gnss-tool-kit/src/main/api/NMEAHandler.js

import nmea from 'nmea'

let events         = {}
const on           = (eventName, callback) => {
  if (!(eventName in events)) {
    events[eventName] = []
  }

  events[eventName].push(callback)
}

const emit         = (eventName, ...args) => {
  if (!(eventName in events)) {
    return
  }
  
  const cbs  = events[eventName]

  cbs.forEach(cb => {
    cb.call(this, ...args)
  });
}

const handle       = (value) => {
  if (value.length <= 0) return

  emit('received', value)

  const strArr = value.split('\r\n')
  for (let i = 0; i < strArr.length; i++) {
    const element = strArr[i];
    doHandle(element)
  }
  
  emit('handled', nmeaObj)
  nmeaObj = resetNMEAObj()
}

const doHandle     = (value) => {
  if (!verify(value)) {
    return
  }

  const result = nmea.parse(value)
  switch (result.sentence) {
    case 'RMC':
      nmeaObj.RMC = result
      break;
    case 'GGA':
      nmeaObj.GGA = result
      break;
    case 'GSA':
      if (result.talker_id === 'BD') nmeaObj.GSA.push(result)
      break;
    case 'GSV':
      if (result.talker_id === 'BD') nmeaObj.GSV.push(result)
      break;
    case 'TXT':
      break;
  }
}

const verify       = (value) => {
  if (!value) {
    return false
  }

  const dollar_index = value.indexOf('$')
  const star_index   = value.indexOf('*')
  if (value.indexOf('$') !== 0 || star_index <= dollar_index) {
    return false
  }
  
  const [sentence, checksum, ] = value.split('*')
  return nmea.Helpers.verifyChecksum(sentence, checksum)
}

const resetNMEAObj = () => {
  return {
    'RMC': null,
    'GGA': null,
    'GSA': [],
    'GSV': []
  }
}

let nmeaObj        = resetNMEAObj()

module.exports = { on, handle }