export const base64ToUint8Array = (base64: string) => {
  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;
};

export const uint8ArrayToBase64 = (bytes: Uint8Array) => {
  let binary = '';
  const len = bytes.byteLength;
  for (let i = 0; i < len; i++) {
    binary += String.fromCharCode(bytes[i]);
  }
  return btoa(binary);
};

export const triggerDownload = (blob: Blob, filename: string) => {
  const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url;
  a.download = filename;
  document.body.appendChild(a);
  a.click();
  document.body.removeChild(a);
  URL.revokeObjectURL(url);
};

export const createWavFileFromPcm = (pcmData: Uint8Array, sampleRate: number = 24000, numChannels: number = 1): Blob => {
  const header = new ArrayBuffer(44);
  const view = new DataView(header);
  
  const writeString = (view: DataView, offset: number, string: string) => {
    for (let i = 0; i < string.length; i++) {
      view.setUint8(offset + i, string.charCodeAt(i));
    }
  };

  writeString(view, 0, 'RIFF');
  view.setUint32(4, 36 + pcmData.length, true);
  writeString(view, 8, 'WAVE');
  writeString(view, 12, 'fmt ');
  view.setUint32(16, 16, true);
  view.setUint16(20, 1, true);
  view.setUint16(22, numChannels, true);
  view.setUint32(24, sampleRate, true);
  view.setUint32(28, sampleRate * numChannels * 2, true);
  view.setUint16(32, numChannels * 2, true);
  view.setUint16(34, 16, true);
  writeString(view, 36, 'data');
  view.setUint32(40, pcmData.length, true);

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

export const processAndDownloadAudio = (base64Data: string, filename: string) => {
  try {
    // Check for RIFF header (WAV)
    // Some base64 strings might have newlines, strip them if necessary, 
    // but generally atob handles it or we assume clean base64.
    const binaryString = atob(base64Data.substring(0, 50).replace(/\s/g, ''));
    const isWav = binaryString.startsWith('RIFF');
    
    if (isWav) {
       const bytes = base64ToUint8Array(base64Data);
       const blob = new Blob([bytes], { type: 'audio/wav' });
       triggerDownload(blob, filename);
    } else {
       // Assume Raw PCM 24kHz 16-bit Mono (Gemini Flash TTS default)
       const bytes = base64ToUint8Array(base64Data);
       const blob = createWavFileFromPcm(bytes, 24000, 1);
       triggerDownload(blob, filename);
    }
  } catch (e) {
    console.error("Error downloading audio", e);
  }
};