using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Reflection;

using System.Collections.ObjectModel;

using System.Threading;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

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

​

//https://stackoverflow.com/questions/72213562/c-sharp-reflection-get-object-value-from-property-value-within-json-contractre

​

    class AddressDto 

    { 

        // PROBLEM 1/2: value does not get serialized, but I want it serialized as its property is [ShouldSerialize] attr tagged

        public int StreetNumber { get; set; } 

    }

​

    class PersonDto 

    { 

        public string Name { get; set; }  // should not serialize as has not attr on it

​

        [ShouldSerialize]

        public string Id { get; set; } 

​

        [ShouldSerialize]

        public AddressDto Address { get; set; }

    }

​

    class SomeOtherDto

    {

        [ShouldSerialize]

        public string SomeOtherValue { get; set; } 

​

        public AddressDto SecretAddress { get; set; }       // Should not get serialized.

        [ShouldSerialize]

        [JsonConverter(typeof(ValueConverter<AddressDto>))]

        public ValueDto<AddressDto> PublicAddress { get; set; }

    }

​

    public class ValueDto<T>

    {

        public T Value { get; set; }

    }

​

    public class ValueConverter<T> : JsonConverter<ValueDto<T>>

    {

        public override void WriteJson(JsonWriter writer, ValueDto<T> value, JsonSerializer serializer) => serializer.Serialize(writer, value == null ? null : value.Value);

        public override ValueDto<T> ReadJson(JsonReader reader, Type objectType, ValueDto<T> existingValue, bool hasExistingValue, JsonSerializer serializer) => new ValueDto<T> { Value = serializer.Deserialize<T>(reader) };

    }

​

    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]

    public class ShouldSerializeAttribute : System.Attribute

    {

    }

​

    public class ShouldSerializeContractResolver: DefaultContractResolver

    {

        static ThreadLocal<bool> inShouldSerialize = new (() => false);

        static bool InShouldSerialize { get => inShouldSerialize.Value; set => inShouldSerialize.Value = value; }

​

        protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)

        {

            var property = base.CreateProperty(member, memberSerialization);

            var attr = member.GetCustomAttribute<ShouldSerializeAttribute>(inherit: false);

​

            if (attr is null)

            {

                var old = property.ShouldSerialize;

                property.ShouldSerialize = instance => InShouldSerialize && (old == null || old(instance));

            }

            else

            {

                var old = property.Converter;

                if (old == null)

                    property.Converter = new InShouldSerializeConverter();

                else

                    property.Converter = new InShouldSerializeConverterDecorator(old);

            }

​

            return property;

        }

        class InShouldSerializeConverter : JsonConverter

        {

            public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

            {

                var old = InShouldSerialize;

                try

                {

                    InShouldSerialize = true;

                    serializer.Serialize(writer, value);

                }

                finally

                {

                    InShouldSerialize = old;

                }

            }

​

            public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) => throw new NotImplementedException();

​

            public override bool CanRead => false;

            public override bool CanConvert(Type objectType) => throw new NotImplementedException();

        }

​

        class InShouldSerializeConverterDecorator : JsonConverter

        {

            readonly JsonConverter innerConverter;

            public InShouldSerializeConverterDecorator(JsonConverter innerConverter) => this.innerConverter = innerConverter ?? throw new ArgumentNullException(nameof(innerConverter));

            public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

            {

                var old = InShouldSerialize;

                try

                {

                    InShouldSerialize = true;

                    if (innerConverter.CanWrite)

                        innerConverter.WriteJson(writer, value, serializer);

                    else

                        serializer.Serialize(writer, value);

                }

                finally

                {

                    InShouldSerialize = old;

                }

            }

​

            public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)

            {

                var old = InShouldSerialize;

                try

                {

                    InShouldSerialize = true;

                    if (innerConverter.CanRead)

                        return innerConverter.ReadJson(reader, objectType, existingValue, serializer);

                    else

                        return serializer.Deserialize(reader, objectType);

