def migrate_groups_and_user_permissions(apps, schema_editor):
    """
    This function migrates the database to the new groups logic:
    - Rename group 'Anonymous' (pk=1) to 'Default'
    - Rename group 'Registered users' (pk=2) to 'Previous group Registered'
    - Add all users who are not in any group to this group (pk=2)
    - Add all permissions of 'Previous group Registered' to all other groups (except 'Default')

    But only run this migration if:
    - there are groups in the database,
    - the name of the first group is 'Guests',
    - the name of the second group is 'Registered users'.
    """
    User = apps.get_model('users', 'User')
    Group = apps.get_model('auth', 'Group')
    try:
        group_default = Group.objects.get(pk=1)
        group_registered = Group.objects.get(pk=2)
    except Group.DoesNotExist:
        pass
    else:
        if (group_default.name == 'Guests' and group_registered.name ==
            'Registered users'):
            group_default.name = 'Default'
            group_default.save()
            group_registered.name = 'Previous group Registered'
            group_registered.save()
            users = User.objects.all()
            for user in users:
                if not user.groups.exists():
                    user.groups.add(group_registered)
            groups = Group.objects.filter(pk__gt=2)
            for group in groups:
                for permission in group_registered.permissions.all():
                    group.permissions.add(permission)
