# 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.

import datetime
import random
import time

from neutron_lib import constants
from oslo_config import cfg
from oslo_log import log as logging
from oslo_service import loopingcall
from oslo_utils import timeutils
import sqlalchemy as sa
from sqlalchemy import orm
from sqlalchemy.orm import exc

from neutron._i18n import _, _LE, _LI, _LW
from neutron.common import constants as n_const
from neutron.common import utils
from neutron import context as ncontext
from neutron.db import agents_db
from neutron.db.availability_zone import network as network_az
from neutron.db import model_base
from neutron.extensions import agent as ext_agent
from neutron.extensions import dhcpagentscheduler


LOG = logging.getLogger(__name__)

AGENTS_SCHEDULER_OPTS = [
    cfg.StrOpt('network_scheduler_driver',
               default='neutron.scheduler.'
                       'dhcp_agent_scheduler.WeightScheduler',
               help=_('Driver to use for scheduling network to DHCP agent')),
    cfg.BoolOpt('network_auto_schedule', default=True,
                help=_('Allow auto scheduling networks to DHCP agent.')),
    cfg.BoolOpt('allow_automatic_dhcp_failover', default=True,
                help=_('Automatically remove networks from offline DHCP '
                       'agents.')),
    cfg.IntOpt('dhcp_agents_per_network', default=1,
               help=_('Number of DHCP agents scheduled to host a tenant '
                      'network. If this number is greater than 1, the '
                      'scheduler automatically assigns multiple DHCP agents '
                      'for a given tenant network, providing high '
                      'availability for DHCP service.')),
    cfg.BoolOpt('enable_services_on_agents_with_admin_state_down',
                default=False,
                help=_('Enable services on an agent with admin_state_up '
                       'False. If this option is False, when admin_state_up '
                       'of an agent is turned False, services on it will be '
                       'disabled. Agents with admin_state_up False are not '
                       'selected for automatic scheduling regardless of this '
                       'option. But manual scheduling to such agents is '
                       'available if this option is True.')),
]

cfg.CONF.register_opts(AGENTS_SCHEDULER_OPTS)


class NetworkDhcpAgentBinding(model_base.BASEV2):
    """Represents binding between neutron networks and DHCP agents."""

    network_id = sa.Column(sa.String(36),
                           sa.ForeignKey("networks.id", ondelete='CASCADE'),
                           primary_key=True)
    dhcp_agent = orm.relation(agents_db.Agent)
    dhcp_agent_id = sa.Column(sa.String(36),
                              sa.ForeignKey("agents.id",
                                            ondelete='CASCADE'),
                              primary_key=True)


class AgentSchedulerDbMixin(agents_db.AgentDbMixin):
    """Common class for agent scheduler mixins."""

    # agent notifiers to handle agent update operations;
    # should be updated by plugins;
    agent_notifiers = {
        constants.AGENT_TYPE_DHCP: None,
        constants.AGENT_TYPE_L3: None,
        constants.AGENT_TYPE_LOADBALANCER: None,
    }

    @staticmethod
    def is_eligible_agent(active, agent):
        if active is None:
            # filtering by activeness is disabled, all agents are eligible
            return True
        else:
            # note(rpodolyaka): original behaviour is saved here: if active
            #                   filter is set, only agents which are 'up'
            #                   (i.e. have a recent heartbeat timestamp)
            #                   are eligible, even if active is False
            return not agents_db.AgentDbMixin.is_agent_down(
                agent['heartbeat_timestamp'])

    def update_agent(self, context, id, agent):
        original_agent = self.get_agent(context, id)
        result = super(AgentSchedulerDbMixin, self).update_agent(
            context, id, agent)
        agent_data = agent['agent']
        agent_notifier = self.agent_notifiers.get(original_agent['agent_type'])
        if (agent_notifier and
            'admin_state_up' in agent_data and
            original_agent['admin_state_up'] != agent_data['admin_state_up']):
            agent_notifier.agent_updated(context,
                                         agent_data['admin_state_up'],
                                         original_agent['host'])
        return result

    def add_agent_status_check(self, function):
        loop = loopingcall.FixedIntervalLoopingCall(function)
        # TODO(enikanorov): make interval configurable rather than computed
        interval = max(cfg.CONF.agent_down_time // 2, 1)
        # add random initial delay to allow agents to check in after the
        # neutron server first starts. random to offset multiple servers
        initial_delay = random.randint(interval, interval * 2)
        loop.start(interval=interval, initial_delay=initial_delay)

        if hasattr(self, 'periodic_agent_loops'):
            self.periodic_agent_loops.append(loop)
        else:
            self.periodic_agent_loops = [loop]

