Add IP bans

Users can be banned by IP address now, either by singular IP or in an IP
range. If they are banned and attempt to post, they will be met with a
"you are banned until X date" screen.

There are a few loose threads with this, and IP bans may be obsolete if
I decide to go the accounts-required-for-posting route. But I think this
is a good start for 4chan style posting.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

board/models.py

@@ -264,32 +264,50 @@ def report_created(sender, instance, created, **kwargs):
 # board =
 
 
-class RangeBan(models.Model):
-    # Starting IP address of the ban
-    start = models.GenericIPAddressField()
-    # Ending IP address of the ban
-    end = models.GenericIPAddressField()
-    # The reason for this ban
-    ban_reason = models.TextField(blank=False)
-    # The time that this ban was created.
-    created = models.DateTimeField(auto_now_add=True)
-    # Expiration date of this ban. If it is null, it is permanent.
-    expires = models.DateTimeField(null=True)
-
-
-class Ban(models.Model):
-    # IP address of the ban
-    ip = models.GenericIPAddressField()
+class BanCommon(models.Model):
     # The reason for this ban
     ban_reason = models.TextField(blank=False)
     # Board that this ban is for. If null, then all boards.
     # Even though this is nullable, we just want to delete all reports for a
     # board if that board is deleted.
-    board = models.ForeignKey("Board", on_delete=models.CASCADE, null=True)
+    board = models.ForeignKey("Board", on_delete=models.CASCADE, null=True, blank=True)
     # The time that this ban was created.
     created = models.DateTimeField(auto_now_add=True)
     # Expiration date of this ban. If it is null, it is permanent.
-    expires = models.DateTimeField(null=True)
+    expires = models.DateTimeField(null=True, blank=True)
+
+    class Meta:
+        abstract = True
+
+
+class RangeBan(BanCommon):
+    # Starting IP address of the ban
+    start = models.GenericIPAddressField()
+    # Ending IP address of the ban
+    end = models.GenericIPAddressField()
+
+    def clean(self):
+        import ipaddress
+
+        start = ipaddress.ip_address(self.start)
+        end = ipaddress.ip_address(self.end)
+        if start.version != end.version:
+            raise ValidationError(
+                _("Start and end IP address must be the same protocol (IPv4 or IPv6)")
+            )
+        if start >= end:
+            raise ValidationError(_("Start IP must be lower than end IP"))
+
+    def __str__(self):
+        return f"Range ban for {self.start}-{self.end}"
+
+
+class Ban(BanCommon):
+    # IP address of the ban
+    ip = models.GenericIPAddressField(unique=True)
+
+    def __str__(self):
+        return f"Ban for {self.ip}"
 
 
 class BanTemplate(models.Model):