station-master/test/step-queue.test.ts

/**
 * THE ANIMATION QUEUE — v0.8.0, `docs/plans/jitsi-common-board.md` § v0.8.0 §§ 5-6.
 *
 * Driven against REAL steps from a real game rather than hand-built fixtures, because the properties
 * that matter are about what actual play produces: a bot's whole switching turn arriving in one
 * burst, and a backlog that is mostly bookkeeping.
 */

import { describe, it } from 'node:test';
import assert from 'node:assert/strict';

import { legalActions } from '../src/engine/legal.ts';
import type { GameConfig } from '../src/engine/state.ts';
import { currentActor, newMultiplayerGame, submit } from '../src/web/game.ts';
import { publicSnapshot } from '../src/sim/view.ts';
import { takeSteps } from '../src/sim/display-step.ts';
import type { DisplayStep } from '../src/sim/display-step.ts';
import { createStepQueue } from '../src/web/step-queue.ts';
import { DWELL } from '../src/sim/pacing.ts';

const config: GameConfig = {
  mode: 'competitive',
  days: 5,
  minCombinedRevenue: 0,
  maxCollisionsPerDay: 0,
  maxCollisionsTotal: 0,
  pvpCardsAllowed: false,
  optionalRules: {
    reducedVisibility: false,
    employeeRotation: false,
    emergencyToolbox: false,
  },
};

/**
 * Plays a real game and returns its steps, preferring switch moves so a burst actually occurs.
 *
 * 400 moves, not 120: switching is not legal until there is track laid and a train in the district,
 * and on this seed the first `switch.move` is at move 144. A shorter run produces a queue with no
 * switching in it at all, which would make the pacing assertions here vacuous.
 */
function realSteps(seed: number, moves: number): { steps: DisplayStep[]; final: ReturnType<typeof publicSnapshot> } {
  const game = newMultiplayerGame(seed, config, ['Alice', 'Bob', 'Carol']);
  takeSteps(game.display);
  const steps: DisplayStep[] = [];
  for (let i = 0; i < moves; i++) {
    const actor = currentActor(game);
    if (actor === null) break;
    const options = legalActions(game.state, actor);
    if (options.length === 0) break;
    const move = options.find((o) => o.type.startsWith('switch.') && o.type !== 'switch.end');
    if (!submit(game, move ?? options.find((o) => o.type === 'localOps.choose') ?? options[0]!)) break;
    steps.push(...takeSteps(game.display));
  }
  return { steps, final: publicSnapshot(game.state) };
}

/** The baseline a queue starts from, matching what a connect push carries. */
function baseline(seed: number): ReturnType<typeof publicSnapshot> {
  const game = newMultiplayerGame(seed, config, ['Alice', 'Bob', 'Carol']);
  return publicSnapshot(game.state);
}

describe('the step queue', () => {
  it('shows the whole burst in order and lands on the real board', () => {
    const { steps, final } = realSteps(1917398, 400);
    assert.ok(steps.length > 30, `only ${steps.length} steps — this proved little`);

    const q = createStepQueue();
    q.reset(baseline(1917398));
    q.push(steps);

    // Run a clock forward until it settles, in 50ms ticks like a render loop would.
    let now = 0;
    for (let i = 0; i < 20_000 && q.busy(); i++) {
      q.advance(now);
      now += 50;
    }
    assert.equal(q.busy(), false, 'the queue never drained');
    assert.deepEqual(q.current(), final, 'the animated board did not land on the real one');
    assert.equal(q.showing()?.seq, steps[steps.length - 1]!.seq, 'the caption is not on the last step');
  });

  it('a burst of switching takes real time, and bookkeeping takes none', () => {
    const { steps } = realSteps(1917398, 400);
    const q = createStepQueue();
    q.reset(baseline(1917398));

    // Only the bookkeeping: it must all collapse into a single advance.
    // `.end` only: `localOps.choose` became an announcement worth watching after the first real play.
    const bookkeeping = steps.filter((s) => s.cause.endsWith('.end'));
    assert.ok(bookkeeping.length > 10, 'not enough bookkeeping steps to prove the collapse');
    q.push(bookkeeping);
    q.advance(0);
    q.advance(0);
    assert.equal(q.busy(), false, `${bookkeeping.length} bookkeeping steps should cost no time at all`);

    // And switching: each one must hold the screen.
    const switching = steps.filter((s) => s.cause.startsWith('switch.') && s.cause !== 'switch.end');
    assert.ok(switching.length >= 6, `only ${switching.length} switching steps found`);
    const q2 = createStepQueue();
    q2.reset(baseline(1917398));
    q2.push(switching.slice(0, 6));
    q2.advance(0);
    assert.equal(q2.behind(), 5, 'the first is shown at once; five are still to watch');
    q2.advance(DWELL.switching - 1);
    assert.equal(q2.behind(), 5, 'a switching move must not be replaced early');
    q2.advance(DWELL.switching);
    assert.equal(q2.behind(), 4, 'and must be replaced once its dwell is up');
  });

  it('counts only what will be watched, so the countdown is steady', () => {
    // The counter's whole purpose: a backlog of mostly-bookkeeping must not read as a huge number
    // that collapses the instant it starts.
    const { steps } = realSteps(1917398, 400);
    const q = createStepQueue();
    q.reset(baseline(1917398));
    q.push(steps);
    const behind = q.behind();
    assert.ok(behind > 0 && behind < steps.length, `behind ${behind} of ${steps.length} queued`);

    q.advance(0);
    let ticks = 0;
    let previous = q.behind();
    let now = 0;
    while (q.busy() && ticks++ < 20_000) {
      now += 50;
      q.advance(now);
      const nowBehind = q.behind();
      assert.ok(nowBehind <= previous, 'the counter must never go up while draining');
      previous = nowBehind;
    }
    assert.equal(q.behind(), 0);
  });

