news-reader-actions-test/services/audioExportService.ts

import { Article, AudioSegment } from '../types';
import { SAMPLE_RATE } from '../constants';

/**
 * Combines multiple audio segments into a single downloadable file.
 * Since browser-based MP3 encoding is complex, we export as WAV format
 * which is widely supported and maintains quality.
 */
export const exportArticleAudio = async (
  article: Article,
  onProgress?: (progress: number) => void
): Promise<Blob> => {
  const audioSegments = article.segments.filter(seg => seg.audioUrl);

  if (audioSegments.length === 0) {
    throw new Error('No audio segments available for export');
  }

  // Fetch all audio data
  const audioBuffers: ArrayBuffer[] = [];
  let totalLength = 0;

  for (let i = 0; i < audioSegments.length; i++) {
    const segment = audioSegments[i];
    if (!segment.audioUrl) continue;

    try {
      const response = await fetch(segment.audioUrl);
      const arrayBuffer = await response.arrayBuffer();
      audioBuffers.push(arrayBuffer);

      // Parse WAV to get PCM data length (skip 44-byte header)
      totalLength += arrayBuffer.byteLength - 44;

      if (onProgress) {
        onProgress(Math.round(((i + 1) / audioSegments.length) * 100));
      }
    } catch (e) {
      console.warn(`Failed to fetch segment ${i}:`, e);
    }
  }

  if (audioBuffers.length === 0) {
    throw new Error('Failed to fetch any audio segments');
  }

  // Combine PCM data from all WAV files
  const combinedPcm = new Uint8Array(totalLength);
  let offset = 0;

  for (const buffer of audioBuffers) {
    // Skip WAV header (44 bytes) and copy PCM data
    const pcmData = new Uint8Array(buffer, 44);
    combinedPcm.set(pcmData, offset);
    offset += pcmData.length;
  }

  // Create new WAV file with combined data
  return createWavFile(combinedPcm, SAMPLE_RATE);
};

/**
 * Creates a WAV file from PCM data
 */
const createWavFile = (pcmData: Uint8Array, sampleRate: number): Blob => {
  const numChannels = 1;
  const bitsPerSample = 16;
  const byteRate = sampleRate * numChannels * (bitsPerSample / 8);
  const blockAlign = numChannels * (bitsPerSample / 8);
  const dataSize = pcmData.length;
  const fileSize = 44 + dataSize;

  const buffer = new ArrayBuffer(fileSize);
  const view = new DataView(buffer);

  // RIFF header
  writeString(view, 0, 'RIFF');
  view.setUint32(4, fileSize - 8, true);
  writeString(view, 8, 'WAVE');

  // fmt chunk
  writeString(view, 12, 'fmt ');
  view.setUint32(16, 16, true); // chunk size
  view.setUint16(20, 1, true); // PCM format
  view.setUint16(22, numChannels, true);
  view.setUint32(24, sampleRate, true);
  view.setUint32(28, byteRate, true);
  view.setUint16(32, blockAlign, true);
  view.setUint16(34, bitsPerSample, true);

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

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

  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));
  }
};

/**
 * Triggers download of the audio file
 */
export const downloadAudio = (blob: Blob, filename: string): void => {
  const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url;
  a.download = filename.endsWith('.wav') ? filename : `${filename}.wav`;
  document.body.appendChild(a);
  a.click();
  document.body.removeChild(a);
  URL.revokeObjectURL(url);
};

/**
 * Export and download article audio with progress tracking
 */
export const exportAndDownloadArticle = async (
  article: Article,
  onProgress?: (progress: number) => void
): Promise<void> => {
  const blob = await exportArticleAudio(article, onProgress);
  const safeTitle = article.title
    .replace(/[^a-zA-Z0-9\s]/g, '')
    .replace(/\s+/g, '_')
    .substring(0, 50);
  downloadAudio(blob, `${safeTitle}_newscaster.wav`);
};