const TARGET_RATE = 16000;
type Control = { kind: "enable"; value: boolean } | { kind: "gate"; enabled: boolean; thresholdDb: number };

/** Preserve the existing 40 ms PCM16 frames and smoothed gate envelope. */
class MicCaptureProcessor extends AudioWorkletProcessor {
  private readonly ratio = sampleRate / TARGET_RATE;
  private readonly chunkSize = 640;
  private scratch = new Float32Array(0);
  private readonly decimated = new Float32Array(this.chunkSize);
  private enabled = true;
  private gateEnabled = false;
  private threshold = 0;
  private gain = 1;
  private hold = 0;
  private readonly attack = Math.exp(-1 / (0.005 * TARGET_RATE));
  private readonly release = Math.exp(-1 / (0.08 * TARGET_RATE));

  constructor() {
    super();
    this.port.onmessage = (event: MessageEvent<Control>) => {
      if (event.data.kind === "enable") {
        this.enabled = event.data.value;
      } else {
        this.gateEnabled = event.data.enabled;
        this.threshold = event.data.enabled ? 10 ** (event.data.thresholdDb / 20) : 0;
      }
    };
  }

  process(inputs: Float32Array[][]) {
    const incoming = inputs[0]?.[0];
    if (!incoming?.length) {
      return true;
    }
    const next = new Float32Array(this.scratch.length + incoming.length);
    next.set(this.scratch);
    next.set(incoming, this.scratch.length);
    this.scratch = next;
    const needed = Math.ceil(this.chunkSize * this.ratio);
    while (this.scratch.length >= needed) {
      let sum = 0;
      for (let index = 0; index < this.chunkSize; index++) {
        const position = index * this.ratio;
        const start = Math.floor(position);
        const a = this.scratch[start] ?? 0;
        const value =
          Math.abs(this.ratio - 3) < 1e-6
            ? (a + (this.scratch[start + 1] ?? 0) + (this.scratch[start + 2] ?? 0)) / 3
            : a + ((this.scratch[start + 1] ?? a) - a) * (position - start);
        this.decimated[index] = value;
        sum += value * value;
      }
      const rms = Math.sqrt(sum / this.chunkSize);
      let target = 1;
      if (this.gateEnabled) {
        if (rms >= this.threshold) {
          this.hold = TARGET_RATE * 0.25;
        } else if (this.hold > 0) {
          this.hold -= this.chunkSize;
        } else {
          target = 0;
        }
      }
      const output = new Int16Array(this.chunkSize);
      for (let index = 0; index < this.chunkSize; index++) {
        const coefficient = target > this.gain ? this.attack : this.release;
        this.gain = target + (this.gain - target) * coefficient;
        const value = Math.max(-1, Math.min(1, (this.decimated[index] ?? 0) * this.gain));
        output[index] = value < 0 ? value * 0x8000 : value * 0x7fff;
      }
      this.scratch = this.scratch.slice(Math.floor(this.chunkSize * this.ratio));
      this.port.postMessage({ kind: "level", rms });
      if (this.enabled) {
        this.port.postMessage(output.buffer, [output.buffer]);
      }
    }
    return true;
  }
}
registerProcessor("mic-capture", MicCaptureProcessor);