/// @file dpf/net/trio.hpp
/// @brief Dial/accept three-party (2+1) socket mesh for libdpf protocols.
/// @details Socket paths live under a driver-created directory:
///          `p0-p1`, `p0-p2`, `p1-p2`. The lower role accepts; the higher
///          dials. Helpers `deal` / `accept_deal` / `open_with` name the
///          protocol steps without exposing ASIO.
/// @copyright Copyright (c) 2019-2026 Ryan Henry and [others](@ref authors)
/// @license Released under a GNU General Public v2.0 (GPLv2) license;
///          see [LICENSE.md](@ref license) for details.

#ifndef LIBDPF_INCLUDE_DPF_NET_TRIO_HPP__
#define LIBDPF_INCLUDE_DPF_NET_TRIO_HPP__

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

#include <unistd.h>

#include "dpf/net/asio_ns.hpp"

#include "dpf/net/channel.hpp"
#include "dpf/net/comm_hook.hpp"
#include "dpf/net/policy.hpp"
#include "dpf/net/round_sink.hpp"
#include "dpf/net/secure_channel.hpp"
#include "dpf/net/security.hpp"
#include "dpf/net/socket_tune.hpp"

#include "hedley/hedley.h"

namespace dpf
{
namespace net
{

/// @brief Party roles in a (2+1) run. p2 is the dealer.
enum class role : unsigned
{
    p0 = 0,
    p1 = 1,
    p2 = 2,
};

HEDLEY_CONST
HEDLEY_NO_THROW
inline constexpr unsigned to_u(role r) noexcept
{
    return static_cast<unsigned>(r);
}

HEDLEY_CONST
HEDLEY_NO_THROW
inline const char * role_name(role r) noexcept
{
    switch (r)
    {
    case role::p0: return "p0";
    case role::p1: return "p1";
    case role::p2: return "p2";
    }
    return "?";
}

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

/// @brief Connected view of the other two parties.
class trio
{
public:
    trio() = default;

    /// @brief Connect local unix-domain sockets under `dir`.
    /// @param self this process's role
    /// @param dir directory holding the three socket paths
    /// @param retries dial/accept attempts before giving up
    /// @param sec same peer TLS policy as `party_session` (default encrypt)
    static trio connect_local(role self, const std::string & dir,
        unsigned retries = 200, const peer_security & sec = {},
        const deadlines & lim = {})
    {
        trio t;
        t.self_ = self;
        t.io_ = std::make_unique<asio::io_context>();
        for (unsigned other = 0; other < 3; ++other)
        {
            if (other == to_u(self))
                continue;
            auto peer = static_cast<role>(other);
            t.link_[other] = connect_one(self, peer, dir, *t.io_, retries, sec,
                lim);
        }
        return t;
    }

    /// @brief Connect the p0–p1 socket only. The dealer link stays closed
    ///        until `install_inbox`.
    static trio connect_pair(role self, const std::string & dir,
        unsigned retries = 200, const peer_security & sec = {},
        const deadlines & lim = {})
    {
        if (self == role::p2)
            throw std::invalid_argument("connect_pair is p0 and p1");
        trio t;
        t.self_ = self;
        t.io_ = std::make_unique<asio::io_context>();
        const role peer = self == role::p0 ? role::p1 : role::p0;
        t.link_[to_u(peer)] = connect_one(self, peer, dir, *t.io_, retries, sec,
            lim);
        return t;
    }

    /// @brief Serve later `to(p2).recv` calls from a local frame buffer.
    void install_inbox(std::vector<std::uint8_t> frames)
    {
        if (self_ == role::p2)
            throw std::logic_error("p2 has no dealer inbox");
        link_[to_u(role::p2)] = channel::from_inbox(std::move(frames));
    }

    /// @brief True when the installed dealer tape has been fully consumed.
    HEDLEY_NO_THROW
    bool dealer_inbox_done() const noexcept
    {
        if (self_ == role::p2)
            return false;
        return link_[to_u(role::p2)].inbox_done();
    }

    /// @brief Connect over TCP loopback. Ports are `base + 10*lo + hi`.
    static trio connect_tcp(role self, std::uint16_t base_port,
        const std::string & host = "127.0.0.1", unsigned retries = 200,
        const peer_security & sec = {}, const deadlines & lim = {},
        const socket_options & so = {})
    {
        trio t;
        t.self_ = self;
        t.io_ = std::make_unique<asio::io_context>();
        for (unsigned other = 0; other < 3; ++other)
        {
            if (other == to_u(self))
                continue;
            auto peer = static_cast<role>(other);
            t.link_[other] = connect_one_tcp(self, peer, base_port, host,
                *t.io_, retries, sec, lim, so);
        }
        return t;
    }

    role self() const noexcept { return self_; }

    /// @brief Sum of byte and frame counters on the open links.
    HEDLEY_NO_THROW
    io_tally tally() const noexcept
    {
        io_tally sum;
        for (const auto & link : link_)
        {
            if (link.open())
                sum += link.tally();
        }
        return sum;
    }

