/**
 * Calculate Mileage (written in JS)
 */

function(err, spots) {

  if (err) throw err;

  var totalDist = 0;
  var dist = 0;
  var radlat1, radlat2, theta, radtheta;
  var timeDiff = 0;
  var diffPerHour = 0;
  var milesPerHour = 0;
  var updateArr = [];

  for(var i=1;i<spots.length;i++){
    if (spots[i].latitude === spots[i-1].latitude && spots[i].longitude === spots[i-1].longitude) {
      /** check for identical lat/lon coords to last spot(duplicate) and mark as invalid */
      spots[i].isValid = false;
      /** push the spot to the pending updates array */
      updateArr.push(spots[i]);

    } else {
      /** lat/long is different so some distance was travelled, do the math */

      /** distance calc from last spot */
      radlat1 = Math.PI * spots[i-1].latitude/180;
      radlat2 = Math.PI * spots[i].latitude/180;
      theta = spots[i-1].longitude-spots[i].longitude;
      radtheta = Math.PI * theta/180;
      dist = Math.sin(radlat1) * Math.sin(radlat2) + Math.cos(radlat1) * Math.cos(radlat2) * Math.cos(radtheta);
      dist = Math.acos(dist);
      dist = dist * 180/Math.PI;
      dist = dist * 60 * 1.1515;

      /** sequential identical lat/lon coords will return NaN(you're trying to divide by 0), so log an error and skip the rest. NaN is special in that it is NOT equal to itself. */
      if (dist != dist) {
        console.log('distance calc returned NaN for:',spots[i-1].id,'to',spots[i].id);
      } else {
        /** if distance was valid, but less the margin of error, set distance to 1 foot(in miles) */
        if (dist === 0) { dist = 0.00018939393; }

        /** calculate time since last spot */
        timeDiff = spots[i].unixTime - spots[i-1].unixTime;
        if (timeDiff > 7200) {
          /** if it's been more than two hours, log a possible handoff or stop */
          console.log(color.yellow('Possible Handoff'));
        }
        diffPerHour = 3600/timeDiff;

        /** calculate time since last spot */
        milesPerHour = dist * diffPerHour;
        var minutes = Math.floor(Math.floor(timeDiff)/60);
        var calc = timeDiff - (parseInt(minutes)*60);

        /** if speed between stops is 15MPH or greater, log a warning */
        if (milesPerHour > 14.99) {
          console.log('Speed: ',spots[i-1].id,' to ',spots[i].id, color.red(dist.toFixed(2)+'mi in '+minutes+'min '+calc+' sec, mph: '+milesPerHour.toFixed(2)));
        }
        if (timeDiff > 0 && timeDiff === timeDiff) { spots[i].timeFromLast = timeDiff }
        if (milesPerHour > 0 && milesPerHour === milesPerHour) { spots[i].speed = milesPerHour }
        spots[i].distFromLast = dist;

        /** push the spot to the pending updates array */
        updateArr.push(spots[i]);
        totalDist = totalDist + dist;
      }
    }
  }

  /** save each spot in the pending updates array */
  async.each(updateArr, function (data, callback) {
    data.save(function (err, savedSpot) {
      if (err) {
        console.log('Error updating mileage for spot ' + data.id, err);
      }
    });
  }, function(err) {
    if(err) {
      console.log('Errors occurred during spot mileage update iteration:', err);
    }
  });

};