/**
 * Looping background music — drop your MP3 at public/audio/ambient.mp3
 * (MP3 preferred; OGG/WAV also work if you update AMBIENT_MUSIC_SRC).
 */
export const BGM_STORAGE_KEY = 'aetherforge-bgm';
export const BGM_VOLUME_KEY = 'aetherforge-bgm-volume';
/** Served from Vite public/ — place ambient.mp3 here before enabling in Settings. */
export const AMBIENT_MUSIC_SRC = '/audio/ambient.mp3';

export function loadBgmEnabled(): boolean {
  try {
    const v = localStorage.getItem(BGM_STORAGE_KEY);
    return v === '1';
  } catch {
    return false;
  }
}

export function loadBgmVolume(): number {
  try {
    const v = localStorage.getItem(BGM_VOLUME_KEY);
    if (v === null) return 0.22;
    const n = parseFloat(v);
    return Number.isFinite(n) ? Math.min(1, Math.max(0, n)) : 0.22;
  } catch {
    return 0.22;
  }
}

function persistBgmEnabled(enabled: boolean) {
  try {
    localStorage.setItem(BGM_STORAGE_KEY, enabled ? '1' : '0');
  } catch {
    /* ignore */
  }
}

function persistBgmVolume(volume: number) {
  try {
    localStorage.setItem(BGM_VOLUME_KEY, String(volume));
  } catch {
    /* ignore */
  }
}

export class AmbientMusicPlayer {
  private audio: HTMLAudioElement | null = null;
  private enabled = loadBgmEnabled();
  private volume = loadBgmVolume();
  private unlocked = false;
  private playing = false;
  private listeners = new Set<(playing: boolean) => void>();

  isEnabled() {
    return this.enabled;
  }

  isPlaying() {
    return this.playing;
  }

  getVolume() {
    return this.volume;
  }

  subscribe(fn: (playing: boolean) => void) {
    this.listeners.add(fn);
    return () => { this.listeners.delete(fn); };
  }

  private setPlaying(v: boolean) {
    if (this.playing === v) return;
    this.playing = v;
    for (const fn of this.listeners) fn(v);
  }

  setEnabled(enabled: boolean) {
    this.enabled = enabled;
    persistBgmEnabled(enabled);
    if (enabled) {
      this.ensureAudio();
      void this.tryPlay();
    } else {
      this.pause();
    }
  }

  setVolume(volume: number) {
    this.volume = Math.min(1, Math.max(0, volume));
    persistBgmVolume(this.volume);
    if (this.audio) this.audio.volume = this.volume;
  }

  /** Browsers block autoplay until a user gesture unlocks audio. */
  unlock() {
    if (this.unlocked) return;
    this.unlocked = true;
    this.ensureAudio();
    if (this.enabled) void this.tryPlay();
  }

  togglePlay() {
    if (this.playing) {
      this.pause();
      return false;
    }
    if (!this.enabled) {
      this.setEnabled(true);
    }
    void this.tryPlay();
    return true;
  }

  private ensureAudio() {
    if (this.audio || typeof document === 'undefined') return;
    const el = new Audio(AMBIENT_MUSIC_SRC);
    el.loop = true;
    el.preload = 'auto';
    el.volume = this.volume;
    el.addEventListener('play', () => this.setPlaying(true));
    el.addEventListener('pause', () => this.setPlaying(false));
    el.addEventListener('ended', () => this.setPlaying(false));
    el.addEventListener('error', () => {
      this.setPlaying(false);
    });
    this.audio = el;
  }

  private pause() {
    if (!this.audio) return;
    this.audio.pause();
    this.setPlaying(false);
  }

  async tryPlay(): Promise<boolean> {
    if (!this.enabled) return false;
    this.ensureAudio();
    if (!this.audio) return false;
    this.audio.volume = this.volume;
    try {
      await this.audio.play();
      this.setPlaying(true);
      return true;
    } catch {
      this.setPlaying(false);
      /* Autoplay policy — wait for Settings toggle or first click */
      return false;
    }
  }
}

export const ambientMusicPlayer = new AmbientMusicPlayer();