riversong-code-showcase/Source/Riversong/Game/Audio/BackgroundMusicSystem.cs

using System;
using Cysharp.Threading.Tasks;
using PrimeTween;
using UnityEngine;

namespace DanieleMarotta.RiversongCodeShowcase
{
    [GameSystemGroup(typeof(AudioSystemGroup))]
    public class BackgroundMusicSystem : GameSystem, IInitializable, IDisposable
    {
        [InjectService]
        private GameConfig _config;

        [InjectService]
        private IScene _scene;

        [InjectService]
        private ISignalBus _signalBus;

        private AudioSource _audioSource;

        private AudioClip _mainThemeClip;

        private AudioClip _gameplayClip;

        public BackgroundMusicSystem(IServiceLocator serviceLocator) : base(serviceLocator)
        {
        }

        public async UniTask InitializeAsync()
        {
            _audioSource = new GameObject("BGM").AddComponent<AudioSource>();
            _audioSource.transform.SetParent(_scene.SceneFolders.AudioSources);
            _audioSource.playOnAwake = false;
            _audioSource.loop = true;

            _mainThemeClip = await _config.Audio.MainThemeClip.LoadAssetAsync<AudioClip>();
            _gameplayClip = await _config.Audio.GameplayClip.LoadAssetAsync<AudioClip>();

            _signalBus.Subscribe<GameInitializationCompletedSignal>(OnGameInitializationCompleted);
            _signalBus.Subscribe<GameStartedSignal>(OnGameStarted);
            _signalBus.Subscribe<WorldReadySignal>(OnWorldReady);
        }

        public void Dispose()
        {
            _signalBus.Unsubscribe<GameInitializationCompletedSignal>(OnGameInitializationCompleted);
            _signalBus.Unsubscribe<GameStartedSignal>(OnGameStarted);
            _signalBus.Unsubscribe<WorldReadySignal>(OnWorldReady);
        }

        private void OnGameInitializationCompleted(GameInitializationCompletedSignal signal)
        {
            Play(_mainThemeClip, _config.Audio.MainThemeVolume);
        }

        private void OnGameStarted(GameStartedSignal signal)
        {
            _ = FadeOutAsync(2);
        }

        private async UniTask FadeOutAsync(float duration)
        {
            await Tween.Custom(_audioSource.volume, 0, duration, value => _audioSource.volume = value, Ease.Linear);
        }

        private void OnWorldReady(WorldReadySignal signal)
        {
            Play(_gameplayClip, _config.Audio.GameplayVolume);
        }

        private void Play(AudioClip clip, float volume)
        {
            _audioSource.Stop();

            _audioSource.clip = clip;
            _audioSource.volume = volume;

            _audioSource.Play();
        }
    }
}