# Copyright (c) 2011-2012 OpenStack Foundation
# All Rights Reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

import nova.conf
from nova.scheduler import filters

CONF = nova.conf.CONF


class IsolatedHostsFilter(filters.BaseHostFilter):
    """Keep specified images to selected hosts."""

    # The configuration values do not change within a request
    run_filter_once_per_request = True

    RUN_ON_REBUILD = True

    def host_passes(self, host_state, spec_obj):
        """Result Matrix with 'restrict_isolated_hosts_to_isolated_images' set
        to True::

        |                | isolated_image | non_isolated_image
        |   -------------+----------------+-------------------
        |   iso_host     |    True        |     False
        |   non_iso_host |    False       |      True

        Result Matrix with 'restrict_isolated_hosts_to_isolated_images' set
        to False::

        |                | isolated_image | non_isolated_image
        |   -------------+----------------+-------------------
        |   iso_host     |    True        |      True
        |   non_iso_host |    False       |      True

        """
        # If the configuration does not list any hosts, the filter will always
        # return True, assuming a configuration error, so letting all hosts
        # through.
        isolated_hosts = CONF.filter_scheduler.isolated_hosts
        isolated_images = CONF.filter_scheduler.isolated_images
        restrict_isolated_hosts_to_isolated_images = (
            CONF.filter_scheduler.restrict_isolated_hosts_to_isolated_images)
        if not isolated_images:
            # As there are no images to match, return True if the filter is
            # not restrictive otherwise return False if the host is in the
            # isolation list.
            return ((not restrict_isolated_hosts_to_isolated_images) or
                   (host_state.host not in isolated_hosts))

        # Check to see if the image id is set since volume-backed instances
        # can be created without an imageRef in the server create request.
        image_ref = spec_obj.image.id \
            if spec_obj.image and 'id' in spec_obj.image else None
        image_isolated = image_ref in isolated_images
        host_isolated = host_state.host in isolated_hosts

        if restrict_isolated_hosts_to_isolated_images:
            return (image_isolated == host_isolated)
        else:
            return (not image_isolated) or host_isolated