SpotiFLAC-Mobile/test/automix_analysis_test.dart

import 'dart:math' as math;
import 'dart:typed_data';

import 'package:flutter_test/flutter_test.dart';
import 'package:spotiflac_android/models/settings.dart';
import 'package:spotiflac_android/services/automix_analysis.dart';

Uint8List drumPattern(double bpm, {double phase = 0.17}) {
  const sampleRate = 11025;
  final bytes = ByteData(sampleRate * 24 * 2);
  final random = math.Random(7);
  for (var i = 0; i < sampleRate * 24; i++) {
    final time = i / sampleRate;
    final sinceBeat = (time - phase) % (60 / bpm);
    final transient = time < phase ? 0.0 : math.exp(-sinceBeat * 50);
    final value =
        0.75 * transient * math.sin(time * 2 * math.pi * 100) +
        (random.nextDouble() - 0.5) * 0.003;
    bytes.setInt16(i * 2, (value * 32767).round(), Endian.little);
  }
  return bytes.buffer.asUint8List();
}

void main() {
  for (final bpm in [90.0, 120.0, 124.0, 160.0]) {
    test('detects $bpm BPM and beat phase from audio', () {
      final grid = analyzeAutoMixPcm(drumPattern(bpm));
      expect(grid.reliable, isTrue, reason: '${grid.bpm}, ${grid.confidence}');
      expect(grid.bpm, closeTo(bpm, 0.75));
      expect(grid.beatAtOrAfter(0), closeTo(0.17, 0.04));
    });
  }

  test('silence and unstructured noise do not invent a reliable beat', () {
    expect(analyzeAutoMixPcm(Uint8List(11025 * 24 * 2)).reliable, isFalse);
    final random = math.Random(11);
    final noise = ByteData(11025 * 24 * 2);
    for (var i = 0; i < noise.lengthInBytes; i += 2) {
      noise.setInt16(i, random.nextInt(32000) - 16000, Endian.little);
    }
    expect(analyzeAutoMixPcm(noise.buffer.asUint8List()).reliable, isFalse);
  });

  AutoMixBeatGrid grid(double bpm, {double confidence = 0.9}) =>
      AutoMixBeatGrid(
        bpm: bpm,
        phase: 0.17,
        confidence: confidence,
        firstSound: 0.1,
      );

  AutoMixPlan plan(double from, double to, {double confidence = 0.9}) =>
      AutoMixPlan.create(
        outgoingDuration: const Duration(seconds: 180),
        incomingDuration: const Duration(seconds: 200),
        outro: grid(from, confidence: confidence),
        intro: grid(to),
        outroOffset: 156,
      )!;

  test('compatible tempi align outgoing and incoming beats', () {
    final transition = plan(120, 124);
    expect(transition.beatMatched, isTrue);
    expect(transition.rate, closeTo(120 / 124, 0.00001));
    final beat = (transition.start.inMicroseconds / 1e6 - 156.17) / 0.5;
    expect(beat, closeTo(beat.round(), 0.00001));
    expect(transition.incomingStart.inMilliseconds, 170);
    expect(
      transition.start + transition.duration,
      lessThanOrEqualTo(const Duration(seconds: 180)),
    );
  });

  test('incompatible or uncertain beats use unstretched crossfade', () {
    for (final transition in [
      plan(120, 160),
      plan(120, 124, confidence: 0.2),
    ]) {
      expect(transition.beatMatched, isFalse);
      expect(transition.rate, 1);
      expect(transition.incomingStart, Duration.zero);
    }
    expect(
      AutoMixPlan.create(
        outgoingDuration: const Duration(seconds: 10),
        incomingDuration: const Duration(minutes: 2),
      ),
      isNull,
    );
  });

  test('equal-power overlap restores normal tempo smoothly', () {
    final transition = plan(120, 124);
    final start = autoMixEnvelope(Duration.zero, transition);
    expect(start.outgoing, 1);
    expect(start.incoming, 0);
    final middle = autoMixEnvelope(transition.duration ~/ 2, transition);
    expect(
      middle.outgoing * middle.outgoing + middle.incoming * middle.incoming,
      closeTo(1, 0.00001),
    );
    expect(middle.rate, transition.rate);
    final recovery = autoMixEnvelope(
      transition.duration + const Duration(seconds: 4),
      transition,
    );
    expect(recovery.rate, closeTo((transition.rate + 1) / 2, 0.00001));
    final end = autoMixEnvelope(
      transition.duration + const Duration(seconds: 8),
      transition,
    );
    expect(end.complete, isTrue);
    expect(end.rate, 1);
    expect(end.incoming, 1);
    expect(end.outgoing, closeTo(0, 0.00001));
  });

  test('AutoMix is off for new and existing settings, and persists opt-in', () {
    expect(const AppSettings().autoMix, isFalse);
    expect(AppSettings.fromJson({}).autoMix, isFalse);
    final enabled = const AppSettings().copyWith(autoMix: true);
    expect(AppSettings.fromJson(enabled.toJson()).autoMix, isTrue);
    expect(enabled.copyWith(autoMix: false).autoMix, isFalse);
  });
}