Add thread pruning for threads that pass the maximum page threshhold

Each board is allowed a number of threads per page, and a maximum number
of pages (default 10 for both). If a thread falls off the last page, it
is deleted.

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

board/models.py

@@ -39,21 +39,30 @@ class Board(models.Model):
     url = models.CharField(max_length=255, null=False, blank=False, unique=True)
     # Human-readable name for the board
     name = models.CharField(max_length=255, null=False, blank=False)
+    # Max pages
+    max_pages = models.IntegerField(default=10)
+    # Threads per page
+    threads_per_page = models.IntegerField(default=10)
 
     @property
     def threads(self):
         return Post.objects.filter(board=self, op=None)
 
+    @property
+    def max_threads(self):
+        return self.max_pages * self.threads_per_page
+
+    def prune_threads(self):
+        to_remove = self.threads.order_by("-last_bump")[self.max_threads :]
+        for thread in to_remove:
+            thread.delete()
+
 
 class Post(models.Model):
     # Board that this post was made on
     board = models.ForeignKey("Board", on_delete=models.CASCADE)
     # Thread that this is a part of
     op = models.ForeignKey(
-        "self", null=True, on_delete=models.CASCADE, related_name="all_replies"
-    )
-    # Post that this is replying to
-    reply = models.ForeignKey(
         "self", null=True, on_delete=models.CASCADE, related_name="replies"
     )
     # User's supplied name for this post
@@ -139,9 +148,14 @@ class Post(models.Model):
 
 @receiver(signals.post_save, sender=Post)
 def post_created(sender, instance, created, **kwargs):
-    if created and instance.op:
-        instance.op.last_bump = timezone.now()
-        instance.op.save()
+    if created:
+        if instance.op:
+            # Update the bump
+            instance.op.last_bump = timezone.now()
+            instance.op.save()
+        else:
+            # Prune threads for the board
+            instance.board.prune_threads()
 
 
 @receiver(signals.post_delete, sender=Post)