using System;
using System.Collections.Generic;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace GB5Shared.FileUpload
{
    internal sealed class AttachmentEnvelopeConverter : JsonConverter<AttachmentResolutionEnvelope>
    {
        public override AttachmentResolutionEnvelope? Read(
            ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
        {
            if (reader.TokenType == JsonTokenType.Null)
                return null;

            if (reader.TokenType == JsonTokenType.StartArray)
            {
                // Frontend sends [] when no attachments — treat as null
                using var skip = JsonDocument.ParseValue(ref reader);
                return null;
            }

            using var doc = JsonDocument.ParseValue(ref reader);
            var result = new AttachmentResolutionEnvelope();
            if (doc.RootElement.TryGetProperty("LevelMappings", out var lm))
                result.LevelMappings = lm.Deserialize<List<LevelAttachmentMap>>(options) ?? new();
            return result;
        }

        public override void Write(
            Utf8JsonWriter writer, AttachmentResolutionEnvelope value, JsonSerializerOptions options)
        {
            writer.WriteStartObject();
            writer.WritePropertyName("LevelMappings");
            JsonSerializer.Serialize(writer, value.LevelMappings, options);
            writer.WriteEndObject();
        }
    }
}