import Redis from "ioredis";
import { config } from "../config";

let _redis: Redis | null = null;

export function redis(): Redis {
  if (!_redis) {
    _redis = new Redis(config.redisUrl, { maxRetriesPerRequest: 2, enableOfflineQueue: true, lazyConnect: false });
    _redis.on("error", (e) => console.error("[redis]", e.message));
  }
  return _redis;
}

export async function pingRedis(): Promise<number> {
  const t = Date.now();
  await redis().ping();
  return Date.now() - t;
}

export async function closeRedis(): Promise<void> {
  if (_redis) {
    await _redis.quit();
    _redis = null;
  }
}

/**
 * Sliding-window rate limit (fixed window with two buckets). Returns retry-after
 * seconds when exceeded, else 0.
 */
export async function rateLimit(key: string, limit: number, windowSec: number): Promise<number> {
  const r = redis();
  const now = Math.floor(Date.now() / 1000);
  const bucket = Math.floor(now / windowSec);
  const k = `rl:${key}:${bucket}`;
  const prevK = `rl:${key}:${bucket - 1}`;
  const [[, cur], [, prev]] = (await r.multi().incr(k).get(prevK).exec()) as [[null, number], [null, string | null]];
  if (cur === 1) await r.expire(k, windowSec * 2);
  const elapsed = (now % windowSec) / windowSec;
  const weighted = cur + Number(prev ?? 0) * (1 - elapsed);
  if (weighted > limit) return Math.max(1, windowSec - (now % windowSec));
  return 0;
}

export async function setJson(key: string, value: unknown, ttlSec: number): Promise<void> {
  await redis().set(key, JSON.stringify(value), "EX", ttlSec);
}

export async function getJson<T>(key: string): Promise<T | null> {
  const v = await redis().get(key);
  return v ? (JSON.parse(v) as T) : null;
}