// First gets geolocation from the browser (end user may have to allow browser to access geolocation).
// Then gets stations list from iRail project and sorts this by distance. It then takes the top element to show to the end user.
function getClosestStation() {
  console.log("getting geolocation");
  navigator.geolocation.getCurrentPosition(function(position) {
    console.log("got geolocation");
    fetch("https://api.irail.be/stations/?format=json").then(function(body) {
      return body.json();
    }).then(function(doc) {
      var stations = doc.station.sort(function(a, b) {
        return haversineDistance({
          latitude: parseFloat(a.locationY),
          longitude: parseFloat(a.locationX)
        }, position.coords) - haversineDistance({
          latitude: parseFloat(b.locationY),
          longitude: parseFloat(b.locationX)
        }, position.coords);
      }, function (e) {
        console.error(e);
        throw "Does not";
      });
      var str = "<p>The closest station to your current location is <em>" + stations[0].name + "</em>.</p><small>Curious what the second closest station is? We already know. Here’s the top 5: ";
      str+= stations[0].name;
      for (var i = 1; i < 5; i++) {
        str+= ", " + stations[i].name;
      }
      str+="</small>";
      document.getElementById("result").innerHTML  = str;
    }).catch(function(err) {
      console.log("error: " + err);
      document.getElementById("result").innerHTML  = "Could not retrieve iRail stations list from your browser";
    });
  }, (error) => {
    console.error(error.message); 
   document.getElementById("result").innerHTML  = "Could not get your current location from your browser I’m afraid. (did you allow me to get your location?)";

  }
  );
}

//Calculates the distance between 2 points on a globe
function haversineDistance(P1, P2) {
  Number.prototype.toRad = function() {
    return this * Math.PI / 180;
  }
  var lat2 = P2.latitude;
  var lon2 = P2.longitude;
  var lat1 = P1.latitude;
  var lon1 = P1.longitude;
  var R = 6371; // km 
  var x1 = lat2 - lat1;
  var dLat = x1.toRad();
  var x2 = lon2 - lon1;
  var dLon = x2.toRad();
  var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.cos(lat1.toRad()) * Math.cos(lat2.toRad()) *
    Math.sin(dLon / 2) * Math.sin(dLon / 2);
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  return R * c;
}