using System;
using System.Threading;
using System.Threading.Tasks;

using FrostFS.Object;

using Grpc.Core;

namespace FrostFS.SDK.ClientV2;

public sealed class ObjectReader(AsyncServerStreamingCall<GetResponse> call) : IObjectReader
{
    private bool disposed;

    public AsyncServerStreamingCall<GetResponse> Call { get; private set; } = call;

    internal async Task<Object.Object> ReadHeader()
    {
        if (!await Call.ResponseStream.MoveNext().ConfigureAwait(false))
            throw new FrostFsStreamException("unexpected end of stream");

        var response = Call.ResponseStream.Current;
        Verifier.CheckResponse(response);

        if (response.Body.ObjectPartCase != GetResponse.Types.Body.ObjectPartOneofCase.Init)
            throw new FrostFsStreamException("unexpected message type");

        return new Object.Object
        {
            ObjectId = response.Body.Init.ObjectId,
            Header = response.Body.Init.Header,
        };
    }

    public async ValueTask<ReadOnlyMemory<byte>?> ReadChunk(CancellationToken cancellationToken = default)
    {
        if (!await Call.ResponseStream.MoveNext(cancellationToken).ConfigureAwait(false))
            return null;

        var response = Call.ResponseStream.Current;
        Verifier.CheckResponse(response);

        if (response.Body.ObjectPartCase != GetResponse.Types.Body.ObjectPartOneofCase.Chunk)
            throw new FrostFsStreamException("unexpected message type");

        return response.Body.Chunk.Memory;
    }

    public void Dispose()
    {
        if (!disposed)
        {
            Call?.Dispose();
            GC.SuppressFinalize(this);

            disposed = true;
        }
    }
}