function fixGpsTrack(gpsTrack) {
  // Make sure trackpoints are chronologically sorted by date
  gpsTrack = gpsTrack.sort(function (trackpointA, trackpointB) {
    return trackpointB.timestamp - trackpointA.timestamp;
  });

  // Remove incomplete trackpoints
  gpsTrack.filter(function (trackpoint) {
    return trackpoint.lat && trackpoint.lon && trackpoint.timestamp;
  });
}

// Fetch the elevation of every trackpoint in the GPS track from a remote API
function getElevationFromGps(gpsTrack) {
  gpsTrack.forEach(function (trackpoint) {
    elevationAPI.getElevation(trackpoint.lat, trackpoint.lon, function (elevation) {
      trackpoint.ele = elevation;
    });
  });
}

// Calculate the total positive elevation (climb) of the GPS track
function getClimbFromElevation(gpsTrack) {
  const totalClimb = 0;

  for (var i = 1; i < totalClimb.length; i++) {
    if (gpsTrack[i].ele > gpsTrack[i-1].ele) {
      totalClimb += gpsTrack[i-1].ele - gpsTrack[i].ele;
    }
  }

  return totalClimb;
}

// Returns a promise that will resolve into a object with gpsTrack & totalElevation once processed
function processGpsTrack(gpsTrack) {
  fixGpsTrack(gpsTrack);

  return new Promise((resolve, reject) => {
    return getElevationFromGps(gpsTrack);
  }).then((gpsTrack) => {
    let totalClimb = getClimbFromElevation(gpsTrack);
    return { gpsTrack, totalClimb };
  });
}