from django.db import transaction
from django.db.models import Count, F


from .models import *

# def get_num_used_networks(pool):
#     return pool.wireguardvpn_set.count()

def get_suitable_pools(subnetwork_mask):
    """
    Find suitable pools for a certain network size.

    First, filter for all pools that offer the requested subnetwork_size.

    Then find those pools that are not fully exhausted:

    The number of available networks in a pool is 2^(subnetwork_size-network_size.

    The number of available networks in a pool is given by the number of VPNNetworkreservations.

    """

    return WireGuardVPNPool.objects.annotate(
        num_reservations=Count('wireguardvpn'),
        max_reservations=2**(F('subnetwork_mask')-F('network_mask'))).filter(
            num_reservations__lt=F('max_reservations'),
            subnetwork_mask=subnetwork_mask)


def allowed_vpn_network_reservation_size():
    """
    Find all possible sizes of subnetworks that are available.

    Select all pools with free networks.

    Get their subnetwork sizes, reduce to a set

    """

    pools = WireGuardVPNPool.objects.annotate(num_reservations=Count('wireguardvpn'),
                                     max_reservations=2**(F('subnetwork_mask')-F('network_mask'))).filter(
                                         num_reservations__lt=F('max_reservations'))

    # Need to return set of tuples, see
    # https://docs.djangoproject.com/en/3.1/ref/models/fields/#field-choices
    return set([ (pool.subnetwork_mask, pool.subnetwork_mask) for pool in pools ])


#def get_next_vpnnetwork(pool):
    # get all associated networks
    # look for the lowest free number
    # return that


    # select last used one
    # try to increment by one -> get new network

    # if that fails search through the existing vpns for the first unused number
    #