from collections import Counter
from functools import reduce

import bitmath

from ucloud.common.host import HostStatus
from ucloud.common.request import RequestEntry, RequestType
from ucloud.common.vm import VMStatus
from ucloud.config import vm_pool, host_pool, request_pool, config


def accumulated_specs(vms_specs):
    if not vms_specs:
        return {}
    return reduce((lambda x, y: Counter(x) + Counter(y)), vms_specs)


def remaining_resources(host_specs, vms_specs):
    # Return remaining resources host_specs - vms

    _vms_specs = Counter(vms_specs)
    _remaining = Counter(host_specs)

    for component in _vms_specs:
        if isinstance(_vms_specs[component], str):
            _vms_specs[component] = int(bitmath.parse_string_unsafe(_vms_specs[component]).to_MB())
        elif isinstance(_vms_specs[component], list):
            _vms_specs[component] = map(lambda x: int(bitmath.parse_string_unsafe(x).to_MB()), _vms_specs[component])
            _vms_specs[component] = reduce(lambda x, y: x + y, _vms_specs[component], 0)

    for component in _remaining:
        if isinstance(_remaining[component], str):
            _remaining[component] = int(bitmath.parse_string_unsafe(_remaining[component]).to_MB())
        elif isinstance(_remaining[component], list):
            _remaining[component] = map(lambda x: int(bitmath.parse_string_unsafe(x).to_MB()), _remaining[component])
            _remaining[component] = reduce(lambda x, y: x + y, _remaining[component], 0)

    _remaining.subtract(_vms_specs)

    return _remaining


class NoSuitableHostFound(Exception):
    """Exception when no host found that can host a VM."""


def get_suitable_host(vm_specs, hosts=None):
    if hosts is None:
        hosts = host_pool.by_status(HostStatus.alive)

    for host in hosts:
        # Filter them by host_name
        vms = vm_pool.by_host(host.key)

        # Filter them by status
        vms = vm_pool.by_status(VMStatus.running, vms)

        running_vms_specs = [vm.specs for vm in vms]

        # Accumulate all of their combined specs
        running_vms_accumulated_specs = accumulated_specs(running_vms_specs)

        # Find out remaining resources after
        # host_specs - already running vm_specs
        remaining = remaining_resources(host.specs, running_vms_accumulated_specs)

        # Find out remaining - new_vm_specs
        remaining = remaining_resources(remaining, vm_specs)

        if all(map(lambda x: x >= 0, remaining.values())):
            return host.key

    raise NoSuitableHostFound


def dead_host_detection():
    # Bring out your dead! - Monty Python and the Holy Grail
    hosts = host_pool.by_status(HostStatus.alive)
    dead_hosts_keys = []

    for host in hosts:
        # Only check those who claims to be alive
        if host.status == HostStatus.alive:
            if not host.is_alive():
                dead_hosts_keys.append(host.key)

    return dead_hosts_keys


def dead_host_mitigation(dead_hosts_keys):
    for host_key in dead_hosts_keys:
        host = host_pool.get(host_key)
        host.declare_dead()

        vms_hosted_on_dead_host = vm_pool.by_host(host_key)
        for vm in vms_hosted_on_dead_host:
            vm.declare_killed()
            vm_pool.put(vm)
        host_pool.put(host)


def assign_host(vm):
    vm.hostname = get_suitable_host(vm.specs)
    vm_pool.put(vm)

    r = RequestEntry.from_scratch(type=RequestType.StartVM,
                                  uuid=vm.uuid,
                                  hostname=vm.hostname,
                                  request_prefix=config['etcd']['REQUEST_PREFIX'])
    request_pool.put(r)

    vm.log.append("VM scheduled for starting")
    return vm.hostname