// Finished in earlier steps — reuse, don't rewrite.
export type Vec = { x: number; y: number };
export const vec = (x: number, y: number): Vec => ({ x, y });

export type AABB = { x: number; y: number; w: number; h: number };
export type Span = { entry: number; exit: number };
export type Hit = { time: number; normal: Vec };

/** Step 05, finished. */
export function sweepInterval(
	p: number,
	v: number,
	min: number,
	max: number,
): Span | null {
	if (v === 0) {
		return min <= p && p <= 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 };
}

/** Step 06, finished. A moving point vs a static box. */
export function rayVsAABB(p: Vec, v: Vec, box: AABB): Hit | null {
	const spanX = sweepInterval(p.x, v.x, box.x, box.x + box.w);
	const spanY = sweepInterval(p.y, v.y, box.y, box.y + box.h);
	if (spanX === null || spanY === null) {
		return null;
	}

	const entry = Math.max(spanX.entry, spanY.entry);
	const exit = Math.min(spanX.exit, spanY.exit);
	if (entry > exit) {
		return null;
	}
	if (entry >= 1 || exit <= 0) {
		return null;
	}

	const normal =
		spanX.entry > spanY.entry
			? { x: v.x > 0 ? -1 : 1, y: 0 }
			: { x: 0, y: v.y > 0 ? -1 : 1 };

	return { time: entry, normal };
}