# Copyright (c) 2011 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.

"""
The FilterScheduler is for creating instances locally.
You can customize this scheduler by specifying your own Host Filters and
Weighing Functions.
"""

import random

from oslo.config import cfg

from nova import exception
from nova.openstack.common import log as logging
from nova.openstack.common.notifier import api as notifier
from nova.scheduler import driver
from nova.scheduler import scheduler_options

CONF = cfg.CONF
LOG = logging.getLogger(__name__)


filter_scheduler_opts = [
    cfg.IntOpt('scheduler_host_subset_size',
               default=1,
               help='New instances will be scheduled on a host chosen '
                    'randomly from a subset of the N best hosts. This '
                    'property defines the subset size that a host is '
                    'chosen from. A value of 1 chooses the '
                    'first host returned by the weighing functions. '
                    'This value must be at least 1. Any value less than 1 '
                    'will be ignored, and 1 will be used instead')
]

CONF.register_opts(filter_scheduler_opts)


class FilterScheduler(driver.Scheduler):
    """Scheduler that can be used for filtering and weighing."""
    def __init__(self, *args, **kwargs):
        super(FilterScheduler, self).__init__(*args, **kwargs)
        self.cost_function_cache = None
        self.options = scheduler_options.SchedulerOptions()

    def schedule_run_instance(self, context, request_spec,
                              admin_password, injected_files,
                              requested_networks, is_first_time,
                              filter_properties):
        """This method is called from nova.compute.api to provision
        an instance.  We first create a build plan (a list of WeightedHosts)
        and then provision.

        Returns a list of the instances created.
        """
        payload = dict(request_spec=request_spec)
        notifier.notify(context, notifier.publisher_id("scheduler"),
                        'scheduler.run_instance.start', notifier.INFO, payload)

        instance_uuids = request_spec.pop('instance_uuids')
        num_instances = len(instance_uuids)
        LOG.debug(_("Attempting to build %(num_instances)d instance(s)") %
                locals())

        weighed_hosts = self._schedule(context, request_spec,
                filter_properties, instance_uuids)

        # NOTE(comstud): Make sure we do not pass this through.  It
        # contains an instance of RpcContext that cannot be serialized.
        filter_properties.pop('context', None)

        for num, instance_uuid in enumerate(instance_uuids):
            request_spec['instance_properties']['launch_index'] = num

            try:
                try:
                    weighed_host = weighed_hosts.pop(0)
                except IndexError:
                    raise exception.NoValidHost(reason="")

                self._provision_resource(context, weighed_host,
                                         request_spec,
                                         filter_properties,
                                         requested_networks,
                                         injected_files, admin_password,
                                         is_first_time,
                                         instance_uuid=instance_uuid)
            except Exception as ex:
                # NOTE(vish): we don't reraise the exception here to make sure
                #             that all instances in the request get set to
                #             error properly
                driver.handle_schedule_error(context, ex, instance_uuid,
                                             request_spec)
            # scrub retry host list in case we're scheduling multiple
            # instances:
            retry = filter_properties.get('retry', {})
            retry['hosts'] = []

        notifier.notify(context, notifier.publisher_id("scheduler"),
                        'scheduler.run_instance.end', notifier.INFO, payload)

    def schedule_prep_resize(self, context, image, request_spec,
                             filter_properties, instance, instance_type,
                             reservations):
        """Select a target for resize.

        Selects a target host for the instance, post-resize, and casts
        the prep_resize operation to it.
        """

        weighed_hosts = self._schedule(context, request_spec,
                filter_properties, [instance['uuid']])
        if not weighed_hosts:
            raise exception.NoValidHost(reason="")
        weighed_host = weighed_hosts.pop(0)

        self._post_select_populate_filter_properties(filter_properties,
                weighed_host.obj)

