export type Span = { entry: number; exit: number };

/**
 * When is a point at `p`, moving by `v` over the frame, inside [min, max]?
 *
 * Returns the entry/exit times (t, where the position is p + v*t).
 * `entry` is always <= `exit`. Values may be < 0 or > 1.
 *
 * Special case: if v === 0, return {entry:-Infinity, exit:Infinity} when the
 * point is already inside [min, max], otherwise return null.
 */
export function sweepInterval(
	p: number,
	v: number,
	min: number,
	max: number,
): Span | null {
	if (v === 0) {
		return isInBetween(p, min, max)
			? {
					entry: -Infinity,
					exit: +Infinity,
				}
			: null;
	}

	let t1 = (min - p) / v;
	let t2 = (max - p) / v;

	if (t1 > t2) {
		[t1, t2] = [t2, t1];
	}

	return {
		entry: t1,
		exit: t2,
	};
}

function isInBetween(p: number, min: number, max: number): boolean {
	return min <= p && p <= max;
}