    /// @brief Counters on the link to `peer` only.
    HEDLEY_NO_THROW
    io_tally tally_to(role peer) const noexcept
    {
        if (peer == self_ || !link_[to_u(peer)].open())
            return {};
        return link_[to_u(peer)].tally();
    }

    /// @brief Bytes received from the dealer (p2). Empty for the dealer itself.
    HEDLEY_NO_THROW
    io_tally tally_from_p2() const noexcept
    {
        if (self_ == role::p2)
            return {};
        return tally_to(role::p2);
    }

    /// @brief Bytes with the other computing party (p0↔p1).
    /// @details For p2 this is the sum of the links to p0 and p1.
    HEDLEY_NO_THROW
    io_tally tally_from_peer() const noexcept
    {
        if (self_ == role::p0)
            return tally_to(role::p1);
        if (self_ == role::p1)
            return tally_to(role::p0);
        io_tally sum;
        sum += tally_to(role::p0);
        sum += tally_to(role::p1);
        return sum;
    }

    /// @brief Zero counters on every open link.
    HEDLEY_NO_THROW
    void reset_tally() noexcept
    {
        for (auto & link : link_)
        {
            if (link.open())
                link.reset_tally();
        }
    }

    /// @brief The open channel to `peer` (raw bypass; does not use the hook).
    /// @param peer the other party
    /// @return that channel
    /// @throws std::invalid_argument if `peer` is this process
    /// @throws std::logic_error if that link was not connected
    channel & to(role peer)
    {
        if (peer == self_)
            throw std::invalid_argument("trio::to(self)");
        auto & c = link_[to_u(peer)];
        if (!c.open())
            throw std::logic_error("trio link is not open");
        return c;
    }

    /// @brief Install a replaceable transport for helpers and `batch`.
    /// @details Non-owning. Null restores the framed mesh defaults.
    void set_hook(comm_hook * hook) noexcept { hook_ = hook; }

    /// @brief Current hook, or null when helpers use the mesh directly.
    HEDLEY_NO_THROW
    comm_hook * hook() const noexcept { return hook_; }

    /// @brief One-way send through the hook (or the mesh when unset).
    template <typename T>
    void send_to(role peer, msg tag, const T & value)
    {
        static_assert(std::is_trivially_copyable_v<T>,
            "trio::send_to requires a trivially copyable type");
        if (hook_)
        {
            hook_->send_bytes(*this, to_u(peer), tag, &value, sizeof(T));
            return;
        }
        to(peer).send(tag, value);
    }

    /// @brief Homogeneous vector send through the hook (or the mesh).
    template <typename T>
    void send_vec_to(role peer, msg tag, const std::vector<T> & values)
    {
        static_assert(std::is_trivially_copyable_v<T>,
            "trio::send_vec_to requires a trivially copyable type");
        if (hook_)
        {
            const std::size_t nbytes = values.size() * sizeof(T);
            hook_->send_bytes(*this, to_u(peer), tag, values.data(), nbytes);
            return;
        }
        to(peer).send_vec(values, tag);
    }

    /// @brief Untyped one-way send through the hook (or the mesh).
    void send_bytes_to(role peer, msg tag, const void * data, std::size_t n)
    {
        if (hook_)
        {
            hook_->send_bytes(*this, to_u(peer), tag, data, n);
            return;
        }
        to(peer).send_bytes(tag, data, n);
    }

    /// @brief Untyped one-way receive through the hook (or the mesh).
    HEDLEY_WARN_UNUSED_RESULT
    std::vector<std::uint8_t> recv_bytes_from(role peer, msg tag)
    {
        if (hook_)
            return hook_->recv_bytes(*this, to_u(peer), tag);
        return to(peer).recv_bytes(tag);
    }

    /// @brief One-way receive through the hook (or the mesh when unset).
    template <typename T>
    HEDLEY_WARN_UNUSED_RESULT
    T recv_from(role peer, msg tag)
    {
        static_assert(std::is_trivially_copyable_v<T>,
            "trio::recv_from requires a trivially copyable type");
        if (hook_)
        {
            auto bytes = hook_->recv_bytes(*this, to_u(peer), tag);
            if (bytes.size() != sizeof(T))
                throw std::runtime_error("trio::recv_from size mismatch");
            T value{};
            if constexpr (sizeof(T) != 0)
                std::memcpy(&value, bytes.data(), sizeof(T));
            return value;
        }
        return to(peer).template recv<T>(tag);
    }

