const SERVICE_UUID = "your-service-uuid";
const CHAR_UUID    = "your-char-uuid";

let device, characteristic;

// --- Connect ---
async function connect() {
  device = await navigator.bluetooth.requestDevice({
    filters: [{ services: [SERVICE_UUID] }]
  });
  const server = await device.gatt.connect();
  const service = await server.getPrimaryService(SERVICE_UUID);
  characteristic = await service.getCharacteristic(CHAR_UUID);

  // Listen for indications from the ESP32
  await characteristic.startNotifications();
  characteristic.addEventListener("characteristicvaluechanged", onReceive);
  console.log("Connected");
}

// --- Receive (chunk reassembly) ---
let rxBuffer = new Uint8Array(0);
let expectedLen = 0;
let expectedType = 0;
let headerReceived = false;

function onReceive(event) {
  const chunk = new Uint8Array(event.target.value.buffer);

  // Append chunk to buffer
  const tmp = new Uint8Array(rxBuffer.length + chunk.length);
  tmp.set(rxBuffer);
  tmp.set(chunk, rxBuffer.length);
  rxBuffer = tmp;

  // Parse header once we have 3 bytes
  if (!headerReceived && rxBuffer.length >= 3) {
    expectedType = rxBuffer[0];
    expectedLen = rxBuffer[1] | (rxBuffer[2] << 8);
    rxBuffer = rxBuffer.slice(3);
    headerReceived = true;
  }

  // Complete message?
  if (headerReceived && rxBuffer.length >= expectedLen) {
    const payload = rxBuffer.slice(0, expectedLen);

    if (expectedType === 0x00) {
      const json = JSON.parse(new TextDecoder().decode(payload));
      console.log("Received JSON:", json);
    } else {
      console.log(`Received Binary: type=${expectedType}, ${payload.length} bytes`);
    }

    // Reset for next message
    rxBuffer = new Uint8Array(0);
    headerReceived = false;
  }
}

// --- Send JSON ---
async function sendJson(obj) {
  const text = JSON.stringify(obj);
  const payload = new TextEncoder().encode(text);
  const len = payload.length;

  // Header: [TYPE=0x00][LEN_LO][LEN_HI] + payload
  const buffer = new Uint8Array(3 + len);
  buffer[0] = 0x00;
  buffer[1] = len & 0xFF;
  buffer[2] = (len >> 8) & 0xFF;
  buffer.set(payload, 3);

  await characteristic.writeValueWithResponse(buffer);
}

// --- Usage ---
await connect();
await sendJson({ cmd: "get_info" });