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

namespace GB5Shared.DateConverter
{
    /// <summary>
    /// GB5 standard DateOnly converter.
    /// READ : "yyyy-MM-dd" ISO date string only
    /// WRITE: "yyyy-MM-dd"
    ///
    /// Epoch /Date(N)/ format is NO LONGER accepted — removed by design.
    /// </summary>
    public sealed class DateOnlyJsonConverter : JsonConverter<DateOnly>
    {
        public override DateOnly Read(
            ref Utf8JsonReader reader,
            Type typeToConvert,
            JsonSerializerOptions options)
        {
            if (reader.TokenType == JsonTokenType.Null)
                return DateOnly.MinValue;

            if (reader.TokenType == JsonTokenType.String)
            {
                var raw = reader.GetString();

                if (string.IsNullOrWhiteSpace(raw))
                    return DateOnly.MinValue;

                if (DateOnly.TryParseExact(raw, "yyyy-MM-dd",
                        System.Globalization.CultureInfo.InvariantCulture,
                        System.Globalization.DateTimeStyles.None, out var date))
                    return date;

                // Accept full ISO datetime string — extract date portion only
                if (DateTime.TryParse(raw, System.Globalization.CultureInfo.InvariantCulture,
                        System.Globalization.DateTimeStyles.RoundtripKind, out var dt))
                    return DateOnly.FromDateTime(dt);

                throw new JsonException(
                    $"Invalid date value '{raw}'. Expected ISO format 'yyyy-MM-dd'.");
            }

            throw new JsonException(
                $"Unexpected token {reader.TokenType} for DateOnly; expected a string.");
        }

        public override void Write(
            Utf8JsonWriter writer,
            DateOnly value,
            JsonSerializerOptions options)
        {
            if (value == DateOnly.MinValue)
            {
                writer.WriteNullValue();
                return;
            }

            writer.WriteStringValue(value.ToString("yyyy-MM-dd"));
        }
    }

    public sealed class NullableDateOnlyJsonConverter : JsonConverter<DateOnly?>
    {
        private static readonly DateOnlyJsonConverter _inner = new();

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

            var val = _inner.Read(ref reader, typeof(DateOnly), options);
            return val == DateOnly.MinValue ? null : val;
        }

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

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