minstrel/web/src/lib/player/gain.test.ts

import { describe, expect, test } from 'vitest';
import { dbToLinear, gainDb, playingAsAlbum, MAX_BOOST_DB } from './gain';
import type { NormalizationPrefs } from '$lib/api/normalization';
import type { TrackRef } from '$lib/api/types';
import { makeTrack } from '$test-utils/fixtures/track';

const prefs = (over: Partial<NormalizationPrefs> = {}): NormalizationPrefs => ({
  mode: 'auto',
  target_lufs: -18,
  boost: 'headroom',
  ...over
});

const track = (id: string, album: string, n?: number, disc?: number): TrackRef =>
  makeTrack({ id, album_id: album, track_number: n, disc_number: disc });

describe('gainDb', () => {
  const g = { track_gain: -6, track_peak: 1, album_gain: -4, album_peak: 1 };

  test('off and unmeasured tracks play as mastered', () => {
    expect(gainDb(prefs({ mode: 'off' }), g, false)).toBe(0);
    expect(gainDb(prefs(), undefined, false)).toBe(0);
    expect(gainDb(prefs(), {}, false)).toBe(0);
  });

  test('mode picks the gain; auto follows album play', () => {
    expect(gainDb(prefs({ mode: 'track' }), g, true)).toBe(-6);
    expect(gainDb(prefs({ mode: 'album' }), g, false)).toBe(-4);
    expect(gainDb(prefs({ mode: 'auto' }), g, true)).toBe(-4);
    expect(gainDb(prefs({ mode: 'auto' }), g, false)).toBe(-6);
  });

  test('album gain falls back to track gain until the album is measured', () => {
    expect(gainDb(prefs({ mode: 'album' }), { track_gain: -6, track_peak: 1 }, true)).toBe(-6);
  });

  test('a louder target raises every gain by the difference', () => {
    expect(gainDb(prefs({ mode: 'track', target_lufs: -14 }), g, false)).toBe(-2);
  });

  test('headroom stops a boost 1 dB under the true peak; the limiter lets it through', () => {
    // +8 dB wanted; the peak at 0.5 (about -6 dBTP) leaves 5 dB of room.
    const quiet = { track_gain: 8, track_peak: 0.5 };
    expect(gainDb(prefs({ mode: 'track' }), quiet, false)).toBeCloseTo(-1 - 20 * Math.log10(0.5), 5);
    expect(gainDb(prefs({ mode: 'track', boost: 'limiter' }), quiet, false)).toBe(8);
  });

  test('no boost passes the cap, limiter or not', () => {
    const silent = { track_gain: 30, track_peak: 0.001 };
    expect(gainDb(prefs({ mode: 'track', boost: 'limiter' }), silent, false)).toBe(MAX_BOOST_DB);
  });

  test('cuts are never limited by the peak', () => {
    expect(gainDb(prefs({ mode: 'track' }), { track_gain: -9, track_peak: 1.4 }, false)).toBe(-9);
  });
});

describe('playingAsAlbum', () => {
  test('in-order neighbours from the same album', () => {
    const q = [track('1', 'x', 1), track('2', 'x', 2), track('3', 'x', 3)];
    expect(playingAsAlbum(q, 0)).toBe(true);
    expect(playingAsAlbum(q, 1)).toBe(true);
    expect(playingAsAlbum(q, 2)).toBe(true);
  });

  test('a shuffled album, a mix and a lone track are not album play', () => {
    expect(playingAsAlbum([track('3', 'x', 3), track('1', 'x', 1)], 0)).toBe(false);
    expect(playingAsAlbum([track('1', 'x', 1), track('2', 'y', 2)], 0)).toBe(false);
    expect(playingAsAlbum([track('1', 'x', 1)], 0)).toBe(false);
  });

  test('disc order counts: disc 2 track 1 follows disc 1 track 12', () => {
    const q = [track('a', 'x', 12, 1), track('b', 'x', 1, 2)];
    expect(playingAsAlbum(q, 1)).toBe(true);
  });

  test('neighbours without track numbers are not evidence of order', () => {
    expect(playingAsAlbum([track('1', 'x'), track('2', 'x')], 0)).toBe(false);
  });
});

test('dbToLinear', () => {
  expect(dbToLinear(0)).toBe(1);
  expect(dbToLinear(-20)).toBeCloseTo(0.1, 6);
  expect(dbToLinear(6)).toBeCloseTo(1.995, 3);
});