# Copyright 2014 Budapest University of Technology and Economics (BME IK)
#
# This file is part of CIRCLE Cloud.
#
# CIRCLE is free software: you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option)
# any later version.
#
# CIRCLE is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
# details.
#
# You should have received a copy of the GNU General Public License along
# with CIRCLE.  If not, see <http://www.gnu.org/licenses/>.

import datetime
import json
import random
from logging import getLogger

from django.conf import settings
from django.core.cache import cache
from django.utils import timezone
from django.utils.translation import ugettext_noop

from circle.settings.base import SCHEDULER_METHOD
from common.models import HumanReadableException

logger = getLogger(__name__)


class SchedulerError(HumanReadableException):
    admin_message = None

    def __init__(self, params=None, level=None, **kwargs):
        kwargs.update(params or {})
        super(SchedulerError, self).__init__(
            level, self.message, self.admin_message or self.message,
            kwargs)


class NotEnoughMemoryException(SchedulerError):
    message = ugettext_noop(
        "The resources required for launching the virtual machine are not "
        "available currently. Please try again later.")

    admin_message = ugettext_noop(
        "The required free memory for launching the virtual machine is not "
        "available on any usable node currently. Please try again later.")


class TraitsUnsatisfiableException(SchedulerError):
    message = ugettext_noop(
        "No node can satisfy the required traits of the "
        "new virtual machine currently.")


def common_select(instance, nodes):
    # check required traits
    nodes = [n for n in nodes
             if n.schedule_enabled and n.online and
             has_traits(instance.req_traits.all(), n)]
    logger.debug('capab: %s selected_nodes: %s', instance.capability_group, nodes)
    if instance.capability_group:
        nodes = [n for n in nodes if not n.capability or n.capability == instance.capability_group]
    logger.debug('capab: %s selected_nodes: %s', instance.capability_group, nodes)
    if not nodes:
        logger.warning('select_node: no usable node for %s', unicode(instance))
        raise TraitsUnsatisfiableException()

    # check required RAM
    nodes = [n for n in nodes if has_enough_ram(instance.ram_size, n)]
    if not nodes:
        logger.warning('select_node: no enough RAM for %s', unicode(instance))
        raise NotEnoughMemoryException()

    # sort nodes first by priority
    nodes.sort(key=lambda n: n.priority, reverse=True)
    return nodes


def common_evenly(instance, nodes):
    nodes = common_select(instance, nodes)
    nodes.sort(key=free_cpu_time, reverse=True)
    result = nodes[0]
    return result


def common_random(instance, nodes):
    nodes = common_select(instance, nodes)
    result = random.choice(nodes)
    return result


def advanced_with_time_stamp(instance, nodes):
    nodes = common_select(instance, nodes)
    nodes.sort(key=sorting_key, reverse=True)
    logger.debug("SCHEDLOG: {}".format(json.dumps({
        "event": "after_sort", 
        "list": map(lambda node: unicode(node), nodes)})))
    result = nodes[0]
    return result


def select_node(instance, nodes):
    ''' Select a node for hosting an instance based on its requirements.
    '''
    if SCHEDULER_METHOD == 'evenly':
        result = common_evenly(instance, nodes)
    elif SCHEDULER_METHOD == 'random':
        result = common_random(instance, nodes)
    elif SCHEDULER_METHOD == 'advanced':
        result = advanced_with_time_stamp(instance, nodes)
    else:  # Default method is the random
        result = common_random(instance, nodes)

    logger.debug("SCHEDLOG: {}".format(json.dumps(
        {"event": "select",
         "node": unicode(result),
          "vm": unicode(instance)})))

    set_time_stamp(result)

    return result


def sorting_key(node):
    """Determines how valuable a node is for scheduling.
    """
    key = 0
    corr = last_scheduled_correction_factor(node)
    if free_cpu_time(node) < free_ram(node):
        key = free_cpu_time(node) * corr
    else:
        key = free_ram(node) * corr
    logger.debug("SCHEDLOG: {}".format(json.dumps({
        "event": "sort",
        "node": unicode(node),
        "sorting_key": unicode(key),
        "free_cpu_time": unicode(free_cpu_time(node)),
        "free_ram": unicode(free_ram(node)),
        "last_scheduled_correction_factor": unicode(last_scheduled_correction_factor(node))})))
    return key


def set_time_stamp(node):
    cache.set('time_stamp{}'.format(node.id), timezone.now())


def get_time_stamp(node):
    time_stamp = cache.get('time_stamp{}'.format(node.id))
    if time_stamp:
        return time_stamp
    return datetime.datetime(1970, 1, 1, tzinfo=timezone.get_current_timezone())


def last_scheduled_correction_factor(node):
    """Returns the time correction factor for a node.

    The monitor data may be outdated, because of recent scheduling for a given node.
    The return value is between 0 and 1, higher value indicates more time since the
    last scheduling for the given node.
    """
    factor = 0
    max_time_diff = settings.SCHEDULER_TIME_SENSITIVITY_IN_SECONDS
    current_time = timezone.now()
    time_difference_in_seconds = (
        current_time - get_time_stamp(node)).total_seconds()
    factor = time_difference_in_seconds/float(max_time_diff)
    if factor > 1:
        factor = 1
    elif factor < 0:
        factor = 1
    logger.debug('Scheduler set factor to %s', unicode(factor))
    return factor


def has_traits(traits, node):
    """True, if the node has all specified traits; otherwise, false.
    """
    traits = set(traits)
    return traits.issubset(node.traits.all())


def has_enough_ram(ram_size, node):
    """True, if the node has enough memory to accomodate a guest requiring
       ram_size mebibytes of memory; otherwise, false.
    """
    ram_size = ram_size * 1024 * 1024
    try:
        total = node.ram_size
        used = node.byte_ram_usage
        unused = total - used

        overcommit = node.ram_size_with_overcommit
        reserved = node.allocated_ram
        free = overcommit - reserved

        retval = ram_size < unused and ram_size < free

        logger.debug('has_enough_ram(%d, %s)=%s (total=%s unused=%s'
                     ' overcommit=%s free=%s free_ok=%s overcommit_ok=%s)',
                     ram_size, node, retval, total, unused, overcommit, free,
                     ram_size < unused, ram_size < free)
        return retval
    except TypeError as e:
        logger.exception('Got incorrect monitoring data for node %s. %s',
                         unicode(node), unicode(e))
        return False


def free_cpu_time(node):
    """Get an indicator number for idle processor time on the node.

    Higher values indicate more idle time.
    """
    try:
        free_cpu_percent = 1 - node.cpu_usage
        weight = node.cpu_weight
        weighted_value = free_cpu_percent * weight
        return weighted_value
    except TypeError as e:
        logger.exception('Got incorrect monitoring data for node %s. %s',
                         unicode(node), unicode(e))
        return 0  # will result lowest priority


def free_ram(node):
    """Get an indicator number for free RAM on the node.

    Higher value indicates more RAM.
    """
    try:
        free_ram_percent = 1 - node.ram_usage
        weight = node.ram_weight
        weighted_value = free_ram_percent * weight
        return weighted_value
    except TypeError as e:
        logger.exception('Got incorrect monitoring data for node %s. %s',
                         unicode(node), unicode(e))
        return 0  # will result lowest priority
