Add antispam app

* update_spam_database command to update suspicious domains from an
   external provider
* Add a AntiSpamEmailField that deny emails from suspicious domains
* Update documentation

antispam/management/commands/update_spam_database.py

@@ -0,0 +1,69 @@
+import requests
+from django.conf import settings
+from django.core.management import BaseCommand
+from django.db.models import Max
+from django.utils import timezone
+
+from antispam.models import ToxicDomain
+
+
+class Command(BaseCommand):
+    """Update blocked ips/mails database"""
+
+    help = "Update blocked ips/mails database"
+
+    def add_arguments(self, parser):
+        parser.add_argument(
+            "--force", action="store_true", help="Force re-creation even if up to date"
+        )
+
+    def _should_update(self, *, force: bool = False) -> bool:
+        if force:
+            return True
+        oldest = ToxicDomain.objects.filter(is_externally_managed=True).aggregate(
+            res=Max("created")
+        )["res"]
+        return not (oldest and timezone.now() < (oldest + timezone.timedelta(days=1)))
+
+    def _download_domains(self, providers: list[str]) -> set[str]:
+        domains = set()
+        for provider in providers:
+            res = requests.get(provider)
+            if not res.ok:
+                self.stderr.write(
+                    f"Source {provider} responded with code {res.status_code}"
+                )
+                continue
+            domains |= set(res.content.decode().splitlines())
+        return domains
+
+    def _update_domains(self, domains: set[str]):
+        # Cleanup database
+        ToxicDomain.objects.filter(is_externally_managed=True).delete()
+
+        # Create database
+        ToxicDomain.objects.bulk_create(
+            [
+                ToxicDomain(domain=domain, is_externally_managed=True)
+                for domain in domains
+            ],
+            ignore_conflicts=True,
+        )
+        self.stdout.write("Domain database updated")
+
+    def handle(self, *args, **options):
+        if not self._should_update(force=options["force"]):
+            self.stdout.write("Domain database is up to date")
+            return
+        self.stdout.write("Updating domain database")
+
+        domains = self._download_domains(settings.TOXIC_DOMAINS_PROVIDERS)
+
+        if not domains:
+            self.stderr.write(
+                "No domains could be fetched from settings.TOXIC_DOMAINS_PROVIDERS. "
+                "Please, have a look at your settings."
+            )
+            return
+
+        self._update_domains(domains)