# Copyright (c) 2013 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.
from oslo_config import cfg
from oslo_db import exception as db_exc
import oslo_messaging
import sqlalchemy as sa
from sqlalchemy import func
from sqlalchemy import or_
from sqlalchemy import orm
from sqlalchemy.orm import exc
from sqlalchemy.orm import joinedload
from sqlalchemy import sql

from neutron.common import constants
from neutron.common import utils as n_utils
from neutron import context as n_ctx
from neutron.db import agents_db
from neutron.db import agentschedulers_db
from neutron.db import l3_attrs_db
from neutron.db import model_base
from neutron.extensions import l3agentscheduler
from neutron.i18n import _LE, _LI, _LW
from neutron import manager
from neutron.openstack.common import log as logging


LOG = logging.getLogger(__name__)

L3_AGENTS_SCHEDULER_OPTS = [
    cfg.StrOpt('router_scheduler_driver',
               default='neutron.scheduler.l3_agent_scheduler.ChanceScheduler',
               help=_('Driver to use for scheduling '
                      'router to a default L3 agent')),
    cfg.BoolOpt('router_auto_schedule', default=True,
                help=_('Allow auto scheduling of routers to L3 agent.')),
    cfg.BoolOpt('allow_automatic_l3agent_failover', default=False,
                help=_('Automatically reschedule routers from offline L3 '
                       'agents to online L3 agents.')),
]

cfg.CONF.register_opts(L3_AGENTS_SCHEDULER_OPTS)


class RouterL3AgentBinding(model_base.BASEV2):
    """Represents binding between neutron routers and L3 agents."""

    router_id = sa.Column(sa.String(36),
                          sa.ForeignKey("routers.id", ondelete='CASCADE'),
                          primary_key=True)
    l3_agent = orm.relation(agents_db.Agent)
    l3_agent_id = sa.Column(sa.String(36),
                            sa.ForeignKey("agents.id", ondelete='CASCADE'),
                            primary_key=True)


class L3AgentSchedulerDbMixin(l3agentscheduler.L3AgentSchedulerPluginBase,
                              agentschedulers_db.AgentSchedulerDbMixin):
    """Mixin class to add l3 agent scheduler extension to plugins
    using the l3 agent for routing.
    """

    router_scheduler = None

    def start_periodic_l3_agent_status_check(self):
        if not cfg.CONF.allow_automatic_l3agent_failover:
            LOG.info(_LI("Skipping period L3 agent status check because "
                         "automatic router rescheduling is disabled."))
            return

        self.setup_agent_status_check(
            self.reschedule_routers_from_down_agents)

    def reschedule_routers_from_down_agents(self):
        """Reschedule routers from down l3 agents if admin state is up."""
        agent_dead_limit = self.agent_dead_limit_seconds()
        self.wait_down_agents('L3', agent_dead_limit)
        cutoff = self.get_cutoff_time(agent_dead_limit)

        context = n_ctx.get_admin_context()
        down_bindings = (
            context.session.query(RouterL3AgentBinding).
            join(agents_db.Agent).
            filter(agents_db.Agent.heartbeat_timestamp < cutoff,
                   agents_db.Agent.admin_state_up).
            outerjoin(l3_attrs_db.RouterExtraAttributes,
                      l3_attrs_db.RouterExtraAttributes.router_id ==
                      RouterL3AgentBinding.router_id).
            filter(sa.or_(l3_attrs_db.RouterExtraAttributes.ha == sql.false(),
                          l3_attrs_db.RouterExtraAttributes.ha == sql.null())))
        try:
            for binding in down_bindings:
                LOG.warn(_LW(
                    "Rescheduling router %(router)s from agent %(agent)s "
                    "because the agent did not report to the server in "
                    "the last %(dead_time)s seconds."),
                    {'router': binding.router_id,
                     'agent': binding.l3_agent_id,
                     'dead_time': agent_dead_limit})
                try:
                    self.reschedule_router(context, binding.router_id)
                except (l3agentscheduler.RouterReschedulingFailed,
                        oslo_messaging.RemoteError):
                    # Catch individual router rescheduling errors here
                    # so one broken one doesn't stop the iteration.
                    LOG.exception(_LE("Failed to reschedule router %s"),
                                  binding.router_id)
        except db_exc.DBError:
            # Catch DB errors here so a transient DB connectivity issue
            # doesn't stop the loopingcall.
            LOG.exception(_LE("Exception encountered during router "
                              "rescheduling."))

    def validate_agent_router_combination(self, context, agent, router):
        """Validate if the router can be correctly assigned to the agent.

