# Copyright (c) 2011 OpenStack Foundation
# 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.

"""
SchedulerOptions monitors a local .json file for changes and loads
it if needed. This file is converted to a data structure and passed
into the filtering and weighing functions which can use it for
dynamic configuration.
"""

import datetime
import json
import os

from oslo.config import cfg

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


scheduler_json_config_location_opt = cfg.StrOpt(
        'scheduler_json_config_location',
        default='',
        help='Absolute path to scheduler configuration JSON file.')

CONF = cfg.CONF
CONF.register_opt(scheduler_json_config_location_opt)

LOG = logging.getLogger(__name__)


class SchedulerOptions(object):
    """SchedulerOptions monitors a local .json file for changes and loads it
    if needed. This file is converted to a data structure and passed into
    the filtering and weighing functions which can use it for dynamic
    configuration.
    """

    def __init__(self):
        super(SchedulerOptions, self).__init__()
        self.data = {}
        self.last_modified = None
        self.last_checked = None

    def _get_file_handle(self, filename):
        """Get file handle. Broken out for testing."""
        return open(filename)

    def _get_file_timestamp(self, filename):
        """Get the last modified datetime. Broken out for testing."""
        try:
            return os.path.getmtime(filename)
        except os.error as e:
            with excutils.save_and_reraise_exception():
                LOG.exception(_("Could not stat scheduler options file "
                                "%(filename)s: '%(e)s'"),
                              {'filename': filename, 'e': e})

    def _load_file(self, handle):
        """Decode the JSON file. Broken out for testing."""
        try:
            return json.load(handle)
        except ValueError as e:
            LOG.exception(_("Could not decode scheduler options: '%s'"), e)
            return {}

    def _get_time_now(self):
        """Get current UTC. Broken out for testing."""
        return timeutils.utcnow()

    def get_configuration(self, filename=None):
        """Check the json file for changes and load it if needed."""
        if not filename:
            filename = CONF.scheduler_json_config_location
        if not filename:
            return self.data
        if self.last_checked:
            now = self._get_time_now()
            if now - self.last_checked < datetime.timedelta(minutes=5):
                return self.data

        last_modified = self._get_file_timestamp(filename)
        if (not last_modified or not self.last_modified or
                last_modified > self.last_modified):
            self.data = self._load_file(self._get_file_handle(filename))
            self.last_modified = last_modified
        if not self.data:
            self.data = {}

        return self.data