#ifndef MPL_ENUMS_H

#define MPL_ENUMS_H

#include <pybind11/pybind11.h>

#define P11X_ENUM_TYPE(a1, a2, ...) decltype(std::pair a1, a2)::second_type

#define P11X_CAT2(a, b) a##b

#define P11X_CAT(a, b) P11X_CAT2(a, b)

namespace p11x {

namespace {

namespace py = pybind11;

// Holder is (py_base_cls, [(name, value), ...]) before module init;

// converted to the Python class object after init.

auto enums = std::unordered_map<std::string, py::object>{};

auto bind_enums(py::module mod) -> void

}

}

}

#define P11X_DECLARE_ENUM(py_name, py_base_cls, ...) \

namespace p11x { \

namespace { \

[[maybe_unused]] auto const P11X_CAT(enum_placeholder_, __COUNTER__) = \

[](auto args) { \

py::gil_scoped_acquire gil; \

using int_t = std::underlying_type_t<decltype(args[0].second)>; \

auto pairs = std::vector<std::pair<std::string, int_t>>{}; \

for (auto& [k, v]: args) { \

pairs.emplace_back(k, int_t(v)); \

} \

p11x::enums[py_name] = pybind11::cast(std::pair{py_base_cls, pairs}); \

return 0; \

} (std::vector{std::pair __VA_ARGS__}); \

} \

} \

namespace pybind11::detail { \

template<> struct type_caster<P11X_ENUM_TYPE(__VA_ARGS__)> { \

using type = P11X_ENUM_TYPE(__VA_ARGS__); \

static_assert(std::is_enum_v<type>, "Not an enum"); \

PYBIND11_TYPE_CASTER(type, _(py_name)); \

bool load(handle src, bool) { \

auto cls = p11x::enums.at(py_name); \

PyObject* tmp = nullptr; \

if (pybind11::isinstance(src, cls) \

&& (tmp = PyNumber_Index(src.attr("value").ptr()))) { \

auto ival = PyLong_AsLong(tmp); \

value = decltype(value)(ival); \

Py_DECREF(tmp); \

return !(ival == -1 && PyErr_Occurred()); \

} else { \

return false; \

} \

} \

static handle cast(decltype(value) obj, return_value_policy, handle) { \

auto cls = p11x::enums.at(py_name); \

return cls(std::underlying_type_t<type>(obj)).inc_ref(); \

} \

}; \

}

#endif /* MPL_ENUMS_H */