const LINE_PARALLEL_EPSILON = 1e-10;

export function lineEdgeIntersection({
	lineX,
	lineY,
	normalX,
	normalY,
	x1,
	y1,
	x2,
	y2,
}: {
	lineX: number;
	lineY: number;
	normalX: number;
	normalY: number;
	x1: number;
	y1: number;
	x2: number;
	y2: number;
}): { x: number; y: number } | null {
	const distance1 = halfPlaneSign({
		lineX,
		lineY,
		normalX,
		normalY,
		x: x1,
		y: y1,
	});
	const distance2 = halfPlaneSign({
		lineX,
		lineY,
		normalX,
		normalY,
		x: x2,
		y: y2,
	});
	const denom = distance1 - distance2;
	if (Math.abs(denom) < LINE_PARALLEL_EPSILON) return null;
	const t = distance1 / denom;
	if (t < 0 || t > 1) return null;
	return {
		x: x1 + (x2 - x1) * t,
		y: y1 + (y2 - y1) * t,
	};
}

export function halfPlaneSign({
	lineX,
	lineY,
	normalX,
	normalY,
	x,
	y,
}: {
	lineX: number;
	lineY: number;
	normalX: number;
	normalY: number;
	x: number;
	y: number;
}): number {
	return (x - lineX) * normalX + (y - lineY) * normalY;
}