        # context is not serializable
        filter_properties.pop('context', None)

        # Forward off to the host
        self.compute_rpcapi.prep_resize(context, image, instance,
                instance_type, weighed_host.obj.host, reservations,
                request_spec=request_spec, filter_properties=filter_properties,
                node=weighed_host.obj.nodename)

    def select_hosts(self, context, request_spec, filter_properties):
        """Selects a filtered set of hosts."""
        instance_uuids = request_spec.get('instance_uuids')
        hosts = [host.obj.host for host in self._schedule(context,
            request_spec, filter_properties, instance_uuids)]
        if not hosts:
            raise exception.NoValidHost(reason="")
        return hosts

    def _provision_resource(self, context, weighed_host, request_spec,
            filter_properties, requested_networks, injected_files,
            admin_password, is_first_time, instance_uuid=None):
        """Create the requested resource in this Zone."""
        # NOTE(vish): add our current instance back into the request spec
        request_spec['instance_uuids'] = [instance_uuid]
        payload = dict(request_spec=request_spec,
                       weighted_host=weighed_host.to_dict(),
                       instance_id=instance_uuid)
        notifier.notify(context, notifier.publisher_id("scheduler"),
                        'scheduler.run_instance.scheduled', notifier.INFO,
                        payload)

        # Update the metadata if necessary
        scheduler_hints = filter_properties.get('scheduler_hints') or {}
        group = scheduler_hints.get('group', None)
        values = None
        if group:
            values = request_spec['instance_properties']['system_metadata']
            values.update({'group': group})
            values = {'system_metadata': values}

        updated_instance = driver.instance_update_db(context,
                instance_uuid, extra_values=values)

        self._post_select_populate_filter_properties(filter_properties,
                weighed_host.obj)

        self.compute_rpcapi.run_instance(context, instance=updated_instance,
                host=weighed_host.obj.host,
                request_spec=request_spec, filter_properties=filter_properties,
                requested_networks=requested_networks,
                injected_files=injected_files,
                admin_password=admin_password, is_first_time=is_first_time,
                node=weighed_host.obj.nodename)

    def _post_select_populate_filter_properties(self, filter_properties,
            host_state):
        """Add additional information to the filter properties after a node has
        been selected by the scheduling process.
        """
        # Add a retry entry for the selected compute host and node:
        self._add_retry_host(filter_properties, host_state.host,
                             host_state.nodename)

        self._add_oversubscription_policy(filter_properties, host_state)

    def _add_retry_host(self, filter_properties, host, node):
        """Add a retry entry for the selected compute node. In the event that
        the request gets re-scheduled, this entry will signal that the given
        node has already been tried.
        """
        retry = filter_properties.get('retry', None)
        if not retry:
            return
        hosts = retry['hosts']
        hosts.append([host, node])

    def _add_oversubscription_policy(self, filter_properties, host_state):
        filter_properties['limits'] = host_state.limits

    def _get_configuration_options(self):
        """Fetch options dictionary. Broken out for testing."""
        return self.options.get_configuration()

    def populate_filter_properties(self, request_spec, filter_properties):
        """Stuff things into filter_properties.  Can be overridden in a
        subclass to add more data.
        """
        # Save useful information from the request spec for filter processing:
        project_id = request_spec['instance_properties']['project_id']
        os_type = request_spec['instance_properties']['os_type']
        filter_properties['project_id'] = project_id
        filter_properties['os_type'] = os_type

    def _max_attempts(self):
        max_attempts = CONF.scheduler_max_attempts
        if max_attempts < 1:
            raise exception.NovaException(_("Invalid value for "
                "'scheduler_max_attempts', must be >= 1"))
        return max_attempts

    def _log_compute_error(self, instance_uuid, retry):
        """If the request contained an exception from a previous compute
        build/resize operation, log it to aid debugging
        """
        exc = retry.pop('exc', None)  # string-ified exception from compute
        if not exc:
            return  # no exception info from a prevous attempt, skip

        hosts = retry.get('hosts', None)
        if not hosts:
            return  # no previously attempted hosts, skip

        last_host, last_node = hosts[-1]
        msg = _("Error from last host: %(last_host)s (node %(last_node)s): "
                "%(exc)s") % locals()
        LOG.error(msg, instance_uuid=instance_uuid)

    def _populate_retry(self, filter_properties, instance_properties):
        """Populate filter properties with history of retries for this
        request. If maximum retries is exceeded, raise NoValidHost.
        """
        max_attempts = self._max_attempts()
        retry = filter_properties.pop('retry', {})

        if max_attempts == 1:
            # re-scheduling is disabled.
            return

