// default zoom, center and rotation
var zoom = 2;
var center = [0, 0];
var rotation = 0;

if (window.location.hash !== '') {
  // try to restore center, zoom-level and rotation from the URL
  var hash = window.location.hash.replace('#map=', '');
  var parts = hash.split('/');
  if (parts.length === 4) {
    zoom = parseInt(parts[0], 10);
    center = [
      parseFloat(parts[1]),
      parseFloat(parts[2])
    ];
    rotation = parseFloat(parts[3]);
  }
}

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

var shouldUpdate = true;
var view = map.getView();
var updatePermalink = function() {
  if (!shouldUpdate) {
    // do not update the URL when the view was changed in the 'popstate' handler
    shouldUpdate = true;
    return;
  }

  var center = view.getCenter();
  var hash = '#map=' +
      view.getZoom() + '/' +
      Math.round(center[0] * 100) / 100 + '/' +
      Math.round(center[1] * 100) / 100 + '/' +
      view.getRotation();
  var state = {
    zoom: view.getZoom(),
    center: view.getCenter(),
    rotation: view.getRotation()
  };
  window.history.pushState(state, 'map', hash);
};

map.on('moveend', updatePermalink);

// restore the view state when navigating through the history, see
// https://developer.mozilla.org/en-US/docs/Web/API/WindowEventHandlers/onpopstate
window.addEventListener('popstate', function(event) {
  if (event.state === null) {
    return;
  }
  map.getView().setCenter(event.state.center);
  map.getView().setZoom(event.state.zoom);
  map.getView().setRotation(event.state.rotation);
  shouldUpdate = false;
});
