/**
 * Converts a Base64 string (Raw PCM) to a Uint8Array.
 */
export const base64ToUint8Array = (base64: string): Uint8Array => {
  const binaryString = atob(base64);
  const len = binaryString.length;
  const bytes = new Uint8Array(len);
  for (let i = 0; i < len; i++) {
    bytes[i] = binaryString.charCodeAt(i);
  }
  return bytes;
};

/**
 * Wraps raw PCM data in a WAV container so it can be played by standard HTML5 Audio elements.
 * This allows us to use `playbackRate` with automatic pitch preservation.
 */
export const createWavBlob = (pcmData: Uint8Array, sampleRate: number = 24000): Blob => {
  const numChannels = 1;
  const bitsPerSample = 16;
  const byteRate = (sampleRate * numChannels * bitsPerSample) / 8;
  const blockAlign = (numChannels * bitsPerSample) / 8;
  const dataSize = pcmData.length;
  const chunkSize = 36 + dataSize;

  const buffer = new ArrayBuffer(44 + dataSize);
  const view = new DataView(buffer);

  // RIFF chunk descriptor
  writeString(view, 0, 'RIFF');
  view.setUint32(4, chunkSize, true);
  writeString(view, 8, 'WAVE');

  // fmt sub-chunk
  writeString(view, 12, 'fmt ');
  view.setUint32(16, 16, true); // Subchunk1Size (16 for PCM)
  view.setUint16(20, 1, true); // AudioFormat (1 for PCM)
  view.setUint16(22, numChannels, true); // NumChannels
  view.setUint32(24, sampleRate, true); // SampleRate
  view.setUint32(28, byteRate, true); // ByteRate
  view.setUint16(32, blockAlign, true); // BlockAlign
  view.setUint16(34, bitsPerSample, true); // BitsPerSample

  // data sub-chunk
  writeString(view, 36, 'data');
  view.setUint32(40, dataSize, true);

  // Write PCM data
  const dataView = new Uint8Array(buffer, 44);
  dataView.set(pcmData);

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

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