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.Buffers;

​

using System.Text.Json;

using System.Text.Json.Serialization;

​

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

​

//https://stackoverflow.com/questions/61079767/deserialize-very-large-json-from-a-chunked-array-of-strings-using-system-text-js

​

    public static partial class JsonExtensions

    {

        public static TValue Deserialize<TValue>(IEnumerable<string> buffers, JsonSerializerOptions options = null)

        {

            return Deserialize<TValue>(ToByteArrayChunks(buffers));

        }

        public static TValue Deserialize<TValue>(IEnumerable<byte []> buffers, JsonSerializerOptions options = null)

        {

            var sequence = ReadOnlySequenceFactory.Create(buffers);

            var reader = new Utf8JsonReader(sequence, options.GetReaderOptions());                      

            return JsonSerializer.Deserialize<TValue>(ref reader, options);

        }

​

        public static JsonReaderOptions GetReaderOptions(this JsonSerializerOptions options)

        {

            if (options == null)

                return new JsonReaderOptions();

            else

                return new JsonReaderOptions

                {

                    AllowTrailingCommas = options.AllowTrailingCommas,

                    CommentHandling = options.ReadCommentHandling,

                    MaxDepth = options.MaxDepth

                };          

        }

        static readonly Encoding encoding = new UTF8Encoding(false);

        static IEnumerable<byte []> ToByteArrayChunks(IEnumerable<string> buffers)

        {

            // By using an encoder we can handle the situation in which surrogate pairs enbedded in JSON string literals

            // are split between chunks.

            var encoder = encoding.GetEncoder();

            foreach (var s in buffers)

            {

                ReadOnlySpan<char> charSpan = s;

                var count = encoder.GetByteCount(charSpan, false);

                var bytes = new byte[count];

                Span<byte> byteSpan = bytes;

                encoder.GetBytes(charSpan, byteSpan, false);

                yield return bytes;

            }

        }

    }

​

    public static class ReadOnlySequenceFactory

    {

        // There is no public concrete implementation of ReadOnlySequenceSegment<T> so we must create one ourselves.

        // This is modeled on https://github.com/dotnet/runtime/blob/master/src/libraries/System.Text.Json/tests/BufferFactory.cs

        // by https://github.com/ahsonkhan

        class ReadOnlyMemorySegment<T> : ReadOnlySequenceSegment<T>

        {

            public static ReadOnlySequence<T> Create(IEnumerable<ReadOnlyMemory<T>> buffers)

            {

                ReadOnlyMemorySegment<T> first = null;

                ReadOnlyMemorySegment<T> current = null;

                foreach (var buffer in buffers)

                {

                    var next = new ReadOnlyMemorySegment<T> { Memory = buffer };

                    if (first == null)

                    {

                        first = next;

                    }

                    else

                    {

                        current.Next = next;

                        next.RunningIndex = current.RunningIndex + current.Memory.Length;

                    }

                    current = next;

                }

                if (first == null)

                {

                    first = current = new ReadOnlyMemorySegment<T>();

                }

​

                return new ReadOnlySequence<T>(first, 0, current, current.Memory.Length);

            }

        }

​

        public static ReadOnlySequence<T> Create<T>(IEnumerable<T []> buffers)

        {

            return ReadOnlyMemorySegment<T>.Create(buffers.Select(b => new ReadOnlyMemory<T>(b)));

        }

    }

​

    public class RootObject

    {

        public int Value { get; set; }

    }

​

    class TestClass

    {

        const string  hokketonian = "\U00029E3D\u0302";

​

        public static void Test()

        {

            TestSurrogate();

            Test(0, true);

            Test(1, true);

            Test(5, true);

            Test(500, false);

        }

        static void Test(int count, bool print)

        {

            var jsonResults = GetJson(count).ToList();

​

            if (print)

            {

                Console.WriteLine("\nInput JSON:");

                foreach (var s in jsonResults)

                    Console.WriteLine(s);

            }

            var list = JsonExtensions.Deserialize<List<RootObject>>(jsonResults);

            if (print)

            {

                Console.WriteLine("Re-serialized JSON:");

                Console.WriteLine(JsonSerializer.Serialize(list, new JsonSerializerOptions { WriteIndented = true }));

            }

            Assert.AreEqual(count, list.Count);

            Assert.IsTrue(Enumerable.Range(0, count).SequenceEqual(list.Select(i => i.Value)));

        }   

        static void TestSurrogate()

        {

            int count = 5;

​

            var expected = string.Concat(Enumerable.Repeat(hokketonian, count));

            Console.Write("Expected JSON string: ");

            Console.WriteLine(expected);

            var jsonResults = GetJsonWithSurrogateStrings(hokketonian, count);

            var s = JsonExtensions.Deserialize<string>(jsonResults);

            Console.Write("Actual JSON string  : ");

            Console.WriteLine(s);

            Assert.AreEqual(expected, s);

        }

        static IEnumerable<string> GetJson(int count)

        {

            if (count == 0)

                return new [] { "[]" };

            return new [] { "", "[" }

                .Concat(Enumerable.Range(0, count).Select(i => JsonSerializer.Serialize(new RootObject { Value = i }) + (i < count - 1 ? "," : "")))

                .Concat(new [] { "]" });

        }

        static IEnumerable<string> GetJsonWithSurrogateStrings(string input, int count)

        {

            var quote = new [] { "\"" };

            return quote.Concat(Enumerable.Repeat(input, 5).SelectMany(s => s).Select(c => c.ToString())).Concat(quote);

        }

    }

​

    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.CodeBase.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;

        }

    }

​