#include <boost/asio.hpp>
#include <boost/asio/spawn.hpp>
#include <iostream>
#include <memory>
#include <deque>

class Suspender
{
    private:
        using handler_type  = boost::asio::handler_type<boost::asio::yield_context, void()>::type;
        using result_type   = boost::asio::async_result<handler_type>;

        class HandlerWrapper
        {
            private:
                std::shared_ptr<handler_type>   _handler;
            public:
                HandlerWrapper(boost::asio::yield_context yield) :
                    _handler(std::make_shared<handler_type>(yield))
                {}

                HandlerWrapper(const HandlerWrapper &that) = default;
                HandlerWrapper(HandlerWrapper &&that) = default;

                void operator()()
                {
                    return _handler->operator()();
                }

                handler_type &operator*()
                {
                    return *_handler;
                }
        };

        std::deque<HandlerWrapper> _handlers;

    public:
        Suspender() = default;

        void suspend(boost::asio::yield_context yield)
        {
            _handlers.emplace_back(yield);
            result_type result{ *_handlers.back() };
            result.get();
        }

        void resume(boost::asio::io_service &service)
        {
            std::cout << "Resuming one of " << _handlers.size() << " waiting coroutines" << std::endl;

            if (_handlers.empty()) {
                return;
            }

            service.post(_handlers.front());
            _handlers.pop_front();
        }
};

int main()
{
    boost::asio::io_service service;
    Suspender suspender;

    boost::asio::spawn(service, [&suspender](boost::asio::yield_context yield) {
        std::cout << "Suspending" << std::endl;
        suspender.suspend(yield);
        std::cout << "Woke up" << std::endl;
    });

    boost::asio::spawn(service, [&service, &suspender](boost::asio::yield_context yield) {
        suspender.resume(service);
    });

    service.run();

    return 0;
}