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.Collections.Concurrent;

​

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/78216715/serializing-custom-types-in-a-c-sharp-concurrentdictionary

​

#nullable enable

​

    public class DictionaryValueConverterDecorator<TItemConverter> : JsonConverterFactory where TItemConverter : JsonConverter, new()

    {

        readonly TItemConverter itemConverter = new TItemConverter();

​

        public override bool CanConvert(Type typeToConvert) =>

            GetStringKeyedDictionaryValueType(typeToConvert) != null && GetConcreteTypeToConvert(typeToConvert) != null;

​

        public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options)

        {

            if (!(GetStringKeyedDictionaryValueType(typeToConvert) is {} valueType)

                || !(GetConcreteTypeToConvert(typeToConvert) is {} concreteTypeToConvert))

                throw new ArgumentException($"Invalid type {typeToConvert}");

            // Clone the incoming options and insert the item converter at the beginning of the clone.

            // Then if converter is actually a JsonConverterFactory (e.g. JsonStringEnumConverter) then the correct JsonConverter<T> will be manufactured or fetched.

            var modifiedOptions = new JsonSerializerOptions(options);

            modifiedOptions.Converters.Insert(0, itemConverter);

            var actualInnerConverter = modifiedOptions.GetConverter(valueType);

            return (JsonConverter)Activator.CreateInstance(typeof(DictionaryValueConverterDecoratorInner<,>).MakeGenericType(new [] { concreteTypeToConvert, valueType }), new object [] { actualInnerConverter })!;

        }

        static Type? GetStringKeyedDictionaryValueType(Type typeToConvert)

        {

            if (!(typeToConvert.GetDictionaryKeyValueType() is {} types))

                return null;

            if (types[0] != typeof(string))

                return null;

            return types[1];

        }

        static Type? GetConcreteTypeToConvert(Type typeToConvert) =>

            typeToConvert.IsInterface switch

            {

                false when typeToConvert.GetConstructor(Type.EmptyTypes) != null => 

                    typeToConvert,

                true when typeToConvert.IsGenericType && typeToConvert.GetGenericTypeDefinition() is var generic && (generic == typeof(IDictionary<,>) || generic == typeof(IReadOnlyDictionary<,>)) => 

                    typeof(Dictionary<,>).MakeGenericType(typeToConvert.GetGenericArguments()),

                _ => null,

            };

    }

​

    internal class DictionaryValueConverterDecoratorInner<TDictionary, TValue> : JsonConverter<TDictionary> where TDictionary : IDictionary<string, TValue>, new()

    {

        readonly JsonConverter<TValue> innerConverter;

​

        public DictionaryValueConverterDecoratorInner(JsonConverter<TValue> innerConverter) => this.innerConverter = innerConverter ?? throw new ArgumentNullException(nameof(innerConverter));

        public override TDictionary? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) 

        {

            if (reader.TokenType == JsonTokenType.Null)

                return (TDictionary?)(object?)null;

            else if (reader.TokenType != JsonTokenType.StartObject)

                throw new JsonException();

            var dictionary = new TDictionary();

            while (reader.Read())

            {

                if (reader.TokenType == JsonTokenType.EndObject)

                    break;

                else if (reader.TokenType != JsonTokenType.PropertyName)

                    throw new JsonException();

                var key = reader.GetString().ThrowOnNull();

                reader.ReadAndAssert();

                var value = innerConverter.Read(ref reader, typeof(TValue), options);

                dictionary.Add(key, value!);

            }

            return dictionary;

        }

​

        public override void Write(Utf8JsonWriter writer, TDictionary value, JsonSerializerOptions options)

        {

            writer.WriteStartObject();

            foreach (var pair in value)

            {

                writer.WritePropertyName(pair.Key);

                if (value == null && !innerConverter.HandleNull)

                    writer.WriteNullValue();

                else

                    innerConverter.Write(writer, pair.Value, options);

            }

            writer.WriteEndObject();

        }

    }

​

    public static partial class JsonExtensions

    {

        public static ref Utf8JsonReader ReadAndAssert(ref this Utf8JsonReader reader) { if (!reader.Read()) { throw new JsonException(); } return ref reader; }

        public static T ThrowOnNull<T>(this T? value, [System.Runtime.CompilerServices.CallerArgumentExpression(nameof(value))] string? paramName = null) where T : class => value ?? throw new ArgumentNullException(paramName);

    }

​

    public static class TypeExtensions

    {

        public static IEnumerable<Type> GetInterfacesAndSelf(this Type type)

            => (type ?? throw new ArgumentNullException()).IsInterface ? new[] { type }.Concat(type.GetInterfaces()) : type.GetInterfaces();

​

        public static IEnumerable<Type []> GetDictionaryKeyValueTypes(this Type type)

            => type.GetInterfacesAndSelf().Where(t => t.IsGenericType && t.GetGenericTypeDefinition() == typeof(IDictionary<,>)).Select(t => t.GetGenericArguments());

​

        public static Type []? GetDictionaryKeyValueType(this Type type)

            => type.GetDictionaryKeyValueTypes().SingleOrDefaultIfMultiple();

    }

​

    public static class LinqExtensions

    {

        // Copied from this answer https://stackoverflow.com/a/25319572

        // By https://stackoverflow.com/users/3542863/sean-rose

        // To https://stackoverflow.com/questions/3185067/singleordefault-throws-an-exception-on-more-than-one-element

        public static TSource? SingleOrDefaultIfMultiple<TSource>(this IEnumerable<TSource> source)

        {

            var elements = source.Take(2).ToArray();

            return (elements.Length == 1) ? elements[0] : default(TSource);

        }

    }

​

    //=======================================

​

    public partial class Model

    {

        //[JsonProperty(PropertyName = "substances", ItemConverterType = typeof(SaturationJsonConverter))]

        [JsonPropertyName("substances"), 

         JsonInclude, 

         JsonConverter(typeof(DictionaryValueConverterDecorator<SaturationJsonConverter>))]

        protected ConcurrentDictionary<string, Saturation> Substances { get; private set; } = new();        

    }

​

    public partial class Model

    {

        [JsonIgnore]

        public IDictionary<string, Saturation> SubstancesSurrogate => Substances;

    }

​

    public class Saturation

    {

        public string? Value { get; set; }

    }

​

    public class SaturationJsonConverter : JsonConverter<Saturation>

    {

        public override Saturation? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) =>

            new Saturation { Value = reader.GetString() };

​

        public override void Write(Utf8JsonWriter writer, Saturation? value, JsonSerializerOptions options) => 

            // Write the value as a string

            writer.WriteStringValue(value?.Value);

    }

​

​

    class TestClass

    {

        public static void Test()

        {

            var model = new Model

            {

                SubstancesSurrogate = 

                {

                    ["Item1"] = new Saturation { Value  = "Item1" },

                    ["Item2"] = new Saturation { Value  = "Item2" },

                },

            };

            var json = JsonSerializer.Serialize(model);

            Console.WriteLine(json);

​

            Assert.AreEqual("""{"substances":{"Item2":"Item2","Item1":"Item1"}}""", json);

            var model2 = JsonSerializer.Deserialize<Model>(json);

​

            var json2 = JsonSerializer.Serialize(model2);

            Assert.That(JsonNode.DeepEquals(JsonNode.Parse(json), JsonNode.Parse(json2)));

            Assert.That(model.SubstancesSurrogate.Count == model2?.SubstancesSurrogate.Count);

        }

    }

​

    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;

            }

        }

    }

​