audio-ui/lib/audio/player.ts

/**
 * Audio playback controller
 */

import { getAudioContext, resumeAudioContext } from './context';

export class AudioPlayer {
  private audioContext: AudioContext;
  private audioBuffer: AudioBuffer | null = null;
  private sourceNode: AudioBufferSourceNode | null = null;
  private gainNode: GainNode;
  private startTime: number = 0;
  private pauseTime: number = 0;
  private isPlaying: boolean = false;
  private isPaused: boolean = false;

  constructor() {
    this.audioContext = getAudioContext();
    this.gainNode = this.audioContext.createGain();
    this.gainNode.connect(this.audioContext.destination);
  }

  /**
   * Load an audio buffer for playback
   */
  loadBuffer(buffer: AudioBuffer): void {
    this.stop();
    this.audioBuffer = buffer;
    this.pauseTime = 0;
  }

  /**
   * Start playback from current position
   */
  async play(startOffset: number = 0): Promise<void> {
    if (!this.audioBuffer) {
      throw new Error('No audio buffer loaded');
    }

    // Resume audio context if needed
    await resumeAudioContext();

    // Calculate start offset BEFORE stopping (since stop() resets pauseTime)
    const offset = this.isPaused ? this.pauseTime : startOffset;

    // Stop any existing playback
    this.stop();

    // Create new source node
    this.sourceNode = this.audioContext.createBufferSource();
    this.sourceNode.buffer = this.audioBuffer;
    this.sourceNode.connect(this.gainNode);

    // Set start time
    this.startTime = this.audioContext.currentTime - offset;

    // Start playback
    this.sourceNode.start(0, offset);
    this.isPlaying = true;
    this.isPaused = false;

    // Handle playback end
    this.sourceNode.onended = () => {
      if (this.isPlaying) {
        this.isPlaying = false;
        this.isPaused = false;
        this.pauseTime = 0;
      }
    };
  }

  /**
   * Pause playback
   */
  pause(): void {
    if (!this.isPlaying) return;

    this.pauseTime = this.getCurrentTime();
    this.stop();
    this.isPaused = true;
  }

  /**
   * Stop playback
   */
  stop(): void {
    if (this.sourceNode) {
      try {
        this.sourceNode.stop();
      } catch (error) {
        // Ignore errors if already stopped
      }
      this.sourceNode.disconnect();
      this.sourceNode = null;
    }
    this.isPlaying = false;
    this.isPaused = false;
    this.pauseTime = 0;
    this.startTime = 0;
  }

  /**
   * Get current playback time in seconds
   */
  getCurrentTime(): number {
    if (!this.audioBuffer) return 0;

    if (this.isPlaying) {
      const currentTime = this.audioContext.currentTime - this.startTime;
      return Math.min(currentTime, this.audioBuffer.duration);
    }

    return this.pauseTime;
  }

  /**
   * Seek to a specific time
   * @param time - Time in seconds to seek to
   * @param autoPlay - Whether to automatically start playback after seeking (default: false)
   */
  async seek(time: number, autoPlay: boolean = false): Promise<void> {
    if (!this.audioBuffer) return;

    const wasPlaying = this.isPlaying;
    const clampedTime = Math.max(0, Math.min(time, this.audioBuffer.duration));

    this.stop();
    this.pauseTime = clampedTime;

    // Auto-play if requested, or continue playing if was already playing
    if (autoPlay || wasPlaying) {
      await this.play(clampedTime);
    } else {
      this.isPaused = true;
    }
  }

  /**
   * Set playback volume (0 to 1)
   */
  setVolume(volume: number): void {
    const clampedVolume = Math.max(0, Math.min(1, volume));
    this.gainNode.gain.setValueAtTime(clampedVolume, this.audioContext.currentTime);
  }

  /**
   * Get current volume
   */
  getVolume(): number {
    return this.gainNode.gain.value;
  }

  /**
   * Get playback state
   */
  getState(): {
    isPlaying: boolean;
    isPaused: boolean;
    currentTime: number;
    duration: number;
  } {
    return {
      isPlaying: this.isPlaying,
      isPaused: this.isPaused,
      currentTime: this.getCurrentTime(),
      duration: this.audioBuffer?.duration ?? 0,
    };
  }

  /**
   * Get audio buffer
   */
  getBuffer(): AudioBuffer | null {
    return this.audioBuffer;
  }

  /**
   * Check if audio is loaded
   */
  hasBuffer(): boolean {
    return this.audioBuffer !== null;
  }

  /**
   * Cleanup resources
   */
  dispose(): void {
    this.stop();
    this.gainNode.disconnect();
    this.audioBuffer = null;
  }
}