using System;

using System.Reflection;

using System.Text.Json;

using System.Text.Json.Serialization;

​

#nullable enable

​

namespace JsonStuff;

​

internal class Program

{

    static void Main()

    {

        TestPayload payload = new(1, "test", true);

        ApiResponse<TestPayload> response1 = new() { StatusCode = "OK", Message = "Retrieved something", Data = payload, DataPropName = "user" };

​

        JsonSerializerOptions options = new() { WriteIndented = true };

​

        string json = JsonSerializer.Serialize(response1, options);

        Console.WriteLine("JSON:");

        Console.WriteLine(json);

        Console.WriteLine();

​

        ApiResponse<TestPayload>? response2 = JsonSerializer.Deserialize<ApiResponse<TestPayload>>(json, options);

        if (response2 is null)

            Console.WriteLine("Failed to deserialize JSON to ApiResponse<TestPayload>.");

        else if (response2.Data is null)

            Console.WriteLine("Deserialization of variable-name property 'Data' failed.");

        else if 

        (

            response2.StatusCode != response1.StatusCode || 

            response2.Message != response1.Message ||

            response2.Data != response1.Data ||

            response2.DataPropName != response1.DataPropName

        )

            Console.WriteLine("Deserialization resulted in different data.");

        else

            Console.WriteLine("Round-trip serialization/deserialization completed.");

    }

}

​

public record TestPayload(int ID, string Name, bool Active);

​

[JsonConverter(typeof(ApiResponseConverterFactory))]

public class ApiResponse<T>

{

    public string StatusCode { get; set; } = string.Empty;

    public string Message { get; set; } = string.Empty;

    public T? Data { get; set; }

​

    [JsonIgnore]

    public string? DataPropName { get; set; }

}

​

public class ApiResponseConverterFactory : JsonConverterFactory

{

    public override bool CanConvert(Type typeToConvert)

    {

        return typeToConvert.IsGenericType && typeToConvert.GetGenericTypeDefinition() == typeof(ApiResponse<>);

    }

​

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

    {

        Type[] typeArguments = typeToConvert.GetGenericArguments();

        Type payloadType = typeArguments[0];

​

        JsonConverter converter = (JsonConverter?)Activator.CreateInstance

            (

                typeof(ApiResponseConverter<>).MakeGenericType([payloadType]),

                BindingFlags.Instance | BindingFlags.Public,

                binder: null,

                args: [options],

                culture: null

            ) ?? throw new Exception();

        return converter;

    }

​

    private class ApiResponseConverter<T> : JsonConverter<ApiResponse<T>>

    {

        private readonly JsonConverter<T> _valueConverter;

        private readonly Type _valType;

​

        public ApiResponseConverter(JsonSerializerOptions options)

        {

            _valueConverter = (JsonConverter<T>)options.GetConverter(typeof(T));

            _valType = typeof(T);

        }

​

        public override ApiResponse<T>? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)

        {

            if (reader.TokenType != JsonTokenType.StartObject)

                throw new JsonException();

​

            ApiResponse<T> result = new();

​

            while (reader.Read())

            {

                if (reader.TokenType == JsonTokenType.EndObject)

                    return result;

​

                if (reader.TokenType != JsonTokenType.PropertyName)

                    throw new JsonException();

​

                string? propName = reader.GetString();

                reader.Read();

​

                if (string.Compare(propName, "StatusCode", true) == 0)

                {

                    string? value = reader.GetString();

                    result.StatusCode = value ?? throw new JsonException();

                }

                else if (string.Compare(propName, "Message", true) == 0)

                {

                    string? value = reader.GetString();

                    result.Message = value ?? throw new JsonException();

                }

                else if (_valueConverter.Read(ref reader, _valType, options) is T data)

                { 

                    result.DataPropName = propName;

                    result.Data = data;

                }

                else

                    throw new JsonException();

            }

​

            throw new JsonException("Unexpected end of input.");

        }

​

        public override void Write(Utf8JsonWriter writer, ApiResponse<T> value, JsonSerializerOptions options)

        {

            writer.WriteStartObject();

            writer.WriteString("StatusCode", value.StatusCode);

            writer.WriteString("Message", value.Message);

​

            string propName = value.DataPropName ?? "Data";

            propName = options.PropertyNamingPolicy?.ConvertName(propName) ?? propName;

            writer.WritePropertyName(propName);

            if (value.Data is null)

                writer.WriteNullValue();

            else

                _valueConverter.Write(writer, value.Data, options);

​

            writer.WriteEndObject();

        }

    }

}

​