audio-ui/lib/audio/decoder.ts

/**
 * Audio file decoding utilities
 */

import { getAudioContext } from './context';

export interface ImportOptions {
  convertToMono?: boolean;
  targetSampleRate?: number; // If specified, resample to this rate
  normalizeOnImport?: boolean;
}

export interface AudioFileInfo {
  buffer: AudioBuffer;
  metadata: AudioMetadata;
}

export interface AudioMetadata {
  fileName: string;
  fileSize: number;
  fileType: string;
  duration: number;
  sampleRate: number;
  channels: number;
  bitDepth?: number;
  codec?: string;
}

/**
 * Decode an audio file to AudioBuffer with optional conversions
 */
export async function decodeAudioFile(
  file: File,
  options: ImportOptions = {}
): Promise<AudioBuffer> {
  const arrayBuffer = await file.arrayBuffer();
  const audioContext = getAudioContext();

  try {
    let audioBuffer = await audioContext.decodeAudioData(arrayBuffer);

    // Apply conversions if requested
    if (options.convertToMono && audioBuffer.numberOfChannels > 1) {
      audioBuffer = convertToMono(audioBuffer);
    }

    if (options.targetSampleRate && audioBuffer.sampleRate !== options.targetSampleRate) {
      audioBuffer = await resampleAudioBuffer(audioBuffer, options.targetSampleRate);
    }

    if (options.normalizeOnImport) {
      audioBuffer = normalizeAudioBuffer(audioBuffer);
    }

    return audioBuffer;
  } catch (error) {
    throw new Error(`Failed to decode audio file: ${error}`);
  }
}

/**
 * Decode audio file and return both buffer and metadata
 */
export async function importAudioFile(
  file: File,
  options: ImportOptions = {}
): Promise<AudioFileInfo> {
  const audioBuffer = await decodeAudioFile(file, options);
  const metadata = extractMetadata(file, audioBuffer);

  return {
    buffer: audioBuffer,
    metadata,
  };
}

/**
 * Convert stereo (or multi-channel) audio to mono
 */
function convertToMono(audioBuffer: AudioBuffer): AudioBuffer {
  const audioContext = getAudioContext();
  const numberOfChannels = audioBuffer.numberOfChannels;

  if (numberOfChannels === 1) {
    return audioBuffer; // Already mono
  }

  // Create a new mono buffer
  const monoBuffer = audioContext.createBuffer(
    1,
    audioBuffer.length,
    audioBuffer.sampleRate
  );

  const monoData = monoBuffer.getChannelData(0);

  // Mix all channels equally
  for (let i = 0; i < audioBuffer.length; i++) {
    let sum = 0;
    for (let channel = 0; channel < numberOfChannels; channel++) {
      sum += audioBuffer.getChannelData(channel)[i];
    }
    monoData[i] = sum / numberOfChannels;
  }

  return monoBuffer;
}

/**
 * Resample audio buffer to a different sample rate
 */
async function resampleAudioBuffer(
  audioBuffer: AudioBuffer,
  targetSampleRate: number
): Promise<AudioBuffer> {
  const audioContext = getAudioContext();

  // Create an offline context at the target sample rate
  const offlineContext = new OfflineAudioContext(
    audioBuffer.numberOfChannels,
    Math.ceil(audioBuffer.duration * targetSampleRate),
    targetSampleRate
  );

  // Create a buffer source
  const source = offlineContext.createBufferSource();
  source.buffer = audioBuffer;
  source.connect(offlineContext.destination);
  source.start(0);

  // Render the audio at the new sample rate
  const resampledBuffer = await offlineContext.startRendering();
  return resampledBuffer;
}

/**
 * Normalize audio buffer to peak amplitude
 */
function normalizeAudioBuffer(audioBuffer: AudioBuffer): AudioBuffer {
  const audioContext = getAudioContext();

