#pragma once

#include <atomic>

namespace rcp_internal
{
    class root
    {
    private:
        mutable std::atomic<int> ref_count{0};

        rcp<root> root_rcp;

    protected:
        root()
        {
            root_rcp = rcp<root>(this);
        }

        virtual ~root() = default;

    public:
        void add_ref() const
        {
            ref_count.fetch_add(1, std::memory_order_relaxed);
        }

        void release_ref() const
        {
            if (ref_count.fetch_sub(1, std::memory_order_acq_rel) == 0)
            {
                delete this;
            }
        }

        rcp<root> & get_root_rcp()
        {
            return root_rcp;
        }
    }

    template <typename T>
    class managed
    {
    public:
        static_assert(std::is_base_of<root, T>::value,
                "T must inherit from rcp::root to use rcp::managed<T>");

        rcp<T> get_rcp()
        {
            root * r = (root *)this;
            return rcp<T>(r->get_root_ref());
        }
    }
}

/**
 * Reference-counting pointer.
 */
template <typename T>
class rcp
{
private:
    T * ptr = nullptr;

    explicit rcp(T * p) : ptr(p)
    {
        if (p)
        {
            ptr->add_ref();
        }
    }

    friend T;

public:
    rcp() = default;

    rcp(const rcp & other) : ptr(other.ptr)
    {
        if (ptr)
        {
            ptr->add_ref();
        }
    }

    ~rcp()
    {
        if (ptr)
        {
            ptr->release_ref();
        }
    }

    /* Casting constructor: allows rcp<Base> -> rcp<Derived> */
    template <typename U>
    rcp(const rcp<U> & other) : ptr(static_cast<T *>(other.get_raw()))
    {
        if (ptr)
        {
            ptr->add_ref();
        }
    }

    T * get_raw() const
    {
        return ptr;
    }

    T * operator->() const
    {
        return ptr;
    }

    bool operator!() const
    {
        return !ptr;
    }

    using root = rcp_internal::root;

    using managed = rcp_internal::managed;
}