    /// @brief Homogeneous vector receive through the hook (or the mesh).
    template <typename T>
    HEDLEY_WARN_UNUSED_RESULT
    std::vector<T> recv_vec_from(role peer, msg tag = msg::beaver_tape)
    {
        static_assert(std::is_trivially_copyable_v<T>,
            "trio::recv_vec_from requires a trivially copyable type");
        if (hook_)
        {
            auto bytes = hook_->recv_bytes(*this, to_u(peer), tag);
            if constexpr (sizeof(T) == 0)
            {
                if (!bytes.empty())
                    throw std::runtime_error("trio::recv_vec_from size");
                return {};
            }
            if (bytes.size() % sizeof(T) != 0)
                throw std::runtime_error("trio::recv_vec_from size mismatch");
            std::vector<T> out(bytes.size() / sizeof(T));
            if (!out.empty())
                std::memcpy(out.data(), bytes.data(), bytes.size());
            return out;
        }
        return to(peer).template recv_vec<T>(tag);
    }

    /// @brief Round-batched peer sink. Default is a mux on the p0–p1 link.
    /// @details Defined next to `mux_sink` so the default factory can build one.
    std::unique_ptr<RoundSink> batch(std::size_t count,
        std::vector<std::size_t> slot_bytes);

    /// @brief Dealer sends one side of a split to each computing party.
    /// @tparam Split a type with `p0` and `p1` members
    /// @param s the split
    /// @throws std::logic_error if this process is not p2
    template <typename Split>
    void deal(const Split & s)
    {
        if (self_ != role::p2)
            throw std::logic_error("only the dealer may deal");
        send_to(role::p0, msg::beaver_tape, s.p0);
        send_to(role::p1, msg::beaver_tape, s.p1);
    }

    /// @brief Computing party receives its share of a dealt value.
    /// @tparam Ring the dealt type
    /// @return this party's share
    /// @throws std::logic_error if this process is p2
    template <typename Ring>
    HEDLEY_WARN_UNUSED_RESULT
    Ring accept_deal()
    {
        if (self_ == role::p2)
            throw std::logic_error("dealer does not accept_deal");
        return recv_from<Ring>(role::p2, msg::beaver_tape);
    }

    /// @brief Open an additive share with the peer computing party.
    /// @tparam Ring additive ring
    /// @param peer the other computing party
    /// @param mine this party's share
    /// @return reconstructed public value (`mine + peer`)
    /// @throws std::logic_error if either side is p2
    template <typename Ring>
    HEDLEY_WARN_UNUSED_RESULT
    Ring open_with(role peer, const Ring & mine)
    {
        if (self_ == role::p2 || peer == role::p2)
            throw std::logic_error("open_with is between p0 and p1");
        Ring theirs = exchange_with(peer, mine, msg::delta);
        return static_cast<Ring>(mine + theirs);
    }

    /// @brief Exchange raw values (no algebra) with a peer.
    /// @tparam T trivially copyable payload
    /// @param peer the other party
    /// @param mine this party's value
    /// @param tag the message tag
    /// @return the peer's value
    template <typename T>
    HEDLEY_WARN_UNUSED_RESULT
    T exchange_with(role peer, const T & mine, msg tag = msg::delta)
    {
        static_assert(std::is_trivially_copyable_v<T>,
            "trio::exchange_with requires a trivially copyable type");
        if (hook_)
        {
            auto bytes = hook_->exchange_bytes(*this, to_u(peer), tag, &mine,
                sizeof(T));
            if (bytes.size() != sizeof(T))
                throw std::runtime_error("trio::exchange_with size mismatch");
            T theirs{};
            if constexpr (sizeof(T) != 0)
                std::memcpy(&theirs, bytes.data(), sizeof(T));
            return theirs;
        }
        return to(peer).template exchange<T>(to_u(self_), to_u(peer), mine, tag);
    }

    /// @brief Exchange a homogeneous vector with a peer (one barrier).
    /// @tparam T trivially copyable element
    /// @param peer the other party
    /// @param mine this party's values
    /// @param tag the message tag
    /// @return the peer's values
    template <typename T>
    HEDLEY_WARN_UNUSED_RESULT
    std::vector<T> exchange_vec_with(role peer, const std::vector<T> & mine,
        msg tag = msg::ring_vector)
    {
        static_assert(std::is_trivially_copyable_v<T>,
            "trio::exchange_vec_with requires a trivially copyable type");
        if (mine.empty())
            return {};
        if (hook_)
        {
            const std::size_t nbytes = mine.size() * sizeof(T);
            auto bytes = hook_->exchange_vec_bytes(*this, to_u(peer), tag,
                mine.data(), nbytes);
            if (bytes.size() != nbytes)
                throw std::runtime_error("trio::exchange_vec_with size mismatch");
            std::vector<T> theirs(mine.size());
            std::memcpy(theirs.data(), bytes.data(), nbytes);
            return theirs;
        }
        return to(peer).template exchange_vec<T>(
            to_u(self_), to_u(peer), mine, tag);
    }

