# -*- encoding: utf-8 -*-
# Copyright (c) 2016 Servionica LLC
#
# Authors: Alexander Chadin <a.chadin@servionica.ru>
#
# 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.
#
"""
*Workload Stabilization control using live migration*

This is workload stabilization strategy based on standard deviation
algorithm. The goal is to determine if there is an overload in a cluster
and respond to it by migrating VMs to stabilize the cluster.

It assumes that live migrations are possible in your cluster.

"""

import copy
import itertools
import math
import random
import re

import oslo_cache
from oslo_config import cfg
from oslo_log import log
import oslo_utils

from watcher._i18n import _
from watcher.common import exception
from watcher.decision_engine.model import element
from watcher.decision_engine.strategy.strategies import base

LOG = log.getLogger(__name__)
CONF = cfg.CONF


def _set_memoize(conf):
    oslo_cache.configure(conf)
    region = oslo_cache.create_region()
    configured_region = oslo_cache.configure_cache_region(conf, region)
    return oslo_cache.core.get_memoization_decorator(conf,
                                                     configured_region,
                                                     'cache')


class WorkloadStabilization(base.WorkloadStabilizationBaseStrategy):
    """Workload Stabilization control using live migration"""

    MIGRATION = "migrate"
    MEMOIZE = _set_memoize(CONF)

    DATASOURCE_METRICS = ['host_cpu_usage', 'instance_cpu_usage',
                          'instance_ram_usage', 'host_memory_usage']

    def __init__(self, config, osc=None):
        """Workload Stabilization control using live migration

        :param config: A mapping containing the configuration of this strategy
        :type config: :py:class:`~.Struct` instance
        :param osc: :py:class:`~.OpenStackClients` instance
        """
        super(WorkloadStabilization, self).__init__(config, osc)
        self.weights = None
        self.metrics = None
        self.thresholds = None
        self.host_choice = None
        self.instance_metrics = None
        self.retry_count = None
        self.periods = None

    @classmethod
    def get_name(cls):
        return "workload_stabilization"

    @classmethod
    def get_display_name(cls):
        return _("Workload stabilization")

    @classmethod
    def get_translatable_display_name(cls):
        return "Workload stabilization"

    @property
    def granularity(self):
        return self.input_parameters.get('granularity', 300)

    @classmethod
    def get_schema(cls):
        return {
            "properties": {
                "metrics": {
                    "description": "Metrics used as rates of cluster loads.",
                    "type": "array",
                    "default": ["cpu_util", "memory.resident"]
                },
                "thresholds": {
                    "description": "Dict where key is a metric and value "
                                   "is a trigger value.",
                    "type": "object",
                    "default": {"cpu_util": 0.2, "memory.resident": 0.2}
                },
                "weights": {
                    "description": "These weights used to calculate "
                                   "common standard deviation. Name of weight"
                                   " contains meter name and _weight suffix.",
                    "type": "object",
                    "default": {"cpu_util_weight": 1.0,
                                "memory.resident_weight": 1.0}
                },
                "instance_metrics": {
                    "description": "Mapping to get hardware statistics using"
                                   " instance metrics",
                    "type": "object",
                    "default": {"cpu_util": "compute.node.cpu.percent",
                                "memory.resident": "hardware.memory.used"}
                },
                "host_choice": {
                    "description": "Method of host's choice. There are cycle,"
                                   " retry and fullsearch methods. "
                                   "Cycle will iterate hosts in cycle. "
                                   "Retry will get some hosts random "
                                   "(count defined in retry_count option). "
                                   "Fullsearch will return each host "
                                   "from list.",
                    "type": "string",
                    "default": "retry"
                },
                "retry_count": {
                    "description": "Count of random returned hosts",
                    "type": "number",
                    "default": 1
                },
                "periods": {
                    "description": "These periods are used to get statistic "
                                   "aggregation for instance and host "
                                   "metrics. The period is simply a repeating"
                                   " interval of time into which the samples"
                                   " are grouped for aggregation. Watcher "
                                   "uses only the last period of all received"
                                   " ones.",
                    "type": "object",
                    "default": {"instance": 720, "node": 600}
                },
                "granularity": {
                    "description": "The time between two measures in an "
                                   "aggregated timeseries of a metric.",
                    "type": "number",
                    "default": 300
                },
            }
        }

