/*
 * Copyright (C) 2026 Josh Holtrop
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the “Software”), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#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 rcp_inc() const
        {
            ref_count.fetch_add(1, std::memory_order_relaxed);
        }

        void rcp_dec() 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->rcp_inc();
        }
    }

    friend T;

public:
    rcp() = default;

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

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

    /* 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->rcp_inc();
        }
    }

    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;
}