# Copyright 2012 IBM Corp.
# Copyright (c) AT&T Labs Inc. 2012 Yun Mao <yunmao@gmail.com>
#
# 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.

"""Define APIs for the servicegroup access."""

import random

from oslo.config import cfg

from nova.openstack.common import importutils
from nova.openstack.common import log as logging
from nova import utils

LOG = logging.getLogger(__name__)
_default_driver = 'db'
servicegroup_driver_opt = cfg.StrOpt('servicegroup_driver',
                                     default=_default_driver,
                                     help='The driver for servicegroup '
                                          'service (valid options are: '
                                          'db, zk, mc)')

CONF = cfg.CONF
CONF.register_opt(servicegroup_driver_opt)


class API(object):

    _driver = None
    _driver_name_class_mapping = {
        'db': 'nova.servicegroup.drivers.db.DbDriver',
        'zk': 'nova.servicegroup.drivers.zk.ZooKeeperDriver',
        'mc': 'nova.servicegroup.drivers.mc.MemcachedDriver'
    }

    def __new__(cls, *args, **kwargs):
        '''Create an instance of the servicegroup API.

        args and kwargs are passed down to the servicegroup driver when it gets
        created.  No args currently exist, though.  Valid kwargs are:

        db_allowed - Boolean. False if direct db access is not allowed and
                     alternative data access (conductor) should be used
                     instead.
        '''

        if not cls._driver:
            LOG.debug(_('ServiceGroup driver defined as an instance of %s'),
                      str(CONF.servicegroup_driver))
            driver_name = CONF.servicegroup_driver
            try:
                driver_class = cls._driver_name_class_mapping[driver_name]
            except KeyError:
                raise TypeError(_("unknown ServiceGroup driver name: %s")
                                % driver_name)
            cls._driver = importutils.import_object(driver_class,
                                                    *args, **kwargs)
            utils.check_isinstance(cls._driver, ServiceGroupDriver)
            # we don't have to check that cls._driver is not NONE,
            # check_isinstance does it
        return super(API, cls).__new__(cls)

    def join(self, member_id, group_id, service=None):
        """Add a new member to the ServiceGroup

        @param member_id: the joined member ID
        @param group_id: the group name, of the joined member
        @param service: the parameter can be used for notifications about
        disconnect mode and update some internals
        """
        msg = _('Join new ServiceGroup member %(member_id)s to the '
                '%(group_id)s group, service = %(service)s')
        LOG.debug(msg, locals())
        return self._driver.join(member_id, group_id, service)

    def service_is_up(self, member):
        """Check if the given member is up."""
        msg = _('Check if the given member [%s] is part of the '
                'ServiceGroup, is up')
        LOG.debug(msg, member)
        return self._driver.is_up(member)

    def leave(self, member_id, group_id):
        """Explicitly remove the given member from the ServiceGroup
        monitoring.
        """
        msg = _('Explicitly remove the given member %(member_id)s from the'
                '%(group_id)s group monitoring')
        LOG.debug(msg, locals())
        return self._driver.leave(member_id, group_id)

    def get_all(self, group_id):
        """Returns ALL members of the given group."""
        LOG.debug(_('Returns ALL members of the [%s] '
                    'ServiceGroup'), group_id)
        return self._driver.get_all(group_id)

    def get_one(self, group_id):
        """Returns one member of the given group. The strategy to select
        the member is decided by the driver (e.g. random or round-robin).
        """
        LOG.debug(_('Returns one member of the [%s] group'), group_id)
        return self._driver.get_one(group_id)


class ServiceGroupDriver(object):
    """Base class for ServiceGroup drivers."""

    def join(self, member_id, group_id, service=None):
        """Join the given service with it's group."""
        raise NotImplementedError()

    def is_up(self, member):
        """Check whether the given member is up."""
        raise NotImplementedError()

    def leave(self, member_id, group_id):
        """Remove the given member from the ServiceGroup monitoring."""
        raise NotImplementedError()

    def get_all(self, group_id):
        """Returns ALL members of the given group."""
        raise NotImplementedError()

    def get_one(self, group_id):
        """The default behavior of get_one is to randomly pick one from
        the result of get_all(). This is likely to be overridden in the
        actual driver implementation.
        """
        members = self.get_all(group_id)
        if members is None:
            return None
        length = len(members)
        if length == 0:
            return None
        return random.choice(members)