audio.js

// audio.js - Multi-tier natural neural voice pronunciation manager

let currentAudioInstance = null;

// Ensure browser voices are pre-loaded into cache upon extension initialization
if (typeof window !== 'undefined' && window.speechSynthesis) {
  window.speechSynthesis.getVoices();
  if (window.speechSynthesis.onvoiceschanged !== undefined) {
    window.speechSynthesis.onvoiceschanged = () => {
      window.speechSynthesis.getVoices();
    };
  }
}

/**
 * Immediately stop all active audio playback (both HTML5 Audio and Web Speech API)
 */
function stopAudio() {
  if (currentAudioInstance) {
    try {
      currentAudioInstance.pause();
      currentAudioInstance.currentTime = 0;
    } catch (e) {}
    currentAudioInstance = null;
  }
  if (typeof window !== 'undefined' && window.speechSynthesis) {
    try {
      window.speechSynthesis.cancel();
    } catch (e) {}
  }
}

/**
 * Main entrance to play human-like natural voice pronunciation
 */
function playPronunciation(word, lang, dictAudioUrl) {
  stopAudio();

  const cleanText = (word || '').replace(/\s+/g, ' ').trim();
  if (!cleanText) return;

  // 1. For paragraph/long text (>180 chars), use local Web Speech API (handles paragraphs natively)
  if (cleanText.length > 180) {
    speakWordLocal(cleanText, lang);
    return;
  }

  // 2. Try playing Free Dictionary API direct human recording (MP3) if available
  if (lang === 'en' && dictAudioUrl) {
    currentAudioInstance = new Audio(dictAudioUrl);
    currentAudioInstance.play().then(() => {
      console.log('Played Free Dictionary human audio');
    }).catch(err => {
      console.warn('Free Dictionary audio playback failed, falling back to Neural TTS:', err);
      playGoogleNeuralTts(cleanText, lang);
    });
    return;
  }

  // 3. Play Google Translate HD Neural TTS (high-definition natural voice)
  playGoogleNeuralTts(cleanText, lang);
}

/**
 * Play Google Neural Wavenet TTS (24kHz HD Natural Voice)
 */
function playGoogleNeuralTts(word, lang) {
  const ttsLang = lang === 'en' ? 'en' : 'fr';
  // Use client=gtx endpoint for high-definition Wavenet neural voice
  const ttsUrl = `https://translate.google.com/translate_tts?ie=UTF-8&tl=${ttsLang}&client=gtx&q=${encodeURIComponent(word)}`;
  
  currentAudioInstance = new Audio(ttsUrl);
  currentAudioInstance.play().then(() => {
    console.log('Played Google HD Neural TTS audio');
  }).catch(err => {
    console.warn('Google Neural TTS playback failed, falling back to Web Speech API:', err);
    speakWordLocal(word, lang);
  });
}

/**
 * Maps language codes (en, fr, es, de, ja, ko, it, pt, zh-TW, zh-CN) to SpeechVoice locales
 */
function getSpeechVoiceLocale(lang) {
  const map = {
    'en': 'en-US',
    'fr': 'fr-FR',
    'es': 'es-ES',
    'de': 'de-DE',
    'ja': 'ja-JP',
    'ko': 'ko-KR',
    'it': 'it-IT',
    'pt': 'pt-PT',
    'zh-TW': 'zh-TW',
    'zh-CN': 'zh-CN',
    'zh': 'zh-TW'
  };
  return map[lang] || `${lang}-${lang.toUpperCase()}`;
}

/**
 * Maps language codes to UI display segment labels
 */
function getLanguageLabel(code) {
  const labels = {
    'en': 'EN',
    'fr': 'FR',
    'es': 'ES',
    'de': 'DE',
    'ja': 'JA',
    'ko': 'KO',
    'it': 'IT',
    'pt': 'PT',
    'zh-TW': '繁中',
    'zh-CN': '簡中',
    'zh': '繁中'
  };
  return labels[code] || (code ? code.toUpperCase() : 'EN');
}

/**
 * Native SpeechSynthesis Local Voice Fallback
 */
function speakWordLocal(text, lang) {
  if (typeof window === 'undefined' || !window.speechSynthesis) return;

  const utterance = new SpeechSynthesisUtterance(text);
  const langPrefix = lang.split('-')[0];
  utterance.lang = getSpeechVoiceLocale(lang);

  const voices = window.speechSynthesis.getVoices();
  const matchingVoices = voices.filter(v => v.lang.startsWith(langPrefix));

  if (matchingVoices.length > 0) {
    // Score voices by quality tier to pick the most natural human-like voice
    const scoredVoices = matchingVoices.map(voice => {
      const name = voice.name.toLowerCase();
      let score = 0;

      // Tier 1: Modern Neural / Wavenet / Premium / Enhanced / Natural online voices
      if (name.includes('google') || name.includes('natural') || name.includes('neural') || name.includes('enhanced') || name.includes('premium') || name.includes('online') || name.includes('wavenet')) {
        score += 100;
      }
      // Tier 2: Siri & Premium Human Voice Models
      if (name.includes('siri') || name.includes('samantha') || name.includes('thomas') || name.includes('amélie') || name.includes('amelie') || name.includes('audrey') || name.includes('daniel') || name.includes('karen')) {
        score += 50;
      }
      // Penalty: Known legacy robotic synthesizer voices
      if (name.includes('alex') || name.includes('fred') || name.includes('zarvox') || name.includes('albert') || name.includes('boing') || name.includes('cellos') || name.includes('pipe organ')) {
        score -= 200;
      }

      return { voice, score };
    });

    // Sort descending by score
    scoredVoices.sort((a, b) => b.score - a.score);
    utterance.voice = scoredVoices[0].voice;
  }

  utterance.rate = 0.92; // Natural human speech tempo (slightly relaxed)
  utterance.pitch = 1.0; // Natural pitch
  window.speechSynthesis.speak(utterance);
}