#    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.

from oslo_config import cfg
from oslo_log import log as logging

from nova.compute import power_state
from nova.compute import rpcapi as compute_rpcapi
from nova import exception
from nova.i18n import _
from nova import image
from nova import objects
from nova.scheduler import client as scheduler_client
from nova.scheduler import utils as scheduler_utils
from nova import servicegroup
from nova import utils

LOG = logging.getLogger(__name__)

migrate_opt = cfg.IntOpt('migrate_max_retries',
        default=-1,
        help='Number of times to retry live-migration before failing. '
             'If == -1, try until out of hosts. '
             'If == 0, only try once, no retries.')

CONF = cfg.CONF
CONF.register_opt(migrate_opt)


class LiveMigrationTask(object):
    def __init__(self, context, instance, destination,
                 block_migration, disk_over_commit):
        self.context = context
        self.instance = instance
        self.destination = destination
        self.block_migration = block_migration
        self.disk_over_commit = disk_over_commit
        self.source = instance.host
        self.migrate_data = None
        self.compute_rpcapi = compute_rpcapi.ComputeAPI()
        self.servicegroup_api = servicegroup.API()
        self.scheduler_client = scheduler_client.SchedulerClient()
        self.image_api = image.API()

    def execute(self):
        self._check_instance_is_active()
        self._check_host_is_up(self.source)

        if not self.destination:
            self.destination = self._find_destination()
        else:
            self._check_requested_destination()

        # TODO(johngarbutt) need to move complexity out of compute manager
        # TODO(johngarbutt) disk_over_commit?
        return self.compute_rpcapi.live_migration(self.context,
                host=self.source,
                instance=self.instance,
                dest=self.destination,
                block_migration=self.block_migration,
                migrate_data=self.migrate_data)

    def rollback(self):
        # TODO(johngarbutt) need to implement the clean up operation
        # but this will make sense only once we pull in the compute
        # calls, since this class currently makes no state changes,
        # except to call the compute method, that has no matching
        # rollback call right now.
        raise NotImplementedError()

    def _check_instance_is_active(self):
        if self.instance.power_state not in (power_state.RUNNING,
                                             power_state.PAUSED):
            raise exception.InstanceInvalidState(
                    instance_uuid = self.instance.uuid,
                    attr = 'power_state',
                    state = self.instance.power_state,
                    method = 'live migrate')

    def _check_host_is_up(self, host):
        try:
            service = objects.Service.get_by_compute_host(self.context, host)
        except exception.NotFound:
            raise exception.ComputeServiceUnavailable(host=host)

        if not self.servicegroup_api.service_is_up(service):
            raise exception.ComputeServiceUnavailable(host=host)

    def _check_requested_destination(self):
        self._check_destination_is_not_source()
        self._check_host_is_up(self.destination)
        self._check_destination_has_enough_memory()
        self._check_compatible_with_source_hypervisor(self.destination)
        self._call_livem_checks_on_host(self.destination)

    def _check_destination_is_not_source(self):
        if self.destination == self.source:
            raise exception.UnableToMigrateToSelf(
                    instance_id=self.instance.uuid, host=self.destination)

    def _check_destination_has_enough_memory(self):
        avail = self._get_compute_info(self.destination)['free_ram_mb']
        mem_inst = self.instance.memory_mb

        if not mem_inst or avail <= mem_inst:
            instance_uuid = self.instance.uuid
            dest = self.destination
            reason = _("Unable to migrate %(instance_uuid)s to %(dest)s: "
                       "Lack of memory(host:%(avail)s <= "
                       "instance:%(mem_inst)s)")
            raise exception.MigrationPreCheckError(reason=reason % dict(
                    instance_uuid=instance_uuid, dest=dest, avail=avail,
                    mem_inst=mem_inst))

    def _get_compute_info(self, host):
        return objects.ComputeNode.get_first_node_by_host_for_old_compat(
            self.context, host)

    def _check_compatible_with_source_hypervisor(self, destination):
        source_info = self._get_compute_info(self.source)
        destination_info = self._get_compute_info(destination)

        source_type = source_info['hypervisor_type']
        destination_type = destination_info['hypervisor_type']
        if source_type != destination_type:
            raise exception.InvalidHypervisorType()

        source_version = source_info['hypervisor_version']
        destination_version = destination_info['hypervisor_version']
        if source_version > destination_version:
            raise exception.DestinationHypervisorTooOld()

    def _call_livem_checks_on_host(self, destination):
        self.migrate_data = self.compute_rpcapi.\
            check_can_live_migrate_destination(self.context, self.instance,
                destination, self.block_migration, self.disk_over_commit)

    def _find_destination(self):
        # TODO(johngarbutt) this retry loop should be shared
        attempted_hosts = [self.source]
        image = utils.get_image_from_system_metadata(
            self.instance.system_metadata)
        request_spec = scheduler_utils.build_request_spec(self.context, image,
                                                          [self.instance])

        host = None
        while host is None:
            self._check_not_over_max_retries(attempted_hosts)
            filter_properties = {'ignore_hosts': attempted_hosts}
            scheduler_utils.setup_instance_group(self.context, request_spec,
                                                 filter_properties)
            host = self.scheduler_client.select_destinations(self.context,
                            request_spec, filter_properties)[0]['host']
            try:
                self._check_compatible_with_source_hypervisor(host)
                self._call_livem_checks_on_host(host)
            except exception.Invalid as e:
                LOG.debug("Skipping host: %(host)s because: %(e)s",
                    {"host": host, "e": e})
                attempted_hosts.append(host)
                host = None
        return host

    def _check_not_over_max_retries(self, attempted_hosts):
        if CONF.migrate_max_retries == -1:
            return

        retries = len(attempted_hosts) - 1
        if retries > CONF.migrate_max_retries:
            msg = (_('Exceeded max scheduling retries %(max_retries)d for '
                     'instance %(instance_uuid)s during live migration')
                   % {'max_retries': retries,
                      'instance_uuid': self.instance.uuid})
            raise exception.NoValidHost(reason=msg)


def execute(context, instance, destination,
            block_migration, disk_over_commit):
    task = LiveMigrationTask(context, instance,
                             destination,
                             block_migration,
                             disk_over_commit)
    # TODO(johngarbutt) create a superclass that contains a safe_execute call
    return task.execute()
