import { lerp } from "./lerp.ts";
import type { Vector } from "./Vector.ts";

export type Segment = [Vector, Vector];

export type SegmentIntersection = {
	position: Vector;
	offset: number;
};

export function createSegmentIntersection(): SegmentIntersection {
	return {
		position: {
			x: Number.NaN,
			y: Number.NaN,
		},
		offset: Number.NaN,
	};
}

export function setSegmentIntersection(
	segmentIntersection: SegmentIntersection,
	a: Segment,
	b: Segment,
): void {
	const bottom =
		(b[1].y - b[0].y) * (a[1].x - a[0].x) -
		(b[1].x - b[0].x) * (a[1].y - a[0].y);

	if (bottom === 0) {
		segmentIntersection.position.x = Number.NaN;
		segmentIntersection.position.y = Number.NaN;
		segmentIntersection.offset = Number.NaN;

		return;
	}

	const tTop =
		(b[1].x - b[0].x) * (a[0].y - b[0].y) -
		(b[1].y - b[0].y) * (a[0].x - b[0].x);
	const uTop =
		(b[0].y - a[0].y) * (a[0].x - a[1].x) -
		(b[0].x - a[0].x) * (a[0].y - a[1].y);

	const t = tTop / bottom;
	const u = uTop / bottom;

	if (t < 0 || t > 1 || u < 0 || u > 1) {
		segmentIntersection.position.x = Number.NaN;
		segmentIntersection.position.y = Number.NaN;
		segmentIntersection.offset = Number.NaN;

		return;
	}

	segmentIntersection.position.x = lerp(a[0].x, a[1].x, t);
	segmentIntersection.position.y = lerp(a[0].y, a[1].y, t);
	segmentIntersection.offset = t;
}

export function drawSegment(
	segment: Segment,
	ctx: CanvasRenderingContext2D,
	color: string,
): void {
	ctx.lineWidth = 2;
	ctx.strokeStyle = color;
	ctx.beginPath();
	ctx.moveTo(segment[0].x, segment[0].y);
	ctx.lineTo(segment[1].x, segment[1].y);
	ctx.stroke();
}