teknav-bak/app/backend/src/lib/cache.ts

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;
}