class SoundShared {
  readonly context: AudioContext;
  bgmSource: AudioBufferSourceNode | null;
  bgmGain: GainNode | null;

  constructor() {
    this.context = new AudioContext();
    this.bgmSource = null;
    this.bgmGain = null;
  }
}
const shared = new SoundShared();

export class Sound {
  #link: string;
  #audioBufferPromise: Promise<AudioBuffer>;

  constructor(link: string) {
    this.#link = link;
    this.#audioBufferPromise = this.#unsafeGetAudioBuffer();
  }
  async #unsafeGetAudioBuffer(): Promise<AudioBuffer> {
    let resp = await fetch(this.#link);
    let buf = await resp.arrayBuffer();
    return await shared.context.decodeAudioData(buf);
  }

  async #getAudioBuffer(): Promise<AudioBuffer> {
    return await this.#audioBufferPromise;
  }

  play(options?: { volume?: number; bgm?: boolean }) {
    this.#getAudioBuffer().then((adata) => {
      let source = shared.context.createBufferSource();
      source.buffer = adata;
      let gain = shared.context.createGain();
      gain.gain.value = options?.volume ?? 1.0;
      source.connect(gain);
      gain.connect(shared.context.destination);
      source.start();

      if (options?.bgm) {
        shared.bgmSource?.stop(shared.context.currentTime + 1);
        shared.bgmGain?.gain?.linearRampToValueAtTime(
          0.0,
          shared.context.currentTime + 1,
        );
        shared.bgmSource = source;
        shared.bgmGain = gain;
      }
    });
  }
}