/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */
// Stolen from https://svelte.dev/repl/c6a402704224403f96a3db56c2f48dfc?version=3.55.0
let intersectionObserver;

function ensureIntersectionObserver() {
	if (intersectionObserver) return;

	intersectionObserver = new IntersectionObserver((entries) => {
		entries.forEach((entry) => {
			const eventName = entry.isIntersecting ? 'enterViewport' : 'exitViewport';
			entry.target.dispatchEvent(new CustomEvent(eventName));
		});
	});
}

export default function viewport(element) {
	ensureIntersectionObserver();

	intersectionObserver.observe(element);

	return {
		destroy() {
			intersectionObserver.unobserve(element);
		}
	};
}