#
#    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 abc
import copy
import secrets

from oslo_log import log

from neutron.common.ovn import constants as ovn_const
from neutron.common.ovn import utils
from neutron.conf.plugins.ml2.drivers.ovn import ovn_conf


LOG = log.getLogger(__name__)

OVN_SCHEDULER_CHANCE = 'chance'
OVN_SCHEDULER_LEAST_LOADED = 'leastloaded'


class OVNGatewayScheduler(object, metaclass=abc.ABCMeta):

    def __init__(self):
        pass

    @abc.abstractmethod
    def select(self, nb_idl, sb_idl, gateway_name, candidates=None,
               existing_chassis=None, target_lrouter=None):
        """Schedule the gateway port of a router to an OVN chassis.

        Schedule the gateway router port only if it is not already
        scheduled.
        """

    def filter_existing_chassis(self, nb_idl, gw_chassis,
                                physnet, chassis_physnets,
                                existing_chassis, az_hints, chassis_with_azs):
        chassis_list = copy.copy(existing_chassis)
        for chassis_name in existing_chassis or []:
            if utils.is_gateway_chassis_invalid(chassis_name, gw_chassis,
                                                physnet, chassis_physnets,
                                                az_hints, chassis_with_azs):
                LOG.debug("Chassis %(chassis)s is invalid for scheduling "
                          "router in physnet: %(physnet)s.",
                          {'chassis': chassis_name,
                           'physnet': physnet})
                chassis_list.remove(chassis_name)
        return chassis_list

    def _schedule_gateway(self, nb_idl, sb_idl, gateway_name, candidates,
                          existing_chassis, target_lrouter):
        existing_chassis = existing_chassis or []
        candidates = candidates or []
        candidates = list(set(candidates) - set(existing_chassis))
        # If no candidates, or gateway scheduled on MAX_GW_CHASSIS nodes
        # or all candidates in existing_chassis, return existing_chassis.
        # Otherwise, if more candidates present, then schedule them.
        if existing_chassis:
            if not candidates or (
                    len(existing_chassis) == ovn_const.MAX_GW_CHASSIS):
                return existing_chassis
        if not candidates:
            LOG.warning('Gateway %s was not scheduled on any chassis, no '
                        'candidates are available', gateway_name)
            return
        chassis_count = min(
            ovn_const.MAX_GW_CHASSIS - len(existing_chassis),
            len(candidates)
        )
        # The actual binding of the gateway to a chassis via the options
        # column or gateway_chassis column in the OVN_Northbound is done
        # by the caller
        chassis = self._select_gateway_chassis(
            nb_idl, sb_idl, candidates, 1, chassis_count, target_lrouter
        )[:chassis_count]
        # priority of existing chassis is higher than candidates
        chassis = existing_chassis + chassis

        LOG.debug("Gateway %s scheduled on chassis %s",
                  gateway_name, chassis)
        return chassis

    def _reorder_by_az(self, nb_idl, sb_idl, candidates):
        chassis_selected = []
        other_chassis = []
        azs = set()

        # Check if candidates list valid
        if not candidates:
            return candidates

        chassis_with_azs = sb_idl.get_chassis_and_azs()

        # Get list of all AZs
        for chassis in candidates:
            try:
                azs.update(chassis_with_azs[chassis])
            except KeyError:
                continue

        for chassis in candidates:
            # Verify if chassis is in an AZ not already used
            # and delete AZs of chassis from list
            try:
                chassis_azs = chassis_with_azs[chassis]
                if azs.intersection(chassis_azs):
                    azs = azs.difference(chassis_azs)
                    chassis_selected += [chassis]
                else:
                    other_chassis += [chassis]
            except KeyError:
                other_chassis += [chassis]

        chassis_selected += other_chassis

        return chassis_selected

    @abc.abstractmethod
    def _select_gateway_chassis(self, nb_idl, sb_idl, candidates,
                                priority_min, priority_max, target_lrouter):
        """Choose a chassis from candidates based on a specific policy.

