Import source: app/backend/src/lib/cache

Import the existing local project snapshot. This commit organizes existing files; it does not represent newly developed functionality.

app/backend/src/lib/cache.ts

@@ -0,0 +1,54 @@
+import { redis } from '../redis.js';
+
+export interface CacheOptions {
+  ttlSeconds: number;
+  graceSeconds?: number;
+}
+
+export async function cached<T>(key: string, ttlSeconds: number | CacheOptions, fetcher: () => Promise<T>): Promise<T> {
+  const opts: CacheOptions = typeof ttlSeconds === 'number'
+    ? { ttlSeconds }
+    : ttlSeconds;
+
+  const graceSeconds = opts.graceSeconds ?? Math.max(Math.floor(opts.ttlSeconds * 0.25), 30);
+  const totalTtl = opts.ttlSeconds + graceSeconds;
+
+  const hit = await redis.get(key);
+  if (hit !== null) {
+    try {
+      const parsed = JSON.parse(hit) as T;
+      const ttlRemaining = await redis.ttl(key);
+      if (ttlRemaining >= 0 && ttlRemaining <= graceSeconds) {
+        fetcher()
+          .then((fresh) => {
+            if (fresh !== undefined) {
+              redis.set(key, JSON.stringify(fresh), 'EX', totalTtl).catch(() => {});
+            }
+          })
+          .catch(() => {});
+      }
+      return parsed;
+    } catch {
+      await redis.del(key);
+    }
+  }
+
+  const fresh = await fetcher();
+  if (fresh !== undefined) {
+    await redis.set(key, JSON.stringify(fresh), 'EX', totalTtl);
+  }
+  return fresh;
+}
+
+export async function bust(pattern: string): Promise<number> {
+  let cursor = '0';
+  let removed = 0;
+  do {
+    const [next, batch] = await redis.scan(cursor, 'MATCH', pattern, 'COUNT', 100);
+    cursor = next;
+    if (batch.length > 0) {
+      removed += await redis.del(...batch);
+    }
+  } while (cursor !== '0');
+  return removed;
+}