#ifndef __PYTHON_OPTIONAL_H__
#define __PYTHON_OPTIONAL_H__

#include <boost/python.hpp>

// Taken from an email by John Wiegley; 
// http://mail.python.org/pipermail/cplusplus-sig/2007-May/012003.html

template <typename T, typename TfromPy>
struct object_from_python
{
    object_from_python() 
    {
        boost::python::converter::registry::push_back(&TfromPy::convertible, 
                                                      &TfromPy::construct, 
                                                      boost::python::type_id<T>());
    }
};

template <typename T, typename TtoPy, typename TfromPy>
struct register_python_conversion
{
    register_python_conversion() 
    {
        boost::python::to_python_converter<T, TtoPy>();
        object_from_python<T, TfromPy>();
    }
};

template <typename T>
struct python_optional : public boost::noncopyable
{
    struct optional_to_python
    {
        static PyObject * convert(const boost::optional<T>& value)
        {
            return (value ? boost::python::to_python_value<T>()(*value) :
                            boost::python::detail::none());
        }
    };

    struct optional_from_python
    {
        static void * convertible(PyObject * source)
        {
            using namespace boost::python::converter;

            if (source == Py_None)
                return source;

            const registration& converters(registered<T>::converters);

            if (implicit_rvalue_convertible_from_python(source, converters)) 
            {
                rvalue_from_python_stage1_data data = rvalue_from_python_stage1(source, converters);
                return rvalue_from_python_stage2(source, data, converters);
            }
            return NULL;
        }

        static void construct(PyObject * source,
                              boost::python::converter::rvalue_from_python_stage1_data * data)
        {
            using namespace boost::python::converter;

            void * const storage = ((rvalue_from_python_storage<T> *) data)->storage.bytes;

            if (data->convertible == source)     // == None
                new (storage) boost::optional<T>(); // A Boost uninitialized value
            else
                new (storage) boost::optional<T>(*static_cast<T *>(data->convertible));

            data->convertible = storage;
        }
    };

    explicit python_optional() 
    {
        register_python_conversion<boost::optional<T>, optional_to_python, optional_from_python>();
    }
};

#endif