                }

                finally

                {

                    InShouldSerialize = old;

                }

            }

​

            public override bool CanConvert(Type objectType) => throw new NotImplementedException();

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            TestAddress();

            TestOther();

        }

        public static void TestAddress()

        {

            var address = new AddressDto

            {

                StreetNumber = 202,

            };

            var person = new PersonDto

            {

                Name = "ShouldNotAppear",

                Id = "ShouldAppear",

                Address = address,

            };

            var otherDto = new SomeOtherDto

            {

                SomeOtherValue = "ShouldAppear",

                SecretAddress = address,

            };

            IContractResolver resolver = new ShouldSerializeContractResolver(); // Cache statically & reuse for best performance

            var settings = new JsonSerializerSettings

            {

                ContractResolver = resolver,

            };

            var json = JsonConvert.SerializeObject(person, Formatting.Indented, settings);

            Console.WriteLine("Serializing {0}:", person);

            Console.WriteLine(json);

            var person2 = JsonConvert.DeserializeObject<PersonDto>(json, settings);

            Assert.AreEqual(person.Id, person2.Id);

            Assert.AreEqual(person.Address?.StreetNumber, person2.Address?.StreetNumber);

            Assert.AreNotEqual(person.Name, person2.Name);

            Assert.IsTrue(!json.Contains("ShouldNotAppear"));

        }

        public static void TestOther()

        {

            var address = new AddressDto

            {

                StreetNumber = 101,

            };

            var publicAddress = new AddressDto

            {

                StreetNumber = 202,

            };

            var otherDto = new SomeOtherDto

            {

                SomeOtherValue = "ShouldAppear",

                SecretAddress = address,

                PublicAddress = new ValueDto<AddressDto> { Value = publicAddress },

            };

            IContractResolver resolver = new ShouldSerializeContractResolver();

            var settings = new JsonSerializerSettings

            {

                ContractResolver = resolver,

            };

            var json2 = JsonConvert.SerializeObject(otherDto, Formatting.Indented, settings);

            Console.WriteLine("Serializing {0}:", otherDto);

            Console.WriteLine(json2);

            var other2 = JsonConvert.DeserializeObject<SomeOtherDto>(json2, settings);

            Assert.AreEqual(otherDto.SomeOtherValue, other2.SomeOtherValue);

            Assert.AreNotEqual(otherDto.SecretAddress?.StreetNumber, other2.SecretAddress?.StreetNumber);

            Assert.IsTrue(!json2.Contains("ShouldNotAppear"));

            Assert.AreEqual(otherDto.PublicAddress.Value.StreetNumber, other2.PublicAddress.Value.StreetNumber);

        }   

    }

​

    public static partial class JsonExtensions

    {

        public static JsonReader AssertTokenType(this JsonReader reader, JsonToken tokenType) => 

            reader.TokenType == tokenType ? reader : throw new JsonSerializationException(string.Format("Unexpected token {0}, expected {1}", reader.TokenType, tokenType));

        public static JsonReader ReadToContentAndAssert(this JsonReader reader) =>

            reader.ReadAndAssert().MoveToContentAndAssert();

​

        public static JsonReader MoveToContentAndAssert(this JsonReader reader)

        {

            if (reader == null)

                throw new ArgumentNullException();

            if (reader.TokenType == JsonToken.None)       // Skip past beginning of stream.

                reader.ReadAndAssert();

            while (reader.TokenType == JsonToken.Comment) // Skip past comments.

                reader.ReadAndAssert();

            return reader;

        }

​

        public static JsonReader ReadAndAssert(this JsonReader reader)

        {

            if (reader == null)

                throw new ArgumentNullException();

            if (!reader.Read())

                throw new JsonReaderException("Unexpected end of JSON stream.");

            return reader;

        }

    }

​

    public class Program

    {

        public static void Main()

        {

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

            Console.WriteLine("{0} version: {1}", typeof(JsonSerializer).Assembly.GetName().Name,  typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​