        :raises: RouterL3AgentMismatch if attempting to assign DVR router
          to legacy agent, or centralized router to compute's L3 agents.
        :raises: InvalidL3Agent if attempting to assign router to an
          unsuitable agent (disabled, type != L3, incompatible configuration)
        :raises: DVRL3CannotAssignToDvrAgent if attempting to assign DVR
          router from one DVR Agent to another.
        """
        is_distributed = router.get('distributed')
        agent_conf = self.get_configuration_dict(agent)
        agent_mode = agent_conf.get(constants.L3_AGENT_MODE,
                                    constants.L3_AGENT_MODE_LEGACY)
        router_type = (
            'distributed' if is_distributed else
            'centralized')

        is_agent_router_types_incompatible = (
            agent_mode == constants.L3_AGENT_MODE_DVR and not is_distributed
            or agent_mode == constants.L3_AGENT_MODE_LEGACY and is_distributed
        )
        if is_agent_router_types_incompatible:
            raise l3agentscheduler.RouterL3AgentMismatch(
                router_type=router_type, router_id=router['id'],
                agent_mode=agent_mode, agent_id=agent['id'])
        if agent_mode == constants.L3_AGENT_MODE_DVR and is_distributed:
            raise l3agentscheduler.DVRL3CannotAssignToDvrAgent(
                router_type=router_type, router_id=router['id'],
                agent_id=agent['id'])

        is_wrong_type_or_unsuitable_agent = (
            agent['agent_type'] != constants.AGENT_TYPE_L3 or
            not agent['admin_state_up'] or
            not self.get_l3_agent_candidates(context, router, [agent])
        )
        if is_wrong_type_or_unsuitable_agent:
            raise l3agentscheduler.InvalidL3Agent(id=agent['id'])

    def check_agent_router_scheduling_needed(self, context, agent, router):
        """Check if the router scheduling is needed.

        :raises: RouterHostedByL3Agent if router is already assigned
          to a different agent.
        :returns: True if scheduling is needed, otherwise False
        """
        router_id = router['id']
        agent_id = agent['id']
        query = context.session.query(RouterL3AgentBinding)
        bindings = query.filter_by(router_id=router_id).all()
        if not bindings:
            return True
        for binding in bindings:
            if binding.l3_agent_id == agent_id:
                # router already bound to the agent we need
                return False
        if router.get('distributed'):
            return False
        # non-dvr case: centralized router is already bound to some agent
        raise l3agentscheduler.RouterHostedByL3Agent(
            router_id=router_id,
            agent_id=bindings[0].l3_agent_id)

    def create_router_to_agent_binding(self, context, agent, router):
        """Create router to agent binding."""
        router_id = router['id']
        agent_id = agent['id']
        if self.router_scheduler:
            try:
                self.router_scheduler.bind_router(context, router_id, agent)
            except db_exc.DBError:
                raise l3agentscheduler.RouterSchedulingFailed(
                    router_id=router_id, agent_id=agent_id)

    def add_router_to_l3_agent(self, context, agent_id, router_id):
        """Add a l3 agent to host a router."""
        with context.session.begin(subtransactions=True):
            router = self.get_router(context, router_id)
            agent = self._get_agent(context, agent_id)
            self.validate_agent_router_combination(context, agent, router)
            if self.check_agent_router_scheduling_needed(
                context, agent, router):
                self.create_router_to_agent_binding(context, agent, router)
            else:
                return

        l3_notifier = self.agent_notifiers.get(constants.AGENT_TYPE_L3)
        if l3_notifier:
            l3_notifier.router_added_to_agent(
                context, [router_id], agent.host)

    def remove_router_from_l3_agent(self, context, agent_id, router_id):
        """Remove the router from l3 agent.

        After removal, the router will be non-hosted until there is update
        which leads to re-schedule or be added to another agent manually.
        """
        agent = self._get_agent(context, agent_id)
        self._unbind_router(context, router_id, agent_id)
        l3_notifier = self.agent_notifiers.get(constants.AGENT_TYPE_L3)
        if l3_notifier:
            l3_notifier.router_removed_from_agent(
                context, router_id, agent.host)

    def _unbind_router(self, context, router_id, agent_id):
        with context.session.begin(subtransactions=True):
            query = context.session.query(RouterL3AgentBinding)
            query = query.filter(
                RouterL3AgentBinding.router_id == router_id,
                RouterL3AgentBinding.l3_agent_id == agent_id)
            try:
                binding = query.one()
            except exc.NoResultFound:
                raise l3agentscheduler.RouterNotHostedByL3Agent(
                    router_id=router_id, agent_id=agent_id)
            context.session.delete(binding)

    def reschedule_router(self, context, router_id, candidates=None):
        """Reschedule router to a new l3 agent

        Remove the router from the agent(s) currently hosting it and
        schedule it again
        """
        cur_agents = self.list_l3_agents_hosting_router(