    def agent_dead_limit_seconds(self):
        return cfg.CONF.agent_down_time * 2

    def wait_down_agents(self, agent_type, agent_dead_limit):
        """Gives chance for agents to send a heartbeat."""
        # check for an abrupt clock change since last check. if a change is
        # detected, sleep for a while to let the agents check in.
        tdelta = timeutils.utcnow() - getattr(self, '_clock_jump_canary',
                                              timeutils.utcnow())
        if tdelta.total_seconds() > cfg.CONF.agent_down_time:
            LOG.warning(_LW("Time since last %s agent reschedule check has "
                            "exceeded the interval between checks. Waiting "
                            "before check to allow agents to send a heartbeat "
                            "in case there was a clock adjustment."),
                        agent_type)
            time.sleep(agent_dead_limit)
        self._clock_jump_canary = timeutils.utcnow()

    def get_cutoff_time(self, agent_dead_limit):
        cutoff = timeutils.utcnow() - datetime.timedelta(
            seconds=agent_dead_limit)
        return cutoff


class DhcpAgentSchedulerDbMixin(dhcpagentscheduler
                                .DhcpAgentSchedulerPluginBase,
                                AgentSchedulerDbMixin):
    """Mixin class to add DHCP agent scheduler extension to db_base_plugin_v2.
    """

    network_scheduler = None

    def start_periodic_dhcp_agent_status_check(self):
        if not cfg.CONF.allow_automatic_dhcp_failover:
            LOG.info(_LI("Skipping periodic DHCP agent status check because "
                         "automatic network rescheduling is disabled."))
            return

        self.add_agent_status_check(self.remove_networks_from_down_agents)

    def is_eligible_agent(self, context, active, agent):
        # eligible agent is active or starting up
        return (AgentSchedulerDbMixin.is_eligible_agent(active, agent) or
                self.agent_starting_up(context, agent))

    def agent_starting_up(self, context, agent):
        """Check if agent was just started.

        Method returns True if agent is in its 'starting up' period.
        Return value depends on amount of networks assigned to the agent.
        It doesn't look at latest heartbeat timestamp as it is assumed
        that this method is called for agents that are considered dead.
        """
        agent_dead_limit = datetime.timedelta(
            seconds=self.agent_dead_limit_seconds())
        network_count = (context.session.query(NetworkDhcpAgentBinding).
                         filter_by(dhcp_agent_id=agent['id']).count())
        # amount of networks assigned to agent affect amount of time we give
        # it so startup. Tests show that it's more or less sage to assume
        # that DHCP agent processes each network in less than 2 seconds.
        # So, give it this additional time for each of the networks.
        additional_time = datetime.timedelta(seconds=2 * network_count)
        LOG.debug("Checking if agent starts up and giving it additional %s",
                  additional_time)
        agent_expected_up = (agent['started_at'] + agent_dead_limit +
                             additional_time)
        return agent_expected_up > timeutils.utcnow()

    def _schedule_network(self, context, network_id, dhcp_notifier):
        LOG.info(_LI("Scheduling unhosted network %s"), network_id)
        try:
            # TODO(enikanorov): have to issue redundant db query
            # to satisfy scheduling interface
            network = self.get_network(context, network_id)
            agents = self.schedule_network(context, network)
            if not agents:
                LOG.info(_LI("Failed to schedule network %s, "
                             "no eligible agents or it might be "
                             "already scheduled by another server"),
                         network_id)
                return
            if not dhcp_notifier:
                return
            for agent in agents:
                LOG.info(_LI("Adding network %(net)s to agent "
                             "%(agent)s on host %(host)s"),
                         {'net': network_id,
                          'agent': agent.id,
                          'host': agent.host})
                dhcp_notifier.network_added_to_agent(
                    context, network_id, agent.host)
        except Exception:
            # catching any exception during scheduling
            # so if _schedule_network is invoked in the loop it could
            # continue in any case
            LOG.exception(_LE("Failed to schedule network %s"), network_id)

    def _filter_bindings(self, context, bindings):
        """Skip bindings for which the agent is dead, but starting up."""

        # to save few db calls: store already checked agents in dict
        # id -> is_agent_starting_up
        checked_agents = {}
        for binding in bindings:
            try:
                agent_id = binding.dhcp_agent['id']
                if agent_id not in checked_agents:
                    if self.agent_starting_up(context, binding.dhcp_agent):
                        # When agent starts and it has many networks to process
                        # it may fail to send state reports in defined interval
                        # The server will consider it dead and try to remove
                        # networks from it.
                        checked_agents[agent_id] = True
                        LOG.debug("Agent %s is starting up, skipping",
                                  agent_id)
                    else:
                        checked_agents[agent_id] = False
                if not checked_agents[agent_id]:
                    yield binding
            except exc.ObjectDeletedError:
                # we're not within a transaction, so object can be lost
                # because underlying row is removed, just ignore this issue
                LOG.debug("binding was removed concurrently, skipping it")

    def remove_networks_from_down_agents(self):
        """Remove networks from down DHCP agents if admin state is up.

