# Copyright 2019 Red Hat, Inc.
# 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

from oslo_log import log
from oslo_utils import timeutils
from tooz import hashring

from neutron.common.ovn import constants
from neutron.common.ovn import exceptions
from neutron.db import ovn_hash_ring_db as db_hash_ring
from neutron import service
from neutron_lib import context

LOG = log.getLogger(__name__)


class HashRingManager:

    def __init__(self, group_name):
        self._hash_ring = None
        self._last_time_loaded = None
        self._check_hashring_startup = True
        self._group = group_name
        # Flag to rate limit the caching log
        self._prev_num_nodes = -1
        self.admin_ctx = context.get_admin_context()
        self._offline_node_count = 0

    @property
    def _wait_startup_before_caching(self):
        # NOTE(lucasagomes): Some events are processed at the service's
        # startup time and since many services may be started concurrently
        # we do not want to use a cached hash ring at that point. This
        # method ensures that we start allowing the use of cached HashRings
        # once the number of HashRing nodes >= the number of api workers.

        # If the startup timeout already expired, there's no reason to
        # keep reading from the DB. At this point this will always
        # return False
        if not self._check_hashring_startup:
            return False

        api_workers = service._get_api_workers()
        nodes = db_hash_ring.get_active_nodes(
            self.admin_ctx,
            constants.HASH_RING_CACHE_TIMEOUT, self._group, from_host=True)

        num_nodes = len(nodes)
        if num_nodes >= api_workers:
            LOG.debug("Allow caching, nodes %s>=%s", num_nodes, api_workers)
            self._check_hashring_startup = False
            return False

        # NOTE(lucasagomes): We only log when the number of connected
        # nodes are different to prevent this message from being spammed
        if self._prev_num_nodes != num_nodes:
            LOG.debug("Disallow caching, nodes %s<%s", num_nodes, api_workers)
            self._prev_num_nodes = num_nodes

        return True

    def _load_hash_ring(self, refresh=False):
        cache_timeout = timeutils.utcnow() - datetime.timedelta(
            seconds=constants.HASH_RING_CACHE_TIMEOUT)

        # Refresh the cache if:
        # - Refreshed is forced (refresh=True)
        # - Service just started (_wait_startup_before_caching)
        # - Hash Ring is not yet instantiated
        # - Cache has timed out
        if (refresh or
                self._wait_startup_before_caching or
                self._hash_ring is None or
                not self._hash_ring.nodes or
                cache_timeout >= self._last_time_loaded):
            nodes = db_hash_ring.get_active_nodes(
                self.admin_ctx,
                constants.HASH_RING_NODES_TIMEOUT, self._group)
            self._hash_ring = hashring.HashRing({node.node_uuid
                                                 for node in nodes})
            self._last_time_loaded = timeutils.utcnow()
            self._offline_node_count = db_hash_ring.count_offline_nodes(
                self.admin_ctx, constants.HASH_RING_NODES_TIMEOUT,
                self._group)
            LOG.debug("Hash Ring loaded. %d active nodes. %d offline nodes",
                      len(nodes), self._offline_node_count)

    def refresh(self):
        self._load_hash_ring(refresh=True)

    def get_node(self, key):
        self._load_hash_ring()

        # tooz expects a byte string for the hash
        if isinstance(key, str):
            key = key.encode('utf-8')

        try:
            # We need to pop the value from the set. If empty,
            # KeyError is raised
            return self._hash_ring[key].pop()
        except KeyError:
            raise exceptions.HashRingIsEmpty(
                key=key, node_count=self._offline_node_count)