class BaseValue(object):
    def __init__(self, inference_state, parent_context=None):
        self.inference_state = inference_state
        self.parent_context = parent_context

    def get_root_context(self):
        value = self
        while True:
            if value.parent_context is None:
                return value
            value = value.parent_context

    def infer_type_vars(self, value_set, is_class_value=False):
        """
        When the current instance represents a type annotation, this method
        tries to find information about undefined type vars and returns a dict
        from type var name to value set.

        This is for example important to understand what `iter([1])` returns.
        According to typeshed, `iter` returns an `Iterator[_T]`:

            def iter(iterable: Iterable[_T]) -> Iterator[_T]: ...

        This functions would generate `int` for `_T` in this case, because it
        unpacks the `Iterable`.

        Parameters
        ----------

        `self`: represents the annotation of the current parameter to infer the
            value for. In the above example, this would initially be the
            `Iterable[_T]` of the `iterable` parameter and then, when recursing,
            just the `_T` generic parameter.

        `value_set`: represents the actual argument passed to the parameter
            we're inferrined for, or (for recursive calls) their types. In the
            above example this would first be the representation of the list
            `[1]` and then, when recursing, just of `1`.

        `is_class_value`: tells us whether or not to treat the `value_set` as
            representing the instances or types being passed, which is neccesary
            to correctly cope with `Type[T]` annotations. When it is True, this
            means that we are being called with a nested portion of an
            annotation and that the `value_set` represents the types of the
            arguments, rather than their actual instances. Note: not all
            recursive calls will neccesarily set this to True.
        """
        return {}


class BaseValueSet(object):
    def __init__(self, iterable):
        self._set = frozenset(iterable)
        for value in iterable:
            assert not isinstance(value, BaseValueSet)

    @classmethod
    def _from_frozen_set(cls, frozenset_):
        self = cls.__new__(cls)
        self._set = frozenset_
        return self

    @classmethod
    def from_sets(cls, sets):
        """
        Used to work with an iterable of set.
        """
        aggregated = set()
        for set_ in sets:
            if isinstance(set_, BaseValueSet):
                aggregated |= set_._set
            else:
                aggregated |= frozenset(set_)
        return cls._from_frozen_set(frozenset(aggregated))

    def __or__(self, other):
        return self._from_frozen_set(self._set | other._set)

    def __and__(self, other):
        return self._from_frozen_set(self._set & other._set)

    def __iter__(self):
        for element in self._set:
            yield element

    def __bool__(self):
        return bool(self._set)

    def __len__(self):
        return len(self._set)

    def __repr__(self):
        return 'S{%s}' % (', '.join(str(s) for s in self._set))

    def filter(self, filter_func):
        return self.__class__(filter(filter_func, self._set))

    def __getattr__(self, name):
        def mapper(*args, **kwargs):
            return self.from_sets(
                getattr(value, name)(*args, **kwargs)
                for value in self._set
            )
        return mapper

    def __eq__(self, other):
        return self._set == other._set

    def __ne__(self, other):
        return not self.__eq__(other)

    def __hash__(self):
        return hash(self._set)