#ifndef asp_h
#define asp_h

#include <boost/smart_ptr/atomic_shared_ptr.hpp>
#include <boost/smart_ptr/make_shared.hpp>
#include <boost/smart_ptr/shared_ptr.hpp>
#include <memory>
#include <optional>

template<typename T> class stack
{
public:
    ~stack() { while (pop()); }

    void push(T t)
    {
        auto n =
            boost::make_shared<node>(head.load(std::memory_order_relaxed), t);
        while (!head.compare_exchange_weak(
            n->next, n, std::memory_order_release, std::memory_order_relaxed));
    }

    std::optional<T> pop()
    {
        auto p = head.load(std::memory_order_acquire);
        while (p && !head.compare_exchange_weak(p, p->next,
                                                std::memory_order_release,
                                                std::memory_order_relaxed));
        if (p)
            return std::optional<T>(p->data);
        else
            return std::nullopt;
    }

private:
    struct node
    {
        boost::shared_ptr<node> next;
        T data;
    };

    boost::atomic_shared_ptr<node> head; // NO LOCKFREE!!!
};

#endif // asp_h