import time

from django.conf import settings
from django.core.mail import get_connection, mail_admins
from django.core.management import BaseCommand
from django.utils import timezone
import dns.message, dns.rdatatype, dns.query

from desecapi import models, serializers
from desecapi.pdns_change_tracker import PDNSChangeTracker


class Command(BaseCommand):

    @staticmethod
    def delete_expired_captchas():
        models.Captcha.objects.filter(created__lt=timezone.now() - settings.CAPTCHA_VALIDITY_PERIOD).delete()

    @staticmethod
    def delete_never_activated_users():
        # delete inactive users whose activation link expired and who never logged in
        # (this will not delete users who have used their account and were later disabled)
        models.User.objects.filter(is_active=False, last_login__exact=None,
                            created__lt=timezone.now() - settings.VALIDITY_PERIOD_VERIFICATION_SIGNATURE).delete()

    @staticmethod
    def update_healthcheck_timestamp():
        name = 'internal-timestamp.desec.test'
        try:
            domain = models.Domain.objects.get(name=name)
        except models.Domain.DoesNotExist:
            # Fail silently. If external alerting is configured, it will catch the problem; otherwise, we don't need it.
            print(f'{name} zone is not configured; skipping TXT record update')
            return

        instances = domain.rrset_set.filter(subname='', type='TXT').all()
        timestamp = int(time.time())
        content = f'"{timestamp}"'
        data = [{
            'subname': '',
            'type': 'TXT',
            'ttl': '3600',
            'records': [content]
        }]
        serializer = serializers.RRsetSerializer(instances, domain=domain, data=data, many=True, partial=True)
        serializer.is_valid(raise_exception=True)
        with PDNSChangeTracker():
            serializer.save()
        print(f'TXT {name} updated to {content}')

    @staticmethod
    def alerting_healthcheck():
        name = 'external-timestamp.desec.test'
        try:
            models.Domain.objects.get(name=name)
        except models.Domain.DoesNotExist:
            print(f'{name} zone is not configured; skipping alerting health check')
            return

        timestamps = []
        qname = dns.name.from_text(name)
        query = dns.message.make_query(qname, dns.rdatatype.TXT)
        server = 'ns1.desec.io'
        response = None
        try:
            response = dns.query.tcp(query, server, timeout=5)
            for content in response.find_rrset(dns.message.ANSWER, qname, dns.rdataclass.IN, dns.rdatatype.TXT):
                timestamps.append(str(content)[1:-1])
        except Exception:
            pass

        now = time.time()
        if any(now - 600 <= int(timestamp) <= now for timestamp in timestamps):
            print(f'TXT {name} up to date.')
            return

        timestamps = ', '.join(timestamps)
        print(f'TXT {name} out of date! Timestamps: {timestamps}')
        subject = 'ALERT Alerting system down?'
        message = f'TXT query for {name} on {server} gave the following response:\n'
        message += f'{str(response)}\n\n'
        message += f'Extracted timestamps in TXT RRset:\n{timestamps}'
        mail_admins(subject, message, connection=get_connection('django.core.mail.backends.smtp.EmailBackend'))

    def handle(self, *args, **kwargs):
        try:
            self.alerting_healthcheck()
            self.update_healthcheck_timestamp()
            self.delete_expired_captchas()
            self.delete_never_activated_users()
        except Exception as e:
            subject = 'chores Exception!'
            message = f'{type(e)}\n\n{str(e)}'
            print(f'Chores exception: {type(e)}, {str(e)}')
            mail_admins(subject, message, connection=get_connection('django.core.mail.backends.smtp.EmailBackend'))