    @classmethod
    def get_config_opts(cls):
        return [
            cfg.ListOpt(
                "datasources",
                help="Datasources to use in order to query the needed metrics."
                     " If one of strategy metric isn't available in the first"
                     " datasource, the next datasource will be chosen.",
                item_type=cfg.types.String(choices=['gnocchi', 'ceilometer',
                                                    'monasca']),
                default=['gnocchi', 'ceilometer', 'monasca'])
        ]

    def transform_instance_cpu(self, instance_load, host_vcpus):
        """Transform instance cpu utilization to overall host cpu utilization.

        :param instance_load: dict that contains instance uuid and
            utilization info.
        :param host_vcpus: int
        :return: float value
        """
        return (instance_load['cpu_util'] *
                (instance_load['vcpus'] / float(host_vcpus)))

    @MEMOIZE
    def get_instance_load(self, instance):
        """Gathering instance load through ceilometer/gnocchi statistic.

        :param instance: instance for which statistic is gathered.
        :return: dict
        """
        LOG.debug('get_instance_load started')
        instance_load = {'uuid': instance.uuid, 'vcpus': instance.vcpus}
        for meter in self.metrics:
            avg_meter = self.datasource_backend.statistic_aggregation(
                instance.uuid, meter, self.periods['instance'],
                self.granularity, aggregation='mean')
            if avg_meter is None:
                LOG.warning(
                    "No values returned by %(resource_id)s "
                    "for %(metric_name)s" % dict(
                        resource_id=instance.uuid, metric_name=meter))
                return
            if meter == 'cpu_util':
                avg_meter /= float(100)
            instance_load[meter] = avg_meter
        return instance_load

    def normalize_hosts_load(self, hosts):
        normalized_hosts = copy.deepcopy(hosts)
        for host in normalized_hosts:
            if 'memory.resident' in normalized_hosts[host]:
                node = self.compute_model.get_node_by_uuid(host)
                normalized_hosts[host]['memory.resident'] /= float(node.memory)

        return normalized_hosts

    def get_available_nodes(self):
        return {node_uuid: node for node_uuid, node in
                self.compute_model.get_all_compute_nodes().items()
                if node.state == element.ServiceState.ONLINE.value and
                node.status == element.ServiceState.ENABLED.value}

    def get_hosts_load(self):
        """Get load of every available host by gathering instances load"""
        hosts_load = {}
        for node_id, node in self.get_available_nodes().items():
            hosts_load[node_id] = {}
            hosts_load[node_id]['vcpus'] = node.vcpus
            for metric in self.metrics:
                resource_id = ''
                avg_meter = None
                meter_name = self.instance_metrics[metric]
                if re.match('^compute.node', meter_name) is not None:
                    resource_id = "%s_%s" % (node.uuid, node.hostname)
                else:
                    resource_id = node_id
                avg_meter = self.datasource_backend.statistic_aggregation(
                    resource_id, self.instance_metrics[metric],
                    self.periods['node'], self.granularity, aggregation='mean')
                if avg_meter is None:
                    LOG.warning('No values returned by node %s for %s',
                                node_id, meter_name)
                    del hosts_load[node_id]
                    break
                else:
                    if meter_name == 'hardware.memory.used':
                        avg_meter /= oslo_utils.units.Ki
                    if meter_name == 'compute.node.cpu.percent':
                        avg_meter /= 100
                hosts_load[node_id][metric] = avg_meter
        return hosts_load

