index.js

'use strict';

(function () {

  var utils = {};

  utils.RATIOS = {
    // DISTANCE
    NM_IN_KM: 1.852,
    KM_IN_NM: 0.539956803,
    // SPEED
    // Knots
    KNOTS_IN_MS: 0.514444,
    KNOTS_IN_MPH: 1.150779,
    KNOTS_IN_KPH: 1.852,
    // MPH
    MPH_IN_MS: 0.44704,
    MPH_IN_KPH: 1.609344,
    MPH_IN_KNOTS: 0.868976,
    // KPH
    KPH_IN_MS: 0.277778,
    KPH_IN_MPH: 0.621371,
    KPH_IN_KNOTS: 0.539957,
    // MS
    MS_IN_KPH: 3.6,
    MS_IN_MPH: 2.236936,
    MS_IN_KNOTS: 1.943844,
    // DEGREE
    DEG_IN_RAD: 0.0174532925,
    RAD_IN_DEG: 57.2957795,
    // TEMPERATURES
    // Celcius
    CELCIUS_IN_KELVIN: 273.15,
    // Length
    METER_IN_FEET: 3.2808,
    METER_IN_FATHOM: 0.5468,
  };

  function checksum(sentencePart) {
    let check = 0;
    for (let i = 1; i < sentencePart.length; i++) {
      check = check ^ sentencePart.charCodeAt(i);
    };
    return check;
  }

  exports.valid = function (sentence, validateChecksum) {
    sentence = String(sentence).trim();

    if (sentence === "") {
      return false;
    }

    var validateChecksum = typeof validateChecksum === 'undefined' || validateChecksum

    if ((sentence.charAt(0) == '$' || sentence.charAt(0) == '!') && (validateChecksum == false || sentence.charAt(sentence.length - 3) == '*')) {
      if (validateChecksum) {
        let split = sentence.split('*');
        return (parseInt(split[1], 16) == checksum(split[0]));
      } else {
        return true
      }
    }
    return false;
  };

  exports.appendChecksum = function (sentence) {
    let split = String(sentence).trim().split('*');
    if (split.length === 1) {
      if (split[0].charAt(0) == '$' || split[0].charAt(0) == '!') {
        return split[0].concat('*').concat(checksum(split[0]).toString(16).padStart(2, '0').toUpperCase());
      }
    }
    return sentence;
  };

  exports.source = function (sentence) {
    return {
      type: 'NMEA0183',
      label: 'signalk-parser-nmea0183',
      sentence: sentence || ''
    };
  };

  exports.transform = function (value, inputFormat, outputFormat) {
    value = exports.float(value);

    inputFormat = inputFormat.toLowerCase();
    outputFormat = outputFormat.toLowerCase();

    if (inputFormat === outputFormat) {
      return value;
    }

    // KM
    if (inputFormat == 'km') {
      if (outputFormat == 'nm') return value / utils.RATIOS.NM_IN_KM;
    }

    // NM
    if (inputFormat == 'nm') {
      if (outputFormat == 'km') return value / utils.RATIOS.KM_IN_NM;
      if (outputFormat == 'm') return value * 1000 / utils.RATIOS.KM_IN_NM;
    }

    // KNOTS
    if (inputFormat == 'knots') {
      if (outputFormat == 'kph') return value / utils.RATIOS.KPH_IN_KNOTS;
      if (outputFormat == 'ms') return value / utils.RATIOS.MS_IN_KNOTS;
      if (outputFormat == 'mph') return value / utils.RATIOS.MPH_IN_KNOTS;
    }

    // KPH
    if (inputFormat == 'kph') {
      if (outputFormat == 'knots') return value / utils.RATIOS.KNOTS_IN_KPH;
      if (outputFormat == 'ms') return value / utils.RATIOS.MS_IN_KPH;
      if (outputFormat == 'mph') return value / utils.RATIOS.MPH_IN_KPH;
    }

    // MPH
    if (inputFormat == 'mph') {
      if (outputFormat == 'knots') return value / utils.RATIOS.KNOTS_IN_MPH;
      if (outputFormat == 'ms') return value / utils.RATIOS.MS_IN_MPH;
      if (outputFormat == 'kph') return value / utils.RATIOS.KPH_IN_MPH;
    }

