/** A Reverb (#328): the impulse response it makes for itself. */
import { describe, expect, it } from 'vitest';
import { REVERB_MAX_DECAY, REVERB_PRESETS, reverbImpulse } from '../../src/core/soundfx/reverb';

const RATE = 48000;

/** The RMS of a stretch of samples, in dB. */
function db(data: Float32Array, from: number, to: number): number {
  let sum = 0;
  for (let i = from; i < to; i++) sum += data[i]! ** 2;
  return 10 * Math.log10(sum / (to - from));
}

/** The share of a stretch's energy that is above a few kHz: what is left after a two-tap average. */
function highShare(data: Float32Array, from: number, to: number): number {
  let all = 0;
  let high = 0;
  for (let i = from + 1; i < to; i++) {
    all += data[i]! ** 2;
    high += ((data[i]! - data[i - 1]!) / 2) ** 2;
  }
  return high / all;
}

describe('the impulse response of a Reverb', () => {
  it('lasts its decay and falls by 60 dB over it, two channels of their own noise', () => {
    const [left, right] = reverbImpulse(RATE, 2, 0);
    expect(left!.length).toBe(2 * RATE);
    expect(left).not.toEqual(right);
    // A tenth of the way at the start and at the end: 54 dB apart, 6 dB a tenth.
    expect(db(left!, 0, RATE / 5) - db(left!, (9 * RATE) / 5, 2 * RATE)).toBeCloseTo(54, 0);
  });

  it('is the same every time, and never longer than 10 s', () => {
    expect(reverbImpulse(RATE, 1, 0.5)).toEqual(reverbImpulse(RATE, 1, 0.5));
    expect(reverbImpulse(RATE, 60, 0)[0]!.length).toBe(REVERB_MAX_DECAY * RATE);
  });

  it('loses its highs faster with damping', () => {
    const [open] = reverbImpulse(RATE, 1, 0);
    const [damped] = reverbImpulse(RATE, 1, 1);
    const late = [0.8 * RATE, RATE] as const;
    expect(highShare(damped!, ...late)).toBeLessThan(highShare(open!, ...late) / 4);
    // At the start both are open.
    expect(highShare(damped!, 0, RATE / 20)).toBeCloseTo(highShare(open!, 0, RATE / 20), 1);
  });

  it('has four spaces from a small room to a cave', () => {
    expect(Object.keys(REVERB_PRESETS)).toEqual(['room', 'hall', 'cave', 'plate']);
    expect(REVERB_PRESETS.room.decay).toBeLessThan(REVERB_PRESETS.hall.decay);
    expect(REVERB_PRESETS.hall.decay).toBeLessThan(REVERB_PRESETS.cave.decay);
  });
});