[#219] Add rate limiting to view count API

src/app/api/views/route.ts

@@ -5,6 +5,42 @@ function error(message: string, status = 400) {
   return NextResponse.json({ error: message }, { status });
 }
 
+// ---------------------------------------------------------------------------
+// In-memory rate limiter: max 10 POST requests per IP per storyline per hour
+// ---------------------------------------------------------------------------
+
+const RATE_LIMIT_MAX = 10;
+const RATE_LIMIT_WINDOW_MS = 60 * 60 * 1000; // 1 hour
+
+const rateLimitMap = new Map<string, { count: number; resetAt: number }>();
+
+function checkRateLimit(ip: string, storylineId: number, plotIndex: number | null): boolean {
+  const key = `${ip}:${storylineId}:${plotIndex ?? "s"}`;
+  const now = Date.now();
+  const entry = rateLimitMap.get(key);
+
+  if (!entry || now >= entry.resetAt) {
+    rateLimitMap.set(key, { count: 1, resetAt: now + RATE_LIMIT_WINDOW_MS });
+    return true;
+  }
+
+  if (entry.count >= RATE_LIMIT_MAX) return false;
+
+  entry.count++;
+  return true;
+}
+
+// Periodically prune expired entries to prevent memory leak
+let lastPrune = Date.now();
+function pruneIfNeeded() {
+  const now = Date.now();
+  if (now - lastPrune < RATE_LIMIT_WINDOW_MS) return;
+  lastPrune = now;
+  for (const [key, entry] of rateLimitMap) {
+    if (now >= entry.resetAt) rateLimitMap.delete(key);
+  }
+}
+
 // ---------------------------------------------------------------------------
 // GET /api/views?storylineId=N
 // ---------------------------------------------------------------------------
@@ -61,11 +97,21 @@ export async function POST(req: NextRequest) {
     return error("Missing or invalid sessionId");
   }
 
+  // Rate limit: max 10 requests per IP per storyline per hour
+  pruneIfNeeded();
+  const ip = req.headers.get("x-forwarded-for")?.split(",")[0]?.trim() ?? "unknown";
+  const plotVal = plotIndex ?? null;
+  if (!checkRateLimit(ip, storylineId, plotVal)) {
+    return NextResponse.json(
+      { error: "Too many requests" },
+      { status: 429, headers: { "Retry-After": "3600" } },
+    );
+  }
+
   const serverClient = createServerClient();
   if (!serverClient) return error("Supabase not configured", 500);
 
   const oneHourAgo = new Date(Date.now() - 60 * 60 * 1000).toISOString();
-  const plotVal = plotIndex ?? null;
 
   // Dedup: check if this session already viewed this page in the last hour
   // eslint-disable-next-line @typescript-eslint/no-explicit-any