var wgs84Sphere = new ol.Sphere(6378137);

var raster = new ol.layer.Tile({
  source: new ol.source.OSM()
});

var source = new ol.source.Vector();

var vector = new ol.layer.Vector({
  source: source,
  style: new ol.style.Style({
    fill: new ol.style.Fill({
      color: 'rgba(255, 255, 255, 0.2)'
    }),
    stroke: new ol.style.Stroke({
      color: '#ffcc33',
      width: 2
    }),
    image: new ol.style.Circle({
      radius: 7,
      fill: new ol.style.Fill({
        color: '#ffcc33'
      })
    })
  })
});


/**
 * Currently drawn feature.
 * @type {ol.Feature}
 */
var sketch;


/**
 * The help tooltip element.
 * @type {Element}
 */
var helpTooltipElement;


/**
 * Overlay to show the help messages.
 * @type {ol.Overlay}
 */
var helpTooltip;


/**
 * The measure tooltip element.
 * @type {Element}
 */
var measureTooltipElement;


/**
 * Overlay to show the measurement.
 * @type {ol.Overlay}
 */
var measureTooltip;


/**
 * Message to show when the user is drawing a polygon.
 * @type {string}
 */
var continuePolygonMsg = 'Click to continue drawing the polygon';


/**
 * Message to show when the user is drawing a line.
 * @type {string}
 */
var continueLineMsg = 'Click to continue drawing the line';


/**
 * Handle pointer move.
 * @param {ol.MapBrowserEvent} evt The event.
 */
var pointerMoveHandler = function(evt) {
  if (evt.dragging) {
    return;
  }
  /** @type {string} */
  var helpMsg = 'Click to start drawing';

  if (sketch) {
    var geom = (sketch.getGeometry());
    if (geom instanceof ol.geom.Polygon) {
      helpMsg = continuePolygonMsg;
    } else if (geom instanceof ol.geom.LineString) {
      helpMsg = continueLineMsg;
    }
  }

  helpTooltipElement.innerHTML = helpMsg;
  helpTooltip.setPosition(evt.coordinate);

  helpTooltipElement.classList.remove('hidden');
};


var map = new ol.Map({
  layers: [raster, vector],
  target: 'map',
  view: new ol.View({
    center: [-11000000, 4600000],
    zoom: 15
  })
});

map.on('pointermove', pointerMoveHandler);

map.getViewport().addEventListener('mouseout', function() {
  helpTooltipElement.classList.add('hidden');
});

var typeSelect = document.getElementById('type');
var geodesicCheckbox = document.getElementById('geodesic');

var draw; // global so we can remove it later


/**
 * Format length output.
 * @param {ol.geom.LineString} line The line.
 * @return {string} The formatted length.
 */
var formatLength = function(line) {
  var length;
  if (geodesicCheckbox.checked) {
    var coordinates = line.getCoordinates();
    length = 0;
    var sourceProj = map.getView().getProjection();
    for (var i = 0, ii = coordinates.length - 1; i < ii; ++i) {
      var c1 = ol.proj.transform(coordinates[i], sourceProj, 'EPSG:4326');
      var c2 = ol.proj.transform(coordinates[i + 1], sourceProj, 'EPSG:4326');
      length += wgs84Sphere.haversineDistance(c1, c2);
    }
  } else {
    length = Math.round(line.getLength() * 100) / 100;
  }
  var output;
  if (length > 100) {
    output = (Math.round(length / 1000 * 100) / 100) +
        ' ' + 'km';
  } else {
    output = (Math.round(length * 100) / 100) +
        ' ' + 'm';
  }
  return output;
};


/**
 * Format area output.
 * @param {ol.geom.Polygon} polygon The polygon.
 * @return {string} Formatted area.
 */
var formatArea = function(polygon) {
  var area;
  if (geodesicCheckbox.checked) {
    var sourceProj = map.getView().getProjection();
    var geom = /** @type {ol.geom.Polygon} */(polygon.clone().transform(
        sourceProj, 'EPSG:4326'));
    var coordinates = geom.getLinearRing(0).getCoordinates();
    area = Math.abs(wgs84Sphere.geodesicArea(coordinates));
  } else {
    area = polygon.getArea();
  }
  var output;
  if (area > 10000) {
    output = (Math.round(area / 1000000 * 100) / 100) +
        ' ' + 'km<sup>2</sup>';
  } else {
    output = (Math.round(area * 100) / 100) +
        ' ' + 'm<sup>2</sup>';
  }
  return output;
};

function addInteraction() {
  var type = (typeSelect.value == 'area' ? 'Polygon' : 'LineString');
  draw = new ol.interaction.Draw({
    source: source,
    type: /** @type {ol.geom.GeometryType} */ (type),
    style: new ol.style.Style({
      fill: new ol.style.Fill({
        color: 'rgba(255, 255, 255, 0.2)'
      }),
      stroke: new ol.style.Stroke({
        color: 'rgba(0, 0, 0, 0.5)',
        lineDash: [10, 10],
        width: 2
      }),
      image: new ol.style.Circle({
        radius: 5,
        stroke: new ol.style.Stroke({
          color: 'rgba(0, 0, 0, 0.7)'
        }),
        fill: new ol.style.Fill({
          color: 'rgba(255, 255, 255, 0.2)'
        })
      })
    })
  });
  map.addInteraction(draw);

  createMeasureTooltip();
  createHelpTooltip();

  var listener;
  draw.on('drawstart',
      function(evt) {
        // set sketch
        sketch = evt.feature;

        /** @type {ol.Coordinate|undefined} */
        var tooltipCoord = evt.coordinate;

        listener = sketch.getGeometry().on('change', function(evt) {
          var geom = evt.target;
          var output;
          if (geom instanceof ol.geom.Polygon) {
            output = formatArea(geom);
            tooltipCoord = geom.getInteriorPoint().getCoordinates();
          } else if (geom instanceof ol.geom.LineString) {
            output = formatLength(geom);
            tooltipCoord = geom.getLastCoordinate();
          }
          measureTooltipElement.innerHTML = output;
          measureTooltip.setPosition(tooltipCoord);
        });
      }, this);

  draw.on('drawend',
      function() {
        measureTooltipElement.className = 'tooltip tooltip-static';
        measureTooltip.setOffset([0, -7]);
        // unset sketch
        sketch = null;
        // unset tooltip so that a new one can be created
        measureTooltipElement = null;
        createMeasureTooltip();
        ol.Observable.unByKey(listener);
      }, this);
}


/**
 * Creates a new help tooltip
 */
function createHelpTooltip() {
  if (helpTooltipElement) {
    helpTooltipElement.parentNode.removeChild(helpTooltipElement);
  }
  helpTooltipElement = document.createElement('div');
  helpTooltipElement.className = 'tooltip hidden';
  helpTooltip = new ol.Overlay({
    element: helpTooltipElement,
    offset: [15, 0],
    positioning: 'center-left'
  });
  map.addOverlay(helpTooltip);
}


/**
 * Creates a new measure tooltip
 */
function createMeasureTooltip() {
  if (measureTooltipElement) {
    measureTooltipElement.parentNode.removeChild(measureTooltipElement);
  }
  measureTooltipElement = document.createElement('div');
  measureTooltipElement.className = 'tooltip tooltip-measure';
  measureTooltip = new ol.Overlay({
    element: measureTooltipElement,
    offset: [0, -15],
    positioning: 'bottom-center'
  });
  map.addOverlay(measureTooltip);
}


/**
 * Let user change the geometry type.
 */
typeSelect.onchange = function() {
  map.removeInteraction(draw);
  addInteraction();
};

addInteraction();