    def get_sd(self, hosts, meter_name):
        """Get standard deviation among hosts by specified meter"""
        mean = 0
        variaton = 0
        for host_id in hosts:
            mean += hosts[host_id][meter_name]
        mean /= len(hosts)
        for host_id in hosts:
            variaton += (hosts[host_id][meter_name] - mean) ** 2
        variaton /= len(hosts)
        sd = math.sqrt(variaton)
        return sd

    def calculate_weighted_sd(self, sd_case):
        """Calculate common standard deviation among meters on host"""
        weighted_sd = 0
        for metric, value in zip(self.metrics, sd_case):
            try:
                weighted_sd += value * float(self.weights[metric + '_weight'])
            except KeyError as exc:
                LOG.exception(exc)
                raise exception.WatcherException(
                    _("Incorrect mapping: could not find associated weight"
                      " for %s in weight dict.") % metric)
        return weighted_sd

    def calculate_migration_case(self, hosts, instance, src_node, dst_node):
        """Calculate migration case

        Return list of standard deviation values, that appearing in case of
        migration of instance from source host to destination host
        :param hosts: hosts with their workload
        :param instance: the virtual machine
        :param src_node: the source node
        :param dst_node: the destination node
        :return: list of standard deviation values
        """
        migration_case = []
        new_hosts = copy.deepcopy(hosts)
        instance_load = self.get_instance_load(instance)
        if not instance_load:
            return
        s_host_vcpus = new_hosts[src_node.uuid]['vcpus']
        d_host_vcpus = new_hosts[dst_node.uuid]['vcpus']
        for metric in self.metrics:
            if metric is 'cpu_util':
                new_hosts[src_node.uuid][metric] -= (
                    self.transform_instance_cpu(instance_load, s_host_vcpus))
                new_hosts[dst_node.uuid][metric] += (
                    self.transform_instance_cpu(instance_load, d_host_vcpus))
            else:
                new_hosts[src_node.uuid][metric] -= instance_load[metric]
                new_hosts[dst_node.uuid][metric] += instance_load[metric]
        normalized_hosts = self.normalize_hosts_load(new_hosts)
        for metric in self.metrics:
            migration_case.append(self.get_sd(normalized_hosts, metric))
        migration_case.append(new_hosts)
        return migration_case

    def get_current_weighted_sd(self, hosts_load):
        """Calculate current weighted sd"""
        current_sd = []
        normalized_load = self.normalize_hosts_load(hosts_load)
        for metric in self.metrics:
            metric_sd = self.get_sd(normalized_load, metric)
            current_sd.append(metric_sd)
        current_sd.append(hosts_load)
        return self.calculate_weighted_sd(current_sd[:-1])

    def simulate_migrations(self, hosts):
        """Make sorted list of pairs instance:dst_host"""
        def yield_nodes(nodes):
            if self.host_choice == 'cycle':
                for i in itertools.cycle(nodes):
                    yield [i]
            if self.host_choice == 'retry':
                while True:
                    yield random.sample(nodes, self.retry_count)
            if self.host_choice == 'fullsearch':
                while True:
                    yield nodes

        instance_host_map = []
        nodes = sorted(list(self.get_available_nodes()))
        current_weighted_sd = self.get_current_weighted_sd(hosts)
        for src_host in nodes:
            src_node = self.compute_model.get_node_by_uuid(src_host)
            c_nodes = copy.copy(nodes)
            c_nodes.remove(src_host)
            node_list = yield_nodes(c_nodes)
            for instance in self.compute_model.get_node_instances(src_node):
                min_sd_case = {'value': current_weighted_sd}
                if instance.state not in [element.InstanceState.ACTIVE.value,
                                          element.InstanceState.PAUSED.value]:
                    continue
                for dst_host in next(node_list):
                    dst_node = self.compute_model.get_node_by_uuid(dst_host)
                    sd_case = self.calculate_migration_case(
                        hosts, instance, src_node, dst_node)
                    if sd_case is None:
                        break

                    weighted_sd = self.calculate_weighted_sd(sd_case[:-1])

