redesign Edit Contest Modal with improved scoring system UX

Author: GauriGupta21

backend/app/models/contest.py

@@ -522,6 +522,47 @@ def is_organizer(self, username):
         username = username.strip()
         return username in self.get_organizers()
 
+    def can_change_scoring_system(self):
+        """
+        Determine if scoring system can be changed.
+
+        Rules:
+        - Cannot change if contest has any reviewed submissions
+        - Can change if contest is brand new (no submissions)
+        - Can change if only pending submissions exist
+
+        Returns:
+            tuple: (can_change: bool, reason: str or None)
+        """
+        from app.models.submission import Submission
+
+        # Check if any submissions have been reviewed
+        reviewed_count = (
+            Submission.query.filter(Submission.contest_id == self.id)
+            .filter(Submission.status.in_(["accepted", "rejected"]))
+            .count()
+        )
+
+        if reviewed_count > 0:
+            return (
+                False,
+                f"Cannot change scoring system: {reviewed_count} submissions have already been reviewed",
+            )
+
+        return True, None
+
+    def get_scoring_mode(self):
+        """
+        Get the current scoring mode for this contest.
+
+        Returns:
+            str: 'simple' or 'multi_parameter'
+        """
+        params = self.get_scoring_parameters()
+        if params and params.get("enabled") is True:
+            return "multi_parameter"
+        return "simple"
+
     # ------------------------------------------------------------------------
     # SERIALIZATION
     # ------------------------------------------------------------------------

backend/app/routes/contest_routes.py

@@ -744,6 +744,38 @@ def update_contest(contest_id):
         ):
             return jsonify({"error": "Permission denied"}), 403
 
+        # --- CRITICAL: Scoring System Change Validation ---
+        if "scoring_parameters" in data:
+            # Get current and proposed scoring modes
+            current_mode = contest.get_scoring_mode()
+
+            proposed_params = data.get("scoring_parameters")
+            if proposed_params is None:
+                proposed_mode = "simple"
+            elif (
+                isinstance(proposed_params, dict)
+                and proposed_params.get("enabled") is True
+            ):
+                proposed_mode = "multi_parameter"
+            else:
+                proposed_mode = "simple"
+
+            # Check if mode is changing
+            if current_mode != proposed_mode:
+                can_change, reason = contest.can_change_scoring_system()
+                if not can_change:
+                    return (
+                        jsonify(
+                            {
+                                "error": reason,
+                                "current_mode": current_mode,
+                                "attempted_mode": proposed_mode,
+                                "locked": True,
+                            }
+                        ),
+                        400,
+                    )
+
         # --- Basic Metadata Fields ---
         if "name" in data:
             contest.name = data.get("name") or contest.name