/**
 * スクロールイベントを登録
 */
export default function setScrollEvent() {
	// IntersectionObserverをブラウザがサポートしているかどうか
	const isObserveSupported =
		window.IntersectionObserver && 'isIntersecting' in IntersectionObserverEntry.prototype;
	if ( ! isObserveSupported ) return;

	const observerOptions = {
		root: null,
		rootMargin: '0px',
		threshold: 0,
	};
	const scrollObserver = new IntersectionObserver( ( entries ) => {
		entries.forEach( ( entry ) => {
			toggleScrollClass( ! entry.isIntersecting );
		} );
	}, observerOptions );

	const theObserver = document.querySelector( '.l-scrollObserver' );
	scrollObserver.observe( theObserver );
}

function toggleScrollClass( isScrolled ) {
	if ( isScrolled ) {
		document.documentElement.setAttribute( 'data-scrolled', 'true' );
	} else {
		document.documentElement.setAttribute( 'data-scrolled', 'false' );
	}
}