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

#
#    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 datetime
import time

from oslo.config import cfg

from nova.openstack.common.gettextutils import _
from nova.openstack.common import log as logging
from nova.openstack.common import timeutils


periodic_opts = [
    cfg.BoolOpt('run_external_periodic_tasks',
                default=True,
                help=('Some periodic tasks can be run in a separate process. '
                      'Should we run them here?')),
]

CONF = cfg.CONF
CONF.register_opts(periodic_opts)

LOG = logging.getLogger(__name__)

DEFAULT_INTERVAL = 60.0


class InvalidPeriodicTaskArg(Exception):
    message = _("Unexpected argument for periodic task creation: %(arg)s.")


def periodic_task(*args, **kwargs):
    """Decorator to indicate that a method is a periodic task.

    This decorator can be used in two ways:

        1. Without arguments '@periodic_task', this will be run on every cycle
           of the periodic scheduler.

        2. With arguments:
           @periodic_task(spacing=N [, run_immediately=[True|False]])
           this will be run on approximately every N seconds. If this number is
           negative the periodic task will be disabled. If the run_immediately
           argument is provided and has a value of 'True', the first run of the
           task will be shortly after task scheduler starts.  If
           run_immediately is omitted or set to 'False', the first time the
           task runs will be approximately N seconds after the task scheduler
           starts.
    """
    def decorator(f):
        # Test for old style invocation
        if 'ticks_between_runs' in kwargs:
            raise InvalidPeriodicTaskArg(arg='ticks_between_runs')

        # Control if run at all
        f._periodic_task = True
        f._periodic_external_ok = kwargs.pop('external_process_ok', False)
        if f._periodic_external_ok and not CONF.run_external_periodic_tasks:
            f._periodic_enabled = False
        else:
            f._periodic_enabled = kwargs.pop('enabled', True)

        # Control frequency
        f._periodic_spacing = kwargs.pop('spacing', 0)
        f._periodic_immediate = kwargs.pop('run_immediately', False)
        if f._periodic_immediate:
            f._periodic_last_run = None
        else:
            f._periodic_last_run = timeutils.utcnow()
        return f

    # NOTE(sirp): The `if` is necessary to allow the decorator to be used with
    # and without parens.
    #
    # In the 'with-parens' case (with kwargs present), this function needs to
    # return a decorator function since the interpreter will invoke it like:
    #
    #   periodic_task(*args, **kwargs)(f)
    #
    # In the 'without-parens' case, the original function will be passed
    # in as the first argument, like:
    #
    #   periodic_task(f)
    if kwargs:
        return decorator
    else:
        return decorator(args[0])


class _PeriodicTasksMeta(type):
    def __init__(cls, names, bases, dict_):
        """Metaclass that allows us to collect decorated periodic tasks."""
        super(_PeriodicTasksMeta, cls).__init__(names, bases, dict_)

        # NOTE(sirp): if the attribute is not present then we must be the base
        # class, so, go ahead an initialize it. If the attribute is present,
        # then we're a subclass so make a copy of it so we don't step on our
        # parent's toes.
        try:
            cls._periodic_tasks = cls._periodic_tasks[:]
        except AttributeError:
            cls._periodic_tasks = []

        try:
            cls._periodic_last_run = cls._periodic_last_run.copy()
        except AttributeError:
            cls._periodic_last_run = {}

        try:
            cls._periodic_spacing = cls._periodic_spacing.copy()
        except AttributeError:
            cls._periodic_spacing = {}

        for value in cls.__dict__.values():
            if getattr(value, '_periodic_task', False):
                task = value
                name = task.__name__

                if task._periodic_spacing < 0:
                    LOG.info(_('Skipping periodic task %(task)s because '
                               'its interval is negative'),
                             {'task': name})
                    continue
                if not task._periodic_enabled:
                    LOG.info(_('Skipping periodic task %(task)s because '
                               'it is disabled'),
                             {'task': name})
                    continue

                # A periodic spacing of zero indicates that this task should
                # be run every pass
                if task._periodic_spacing == 0:
                    task._periodic_spacing = None

                cls._periodic_tasks.append((name, task))
                cls._periodic_spacing[name] = task._periodic_spacing
                cls._periodic_last_run[name] = task._periodic_last_run


class PeriodicTasks(object):
    __metaclass__ = _PeriodicTasksMeta

    def run_periodic_tasks(self, context, raise_on_error=False):
        """Tasks to be run at a periodic interval."""
        idle_for = DEFAULT_INTERVAL
        for task_name, task in self._periodic_tasks:
            full_task_name = '.'.join([self.__class__.__name__, task_name])

            now = timeutils.utcnow()
            spacing = self._periodic_spacing[task_name]
            last_run = self._periodic_last_run[task_name]

            # If a periodic task is _nearly_ due, then we'll run it early
            if spacing is not None and last_run is not None:
                due = last_run + datetime.timedelta(seconds=spacing)
                if not timeutils.is_soon(due, 0.2):
                    idle_for = min(idle_for, timeutils.delta_seconds(now, due))
                    continue

            if spacing is not None:
                idle_for = min(idle_for, spacing)

            LOG.debug(_("Running periodic task %(full_task_name)s"), locals())
            self._periodic_last_run[task_name] = timeutils.utcnow()

            try:
                task(self, context)
            except Exception as e:
                if raise_on_error:
                    raise
                LOG.exception(_("Error during %(full_task_name)s: %(e)s"),
                              locals())
            time.sleep(0)

        return idle_for
