/**
 * The pitch of a sound FX (#312): a sound played higher or lower keeps its length. Measured on a
 * sine, whose pitch is the number of times it rises through zero per second.
 */
import { describe, expect, it } from 'vitest';
import { pitchShift } from '../../src/core/soundfx/pitchShift';

const RATE = 16000;

function sine(frequency: number, seconds: number): Float32Array {
  const samples = new Float32Array(Math.round(RATE * seconds));
  for (let i = 0; i < samples.length; i++) samples[i] = Math.sin((2 * Math.PI * frequency * i) / RATE);
  return samples;
}

/** Rises through zero per second over the middle half, away from the fade at either end. */
function frequencyOf(samples: Float32Array): number {
  const from = Math.floor(samples.length / 4);
  const to = Math.floor((samples.length * 3) / 4);
  let rises = 0;
  for (let i = from + 1; i < to; i++) if (samples[i - 1]! < 0 && samples[i]! >= 0) rises++;
  return rises / ((to - from) / RATE);
}

const loudest = (samples: Float32Array) => samples.reduce((max, v) => Math.max(max, Math.abs(v)), 0);

describe('pitch shifting', () => {
  it.each([
    [12, 880],
    [-12, 220],
    [7, 440 * 2 ** (7 / 12)],
    [0.5, 440 * 2 ** (0.5 / 12)],
    [-30.5, 440 * 2 ** (-30.5 / 12)],
  ])('moves a 440 Hz tone by %d semitones to about %d Hz, at the same length', (semitones, expected) => {
    const tone = sine(440, 1);
    const shifted = pitchShift(tone, RATE, semitones);
    expect(shifted.length).toBe(tone.length);
    expect(frequencyOf(shifted)).toBeGreaterThan(expected * 0.98);
    expect(frequencyOf(shifted)).toBeLessThan(expected * 1.02);
  });

  it('leaves a sound alone at 0 and does not make it louder', () => {
    const tone = sine(440, 0.5);
    const same = pitchShift(tone, RATE, 0);
    const middle = tone.length / 2;
    expect(same[middle]).toBeCloseTo(tone[middle]!, 5);
    expect(loudest(pitchShift(tone, RATE, 12))).toBeLessThanOrEqual(1.0001);
  });

  it('reads on across the end of a looping sound, so its seam does not fade out', () => {
    const tone = sine(500, 0.25);
    const tail = (samples: Float32Array) => loudest(samples.subarray(samples.length - 40));
    expect(tail(pitchShift(tone, RATE, 12))).toBeLessThan(0.6);
    expect(tail(pitchShift(tone, RATE, 12, true))).toBeGreaterThan(0.95);
  });
});