import Map from 'ol/Map';
import View from 'ol/View';
import {getWidth, getTopLeft} from 'ol/extent';
import TileLayer from 'ol/layer/Tile';
import {get as getProjection} from 'ol/proj';
import OSM from 'ol/source/OSM';
import WMTS from 'ol/source/WMTS';
import WMTSTileGrid from 'ol/tilegrid/WMTS';


// create the WMTS tile grid in the google projection
const projection = getProjection('EPSG:3857');
const tileSizePixels = 256;
const tileSizeMtrs = getWidth(projection.getExtent()) / tileSizePixels;
const matrixIds = [];
const resolutions = [];
for (let i = 0; i <= 14; i++) {
  matrixIds[i] = i;
  resolutions[i] = tileSizeMtrs / Math.pow(2, i);
}
const tileGrid = new WMTSTileGrid({
  origin: getTopLeft(projection.getExtent()),
  resolutions: resolutions,
  matrixIds: matrixIds
});

const scalgoToken = 'CC5BF28A7D96B320C7DFBFD1236B5BEB';

const wmtsSource = new WMTS({
  url: 'http://ts2.scalgo.com/olpatch/wmts?token=' + scalgoToken,
  layer: 'SRTM_4_1:SRTM_4_1_flooded_sealevels',
  format: 'image/png',
  matrixSet: 'EPSG:3857',
  attributions: [
    '<a href="http://scalgo.com">SCALGO</a>',
    '<a href="http://www.cgiar-csi.org/data/' +
        'srtm-90m-digital-elevation-database-v4-1">CGIAR-CSI SRTM</a>'
  ],
  tileGrid: tileGrid,
  style: 'default',
  dimensions: {
    'threshold': 100
  }
});

const map = new Map({
  target: 'map',
  view: new View({
    projection: projection,
    center: [-9871995, 3566245],
    zoom: 6
  }),
  layers: [
    new TileLayer({
      source: new OSM()
    }),
    new TileLayer({
      opacity: 0.5,
      source: wmtsSource
    })
  ]
});

const updateSourceDimension = function(source, sliderVal) {
  source.updateDimensions({'threshold': sliderVal});
  document.getElementById('theinfo').innerHTML = sliderVal + ' meters';
};

updateSourceDimension(wmtsSource, 10);

document.getElementById('slider').addEventListener('input', function() {
  updateSourceDimension(wmtsSource, this.value);
});