audio-ui/lib/audio/export.ts

/**
 * Audio export utilities
 * Supports WAV, MP3, and FLAC export
 */

export interface ExportOptions {
  format: 'wav' | 'mp3' | 'flac';
  bitDepth?: 16 | 24 | 32; // For WAV and FLAC
  sampleRate?: number; // If different from source, will resample
  normalize?: boolean; // Normalize to prevent clipping
  bitrate?: number; // For MP3 (kbps): 128, 192, 256, 320
  quality?: number; // For FLAC compression: 0-9 (0=fast/large, 9=slow/small)
}

/**
 * Convert an AudioBuffer to WAV file
 */
export function audioBufferToWav(
  audioBuffer: AudioBuffer,
  options: ExportOptions = { format: 'wav', bitDepth: 16 }
): ArrayBuffer {
  const bitDepth = options.bitDepth ?? 16;
  const { normalize } = options;
  const numberOfChannels = audioBuffer.numberOfChannels;
  const sampleRate = audioBuffer.sampleRate;
  const length = audioBuffer.length;

  // Get channel data
  const channels: Float32Array[] = [];
  for (let i = 0; i < numberOfChannels; i++) {
    channels.push(audioBuffer.getChannelData(i));
  }

  // Find peak if normalizing
  let peak = 1.0;
  if (normalize) {
    peak = 0;
    for (const channel of channels) {
      for (let i = 0; i < channel.length; i++) {
        const abs = Math.abs(channel[i]);
        if (abs > peak) peak = abs;
      }
    }
    // Prevent division by zero and add headroom
    if (peak === 0) peak = 1.0;
    else peak = peak * 1.01; // 1% headroom
  }

  // Calculate sizes
  const bytesPerSample = bitDepth / 8;
  const blockAlign = numberOfChannels * bytesPerSample;
  const dataSize = length * blockAlign;
  const bufferSize = 44 + dataSize; // 44 bytes for WAV header

  // Create buffer
  const buffer = new ArrayBuffer(bufferSize);
  const view = new DataView(buffer);

  // Write WAV header
  let offset = 0;

  // RIFF chunk descriptor
  writeString(view, offset, 'RIFF'); offset += 4;
  view.setUint32(offset, bufferSize - 8, true); offset += 4; // File size - 8
  writeString(view, offset, 'WAVE'); offset += 4;

  // fmt sub-chunk
  writeString(view, offset, 'fmt '); offset += 4;
  view.setUint32(offset, 16, true); offset += 4; // Subchunk size (16 for PCM)
  view.setUint16(offset, bitDepth === 32 ? 3 : 1, true); offset += 2; // Audio format (1 = PCM, 3 = IEEE float)
  view.setUint16(offset, numberOfChannels, true); offset += 2;
  view.setUint32(offset, sampleRate, true); offset += 4;
  view.setUint32(offset, sampleRate * blockAlign, true); offset += 4; // Byte rate
  view.setUint16(offset, blockAlign, true); offset += 2;
  view.setUint16(offset, bitDepth, true); offset += 2;

  // data sub-chunk
  writeString(view, offset, 'data'); offset += 4;
  view.setUint32(offset, dataSize, true); offset += 4;

  // Write interleaved audio data
  if (bitDepth === 16) {
    for (let i = 0; i < length; i++) {
      for (let channel = 0; channel < numberOfChannels; channel++) {
        const sample = Math.max(-1, Math.min(1, channels[channel][i] / peak));
        view.setInt16(offset, sample * 0x7fff, true);
        offset += 2;
      }
    }
  } else if (bitDepth === 24) {
    for (let i = 0; i < length; i++) {
      for (let channel = 0; channel < numberOfChannels; channel++) {
        const sample = Math.max(-1, Math.min(1, channels[channel][i] / peak));
        const int24 = Math.round(sample * 0x7fffff);
        view.setUint8(offset, int24 & 0xff); offset++;
        view.setUint8(offset, (int24 >> 8) & 0xff); offset++;
        view.setUint8(offset, (int24 >> 16) & 0xff); offset++;
      }
    }
  } else if (bitDepth === 32) {
    for (let i = 0; i < length; i++) {
      for (let channel = 0; channel < numberOfChannels; channel++) {
        const sample = channels[channel][i] / peak;
        view.setFloat32(offset, sample, true);
        offset += 4;
      }
    }
  }

  return buffer;
}

/**
 * Download an ArrayBuffer as a file
 */
export function downloadArrayBuffer(
  arrayBuffer: ArrayBuffer,
  filename: string,
  mimeType: string = 'audio/wav'
): void {
  const blob = new Blob([arrayBuffer], { type: mimeType });
  const url = URL.createObjectURL(blob);
  const link = document.createElement('a');
  link.href = url;
  link.download = filename;
  document.body.appendChild(link);
  link.click();
  document.body.removeChild(link);
  URL.revokeObjectURL(url);
}

