import { expect, test } from "vitest";
import { dot, vec } from "./given.ts";
import { slide } from "./slide.ts";

test("vertical wall kills horizontal motion, keeps vertical", () => {
	// moving (10,5) into a wall with normal (-1,0)
	const s = slide(vec(10, 5), vec(-1, 0));
	expect(s.x).toBeCloseTo(0);
	expect(s.y).toBeCloseTo(5);
});

test("horizontal wall kills vertical motion, keeps horizontal", () => {
	const s = slide(vec(10, 5), vec(0, -1));
	expect(s.x).toBeCloseTo(10);
	expect(s.y).toBeCloseTo(0);
});

test("result always runs along the wall (perpendicular to the normal)", () => {
	// a diagonal (unit) normal: 0.36 + 0.64 = 1
	const normal = vec(-0.6, -0.8);
	const s = slide(vec(10, 0), normal);
	// the slid velocity has no component into the wall -> dot with normal is 0
	expect(dot(s, normal)).toBeCloseTo(0);
});