function decodeUplink(input) {
  
  var payload = {};
  payload = buildPayload(input.bytes, input.fPort);
  
  return {
    data: payload,
    warnings: [],
    errors: []
  };
}

function buildPayload(bytes, port){
  
  var payload = buildCommonPayload(bytes, port);
  let callables = 
  {
    1:payload,
    2:locationHandler(bytes, payload),
    3:payload["status"]["context"]["error"] = noLocationHandler(bytes, payload)
  };
  callables[port];
  return payload;
}


function buildCommonPayload(_bytes, _port)
{
  var payload = {};
  var _deviceStatus = _bytes[0];
  var _temperature = _bytes[1];
  var _ACKAndBatteryVoltage = _bytes[2];
  var _operationMode = _deviceStatus & 0x3;//bit0~1
  var _batteryStatus = _deviceStatus & 0x4;//bi2
  var _motionState = _deviceStatus & (1 << 4);//bit5
  //correction for the sign
  if(_temperature > 128){_temperature -= 256;}
  var _ACK = _ACKAndBatteryVoltage & 0xF;
  var _batteryVoltage = ((_ACKAndBatteryVoltage & 0xF0)>>4)*0.1 + 2.2;
  var payloadType;
  
  if(_port == 0x1){payloadType = "heartbeat-payload";}
  else if(_port == 0x2){payloadType = "location-fixed-payload";}
  else if(_port == 0x3){payloadType = "no-location-fixed-payload";}
  
  payload = { 
          "temperature":{
              "value":_temperature
          }, 
          "battery-voltage":{
              "value":_batteryVoltage
          },
          "status": {
              "value":_port,
              "context":{
                  "payload-type":payloadType,
                  "battery-status":_batteryStatus,
                  "operation-mode":_operationMode,
                  "motion-status":_motionState,
                  "error":"none"
              }
          },
      };
  return payload;
}


function noLocationHandler(bytes)
{
  const ERROR_MESSAGES = {
    0: "WIFI positioning time not enough",
    1: "WIFI position strategies timeout",
    2: "WIFI module is not detected",
    3: "BlueTooth positioning time not enough",
    4: "BlueTooth position strategies timeout",
    5: "BlueTooth broadcasting in progress",
    6: "GPS position time budget over",
    7: "GPS coarse positioning timeout",
    8: "GPS fine positioning timeout",
    9: "GPS position time is not enough",
    10: "GPS aiding positioning timeout",
    11: "GPS cold start positioning timeout",
    12: "Interrupted by downlink for position",
    13: "Interrupted positioning at start of movement"
  }
  return ERROR_MESSAGES[bytes[3]];
}

function timeStampParser(bytes)
{
  var timeStamp = 0;
  var years = bytes[4] << 8 | bytes[5] << 0;
  var months = bytes[6] - 1;
  var days = bytes[7];
  var hours = bytes[8];
  var minutes = bytes[9];
  var seconds = bytes[10];
  var timezone = bytes[11];
  timeStamp = (Date.UTC(years, months, days, hours, minutes, seconds));
  
  if(timezone > 128)
  {
    timezone = timezone -256;
    timeStamp = timeStamp + timezone * (-1) * 60 * 60 * 1000;
  }
  else
  {
    timeStamp = timeStamp - timezone * 60 * 60 * 1000;
  }
  return timeStamp;
}

function coordinatesParser(coordinate)
{
  //2147483648=0x80000000
  //4294967296=0x100000000
  if(coordinate > 2147483648){coordinate -= 4294967296};
  coordinate /= 10000000;
  return coordinate;
}


function locationHandler(bytes, payload)
{
  var fixedType;
  var positioningType = bytes[3];
  var timeStamp = 0;
  timeStamp = timeStampParser(bytes);
  if(positioningType === 0x00){fixedType = "Wifi";}
  else if(positioningType == 0x01){fixedType = "BlueTooth";}
  else if(positioningType == 0x02){fixedType = "GPS";}
  else 
  { 
    payload["status"]["context"]["error"] = "invalid positioning value";
    return;
  }
  Object.assign(payload.temperature, {"context": {"timestamp": timeStamp}});
  Object.assign(payload["battery-voltage"], {"context": {"timestamp": timeStamp}});
  Object.assign(payload["status"]["context"], {"timestamp": timeStamp});

  if(positioningType == 0x02)
  {
    var lat = (bytes[13]<< 24 | bytes[14]<< 16 | bytes[15]<< 8 | bytes[16]<< 0);
    var lng = (bytes[17]<< 24 | bytes[18]<< 16 | bytes[19]<< 8 | bytes[20]<< 0);
    lat = coordinatesParser(lat);
    lng = coordinatesParser(lng);
    
    var positionPayload = {
      "position":{
          "value":1,
          "timestamp":timeStamp,
          "context":{
            "lat":lat,
            "lng":lng,
            "fixed-type":"GPS",
          }     
      },
    };
    
    Object.assign(payload, positionPayload);
  }
}