var view = new ol.View({
  center: [0, 0],
  zoom: 2
});

var map = new ol.Map({
  layers: [
    new ol.layer.Tile({
      source: new ol.source.OSM()
    })
  ],
  target: 'map',
  controls: ol.control.defaults({
    attributionOptions: /** @type {olx.control.AttributionOptions} */ ({
      collapsible: false
    })
  }),
  view: view
});

var geolocation = new ol.Geolocation({
  projection: view.getProjection()
});

function el(id) {
  return document.getElementById(id);
}

el('track').addEventListener('change', function() {
  geolocation.setTracking(this.checked);
});

// update the HTML page when the position changes.
geolocation.on('change', function() {
  el('accuracy').innerText = geolocation.getAccuracy() + ' [m]';
  el('altitude').innerText = geolocation.getAltitude() + ' [m]';
  el('altitudeAccuracy').innerText = geolocation.getAltitudeAccuracy() + ' [m]';
  el('heading').innerText = geolocation.getHeading() + ' [rad]';
  el('speed').innerText = geolocation.getSpeed() + ' [m/s]';
});

// handle geolocation error.
geolocation.on('error', function(error) {
  var info = document.getElementById('info');
  info.innerHTML = error.message;
  info.style.display = '';
});

var accuracyFeature = new ol.Feature();
geolocation.on('change:accuracyGeometry', function() {
  accuracyFeature.setGeometry(geolocation.getAccuracyGeometry());
});

var positionFeature = new ol.Feature();
positionFeature.setStyle(new ol.style.Style({
  image: new ol.style.Circle({
    radius: 6,
    fill: new ol.style.Fill({
      color: '#3399CC'
    }),
    stroke: new ol.style.Stroke({
      color: '#fff',
      width: 2
    })
  })
}));

geolocation.on('change:position', function() {
  var coordinates = geolocation.getPosition();
  positionFeature.setGeometry(coordinates ?
      new ol.geom.Point(coordinates) : null);
});

new ol.layer.Vector({
  map: map,
  source: new ol.source.Vector({
    features: [accuracyFeature, positionFeature]
  })
});
