from django.contrib.auth.models import AbstractUser, Group
from django.db import models
from django.conf import settings
from django.dispatch import receiver, Signal
from django.utils.timezone import make_aware
from rest_framework.authtoken.models import Token
from django.db.models.signals import post_save, pre_delete
# from django.db.models.signals import m2m_changed
from datetime import datetime

from .rabbitmq import RabbitMQInstance

deployment_change = Signal(providing_args=['instance'])


class User(AbstractUser):
    TYPE_CHOICES = (
            ('apiclient', 'API-Client'),
            ('oidcuser', 'OIDC User'),
            ('admin', 'Admin'),
            )
    user_type = models.CharField(
            max_length=20,
            choices=TYPE_CHOICES,
            default='oidcuser',
            )
    sub = models.CharField(max_length=150, blank=True, null=True)
    password = models.CharField(max_length=150, blank=True, null=True)

    # we hide deleted keys here
    # the full list of ssh keys is at self._ssh_keys
    @property
    def ssh_keys(self):
        return self._ssh_keys.filter(deleted=False)


@receiver(post_save, sender=settings.AUTH_USER_MODEL)
def create_auth_token(sender, instance=None, created=False, **kwargs):
    if instance.user_type == 'apiclient' and created:
        Token.objects.create(user=instance)


def construct_user(user_info):
    return User(
            sub=user_info['sub'],
            name=user_info['name'],
            first_name=user_info['given_name'],
            last_name=user_info['family_name'],
            email=user_info['email'],
            username=user_info['email'],
            )


class Site(models.Model):
    client = models.OneToOneField(
            User,
            related_name='site',
            )
    name = models.CharField(max_length=150, unique=True)
    description = models.TextField(max_length=300, blank=True)
    last_fetch = models.DateTimeField(
            default=make_aware(datetime.utcfromtimestamp(0)),
            editable=False)

    def __str__(self):
        return self.name

    def client_updated(self):
        self.last_fetch = make_aware(datetime.now())
        self.save()

    def clientapi_get_deployments(self, all=False):
        services = {}

        for service in self.services.all():
            deployments = (
                service.deployments
                .filter(user__user_type='oidcuser')
                # we do not exclude deployments without ssh_keys, as the
                # ssh_keys_to_withdraw still need to be propagated
                # .exclude(ssh_keys=None)
                )
            if not all:
                deployments = deployments.filter(
                        last_change__gt=self.last_fetch)

            # deployments for this site
            services[service.name] = deployments

            for deployment in deployments.all():
                # TODO replace this optimism with an acknowledgement
                deployment.client_updated()

        # TODO we expect the client to get the update here
        self.client_updated()
        return services


@receiver(post_save, sender=Site)
def register_at_rabbitmq(
        sender, instance=None, created=False, **kwargs):
    if not created:
        return

    RabbitMQInstance().register_site(instance)


@receiver(pre_delete, sender=Site)
def deregister_at_rabbitmq(
        sender, instance=None, **kwargs):

    RabbitMQInstance().deregister_site(instance)


class Service(models.Model):
    name = models.CharField(max_length=150, unique=True)
    description = models.TextField(max_length=300, blank=True)
    site = models.ForeignKey(
            Site,
            related_name='services')
    groups = models.ManyToManyField(
            Group,
            related_name='services',
            blank=True)

    def __str__(self):
        return self.name + '@' + self.site.name


class SSHPublicKey(models.Model):
    name = models.CharField(max_length=150, unique=True)
    key = models.TextField(max_length=1000)
    # hidden field at the user
    user = models.ForeignKey(
            User,
            related_name='_ssh_keys')

    # has the user triggered the deletion of this key
    deleted = models.BooleanField(
            default=False,
            editable=False,
            )

    # does not directly delete the key if the key is deployed or withdrawn
    # somewhere
    # the receiver 'delete_withdrawn_ssh_key' does the actual deletion
    def delete_key(self):
        if (not self.deployments.exists()
                and not self.withdrawn_deployments.exists()):
            self.delete()
            return

        self.deleted = True
        self.save()

        # delete implies withdrawing the key from all clients
        for deployment in self.deployments.all():
            deployment.withdraw_key(self)

    # when a key is withdrawn by a client we try to finally delete it
    def try_final_deletion(self):
        if (self.deleted
                and not self.deployments.exists()
                and not self.withdrawn_deployments.exists()):
            self.delete()
            return

    def __str__(self):
        if self.deleted:
            return "DELETED: {}".format(self.name)
        return self.name


class Deployment(models.Model):
    user = models.ForeignKey(
            User,
            related_name='deployments',
            on_delete=models.CASCADE,
            )
    service = models.ForeignKey(
            Service,
            related_name='deployments',
            on_delete=models.CASCADE,
            )
    # SET_NULL: we allow credentials to be deleted after deployment
    ssh_keys = models.ManyToManyField(
            SSHPublicKey,
            related_name='deployments',
            blank=True,
            )

    # these ssh keys are to be withdrawn by the clients
    ssh_keys_to_withdraw = models.ManyToManyField(
            SSHPublicKey,
            related_name='withdrawn_deployments',
            blank=True,
            )

    last_change = models.DateTimeField(
            auto_now=True
            )

    def __str__(self):
        return '{}@{}'.format(self.user, self.service)

    def deploy_key(self, key):
        # key state: -> (2.5)
        self.ssh_keys.add(key)

        if key in self.ssh_keys_to_withdraw.all():
            self.ssh_keys_to_withdraw.remove(key)
        self.save()
        self.send_change()

    def withdraw_key(self, key):
        # key state: -> (4)
        self.ssh_keys.remove(key)

        # keys which are to be withdrawn by the clients
        self.ssh_keys_to_withdraw.add(key)
        self.save()
        self.send_change()

    def client_updated(self):
        withdrawn_keys = list(self.ssh_keys_to_withdraw.all())

        # the client has withdrawn the keys so we can empty the list
        self.ssh_keys_to_withdraw.clear()

        for key in withdrawn_keys:
            key.try_final_deletion()

        self.save()

    def send_change(self):
        deployment_change.send(sender=self.__class__, instance=self)