Booking engines and API integration for travel brands.

// Retryable hotel-inventory fetch with in-memory cache + circuit breaker
// Runs on Node.js 20+ — no external deps beyond your HTTP client of choice.

type InventoryRequest = { hotelCode: string; checkIn: string; nights: number };
type InventoryResult = { rate: number; currency: string; roomType: string }[];

const CACHE_TTL_MS = 45_000; // stale-fast — supplier prices change every ~60s
const cache = new Map<string, { at: number; data: InventoryResult }>();

const breaker = { failures: 0, openedAt: 0 };
const OPEN_AFTER = 5;
const OPEN_FOR_MS = 30_000;

function key(r: InventoryRequest) {
  return `${r.hotelCode}|${r.checkIn}|${r.nights}`;
}

async function fetchWithTimeout(url: string, opts: RequestInit, ms = 2500) {
  const ctrl = new AbortController();
  const t = setTimeout(() => ctrl.abort(), ms);
  try {
    return await fetch(url, { ...opts, signal: ctrl.signal });
  } finally {
    clearTimeout(t);
  }
}

export async function getInventory(
  req: InventoryRequest,
): Promise<InventoryResult> {
  // 1. Serve from cache when fresh — supplier calls cost money and quota.
  const hit = cache.get(key(req));
  if (hit && Date.now() - hit.at < CACHE_TTL_MS) return hit.data;

  // 2. Short-circuit when the supplier is unhealthy.
  if (
    breaker.failures >= OPEN_AFTER &&
    Date.now() - breaker.openedAt < OPEN_FOR_MS
  ) {
    if (hit) return hit.data; // serve stale rather than block the page
    throw new Error("supplier_unavailable");
  }

  try {
    const res = await fetchWithTimeout(
      `https://api.supplier.example/hotels/${req.hotelCode}/rates`,
      {
        headers: { Authorization: `Bearer ${process.env.SUPPLIER_TOKEN!}` },
      },
    );
    if (!res.ok) throw new Error(`supplier_${res.status}`);
    const data: InventoryResult = await res.json();
    cache.set(key(req), { at: Date.now(), data });
    breaker.failures = 0;
    return data;
  } catch (err) {
    breaker.failures += 1;
    if (breaker.failures === OPEN_AFTER) breaker.openedAt = Date.now();
    if (hit) return hit.data; // graceful stale fallback
    throw err;
  }
}