// Smooth scroll Lenis — import dynamique, une seule instance, gate reduced-motion.
import { prefersReducedMotion } from './tokens';

type Lenis = { raf: (t: number) => void; destroy: () => void; scrollTo: (t: unknown, o?: unknown) => void };

let lenis: Lenis | null = null;
let rafId = 0;

export async function initSmoothScroll(): Promise<() => void> {
	if (prefersReducedMotion() || typeof window === 'undefined') return () => {};
	const { default: Lenis } = await import('lenis');
	lenis = new Lenis({ lerp: 0.11, wheelMultiplier: 1, smoothWheel: true }) as unknown as Lenis;
	const loop = (t: number) => {
		lenis?.raf(t);
		rafId = requestAnimationFrame(loop);
	};
	rafId = requestAnimationFrame(loop);
	return () => {
		cancelAnimationFrame(rafId);
		lenis?.destroy();
		lenis = null;
	};
}

/** Défilement vers une ancre (#id) en respectant Lenis si actif. */
export function scrollToAnchor(hash: string): void {
	const el = document.querySelector(hash);
	if (!el) return;
	if (lenis) lenis.scrollTo(el, { offset: -80 });
	else el.scrollIntoView({ behavior: 'smooth' });
}