using System.Text.Json;
using System.Text.Json.Serialization;
using System.Text.RegularExpressions;

namespace GB5Shared.UnixEpochDate
{
    public sealed class MicrosoftEpochDateTimeConverter : JsonConverter<DateTime>
    {
        private static readonly Regex _regex =
            new(@"^/Date\((\-?\d+)\)/$", RegexOptions.Compiled);

        public override DateTime Read(
            ref Utf8JsonReader reader,
            Type typeToConvert,
            JsonSerializerOptions options)
        {
            if (reader.TokenType == JsonTokenType.Null)
                return default;

            if (reader.TokenType != JsonTokenType.String)
                return default;

            var value = reader.GetString();

            if (string.IsNullOrWhiteSpace(value))
                return default;

            // Try Microsoft format: /Date(123456789)/
            var match = _regex.Match(value);
            if (match.Success)
            {
                var ms = long.Parse(match.Groups[1].Value);
                return DateTimeOffset
                    .FromUnixTimeMilliseconds(ms)
                    .UtcDateTime;
            }

            // Try ISO 8601 (2025-03-01T00:00:00 / with Z)
            if (DateTime.TryParse(value, out var parsed))
                return parsed;

            // /Date(NaN)/ or any other unrecognized format — return default instead of throwing
            return default;
        }

        public override void Write(
            Utf8JsonWriter writer,
            DateTime value,
            JsonSerializerOptions options)
        {
            var epochMs = new DateTimeOffset(
                value.ToUniversalTime())
                .ToUnixTimeMilliseconds();

            writer.WriteStringValue($"/Date({epochMs})/");
        }
    }

    public sealed class MicrosoftEpochNullableDateTimeConverter
        : JsonConverter<DateTime?>
    {
        private static readonly MicrosoftEpochDateTimeConverter _inner = new();

        public override DateTime? Read(
            ref Utf8JsonReader reader,
            Type typeToConvert,
            JsonSerializerOptions options)
        {
            if (reader.TokenType == JsonTokenType.Null)
                return null;

            return _inner.Read(ref reader, typeof(DateTime), options);
        }

        public override void Write(
            Utf8JsonWriter writer,
            DateTime? value,
            JsonSerializerOptions options)
        {
            if (!value.HasValue)
            {
                writer.WriteNullValue();
                return;
            }

            _inner.Write(writer, value.Value, options);
        }
    }
}