# Copyright 2013 Red Hat, Inc.
#
#    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 eventlet

from neutron.agent.linux import async_process
from neutron.openstack.common import log as logging


LOG = logging.getLogger(__name__)


class OvsdbMonitor(async_process.AsyncProcess):
    """Manages an invocation of 'ovsdb-client monitor'."""

    def __init__(self, table_name, columns=None, format=None,
                 root_helper=None, respawn_interval=None):

        cmd = ['ovsdb-client', 'monitor', table_name]
        if columns:
            cmd.append(','.join(columns))
        if format:
            cmd.append('--format=%s' % format)
        super(OvsdbMonitor, self).__init__(cmd,
                                           root_helper=root_helper,
                                           respawn_interval=respawn_interval)

    def _read_stdout(self):
        data = self._process.stdout.readline()
        if not data:
            return
        self._stdout_lines.put(data)
        LOG.debug(_('Output received from ovsdb monitor: %s') % data)
        return data

    def _read_stderr(self):
        data = super(OvsdbMonitor, self)._read_stderr()
        if data:
            LOG.error(_('Error received from ovsdb monitor: %s') % data)
            # Do not return value to ensure that stderr output will
            # stop the monitor.


class SimpleInterfaceMonitor(OvsdbMonitor):
    """Monitors the Interface table of the local host's ovsdb for changes.

    The has_updates() method indicates whether changes to the ovsdb
    Interface table have been detected since the monitor started or
    since the previous access.
    """

    def __init__(self, root_helper=None, respawn_interval=None):
        super(SimpleInterfaceMonitor, self).__init__(
            'Interface',
            columns=['name', 'ofport'],
            format='json',
            root_helper=root_helper,
            respawn_interval=respawn_interval,
        )
        self.data_received = False

    @property
    def is_active(self):
        return (self.data_received and
                self._kill_event and
                not self._kill_event.ready())

    @property
    def has_updates(self):
        """Indicate whether the ovsdb Interface table has been updated.

        True will be returned if the monitor process is not active.
        This 'failing open' minimizes the risk of falsely indicating
        the absence of updates at the expense of potential false
        positives.
        """
        return bool(list(self.iter_stdout())) or not self.is_active

    def start(self, block=False, timeout=5):
        super(SimpleInterfaceMonitor, self).start()
        if block:
            eventlet.timeout.Timeout(timeout)
            while not self.is_active:
                eventlet.sleep()

    def _kill(self, *args, **kwargs):
        self.data_received = False
        super(SimpleInterfaceMonitor, self)._kill(*args, **kwargs)

    def _read_stdout(self):
        data = super(SimpleInterfaceMonitor, self)._read_stdout()
        if data and not self.data_received:
            self.data_received = True
        return data