nkbmusic/lib/audio/sound_settings.dart

import 'dart:convert';
import 'dart:math' as math;

import 'package:flutter/foundation.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:just_audio/just_audio.dart';

import '../data/user_library.dart';
import 'player_providers.dart';

/// Equalizer presets, described as a gain curve over frequency so they fit
/// whatever bands the phone's equalizer has (usually 5).
enum EqPreset {
  flat('Flat'),
  bass('Bass boost'),
  vocal('Vocal'),
  festival('Festival'),
  treble('Treble'),
  custom('Custom');

  const EqPreset(this.label);
  final String label;

  /// Gain in dB for a band centred on [hz]; null for [custom].
  double? gainAt(double hz) => switch (this) {
        flat => 0,
        bass => hz < 120 ? 6 : hz < 400 ? 3.5 : 0,
        vocal => hz < 200 ? -2 : hz < 600 ? 1 : hz < 5000 ? 4 : 1,
        festival => hz < 200 ? 5 : hz < 1500 ? 0 : hz < 5000 ? 2 : 4,
        treble => hz < 1000 ? 0 : hz < 5000 ? 2.5 : 5,
        custom => null,
      };
}

@immutable
class SoundState {
  const SoundState({
    this.eqEnabled = false,
    this.preset = EqPreset.flat,
    this.customGains = const {},
    this.boostDb = 0,
  });

  final bool eqEnabled;
  final EqPreset preset;

  /// Band index -> dB, used when [preset] is custom.
  final Map<int, double> customGains;

  /// Loudness boost for quiet old recordings, 0 to 10 dB.
  final double boostDb;

  SoundState copyWith({bool? eqEnabled, EqPreset? preset, Map<int, double>? customGains, double? boostDb}) =>
      SoundState(
        eqEnabled: eqEnabled ?? this.eqEnabled,
        preset: preset ?? this.preset,
        customGains: customGains ?? this.customGains,
        boostDb: boostDb ?? this.boostDb,
      );

  Map<String, Object> toJson() => {
        'eq': eqEnabled,
        'preset': preset.name,
        'custom': {for (final e in customGains.entries) '${e.key}': e.value},
        'boost': boostDb,
      };

  static SoundState fromJson(Map<String, dynamic> j) => SoundState(
        eqEnabled: j['eq'] as bool? ?? false,
        preset: EqPreset.values.asNameMap()[j['preset']] ?? EqPreset.flat,
        customGains: {
          for (final e in ((j['custom'] as Map?) ?? {}).entries) int.parse(e.key as String): (e.value as num).toDouble(),
        },
        boostDb: (j['boost'] as num?)?.toDouble() ?? 0,
      );
}

/// Whether this platform supports the in-app equalizer and boost.
bool get soundEffectsSupported => !kIsWeb && defaultTargetPlatform == TargetPlatform.android;

class SoundSettings extends Notifier<SoundState> {
  static const _key = 'sound_settings';

  @override
  SoundState build() {
    final raw = ref.read(sharedPrefsProvider).getString(_key);
    SoundState state;
    try {
      state = raw == null ? const SoundState() : SoundState.fromJson(jsonDecode(raw) as Map<String, dynamic>);
    } catch (_) {
      state = const SoundState();
    }
    _apply(state);
    return state;
  }

  AndroidEqualizer get _eq => ref.read(audioHandlerProvider).equalizer;
  AndroidLoudnessEnhancer get _boost => ref.read(audioHandlerProvider).loudness;

  void setEnabled(bool on) => _update(state.copyWith(eqEnabled: on));

  void setPreset(EqPreset preset) => _update(state.copyWith(preset: preset, eqEnabled: true));

  /// Moving a band switches to the custom preset, starting from the current curve.
  Future<void> setBandGain(int index, double db) async {
    final params = await _eq.parameters;
    final gains = {for (final b in params.bands) b.index: b.gain}..[index] = db;
    _update(state.copyWith(preset: EqPreset.custom, customGains: gains, eqEnabled: true));
  }

  void setBoost(double db) => _update(state.copyWith(boostDb: db));

  void reset() => _update(const SoundState());

  void _update(SoundState next) {
    state = next;
    ref.read(sharedPrefsProvider).setString(_key, jsonEncode(next.toJson()));
    _apply(next);
  }

  Future<void> _apply(SoundState s) async {
    if (!soundEffectsSupported) return;
    await _boost.setEnabled(s.boostDb > 0);
    await _boost.setTargetGain(s.boostDb);
    await _eq.setEnabled(s.eqEnabled);
    // Parameters arrive once the player has an audio session (first song loaded).
    final params = await _eq.parameters;
    for (final band in params.bands) {
      final db = s.preset == EqPreset.custom
          ? (s.customGains[band.index] ?? 0)
          : s.preset.gainAt(band.centerFrequency)!;
      await band.setGain(math.max(params.minDecibels, math.min(params.maxDecibels, db)));
    }
  }
}

final soundSettingsProvider = NotifierProvider<SoundSettings, SoundState>(SoundSettings.new);