slime/src/systems/MusicSystem.ts

import { System } from '../core/System.ts';
import { SystemName, ComponentType, GameState } from '../core/Constants.ts';
import type { Entity } from '../core/Entity.ts';
import type { Engine } from '../core/Engine.ts';
import type { Music } from '../components/Music.ts';
import type { MenuSystem } from './MenuSystem.ts';

/**
 * System responsible for managing background music playback.
 */
export class MusicSystem extends System {
  private audioContext: AudioContext | null;
  private wasPaused: boolean;

  constructor() {
    super(SystemName.MUSIC);
    this.requiredComponents = [ComponentType.MUSIC];
    this.priority = 5;
    this.audioContext = null;
    this.wasPaused = false;
  }

  /**
   * Initialize the audio context when system is added to engine.
   */
  init(engine: Engine): void {
    super.init(engine);
  }

  /**
   * Process music entities - ensures audio context exists and handles pause/resume.
   */
  process(_deltaTime: number, entities: Entity[]): void {
    const menuSystem = this.engine.systems.find((s) => s.name === SystemName.MENU) as
      | MenuSystem
      | undefined;
    const gameState = menuSystem ? menuSystem.getGameState() : GameState.PLAYING;
    const isPaused = gameState === GameState.PAUSED;

    entities.forEach((entity) => {
      const music = entity.getComponent<Music>(ComponentType.MUSIC);
      if (!music) return;

      if (!this.audioContext) {
        this.audioContext = new AudioContext();
      }

      if (isPaused && !this.wasPaused) {
        music.pause();
        this.wasPaused = true;
      } else if (!isPaused && this.wasPaused) {
        music.resume();
        this.wasPaused = false;
      }
    });
  }

  /**
   * Get or create the shared audio context.
   */
  getAudioContext(): AudioContext {
    if (!this.audioContext) {
      this.audioContext = new AudioContext();
    }
    return this.audioContext;
  }

  /**
   * Resume audio context (required after user interaction).
   */
  resumeAudioContext(): void {
    if (this.audioContext && this.audioContext.state === 'suspended') {
      this.audioContext.resume();
    }
  }
}