        Reschedule them if configured so.
        """

        agent_dead_limit = self.agent_dead_limit_seconds()
        self.wait_down_agents('DHCP', agent_dead_limit)
        cutoff = self.get_cutoff_time(agent_dead_limit)

        context = ncontext.get_admin_context()
        try:
            down_bindings = (
                context.session.query(NetworkDhcpAgentBinding).
                join(agents_db.Agent).
                filter(agents_db.Agent.heartbeat_timestamp < cutoff,
                       agents_db.Agent.admin_state_up))
            dhcp_notifier = self.agent_notifiers.get(constants.AGENT_TYPE_DHCP)
            dead_bindings = [b for b in
                             self._filter_bindings(context, down_bindings)]
            agents = self.get_agents_db(
                context, {'agent_type': [constants.AGENT_TYPE_DHCP]})
            active_agents = [agent for agent in agents if
                             self.is_eligible_agent(context, True, agent)]
            if not active_agents:
                LOG.warning(_LW("No DHCP agents available, "
                                "skipping rescheduling"))
                return
            for binding in dead_bindings:
                LOG.warning(_LW("Removing network %(network)s from agent "
                                "%(agent)s because the agent did not report "
                                "to the server in the last %(dead_time)s "
                                "seconds."),
                            {'network': binding.network_id,
                             'agent': binding.dhcp_agent_id,
                             'dead_time': agent_dead_limit})
                # save binding object to avoid ObjectDeletedError
                # in case binding is concurrently deleted from the DB
                saved_binding = {'net': binding.network_id,
                                 'agent': binding.dhcp_agent_id}
                try:
                    # do not notify agent if it considered dead
                    # so when it is restarted it won't see network delete
                    # notifications on its queue
                    self.remove_network_from_dhcp_agent(context,
                                                        binding.dhcp_agent_id,
                                                        binding.network_id,
                                                        notify=False)
                except dhcpagentscheduler.NetworkNotHostedByDhcpAgent:
                    # measures against concurrent operation
                    LOG.debug("Network %(net)s already removed from DHCP "
                              "agent %(agent)s",
                              saved_binding)
                    # still continue and allow concurrent scheduling attempt
                except Exception:
                    LOG.exception(_LE("Unexpected exception occurred while "
                                      "removing network %(net)s from agent "
                                      "%(agent)s"),
                                  saved_binding)

                if cfg.CONF.network_auto_schedule:
                    self._schedule_network(
                        context, saved_binding['net'], dhcp_notifier)
        except Exception:
            # we want to be thorough and catch whatever is raised
            # to avoid loop abortion
            LOG.exception(_LE("Exception encountered during network "
                              "rescheduling"))

    def get_dhcp_agents_hosting_networks(
            self, context, network_ids, active=None, admin_state_up=None):
        if not network_ids:
            return []
        query = context.session.query(NetworkDhcpAgentBinding)
        query = query.options(orm.contains_eager(
                              NetworkDhcpAgentBinding.dhcp_agent))
        query = query.join(NetworkDhcpAgentBinding.dhcp_agent)
        if len(network_ids) == 1:
            query = query.filter(
                NetworkDhcpAgentBinding.network_id == network_ids[0])
        elif network_ids:
            query = query.filter(
                NetworkDhcpAgentBinding.network_id in network_ids)
        if admin_state_up is not None:
            query = query.filter(agents_db.Agent.admin_state_up ==
                                 admin_state_up)

        return [binding.dhcp_agent
                for binding in query
                if self.is_eligible_agent(context, active,
                                          binding.dhcp_agent)]

    def add_network_to_dhcp_agent(self, context, id, network_id):
        self._get_network(context, network_id)
        with context.session.begin(subtransactions=True):
            agent_db = self._get_agent(context, id)
            if (agent_db['agent_type'] != constants.AGENT_TYPE_DHCP or
                    not services_available(agent_db['admin_state_up'])):
                raise dhcpagentscheduler.InvalidDHCPAgent(id=id)
            dhcp_agents = self.get_dhcp_agents_hosting_networks(
                context, [network_id])
            for dhcp_agent in dhcp_agents:
                if id == dhcp_agent.id:
                    raise dhcpagentscheduler.NetworkHostedByDHCPAgent(
                        network_id=network_id, agent_id=id)
            binding = NetworkDhcpAgentBinding()
            binding.dhcp_agent_id = id
            binding.network_id = network_id
            context.session.add(binding)
        dhcp_notifier = self.agent_notifiers.get(constants.AGENT_TYPE_DHCP)
        if dhcp_notifier:
            dhcp_notifier.network_added_to_agent(
                context, network_id, agent_db.host)

