const kMillisecondsPerDay = 1000 * 60 * 60 * 24;

export function daysBetween(a, b) {
	console.assert(a instanceof Date, a);
	console.assert(b instanceof Date, b);

	return Math.ceil((b.getTime() - a.getTime()) / kMillisecondsPerDay);
}



export function fromCalendarDateString(string) {
	console.assert(typeof string === "string", string);
	console.assert(string.length === 8, string);

	let year = parseInt(string.substring(0, 4));
	console.assert(!isNaN(year), string);

	let month = parseInt(string.substring(4, 6)) - 1;
	console.assert(!isNaN(month), string);

	let day = parseInt(string.substring(6, 8));
	console.assert(!isNaN(day), string);

	return new Date(Date.UTC(year, month, day));
}



export function toCalendarDateString(date) {
	console.assert(date instanceof Date, date);

	return String(date.getUTCFullYear()) + String(date.getUTCMonth() + 1).padStart(2, "0") + String(date.getUTCDate()).padStart(2, "0");
}