# Copyright 2014 TrilioData Inc.
# All Rights Reserved.


"""
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 workloadmgr import flags
from workloadmgr.openstack.common import log as logging
from workloadmgr.openstack.common import timeutils

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

FLAGS = flags.FLAGS
FLAGS.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:
            LOG.exception(_("Could not stat scheduler options file "
                            "%(filename)s: '%(e)s'"), locals())
            raise

    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: "
                            "'%(e)s'") % locals())
            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 = FLAGS.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