// senderReceiver.cpp
#include <coroutine>
#include <chrono>
#include <iostream>
#include <functional>
#include <string>
#include <stdexcept>
#include <atomic>
#include <thread>
class Event {
public:
    Event() = default;
    Event(const Event &) = delete;
    Event(Event &&) = delete;
    Event& operator=(const Event &) = delete;
    Event& operator=(Event &&) = delete;
    class Awaiter;
    Awaiter operator co_await() const;
    void notify();
private:
    friend class Awaiter;
    mutable std::atomic<void *> suspendedWaiter{nullptr};
    mutable std::atomic<bool> notified{false};
};
class Event::Awaiter {
public:
    Awaiter(const Event &e) : event(e) {}
    bool await_ready() const;
    bool await_suspend(std::coroutine_handle<> ch);
    void await_resume() {}
private:
    friend class Event;
    const Event &event;
    std::coroutine_handle<> coroutineHandle;
};
bool Event::Awaiter::await_ready() const {
    if (event.suspendedWaiter.load() != nullptr) {
        throw std::runtime_error("More than one waiter is not valid");
    }
    return event.notified; // true - корутина выполняется как обычная функция, false - корутина приостановлена
}
bool Event::Awaiter::await_suspend(std::coroutine_handle<> ch) {
    coroutineHandle = ch;
    if (event.notified) {
        return false;
    }
    // сохранить waiter для последующего уведомления
    event.suspendedWaiter.store(this);
    return true;
}
void Event::notify() {
    notified = true;
    // попытка загрузить waiter
    auto *waiter = static_cast<Awaiter *>(suspendedWaiter.load());
    // проверка доступен ли waiter
    if (waiter != nullptr) {
        // возобновить работу корутины
        waiter->coroutineHandle.resume();
    }
}
Event::Awaiter Event::operator co_await() const {
    return Awaiter{*this};
}
struct Task {
    struct promise_type {
        Task get_return_object() { return {}; }
        std::suspend_never initial_suspend() { return {}; }
        std::suspend_never final_suspend() { return {}; }
        void return_void() {}
        void unhandled_exception() {}
    };
};
Task receiver(Event &event) {
    auto start = std::chrono::high_resolution_clock::now();
    co_await event;
    std::cout << "Got the notification!" << std::endl;
    auto end = std::chrono::high_resolution_clock::now();
    std::chrono::duration<double> elapsed = end - start;
    std::cout << "Waited " << elapsed.count() << " seconds." << std::endl;
}
int main() {
    std::cout << "Notification before waiting" << std::endl;
    Event event1{};
    auto senderThread1 = std::thread([&event1] { event1.notify(); });
    auto receiverThread1 = std::thread(receiver, std::ref(event1));
    receiverThread1.join();
    senderThread1.join();
    std::cout << "\nNotification after 2 seconds waiting" << std::endl;
    Event event2{};
    auto receiverThread2 = std::thread(receiver, std::ref(event2));
    auto senderThread2 = std::thread([&event2] {
                                         using namespace std::chrono_literals;
                                         std::this_thread::sleep_for(2s);
                                         event2.notify();
                                     });
    receiverThread2.join();
    senderThread2.join();
}