import {
	type AABB,
	add,
	EPSILON,
	type Hit,
	scale,
	slide,
	sweptAABB,
	type Vec,
} from "./given.ts";

/**
 * Move `box` by the full-frame displacement `v`, sliding along any `walls` it
 * hits, up to 4 iterations. Returns the final corner position.
 *
 * See the README for the algorithm. You already have everything you need in
 * given.ts: sweptAABB, slide, add, scale, EPSILON.
 */
export function moveAndSlide(box: AABB, v: Vec, walls: AABB[]): Vec {
	let pos: Vec = { x: box.x, y: box.y };
	let vel: Vec = { x: v.x, y: v.y };

	let timeLeft = 1;
	let i = 0;
	while (i++ < 4 && timeLeft > 0) {
		const move = scale(vel, timeLeft);
		let nearest: Hit = {
			normal: { x: 0, y: 0 },
			time: 2,
		};

		for (const wall of walls) {
			const hit = sweptAABB(
				{
					x: pos.x,
					y: pos.y,
					w: box.w,
					h: box.h,
				},
				move,
				wall,
			);
			if (hit !== null) {
				nearest = hit.time < nearest.time ? hit : nearest;
			}
		}

		if (nearest.time === 2) {
			pos = add(pos, move);
			break;
		} else {
			pos = add(pos, scale(move, Math.max(0, nearest.time - EPSILON)));
			vel = slide(vel, nearest.normal);
			timeLeft = timeLeft * (1 - nearest.time);
		}
	}

	return pos;
}