# vim: tabstop=4 shiftwidth=4 softtabstop=4

# Copyright (c) 2010 Openstack, LLC.
# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# 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.

"""
Chance (Random) Scheduler implementation
"""

import random

from nova import exception
from nova.scheduler import driver


class ChanceScheduler(driver.Scheduler):
    """Implements Scheduler as a random node selector."""

    def _filter_hosts(self, request_spec, hosts):
        """Filter a list of hosts based on request_spec."""

        # Filter out excluded host
        if (request_spec and 'original_host' in request_spec and
            request_spec.get('avoid_original_host', True)):
            hosts = [host for host in hosts
                     if host != request_spec['original_host']]

        return hosts

    def _schedule(self, context, topic, request_spec, **kwargs):
        """Picks a host that is up at random."""

        elevated = context.elevated()
        hosts = self.hosts_up(elevated, topic)
        if not hosts:
            msg = _("Is the appropriate service running?")
            raise exception.NoValidHost(reason=msg)

        hosts = self._filter_hosts(request_spec, hosts)
        if not hosts:
            msg = _("Could not find another compute")
            raise exception.NoValidHost(reason=msg)

        return hosts[int(random.random() * len(hosts))]

    def schedule(self, context, topic, method, *_args, **kwargs):
        """Picks a host that is up at random."""

        host = self._schedule(context, topic, None, **kwargs)
        driver.cast_to_host(context, topic, host, method, **kwargs)

    def schedule_run_instance(self, context, request_spec, *_args, **kwargs):
        """Create and run an instance or instances"""
        elevated = context.elevated()
        num_instances = request_spec.get('num_instances', 1)
        instances = []
        for num in xrange(num_instances):
            host = self._schedule(context, 'compute', request_spec, **kwargs)
            instance = self.create_instance_db_entry(elevated, request_spec)
            driver.cast_to_compute_host(context, host,
                    'run_instance', instance_uuid=instance['uuid'], **kwargs)
            instances.append(driver.encode_instance(instance))

        return instances

    def schedule_prep_resize(self, context, request_spec, *args, **kwargs):
        """Select a target for resize."""
        host = self._schedule(context, 'compute', request_spec, **kwargs)
        driver.cast_to_host(context, 'compute', host, 'prep_resize', **kwargs)