let audioCtx: AudioContext | null = null;

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

type ToneOptions = {
  readonly frequency: number;
  readonly endFrequency?: number;
  readonly duration: number;
  readonly type?: OscillatorType;
  readonly volume?: number;
  readonly delay?: number;
};

function playTone(ctx: AudioContext, opts: ToneOptions) {
  const { frequency, endFrequency, duration, type = "sine", volume = 0.2, delay = 0 } = opts;
  const osc = ctx.createOscillator();
  const gain = ctx.createGain();
  const t0 = ctx.currentTime + delay;
  osc.type = type;
  osc.frequency.setValueAtTime(Math.max(frequency, 1), t0);
  if (endFrequency && endFrequency !== frequency) {
    osc.frequency.exponentialRampToValueAtTime(Math.max(endFrequency, 1), t0 + duration);
  }
  gain.gain.setValueAtTime(0.0001, t0);
  gain.gain.exponentialRampToValueAtTime(volume, t0 + 0.012);
  gain.gain.exponentialRampToValueAtTime(0.0001, t0 + duration);
  osc.connect(gain);
  gain.connect(ctx.destination);
  osc.start(t0);
  osc.stop(t0 + duration + 0.05);
}

function playNoise(
  ctx: AudioContext,
  opts: { readonly duration: number; readonly volume?: number; readonly delay?: number; readonly lowpass?: number },
) {
  const { duration, volume = 0.2, delay = 0, lowpass = 800 } = opts;
  const bufferSize = Math.max(1, Math.floor(ctx.sampleRate * duration));
  const buffer = ctx.createBuffer(1, bufferSize, ctx.sampleRate);
  const data = buffer.getChannelData(0);
  for (let i = 0; i < bufferSize; i += 1) {
    data[i] = Math.random() * 2 - 1;
  }
  const source = ctx.createBufferSource();
  source.buffer = buffer;
  const filter = ctx.createBiquadFilter();
  filter.type = "lowpass";
  filter.frequency.setValueAtTime(lowpass, ctx.currentTime + delay);
  const gain = ctx.createGain();
  const t0 = ctx.currentTime + delay;
  gain.gain.setValueAtTime(0.0001, t0);
  gain.gain.exponentialRampToValueAtTime(volume, t0 + 0.005);
  gain.gain.exponentialRampToValueAtTime(0.0001, t0 + duration);
  source.connect(filter);
  filter.connect(gain);
  gain.connect(ctx.destination);
  source.start(t0);
}

export function playKeystroke() {
  const ctx = getCtx();
  if (!ctx) return;
  playTone(ctx, { frequency: 520, duration: 0.025, type: "square", volume: 0.025 });
}

export function playCorrect() {
  const ctx = getCtx();
  if (!ctx) return;
  playTone(ctx, { frequency: 620, endFrequency: 920, duration: 0.08, type: "sine", volume: 0.12 });
}

export function playError() {
  const ctx = getCtx();
  if (!ctx) return;
  playTone(ctx, { frequency: 150, endFrequency: 80, duration: 0.16, type: "square", volume: 0.14 });
  playNoise(ctx, { duration: 0.1, volume: 0.08, lowpass: 500 });
}

export function playRoundComplete() {
  const ctx = getCtx();
  if (!ctx) return;
  playTone(ctx, { frequency: 523, duration: 0.1, type: "sine", volume: 0.16 });
  playTone(ctx, { frequency: 659, duration: 0.1, type: "sine", volume: 0.16, delay: 0.1 });
  playTone(ctx, { frequency: 784, duration: 0.18, type: "sine", volume: 0.18, delay: 0.2 });
}

export function playXp() {
  const ctx = getCtx();
  if (!ctx) return;
  playTone(ctx, { frequency: 660, duration: 0.09, type: "sine", volume: 0.18 });
  playTone(ctx, { frequency: 880, duration: 0.16, type: "sine", volume: 0.18, delay: 0.09 });
}

export function playCountdownTick(intensity: "normal" | "fast" | "critical") {
  const ctx = getCtx();
  if (!ctx) return;
  if (intensity === "normal") {
    playTone(ctx, { frequency: 880, duration: 0.03, type: "square", volume: 0.05 });
  } else if (intensity === "fast") {
    playTone(ctx, { frequency: 1046, duration: 0.03, type: "square", volume: 0.07 });
  } else {
    playTone(ctx, { frequency: 1318, duration: 0.045, type: "square", volume: 0.11 });
  }
}

export function playCountdownEnd() {
  const ctx = getCtx();
  if (!ctx) return;
  playTone(ctx, { frequency: 1318, endFrequency: 240, duration: 0.75, type: "sine", volume: 0.16 });
  playTone(ctx, { frequency: 659, endFrequency: 120, duration: 0.75, type: "triangle", volume: 0.1 });
}