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

namespace SatelliteProvider.Common.Json;

public sealed partial class UtcOffsetRequiredDateTimeOffsetConverter : JsonConverter<DateTimeOffset>
{
    [GeneratedRegex(@"T\d{2}:\d{2}(:\d{2}(\.\d+)?)?(Z|[+-]\d{2}:\d{2}|[+-]\d{4})$", RegexOptions.IgnoreCase | RegexOptions.CultureInvariant)]
    private static partial Regex ExplicitOffsetPattern();

    public override DateTimeOffset Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType != JsonTokenType.String)
        {
            throw new JsonException("`capturedAt` must be an ISO-8601 string with an explicit UTC offset.");
        }

        var raw = reader.GetString();
        if (string.IsNullOrWhiteSpace(raw))
        {
            throw new JsonException("`capturedAt` must be an ISO-8601 string with an explicit UTC offset.");
        }

        if (!ExplicitOffsetPattern().IsMatch(raw))
        {
            throw new JsonException("`capturedAt` must include an explicit UTC offset (for example `Z` or `+00:00`).");
        }

        if (!DateTimeOffset.TryParse(raw, CultureInfo.InvariantCulture, DateTimeStyles.RoundtripKind, out var parsed))
        {
            throw new JsonException("`capturedAt` could not be parsed as an ISO-8601 timestamp.");
        }

        return parsed.ToUniversalTime();
    }

    public override void Write(Utf8JsonWriter writer, DateTimeOffset value, JsonSerializerOptions options)
    {
        writer.WriteStringValue(value.ToUniversalTime().ToString("O", CultureInfo.InvariantCulture));
    }
}
