//
// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/boostorg/beast
//

//------------------------------------------------------------------------------
//
// Example: WebSocket server, stackless coroutine
//
//------------------------------------------------------------------------------

#include <boost/beast/core.hpp>
#include <boost/beast/websocket.hpp>
#include <boost/asio/coroutine.hpp>
#include <boost/asio/strand.hpp>
#include <boost/asio/dispatch.hpp>
#include <algorithm>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <memory>
#include <string>
#include <thread>
#include <vector>

namespace beast = boost::beast;         // from <boost/beast.hpp>
namespace http = beast::http;           // from <boost/beast/http.hpp>
namespace websocket = beast::websocket; // from <boost/beast/websocket.hpp>
namespace net = boost::asio;            // from <boost/asio.hpp>
using tcp = boost::asio::ip::tcp;       // from <boost/asio/ip/tcp.hpp>

//------------------------------------------------------------------------------

// Report a failure
void
fail(beast::error_code ec, char const* what)
{
    std::cerr << what << ": " << ec.message() << "\n";
}

// Echoes back all received WebSocket messages
class session
    : public boost::asio::coroutine
    , public std::enable_shared_from_this<session>
{
    websocket::stream<beast::tcp_stream> ws_;
    beast::flat_buffer buffer_;

public:
    // Take ownership of the socket
    explicit
    session(tcp::socket socket)
        : ws_(std::move(socket))
    {
    }

    // Start the asynchronous operation
    void
    run()
    {
        // We need to be executing within a strand to perform async operations
        // on the I/O objects in this session. Although not strictly necessary
        // for single-threaded contexts, this example code is written to be
        // thread-safe by default.
        net::dispatch(ws_.get_executor(),
                      beast::bind_front_handler(&session::loop,
                                                shared_from_this(),
                                                beast::error_code{},
                                                0));
    }

    #include <boost/asio/yield.hpp>

    void
    loop(
        beast::error_code ec,
        std::size_t bytes_transferred)
    {
        boost::ignore_unused(bytes_transferred);
        reenter(*this)
        {
            // Set suggested timeout settings for the websocket
            ws_.set_option(
                websocket::stream_base::timeout::suggested(
                    beast::role_type::server));

            // Set a decorator to change the Server of the handshake
            ws_.set_option(websocket::stream_base::decorator(
                [](websocket::response_type& res)
                {
                    res.set(http::field::server,
                        std::string(BOOST_BEAST_VERSION_STRING) +
                            " websocket-server-stackless");
                }));

            // Accept the websocket handshake
            yield ws_.async_accept(
                std::bind(
                    &session::loop,
                    shared_from_this(),
                    std::placeholders::_1,
                    0));
            if(ec)
                return fail(ec, "accept");

            for(;;)
            {
                // Read a message into our buffer
                yield ws_.async_read(
                    buffer_,
                    std::bind(
                        &session::loop,
                        shared_from_this(),
                        std::placeholders::_1,
                        std::placeholders::_2));
                if(ec == websocket::error::closed)
                {
                    // This indicates that the session was closed
                    return;
                }
                if(ec)
                    fail(ec, "read");

                // Echo the message
                ws_.text(ws_.got_text());
                yield ws_.async_write(
                    buffer_.data(),
                    std::bind(
                        &session::loop,
                        shared_from_this(),
                        std::placeholders::_1,
                        std::placeholders::_2));
                if(ec)
                    return fail(ec, "write");

                // Clear the buffer
                buffer_.consume(buffer_.size());
            }
        }
    }

    #include <boost/asio/unyield.hpp>
};

//------------------------------------------------------------------------------

// Accepts incoming connections and launches the sessions
class listener
    : public boost::asio::coroutine
    , public std::enable_shared_from_this<listener>
{
    net::io_context& ioc_;
    tcp::acceptor acceptor_;
    tcp::socket socket_;

public:
    listener(
        net::io_context& ioc,
        tcp::endpoint endpoint)
        : ioc_(ioc)
        , acceptor_(net::make_strand(ioc))
        , socket_(net::make_strand(ioc))
    {
        beast::error_code ec;

        // Open the acceptor
        acceptor_.open(endpoint.protocol(), ec);
        if(ec)
        {
            fail(ec, "open");
            return;
        }

        // Allow address reuse
        acceptor_.set_option(net::socket_base::reuse_address(true), ec);
        if(ec)
        {
            fail(ec, "set_option");
            return;
        }

        // Bind to the server address
        acceptor_.bind(endpoint, ec);
        if(ec)
        {
            fail(ec, "bind");
            return;
        }

        // Start listening for connections
        acceptor_.listen(
            net::socket_base::max_listen_connections, ec);
        if(ec)
        {
            fail(ec, "listen");
            return;
        }
    }

    // Start accepting incoming connections
    void
    run()
    {
        loop();
    }

private:

    #include <boost/asio/yield.hpp>

    void
    loop(beast::error_code ec = {})
    {
        reenter(*this)
        {
            for(;;)
            {
                yield acceptor_.async_accept(
                    socket_,
                    std::bind(
                        &listener::loop,
                        shared_from_this(),
                        std::placeholders::_1));
                if(ec)
                {
                    fail(ec, "accept");
                }
                else
                {
                    // Create the session and run it
                    std::make_shared<session>(std::move(socket_))->run();
                }

                // Make sure each session gets its own strand
                socket_ = tcp::socket(net::make_strand(ioc_));
            }
        }
    }

    #include <boost/asio/unyield.hpp>
};

//------------------------------------------------------------------------------

int main(int argc, char* argv[])
{
    // Check command line arguments.
    if (argc != 4)
    {
        std::cerr <<
            "Usage: websocket-server-stackless <address> <port> <threads>\n" <<
            "Example:\n" <<
            "    websocket-server-stackless 0.0.0.0 8080 1\n";
        return EXIT_FAILURE;
    }
    auto const address = net::ip::make_address(argv[1]);
    auto const port = static_cast<unsigned short>(std::atoi(argv[2]));
    auto const threads = std::max<int>(1, std::atoi(argv[3]));

    // The io_context is required for all I/O
    net::io_context ioc{threads};

    // Create and launch a listening port
    std::make_shared<listener>(ioc, tcp::endpoint{address, port})->run();

    // Run the I/O service on the requested number of threads
    std::vector<std::thread> v;
    v.reserve(threads - 1);
    for(auto i = threads - 1; i > 0; --i)
        v.emplace_back(
        [&ioc]
        {
            ioc.run();
        });
    ioc.run();

    return EXIT_SUCCESS;
}