#
# Copyright 2013 Julien Danjou
# Copyright 2014 Red Hat, Inc
#
# Authors: Julien Danjou <julien@danjou.info>
#          Eoghan Glynn <eglynn@redhat.com>
#
# 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 collections
import itertools

import six
from six.moves.urllib import parse as urlparse
from stevedore import extension

from ceilometer.openstack.common import context
from ceilometer.openstack.common.gettextutils import _
from ceilometer.openstack.common import log
from ceilometer.openstack.common import service as os_service
from ceilometer import pipeline

LOG = log.getLogger(__name__)


class Resources(object):
    def __init__(self, agent_manager):
        self.agent_manager = agent_manager
        self._resources = []
        self._discovery = []

    def extend(self, pipeline):
        self._resources.extend(pipeline.resources)
        self._discovery.extend(pipeline.discovery)

    @property
    def resources(self):
        source_discovery = (self.agent_manager.discover(self._discovery)
                            if self._discovery else [])
        return self._resources + source_discovery


class PollingTask(object):
    """Polling task for polling samples and inject into pipeline.

    A polling task can be invoked periodically or only once.
    """

    def __init__(self, agent_manager):
        self.manager = agent_manager
        self.pollsters = set()
        # we extend the amalgamation of all static resources for this
        # set of pollsters with a common interval, so as to also
        # include any dynamically discovered resources specific to
        # the matching pipelines (if either is present, the per-agent
        # default discovery is overridden)
        resource_factory = lambda: Resources(agent_manager)
        self.resources = collections.defaultdict(resource_factory)
        self.publish_context = pipeline.PublishContext(
            agent_manager.context)

    def add(self, pollster, pipelines):
        self.publish_context.add_pipelines(pipelines)
        for pipe_line in pipelines:
            self.resources[pollster.name].extend(pipe_line)
        self.pollsters.update([pollster])

    def poll_and_publish(self):
        """Polling sample and publish into pipeline."""
        agent_resources = self.manager.discover()
        with self.publish_context as publisher:
            cache = {}
            for pollster in self.pollsters:
                key = pollster.name
                LOG.info(_("Polling pollster %s"), key)
                source_resources = list(self.resources[key].resources)
                try:
                    samples = list(pollster.obj.get_samples(
                        manager=self.manager,
                        cache=cache,
                        resources=source_resources or agent_resources,
                    ))
                    publisher(samples)
                except Exception as err:
                    LOG.warning(_(
                        'Continue after error from %(name)s: %(error)s')
                        % ({'name': pollster.name, 'error': err}),
                        exc_info=True)


class AgentManager(os_service.Service):

    def __init__(self, namespace, default_discovery=None):
        super(AgentManager, self).__init__()
        default_discovery = default_discovery or []
        self.default_discovery = default_discovery
        self.pollster_manager = self._extensions('poll', namespace)
        self.discovery_manager = self._extensions('discover')
        self.context = context.RequestContext('admin', 'admin', is_admin=True)

    @staticmethod
    def _extensions(category, agent_ns=None):
        namespace = ('ceilometer.%s.%s' % (category, agent_ns) if agent_ns
                     else 'ceilometer.%s' % category)
        return extension.ExtensionManager(
            namespace=namespace,
            invoke_on_load=True,
        )

    def create_polling_task(self):
        """Create an initially empty polling task."""
        return PollingTask(self)

    def setup_polling_tasks(self):
        polling_tasks = {}
        for pipe_line, pollster in itertools.product(
                self.pipeline_manager.pipelines,
                self.pollster_manager.extensions):
            if pipe_line.support_meter(pollster.name):
                polling_task = polling_tasks.get(pipe_line.get_interval())
                if not polling_task:
                    polling_task = self.create_polling_task()
                    polling_tasks[pipe_line.get_interval()] = polling_task
                polling_task.add(pollster, [pipe_line])

        return polling_tasks

    def start(self):
        self.pipeline_manager = pipeline.setup_pipeline()

        for interval, task in six.iteritems(self.setup_polling_tasks()):
            self.tg.add_timer(interval,
                              self.interval_task,
                              task=task)

    @staticmethod
    def interval_task(task):
        task.poll_and_publish()

    @staticmethod
    def _parse_discoverer(url):
        s = urlparse.urlparse(url)
        return (s.scheme or s.path), (s.netloc + s.path if s.scheme else None)

    def _discoverer(self, name):
        for d in self.discovery_manager:
            if d.name == name:
                return d.obj
        return None

    def discover(self, discovery=None):
        resources = []
        for url in (discovery or self.default_discovery):
            name, param = self._parse_discoverer(url)
            discoverer = self._discoverer(name)
            if discoverer:
                try:
                    discovered = discoverer.discover(param)
                    resources.extend(discovered)
                except Exception as err:
                    LOG.exception(_('Unable to discover resources: %s') % err)
            else:
                LOG.warning(_('Unknown discovery extension: %s') % name)
        return resources