        # retry is enabled, update attempt count:
        if retry:
            retry['num_attempts'] += 1
        else:
            retry = {
                'num_attempts': 1,
                'hosts': []  # list of compute hosts tried
            }
        filter_properties['retry'] = retry

        instance_uuid = instance_properties.get('uuid')
        self._log_compute_error(instance_uuid, retry)

        if retry['num_attempts'] > max_attempts:
            msg = _("Exceeded max scheduling attempts %(max_attempts)d for "
                    "instance %(instance_uuid)s") % locals()
            raise exception.NoValidHost(reason=msg)

    def _schedule(self, context, request_spec, filter_properties,
                  instance_uuids=None):
        """Returns a list of hosts that meet the required specs,
        ordered by their fitness.
        """
        elevated = context.elevated()
        instance_properties = request_spec['instance_properties']
        instance_type = request_spec.get("instance_type", None)

        # Get the group
        update_group_hosts = False
        scheduler_hints = filter_properties.get('scheduler_hints') or {}
        group = scheduler_hints.get('group', None)
        if group:
            group_hosts = self.group_hosts(elevated, group)
            update_group_hosts = True
            if 'group_hosts' not in filter_properties:
                filter_properties.update({'group_hosts': []})
            configured_hosts = filter_properties['group_hosts']
            filter_properties['group_hosts'] = configured_hosts + group_hosts

        config_options = self._get_configuration_options()

        # check retry policy.  Rather ugly use of instance_uuids[0]...
        # but if we've exceeded max retries... then we really only
        # have a single instance.
        properties = instance_properties.copy()
        if instance_uuids:
            properties['uuid'] = instance_uuids[0]
        self._populate_retry(filter_properties, properties)

        filter_properties.update({'context': context,
                                  'request_spec': request_spec,
                                  'config_options': config_options,
                                  'instance_type': instance_type})

        self.populate_filter_properties(request_spec,
                                        filter_properties)

        # Find our local list of acceptable hosts by repeatedly
        # filtering and weighing our options. Each time we choose a
        # host, we virtually consume resources on it so subsequent
        # selections can adjust accordingly.

        # Note: remember, we are using an iterator here. So only
        # traverse this list once. This can bite you if the hosts
        # are being scanned in a filter or weighing function.
        hosts = self.host_manager.get_all_host_states(elevated)

        selected_hosts = []
        if instance_uuids:
            num_instances = len(instance_uuids)
        else:
            num_instances = request_spec.get('num_instances', 1)
        for num in xrange(num_instances):
            # Filter local hosts based on requirements ...
            hosts = self.host_manager.get_filtered_hosts(hosts,
                    filter_properties)
            if not hosts:
                # Can't get any more locally.
                break

            LOG.debug(_("Filtered %(hosts)s") % locals())

            weighed_hosts = self.host_manager.get_weighed_hosts(hosts,
                    filter_properties)

            scheduler_host_subset_size = CONF.scheduler_host_subset_size
            if scheduler_host_subset_size > len(weighed_hosts):
                scheduler_host_subset_size = len(weighed_hosts)
            if scheduler_host_subset_size < 1:
                scheduler_host_subset_size = 1

            chosen_host = random.choice(
                weighed_hosts[0:scheduler_host_subset_size])
            LOG.debug(_("Choosing host %(chosen_host)s") % locals())
            selected_hosts.append(chosen_host)

            # Now consume the resources so the filter/weights
            # will change for the next instance.
            chosen_host.obj.consume_from_instance(instance_properties)
            if update_group_hosts is True:
                filter_properties['group_hosts'].append(chosen_host.obj.host)
        return selected_hosts

    def _assert_compute_node_has_enough_memory(self, context,
                                              instance_ref, dest):
        """Checks if destination host has enough memory for live migration.


        :param context: security context
        :param instance_ref: nova.db.sqlalchemy.models.Instance object
        :param dest: destination host

        """
        compute = self._get_compute_info(context, dest)
        node = compute.get('hypervisor_hostname')
        host_state = self.host_manager.host_state_cls(dest, node)
        host_state.update_from_compute_node(compute)

        instance_type = instance_ref['instance_type']
        filter_properties = {'instance_type': instance_type}

        hosts = self.host_manager.get_filtered_hosts([host_state],
                                                     filter_properties,
                                                     'RamFilter')
        if not hosts:
            instance_uuid = instance_ref['uuid']
            reason = _("Unable to migrate %(instance_uuid)s to %(dest)s: "
                       "Lack of memory")
            raise exception.MigrationError(reason=reason % locals())
