#include <cstdlib>
#include <iostream>
#include <memory>
#include <utility>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;

class Session : public std::enable_shared_from_this<Session> {
 public:
  Session(tcp::socket socket): socket_(std::move(socket)) {

  }

  void start() {
    do_read();
  }

 private:
  void do_read() {
    auto self(shared_from_this());
    socket_.async_read_some(boost::asio::buffer(data_, max_length),
      [this, self](boost::system::error_code ec, std::size_t length) {
        if (!ec) {
          do_write(length);
        }
      }
    );
  }

  void do_write(std::size_t length) {
    auto self(shared_from_this());
    boost::asio::async_write(socket_, boost::asio::buffer(data_, length),
      [this, self](boost::system::error_code ec, std::size_t) {
        if (!ec) {
          do_read();
        }
      }
    );
  }

  tcp::socket socket_;
  enum { max_length = 1024 };
  char data_[max_length];
};

class Server {
 public:
  Server(boost::asio::io_service& io_service, short port)
    : acceptor_(io_service, tcp::endpoint(tcp::v4(), port)),
      socket_(io_service) {
    do_accept();
  }

 private:
  void do_accept() {
    acceptor_.async_accept(socket_,
      [this](boost::system::error_code ec) {
        if (!ec) {
          std::make_shared<Session>(std::move(socket_))->start();
        }
        do_accept();
      }
    );
  }

  tcp::acceptor acceptor_;
  tcp::socket socket_;
};

int main(int argc, char const *argv[])
{
  try {
    if (argc != 2) {
      std::cerr << "Usage: async_tcp_echo_server <port>\n";
      return 1;
    }

    boost::asio::io_service io_service;
    Server s(io_service, std::atoi(argv[1]));

    io_service.run();
  } catch (std::exception& e) {
    std::cerr << "Exception: " << e.what() << "\n";
  }
  return 0;
}