/**
 * `On fixed update`: 60 steps a second of game time, each with dt 1/60, however the frames fall –
 * counted by the same rule the physics steps by.
 */
import { describe, expect, it } from 'vitest';
import { SetAssetPropertyCommand } from '../../src/core/commands/assetCommands';
import { FIXED_STEP, fixedSteps, MAX_FIXED_STEPS } from '../../src/core/time';
import { graphEditor, makeBehavior, makeSpriteScene, place, startWorld } from '../helpers';

describe('fixed steps', () => {
  it('spends a frame in steps of 1/60 and keeps the rest for the next', () => {
    expect(fixedSteps(0, FIXED_STEP).steps).toBe(1);
    expect(fixedSteps(0, 1 / 30).steps).toBe(2);
    expect(fixedSteps(0, 0).steps).toBe(0);
    const half = fixedSteps(0, 1 / 120);
    expect(half.steps).toBe(0);
    expect(fixedSteps(half.backlog, 1 / 120).steps).toBe(1);
  });

  it('adds up to the time that passed, however uneven the frames', () => {
    let backlog = 0;
    let steps = 0;
    for (let i = 0; i < 20; i++)
      for (const dt of [0.01, 0.02, 0.005, 0.015]) {
        const next = fixedSteps(backlog, dt);
        backlog = next.backlog;
        steps += next.steps;
      }
    expect(steps).toBe(60);
  });

  it('catches up a hitch only so far and forgets the rest', () => {
    expect(fixedSteps(0, 1)).toEqual({ steps: MAX_FIXED_STEPS, backlog: 0 });
  });
});

/** A behavior logging `fixed <dt of the event> <dt a node reads>` per step and `update` per frame. */
function stepped(runWhilePaused = false) {
  const f = makeSpriteScene('Box');
  const behavior = makeBehavior(f, 'Engine');
  if (runWhilePaused) f.stack.execute(new SetAssetPropertyCommand(behavior.id, 'runWhilePaused', true));
  const edit = graphEditor(f, behavior);
  const fixed = edit.addNode('OnFixedUpdate');
  const eventDt = edit.addNode('Log');
  const nodeDt = edit.addNode('Log');
  const update = edit.addNode('OnUpdate');
  edit.wire([
    [fixed, 'exec', eventDt, 'exec'],
    [fixed, 'dt', eventDt, 'message'],
    [eventDt, 'exec', nodeDt, 'exec'],
    [edit.addNode('Time'), 'dt', nodeDt, 'message'],
    [update, 'exec', edit.addNode('Log', { message: 'update' }), 'exec'],
  ]);
  place(f, behavior.id, { x: 0, y: 0 });
  return startWorld(f, { behaviors: true });
}

const STEP = String(FIXED_STEP);

describe('On fixed update', () => {
  it('runs once per 1/60 of game time, before On update, and dt inside is the step', () => {
    const { world, frame } = stepped();
    frame(1 / 30);
    expect(world.log).toEqual([STEP, STEP, STEP, STEP, 'update']);

    world.log.length = 0;
    frame(1 / 120);
    expect(world.log).toEqual(['update']);
    frame(1 / 120);
    expect(world.log).toEqual(['update', STEP, STEP, 'update']);
  });

  it('stands still while the game is paused, also for a behavior that runs then', () => {
    const { world, frame } = stepped(true);
    world.paused = true;
    frame(1 / 30);
    frame(1 / 30);
    expect(world.log).toEqual(['update', 'update']);
  });
});