/**
 * Alarms and ticks, synthesised with the Web Audio API.
 *
 * No audio files to ship or to 404, and no autoplay surprise: the context is
 * created on the first user gesture (starting a timer counts) and reused.
 */
let context: AudioContext | null = null;

function ensureContext(): AudioContext | null {
  if (typeof window === "undefined") return null;
  if (!context) {
    const Ctor = window.AudioContext ?? (window as unknown as { webkitAudioContext?: typeof AudioContext }).webkitAudioContext;
    if (!Ctor) return null;
    context = new Ctor();
  }
  if (context.state === "suspended") void context.resume();
  return context;
}

function beep(frequency: number, seconds: number, volume: number, at = 0): void {
  const ctx = ensureContext();
  if (!ctx) return;
  const oscillator = ctx.createOscillator();
  const gain = ctx.createGain();
  oscillator.type = "sine";
  oscillator.frequency.value = frequency;
  const start = ctx.currentTime + at;
  // A short ramp instead of a hard stop; a clipped sine clicks.
  gain.gain.setValueAtTime(0.0001, start);
  gain.gain.exponentialRampToValueAtTime(Math.max(0.0002, volume), start + 0.02);
  gain.gain.exponentialRampToValueAtTime(0.0001, start + seconds);
  oscillator.connect(gain).connect(ctx.destination);
  oscillator.start(start);
  oscillator.stop(start + seconds + 0.05);
}

export const sound = {
  /** Work interval finished: three rising notes. */
  workDone(volume: number): void {
    const level = volume / 100;
    beep(660, 0.18, 0.25 * level, 0);
    beep(880, 0.18, 0.25 * level, 0.2);
    beep(1046, 0.4, 0.25 * level, 0.4);
  },
  /** Break finished: two falling notes — back to it. */
  breakDone(volume: number): void {
    const level = volume / 100;
    beep(880, 0.18, 0.22 * level, 0);
    beep(587, 0.35, 0.22 * level, 0.2);
  },
  tick(volume: number): void {
    beep(1200, 0.03, 0.04 * (volume / 100));
  },
  unlock(): void {
    ensureContext();
  },
};

/** A desktop notification, when the browser (or Electron) allows one. */
export function notify(title: string, body: string): void {
  if (typeof Notification === "undefined") return;
  if (Notification.permission === "granted") {
    new Notification(title, { body, icon: undefined });
  } else if (Notification.permission !== "denied") {
    void Notification.requestPermission();
  }
}