaseCommand

    {

        [JsonInclude]

        public const string CommandName = "CreateResourceCommand";

    }

​

    public enum TestEnum

    {

        TestValue

    }

​

    internal sealed class CreateResourceWithAttributeCommand : BaseCommand

    {

        [JsonInclude]

        public const string CommandName = "CreateResourceWithAttributeCommand";

​

        [JsonInclude]

        [JsonPropertyName("commandAttribute")]

        public const TestEnum Attribute = TestEnum.TestValue;

    }

​

    public static partial class JsonExtensions

    {

        public static Action<JsonTypeInfo> AddOptInConstMembers<TOptInAttribute>(Type type) where TOptInAttribute : System.Attribute =>

            typeInfo =>

            {

                if (typeInfo.Type == type)

                    AddOptInConstMembers<TOptInAttribute>(typeInfo);

            };

​

        public static void AddOptInConstMembers<TOptInAttribute>(JsonTypeInfo typeInfo) where TOptInAttribute : System.Attribute

        {

            if (typeInfo.Kind != JsonTypeInfoKind.Object)

                return;

            foreach (var field in typeInfo.Type.GetConstants().Where(f => Attribute.IsDefined(f, typeof(TOptInAttribute))))

            {

                var name = field.GetCustomAttribute<JsonPropertyNameAttribute>()?.Name ?? typeInfo.Options.PropertyNamingPolicy?.ConvertName(field.Name) ?? field.Name;

                var value = field.GetValue(null); // field.GetValue(null); returns enums as enums rathen raw integers.

                var propertyInfo = typeInfo.CreateJsonPropertyInfo(value?.GetType() ?? field.FieldType, name);

                propertyInfo.Get = (o) => value;

                propertyInfo.CustomConverter = field.GetCustomAttribute<JsonConverterAttribute>()?.ConverterType is {} converterType

                    ? (JsonConverter?)Activator.CreateInstance(converterType)

                    : null;

                typeInfo.Properties.Add(propertyInfo);

            }

        }

​

        static IEnumerable<FieldInfo> GetConstants(this Type type) =>

            // From the answer https://stackoverflow.com/a/10261848

            // By https://stackoverflow.com/users/601179/gdoron

            // To https://stackoverflow.com/questions/10261824/how-can-i-get-all-constants-of-a-type-by-reflection

            type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.FlattenHierarchy)

            .Where(fi => fi.IsLiteral && !fi.IsInitOnly);

    }

​

    class TestClass

    {

        public static void Test()

        {

            Test1();

            Test2();

        }

​

        static void Test1()

        {

            var command = new CreateResourceCommand();

​

            var options = new JsonSerializerOptions

            {

                TypeInfoResolver = new DefaultJsonTypeInfoResolver

                {

                    Modifiers = { JsonExtensions.AddOptInConstMembers<JsonIncludeAttribute> },

                },

            };

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

            Console.WriteLine(json); // Prints {"CommandName":"CreateResourceCommand"}

            Assert.AreEqual("""{"CommandName":"CreateResourceCommand"}""", json);

        }   

        static void Test2()

        {

            var command = new CreateResourceWithAttributeCommand();

​

            var options = new JsonSerializerOptions

            {

                TypeInfoResolver = new DefaultJsonTypeInfoResolver

                {

                    Modifiers = { JsonExtensions.AddOptInConstMembers<JsonIncludeAttribute> },

                },

                Converters = { new JsonStringEnumConverter() },

                PropertyNamingPolicy = JsonNamingPolicy.CamelCase,

            };

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

            Console.WriteLine(json);

            Assert.AreEqual("""{"commandName":"CreateResourceWithAttributeCommand","commandAttribute":"TestValue"}""", json);

        }

    }

​

    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;

            }

        }

    }

​