Source

// Small, soft sounds for right and wrong answers and a finished lesson, made on the fly (no audio files).
let ctx: AudioContext | null = null;

function tone(freq: number, start: number, length: number, type: OscillatorType, volume: number) {
  if (!ctx) return;
  const o = ctx.createOscillator();
  const g = ctx.createGain();
  o.type = type;
  o.frequency.value = freq;
  const t = ctx.currentTime + start;
  g.gain.setValueAtTime(0, t);
  g.gain.linearRampToValueAtTime(volume, t + 0.015);
  g.gain.exponentialRampToValueAtTime(0.0001, t + length);
  o.connect(g).connect(ctx.destination);
  o.start(t);
  o.stop(t + length + 0.05);
}

function ready(): boolean {
  try {
    ctx ??= new AudioContext();
    if (ctx.state === "suspended") void ctx.resume();
    return true;
  } catch {
    return false;
  }
}

export function chime(kind: "right" | "wrong" | "done") {
  if (!ready()) return;
  if (kind === "right") { tone(659.25, 0, 0.18, "sine", 0.09); tone(880, 0.09, 0.28, "sine", 0.08); }
  if (kind === "wrong") { tone(196, 0, 0.26, "triangle", 0.07); tone(174.6, 0.1, 0.3, "triangle", 0.06); }
  if (kind === "done") [523.25, 659.25, 783.99, 1046.5].forEach((f, i) => tone(f, i * 0.11, 0.35, "sine", 0.07));
}