/*
   * Decoder of Balloon FTD frames for NodeRED
   * Author: Didier DONSEZ, Université Grenoble Alpes
   */
  
  var p = msg.payload;
  
  if(! p.frmPayload) {
      return undefined;
  }
  
  var e = p.extra;
  if(! e) {
      return undefined;
  }
  
  var applicationName = e.applicationName;
  if(! applicationName) {
      return undefined;
  }
  
  if(applicationName !== "BALLOON_FTD") {
      return undefined;
  }
  
  // Decoder here
  
  // Decode decodes an array of bytes into an object.
  //  - fPort contains the LoRaWAN fPort number
  //  - bytes is an array of bytes, e.g. [225, 230, 255, 0]
  //  - variables contains the device variables e.g. {"calibration": "3.5"} (both the key / value are of type string)
  // The function must return an object, e.g. {"temperature": 22.5}
  function Decode(fPort, bytes, variables) {
  
    var o = {};
  
    if(fPort === 202) {
    	// App Clock Synchronization (https://lora-alliance.org/resource-hub/lorawanr-application-layer-clock-synchronization-specification-v100).
    	// Remark: The synchronization is done at the Chirpstack LNS level.
      // TODO
    } else {
      var size = bytes.length;
      
      o.benchmark_id = fPort;
      
      o.size = size;
  
      if(size < 2) { return o; }
  
      o.txpower = bytes.readUInt8(0);
      o.dataRate = bytes.readUInt8(1);
  
      if(size < 4) { return o; }
  
      o.temperature = bytes.readInt16BE(2)/100.0;
  
      if(size < 12) { return o; }
  
      // Value used for the conversion of the position from DMS to decimal.
      const MaxNorthPosition = 8388607; // 2^23 - 1
      const MaxEastPosition  = 8388607; // 2^23 - 1
  
      // Extract latitude.
      var Latitude = (bytes.readUInt32BE(4) >> 8) & 0x7FFF;
      Latitude = Latitude * 90 / MaxNorthPosition;
      o.latitude = Math.round(Latitude * 1000000) / 1000000;
  
      // Extract longitude.
      var Longitude = (bytes.readInt32BE(7) >> 8);
      Longitude = Longitude * 180 / MaxEastPosition;
      o.longitude = Math.round(Longitude * 1000000) / 1000000;
  
      // Extract altitude.
      o.altitude = bytes.readUInt16BE(10);
    }
    return o;
  }
  // Decode here
  
  var l = p.metadata.network.lora;
  
  var o = Decode(l.port,p.frmPayload,undefined);
  
  msg.payload.object = o;
  
  // For worldmap
  msg.payload.img = "ds75lx.png";
  
  return msg;