# Copyright: 2009 DmitrijsMilajevs
# License: GNU GPL v2 (or any later version), see LICENSE.txt for details.

"""
MoinMoin - Group access via various backends.

The composite_groups backend does not have direct storage; it composes other backends into a new
one, so group definitions are retrieved from several backends. This allows mixing different backends.
"""


from moin.datastructures.backends import BaseGroupsBackend, GroupDoesNotExistError


class CompositeGroups(BaseGroupsBackend):
    """
    Manage several group backends.
    """

    def __init__(self, *backends):
        """
        :param backends: list of group backends which are used to get
                         access to the group definitions.
        """
        super().__init__()
        self._backends = backends

    def __getitem__(self, group_name):
        """
        Get a group by its name. First match counts.
        """
        for backend in self._backends:
            try:
                return backend[group_name]
            except GroupDoesNotExistError:
                pass
        raise GroupDoesNotExistError(group_name)

    def __iter__(self):
        """
        Iterate over group names in all backends (filtering duplicates).

        If a group with the same name is defined in several backends, the composite_groups backend yields
        only the one from the backend that is listed earlier in self._backends.
        """
        yielded_groups = set()

        for backend in self._backends:
            for group_name in backend:
                if group_name not in yielded_groups:
                    yield group_name
                    yielded_groups.add(group_name)

    def __contains__(self, group_name):
        """
        Check if a group called group_name is available in any of the backends.

        :param group_name: name of the group [unicode]
        """
        for backend in self._backends:
            if group_name in backend:
                return True
        return False

    def __repr__(self):
        return f"<{self.__class__} backends={self._backends}>"
