frontend/src/tts.js

// Shared browser text-to-speech helper (French voice).
//
// `getVoices()` is unreliable on first call (especially Chrome): the voice
// list often loads asynchronously, so an early call returns `[]`. We cache
// the list, refresh it on the `voiceschanged` event, and pick a French voice
// once it's available — `lang` is always set to 'fr-FR' regardless, so the
// browser still defaults sanely if no matching voice is found.
//
// Beginners need speech slowed down, and we prefer a female voice (common
// names across Chrome/macOS/Edge French voice packs).

const SPEECH_RATE = 0.85

const FEMALE_VOICE_NAMES = [
  'amélie', 'amelie', 'audrey', 'marie', 'julie', 'hortense',
  'céline', 'celine', 'virginie', 'chantal', 'aurélie', 'aurelie',
  'google français', 'female',
]

let cachedVoices = []

function refreshVoices() {
  if (!window.speechSynthesis) return
  const voices = window.speechSynthesis.getVoices()
  if (voices.length) cachedVoices = voices
}

if (window.speechSynthesis) {
  refreshVoices()
  window.speechSynthesis.addEventListener('voiceschanged', refreshVoices)
}

function isFemaleVoice(voice) {
  const name = voice.name.toLowerCase()
  return FEMALE_VOICE_NAMES.some((n) => name.includes(n))
}

function frenchVoice() {
  refreshVoices()
  const frFR = cachedVoices.filter((v) => v.lang === 'fr-FR')
  const frAny = cachedVoices.filter((v) => v.lang && v.lang.startsWith('fr'))
  return (
    frFR.find(isFemaleVoice) ||
    frAny.find(isFemaleVoice) ||
    frFR[0] ||
    frAny[0] ||
    null
  )
}

function makeUtterance(text) {
  const u = new SpeechSynthesisUtterance(text)
  u.lang = 'fr-FR'
  u.rate = SPEECH_RATE
  const voice = frenchVoice()
  if (voice) u.voice = voice
  return u
}

export function speak(text) {
  if (!text || !window.speechSynthesis) return
  window.speechSynthesis.cancel()
  window.speechSynthesis.speak(makeUtterance(text))
}

// Speak several lines back-to-back (e.g. consecutive dialogue turns from the
// same speaker) without one cancelling the next.
export function speakAll(texts) {
  const list = (texts || []).filter(Boolean)
  if (!list.length || !window.speechSynthesis) return
  window.speechSynthesis.cancel()
  for (const text of list) {
    window.speechSynthesis.speak(makeUtterance(text))
  }
}