                    if weighted_sd < min_sd_case['value']:
                        min_sd_case = {
                            'host': dst_node.uuid, 'value': weighted_sd,
                            's_host': src_node.uuid, 'instance': instance.uuid}
                        instance_host_map.append(min_sd_case)
                if sd_case is None:
                    continue
        return sorted(instance_host_map, key=lambda x: x['value'])

    def check_threshold(self):
        """Check if cluster is needed in balancing"""
        hosts_load = self.get_hosts_load()
        normalized_load = self.normalize_hosts_load(hosts_load)
        for metric in self.metrics:
            metric_sd = self.get_sd(normalized_load, metric)
            LOG.info("Standard deviation for %s is %s."
                     % (metric, metric_sd))
            if metric_sd > float(self.thresholds[metric]):
                LOG.info("Standard deviation of %s exceeds"
                         " appropriate threshold %s."
                         % (metric, metric_sd))
                return self.simulate_migrations(hosts_load)

    def add_migration(self,
                      resource_id,
                      migration_type,
                      source_node,
                      destination_node):
        parameters = {'migration_type': migration_type,
                      'source_node': source_node,
                      'destination_node': destination_node}
        self.solution.add_action(action_type=self.MIGRATION,
                                 resource_id=resource_id,
                                 input_parameters=parameters)

    def create_migration_instance(self, mig_instance, mig_source_node,
                                  mig_destination_node):
        """Create migration VM"""
        if self.compute_model.migrate_instance(
                mig_instance, mig_source_node, mig_destination_node):
            self.add_migration(mig_instance.uuid, 'live',
                               mig_source_node.uuid,
                               mig_destination_node.uuid)

    def migrate(self, instance_uuid, src_host, dst_host):
        mig_instance = self.compute_model.get_instance_by_uuid(instance_uuid)
        mig_source_node = self.compute_model.get_node_by_uuid(
            src_host)
        mig_destination_node = self.compute_model.get_node_by_uuid(
            dst_host)
        self.create_migration_instance(mig_instance, mig_source_node,
                                       mig_destination_node)

    def fill_solution(self):
        self.solution.model = self.compute_model
        return self.solution

    def pre_execute(self):
        LOG.info("Initializing Workload Stabilization")

        if not self.compute_model:
            raise exception.ClusterStateNotDefined()

        if self.compute_model.stale:
            raise exception.ClusterStateStale()

        self.weights = self.input_parameters.weights
        self.metrics = self.input_parameters.metrics
        self.thresholds = self.input_parameters.thresholds
        self.host_choice = self.input_parameters.host_choice
        self.instance_metrics = self.input_parameters.instance_metrics
        self.retry_count = self.input_parameters.retry_count
        self.periods = self.input_parameters.periods

    def do_execute(self):
        migration = self.check_threshold()
        if migration:
            hosts_load = self.get_hosts_load()
            min_sd = 1
            balanced = False
            for instance_host in migration:
                instance = self.compute_model.get_instance_by_uuid(
                    instance_host['instance'])
                src_node = self.compute_model.get_node_by_uuid(
                    instance_host['s_host'])
                dst_node = self.compute_model.get_node_by_uuid(
                    instance_host['host'])
                if instance.disk > dst_node.disk:
                    continue
                instance_load = self.calculate_migration_case(
                    hosts_load, instance, src_node, dst_node)
                weighted_sd = self.calculate_weighted_sd(instance_load[:-1])
                if weighted_sd < min_sd:
                    min_sd = weighted_sd
                    hosts_load = instance_load[-1]
                    self.migrate(instance_host['instance'],
                                 instance_host['s_host'],
                                 instance_host['host'])

                for metric, value in zip(self.metrics, instance_load[:-1]):
                    if value < float(self.thresholds[metric]):
                        balanced = True
                        break
                if balanced:
                    break

    def post_execute(self):
        """Post-execution phase

        This can be used to compute the global efficacy
        """
        self.fill_solution()

        LOG.debug(self.compute_model.to_string())