    /// @brief Open additive shares packed into one vector exchange.
    /// @tparam Ring additive ring
    /// @param peer the other computing party
    /// @param mine this party's shares
    /// @return reconstructed public values (`mine[i] + peer[i]`)
    template <typename Ring>
    HEDLEY_WARN_UNUSED_RESULT
    std::vector<Ring> open_vec_with(role peer, const std::vector<Ring> & mine)
    {
        if (self_ == role::p2 || peer == role::p2)
            throw std::logic_error("open_vec_with is between p0 and p1");
        auto theirs = exchange_vec_with(peer, mine);
        std::vector<Ring> out(mine.size());
        for (std::size_t i = 0; i < mine.size(); ++i)
            out[i] = static_cast<Ring>(mine[i] + theirs[i]);
        return out;
    }

private:
    role self_ = role::p0;
    std::unique_ptr<asio::io_context> io_;
    channel link_[3];
    comm_hook * hook_ = nullptr;

    static channel connect_one(role self, role peer, const std::string & dir,
        asio::io_context & io, unsigned retries, const peer_security & sec,
        const deadlines & lim)
    {
        using proto = asio::local::stream_protocol;
        const bool accept = to_u(self) < to_u(peer);
        const auto path = link_path(dir, self, peer);
        const std::string who = role_name(peer);
        if (accept)
        {
            ::unlink(path.c_str());
            proto::endpoint ep(path);
            proto::acceptor acc(io, ep);
            for (unsigned i = 0; i < retries; ++i)
            {
                asio::error_code ec;
                proto::socket sock(io);
                acc.accept(sock, ec);
                if (!ec)
                    return secure_local_channel(io, std::move(sock), true,
                        to_u(peer), sec, lim.handshake, who, "accept");
                std::this_thread::sleep_for(std::chrono::milliseconds(10));
            }
            throw std::runtime_error("trio accept failed: " + path);
        }
        proto::endpoint ep(path);
        for (unsigned i = 0; i < retries; ++i)
        {
            asio::error_code ec;
            proto::socket sock(io);
            sock.connect(ep, ec);
            if (!ec)
                return secure_local_channel(io, std::move(sock), false,
                    to_u(peer), sec, lim.handshake, who, "connect");
            std::this_thread::sleep_for(std::chrono::milliseconds(10));
        }
        throw std::runtime_error("trio connect failed: " + path);
    }

    static std::uint16_t tcp_port(std::uint16_t base, role a, role b)
    {
        if (to_u(a) > to_u(b))
            std::swap(a, b);
        return static_cast<std::uint16_t>(base + 10u * to_u(a) + to_u(b));
    }

    static channel connect_one_tcp(role self, role peer, std::uint16_t base,
        const std::string & host, asio::io_context & io, unsigned retries,
        const peer_security & sec, const deadlines & lim,
        const socket_options & so)
    {
        using tcp = asio::ip::tcp;
        const bool accept = to_u(self) < to_u(peer);
        const auto port = tcp_port(base, self, peer);
        const std::string who = role_name(peer);
        if (accept)
        {
            tcp::endpoint ep(tcp::v4(), port);
            tcp::acceptor acc(io);
            asio::error_code ec;
            acc.open(ep.protocol(), ec);
            acc.set_option(tcp::acceptor::reuse_address(true), ec);
            acc.bind(ep, ec);
            if (ec)
                throw std::runtime_error("trio tcp bind: " + ec.message());
            acc.listen(1, ec);
            for (unsigned i = 0; i < retries; ++i)
            {
                tcp::socket sock(io);
                acc.accept(sock, ec);
                if (!ec)
                    return secure_tcp_channel(io, std::move(sock), true,
                        to_u(peer), sec, so, lim.handshake, who, "accept");
                std::this_thread::sleep_for(std::chrono::milliseconds(10));
            }
            throw std::runtime_error("trio tcp accept failed");
        }
        tcp::resolver resolver(io);
        auto endpoints = resolver.resolve(host, std::to_string(port));
        for (unsigned i = 0; i < retries; ++i)
        {
            asio::error_code ec;
            tcp::socket sock(io);
            asio::connect(sock, endpoints, ec);
            if (!ec)
                return secure_tcp_channel(io, std::move(sock), false,
                    to_u(peer), sec, so, lim.handshake, who, "connect");
            std::this_thread::sleep_for(std::chrono::milliseconds(10));
        }
        throw std::runtime_error("trio tcp connect failed");
    }
};

}  // namespace net
}  // namespace dpf

#endif  // LIBDPF_INCLUDE_DPF_NET_TRIO_HPP__