#ifndef stack_h
#define stack_h 1

#include <atomic>
#include <chrono>
#include <mutex>
#include <optional>
#include <stack>
#include <thread>

using namespace std::chrono_literals;

class spinlock
{
public:
    void lock()
    {
        auto delay = 50us;
        while (flag.test_and_set(std::memory_order_acquire))
            std::this_thread::sleep_for(delay *= 2);
    }

    void unlock()
    {
        flag.clear(std::memory_order_release);
    }

private:
    std::atomic_flag flag;
};

template <class T>
class stack
{
public:
    void push(const T &t)
    {
        std::lock_guard<spinlock> l(s);
        container.push(t);
    }

    std::optional<T> pop()
    {
        std::lock_guard<spinlock> l(s);
        if (!container.empty())
        {
            auto data = container.top();
            container.pop();
            return data;
        }
        else
        {
            return std::nullopt;
        }
    }

private:
    spinlock s;
    std::stack<T> container;
};

#endif // stack_h