#nullable enable
using System;
using System.Buffers;
using MessagePack;
using MessagePack.Formatters;

namespace ShrinkNetwork.MessagePack
{
    /// <summary>Pass a generated-only resolver; register all message types before starting transports.</summary>
    public sealed class ShrinkMessagePackNetworkSerializer : ShrinkRegisteredNetworkSerializer
    {
        private readonly MessagePackSerializerOptions _options;
        public ShrinkMessagePackNetworkSerializer(IFormatterResolver generatedResolver)
        {
            _options = MessagePackSerializerOptions.Standard
                .WithResolver(global::MessagePack.Resolvers.CompositeResolver.Create(
                    generatedResolver ?? throw new ArgumentNullException(nameof(generatedResolver)),
                    global::MessagePack.Resolvers.BuiltinResolver.Instance))
                .WithSecurity(MessagePackSecurity.UntrustedData);
        }
        public void Register<T>() => Register(new FormatterCodec<T>(_options));

        private sealed class FormatterCodec<T> : IShrinkMessageCodec<T>
        {
            private readonly IMessagePackFormatter<T> _formatter;
            private readonly MessagePackSerializerOptions _options;
            public FormatterCodec(MessagePackSerializerOptions options)
            {
                _options = options;
                _formatter = options.Resolver.GetFormatter<T>() ?? throw new InvalidOperationException($"No generated MessagePack formatter for {typeof(T).FullName}.");
            }
            public void Write(IBufferWriter<byte> buffer, T value)
            {
                var writer = new MessagePackWriter(buffer);
                _formatter.Serialize(ref writer, value, _options);
                writer.Flush();
            }
            public T Read(ReadOnlyMemory<byte> payload)
            {
                var reader = new MessagePackReader(payload);
                var result = _formatter.Deserialize(ref reader, _options);
                if (!reader.End) throw new System.IO.InvalidDataException("Trailing MessagePack payload.");
                return result;
            }
        }
    }
}