import Map from 'ol/Map';
import View from 'ol/View';
import {platformModifierKeyOnly} from 'ol/events/condition';
import GeoJSON from 'ol/format/GeoJSON';
import {DragBox, Select} from 'ol/interaction';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';
import {OSM, Vector as VectorSource} from 'ol/source';


const vectorSource = new VectorSource({
  url: 'data/geojson/countries.geojson',
  format: new GeoJSON()
});


const map = new Map({
  layers: [
    new TileLayer({
      source: new OSM()
    }),
    new VectorLayer({
      source: vectorSource
    })
  ],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2
  })
});

// a normal select interaction to handle click
const select = new Select();
map.addInteraction(select);

const selectedFeatures = select.getFeatures();

// a DragBox interaction used to select features by drawing boxes
const dragBox = new DragBox({
  condition: platformModifierKeyOnly
});

map.addInteraction(dragBox);

dragBox.on('boxend', function() {
  // features that intersect the box are added to the collection of
  // selected features
  const extent = dragBox.getGeometry().getExtent();
  vectorSource.forEachFeatureIntersectingExtent(extent, function(feature) {
    selectedFeatures.push(feature);
  });
});

// clear selection when drawing a new box and when clicking on the map
dragBox.on('boxstart', function() {
  selectedFeatures.clear();
});

const infoBox = document.getElementById('info');

selectedFeatures.on(['add', 'remove'], function() {
  const names = selectedFeatures.getArray().map(function(feature) {
    return feature.get('name');
  });
  if (names.length > 0) {
    infoBox.innerHTML = names.join(', ');
  } else {
    infoBox.innerHTML = 'No countries selected';
  }
});