GPS Plugin for BMW ibus interface

gps-plugin.js

/**
 * This plugin will emit events with GPS coordinates
 *
 * const gps = new GPSPlugin();
 * gps.on('gps', ({ lat, lng, alt }) => console.log(lat, lng, alt));
 * MINI.addPlugin(gps);
 */
class GPSPlugin {

  /**
   * @var {bool} Flag determines if GPS has a fix or not.
   */
  isFixed = false;

  /**
   * @var {object} List of attached events.
   */
  events = {
    gps: () => {},
  };

  /**
   * Attach a event listener
   *
   * @todo Use event emitter
   * @param {string} Name of event
   * @param {function} Callback function
   */
  on(name, cb) {
    this.events[name] = cb;
  }

  /**
   * Check if last bit in byte is true
   *
   * 0000 0101 -> true
   * 1100 -> false
   *
   * @param {byte}
   * @return {bool}
   */
  toBool(byte) {
    return Boolean(+(byte >>> 0).toString(2).split('').pop());
  }

  /**
   * Convert 5 bytes to a single coordinate
   *
   * 00 36 42 06 61 = 0036°42'06.6" = -36.88516666666666
   *
   * @param {array} Bytes of [deg0, deg1, minutes, fragment+signed]
   * @return {float} /-?0+\.0+/
   */
  toDD(bytes) {
    const deg = Number(bytes.slice(0, 2).map(d => d.toString(16)).join(''));
    const min = Number(bytes[2].toString(16));
    const frag = String(bytes[4].toString(16))[0] / 10;
    const sec = Number(bytes[3].toString(16)) + frag;
    const signed = this.toBool(bytes[4].toString(16));
    const dd = deg + min / 60 + sec / (60 * 60);
    console.log(deg, min, sec, frag, signed, dd);
    return signed ? -dd : dd;
  }

  /**
   * Convert three bytes to UTC Date
   * 06 13 49 = 06:13:49 (hh:mm:ss)
   * @param {array}
   * @return {Date}
   */
  toUTC([hh, mm, ss]) {
    const date = new Date();
    date.setHours(hh.toString(16));
    date.setMinutes(mm.toString(16));
    date.setSeconds(ss.toString(16));
    return date;
  }

  /**
   * Fired from ibus driver.
   * @param {object} IBus message
   * @return {void}
   */
  onMessage({ src, dst, msg }) {
    if (src === 0x7F && dst === 0xC8) {
      if (msg[0] === 0xA2) {
        // Check if GPS has a fix or not
        this.isFixed = this.toBool(msg[1]);
        // Parse latitude
        const lat = this.toDD(msg.slice(2, 7));
        // Parse longitude
        const lng = this.toDD(msg.slice(7, 12));
        // Cast two bytes to 16 bit integer
        const alt = (msg[12] << 8) + msg[13];
        // Parse UTC date
        const utc = this.toUTC(msg.slice(15, 18));
        // Dispatch the event
        this.events.gps({ lat, lng, alt, utc });
      }
    }
  }
}