    // MS
    if (inputFormat == 'ms') {
      if (outputFormat == 'knots') return value / utils.RATIOS.KNOTS_IN_MS;
      if (outputFormat == 'mph') return value / utils.RATIOS.MPH_IN_MS;
      if (outputFormat == 'kph') return value / utils.RATIOS.KPH_IN_MS;
    }

    // ANGLES
    if (inputFormat == 'deg') {
      if (outputFormat == 'rad') return value / utils.RATIOS.RAD_IN_DEG;
    }

    if (inputFormat == 'rad') {
      if (outputFormat == 'deg') return value / utils.RATIOS.DEG_IN_RAD;
    }

    if (inputFormat == 'c') {
      if (outputFormat == 'k') return value + utils.RATIOS.CELCIUS_IN_KELVIN;
    }

    if (inputFormat == 'k') {
      if (outputFormat == 'c') return value - utils.RATIOS.CELCIUS_IN_KELVIN;
      if (outputFormat == 'f') return (1.8 * (value - 273)) + 32;
    }
    // LENGTH
    if (inputFormat == 'ft') {
      if (outputFormat == 'm') return value / utils.RATIOS.METER_IN_FEET;
    }

    if (inputFormat == 'fa') {
      if (outputFormat == 'm') return value / utils.RATIOS.METER_IN_FATHOM;
    }
    // Just return input if input/output formats are not recognised.
    return value;
  };

  exports.magneticVariaton = function (degrees, pole) {
    pole = pole.toUpperCase();
    degrees = this.float(degrees);

    if (pole == "S" || pole == "W") {
      degrees *= -1;
    }

    return degrees;
  };

  exports.timestamp = function (time, date) {
    /* TIME (UTC) */
    var hours, minutes, seconds, year, month, day;

    if (time) {
      hours = this.int(time.slice(0, 2), true);
      minutes = this.int(time.slice(2, 4), true);
      seconds = this.int(time.slice(4, 6), true);
    } else {
      var dt = new Date();
      hours = dt.getUTCHours();
      minutes = dt.getUTCMinutes();
      seconds = dt.getUTCSeconds();
    }

    /* DATE (UTC) */
    if (date) {
      var year, month, day;
      day = this.int(date.slice(0, 2), true);
      month = this.int(date.slice(2, 4), true);
      year = this.int(date.slice(-2));
      year = 2000 + year;
    } else {
      var dt = new Date();
      year = dt.getUTCFullYear();
      month = dt.getUTCMonth();
      day = dt.getUTCDate();
    }

    /* construct */
    var d = new Date(Date.UTC(year, (month - 1), day, hours, minutes, seconds));
    return d.toISOString();
  };

  exports.coordinate = function (value, pole) {
    // N 5222.3277 should be read as 52°22.3277'
    // E 454.5824 should be read as 4°54.5824'
    //
    // 1. split at .
    // 2. last two characters of split[0] (.slice(-2)) + everything after . (split[1]) are the minutes
    // 3. degrees: split[0][a]
    // 4. minutes: split[0][b] + '.' + split[1]
    //
    // 52°22'19.662'' N -> 52.372128333
    // 4°54'34.944'' E -> 4.909706667
    // S & W should be negative.

    pole = pole.toUpperCase();

    var split = value.split('.');
    var degrees = this.float(split[0].slice(0, -2));
    var minsec = this.float(split[0].slice(-2) + '.' + split[1]);
    var decimal = this.float(degrees + (minsec / 60));

    if (pole == "S" || pole == "W") {
      decimal *= -1;
    }

    return exports.float(decimal);
  };

  exports.zero = function (n) {
    if (this.float(n) < 10) {
      return "0" + n;
    } else {
      return "" + n;
    }
  };

  exports.int = function (n) {
    if (("" + n).trim() === '') {
      return 0;
    } else {
      return parseInt(n, 10);
    }
  };

  exports.integer = function (n) {
    return exports.int(n);
  };

  exports.float = function (n) {
    if (("" + n).trim() === '') {
      return 0.0;
    } else {
      return parseFloat(n);
    }
  };

  exports.double = function (n) {
    return exports.float(n);
  };

})();