audio-ui/lib/workers/audio.worker.ts

/**
 * Web Worker for heavy audio computations
 * Offloads waveform generation, analysis, and normalization to background thread
 */

export interface WorkerMessage {
  id: string;
  type: 'generatePeaks' | 'generateMinMaxPeaks' | 'normalizePeaks' | 'analyzeAudio' | 'findPeak';
  payload: any;
}

export interface WorkerResponse {
  id: string;
  type: string;
  result?: any;
  error?: string;
}

// Message handler
self.onmessage = (event: MessageEvent<WorkerMessage>) => {
  const { id, type, payload } = event.data;

  try {
    let result: any;

    switch (type) {
      case 'generatePeaks':
        result = generatePeaks(
          payload.channelData,
          payload.width
        );
        break;

      case 'generateMinMaxPeaks':
        result = generateMinMaxPeaks(
          payload.channelData,
          payload.width
        );
        break;

      case 'normalizePeaks':
        result = normalizePeaks(
          payload.peaks,
          payload.targetMax
        );
        break;

      case 'analyzeAudio':
        result = analyzeAudio(payload.channelData);
        break;

      case 'findPeak':
        result = findPeak(payload.channelData);
        break;

      default:
        throw new Error(`Unknown worker message type: ${type}`);
    }

    const response: WorkerResponse = { id, type, result };
    self.postMessage(response);
  } catch (error) {
    const response: WorkerResponse = {
      id,
      type,
      error: error instanceof Error ? error.message : String(error),
    };
    self.postMessage(response);
  }
};

/**
 * Generate waveform peaks from channel data
 */
function generatePeaks(channelData: Float32Array, width: number): Float32Array {
  const peaks = new Float32Array(width);
  const samplesPerPeak = Math.floor(channelData.length / width);

  for (let i = 0; i < width; i++) {
    const start = i * samplesPerPeak;
    const end = Math.min(start + samplesPerPeak, channelData.length);

    let max = 0;
    for (let j = start; j < end; j++) {
      const abs = Math.abs(channelData[j]);
      if (abs > max) {
        max = abs;
      }
    }

    peaks[i] = max;
  }

  return peaks;
}

/**
 * Generate min/max peaks for more detailed waveform visualization
 */
function generateMinMaxPeaks(
  channelData: Float32Array,
  width: number
): { min: Float32Array; max: Float32Array } {
  const min = new Float32Array(width);
  const max = new Float32Array(width);
  const samplesPerPeak = Math.floor(channelData.length / width);

  for (let i = 0; i < width; i++) {
    const start = i * samplesPerPeak;
    const end = Math.min(start + samplesPerPeak, channelData.length);

    let minVal = 1;
    let maxVal = -1;

    for (let j = start; j < end; j++) {
      const val = channelData[j];
      if (val < minVal) minVal = val;
      if (val > maxVal) maxVal = val;
    }

    min[i] = minVal;
    max[i] = maxVal;
  }

  return { min, max };
}

/**
 * Normalize peaks to a given range
 */
function normalizePeaks(peaks: Float32Array, targetMax: number = 1): Float32Array {
  const normalized = new Float32Array(peaks.length);
  let max = 0;

  // Find max value
  for (let i = 0; i < peaks.length; i++) {
    if (peaks[i] > max) {
      max = peaks[i];
    }
  }

  // Normalize
  const scale = max > 0 ? targetMax / max : 1;
  for (let i = 0; i < peaks.length; i++) {
    normalized[i] = peaks[i] * scale;
  }

  return normalized;
}

/**
 * Analyze audio data for statistics
 */
function analyzeAudio(channelData: Float32Array): {
  peak: number;
  rms: number;
  crestFactor: number;
  dynamicRange: number;
} {
  let peak = 0;
  let sumSquares = 0;
  let min = 1;
  let max = -1;

  for (let i = 0; i < channelData.length; i++) {
    const val = channelData[i];
    const abs = Math.abs(val);

    if (abs > peak) peak = abs;
    if (val < min) min = val;
    if (val > max) max = val;

    sumSquares += val * val;
  }

  const rms = Math.sqrt(sumSquares / channelData.length);
  const crestFactor = rms > 0 ? peak / rms : 0;
  const dynamicRange = max - min;

  return {
    peak,
    rms,
    crestFactor,
    dynamicRange,
  };
}

/**
 * Find peak value in channel data
 */
function findPeak(channelData: Float32Array): number {
  let peak = 0;

  for (let i = 0; i < channelData.length; i++) {
    const abs = Math.abs(channelData[i]);
    if (abs > peak) peak = abs;
  }

  return peak;
}