  // Find peak amplitude across all channels
  let peak = 0;
  for (let channel = 0; channel < audioBuffer.numberOfChannels; channel++) {
    const channelData = audioBuffer.getChannelData(channel);
    for (let i = 0; i < channelData.length; i++) {
      const abs = Math.abs(channelData[i]);
      if (abs > peak) peak = abs;
    }
  }

  if (peak === 0 || peak === 1.0) {
    return audioBuffer; // Already normalized or silent
  }

  // Create normalized buffer
  const normalizedBuffer = audioContext.createBuffer(
    audioBuffer.numberOfChannels,
    audioBuffer.length,
    audioBuffer.sampleRate
  );

  // Apply normalization with 1% headroom
  const scale = 0.99 / peak;
  for (let channel = 0; channel < audioBuffer.numberOfChannels; channel++) {
    const inputData = audioBuffer.getChannelData(channel);
    const outputData = normalizedBuffer.getChannelData(channel);
    for (let i = 0; i < inputData.length; i++) {
      outputData[i] = inputData[i] * scale;
    }
  }

  return normalizedBuffer;
}

/**
 * Extract metadata from file and audio buffer
 */
function extractMetadata(file: File, audioBuffer: AudioBuffer): AudioMetadata {
  // Detect codec from file extension or MIME type
  const codec = detectCodec(file);

  return {
    fileName: file.name,
    fileSize: file.size,
    fileType: file.type || 'unknown',
    duration: audioBuffer.duration,
    sampleRate: audioBuffer.sampleRate,
    channels: audioBuffer.numberOfChannels,
    codec,
  };
}

/**
 * Detect audio codec from file
 */
function detectCodec(file: File): string {
  const ext = file.name.split('.').pop()?.toLowerCase();
  const mimeType = file.type.toLowerCase();

  if (mimeType.includes('wav') || ext === 'wav') return 'WAV (PCM)';
  if (mimeType.includes('mpeg') || mimeType.includes('mp3') || ext === 'mp3') return 'MP3';
  if (mimeType.includes('ogg') || ext === 'ogg') return 'OGG Vorbis';
  if (mimeType.includes('flac') || ext === 'flac') return 'FLAC';
  if (mimeType.includes('m4a') || mimeType.includes('aac') || ext === 'm4a') return 'AAC (M4A)';
  if (ext === 'aiff' || ext === 'aif') return 'AIFF';
  if (mimeType.includes('webm') || ext === 'webm') return 'WebM Opus';

  return 'Unknown';
}

/**
 * Get audio file metadata without decoding the entire file
 */
export async function getAudioFileMetadata(file: File): Promise<{
  name: string;
  size: number;
  type: string;
}> {
  return {
    name: file.name,
    size: file.size,
    type: file.type,
  };
}

/**
 * Check if a file is a supported audio format
 */
export function isSupportedAudioFormat(file: File): boolean {
  const supportedFormats = [
    'audio/wav',
    'audio/wave',
    'audio/x-wav',
    'audio/mpeg',
    'audio/mp3',
    'audio/ogg',
    'audio/webm',
    'audio/flac',
    'audio/aac',
    'audio/m4a',
    'audio/x-m4a',
    'audio/aiff',
    'audio/x-aiff',
  ];

  return supportedFormats.includes(file.type) ||
         /\.(wav|mp3|ogg|webm|flac|aac|m4a|aiff|aif)$/i.test(file.name);
}

/**
 * Format duration in seconds to MM:SS format
 */
export function formatDuration(seconds: number): string {
  const mins = Math.floor(seconds / 60);
  const secs = Math.floor(seconds % 60);
  return `${mins.toString().padStart(2, '0')}:${secs.toString().padStart(2, '0')}`;
}

/**
 * Format file size to human-readable format
 */
export function formatFileSize(bytes: number): string {
  if (bytes === 0) return '0 B';

  const k = 1024;
  const sizes = ['B', 'KB', 'MB', 'GB'];
  const i = Math.floor(Math.log(bytes) / Math.log(k));

  return `${parseFloat((bytes / Math.pow(k, i)).toFixed(2))} ${sizes[i]}`;
}