# Service heartbeat driver using Memcached
# Copyright (c) 2013 Akira Yoshiyama <akirayoshiyama at gmail dot com>
#
# This is derived from nova/servicegroup/drivers/db.py.
# Copyright 2012 IBM Corp.
#
# 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 oslo_utils import timeutils

from nova import context
from nova.i18n import _, _LE
from nova import objects
from nova.openstack.common import memorycache
from nova.servicegroup import api
from nova.servicegroup.drivers import base


CONF = cfg.CONF
CONF.import_opt('service_down_time', 'nova.service')


LOG = logging.getLogger(__name__)


class MemcachedDriver(base.Driver):

    def __init__(self, *args, **kwargs):
        if not CONF.memcached_servers:
            raise RuntimeError(_('memcached_servers not defined'))
        self.mc = memorycache.get_client()

    def join(self, member_id, group_id, service=None):
        """Join the given service with its group."""

        LOG.debug('Memcached_Driver: join new ServiceGroup member '
                  '%(member_id)s to the %(group_id)s group, '
                  'service = %(service)s',
                  {'member_id': member_id,
                   'group_id': group_id,
                   'service': service})
        if service is None:
            raise RuntimeError(_('service is a mandatory argument for '
                                 'Memcached based ServiceGroup driver'))
        report_interval = service.report_interval
        if report_interval:
            service.tg.add_timer(report_interval, self._report_state,
                                 api.INITIAL_REPORTING_DELAY, service)

    def is_up(self, service_ref):
        """Moved from nova.utils
        Check whether a service is up based on last heartbeat.
        """
        key = "%(topic)s:%(host)s" % service_ref
        is_up = self.mc.get(str(key)) is not None
        if not is_up:
            LOG.debug('Seems service %s is down' % key)

        return is_up

    def get_all(self, group_id):
        """Returns ALL members of the given group
        """
        LOG.debug('Memcached_Driver: get_all members of the %s group',
                  group_id)
        rs = []
        ctxt = context.get_admin_context()
        services = objects.ServiceList.get_by_topic(ctxt, group_id)
        for service in services:
            if self.is_up(service):
                rs.append(service.host)
        return rs

    def _report_state(self, service):
        """Update the state of this service in the datastore."""
        try:
            key = "%(topic)s:%(host)s" % service.service_ref
            # memcached has data expiration time capability.
            # set(..., time=CONF.service_down_time) uses it and
            # reduces key-deleting code.
            self.mc.set(str(key),
                        timeutils.utcnow(),
                        time=CONF.service_down_time)

            # TODO(termie): make this pattern be more elegant.
            if getattr(service, 'model_disconnected', False):
                service.model_disconnected = False
                LOG.error(_LE('Recovered model server connection!'))

        # TODO(vish): this should probably only catch connection errors
        except Exception:
            if not getattr(service, 'model_disconnected', False):
                service.model_disconnected = True
                LOG.exception(_LE('model server went away'))
