feuerwerk/tests/core/music.test.ts

import { describe, expect, it } from 'vitest';
import {
  INTERVAL,
  LEAD,
  LOOKAHEAD,
  type ScheduledNote,
  Scheduler,
  type SchedulerHost,
} from '../../src/core/music/Scheduler';
import {
  heldLoop,
  notesIn,
  playheadAt,
  type Sequence,
  type SequenceNote,
} from '../../src/core/music/sequence';
import {
  heldMeter,
  heldTempo,
  positionOf,
  secondsOfQuarters,
  secondsOfTicks,
  TICKS_PER_QUARTER,
  ticksOfSeconds,
  ticksPerBar,
  ticksPerBeat,
} from '../../src/core/music/time';

const Q = TICKS_PER_QUARTER;

function note(tick: number, length = Q / 2, pitch = 60): SequenceNote {
  return { tick, length, note: pitch, velocity: 1, instrument: 'piano' };
}

describe('musical time (#332)', () => {
  it('counts 480 ticks to the quarter, so triplets and quintuplets land on whole ticks', () => {
    expect([Q / 3, Q / 5, Q / 6, Q / 8, Q / 12].every(Number.isInteger)).toBe(true);
    expect(secondsOfTicks(Q, 120)).toBe(0.5);
    expect(secondsOfTicks(Q / 3, 120)).toBeCloseTo(1 / 6);
    expect(ticksOfSeconds(0.5, 120)).toBe(Q);
    expect(secondsOfQuarters(0.75, 120)).toBe(0.375);
  });

  it('takes any meter: a beat is the note value under the line, a bar so many of them', () => {
    expect([ticksPerBeat({ beats: 4, unit: 4 }), ticksPerBar({ beats: 4, unit: 4 })]).toEqual([Q, 4 * Q]);
    expect([ticksPerBeat({ beats: 6, unit: 8 }), ticksPerBar({ beats: 6, unit: 8 })]).toEqual([Q / 2, 3 * Q]);
    expect(ticksPerBar({ beats: 7, unit: 8 })).toBe(3.5 * Q);
    expect(heldMeter({ beats: 3, unit: 4 })).toEqual({ beats: 3, unit: 4 });
    for (const odd of [
      { beats: 0, unit: 4 },
      { beats: 3.5, unit: 4 },
      { beats: 4, unit: 3 },
      { beats: 33, unit: 4 },
    ])
      expect(heldMeter(odd)).toEqual({ beats: 4, unit: 4 });
  });

  it('holds a tempo to 20 to 400 BPM, 120 where it is none', () => {
    expect([heldTempo(90), heldTempo(5), heldTempo(1000), heldTempo(0), heldTempo(Number.NaN)]).toEqual([
      90, 20, 400, 120, 120,
    ]);
  });

  it('names a tick as a musician counts it: bar and beat from 1, the tick in the beat from 0', () => {
    expect(positionOf(0, { beats: 4, unit: 4 })).toEqual({ bar: 1, beat: 1, tick: 0 });
    expect(positionOf(5 * Q + 120, { beats: 4, unit: 4 })).toEqual({ bar: 2, beat: 2, tick: 120 });
    // 7/8: seven eighths of 240 ticks to the bar.
    expect(positionOf(7 * 240 + 6 * 240 + 10, { beats: 7, unit: 8 })).toEqual({ bar: 2, beat: 7, tick: 10 });
    expect(positionOf(-30, { beats: 4, unit: 4 })).toEqual({ bar: 1, beat: 1, tick: 0 });
  });
});

describe('the notes of a window of playing time (#332)', () => {
  const sequence: Sequence = { notes: [note(0), note(Q), note(2 * Q), note(3 * Q)] };

