Add flagging functionality for exam questions with a reusable Flag model and toggle feature

generic/models.py

@@ -1704,6 +1704,48 @@ class CidUserExam(models.Model):
         self.save()
 
 
+class Flag(models.Model):
+    """A reusable flag model that can be attached to any object via a
+    GenericForeignKey. Useful for marking questions, items or other objects
+    across apps.
+    """
+    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
+    object_id = models.PositiveIntegerField()
+    content_object = GenericForeignKey("content_type", "object_id")
+
+    # Optional actor who created the flag (either a user or a CID user)
+    user = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        null=True,
+        blank=True,
+        related_name="flags",
+    )
+    cid_user = models.ForeignKey(
+        "CidUser",
+        on_delete=models.CASCADE,
+        null=True,
+        blank=True,
+        related_name="flags",
+    )
+
+    note = models.TextField(blank=True)
+    created_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        ordering = ("-created_at",)
+
+    def __str__(self) -> str:
+        actor = None
+        if self.user:
+            actor = f"user:{self.user.username}"
+        elif self.cid_user:
+            actor = f"cid:{self.cid_user.cid}"
+        else:
+            actor = "anon"
+        return f"Flag [{actor}] -> {self.content_type}({self.object_id})"
+
+
 CID_GROUP_EXAMS = (
     ("SBAs", "sba_cid_user_groups"),
     ("Physics", "physics_cid_user_groups"),