// Web Audio playback of a Float32Array signal with position reporting.

export class Player {
  private ctx: AudioContext | null = null;
  private source: AudioBufferSourceNode | null = null;
  private startedAt = 0;
  private offset = 0;
  private length = 0;
  onEnded: (() => void) | null = null;

  get playing(): boolean {
    return this.source !== null;
  }

  /** Current playback position [s], or null when stopped. */
  position(): number | null {
    if (!this.source || !this.ctx) return null;
    return Math.min(this.length, this.offset + this.ctx.currentTime - this.startedAt);
  }

  play(samples: Float32Array, fs: number, offset = 0, peak = 0.9): void {
    this.stop();
    if (samples.length === 0) return;
    if (!this.ctx) this.ctx = new AudioContext({ sampleRate: fs });
    const ctx = this.ctx;
    const buffer = ctx.createBuffer(1, samples.length, fs);
    const ch = buffer.getChannelData(0);
    let max = 0;
    for (let k = 0; k < samples.length; k++) max = Math.max(max, Math.abs(samples[k]));
    const gain = max > 0 ? peak / max : 0;
    for (let k = 0; k < samples.length; k++) ch[k] = samples[k] * gain;
    const src = ctx.createBufferSource();
    src.buffer = buffer;
    src.connect(ctx.destination);
    src.onended = () => {
      if (this.source === src) {
        this.source = null;
        this.onEnded?.();
      }
    };
    this.length = samples.length / fs;
    this.offset = Math.max(0, Math.min(offset, this.length));
    this.startedAt = ctx.currentTime;
    this.source = src;
    src.start(0, this.offset);
    void ctx.resume();
  }

  stop(): void {
    if (this.source) {
      const s = this.source;
      this.source = null;
      try { s.stop(); } catch { /* already stopped */ }
    }
  }
}