import { ensureNavId, peekNavId } from "./history";
import { createStore } from "./store";

// A one-shot "…and surprise me straight away" request for the Home surface (E24), handed over by
// callers that cannot reach its state — today the command palette's "Meglepetés".
//
// A TOKEN that waits, not an event that fires: Home is a lazy module and is normally NOT mounted
// when the request is made (the palette navigates to it in the same click), so an event would be
// shouted into an empty room. Home takes the token on arrival, which clears it.
//
// The token is the HISTORY ENTRY it was requested for, and Home honours it only on that entry. A
// plain counter outlived a navigation that never mounted Home — a lazy chunk that failed, a Back
// before the module arrived — and replayed on the next visit, an hour later: the page deciding on
// its own that the answer you came back for was wrong. So it is minted AFTER the push
// (`setPage`'s `then`), on the entry the push made; Home mounting on any other entry drops it.
const surprise = createStore<number | null>(null);

/** Ask Home to reroll its hero on THIS history entry. Call it once the navigation to Home has
 *  pushed — `setPage("home", requestSurprise)` — so the token names Home's own entry. */
export const requestSurprise = (): void => surprise.set(ensureNavId());

/** The pending token (null = nothing pending) — the render subscription that wakes Home up. Home only. */
export const useSurpriseRequest = (): number | null => surprise.use();

/** Take the pending request, clearing it; true only when it was requested for the entry Home is on.
 *
 *  Compare-and-clear rather than a plain read + `consume()`, because a reroll is NOT idempotent — it
 *  spends a `/discover/pick` and steps the tier rotation — and React 18's StrictMode invokes a mount
 *  effect twice with the same render snapshot. Measured in the browser (2026-09-07): the palette's
 *  "Meglepetés" from another module arrived at Home as `start=2`, two picks deep, before the page had
 *  painted once. Checking the LIVE store is what makes the second pass a no-op. */
export const takeSurprise = (): boolean => {
  const entry = surprise.get();
  if (entry === null) return false;
  surprise.set(null);
  return entry === peekNavId();
};