/**
 * Encode PCM Int16 samples into a WAV file blob.
 * Assumes mono channel at the given sample rate.
 */
export function encodeWav(samples: Int16Array, sampleRate: number): Blob {
  const byteLength = samples.length * 2;
  const buffer = new ArrayBuffer(44 + byteLength);
  const view = new DataView(buffer);

  // RIFF header
  writeString(view, 0, "RIFF");
  view.setUint32(4, 36 + byteLength, true);
  writeString(view, 8, "WAVE");

  // fmt chunk
  writeString(view, 12, "fmt ");
  view.setUint32(16, 16, true); // chunk size
  view.setUint16(20, 1, true); // PCM format
  view.setUint16(22, 1, true); // mono
  view.setUint32(24, sampleRate, true);
  view.setUint32(28, sampleRate * 2, true); // byte rate
  view.setUint16(32, 2, true); // block align
  view.setUint16(34, 16, true); // bits per sample

  // data chunk
  writeString(view, 36, "data");
  view.setUint32(40, byteLength, true);

  // PCM samples
  const output = new Int16Array(buffer, 44);
  output.set(samples);

  return new Blob([buffer], { type: "audio/wav" });
}

function writeString(view: DataView, offset: number, str: string) {
  for (let i = 0; i < str.length; i++) {
    view.setUint8(offset + i, str.charCodeAt(i));
  }
}