/**
 * SSR-safe synchronous read of a localStorage value with a typed parser.
 *
 * Use inside `useState(() => readLocalStoragePref(...))` so the first render
 * already has the persisted value — no useEffect-driven re-render flicker.
 *
 * On the server `window` is undefined → returns `fallback`. On the client the
 * raw value is parsed; if the parser returns `null` the fallback is used.
 * Hydration mismatches between server-rendered HTML (default) and the
 * client-rendered tree (persisted) are accepted: React adapts the DOM in the
 * same hydration pass without a visible flicker for matching values.
 */
export function readLocalStoragePref<T>(
  key: string,
  parse: (raw: string) => T | null,
  fallback: T,
): T {
  if (typeof window === 'undefined') return fallback
  const raw = window.localStorage.getItem(key)
  if (raw === null) return fallback
  return parse(raw) ?? fallback
}