# Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""A collection of context managers for working with shill objects."""

import errno
import logging
import os

from contextlib import contextmanager

from autotest_lib.client.common_lib import error
from autotest_lib.client.common_lib import utils
from autotest_lib.client.cros.networking import shill_proxy

SHILL_START_LOCK_PATH = '/var/lock/shill-start.lock'

class ContextError(Exception):
    """An error raised by a context managers dealing with shill objects."""
    pass


class ServiceAutoConnectContext(object):
    """A context manager for overriding a service's 'AutoConnect' property.

    As the service object of the same service may change during the lifetime
    of the context, this context manager does not take a service object at
    construction. Instead, it takes a |get_service| function at construction,
    which it invokes to obtain a service object when entering and exiting the
    context. It is assumed that |get_service| always returns a service object
    that refers to the same service.

    Usage:
        def get_service():
            # Some function that returns a service object.

        with ServiceAutoConnectContext(get_service, False):
            # Within this context, the 'AutoConnect' property of the service
            # returned by |get_service| is temporarily set to False if it's
            # initially set to True. The property is restored to its initial
            # value after the context ends.

    """
    def __init__(self, get_service, autoconnect):
        self._get_service = get_service
        self._autoconnect = autoconnect
        self._initial_autoconnect = None


    def __enter__(self):
        service = self._get_service()
        if service is None:
            raise ContextError('Could not obtain a service object.')

        # Always set the AutoConnect property even if the requested value
        # is the same so that shill will retain the AutoConnect property, else
        # shill may override it.
        service_properties = service.GetProperties()
        self._initial_autoconnect = shill_proxy.ShillProxy.dbus2primitive(
            service_properties[
                shill_proxy.ShillProxy.SERVICE_PROPERTY_AUTOCONNECT])
        logging.info('ServiceAutoConnectContext: change autoconnect to %s',
                     self._autoconnect)
        service.SetProperty(
            shill_proxy.ShillProxy.SERVICE_PROPERTY_AUTOCONNECT,
            self._autoconnect)

        # Make sure the cellular service gets persisted by taking it out of
        # the ephemeral profile.
        if not service_properties[
                shill_proxy.ShillProxy.SERVICE_PROPERTY_PROFILE]:
            shill = shill_proxy.ShillProxy.get_proxy()
            manager_properties = shill.manager.GetProperties(utf8_strings=True)
            active_profile = manager_properties[
                    shill_proxy.ShillProxy.MANAGER_PROPERTY_ACTIVE_PROFILE]
            logging.info('ServiceAutoConnectContext: change cellular service '
                         'profile to %s', active_profile)
            service.SetProperty(
                    shill_proxy.ShillProxy.SERVICE_PROPERTY_PROFILE,
                    active_profile)

        return self


    def __exit__(self, exc_type, exc_value, traceback):
        if self._initial_autoconnect != self._autoconnect:
            service = self._get_service()
            if service is None:
                raise ContextError('Could not obtain a service object.')

            logging.info('ServiceAutoConnectContext: restore autoconnect to %s',
                         self._initial_autoconnect)
            service.SetProperty(
                shill_proxy.ShillProxy.SERVICE_PROPERTY_AUTOCONNECT,
                self._initial_autoconnect)
        return False


    @property
    def autoconnect(self):
        """AutoConnect property value within this context."""
        return self._autoconnect


    @property
    def initial_autoconnect(self):
        """Initial AutoConnect property value when entering this context."""
        return self._initial_autoconnect


@contextmanager
def stopped_shill():
    """A context for executing code which requires shill to be stopped.

    This context stops shill on entry to the context, and starts shill
    before exit from the context. This context further guarantees that
    shill will be not restarted by recover_duts, while this context is
    active.

    Note that the no-restart guarantee applies only if the user of
    this context completes with a 'reasonable' amount of time. In
    particular: if networking is unavailable for 15 minutes or more,
    recover_duts will reboot the DUT.

    """
    def get_lock_holder(lock_path):
        lock_holder = os.readlink(lock_path)
        try:
            os.stat(lock_holder)
            return lock_holder  # stat() success -> valid link -> locker alive
        except OSError as e:
            if e.errno == errno.ENOENT:  # dangling link -> locker is gone
                return None
            else:
                raise

    our_proc_dir = '/proc/%d/' % os.getpid()
    try:
        os.symlink(our_proc_dir, SHILL_START_LOCK_PATH)
    except OSError as e:
        if e.errno != errno.EEXIST:
            raise
        lock_holder = get_lock_holder(SHILL_START_LOCK_PATH)
        if lock_holder is not None:
            raise error.TestError('Shill start lock held by %s' % lock_holder)
        os.remove(SHILL_START_LOCK_PATH)
        os.symlink(our_proc_dir, SHILL_START_LOCK_PATH)

    utils.stop_service('shill')
    yield
    utils.start_service('shill')
    os.remove(SHILL_START_LOCK_PATH)