import WaveSurfer from "wavesurfer.js";
import { usePlayerStore } from "../stores/playerStore";

class AudioService {
  private static instance: AudioService;
  private wavesurfer: WaveSurfer | null = null;
  private currentUrl: string | null = null;
  private currentContainer: HTMLElement | null = null;
  private isReady = false;
  private lastTimeUpdate = 0;
  // Persistent audio element attached to document.body so playback survives
  // SongPage unmounts. WaveSurfer v7 supports passing an existing media element
  // via the `media` option — it uses it for playback but does NOT destroy it
  // when WaveSurfer.destroy() is called.
  private mediaElement: HTMLAudioElement | null = null;

  private constructor() {}

  public static getInstance(): AudioService {
    if (!this.instance) {
      this.instance = new AudioService();
    }
    return this.instance;
  }

  // For use in tests only
  public static resetInstance(): void {
    this.instance?.cleanup();
    this.instance = undefined as unknown as AudioService;
  }

  private createMediaElement(): HTMLAudioElement {
    // Always create a fresh element — never reuse the one from a destroyed
    // WaveSurfer instance. WaveSurfer.destroy() aborts its internal fetch
    // signal, which can poison the same element when the next instance tries
    // to load a new URL. A new element has no lingering aborted state.
    // The element is appended to document.body so it outlives SongPage unmounts.
    const el = document.createElement('audio');
    el.style.display = 'none';
    document.body.appendChild(el);
    return el;
  }

  public async initialize(container: HTMLElement, url: string, peaks?: number[] | null): Promise<void> {
    if (!container) throw new Error('Container element is required');
    if (!url) throw new Error('Valid audio URL is required');

    // Same URL and same container — nothing to do
    if (this.currentUrl === url && this.wavesurfer && this.currentContainer === container) return;

    // Same URL, different container: navigated away and back to the same song.
    // Move the waveform canvas to the new container without reloading audio.
    if (this.currentUrl === url && this.wavesurfer) {
      this.wavesurfer.setOptions({ container });
      this.currentContainer = container;
      return;
    }

    // Different URL — tear down the previous instance and clear stale store state
    if (this.wavesurfer) {
      this.destroyWaveSurfer();
      usePlayerStore.getState().batchUpdate({ isPlaying: false, currentTime: 0, duration: 0 });
    }

    this.mediaElement = this.createMediaElement();

    const ws = WaveSurfer.create({
      container,
      // Fresh audio element per song. Lives on document.body so playback
      // continues even when the SongPage container is removed from the DOM.
      media: this.mediaElement,
      waveColor: "rgba(20,184,166,0.18)",
      progressColor: "#14b8a6",
      cursorColor: "#2dd4bf",
      barWidth: 2,
      barRadius: 2,
      height: 104,
      normalize: true,
      autoplay: false,
    });

    this.wavesurfer = ws;
    this.currentUrl = url;
    this.currentContainer = container;
    this.setupEventHandlers(ws);

    await new Promise<void>((resolve, reject) => {
      const onReady = async () => {
        const duration = ws.getDuration();
        if (duration > 0) {
          usePlayerStore.getState().setDuration(duration);
          this.isReady = true;
          resolve();
        } else {
          reject(new Error('Audio loaded but duration is 0'));
        }
      };

      ws.on('ready', () => { onReady().catch(reject); });
      ws.on('error', (err) => reject(err instanceof Error ? err : new Error(String(err))));

      // Pass pre-computed peaks to WaveSurfer so the waveform renders immediately
      // without waiting for the full audio to decode (WaveSurfer v7 feature).
      if (peaks && peaks.length > 0) {
        ws.load(url, [new Float32Array(peaks)]);
      } else {
        ws.load(url);
      }
    });
  }

  private setupEventHandlers(ws: WaveSurfer): void {
    ws.on('play', () => usePlayerStore.getState().batchUpdate({ isPlaying: true }));
    ws.on('pause', () => usePlayerStore.getState().batchUpdate({ isPlaying: false }));
    ws.on('finish', () => usePlayerStore.getState().batchUpdate({ isPlaying: false }));
    ws.on('audioprocess', (time) => {
      const now = Date.now();
      if (now - this.lastTimeUpdate >= 250) {
        usePlayerStore.getState().batchUpdate({ currentTime: time });
        this.lastTimeUpdate = now;
      }
    });
  }

  public async play(songId: string | null = null, bandId: string | null = null): Promise<void> {
    if (!this.wavesurfer || !this.isReady) return;
    await this.wavesurfer.play();
    if (songId && bandId) {
      usePlayerStore.getState().setCurrentSong(songId, bandId);
    }
  }

  public pause(): void {
    this.wavesurfer?.pause();
  }

  public seekTo(time: number): void {
    if (this.wavesurfer && this.isReady && isFinite(time)) {
      this.wavesurfer.setTime(time);
    }
  }

  public getCurrentTime(): number {
    return this.wavesurfer?.getCurrentTime() ?? 0;
  }

  public getDuration(): number {
    return this.wavesurfer?.getDuration() ?? 0;
  }

  public isPlaying(): boolean {
    return this.wavesurfer?.isPlaying() ?? false;
  }

  public isWaveformReady(): boolean {
    return this.isReady && !!this.wavesurfer;
  }

  public cleanup(): void {
    this.destroyWaveSurfer();
    const store = usePlayerStore.getState();
    store.setCurrentSong(null, null);
    store.batchUpdate({ isPlaying: false, currentTime: 0, duration: 0 });
  }

  private destroyWaveSurfer(): void {
    if (!this.wavesurfer) return;
    try {
      this.wavesurfer.unAll();
      this.wavesurfer.destroy();
      // Remove the old media element after WaveSurfer finishes its own cleanup.
      if (this.mediaElement) {
        this.mediaElement.pause();
        this.mediaElement.remove();
      }
    } catch (err) {
      console.error('[AudioService] Error destroying WaveSurfer:', err);
    }
    this.mediaElement = null;
    this.wavesurfer = null;
    this.currentUrl = null;
    this.currentContainer = null;
    this.isReady = false;
  }
}

export const audioService = AudioService.getInstance();
export { AudioService };