// ttn application function to decode uplink data.
// Decode decodes an array of bytes into an object.
//  - port contains the LoRaWAN fPort number
//  - bytes is an array of bytes, e.g. [225, 230, 255, 0]
// The function must return an object, e.g. {"temperature": 22.5}
function Decoder(bytes, port) {
  var decoded = {};
  var hexString=bin2HexStr(bytes);
  return rakSensorDataDecode(hexString);
}

// convert array of bytes to hex string.
// e.g: 0188053797109D5900DC140802017A0768580673256D0267011D040214AF0371FFFFFFDDFC2E
function bin2HexStr(bytesArr) {
  var str = "";
  for(var i=0; i<bytesArr.length; i++) {
    var tmp = (bytesArr[i] & 0xff).toString(16);
    if(tmp.length == 1) {
      tmp = "0" + tmp;
    }
    str += tmp;
  }
  return str;
}

// convert string to short integer
function parseShort(str, base) {
  var n = parseInt(str, base);
  return (n << 16) >> 16;
}

// convert string to triple bytes integer
function parseTriple(str, base) {
  var n = parseInt(str, base);
  return (n << 8) >> 8;
}

// decode Hex sensor string data to object
function rakSensorDataDecode(hexStr) {
  var str = hexStr;
  var myObj = {};

  while (str.length > 4) {
    var flag = parseInt(str.substring(0, 4), 16);
    switch (flag) {
      case 0x0768:// Humidity
        myObj.humidity = parseFloat(((parseShort(str.substring(4, 6), 16) * 0.01 / 2) * 100).toFixed(1)) + "%RH";//unit:%RH
        str = str.substring(6);
        break;
      case 0x0673:// Atmospheric pressure
        myObj.barometer = parseFloat((parseShort(str.substring(4, 8), 16) * 0.1).toFixed(2)) + "hPa";//unit:hPa
        str = str.substring(8);
        break;
      case 0x0267:// Temperature
        myObj.temperature = parseFloat((parseShort(str.substring(4, 8), 16) * 0.1).toFixed(2)) + "°C";//unit: °C
        str = str.substring(8);
        break;
      case 0x0188:// GPS
        myObj.latitude = parseFloat((parseTriple(str.substring(4, 10), 16) * 0.0001).toFixed(4)) + "°";//unit:°
        myObj.longitude = parseFloat((parseTriple(str.substring(10, 16), 16) * 0.0001).toFixed(4)) + "°";//unit:°
        myObj.altitude = parseFloat((parseTriple(str.substring(16, 22), 16) * 0.01).toFixed(1)) + "m";//unit:m
        str = str.substring(22);
        break;
      case 0x0371:// Triaxial acceleration
        myObj.acceleration_x = parseFloat((parseShort(str.substring(4, 8), 16) * 0.001).toFixed(3)) + "g";//unit:g
        myObj.acceleration_y = parseFloat((parseShort(str.substring(8, 12), 16) * 0.001).toFixed(3)) + "g";//unit:g
        myObj.acceleration_z = parseFloat((parseShort(str.substring(12, 16), 16) * 0.001).toFixed(3)) + "g";//unit:g
        str = str.substring(16);
        break;
      case 0x0402:// air resistance
        myObj.gasResistance = parseFloat((parseShort(str.substring(4, 8), 16) * 0.01).toFixed(2)) + "KΩ";//unit:KΩ
        str = str.substring(8);
        break;
      case 0x0802:// Battery Voltage
        myObj.battery = parseFloat((parseShort(str.substring(4, 8), 16) * 0.01).toFixed(2)) + "V";//unit:V
        str = str.substring(8);
        break;
      case 0x0586:// gyroscope
        myObj.gyroscope_x = parseFloat((parseShort(str.substring(4, 8), 16) * 0.01).toFixed(2)) + "°/s";//unit:°/s
        myObj.gyroscope_y = parseFloat((parseShort(str.substring(8, 12), 16) * 0.01).toFixed(2)) + "°/s";//unit:°/s
        myObj.gyroscope_z = parseFloat((parseShort(str.substring(12, 16), 16) * 0.01).toFixed(2)) + "°/s";//unit:°/s
        str = str.substring(16);
        break;
      case 0x0902:// magnetometer x
        myObj.magnetometer_x = parseFloat((parseShort(str.substring(4, 8), 16) * 0.01).toFixed(2)) + "μT";//unit:μT
        str = str.substring(8);
        break;
      case 0x0a02:// magnetometer y
        myObj.magnetometer_y = parseFloat((parseShort(str.substring(4, 8), 16) * 0.01).toFixed(2)) + "μT";//unit:μT
        str = str.substring(8);
        break;
      case 0x0b02:// magnetometer z
        myObj.magnetometer_z = parseFloat((parseShort(str.substring(4, 8), 16) * 0.01).toFixed(2)) + "μT";//unit:μT
        str = str.substring(8);
        break;
      default:
        str = str.substring(7);
        break;
    }
  }

  return myObj;
}