import * as React from 'react';

/** Where the collapsed/expanded choice is remembered between visits. */
const RAIL_KEY = 'cbar-showcase:rail';

/**
 * Is the desktop rail on screen?
 *
 * Deliberately **not** in the hash, unlike `theme` and `lang`. Those describe
 * the view being shared; whether the person sending the link happened to have
 * the rail collapsed is not something the person opening it should inherit —
 * the same reasoning `Sidebar` already applies to the drawer's `open`.
 *
 * But it is a preference rather than a gesture: someone who collapses the rail
 * to read a wide matrix means it for the session and the next one, not for one
 * page. That is why this is the showcase's first piece of `localStorage`
 * (`use-tour.ts` follows it), and why it lives here rather than being
 * re-derived per component. Every access is wrapped, because storage throws
 * outright in a Safari private window rather than returning null.
 *
 * Its own file rather than `sidebar.tsx` because its only consumer is
 * `app.tsx` — the shell owns the layout, `Sidebar` only draws inside it.
 */
export function useRailVisible(): [boolean, () => void] {
  const [visible, setVisible] = React.useState(() => {
    try {
      return window.localStorage.getItem(RAIL_KEY) !== 'hidden';
    } catch {
      return true;
    }
  });

  /* In an effect rather than inside the updater: React runs an updater twice
     under StrictMode, and a write is not the sort of thing to do twice. */
  React.useEffect(() => {
    try {
      window.localStorage.setItem(RAIL_KEY, visible ? 'shown' : 'hidden');
    } catch {
      /* No storage — the toggle still works, it just forgets. */
    }
  }, [visible]);

  const toggle = React.useCallback(() => setVisible((current) => !current), []);

  return [visible, toggle];
}