cache-handler.mjs

// ============================================================
// Vercel Remote Cache Handler — ISR + Data Cache
// ============================================================
// This file is referenced by next.config.ts via the
// `cacheHandler` option. It stores ISR-rendered pages and
// fetch() cache in Upstash Redis so they survive deployments
// and are shared across all Vercel regions.
//
// Falls back to the default in-memory cache when Redis is
// unavailable (local dev, build phase).
// ============================================================

import { Redis } from "@upstash/redis";

const redisUrl = process.env.UPSTASH_REDIS_REST_URL;
const redisToken = process.env.UPSTASH_REDIS_REST_TOKEN;
const hasRedis = !!(redisUrl && redisToken);

const redis = hasRedis
  ? new Redis({ url: redisUrl, token: redisToken })
  : null;

const PREFIX = "suplecost:isr:";

export default class RemoteCache {
  /** @type {Map<string, any>} */
  _cache = new Map();

  async get(key) {
    // Try local (fast path) first
    const local = this._cache.get(key);
    if (local !== undefined) return local;

    // Fall back to Redis
    if (redis) {
      try {
        const val = await redis.get(`${PREFIX}${key}`);
        if (val !== null && val !== undefined) {
          // Warm local cache
          this._cache.set(key, val);
          return val;
        }
      } catch {
        // Redis unavailable — fall back
      }
    }

    return null;
  }

  async set(key, value, { ttl } = {}) {
    // Always store locally
    this._cache.set(key, value);

    // Fire-and-forget to Redis
    if (redis) {
      const redisKey = `${PREFIX}${key}`;
      if (ttl) {
        redis.set(redisKey, value, { ex: ttl }).catch(() => {});
      } else {
        redis.set(redisKey, value).catch(() => {});
      }
    }
  }

  async revalidateTag(tag) {
    // Tags are stored as keys under suplecost:isr:tag:{tag}
    // Invalidation is handled by the app-level cache system.
    // For ISR tag-based revalidation, clear the local cache
    // and let the app's revalidation logic handle Redis.
    this._cache.clear();
  }

  async resetRequestCache() {
    // Called per-request — no-op for persistent cache
  }
}