/*
Crafter®.Network
Copyright (C) 2026 Catcrafts®
Catcrafts.net

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 3.0 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
*/

module;
module Crafter.Network:WebTransport_impl;
import :WebTransport;
import :ClientQUIC;
import :HTTP3;
import Crafter.Thread;
import std;

using namespace Crafter;

struct WebTransportSession::Impl {
    // Non-owning. The session is constructed and owned by ListenerHTTP, and
    // ListenerHTTP keeps the underlying ClientQUIC alive in its PeerState
    // for the duration of the connection — so this pointer is valid as
    // long as the session is.
    ClientQUIC* connection = nullptr;

    // The HTTP/3 extended-CONNECT bidi stream the session was upgraded on.
    // Stays open for the session's lifetime. Phase 1 closes it with a bare
    // FIN; later phases will emit a CLOSE_WEBTRANSPORT_SESSION capsule.
    QUICStream connectStream;

    std::mutex mtx;
    std::function<void(QUICStream)> onStream;
    std::deque<QUICStream> pendingStreams;
    std::function<void(std::vector<char>)> onDatagram; // Phase 2

    bool closed = false;
};

WebTransportSession::WebTransportSession()
    : impl(std::make_unique<Impl>())
{}

WebTransportSession::WebTransportSession(WebTransportSession&&) noexcept = default;
WebTransportSession& WebTransportSession::operator=(WebTransportSession&&) noexcept = default;

WebTransportSession::~WebTransportSession() {
    if (impl) Close();
}

QUICStream WebTransportSession::OpenStream(bool unidirectional) {
    if (!impl || impl->closed || !impl->connection) {
        throw QUICClosedException();
    }
    QUICStream stream = impl->connection->OpenStream(unidirectional);
    auto prefix = unidirectional
        ? HTTP3::BuildWtUnidiPrefix(sessionId)
        : HTTP3::BuildWtBidiPrefix(sessionId);
    // Write the WT_STREAM (bidi) or stream-type (unidi) prefix as the
    // first send on the stream. The peer reads it to associate this
    // stream with our session before treating the rest as opaque payload.
    stream.SendSync(prefix.data(), static_cast<std::uint32_t>(prefix.size()), /*finish=*/false);
    return stream;
}

void WebTransportSession::OnStream(std::function<void(QUICStream)> callback) {
    std::deque<QUICStream> drained;
    {
        std::lock_guard lk(impl->mtx);
        impl->onStream = callback;
        drained.swap(impl->pendingStreams);
    }
    // Dispatch any streams that arrived before the handler was installed.
    // Each goes to the ThreadPool so user code runs off the demuxer thread.
    for (auto& s : drained) {
        auto* shared = new QUICStream(std::move(s));
        ThreadPool::Enqueue([callback, shared]{
            callback(std::move(*shared));
            delete shared;
        });
    }
}

void WebTransportSession::OnDatagram(std::function<void(std::vector<char>)> callback) {
    // Phase 1 stub. Phase 2 will plumb QUIC datagrams through here after
    // demuxing on quarter_session_id.
    if (impl) impl->onDatagram = std::move(callback);
}

void WebTransportSession::SendDatagram(const void*, std::uint32_t) {
    // Phase 1 stub — would prepend quarter_session_id varint and call
    // connection->SendDatagram. Drops silently for now.
}

void WebTransportSession::Close() {
    if (!impl || impl->closed) return;
    impl->closed = true;
    try {
        // Empty FIN on the CONNECT stream. Chrome / Firefox both treat
        // peer-FIN of the CONNECT stream as session-close.
        impl->connectStream.SendSync(nullptr, 0, /*finish=*/true);
    } catch (...) {
        // Connection may already be gone — that's fine.
    }
}

// ─── Internal ListenerHTTP-facing helpers ───────────────────────────────
//
// Declared (not exported) in the interface partition so ListenerHTTP_impl
// can call them; defined here. Friendship in WebTransportSession gives
// them access to the private Impl.

namespace Crafter {
    void WebTransportInitialise(WebTransportSession& session,
                                ClientQUIC* connection,
                                QUICStream connectStream,
                                std::uint64_t sessionId,
                                std::string path) {
        session.impl->connection = connection;
        session.impl->connectStream = std::move(connectStream);
        session.sessionId = sessionId;
        session.path = std::move(path);
    }

    void WebTransportDeliverStream(WebTransportSession& session, QUICStream stream) {
        std::function<void(QUICStream)> cb;
        {
            std::lock_guard lk(session.impl->mtx);
            cb = session.impl->onStream;
            if (!cb) {
                session.impl->pendingStreams.push_back(std::move(stream));
                return;
            }
        }
        auto* shared = new QUICStream(std::move(stream));
        ThreadPool::Enqueue([cb, shared]{
            cb(std::move(*shared));
            delete shared;
        });
    }
}