using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.IO;

using System.Data;

using System.Buffers;

using System.Dynamic;

​

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

​

#nullable enable

​

//https://stackoverflow.com/questions/78507408/in-system-text-json-is-it-possible-to-minify-only-array-items

​

    public class NoIndentationConverter<T> : DefaultConverterFactory<T>

    {

        protected override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions modifiedOptions) 

        {

            // TODO: investigate https://learn.microsoft.com/en-us/dotnet/api/microsoft.toolkit.highperformance.buffers.arraypoolbufferwriter-1

            var bufferWriter = new ArrayBufferWriter<byte>();

            Span<byte> buffer = stackalloc byte[4];

            // Prepend the indentation that comes before the current value.

            foreach (var rune in writer.GetCurrentUtf8Indent(includeNewline : true))

            {

                int length = rune.EncodeToUtf8(buffer);

                bufferWriter.Write(buffer.Slice(0, length));

            }

            // Then serialize the current value without indentation

            using (var innerWriter = new Utf8JsonWriter(bufferWriter))

                JsonSerializer.Serialize(innerWriter, value, modifiedOptions);

            // And write the raw value without.

            writer.WriteRawValue(bufferWriter.WrittenSpan, skipInputValidation : true);

        }

​

        protected override JsonSerializerOptions ModifyOptions(JsonSerializerOptions options) { (options = base.ModifyOptions(options)).WriteIndented = false; return options; }

    }

​

    public abstract class DefaultConverterFactory<T> : JsonConverterFactory

    {

        // Adapted from this answer https://stackoverflow.com/a/65430421/3744182

        // To https://stackoverflow.com/questions/65430420/how-to-use-default-serialization-in-a-custom-system-text-json-jsonconverter

        class DefaultConverter : JsonConverter<T> 

        {

            readonly JsonSerializerOptions modifiedOptions;

            readonly DefaultConverterFactory<T> factory;

​

            public DefaultConverter(JsonSerializerOptions modifiedOptions, DefaultConverterFactory<T> factory) => (this.modifiedOptions, this.factory) = (modifiedOptions, factory);

​

            public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options) => factory.Write(writer, value, modifiedOptions);

            public override T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) => factory.Read(ref reader, typeToConvert, modifiedOptions);

            public override bool CanConvert(Type typeToConvert) => typeof(T).IsAssignableFrom(typeToConvert);

        }

​

        protected virtual JsonSerializerOptions ModifyOptions(JsonSerializerOptions options) 

            => options.CopyAndRemoveConverter(this.GetType());

​

        protected virtual T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions modifiedOptions)

            => (T?)JsonSerializer.Deserialize(ref reader, typeToConvert, modifiedOptions);

​

        protected virtual void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions modifiedOptions) 

            => JsonSerializer.Serialize(writer, value, modifiedOptions);

​

        public override bool CanConvert(Type typeToConvert) => typeof(T) == typeToConvert;

​

        public sealed override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options) => new DefaultConverter(ModifyOptions(options), this);

    }

​

    public static class JsonSerializerExtensions

    {

        public static IEnumerable<Rune> GetCurrentUtf8Indent(this Utf8JsonWriter writer, bool includeNewline = true)

        {

            if (!writer.Options.Indented || writer.CurrentDepth == 0)

                return Array.Empty<Rune>();

            var indentCharacter = ' '; // In .NET 9 use Utf8JsonWriter.IndentCharacter;

            var indentSize = 2;        // In .NET 9 use Utf8JsonWriter.IndentSize;

            var runes = Enumerable.Range(0, indentSize * writer.CurrentDepth).Select(i => new Rune(indentCharacter));

            if (includeNewline)

                runes = Environment.NewLine.EnumerateRunes().Concat(runes);

            return runes;

        }

        public static JsonSerializerOptions CopyAndRemoveConverter(this JsonSerializerOptions options, Type converterType)

        {

            var copy = new JsonSerializerOptions(options);

            for (var i = copy.Converters.Count - 1; i >= 0; i--)

                if (copy.Converters[i].GetType() == converterType)

                    copy.Converters.RemoveAt(i);

            return copy;

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            const int itemCount = 2;

            List<ExpandoObject> items = new List<ExpandoObject>();

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

            {

                dynamic item = new ExpandoObject();

                item.prop1 = i;

                item.prop2 = (char)('a' + i);

                items.Add(item);

            }

​

            string outputJson;

            using (MemoryStream outputStream = new MemoryStream())

            {   

                JsonSerializerOptions writeItemOptions = new JsonSerializerOptions()

                {

                    Converters = 

                    {

                        { new NoIndentationConverter<ExpandoObject>() },

                    },

                    WriteIndented = true,

                    PropertyNamingPolicy = JsonNamingPolicy.CamelCase,

                };              

​

                JsonSerializer.Serialize(outputStream, items, writeItemOptions);

                // read json string

                outputStream.Position = 0;

                using (StreamReader sr = new StreamReader(outputStream, leaveOpen: true))

                {

                    outputJson = sr.ReadToEnd();

                }

                string requiredJson = 

                    """

                    [

                      {"prop1":0,"prop2":"a"},

                      {"prop1":1,"prop2":"b"}

                    ]

                    """;

                Console.WriteLine(outputJson);

                Assert.That(requiredJson == outputJson);

            }

        }   

    }

​

    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;

            }

        }

    }

​