  it('runs the playhead round a loop it started in front of, and on past one it started behind', () => {
    const loop = { start: Q, end: 3 * Q };
    expect([0, Q, 3 * Q - 1, 3 * Q, 4 * Q, 5 * Q].map((e) => playheadAt(e, 0, loop))).toEqual([
      0,
      Q,
      3 * Q - 1,
      Q,
      2 * Q,
      Q,
    ]);
    expect(playheadAt(Q, 4 * Q, loop)).toBe(5 * Q);
    expect(playheadAt(Q, 0, null)).toBe(Q);
    expect([heldLoop({ start: Q, end: Q }), heldLoop({ start: -1, end: Q })]).toEqual([null, null]);
  });

  it('gives the notes starting in it, by their start in playing time, and none twice across windows', () => {
    expect(notesIn(sequence, 0, null, 0, Q + 1).map((n) => n.at)).toEqual([0, Q]);
    const pieces = [0, 100, Q, Q + 1, 2 * Q + 37, 4 * Q]
      .slice(1)
      .map((end, i, ends) => [ends[i - 1] ?? 0, end]);
    const joined = pieces.flatMap(([start, end]) =>
      notesIn(sequence, 0, null, start!, end!).map((n) => n.at),
    );
    expect(joined).toEqual([0, Q, 2 * Q, 3 * Q]);
  });

  it('looks across the end of a loop into the next round, so the seam has no gap', () => {
    const loop = { start: Q, end: 3 * Q };
    // Playing time 2.5 to 4.5 quarters: the end of the first round and the start of the second.
    const due = notesIn(sequence, 0, loop, 2.5 * Q, 4.5 * Q);
    expect(due.map((n) => [n.at, n.tick])).toEqual([
      [3 * Q, Q],
      [4 * Q, 2 * Q],
    ]);
    // Round after round, every note once, two quarters apart.
    const rounds = notesIn(sequence, 0, loop, 0, 11 * Q).map((n) => n.at);
    expect(rounds).toEqual([0, Q, 2 * Q, 3 * Q, 4 * Q, 5 * Q, 6 * Q, 7 * Q, 8 * Q, 9 * Q, 10 * Q]);
    const split = [0, 3 * Q - 7, 3 * Q, 3 * Q + 1, 7 * Q, 11 * Q];
    const pieces = split
      .slice(1)
      .flatMap((end, i) => notesIn(sequence, 0, loop, split[i]!, end).map((n) => n.at));
    expect(pieces).toEqual(rounds);
  });

  it('ends a note at the end of the loop, where the playhead jumps back', () => {
    const long: Sequence = { notes: [note(2 * Q, 4 * Q)] };
    expect(notesIn(long, 0, { start: 0, end: 3 * Q }, 0, 3 * Q)[0]!.length).toBe(Q);
    expect(notesIn(long, 0, null, 0, 3 * Q)[0]!.length).toBe(4 * Q);
  });

  it('keeps notes struck together in the order of their pitch', () => {
    const chord: Sequence = { notes: [note(0, Q, 67), note(0, Q, 60), note(0, Q, 64)] };
    expect(notesIn(chord, 0, null, 0, 1).map((n) => n.note)).toEqual([60, 64, 67]);
  });
});

/** An audio clock the test moves by hand, and a player that only writes down what it is given. */
function fakeHost() {
  const host = {
    time: 10,
    latency: 0,
    played: [] as ScheduledNote[],
    stopped: [] as number[][],
    sounding: new Set<number>(),
    pump: null as (() => void) | null,
    asleep: 0,
  };
  const sink: SchedulerHost = {
    now: () => host.time,
    latency: () => host.latency,
    play: (scheduled) => {
      host.played.push(scheduled);
      host.sounding.add(host.played.length);
      return host.played.length;
    },
    playing: (voice) => host.sounding.has(voice),
    stop: (voices) => void host.stopped.push([...voices]),
    wake: (pump) => {
      host.pump = pump;
      return () => {
        host.pump = null;
        host.asleep += 1;
      };
    },
  };
  /** Lets the clock run, the timer firing every `INTERVAL` on the way, as late as `jitter` says. */
  const run = (seconds: number, jitter = () => 0) => {
    const end = host.time + seconds;
    while (host.time + INTERVAL <= end + 1e-9) {
      host.time += INTERVAL + jitter();
      host.pump?.();
    }
  };
  return { host, sink, run };
}

