async function connect(props) {
  const device = await navigator.bluetooth.requestDevice({
    filters: [{ services: ["cycling_speed_and_cadence"] }],
    acceptAllDevices: false,
  });
  console.log(`%c\n👩🏼‍⚕️`, "font-size: 82px;", "Starting CSC...\n\n");
  const server = await device.gatt.connect();
  const service = await server.getPrimaryService("cycling_speed_and_cadence");
  const char = await service.getCharacteristic("csc_measurement");
  char.oncharacteristicvaluechanged = props.onChange;
  char.startNotifications();
  return char;
}

function parseCSC({ value }) {
  const flags = value.getUint8(0, true);
  const hasWheel = !!(flags & 0x01);
  const hasCrank = !!(flags & 0x02);
  let index = 1;
  const res = {
    wheelRevs: null,
    wheelTime: null,
    crankRevs: null,
    crankTime: null,
  };
  if (hasWheel) {
    res.wheelRevs = value.getUint32(index, true);
    index += 4;
    res.wheelTime = value.getUint16(index, true);
    index += 2;
  }
  if (hasCrank) {
    res.crankRevs = value.getUint16(index, true);
    index += 2;
    res.crankTime = value.getUint16(index, true);
    index += 2;
  }
  console.log("CSC", res);
  const pre = document.createElement("pre");
  pre.style.border = "1px solid red";
  pre.textContent = JSON.stringify(res, null, 2);
  document.body.appendChild(pre);
  return res;
}

function revsToRPM(t1, t2) {
  const deltaRevs = t2.revs - t1.revs;
  if (deltaRevs === 0) {
    // no rotation
    return 0;
  }

  let deltaTime = (t2.time - t1.time) / 1024;
  if (deltaTime < 0) {
    // time counter wraparound
    deltaTime += Math.pow(2, 16) / 1024;
  }
  deltaTime /= 60; // seconds to minutes

  const rpm = deltaRevs / deltaTime;
  return rpm;
}

document.querySelector("#ble-connect").addEventListener("click", () =>
  connect({
    onChange: parseCSC,
  }).catch(console.error)
);