TTS engine

ttsEngine.ts

const synth = window.speechSynthesis;

let currentReadoutStrings: string[] = [];
let currentAlertStrings: string[] = [];
let currentSSU: SpeechSynthesisUtterance;

function reset(): void {
  currentReadoutStrings = [];
  currentAlertStrings = [];
}

function getNextReadoutString(): string {
  if (currentAlertStrings.length > 0) {
    return currentAlertStrings[0];
  }
  return currentReadoutStrings[0];
}

function removeLastReadoutString(): void {
  if (currentAlertStrings.length > 0) {
    currentAlertStrings.shift();
    return;
  }
  currentReadoutStrings.shift();
}

function speak(readoutStrings: string[]): void {
  currentReadoutStrings = readoutStrings;
  if (currentAlertStrings.length === 0) {
    stop();
    read();
  }
}

function interruptAndSpeak(readoutStrings: string[]): void {
  stop();
  currentAlertStrings = readoutStrings;
  read();
}

function appendAndSpeak(readoutStrings: string[]): void {
  if (currentReadoutStrings.length === 0) {
    speak(readoutStrings);
  } else {
    currentReadoutStrings = currentReadoutStrings.concat(readoutStrings);
  }
}

function stop(): void {
  if (currentSSU) {
    currentSSU.onend = () => {};
  }
  synth.cancel();
}

function read(): void {
  const nextReadoutString = getNextReadoutString();
  if (nextReadoutString === undefined) {
    return;
  }

  currentSSU = new SpeechSynthesisUtterance(nextReadoutString);
  currentSSU.onend = () => {
    removeLastReadoutString();
    read();
  };
  synth.speak(currentSSU);
}

export {
  speak,
  appendAndSpeak,
  interruptAndSpeak,
  stop,
  reset,
};