import { Ratelimit } from '@upstash/ratelimit';
import { Redis } from '@upstash/redis';

// Lazy singleton. Module-load init would throw in environments without
// Upstash env vars (local dev pre-onboarding, tests that transitively
// import the auth handlers, Vercel build-time bundling). Defer construction
// until the first request actually arrives.
let cached = null;

function init() {
  // Env-var names match Vercel's Upstash Marketplace integration, which
  // auto-provisions KV_REST_API_URL and KV_REST_API_TOKEN. See
  // https://upstash.com/docs/redis/howto/vercelintegration. Single-source-
  // of-truth — do NOT alias to UPSTASH_REDIS_REST_*.
  const url = process.env.KV_REST_API_URL;
  const token = process.env.KV_REST_API_TOKEN;

  if (url && token) {
    const redis = new Redis({ url, token });
    const ratelimit = new Ratelimit({
      redis,
      limiter: Ratelimit.slidingWindow(5, '15 m'),
      prefix: 'tcgvault:auth',
    });
    return { mode: 'live', ratelimit };
  }

  if (process.env.NODE_ENV === 'production') {
    // Fail-closed in production. A single failed login is a better outcome
    // than silently disabling brute-force protection on the live site.
    throw new Error(
      '[rate-limit] Upstash not configured. Set KV_REST_API_URL and KV_REST_API_TOKEN in the deployment environment (auto-provisioned by the Vercel Upstash Marketplace integration) before serving auth traffic.'
    );
  }

  console.warn(
    '[rate-limit] KV_REST_API_URL / KV_REST_API_TOKEN not set — rate limiting disabled (dev/test only)'
  );
  return { mode: 'noop' };
}

function extractIdentifier(req) {
  const xff = req.headers?.['x-forwarded-for'];
  const firstHop = Array.isArray(xff) ? xff[0] : xff?.split(',')[0]?.trim();
  return firstHop || req.socket?.remoteAddress || 'anonymous';
}

export async function checkAuthRateLimit(req) {
  if (!cached) {
    cached = init();
  }

  if (cached.mode === 'noop') {
    return { allowed: true, remaining: Infinity, reset: 0 };
  }

  const identifier = extractIdentifier(req);

  try {
    const { success, remaining, reset } = await cached.ratelimit.limit(identifier);
    return { allowed: success, remaining, reset };
  } catch (err) {
    // Fail-open on Upstash outage. A hard outage at the rate-limit backend
    // should not lock the entire user base out of login. Brute-force
    // protection lives behind defense-in-depth (Vercel firewall, etc.).
    console.error('[rate-limit]', err);
    return { allowed: true, remaining: Infinity, reset: 0 };
  }
}