using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;

namespace GB5Shared.UnixEpochDate
{
    public sealed class UnixEpochDateTimeConverter : JsonConverter<DateTime>
    {
        private static readonly DateTime Epoch =
            new(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);

        public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
            => Epoch.AddSeconds(reader.GetInt64());

        public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
        {
            var seconds = (long)(value.ToUniversalTime() - Epoch).TotalSeconds;
            writer.WriteNumberValue(seconds);
        }
    }

    public static class JsonOptionsFactory
    {
        // ✅ Default (ISO 8601)
        public static readonly JsonSerializerOptions IsoOptions =
            new JsonSerializerOptions
            {
                PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
                WriteIndented = false
            };

        // ✅ Legacy (Unix Epoch)
        public static readonly JsonSerializerOptions EpochOptions =
            new JsonSerializerOptions
            {
                PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
                WriteIndented = false,
                Converters =
                {
                    new UnixEpochDateTimeConverter()
                }
            };
    }

    public sealed class EpochAwareResponseSerializer : IResponseSerializer
    {
        public async Task SerializeAsync(
            HttpContext context,
            object? response,
            CancellationToken cancellationToken)
        {
            // Nothing to serialize
            if (response is null)
                return;

            // Read header: epochformat (0 = epoch, 1 = iso)
            var epochHeader = context.Request.Headers["epochformat"].ToString();

            bool useEpoch = epochHeader == "0";

            var options = useEpoch
                ? JsonOptionsFactory.EpochOptions
                : JsonOptionsFactory.IsoOptions;

            context.Response.ContentType = "application/json";

            await JsonSerializer.SerializeAsync(
                context.Response.Body,
                response,
                response.GetType(),
                options,
                cancellationToken);
        }
    }

}