feat: harden analytics dashboard

lib/query-cache.ts

@@ -0,0 +1,39 @@
+export interface QueryCacheOptions {
+  ttlMs: number;
+  maxEntries: number;
+  now?: () => number;
+}
+
+export function createQueryCache(options: QueryCacheOptions) {
+  const now = options.now ?? Date.now;
+  const entries = new Map<string, { data: unknown; ts: number }>();
+
+  async function cached<T>(key: string, fn: () => Promise<T>): Promise<T> {
+    const hit = entries.get(key);
+    if (hit && now() - hit.ts < options.ttlMs) {
+      return hit.data as T;
+    }
+
+    const data = await fn();
+    entries.set(key, { data, ts: now() });
+
+    while (entries.size > options.maxEntries) {
+      const oldestKey = entries.keys().next().value;
+      if (oldestKey === undefined) break;
+      entries.delete(oldestKey);
+    }
+
+    return data;
+  }
+
+  function clear() {
+    entries.clear();
+  }
+
+  return { cached, clear };
+}
+
+export const queryCache = createQueryCache({
+  ttlMs: 120_000,
+  maxEntries: 500,
+});