# vim: tabstop=4 shiftwidth=4 softtabstop=4

# Copyright 2011 Nicira Networks, 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.
# @author: Somik Behera, Nicira Networks, Inc.

from oslo.config import cfg

from quantum.common.exceptions import ClassNotFound
from quantum.openstack.common import importutils
from quantum.openstack.common import lockutils
from quantum.openstack.common import log as logging
from quantum.openstack.common import periodic_task
from quantum.plugins.common import constants


LOG = logging.getLogger(__name__)


class Manager(periodic_task.PeriodicTasks):

    # Set RPC API version to 1.0 by default.
    RPC_API_VERSION = '1.0'

    def __init__(self, host=None):
        if not host:
            host = cfg.CONF.host
        self.host = host
        super(Manager, self).__init__()

    def periodic_tasks(self, context, raise_on_error=False):
        self.run_periodic_tasks(context, raise_on_error=raise_on_error)

    def init_host(self):
        """Handle initialization if this is a standalone service.

        Child classes should override this method.

        """
        pass

    def after_start(self):
        """Handler post initialization stuff.

        Child classes can override this method.
        """
        pass


class QuantumManager(object):
    """
    Quantum's Manager class is responsible for parsing a config file and
    instantiating the correct plugin that concretely implement
    quantum_plugin_base class.
    The caller should make sure that QuantumManager is a singleton.
    """
    _instance = None

    def __init__(self, options=None, config_file=None):
        # If no options have been provided, create an empty dict
        if not options:
            options = {}

        if cfg.CONF.core_plugin is None:
            msg = _('Quantum core_plugin not configured!')
            LOG.critical(msg)
            raise Exception(msg)

        # NOTE(jkoelker) Testing for the subclass with the __subclasshook__
        #                breaks tach monitoring. It has been removed
        #                intentianally to allow v2 plugins to be monitored
        #                for performance metrics.
        plugin_provider = cfg.CONF.core_plugin
        LOG.debug(_("Plugin location: %s"), plugin_provider)
        # If the plugin can't be found let them know gracefully
        try:
            LOG.info(_("Loading Plugin: %s"), plugin_provider)
            plugin_klass = importutils.import_class(plugin_provider)
        except ClassNotFound:
            LOG.exception(_("Error loading plugin"))
            raise Exception(_("Plugin not found.  You can install a "
                            "plugin with: pip install <plugin-name>\n"
                            "Example: pip install quantum-sample-plugin"))
        self.plugin = plugin_klass()

        # core plugin as a part of plugin collection simplifies
        # checking extensions
        # TODO (enikanorov): make core plugin the same as
        # the rest of service plugins
        self.service_plugins = {constants.CORE: self.plugin}
        self._load_service_plugins()

    def _load_service_plugins(self):
        plugin_providers = cfg.CONF.service_plugins
        LOG.debug(_("Loading service plugins: %s"), plugin_providers)
        for provider in plugin_providers:
            if provider == '':
                continue
            try:
                LOG.info(_("Loading Plugin: %s"), provider)
                plugin_class = importutils.import_class(provider)
            except ClassNotFound:
                LOG.exception(_("Error loading plugin"))
                raise Exception(_("Plugin not found."))
            plugin_inst = plugin_class()

            # only one implementation of svc_type allowed
            # specifying more than one plugin
            # for the same type is a fatal exception
            if plugin_inst.get_plugin_type() in self.service_plugins:
                raise Exception(_("Multiple plugins for service "
                                "%s were configured"),
                                plugin_inst.get_plugin_type())

            self.service_plugins[plugin_inst.get_plugin_type()] = plugin_inst

            LOG.debug(_("Successfully loaded %(type)s plugin. "
                        "Description: %(desc)s"),
                      {"type": plugin_inst.get_plugin_type(),
                       "desc": plugin_inst.get_plugin_description()})

    @classmethod
    @lockutils.synchronized("qmlock", "qml-")
    def _create_instance(cls):
        if cls._instance is None:
            cls._instance = cls()

    @classmethod
    def get_instance(cls):
        # double checked locking
        if cls._instance is None:
            cls._create_instance()
        return cls._instance

    @classmethod
    def get_plugin(cls):
        return cls.get_instance().plugin

    @classmethod
    def get_service_plugins(cls):
        return cls.get_instance().service_plugins