import uuid
import ipaddress

from django.db import models
from django.contrib.auth import get_user_model
from django.core.validators import MinValueValidator, MaxValueValidator
from django.core.exceptions import FieldError, ValidationError

from uncloud_pay.models import Order

class MACAdress(models.Model):
    default_prefix = 0x420000000000

class VPNPool(models.Model):
    """
    Network address pools from which VPNs can be created
    """

    uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)

    network = models.GenericIPAddressField(unique=True)
    network_size = models.IntegerField(validators=[MinValueValidator(0),
                                                   MaxValueValidator(128)])

    subnetwork_size = models.IntegerField(validators=[
                                              MinValueValidator(0),
                                              MaxValueValidator(128)
                                          ])

    vpn_hostname = models.CharField(max_length=256)

    wireguard_private_key = models.CharField(max_length=48)

    @property
    def num_maximum_networks(self):
        """
        sample:
        network_size = 40
        subnetwork_size = 48
        maximum_networks = 2^(48-40)

        2nd sample:
        network_size = 8
        subnetwork_size = 24
        maximum_networks = 2^(24-8)
        """

        return 2**(self.subnetwork_size - self.network_size)

    @property
    def used_networks(self):
        return self.vpnnetworkreservation_set.filter(vpnpool=self, status='used')

    @property
    def free_networks(self):
        return self.vpnnetworkreservation_set.filter(vpnpool=self, status='free')

    @property
    def num_used_networks(self):
        return len(self.used_networks)

    @property
    def num_free_networks(self):
        return self.num_maximum_networks - self.num_used_networks + len(self.free_networks)

    @property
    def next_free_network(self):
        if self.num_free_networks == 0:
            # FIXME: use right exception
            raise Exception("No free networks")

        if len(self.free_networks) > 0:
            return self.free_networks[0].address

        if len(self.used_networks) > 0:
            """
            sample:

            pool = 2a0a:e5c1:200::/40
            last_used = 2a0a:e5c1:204::/48

            next:
            """

            last_net = ipaddress.ip_network(self.used_networks.last().address)
            last_net_ip = last_net[0]

            if last_net_ip.version == 6:
                offset_to_next = 2**(128 - self.subnetwork_size)
            elif last_net_ip.version == 4:
                offset_to_next = 2**(32 - self.subnetwork_size)

            next_net_ip = last_net_ip + offset_to_next

            return str(next_net_ip)
        else:
            # first network to be created
            return self.network

    @property
    def wireguard_config_filename(self):
        return '/etc/wireguard/{}.conf'.format(self.network)

    @property
    def wireguard_config(self):
        wireguard_config = [
            """
[Interface]
ListenPort = 51820
PrivateKey = {privatekey}
""".format(privatekey=self.wireguard_private_key) ]

        peers = []

        for reservation in self.vpnnetworkreservation_set.filter(status='used'):
            public_key = reservation.vpnnetwork_set.first().wireguard_public_key
            peer_network = "{}/{}".format(reservation.address, self.subnetwork_size)
            owner = reservation.vpnnetwork_set.first().owner

            peers.append("""
# Owner: {owner}
[Peer]
PublicKey = {public_key}
AllowedIPs = {peer_network}
""".format(
    owner=owner,
    public_key=public_key,
    peer_network=peer_network))

        wireguard_config.extend(peers)

        return "\n".join(wireguard_config)


    def configure_wireguard_vpnserver(self):
        """
        This method is designed to run as a celery task and should
        not be called directly from the web
        """

        # subprocess, ssh

        pass


class VPNNetworkReservation(models.Model):
    """
     This class tracks the used VPN networks. It will be deleted, when the product is cancelled.
     """
    vpnpool = models.ForeignKey(VPNPool,
                                 on_delete=models.CASCADE)

    address = models.GenericIPAddressField(primary_key=True)

    status = models.CharField(max_length=256,
                              default='used',
                              choices = (
                                  ('used', 'used'),
                                  ('free', 'free')
                              )
    )


class VPNNetwork(models.Model):
    """
    A selected network. Used for tracking reservations / used networks
    """
    network = models.ForeignKey(VPNNetworkReservation,
                               on_delete=models.CASCADE,
                               editable=False)

    wireguard_public_key = models.CharField(max_length=48)

#    default_recurring_period = RecurringPeriod.PER_365D

    @property
    def recurring_price(self):
        return 120


    def delete(self, *args, **kwargs):
        self.network.status = 'free'
        self.network.save()
        super().save(*args, **kwargs)
        print("deleted {}".format(self))


class ReverseDNSEntry(models.Model):
    """
    A reverse DNS entry
    """
    owner = models.ForeignKey(get_user_model(),
            on_delete=models.CASCADE)

    ip_address = models.GenericIPAddressField(null=False, unique=True)

    name = models.CharField(max_length=253, null=False)

    @property
    def reverse_pointer(self):
        return ipaddress.ip_address(self.ip_address).reverse_pointer

    def implement(self):
        """
        The implement function implements the change
        """

        # Get all DNS entries (?) / update this DNS entry
        # convert to DNS name
        #
        pass


    def save(self, *args, **kwargs):
        # Product.objects.filter(config__parameters__contains='reverse_dns_network')
        # FIXME: check if order is still active / not replaced

        allowed = False
        product = None

        for order in Order.objects.filter(config__parameters__reverse_dns_network__isnull=False,
                             owner=self.owner):
            network = order.config['parameters']['reverse_dns_network']

            net = ipaddress.ip_network(network)
            addr = ipaddress.ip_address(self.ip_address)

            if addr in net:
                allowed = True
                product = order.product
                break


        if not allowed:
            raise ValidationError(f"User {self.owner} does not have the right to create reverse DNS entry for {self.ip_address}")

        super().save(*args, **kwargs)


    def __str__(self):
        return f"{self.ip_address} - {self.name}"