cinny/src/app/hooks/useReducedMotion.ts

import { useEffect, useState } from 'react';

const REDUCED_MOTION_QUERY = '(prefers-reduced-motion: reduce)';

const readReducedMotion = (): boolean =>
  typeof window !== 'undefined' &&
  typeof window.matchMedia === 'function' &&
  window.matchMedia(REDUCED_MOTION_QUERY).matches;

/**
 * Reactively tracks the OS `prefers-reduced-motion: reduce` setting.
 *
 * Unlike a one-off `window.matchMedia(...).matches` read, this subscribes to the
 * media query's `change` event, so toggling the OS setting mid-session updates
 * the returned value (and any animation gated on it) without a page reload.
 * SSR/undefined-safe: returns `false` when `window`/`matchMedia` is unavailable.
 */
export function useReducedMotion(): boolean {
  const [reduced, setReduced] = useState<boolean>(readReducedMotion);

  useEffect(() => {
    if (typeof window === 'undefined' || typeof window.matchMedia !== 'function') {
      return undefined;
    }
    const mql = window.matchMedia(REDUCED_MOTION_QUERY);
    const onChange = (event: MediaQueryListEvent) => setReduced(event.matches);
    // Re-sync in case the setting changed between the initial render and this effect.
    setReduced(mql.matches);
    mql.addEventListener('change', onChange);
    return () => mql.removeEventListener('change', onChange);
  }, []);

  return reduced;
}