#include <pybind11/pybind11.h>
#include <functional>
#include <iostream>
namespace py=pybind11;

class Animal
{
  public:
    virtual void speak() {std::cout << "I am just a generic animal, I have no voice." << std::endl;}
};

class Animal_wrapper
{
  public:
    Animal_wrapper(py::object o) : obj(o) {}
    std::shared_ptr<Animal> operator()() { py::object animal = obj();
                                           return animal.cast< std::shared_ptr<Animal> >();}
    py::object obj;
};

class Animal_trampoline : public Animal
{
  public:
    void speak() override { PYBIND11_OVERLOAD(void, Animal, speak, ); }
};

class Animal_Factory
{
  public:
    Animal_Factory() = default;
    Animal_Factory(std::function<std::shared_ptr<Animal>()> anm) : factory(anm) {}
    std::function<std::shared_ptr<Animal>()> factory;
};

Animal_Factory my_factory;
void set_factory(py::object obj);
std::shared_ptr<Animal> get_animal();

PYBIND11_MODULE(example, m)
{
  py::class_<Animal, Animal_trampoline, std::shared_ptr<Animal>>(m, "Animal")
  .def(py::init<>())
  .def("speak", &Animal::speak);

  py::class_<Animal_Factory>(m, "Animal_Factory")
  .def(py::init<std::function<std::shared_ptr<Animal>()>>())
  ;

  m.def("set_factory", &set_factory, py::arg("f"));
  m.def("get_animal", &get_animal);

}

void
set_factory(py::object obj)
{
  std::cout << "Setting factory" << std::endl;
  Animal_wrapper const wrap(obj);
  my_factory = Animal_Factory(wrap);
}

std::shared_ptr<Animal>
get_animal()
{
  std::cout << "Making new animal from factory" << std::endl;
  return my_factory.factory();
}