        Returns a list of chassis to use for scheduling. The value at
        ``ret[0]`` will be used for the chassis with ``priority_max``, the
        value at ``ret[-1]`` will be used for the chassis with ``priority_min``
        """


class OVNGatewayChanceScheduler(OVNGatewayScheduler):
    """Randomly select an chassis for a gateway port of a router"""

    def select(self, nb_idl, sb_idl, gateway_name, candidates=None,
               existing_chassis=None, target_lrouter=None):
        return self._schedule_gateway(nb_idl, sb_idl, gateway_name,
              candidates, existing_chassis, target_lrouter)

    def _select_gateway_chassis(self, nb_idl, sb_idl, candidates,
                                priority_min, priority_max, target_lrouter):
        candidates = copy.deepcopy(candidates)
        secrets.SystemRandom().shuffle(candidates)
        return self._reorder_by_az(nb_idl, sb_idl, candidates)


class OVNGatewayLeastLoadedScheduler(OVNGatewayScheduler):
    """Select the least loaded chassis for a gateway port of a router"""

    def select(self, nb_idl, sb_idl, gateway_name, candidates=None,
               existing_chassis=None, target_lrouter=None):
        return self._schedule_gateway(nb_idl, sb_idl, gateway_name,
                                      candidates, existing_chassis,
                                      target_lrouter)

    def _lrp_anti_affinity_score(self, nb_idl, target_lrouter, lrp_name):
        """Provide elevated score if LRP is part of LR with multiple LRPs.

        The artificial score can be added to chassis load to make it less
        likely that the chassis is selected for scheduling.

        :param nb_idl:         IDL for the OVN NB API
        :type nb_idl:          :class:`OvsdbNbOvnIdl`
        :param target_lrouter: Logical Router object
        :type target_lrouter:  :class:`RowView`
        :param lrp_name:       Name of LRP.
        :type lrp_name:        str
        :returns:              Number, if lrp_name belongs to LR with multiple
                               LRPs.
        :rtype:                int
        """
        if target_lrouter:
            lrouter_ports = getattr(target_lrouter, 'ports', set())
            if len(lrouter_ports) and nb_idl.get_lrouter_by_lrouter_port(
                    lrp_name) == target_lrouter:
                # The `MAX_GW_CHASSIS` constant here is used mostly to get a
                # multiplier that guarantees our score will outweigh natural
                # LRP priority so that when other chassis are available those
                # will be chosen rather than a chassis already hosting a LRP
                # for this LR.
                return ovn_const.MAX_GW_CHASSIS * len(target_lrouter.ports)
        return 0

    def _select_gateway_chassis(self, nb_idl, sb_idl, candidates,
                                priority_min, priority_max, target_lrouter):
        """Returns a lit of chassis from candidates ordered by priority
        (highest first). Each chassis in every priority will be selected, as it
        is the least loaded for that specific priority.
        """
        selected_chassis = []
        priorities = list(range(priority_max, priority_min - 1, -1))
        all_chassis_bindings = nb_idl.get_all_chassis_gateway_bindings(
                candidates, priorities=priorities)
        for priority in priorities:
            chassis_load = {}
            for chassis, lrps in all_chassis_bindings.items():
                if chassis in selected_chassis:
                    continue
                lrps_with_prio = 0
                anti_affinity_score = 0
                for lrp, prio in lrps:
                    if prio == priority:
                        lrps_with_prio += 1
                    anti_affinity_score += self._lrp_anti_affinity_score(
                        nb_idl, target_lrouter, lrp)
                chassis_load[chassis] = lrps_with_prio + anti_affinity_score
            if len(chassis_load) == 0:
                break
            leastload = min(chassis_load.values())
            chassis = secrets.SystemRandom().choice(
                [chassis for chassis, load in chassis_load.items()
                 if load == leastload])
            selected_chassis.append(chassis)
        return self._reorder_by_az(nb_idl, sb_idl, selected_chassis)


OVN_SCHEDULER_STR_TO_CLASS = {
    OVN_SCHEDULER_CHANCE: OVNGatewayChanceScheduler,
    OVN_SCHEDULER_LEAST_LOADED: OVNGatewayLeastLoadedScheduler}


def get_scheduler():
    return OVN_SCHEDULER_STR_TO_CLASS[ovn_conf.get_ovn_l3_scheduler()]()
