A Web Bluetooth Template

const SERVICE_UUID = "19b10000-e8f2-537e-4f6c-d104768a1214";
const STATUS_CHAR  = "19b10001-e8f2-537e-4f6c-d104768a1214";
const CMD_CHAR     = "19b10002-e8f2-537e-4f6c-d104768a1214";

let bleDevice = null;
let cmdChar = null;

async function connectToCar() {
  try {
    // 1. Prompt user to choose the Bluetooth device
    bleDevice = await navigator.bluetooth.requestDevice({
      filters: [{ namePrefix: "EVDrive" }],
      optionalServices: [SERVICE_UUID],
    });

    bleDevice.addEventListener("gattserverdisconnected", () => {
      cmdChar = null;
      console.log("Car disconnected");
    });

    // 2. Connect to the GATT server
    const server = await bleDevice.gatt.connect();
    const service = await server.getPrimaryService(SERVICE_UUID);

    // 3. Listen for notifications from the car
    const statusChar = await service.getCharacteristic(STATUS_CHAR);
    await statusChar.startNotifications();
    statusChar.addEventListener("characteristicvaluechanged", handleIncomingData);

    // 4. Get the characteristic used for sending commands
    cmdChar = await service.getCharacteristic(CMD_CHAR);

    console.log("Connected to car!");
  } catch (err) {
    console.error("Connection failed:", err);
  }
}

function handleIncomingData(event) {
  // Decode raw bytes to text
  const message = new TextDecoder().decode(event.target.value).trim();

  // Human-readable events: log them and stop
  if (message.startsWith("STATUS:") || message.startsWith("STOP:")) {
    console.log("Car says:", message);
    return;
  }

  // CFG readback starts with "CFG:", so strip it, then parse like telemetry
  const body = message.startsWith("CFG:") ? message.slice(4) : message;

  // Split "KEY:value KEY:value ..." into an object
  const values = {};
  for (const token of body.split(" ")) {
    const i = token.indexOf(":");
    if (i > 0) values[token.slice(0, i)] = token.slice(i + 1);
  }

  if (message.startsWith("CFG:")) {
    console.log("Config:", values); // { DF: "7.000", KP: "28.0", ... }
  } else {
    console.log("Phase:", values.P);
    console.log("Distance:", parseFloat(values.D), "m");
    console.log("Heading:", parseFloat(values.H), "deg");
    console.log("Battery:", parseFloat(values.B), "V");
  }
}

async function sendCommand(commandText) {
  if (!cmdChar) {
    console.warn("Not connected to car");
    return;
  }

  // Encode string into bytes and write to the command characteristic
  const data = new TextEncoder().encode(commandText.trim());
  await cmdChar.writeValue(data);
  console.log("Sent command:", commandText);
}

// Example usage:
// sendCommand("DIST_F:7.0");
// sendCommand("TIME_F:6.5");
// sendCommand("START");