#ifndef REFPTR_H
#define REFPTR_H REFPTR_H

#include <stdlib.h>             /* NULL */
#include <atomic>               /* std::atomic */

template <typename T>
class refptr
{
    public:
        refptr();
        refptr(T * ptr);
        refptr(const refptr<T> & orig);
        refptr & operator=(const refptr<T> & orig);
        refptr & operator=(T * ptr);
        ~refptr();
        T & operator*() const;
        T * operator->() const;
        bool isNull() const { return m_ptr == NULL; }
        bool operator==(const refptr<T> & right) const;
        bool operator!=(const refptr<T> & right) const;

    private:
        void cloneFrom(const refptr<T> & orig);
        void destroy();

        T * m_ptr;
        /* reference count is atomic so that refptr copies may be made
         * concurrently from multiple threads (e.g. the multithreaded
         * renderer) without corrupting the count */
        std::atomic<int> * m_refCount;
};

template <typename T> refptr<T>::refptr()
{
    m_ptr = NULL;
    m_refCount = NULL;
}

template <typename T> refptr<T>::refptr(T * ptr)
{
    m_ptr = ptr;
    m_refCount = new std::atomic<int>(1);
}

template <typename T> refptr<T>::refptr(const refptr<T> & orig)
{
    cloneFrom(orig);
}

template <typename T> refptr<T> & refptr<T>::operator=(const refptr<T> & orig)
{
    destroy();
    cloneFrom(orig);
    return *this;
}

template <typename T> refptr<T> & refptr<T>::operator=(T * ptr)
{
    destroy();
    m_ptr = ptr;
    m_refCount = new std::atomic<int>(1);
    return *this;
}

template <typename T> void refptr<T>::cloneFrom(const refptr<T> & orig)
{
    this->m_ptr = orig.m_ptr;
    this->m_refCount = orig.m_refCount;
    if (m_refCount != NULL)
        m_refCount->fetch_add(1, std::memory_order_relaxed);
}

template <typename T> refptr<T>::~refptr()
{
    destroy();
}

template <typename T> void refptr<T>::destroy()
{
    if (m_refCount != NULL)
    {
        /* fetch_sub returns the value prior to the decrement; if it was 1
         * then this was the last reference and we own the cleanup */
        if (m_refCount->fetch_sub(1, std::memory_order_acq_rel) == 1)
        {
            delete m_ptr;
            delete m_refCount;
        }
    }
}

template <typename T> T & refptr<T>::operator*() const
{
    return *m_ptr;
}

template <typename T> T * refptr<T>::operator->() const
{
    return m_ptr;
}

template <typename T> bool refptr<T>::operator==(const refptr<T> & right) const
{
    return m_ptr == right.m_ptr;
}

template <typename T> bool refptr<T>::operator!=(const refptr<T> & right) const
{
    return m_ptr != right.m_ptr;
}

#endif