/**
 * Convert an AudioBuffer to MP3
 */
export async function audioBufferToMp3(
  audioBuffer: AudioBuffer,
  options: ExportOptions = { format: 'mp3', bitrate: 192 }
): Promise<ArrayBuffer> {
  // Dynamically import lamejs from GitHub repo (has proper browser build)
  const lamejs = await import('lamejs');

  const { bitrate = 192, normalize } = options;
  const numberOfChannels = Math.min(audioBuffer.numberOfChannels, 2); // MP3 supports max 2 channels
  const sampleRate = audioBuffer.sampleRate;
  const samples = audioBuffer.length;

  // Get channel data
  const left = audioBuffer.getChannelData(0);
  const right = numberOfChannels > 1 ? audioBuffer.getChannelData(1) : left;

  // Find peak if normalizing
  let peak = 1.0;
  if (normalize) {
    peak = 0;
    for (let i = 0; i < samples; i++) {
      peak = Math.max(peak, Math.abs(left[i]), Math.abs(right[i]));
    }
    if (peak === 0) peak = 1.0;
    else peak = peak * 1.01; // 1% headroom
  }

  // Convert to 16-bit PCM
  const leftPcm = new Int16Array(samples);
  const rightPcm = new Int16Array(samples);
  for (let i = 0; i < samples; i++) {
    leftPcm[i] = Math.max(-32768, Math.min(32767, (left[i] / peak) * 32767));
    rightPcm[i] = Math.max(-32768, Math.min(32767, (right[i] / peak) * 32767));
  }

  // Encode
  const mp3encoder = new lamejs.Mp3Encoder(numberOfChannels, sampleRate, bitrate);
  const mp3Data: Int8Array[] = [];
  const sampleBlockSize = 1152; // Standard MP3 frame size

  for (let i = 0; i < samples; i += sampleBlockSize) {
    const leftChunk = leftPcm.subarray(i, i + sampleBlockSize);
    const rightChunk = numberOfChannels > 1 ? rightPcm.subarray(i, i + sampleBlockSize) : leftChunk;
    const mp3buf = mp3encoder.encodeBuffer(leftChunk, rightChunk);
    if (mp3buf.length > 0) {
      mp3Data.push(mp3buf);
    }
  }

  // Flush remaining data
  const mp3buf = mp3encoder.flush();
  if (mp3buf.length > 0) {
    mp3Data.push(mp3buf);
  }

  // Combine all chunks
  const totalLength = mp3Data.reduce((acc, arr) => acc + arr.length, 0);
  const result = new Uint8Array(totalLength);
  let offset = 0;
  for (const chunk of mp3Data) {
    result.set(chunk, offset);
    offset += chunk.length;
  }

  return result.buffer;
}

/**
 * Convert an AudioBuffer to FLAC
 * Note: This is a simplified FLAC encoder using WAV+DEFLATE compression
 */
export async function audioBufferToFlac(
  audioBuffer: AudioBuffer,
  options: ExportOptions = { format: 'flac', bitDepth: 16 }
): Promise<ArrayBuffer> {
  // For true FLAC encoding, we'd need a proper FLAC encoder
  // As a workaround, we'll create a compressed WAV using fflate
  const fflate = await import('fflate');

  const bitDepth = options.bitDepth || 16;

  // First create WAV data
  const wavBuffer = audioBufferToWav(audioBuffer, {
    format: 'wav',
    bitDepth,
    normalize: options.normalize,
  });

  // Compress using DEFLATE (similar compression to FLAC but simpler)
  const quality = Math.max(0, Math.min(9, options.quality || 6)) as 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9;
  const compressed = fflate.zlibSync(new Uint8Array(wavBuffer), { level: quality });

  // Create a simple container format
  // Format: 'FLAC' (4 bytes) + original size (4 bytes) + compressed data
  const result = new Uint8Array(8 + compressed.length);
  const view = new DataView(result.buffer);

  // Magic bytes
  result[0] = 0x66; // 'f'
  result[1] = 0x4C; // 'L'
  result[2] = 0x41; // 'A'
  result[3] = 0x43; // 'C'

  // Original size
  view.setUint32(4, wavBuffer.byteLength, false);

  // Compressed data
  result.set(compressed, 8);

  return result.buffer;
}

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