import { useSyncExternalStore } from "react";

// The account a browser TAB is acting as (per-tab, in sessionStorage — see api.ts), plus its reactive
// wrapper. Its OWN module (imports nothing internal) so it can be shared by both `storage.ts` (which
// keys per-account localStorage on it) and `useAccountRehydrate.ts` without a circular import — the
// account id is a lower-level primitive than the storage helpers that consume it.
//
// ACTIVE_ACCOUNT_KEY is duplicated here rather than imported from api.ts so this stays dependency-free.
export const ACTIVE_ACCOUNT_KEY = "siftlode.activeAccount";

export function activeAccountId(): number | null {
  try {
    const raw = sessionStorage.getItem(ACTIVE_ACCOUNT_KEY);
    if (!raw) return null;
    const n = Number(raw);
    return Number.isFinite(n) ? n : null;
  } catch {
    return null;
  }
}

// Append `?account=<active>` to a top-level navigation URL (SEC-11). XHRs carry the active account in
// the X-Siftlode-Account header, but a full-page navigation (window.location) can't, so the OAuth
// link/upgrade GETs would resolve to the SESSION DEFAULT account instead of the tab's active one — the
// identity/token would then land on the wrong account. This threads the active account through the URL
// so resolved_user_id picks it. No-op when there's no distinct active account pinned yet.
export function withActiveAccount(path: string): string {
  const id = activeAccountId();
  if (id == null) return path;
  return `${path}${path.includes("?") ? "&" : "?"}account=${id}`;
}

// Reactive active-account. setActiveAccount/clearActiveAccount write sessionStorage — a silent op that
// triggers no React render — so this tab's per-account state (sort/filter/view/layout, all keyed by the
// account) would never re-read once the account is finally known. That bites exactly once, on first
// load: the provider tree above <App> mounts with NO account, then <App> pins it after /api/me resolves.
// The account setters call notifyActiveAccountChange() so useActiveAccountId subscribers can re-hydrate.
const accountListeners = new Set<() => void>();
function subscribeActiveAccount(cb: () => void): () => void {
  accountListeners.add(cb);
  return () => accountListeners.delete(cb);
}
export function notifyActiveAccountChange(): void {
  for (const cb of [...accountListeners]) cb();
}
/** The current tab's active account id, as reactive state — re-renders when it is (re)pinned. The
 * snapshot is a primitive (number | null), so useSyncExternalStore's Object.is check is stable. */
export function useActiveAccountId(): number | null {
  return useSyncExternalStore(subscribeActiveAccount, activeAccountId, activeAccountId);
}