//
//  exchanger.cpp
//  malnati
//
//  Created by Elia Migliore on 19/07/2019.
//  Copyright © 2019 Elia Migliore. All rights reserved.
//

#include "exchanger.hpp"
#include <iostream>
#include <mutex>
#include <thread>

template <typename T>

class Exchanger {
    T exchanged;
    bool is_exchanged;
    std::mutex m_protect_data;
    std::mutex m_protect_sleep;
    std::condition_variable cv;

    Exchanger(T& exchanged) {
        std::unique_lock<std::mutex> l(m_protect_data);

        if (is_exchanged){
            // cv.signal()
            std::swap(exchanged, this->exchanged);
            cv.notify_one();

        } else {

            // exchange the item and set to true the variable
            // that represent the exchanged flag
            this->exchanged = exchanged;
            is_exchanged = true;

            // release the lock for protecting the variable
            l.release();

            // wait for the other thread to wake me up when
            // another element has arrived and the exchanged
            // item is exchanged

            // unique lock per il paradisma RAII
            std::unique_lock<std::mutex> l_s(m_protect_sleep);
            cv.wait(l_s);


            // getting again te lock to protect the flag and data
            l.lock();
            exchanged = this->exchanged;
            is_exchanged = false; // restore the class for next use

            // now RAII paradigm release the second lock for me
        }
        // output to indicate the success
        std::cout << "element to exchange is: " << typeid(exchanged).name() << std::endl;


        // now RAII paradigm release the first lock for me
    }


};