export interface HealthChecks {
  pocketbase: "ok" | "down";
  supertokens: "ok" | "down";
}

export interface HealthSnapshot {
  status: "ok" | "degraded";
  checks: HealthChecks;
  checkedAt: string;
}

const CHECK_TTL_MS = 10_000;
const CHECK_TIMEOUT_MS = 2_000;

let cached: HealthSnapshot | null = null;
let refreshing: Promise<HealthSnapshot> | null = null;

const ping = async (url: string): Promise<boolean> => {
  try {
    const response = await fetch(url, { signal: AbortSignal.timeout(CHECK_TIMEOUT_MS) });
    return response.ok;
  } catch {
    return false;
  }
};

const runChecks = async (): Promise<HealthSnapshot> => {
  const [pocketbase, supertokens] = await Promise.all([
    ping(`${process.env.POCKETBASE_URL}/api/health`),
    ping(`${process.env.SUPERTOKENS_URI}/hello`),
  ]);

  cached = {
    status: pocketbase && supertokens ? "ok" : "degraded",
    checks: {
      pocketbase: pocketbase ? "ok" : "down",
      supertokens: supertokens ? "ok" : "down",
    },
    checkedAt: new Date().toISOString(),
  };
  return cached;
};

// Stale-while-revalidate: k8s probes get the cached snapshot instantly while a
// refresh runs in the background; only the very first request awaits a check.
export const getHealthSnapshot = async (): Promise<HealthSnapshot> => {
  if (cached && Date.now() - Date.parse(cached.checkedAt) < CHECK_TTL_MS) {
    return cached;
  }
  if (!refreshing) {
    refreshing = runChecks().finally(() => {
      refreshing = null;
    });
  }
  return cached ?? refreshing;
};