import typing
from sys import _getframe


class Enum(int):
    __slots__ = []
    """type: typing.FrozenSet[str]"""
    names2values = dict()  # TODO: make it FrozenBimap
    """type: typing.Dict[str, int]"""
    values2names = dict()
    """type: typing.Dict[int, str]"""
    _counter = -1

    def __new__(cls, value):
        cls._counter = value
        return int.__new__(cls, int(value))

enumcls_t = typing.Type[Enum]


def _no_new_instances(*args):
    raise Exception("no new instances permitted")


def _lock_enum_type(cls: typing.Type[Enum]):
    cls.__new__ = _no_new_instances


def begin_enum(cls: typing.Type[Enum]):
    cls._snap_before = frozenset(_getframe(1).f_globals.keys())


def end_enum(cls: typing.Type[Enum]):
    cls_globals = _getframe(1).f_globals
    names = frozenset(cls_globals.keys()) - cls._snap_before
    del cls._snap_before

    cls.names2values = {name: cls_globals[name] for name in names}
    cls.values2names = {cls_globals[name]: name for name in names}

    _lock_enum_type(cls)


def next(cls: typing.Type[Enum]):
    return cls(cls._counter + 1)