from .unmountedtype import UnmountedType


class Structure(UnmountedType):
    '''
    A structure is a GraphQL type instance that
    wraps a main type with certain structure.
    '''

    def __init__(self, of_type, *args, **kwargs):
        super(Structure, self).__init__(*args, **kwargs)
        self.of_type = of_type

    def get_type(self):
        '''
        This function is called when the unmounted type (List or NonNull instance)
        is mounted (as a Field, InputField or Argument)
        '''
        return self


class List(Structure):
    '''
    List Modifier

    A list is a kind of type marker, a wrapping type which points to another
    type. Lists are often created within the context of defining the fields of
    an object type.
    '''

    def __str__(self):
        return '[{}]'.format(self.of_type)

    def __eq__(self, other):
        return isinstance(other, List) and (
            self.of_type == other.of_type and
            self.args == other.args and
            self.kwargs == other.kwargs
        )


class NonNull(Structure):
    '''
    Non-Null Modifier

    A non-null is a kind of type marker, a wrapping type which points to another
    type. Non-null types enforce that their values are never null and can ensure
    an error is raised if this ever occurs during a request. It is useful for
    fields which you can make a strong guarantee on non-nullability, for example
    usually the id field of a database row will never be null.

    Note: the enforcement of non-nullability occurs within the executor.
    '''

    def __init__(self, *args, **kwargs):
        super(NonNull, self).__init__(*args, **kwargs)
        assert not isinstance(self.of_type, NonNull), (
            'Can only create NonNull of a Nullable GraphQLType but got: {}.'
        ).format(type)

    def __str__(self):
        return '{}!'.format(self.of_type)

    def __eq__(self, other):
        return isinstance(other, NonNull) and (
            self.of_type == other.of_type and
            self.args == other.args and
            self.kwargs == other.kwargs
        )