import type { Ticker } from 'pixi.js';
import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
import { BackgroundBeat, beatDue, STALL_MS } from '../../src/viewport/backgroundBeat';

const page = { hidden: false };

/** A ticker that runs its listeners on `update`, as Pixi's does; `frame` is one the page drew itself. */
function fakeTicker() {
  const listeners = new Set<() => void>();
  const ticker = {
    updates: 0,
    add: (fn: () => void) => listeners.add(fn),
    remove: (fn: () => void) => listeners.delete(fn),
    update: () => {
      ticker.updates += 1;
      for (const fn of listeners) fn();
    },
    frame: () => {
      for (const fn of listeners) fn();
    },
  };
  return ticker;
}

describe('beatDue', () => {
  it('ticks a hidden page, and a page that has drawn no frame of its own for a while', () => {
    expect(beatDue(true, 0)).toBe(true);
    expect(beatDue(false, 16)).toBe(false);
    expect(beatDue(false, STALL_MS)).toBe(false);
    expect(beatDue(false, STALL_MS + 1)).toBe(true);
  });
});

describe('BackgroundBeat', () => {
  beforeEach(() => {
    vi.useFakeTimers({ toFake: ['setInterval', 'clearInterval', 'performance'] });
    page.hidden = false;
    vi.stubGlobal('document', {
      get hidden() {
        return page.hidden;
      },
    });
  });

  afterEach(() => {
    vi.useRealTimers();
    vi.unstubAllGlobals();
  });

  it('stands aside while the page draws, and ticks at the rate asked for once it is hidden', () => {
    const ticker = fakeTicker();
    const beat = new BackgroundBeat(ticker as unknown as Ticker);
    beat.start(60);
    for (let i = 0; i < 30; i++) {
      vi.advanceTimersByTime(16);
      ticker.frame();
    }
    expect(ticker.updates).toBe(0);
    page.hidden = true;
    vi.advanceTimersByTime(1600);
    expect(ticker.updates).toBe(96);
    expect(beat.ticks).toBe(96);
    beat.stop();
    vi.advanceTimersByTime(1600);
    expect(ticker.updates).toBe(96);
  });

  it('takes over a page that stopped drawing without saying it is hidden, until it draws again', () => {
    const ticker = fakeTicker();
    const beat = new BackgroundBeat(ticker as unknown as Ticker);
    beat.start(30);
    vi.advanceTimersByTime(STALL_MS - 10);
    expect(ticker.updates).toBe(0);
    // Its own ticks do not count as the page's frames: it goes on at every beat.
    vi.advanceTimersByTime(1000);
    expect(ticker.updates).toBe(30);
    const given = ticker.updates;
    ticker.frame();
    vi.advanceTimersByTime(200);
    expect(ticker.updates).toBe(given);
    beat.stop();
  });
});