/**
 * Authentication Manager
 */

const REFRESH_URL = '/auth/refresh';
const PING_URL = '/auth/ping';
const TOKEN_EXPIRY_BUFFER_MS = 60 * 1000;
const PING_INTERVAL_MS = 60 * 1000;

let tokenExpiresAt: number | null = null;
let refreshPromise: Promise<boolean> | null = null;

export function recordExpiry(expiresIn: number | null | undefined): void {
  tokenExpiresAt = expiresIn != null ? Date.now() + expiresIn * 1000 : null;
}

function isTokenExpiredOrExpiring(): boolean {
  if (tokenExpiresAt === null) return false;
  return Date.now() >= tokenExpiresAt - TOKEN_EXPIRY_BUFFER_MS;
}

async function refreshToken(): Promise<boolean> {
  if (refreshPromise) return refreshPromise;

  refreshPromise = fetch(REFRESH_URL, { method: 'POST', credentials: 'include' })
    .then(async r => {
      if (!r.ok) return false;
      try {
        const body = await r.clone().json();
        recordExpiry(body?.expires_in);
      } catch { /* ignore parse errors */ }
      return true;
    })
    .catch(() => false)
    .finally(() => { refreshPromise = null; });

  return refreshPromise;
}

/**
 * Ensures the token is fresh before a request fires.
 */
export async function ensureFreshToken(): Promise<void> {
  if (isTokenExpiredOrExpiring()) {
    await refreshToken();
  }
}

export interface SessionMonitorOptions {
  onLogout: () => void | Promise<void>;
}

export function createSessionMonitor(options: SessionMonitorOptions) {
  let intervalId: ReturnType<typeof setInterval> | null = null;

  async function ping(): Promise<void> {
    // GET ping — no body, no CSRF needed, just confirm the session cookie is still valid
    const response = await fetch(PING_URL, { credentials: 'include' }).catch(() => null);

    if (!response?.ok) {
      // Session may be expired — attempt a token refresh before giving up
      const refreshed = await refreshToken();
      if (!refreshed) {
        stop();
        await options.onLogout();
      }
    }
  }

  function start(): void {
    if (intervalId !== null) return;
    intervalId = setInterval(ping, PING_INTERVAL_MS);
  }

  function stop(): void {
    if (intervalId === null) return;
    clearInterval(intervalId);
    intervalId = null;
  }

  return { start, stop };
}