  it('skip jumps to the real board without losing a single state on the way', () => {
    const { steps, final } = realSteps(1917398, 400);
    const q = createStepQueue();
    q.reset(baseline(1917398));
    q.push(steps);
    q.advance(0);

    assert.equal(q.skip(), true, 'there was a backlog to skip');
    assert.equal(q.busy(), false);
    assert.equal(q.behind(), 0);
    // Skip applies every delta rather than jumping the chain, so the board is exact.
    assert.deepEqual(q.current(), final, 'skipping produced a board the game was never in');
    assert.equal(q.skip(), false, 'skipping an empty queue changes nothing');
  });

  it('pace 0 turns animation off entirely — TODO #18', () => {
    const { steps, final } = realSteps(1917398, 400);
    const q = createStepQueue(() => 0);
    q.reset(baseline(1917398));
    q.push(steps);
    // One advance at a single instant must consume everything: nothing dwells at all.
    q.advance(0);
    q.advance(0);
    assert.equal(q.busy(), false, 'with animation off, nothing may be left waiting');
    assert.equal(q.behind(), 0, 'nothing is "behind" when nothing is being animated');
    assert.deepEqual(q.current(), final);
  });

  it('pace scales the wait without changing the order', () => {
    const { steps } = realSteps(1917398, 400);
    const switching = steps.filter((s) => s.cause.startsWith('switch.') && s.cause !== 'switch.end').slice(0, 3);
    assert.equal(switching.length, 3);

    const half = createStepQueue(() => 0.5);
    half.reset(baseline(1917398));
    half.push(switching);
    half.advance(0);
    half.advance(DWELL.switching / 2);
    assert.equal(half.behind(), 1, 'at half pace, half the dwell should have advanced one step');
  });

  it('holds the LAST step of a burst for its dwell — the v0.8.0 snap-back bug', () => {
    /**
     * REGRESSION. `busy()` was `pending.length > 0`, so the instant the final step of a burst was
     * shown the queue reported idle: the animation loop stopped and the district panel snapped back
     * to the viewer's own board without that step ever being looked at. Jesse, from the first real
     * play on `phoenix.local`: *"I briefly saw that it was the bot's office area then their turn was
     * done and it pointed back to my office area"*, and the countdown row appeared "very briefly".
     *
     * The panel follows `busy()`, so this is the property that keeps somebody else's board on screen
     * for as long as their move is being shown.
     */
    const { steps } = realSteps(1917398, 400);
    const one = steps.filter((s) => s.cause === 'switch.move').slice(0, 1);
    assert.equal(one.length, 1);

    const q = createStepQueue();
    q.reset(baseline(1917398));
    q.push(one);

    q.advance(0);
    assert.equal(q.behind(), 0, 'nothing is queued behind it');
    assert.equal(q.busy(), true, 'but it is still being shown, so the queue is not idle');

    q.advance(DWELL.switching - 1);
    assert.equal(q.busy(), true, 'still inside its dwell');

    q.advance(DWELL.switching);
    assert.equal(q.busy(), false, 'and idle only once its moment has passed');
  });

  it("does not spend time replaying the viewer's own moves", () => {
    // A seated player's own board is drawn from their authoritative Frame, so they have already seen
    // their own click. Holding it delays the thing they wanted to watch — a bot's turn.
    const { steps } = realSteps(1917398, 400);
    const mine = steps.filter((s) => s.player === 0 && s.cause === 'switch.move').slice(0, 3);
    assert.equal(mine.length, 3, 'need three of seat 0\'s own moves');

    const asSeat0 = createStepQueue(() => 1, () => 0);
    asSeat0.reset(baseline(1917398));
    asSeat0.push(mine);
    // Twice at the same instant: the first call shows the head of the burst, the second collapses the
    // zero-dwell run behind it. In the page that is two animation frames, ~16ms apart.
    asSeat0.advance(0);
    asSeat0.advance(0);
    assert.equal(asSeat0.busy(), false, "the viewer's own moves must cost no time at all");
    assert.equal(asSeat0.behind(), 0, 'and must never be counted as something to wait for');

    // The same steps seen by somebody else are worth watching.
    const asSpectator = createStepQueue(() => 1, () => 1);
    asSpectator.reset(baseline(1917398));
    asSpectator.push(mine);
    asSpectator.advance(0);
    assert.equal(asSpectator.busy(), true, "another seat's moves are worth showing");
    assert.equal(asSpectator.behind(), 2);
  });

  it('a reset discards the backlog rather than merging it onto a new baseline', () => {
    /**
     * A reconnecting client holds steps whose deltas chain off a baseline the server has moved past.
     * Merging them onto the new one would draw a board that never existed — and `applyPublicDelta`
     * would throw the moment a "null means unchanged" field had nothing to merge onto.
     */
    const { steps, final } = realSteps(1917398, 400);
    const q = createStepQueue();
    q.reset(baseline(1917398));
    q.push(steps.slice(0, 10));
    q.advance(0);
    assert.ok(q.busy());

    q.reset(final);
    assert.equal(q.busy(), false, 'a reset must empty the queue');
    assert.equal(q.behind(), 0);
    assert.deepEqual(q.current(), final);
    // And the caption survives: a reconnect should not blank the "what just happened" line.
    assert.ok(q.showing() !== null, 'the caption should survive a reset');
  });

  it('draws nothing before a reset has arrived', () => {
    const q = createStepQueue();
    assert.equal(q.current(), null);
    assert.equal(q.advance(0), false);
    assert.equal(q.behind(), 0);
    assert.equal(q.showing(), null);
  });
});