describe('the scheduler on the audio clock (#332)', () => {
  const quarters: Sequence = { notes: [0, 1, 2, 3, 4, 5, 6, 7].map((i) => note(i * Q)) };

  it('plans each note at its exact second, a lookahead before it, the first a moment after the start', () => {
    const { host, sink, run } = fakeHost();
    const scheduler = new Scheduler(sink, () => quarters, { tempo: 120 });
    scheduler.start();
    expect(host.played.map((n) => n.at)).toEqual([10 + LEAD]);
    run(2);
    // The fifth is due at 2.05 s, inside the 100 ms ahead of 2 s.
    const offsets = host.played.map((n) => n.at - 10 - LEAD);
    expect(offsets).toHaveLength(5);
    offsets.forEach((offset, i) => expect(offset).toBeCloseTo(i * 0.5, 9));
    expect(host.played.every((n) => n.duration === 0.25 && n.tempo === 120 && n.instrument === 'piano')).toBe(
      true,
    );
  });

  it('plans every note before it is due and never twice, however late the timer fires', () => {
    const { host, sink, run } = fakeHost();
    const scheduler = new Scheduler(sink, () => quarters, { tempo: 150 });
    let planned = 0;
    const late: number[] = [];
    const watch = () => {
      for (const n of host.played.slice(planned)) late.push(n.at - host.time);
      planned = host.played.length;
    };
    scheduler.start();
    watch();
    // Up to 60 ms late every time – a busy page – which is still inside the 100 ms ahead.
    let k = 0;
    const jitter = () => [0.06, 0, 0.03, 0.045][k++ % 4]!;
    for (let i = 0; i < 160; i++) {
      run(INTERVAL, jitter);
      watch();
    }
    expect(host.played).toHaveLength(8);
    expect(Math.min(...late)).toBeGreaterThan(0);
    host.played.forEach((n, i) => expect(n.at - 10 - LEAD).toBeCloseTo(i * 0.4, 9));
  });

  it('plans as much further ahead as a note may be started early, its playhead on what is heard (#346)', () => {
    const { host, sink, run } = fakeHost();
    const early = 3 * (2048 / 48000);
    const scheduler = new Scheduler({ ...sink, ahead: () => early }, () => quarters, { tempo: 150 });
    let planned = 0;
    const room: number[] = [];
    const watch = () => {
      // What the player has left once it starts the note that much earlier.
      for (const n of host.played.slice(planned)) room.push(n.at - early - host.time);
      planned = host.played.length;
    };
    scheduler.start();
    watch();
    expect(host.played.map((n) => n.at)).toEqual([10 + LEAD + early]);
    let k = 0;
    const jitter = () => [0.06, 0, 0.03, 0.045][k++ % 4]!;
    for (let i = 0; i < 160; i++) {
      run(INTERVAL, jitter);
      watch();
    }
    expect(host.played).toHaveLength(8);
    expect(Math.min(...room)).toBeGreaterThan(0);
    host.played.forEach((n, i) => expect(n.at - 10 - LEAD - early).toBeCloseTo(i * 0.4, 9));
    host.time = 10 + LEAD + early + 0.4;
    expect(scheduler.position().ticks).toBeCloseTo(ticksOfSeconds(0.4, 150), 6);
  });

  it('runs a loop round and round without a gap at the seam', () => {
    const { host, sink, run } = fakeHost();
    const twoNotes: Sequence = { notes: [note(0), note(Q)] };
    const scheduler = new Scheduler(sink, () => twoNotes, { tempo: 120, loop: { start: 0, end: 2 * Q } });
    scheduler.start();
    run(3);
    const gaps = host.played.slice(1).map((n, i) => n.at - host.played[i]!.at);
    expect(host.played.length).toBeGreaterThanOrEqual(6);
    expect(gaps.every((gap) => Math.abs(gap - 0.5) < 1e-9)).toBe(true);
  });