    def remove_network_from_dhcp_agent(self, context, id, network_id,
                                       notify=True):
        agent = self._get_agent(context, id)
        try:
            query = context.session.query(NetworkDhcpAgentBinding)
            binding = query.filter(
                NetworkDhcpAgentBinding.network_id == network_id,
                NetworkDhcpAgentBinding.dhcp_agent_id == id).one()
        except exc.NoResultFound:
            raise dhcpagentscheduler.NetworkNotHostedByDhcpAgent(
                network_id=network_id, agent_id=id)

        # reserve the port, so the ip is reused on a subsequent add
        device_id = utils.get_dhcp_agent_device_id(network_id,
                                                   agent['host'])
        filters = dict(device_id=[device_id])
        ports = self.get_ports(context, filters=filters)
        # NOTE(kevinbenton): there should only ever be one port per
        # DHCP agent per network so we don't have to worry about one
        # update_port passing and another failing
        for port in ports:
            port['device_id'] = n_const.DEVICE_ID_RESERVED_DHCP_PORT
            self.update_port(context, port['id'], dict(port=port))
        with context.session.begin():
            context.session.delete(binding)

        if not notify:
            return
        dhcp_notifier = self.agent_notifiers.get(constants.AGENT_TYPE_DHCP)
        if dhcp_notifier:
            dhcp_notifier.network_removed_from_agent(
                context, network_id, agent.host)

    def list_networks_on_dhcp_agent(self, context, id):
        query = context.session.query(NetworkDhcpAgentBinding.network_id)
        query = query.filter(NetworkDhcpAgentBinding.dhcp_agent_id == id)

        net_ids = [item[0] for item in query]
        if net_ids:
            return {'networks':
                    self.get_networks(context, filters={'id': net_ids})}
        else:
            # Exception will be thrown if the requested agent does not exist.
            self._get_agent(context, id)
            return {'networks': []}

    def list_active_networks_on_active_dhcp_agent(self, context, host):
        try:
            agent = self._get_agent_by_type_and_host(
                context, constants.AGENT_TYPE_DHCP, host)
        except ext_agent.AgentNotFoundByTypeHost:
            LOG.debug("DHCP Agent not found on host %s", host)
            return []

        if not services_available(agent.admin_state_up):
            return []
        query = context.session.query(NetworkDhcpAgentBinding.network_id)
        query = query.filter(NetworkDhcpAgentBinding.dhcp_agent_id == agent.id)

        net_ids = [item[0] for item in query]
        if net_ids:
            return self.get_networks(
                context,
                filters={'id': net_ids, 'admin_state_up': [True]}
            )
        else:
            return []

    def list_dhcp_agents_hosting_network(self, context, network_id):
        dhcp_agents = self.get_dhcp_agents_hosting_networks(
            context, [network_id])
        agent_ids = [dhcp_agent.id for dhcp_agent in dhcp_agents]
        if agent_ids:
            return {
                'agents': self.get_agents(context, filters={'id': agent_ids})}
        else:
            return {'agents': []}

    def schedule_network(self, context, created_network):
        if self.network_scheduler:
            return self.network_scheduler.schedule(
                self, context, created_network)

    def auto_schedule_networks(self, context, host):
        if self.network_scheduler:
            self.network_scheduler.auto_schedule_networks(self, context, host)


class AZDhcpAgentSchedulerDbMixin(DhcpAgentSchedulerDbMixin,
                                  network_az.NetworkAvailabilityZoneMixin):
    """Mixin class to add availability_zone supported DHCP agent scheduler."""

    def get_network_availability_zones(self, network):
        zones = {agent.availability_zone for agent in network.dhcp_agents}
        return list(zones)


# helper functions for readability.
def services_available(admin_state_up):
    if cfg.CONF.enable_services_on_agents_with_admin_state_down:
        # Services are available regardless admin_state_up
        return True
    return admin_state_up


def get_admin_state_up_filter():
    if cfg.CONF.enable_services_on_agents_with_admin_state_down:
        # Avoid filtering on admin_state_up at all
        return None
    # Filters on admin_state_up is True
    return True
