Rename CreatePostView -> CreateView, add utils.is_banned

The artist formerly known as CreatePostView is a little more generic now
and outsources its ban check to a new util method, is_banned.

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

board/utils.py

@@ -1,6 +1,13 @@
-from board.models import Ban, RangeBan
+from typing import TYPE_CHECKING
+from django.utils import timezone
 import ipaddress
 
+from board.models import Ban, RangeBan
+
+
+if TYPE_CHECKING:
+    from board.models import Board
+
 
 def get_client_ip(request):
     "Get the IP address of a client-side request. Shamelessly copy/pasted from StackOverflow."
@@ -24,3 +31,17 @@ def get_ip_bans(ip: str) -> list:
         if start <= ip_addr <= end:  # type: ignore
             bans += [rangeban]
     return bans
+
+
+def is_banned(ip: str, board: "Board" | None) -> bool:
+    now = timezone.now()
+    bans = [ban for ban in get_ip_bans(ip) if ban.board == board or not ban.board]
+    if bans:
+        active = [ban for ban in bans if ban.expires > now]
+        expired = [ban for ban in bans if ban.expires <= now]
+        # Delete expired bans
+        for ban in expired:
+            ban.delete()
+        return bool(active)
+    else:
+        return False