using System;
using System.Collections.Generic;
using System.Reflection;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

namespace ConsoleApp1
{
    public class JsonFlatAttribute : Attribute
    {
    }

    public class FlatJsonConverter : JsonConverter
    {
        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            writer.WriteStartObject();
            WriteObject(writer, value, serializer);
            writer.WriteEndObject();
        }

        private void WriteObject(JsonWriter writer, object value, JsonSerializer serializer)
        {
            var t = JToken.FromObject(value);
            var flatNames = new List<string>();
            if (t.Type == JTokenType.Object)
            {
                var type = value.GetType();
                foreach (var propertyInfo in type.GetProperties())
                {
                    var flatAttr = propertyInfo.GetCustomAttribute(typeof(JsonFlatAttribute));
                    if (flatAttr != null) flatNames.Add(propertyInfo.Name.ToLower());
                }

                foreach (var token in t.Children())
                {
                    if (token.Type == JTokenType.Property && flatNames.Contains(((JProperty) token).Name.ToLower()))
                    {
                        foreach (var child in token.Children())
                        {
                            WriteObject(writer, child.Value<object>(), serializer);
                        }
                    }
                    else
                    {
                        WriteObject(writer, token.Value<object>(), serializer);
                    }
                }
            }
            else
            {
                t.WriteTo(writer);
            }
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            var jObject = JObject.Load(reader);
            var value = objectType.GetConstructor(new Type[] { }).Invoke(new object[] { });

            return ReadObject(objectType, jObject, value);
        }

        private object ReadObject(Type objectType, JObject jObject, object value)
        {
            var flatNames = new List<string>();
            foreach (var propertyInfo in objectType.GetProperties())
            {
                var flatAttr = propertyInfo.GetCustomAttribute(typeof(JsonFlatAttribute));
                if (flatAttr != null)
                {
                    var obj = propertyInfo.PropertyType.GetConstructor(new Type[] { }).Invoke(new object[] { });
                    foreach (var property in obj.GetType().GetProperties())
                    {
                        var method = typeof(JToken).GetMethod("Value").MakeGenericMethod(property.PropertyType);
                        var val = method.Invoke(jObject, new object[] { property.Name.ToLower() });
                        property.SetValue(obj, val);
                    }

                    propertyInfo.SetValue(value, obj);
                }
                else
                {
                    foreach (var property in value.GetType().GetProperties())
                    {
                        var method = typeof(JToken).GetMethod("Value").MakeGenericMethod(property.PropertyType);
                        var val = method.Invoke(jObject, new object[] { property.Name.ToLower() });
                        property.SetValue(value, val);
                    }
                }
            }

            return value;
        }

        public override bool CanConvert(Type objectType)
        {
            // TODO.
            return true;
        }

        // TODO.
        public override bool CanRead => true;
        public override bool CanWrite => true;
    }

    public class Foo
    {
        public int Y { get; set; }
        public int Z { get; set; }
    }

    public class Bar
    {
        public string X { get; set; }
        public Foo Foo { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var jsonSettings = new JsonSerializerSettings
            {
                Converters = new List<JsonConverter> { new FlatJsonConverter() }
            };

            var obj = JsonConvert.DeserializeObject<Bar>("{\"x\": 1, \"foo\": {\"y\": 2, \"z\": 3}}",
                new JsonSerializerSettings { Converters = new List<JsonConverter> { new FlatJsonConverter() } });
            Console.WriteLine(JsonConvert.SerializeObject(obj));
        }
    }
}