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 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/69524417/newtonsoft-json-net-how-to-conditionally-add-or-skip-items-in-an-array-when

​

    public class MaxLengthArrayConverter<T> : JsonConverter<T []>

    {

        public MaxLengthArrayConverter(int maxLength) => this.MaxLength = maxLength >= 0 ? maxLength : throw new ArgumentException(nameof(maxLength));

        public int MaxLength { get; }

        public override T [] ReadJson(JsonReader reader, Type objectType, T [] existingValue, bool hasExistingValue, JsonSerializer serializer)

        {

            if (reader.MoveToContentAndAssert().TokenType == JsonToken.Null)

                return null;

            reader.AssertTokenType(JsonToken.StartArray);

            var list = new List<T>();

            while (reader.ReadToContentAndAssert().TokenType != JsonToken.EndArray)

            {

                if (list.Count < MaxLength)

                    list.Add(serializer.Deserialize<T>(reader));

                else

                    reader.Skip();

            }

            return list.ToArray();

        }

​

        public override bool CanWrite => false;

        public override void WriteJson(JsonWriter writer, T [] value, JsonSerializer serializer) => throw new NotImplementedException();

    }

​

    public class MaxLengthListConverter<T> : JsonConverter<List<T>>

    {

        public MaxLengthListConverter(int maxLength) => this.MaxLength = maxLength >= 0 ? maxLength : throw new ArgumentException(nameof(maxLength));

        public int MaxLength { get; }

        public override List<T> ReadJson(JsonReader reader, Type objectType, List<T> existingValue, bool hasExistingValue, JsonSerializer serializer)

        {

            if (reader.MoveToContentAndAssert().TokenType == JsonToken.Null)

                return null;

            reader.AssertTokenType(JsonToken.StartArray);

            existingValue ??= (List<T>)serializer.ContractResolver.ResolveContract(objectType).DefaultCreator();

            existingValue.Clear();

            while (reader.ReadToContentAndAssert().TokenType != JsonToken.EndArray)

            {

                if (existingValue.Count < MaxLength)

                    existingValue.Add(serializer.Deserialize<T>(reader));

                else

                    reader.Skip();

            }

            return existingValue;

        }

​

        public override bool CanWrite => false;

        public override void WriteJson(JsonWriter writer, List<T> value, JsonSerializer serializer) => throw new NotImplementedException();

    }

​

    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 Order

    {

        public int Id { get; set; }

    }

​

    public class OrderBook

    {

        public Order [] Orders { get; set; }

​

        public string SomeExtraData { get; set; }

    }

​

    public class OrderList : List<Order> 

    {

        public OrderList() : base() { }

        public OrderList(IEnumerable<Order> orders) : base(orders) { }

    }

​

    public class OrderBookList

    {

        public OrderList Orders { get; set; }

​

        public string SomeExtraData { get; set; }

    }

​

    class TestClass

    {

        public static void Test()

        {

            for(int i = 0; i < 100; i++)

                for (int j = 0; j < i+10; j++)

                {

                    TestArray(i, j);

                    TestList(i, j);

                }

            TestArray(7, 4, true);

            TestList(3, 1, true);

        }   

        public static void TestArray(int initialLength, int maxLength, bool print = false)

        {

            var initialModel = new OrderBook

            {

                Orders = Enumerable.Range(0, initialLength).Select(i => new Order { Id = i }).ToArray(),

                SomeExtraData = "some extra data",

            };

            var settings = new JsonSerializerSettings

            {

                Converters = { new MaxLengthArrayConverter<Order>(maxLength) },

            };

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

            var model = JsonConvert.DeserializeObject<OrderBook>(json, settings);

​

            Assert.IsTrue(model.Orders.Length <= maxLength);

            var expectedLength = Math.Min(maxLength, initialLength);

            Assert.AreEqual(expectedLength, model.Orders.Length);

​

            Assert.IsTrue(Enumerable.SequenceEqual(model.Orders.Select(o => o.Id), initialModel.Orders.Take(expectedLength).Select(o => o.Id)));

            Assert.AreEqual(initialModel.SomeExtraData, model.SomeExtraData);

            if (print)

            {

                Console.WriteLine("Initial {0}:", initialModel);

                Console.WriteLine(json);

                Console.WriteLine("Re-serialized {0} with maxLength {1}:", model, maxLength);

                Console.WriteLine(JsonConvert.SerializeObject(model, Formatting.Indented, settings));

            }

        }   

        public static void TestList(int initialLength, int maxLength, bool print = false)

        {

            var initialModel = new OrderBookList

            {

                Orders = new (Enumerable.Range(0, initialLength).Select(i => new Order { Id = i })),

                SomeExtraData = "some extra data",

            };

            var settings = new JsonSerializerSettings

            {

                Converters = { new MaxLengthListConverter<Order>(maxLength) },

            };

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

            var model = JsonConvert.DeserializeObject<OrderBookList>(json, settings);

​

            Assert.IsTrue(model.Orders.Count <= maxLength);

            var expectedLength = Math.Min(maxLength, initialLength);

            Assert.AreEqual(expectedLength, model.Orders.Count);

​

            Assert.IsTrue(Enumerable.SequenceEqual(model.Orders.Select(o => o.Id), initialModel.Orders.Take(expectedLength).Select(o => o.Id)));

            Assert.AreEqual(initialModel.SomeExtraData, model.SomeExtraData);

            if (print)

            {

                Console.WriteLine("Initial {0}:", initialModel);

                Console.WriteLine(json);

                Console.WriteLine("Re-serialized {0} with maxLength {1}:", model, maxLength);

                Console.WriteLine(JsonConvert.SerializeObject(model, Formatting.Indented, settings));

            }

        }   

    }

​

    public class Program

    {

        public static void Main()

        {

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

            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;

            }

        }

        public static string GetNetCoreVersion()

        {

            //https://techblog.dorogin.com/how-to-detect-net-core-version-in-runtime-ecd65ad695be

            //

            var assembly = typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly;

            var assemblyPath = assembly.Location.Split(new[] { '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);

            int netCoreAppIndex = Array.IndexOf(assemblyPath, "Microsoft.NETCore.App");

            if (netCoreAppIndex > 0 && netCoreAppIndex < assemblyPath.Length - 2)

                return assemblyPath[netCoreAppIndex + 1];

            return null;

        }

    }

​