# 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.

"""
Simple Scheduler
"""

from nova import db
from nova import flags
from nova import exception
from nova.scheduler import driver
from nova.scheduler import chance

FLAGS = flags.FLAGS
flags.DEFINE_integer("max_cores", 16,
                     "maximum number of instance cores to allow per host")
flags.DEFINE_integer("max_gigabytes", 10000,
                     "maximum number of volume gigabytes to allow per host")
flags.DEFINE_integer("max_networks", 1000,
                     "maximum number of networks to allow per host")
flags.DEFINE_string('default_schedule_zone', None,
                    'zone to use when user doesnt specify one')


class SimpleScheduler(chance.ChanceScheduler):
    """Implements Naive Scheduler that tries to find least loaded host."""

    def _schedule_instance(self, context, instance_opts, *_args, **_kwargs):
        """Picks a host that is up and has the fewest running instances."""
        elevated = context.elevated()

        availability_zone = instance_opts.get('availability_zone')

        zone, host = FLAGS.default_schedule_zone, None
        if availability_zone:
            zone, _x, host = availability_zone.partition(':')

        if host and context.is_admin:
            service = db.service_get_by_args(elevated, host, 'nova-compute')
            if not self.service_is_up(service):
                raise exception.WillNotSchedule(host=host)
            return host

        results = db.service_get_all_compute_sorted(elevated)
        if zone:
            results = [(service, cores) for (service, cores) in results
                       if service['availability_zone'] == zone]
        for result in results:
            (service, instance_cores) = result
            if instance_cores + instance_opts['vcpus'] > FLAGS.max_cores:
                msg = _("All hosts have too many cores")
                raise exception.NoValidHost(reason=msg)
            if self.service_is_up(service):
                return service['host']
        msg = _("Is the appropriate service running?")
        raise exception.NoValidHost(reason=msg)

    def schedule_run_instance(self, context, request_spec, *_args, **_kwargs):
        num_instances = request_spec.get('num_instances', 1)
        instances = []
        for num in xrange(num_instances):
            host = self._schedule_instance(context,
                    request_spec['instance_properties'], *_args, **_kwargs)
            instance_ref = self.create_instance_db_entry(context,
                    request_spec)
            driver.cast_to_compute_host(context, host, 'run_instance',
                    instance_uuid=instance_ref['uuid'], **_kwargs)
            instances.append(driver.encode_instance(instance_ref))
        return instances

    def schedule_start_instance(self, context, instance_id, *_args, **_kwargs):
        instance_ref = db.instance_get(context, instance_id)
        host = self._schedule_instance(context, instance_ref,
                *_args, **_kwargs)
        driver.cast_to_compute_host(context, host, 'start_instance',
                instance_id=instance_id, **_kwargs)

    def schedule_create_volume(self, context, volume_id, *_args, **_kwargs):
        """Picks a host that is up and has the fewest volumes."""
        elevated = context.elevated()

        volume_ref = db.volume_get(context, volume_id)
        availability_zone = volume_ref.get('availability_zone')

        zone, host = None, None
        if availability_zone:
            zone, _x, host = availability_zone.partition(':')
        if host and context.is_admin:
            service = db.service_get_by_args(elevated, host, 'nova-volume')
            if not self.service_is_up(service):
                raise exception.WillNotSchedule(host=host)
            driver.cast_to_volume_host(context, host, 'create_volume',
                    volume_id=volume_id, **_kwargs)
            return None

        results = db.service_get_all_volume_sorted(elevated)
        if zone:
            results = [(service, gigs) for (service, gigs) in results
                       if service['availability_zone'] == zone]
        for result in results:
            (service, volume_gigabytes) = result
            if volume_gigabytes + volume_ref['size'] > FLAGS.max_gigabytes:
                msg = _("All hosts have too many gigabytes")
                raise exception.NoValidHost(reason=msg)
            if self.service_is_up(service):
                driver.cast_to_volume_host(context, service['host'],
                        'create_volume', volume_id=volume_id, **_kwargs)
                return None
        msg = _("Is the appropriate service running?")
        raise exception.NoValidHost(reason=msg)

    def schedule_set_network_host(self, context, *_args, **_kwargs):
        """Picks a host that is up and has the fewest networks."""
        elevated = context.elevated()

        results = db.service_get_all_network_sorted(elevated)
        for result in results:
            (service, instance_count) = result
            if instance_count >= FLAGS.max_networks:
                msg = _("All hosts have too many networks")
                raise exception.NoValidHost(reason=msg)
            if self.service_is_up(service):
                driver.cast_to_network_host(context, service['host'],
                        'set_network_host', **_kwargs)
                return None
        msg = _("Is the appropriate service running?")
        raise exception.NoValidHost(reason=msg)