import { describe, expect, it } from 'vitest';
import {
  loadPhysics,
  PIXELS_PER_METRE,
  physicsStatus,
  type Rapier,
  toMetres,
  toPixels,
} from '../../src/runtime/physics/engine';

const STEP = 1 / 60;
const GRAVITY = 980;

/** A 400 × 20 px floor whose top is at y = 290, and a 32 px crate dropped from y = 0. */
function crateOverFloor(rapier: Rapier) {
  const world = new rapier.World({ x: 0, y: toMetres(GRAVITY) });
  world.timestep = STEP;
  const floor = world.createRigidBody(rapier.RigidBodyDesc.fixed().setTranslation(0, toMetres(300)));
  world.createCollider(rapier.ColliderDesc.cuboid(toMetres(200), toMetres(10)), floor);
  const crate = world.createRigidBody(rapier.RigidBodyDesc.dynamic().setTranslation(0, 0));
  world.createCollider(rapier.ColliderDesc.cuboid(toMetres(16), toMetres(16)), crate);
  const run = (steps: number) => {
    for (let i = 0; i < steps; i++) world.step();
  };
  const y = () => toPixels(crate.translation().y);
  return { world, crate, run, y };
}

describe('physics engine', () => {
  it('loads once and reports the Rapier version', async () => {
    const first = loadPhysics();
    expect(loadPhysics()).toBe(first);
    const rapier = await first;
    expect(rapier.version()).toBe('0.20.0');
    expect(physicsStatus()).toMatchObject({ state: 'ready', version: '0.20.0' });
  });

  it('converts at 100 px to the metre', () => {
    expect(PIXELS_PER_METRE).toBe(100);
    expect(toMetres(980)).toBe(9.8);
    expect(toPixels(toMetres(123.5))).toBeCloseTo(123.5, 10);
  });

  it('lets a crate fall freely in pixels per second squared', async () => {
    const { run, y, crate } = crateOverFloor(await loadPhysics());
    run(30);
    // ½ g t² = 122.5 px after half a second; the integrator lands about a pixel past it.
    expect(Math.abs(y() - 0.5 * GRAVITY * 0.25)).toBeLessThan(1.5);
    expect(toPixels(crate.linvel().y)).toBeCloseTo(GRAVITY * 0.5, 3);
  });

  it('keeps a crate resting on the floor', async () => {
    const { run, y, crate } = crateOverFloor(await loadPhysics());
    run(180);
    expect(Math.abs(y() - 274)).toBeLessThan(0.5);
    expect(Math.abs(toPixels(crate.linvel().y))).toBeLessThan(0.5);
    run(120);
    expect(Math.abs(y() - 274)).toBeLessThan(0.5);
  });
});