/// @file dpf/net/stream_sink.hpp
/// @brief RoundSink with one duplex channel per interactive round.
#ifndef LIBDPF_INCLUDE_DPF_NET_STREAM_SINK_HPP__
#define LIBDPF_INCLUDE_DPF_NET_STREAM_SINK_HPP__

#include <chrono>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <memory>
#include <stdexcept>
#include <string>
#include <thread>
#include <utility>
#include <vector>

#include <unistd.h>

#include "dpf/net/asio_ns.hpp"

#include "dpf/net/channel.hpp"
#include "dpf/net/round_sink.hpp"
#include "dpf/net/trio.hpp"

namespace dpf
{
namespace net
{

/// @brief Prefix-flush RoundSink with an independent stream per round.
class stream_sink : public RoundSink
{
public:
    stream_sink(std::vector<channel> links, unsigned self_id, unsigned peer_id,
        std::size_t count, std::vector<std::size_t> slot_bytes)
      : links_(std::move(links)),
        self_id_(self_id),
        peer_id_(peer_id),
        count_(count),
        slot_bytes_(std::move(slot_bytes))
    {
        if (links_.size() != slot_bytes_.size())
            throw std::invalid_argument("stream_sink link count");
        windows_.reserve(slot_bytes_.size());
        for (std::size_t sb : slot_bytes_)
            windows_.emplace_back(count_, sb);
    }

    std::size_t count() const noexcept override { return count_; }
    std::size_t rounds() const noexcept override { return slot_bytes_.size(); }

    std::size_t slot_bytes(std::uint16_t round) const override
    {
        if (round >= slot_bytes_.size())
            throw std::out_of_range("stream_sink round");
        return slot_bytes_[round];
    }

    void submit(std::uint16_t round, std::size_t index,
        const std::uint8_t * bytes, std::size_t n) override
    {
        window(round).submit(index, bytes, n);
    }

    bool peer_ready(std::uint16_t round, std::size_t index) const override
    {
        return window(round).peer_ready(index);
    }

    void read_peer(std::uint16_t round, std::size_t index, std::uint8_t * out,
        std::size_t n) const override
    {
        window(round).read_peer(index, out, n);
    }

    void flush() override
    {
        // Global barrier: every round channel must rendezvous. Parties can have
        // pending on different rounds (schedule_session holes / staggered
        // indices); skipping idle links deadlocks the peer that still waits
        // there. Lockstep callers should use flush_round to avoid O(rounds)
        // exchanges on large sinks.
        for (std::uint16_t r = 0; r < slot_bytes_.size(); ++r)
            flush_one(r);
    }

    void flush_round(std::uint16_t r) override
    {
        if (r >= slot_bytes_.size())
            throw std::out_of_range("stream_sink flush_round");
        flush_one(r);
    }

    void poll() override {}

    std::uint64_t exchanges() const noexcept { return link_exchanges_; }

private:
    round_window & window(std::uint16_t round)
    {
        if (round >= windows_.size())
            throw std::out_of_range("stream_sink round");
        return windows_[round];
    }

    const round_window & window(std::uint16_t round) const
    {
        if (round >= windows_.size())
            throw std::out_of_range("stream_sink round");
        return windows_[round];
    }

    void flush_one(std::uint16_t r)
    {
        std::size_t begin = 0;
        std::size_t nslots = 0;
        const std::uint8_t * pending = windows_[r].pending_out(begin, nslots);
        std::vector<std::uint8_t> payload;
        if (nslots != 0)
        {
            payload.resize(sizeof(std::uint32_t) * 2 + nslots * slot_bytes_[r]);
            const std::uint32_t b = static_cast<std::uint32_t>(begin);
            const std::uint32_t c = static_cast<std::uint32_t>(nslots);
            std::memcpy(payload.data(), &b, 4);
            std::memcpy(payload.data() + 4, &c, 4);
            if (nslots * slot_bytes_[r] != 0)
                std::memcpy(payload.data() + 8, pending,
                    nslots * slot_bytes_[r]);
            windows_[r].mark_flushed(nslots);
        }
        else
        {
            // Peer may still be delivering; exchange an empty prefix header.
            payload.resize(8, 0);
        }
        std::vector<std::uint8_t> theirs;
        if (self_id_ < peer_id_)
        {
            links_[r].send_bytes(msg::round_batch, payload);
            theirs = links_[r].recv_bytes(msg::round_batch);
        }
        else
        {
            theirs = links_[r].recv_bytes(msg::round_batch);
            links_[r].send_bytes(msg::round_batch, payload);
        }
        if (theirs.size() < 8)
            throw std::runtime_error("stream_sink short frame");
        std::uint32_t pb = 0;
        std::uint32_t pc = 0;
        std::memcpy(&pb, theirs.data(), 4);
        std::memcpy(&pc, theirs.data() + 4, 4);
        const std::size_t body = static_cast<std::size_t>(pc) * slot_bytes_[r];
        if (theirs.size() != 8 + body)
            throw std::runtime_error("stream_sink size mismatch");
        if (pc != 0)
            windows_[r].accept_peer_at(pb, theirs.data() + 8, pc);
        ++link_exchanges_;
    }

    std::vector<channel> links_;
    unsigned self_id_ = 0;
    unsigned peer_id_ = 0;
    std::size_t count_ = 0;
    std::vector<std::size_t> slot_bytes_;
    std::vector<round_window> windows_;
    std::uint64_t link_exchanges_ = 0;
};

inline std::string stream_link_path(const std::string & dir, role a, role b,
    std::uint16_t round)
{
    if (to_u(a) > to_u(b))
        std::swap(a, b);
    return dir + "/" + role_name(a) + "-" + role_name(b) + "-r"
        + std::to_string(round);
}

/// @brief Connect one unix-domain stream per round under `dir`.
inline stream_sink connect_stream_sink(role self, role peer,
    const std::string & dir, std::size_t count,
    std::vector<std::size_t> slot_bytes, unsigned retries = 200)
{
    if (self == role::p2 || peer == role::p2)
        throw std::invalid_argument("stream_sink is for computing parties");
    asio::io_context io;
    std::vector<channel> links;
    links.reserve(slot_bytes.size());
    using proto = asio::local::stream_protocol;
    for (std::uint16_t r = 0; r < slot_bytes.size(); ++r)
    {
        const auto path = stream_link_path(dir, self, peer, r);
        const bool accept = to_u(self) < to_u(peer);
        bool opened = false;
        for (unsigned i = 0; i < retries && !opened; ++i)
        {
            asio::error_code ec;
            if (accept)
            {
                ::unlink(path.c_str());
                proto::endpoint ep(path);
                proto::acceptor acc(io, ep);
                proto::socket sock(io);
                acc.accept(sock, ec);
                if (!ec)
                {
                    links.emplace_back(std::move(sock));
                    opened = true;
                }
            }
            else
            {
                proto::endpoint ep(path);
                proto::socket sock(io);
                sock.connect(ep, ec);
                if (!ec)
                {
                    links.emplace_back(std::move(sock));
                    opened = true;
                }
            }
            if (!opened)
                std::this_thread::sleep_for(std::chrono::milliseconds(10));
        }
        if (!opened)
            throw std::runtime_error("stream_sink connect failed: " + path);
    }
    return stream_sink(std::move(links), to_u(self), to_u(peer), count,
        std::move(slot_bytes));
}

}  // namespace net
}  // namespace dpf

#endif  // LIBDPF_INCLUDE_DPF_NET_STREAM_SINK_HPP__