using Microsoft.AspNetCore.Mvc.Formatters;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Microsoft.AspNetCore.Mvc.Formatters
{
    public class RawJsonOutputFormatter : TextOutputFormatter
    {
        public RawJsonOutputFormatter()
        {
            this.SupportedMediaTypes.Add("application/json");
            this.SupportedEncodings.Add(Encoding.UTF8);
            this.SupportedEncodings.Add(Encoding.Unicode);
        }

        public override async Task WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
        {
            if (context == null)
                throw new ArgumentNullException(nameof(context));

            if (selectedEncoding == null)
                throw new ArgumentNullException(nameof(selectedEncoding));

            using (var writer = context.WriterFactory(context.HttpContext.Response.Body, selectedEncoding))
            {
                if (context.Object is string str)
                {
                    writer.Write(str);
                }
                else if (context.Object is List<string> list)
                {
                    writer.Write('[');

                    var index = 0;
                    var last = list.Count - 1;

                    for (var i = 0; i < list.Count; ++i)
                    {
                        writer.Write(list[i]);

                        if(index != last)
                            writer.Write(',');
                    }
                    
                    writer.Write(']');
                }
                else
                    throw new InvalidOperationException();

                await writer.FlushAsync();
            }
        }

        protected override bool CanWriteType(Type type)
        {
            return type == typeof(string)
                || type == typeof(List<string>);
        }
    }
}