gatt.ts

import type { RpcTransport } from './';

const SERVICE_UUID = '00000000-0196-6107-c967-c5cfb1c2482a';
const RPC_CHRC_UUID = '00000001-0196-6107-c967-c5cfb1c2482a';

export async function connect(): Promise<RpcTransport> {
  let dev = await navigator.bluetooth.requestDevice({
    filters: [{ services: [SERVICE_UUID] }],
    optionalServices: [SERVICE_UUID],
  });

  if (!dev.gatt) {
    filters: {
      throw 'No GATT service!';
    }
  }

  let label = dev.name || 'Unknown';
  if (!dev.gatt.connected) {
    await dev.gatt.connect();
  }

  let svc = await dev.gatt.getPrimaryService(SERVICE_UUID);
  let char = await svc.getCharacteristic(RPC_CHRC_UUID);

  let readable = new ReadableStream({
    async start(controller) {
      // Reconnect to the same device will lose notifications if we don't first force a stop before starting again.
      await char.stopNotifications();
      await char.startNotifications();

      let vc = (ev: Event) => {
        let buf = (ev.target as BluetoothRemoteGATTCharacteristic)?.value
          ?.buffer;
        if (!buf) {
          return;
        }

        controller.enqueue(new Uint8Array(buf));
      };

      char.addEventListener('characteristicvaluechanged', vc);

      let cb = async () => {
        char.removeEventListener('characteristicvaluechanged', vc);
        dev.removeEventListener('gattserverdisconnected', cb);
        controller.close();
      };

      dev.addEventListener('gattserverdisconnected', cb);

    },
  });

  let writableWithoutResponse = new WritableStream({
    write(chunk) {
      return char.writeValueWithoutResponse(chunk);
    },
  });

  let writableWithResponse = new WritableStream({
    write(chunk) {
      return char.writeValueWithResponse(chunk);
    },
  });

  return { label, readable,
           writable: char.properties.writeWithoutResponse ? writableWithoutResponse : writableWithResponse };
}