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

namespace GB5Shared.JsonConverter
{
    // Clients (e.g. legacy GB4-style criteria payloads) send enum values as
    // quoted numeric strings ("2") or plain member names ("Equal"), not just
    // the bare integer System.Text.Json expects by default. This converter
    // accepts all three forms for any enum type.
    public class FlexibleEnumConverter<T> : JsonConverter<T> where T : struct, Enum
    {
        public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
        {
            switch (reader.TokenType)
            {
                case JsonTokenType.Number:
                    return (T)Enum.ToObject(typeof(T), reader.GetInt32());

                case JsonTokenType.String:
                    var raw = reader.GetString();
                    if (string.IsNullOrWhiteSpace(raw))
                        return default;

                    if (int.TryParse(raw, out var numeric))
                        return (T)Enum.ToObject(typeof(T), numeric);

                    return Enum.TryParse<T>(raw, ignoreCase: true, out var parsed)
                        ? parsed
                        : throw new JsonException($"Unable to convert \"{raw}\" to enum {typeof(T)}.");

                default:
                    throw new JsonException($"Unexpected token {reader.TokenType} when parsing enum {typeof(T)}.");
            }
        }

        public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
        {
            writer.WriteStringValue(value.ToString());
        }
    }

    // Non-generic factory so it can be registered once in JsonSerializerOptions.Converters
    // and apply to every enum type encountered, rather than listing each enum by hand.
    public class FlexibleEnumConverterFactory : JsonConverterFactory
    {
        public override bool CanConvert(Type typeToConvert) => typeToConvert.IsEnum;

        public override System.Text.Json.Serialization.JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options)
        {
            var converterType = typeof(FlexibleEnumConverter<>).MakeGenericType(typeToConvert);
            return (System.Text.Json.Serialization.JsonConverter)Activator.CreateInstance(converterType)!;
        }
    }
}