export default (el, binding) => {
	let total = document.getElementById(binding).offsetTop;
	let distance = document.documentElement.scrollTop || document.body.scrollTop;
	let step = total / 50;
	if (total > distance) {
		(function smoothDown() {
			if (distance < total) {
				distance += step;
				document.documentElement.scrollTop = distance;
				setTimeout(smoothDown, 5);
			} else {
				document.documentElement.scrollTop = total;
			}
		})();
	} else {
		let newTotal = distance - total;
		step = newTotal / 50;
		(function smoothUp() {
			if (distance > total) {
				distance -= step;
				document.documentElement.scrollTop = distance;
				setTimeout(smoothUp, 5);
			} else {
				document.documentElement.scrollTop = total;
			}
		})();
	}
}