/* eslint-disable @typescript-eslint/no-require-imports -- Next loads cache handlers as CommonJS modules. */
const { createHash } = require("node:crypto");
const RedisModule = require("ioredis");

const Redis = RedisModule.default || RedisModule;
const pendingSets = new Map();
let redis;

function getRedis() {
  if (!process.env.REDIS_URL) {
    throw new Error("REDIS_URL is required for the remote cache handler.");
  }
  if (!redis) {
    redis = new Redis(process.env.REDIS_URL, {
      lazyConnect: true,
      maxRetriesPerRequest: 1,
      enableOfflineQueue: false,
    });
    redis.on("error", () => undefined);
  }
  if (redis.status === "wait") return redis.connect().then(() => redis);
  return Promise.resolve(redis);
}

function prefix() {
  return process.env.REDIS_CACHE_PREFIX || "buzz:next-cache";
}

function entryKey(cacheKey) {
  return `${prefix()}:entry:${createHash("sha256").update(cacheKey).digest("hex")}`;
}

function tagKey() {
  return `${prefix()}:tag-timestamps`;
}

function streamFromBase64(value) {
  const bytes = Buffer.from(value, "base64");
  return new ReadableStream({
    start(controller) {
      controller.enqueue(bytes);
      controller.close();
    },
  });
}

async function readTagStates(client, tags) {
  if (tags.length === 0) return [];
  const values = await client.hmget(tagKey(), ...tags);
  return values.map((value) => {
    if (!value) return {};
    try {
      return JSON.parse(value);
    } catch {
      return {};
    }
  });
}

module.exports = {
  async get(cacheKey, softTags) {
    try {
      const pending = pendingSets.get(cacheKey);
      if (pending) await pending;
      const client = await getRedis();
      const stored = await client.get(entryKey(cacheKey));
      if (!stored) return undefined;
      const entry = JSON.parse(stored);
      const maxAge = process.env.__NEXT_DEV_SERVER
        ? Math.max(entry.expire, 30)
        : entry.revalidate;
      if (Date.now() > entry.timestamp + maxAge * 1000) return undefined;

      const tags = [...new Set([...(entry.tags || []), ...(softTags || [])])];
      const states = await readTagStates(client, tags);
      if (states.some((state) => Number(state.expired || 0) > entry.timestamp)) {
        return undefined;
      }
      const stale = states.some(
        (state) => Number(state.stale || 0) > entry.timestamp,
      );
      return {
        value: streamFromBase64(entry.value),
        tags: entry.tags,
        stale: entry.stale,
        timestamp: entry.timestamp,
        expire: entry.expire,
        revalidate: stale ? -1 : entry.revalidate,
      };
    } catch {
      return undefined;
    }
  },

  async set(cacheKey, pendingEntry) {
    let resolvePending = () => undefined;
    const pending = new Promise((resolve) => {
      resolvePending = resolve;
    });
    pendingSets.set(cacheKey, pending);
    try {
      const entry = await pendingEntry;
      if (!process.env.__NEXT_DEV_SERVER && entry.expire === 0) return;
      const reader = entry.value.getReader();
      const chunks = [];
      let bytes = 0;
      const maximum = Number(process.env.REDIS_CACHE_MAX_ENTRY_BYTES || 5 * 1024 * 1024);
      try {
        while (true) {
          const chunk = await reader.read();
          if (chunk.done) break;
          const buffer = Buffer.from(chunk.value);
          bytes += buffer.byteLength;
          if (bytes > maximum) return;
          chunks.push(buffer);
        }
      } finally {
        reader.releaseLock();
      }
      const serialized = JSON.stringify({
        value: Buffer.concat(chunks).toString("base64"),
        tags: entry.tags,
        stale: entry.stale,
        timestamp: entry.timestamp,
        expire: entry.expire,
        revalidate: entry.revalidate,
      });
      const ttl = Number.isFinite(entry.expire)
        ? Math.max(1, Math.ceil(entry.expire))
        : 86400;
      const client = await getRedis();
      await client.set(entryKey(cacheKey), serialized, "EX", ttl);
    } catch {
      // Cache writes are best effort. The rendered response remains authoritative.
    } finally {
      resolvePending();
      pendingSets.delete(cacheKey);
    }
  },

  async refreshTags() {
    try {
      const client = await getRedis();
      await client.ping();
    } catch {
      // A Redis outage becomes cache misses, not a request failure.
    }
  },

  async getExpiration(tags) {
    try {
      const client = await getRedis();
      const states = await readTagStates(client, tags);
      return Math.max(...states.map((state) => Number(state.expired || 0)), 0);
    } catch {
      return 0;
    }
  },

  async updateTags(tags, durations) {
    try {
      const client = await getRedis();
      const now = Date.now();
      const pipeline = client.pipeline();
      for (const tag of tags) {
        const state = durations
          ? {
              stale: now,
              expired:
                durations.expire === undefined
                  ? undefined
                  : now + durations.expire * 1000,
            }
          : { expired: now };
        pipeline.hset(tagKey(), tag, JSON.stringify(state));
      }
      await pipeline.exec();
    } catch {
      // Outbox-driven invalidations retry independently.
    }
  },
};