  it('plays a change from the next window on and leaves what is planned', () => {
    const { host, sink, run } = fakeHost();
    let sequence: Sequence = quarters;
    const scheduler = new Scheduler(sink, () => sequence, { tempo: 120 });
    scheduler.start();
    run(0.6);
    const before = host.played.length;
    sequence = { notes: quarters.notes.map((n) => ({ ...n, note: 72 })) };
    run(2);
    expect(host.played.slice(0, before).every((n) => n.note === 60)).toBe(true);
    expect(host.played.slice(before).every((n) => n.note === 72)).toBe(true);
    expect(host.played.length).toBeGreaterThan(before);
  });

  it('says where what is heard stands: the clock less the latency, in bars, beats and ticks', () => {
    const { host, sink, run } = fakeHost();
    const scheduler = new Scheduler(sink, () => quarters, { tempo: 120, meter: { beats: 3, unit: 4 } });
    expect(scheduler.position()).toEqual({ bar: 1, beat: 1, tick: 0, ticks: 0 });
    scheduler.start();
    host.latency = 0.05;
    run(1.75);
    // 1.75 s on, less the lead and the latency: 1.65 s, 3.3 quarters – the second bar's first beat.
    const heard = scheduler.position();
    expect([heard.bar, heard.beat]).toEqual([2, 1]);
    expect(Math.abs(heard.tick - 0.3 * Q)).toBeLessThanOrEqual(1);
    expect(heard.ticks).toBeCloseTo(3.3 * Q, 6);
  });

  it('stops every note it started, those still to come too, and plays on from there next time', () => {
    const { host, sink, run } = fakeHost();
    const scheduler = new Scheduler(sink, () => quarters, { tempo: 120 });
    scheduler.start();
    run(0.6);
    // The first note has ended by itself: only the second is left to stop.
    host.sounding.delete(1);
    run(0.025);
    scheduler.stop();
    expect(host.stopped).toEqual([[2]]);
    expect([scheduler.playing, host.pump, host.asleep]).toEqual([false, null, 1]);
    expect(scheduler.position().ticks).toBe(Math.floor(ticksOfSeconds(0.625 - LEAD, 120)));
    host.played = [];
    scheduler.start();
    expect(host.played[0]?.note).toBeUndefined();
    run(0.5);
    expect(host.played[0]!.at - host.time).toBeLessThan(LOOKAHEAD + 1e-9);
  });

  it('jumps: cuts what plays and goes on from the new place at once', () => {
    const { host, sink, run } = fakeHost();
    const scheduler = new Scheduler(sink, () => quarters, { tempo: 120 });
    scheduler.start();
    run(0.3);
    const started = host.time;
    scheduler.seek(6 * Q);
    expect(host.stopped).toEqual([[1]]);
    expect(host.played.at(-1)).toMatchObject({ at: started + LEAD });
    expect(scheduler.position().ticks).toBe(6 * Q);
  });

  it('a new tempo counts from what is planned, and the playhead does not jump meanwhile', () => {
    const { host, sink, run } = fakeHost();
    const scheduler = new Scheduler(sink, () => quarters, { tempo: 120 });
    scheduler.start();
    run(1.2);
    const heard = scheduler.position().ticks;
    const planned = host.played.length;
    scheduler.setTempo(60);
    expect(scheduler.position().ticks).toBeCloseTo(heard, 6);
    run(3);
    const after = host.played.slice(planned - 1).map((n) => n.at);
    const gaps = after.slice(1).map((at, i) => at - after[i]!);
    // The last note at the old tempo, then a second to the quarter.
    expect(gaps.slice(1).every((gap) => Math.abs(gap - 1) < 1e-9)).toBe(true);
    expect(host.played.at(-1)!.tempo).toBe(60);
  });
});