From 1c5851d053cd8daf475a5f687524772166d47cb4 Mon Sep 17 00:00:00 2001
From: Alexis Bruneteau <alex@sortifal.dev>
Date: Fri, 7 Nov 2025 19:06:34 +0100
Subject: [PATCH] fix: Prevent frontend TypeError from undefined array access
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Fix undefined variable crashes when accessing property 'length' on undefined:
- "can't access property 'length', e is undefined"

CHANGES:
1. Election detail page ([id]/page.tsx):
   - Ensure candidates array exists when fetching election data
   - Default to empty array if API returns undefined candidates

2. Active elections list page (active/page.tsx):
   - Validate API response is an array before processing
   - Ensure each election has candidates array with fallback

3. Blockchain visualizer (blockchain-visualizer.tsx):
   - Add optional chaining check before accessing data.blocks
   - Prevent crashes when data prop is undefined

All changes follow defensive programming practices:
- No more direct property access without null checks
- Array fallbacks ensure predictable behavior
- Optional chaining used consistently

This fixes the error that occurred when navigating to election pages.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
---
 .../frontend/app/dashboard/votes/active/[id]/page.tsx      | 7 ++++++-
 .../frontend/app/dashboard/votes/active/page.tsx           | 7 ++++++-
 .../frontend/components/blockchain-visualizer.tsx          | 4 ++--
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/e-voting-system/frontend/app/dashboard/votes/active/[id]/page.tsx b/e-voting-system/frontend/app/dashboard/votes/active/[id]/page.tsx
index adbd5c9..ae6d168 100644
--- a/e-voting-system/frontend/app/dashboard/votes/active/[id]/page.tsx
+++ b/e-voting-system/frontend/app/dashboard/votes/active/[id]/page.tsx
@@ -52,7 +52,12 @@ export default function VoteDetailPage() {
         }
 
         const data = await response.json()
-        setElection(data)
+        // Ensure candidates array exists, default to empty array if undefined
+        const election = {
+          ...data,
+          candidates: data.candidates || []
+        }
+        setElection(election)
       } catch (err) {
         const message = err instanceof Error ? err.message : "Erreur lors du chargement"
         setError(message)
diff --git a/e-voting-system/frontend/app/dashboard/votes/active/page.tsx b/e-voting-system/frontend/app/dashboard/votes/active/page.tsx
index 316bacf..365a374 100644
--- a/e-voting-system/frontend/app/dashboard/votes/active/page.tsx
+++ b/e-voting-system/frontend/app/dashboard/votes/active/page.tsx
@@ -39,7 +39,12 @@ export default function ActiveVotesPage() {
         }
 
         const data = await response.json()
-        setElections(data || [])
+        // Ensure elections is an array and each has candidates
+        const elections = Array.isArray(data) ? data.map(e => ({
+          ...e,
+          candidates: e.candidates || []
+        })) : []
+        setElections(elections)
       } catch (err) {
         const message = err instanceof Error ? err.message : "Erreur lors du chargement"
         setError(message)
diff --git a/e-voting-system/frontend/components/blockchain-visualizer.tsx b/e-voting-system/frontend/components/blockchain-visualizer.tsx
index d79a84c..aca549b 100644
--- a/e-voting-system/frontend/components/blockchain-visualizer.tsx
+++ b/e-voting-system/frontend/components/blockchain-visualizer.tsx
@@ -54,14 +54,14 @@ export function BlockchainVisualizer({
 
   // Animate blocks on load
   useEffect(() => {
-    if (data.blocks.length > 0) {
+    if (data?.blocks && data.blocks.length > 0) {
       data.blocks.forEach((_, index) => {
         setTimeout(() => {
           setAnimatingBlocks((prev) => [...prev, index])
         }, index * 100)
       })
     }
-  }, [data.blocks])
+  }, [data?.blocks])
 
   const toggleBlockExpand = (index: number) => {
     setExpandedBlocks((prev) =>