text: /**
   * Copyright 2019 Google LLC. All Rights Reserved.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  /**
   * @name MarkerClustererPlus for Google Maps V3
   * @author Gary Little
   * @fileoverview
   * The library creates and manages per-zoom-level clusters for large amounts of markers.
   * <p>
   * This is an enhanced V3 implementation of the V2 MarkerClusterer by Xiaoxi Wu. It is
   * based on the V3 MarkerClusterer port by Luke Mahe. MarkerClustererPlus was created
   * by Gary Little.
   * <p>
   * v2.0 release: MarkerClustererPlus v2.0 is backward compatible with MarkerClusterer v1.0. It
   *  adds support for the <code>ignoreHidden</code>, <code>title</code>, <code>batchSizeIE</code>,
   *  and <code>calculator</code> properties as well as support for four more events. It also allows
   *  greater control over the styling of the text that appears on the cluster marker. The
   *  documentation has been significantly improved and the overall code has been simplified and
   *  polished. Very large numbers of markers can now be managed without causing Javascript timeout
   *  errors on Internet Explorer. Note that the name of the <code>clusterclick</code> event has been
   *  deprecated. The new name is <code>click</code>, so please change your application code now.
   */
  
  /**
   * @typedef {Object} ClusterIconStyle
   * Represents the object for values in the <code>styles</code> array passed
   *  to the {@link MarkerClusterer} constructor. The element in this array that is used to
   *  style the cluster icon is determined by calling the <code>calculator</code> function.
   *
   * @property {string} url The URL of the cluster icon image file. Required.
   * @property {number} height The display height (in pixels) of the cluster icon. Required.
   * @property {number} width The display width (in pixels) of the cluster icon. Required.
   * @property {number[]} [anchorText] The position (in pixels) from the center of the cluster icon to
   *  where the text label is to be centered and drawn. The format is <code>[yoffset, xoffset]</code>
   *  where <code>yoffset</code> increases as you go down from center and <code>xoffset</code>
   *  increases to the right of center. The default is <code>[0, 0]</code>.
   * @property {number[]} [anchorIcon] The anchor position (in pixels) of the cluster icon. This is the
   *  spot on the cluster icon that is to be aligned with the cluster position. The format is
   *  <code>[yoffset, xoffset]</code> where <code>yoffset</code> increases as you go down and
   *  <code>xoffset</code> increases to the right of the top-left corner of the icon. The default
   *  anchor position is the center of the cluster icon.
   * @property {string} [textColor="black"] The color of the label text shown on the
   *  cluster icon.
   * @property {number} [textSize=11] The size (in pixels) of the label text shown on the
   *  cluster icon.
   * @property {string} [textDecoration="none"] The value of the CSS <code>text-decoration</code>
   *  property for the label text shown on the cluster icon.
   * @property {string} [fontWeight="bold"] The value of the CSS <code>font-weight</code>
   *  property for the label text shown on the cluster icon.
   * @property {string} [fontStyle="normal"] The value of the CSS <code>font-style</code>
   *  property for the label text shown on the cluster icon.
   * @property {string} [fontFamily="Arial,sans-serif"] The value of the CSS <code>font-family</code>
   *  property for the label text shown on the cluster icon.
   * @property {string} [backgroundPosition="0 0"] The position of the cluster icon image
   *  within the image defined by <code>url</code>. The format is <code>"xpos ypos"</code>
   *  (the same format as for the CSS <code>background-position</code> property). You must set
   *  this property appropriately when the image defined by <code>url</code> represents a sprite
   *  containing multiple images. Note that the position <i>must</i> be specified in px units.
   */
  
  /**
   * @typedef {Object} ClusterIconInfo
   * This is an object containing general information about a cluster icon. This is
   *  the object that a <code>calculator</code> function returns.
   *
   * @property {string} text The text of the label to be shown on the cluster icon.
   * @property {number} index The index plus 1 of the element in the <code>styles</code>
   *  array to be used to style the cluster icon.
   * @property {string} title The tooltip to display when the mouse moves over the cluster icon.
   *  If this value is <code>undefined</code> or <code>""</code>, <code>title</code> is set to the
   *  value of the <code>title</code> property passed to the MarkerClusterer.
   */
  /**
   * A cluster icon.
   *
   * @constructor
   * @extends google.maps.OverlayView
   * @param {Cluster} cluster The cluster with which the icon is to be associated.
   * @param {ClusterIconStyle[]} [styles] An array of {@link ClusterIconStyle} defining the cluster icons
   *  to use for various cluster sizes.
   * @private
   */
  class ClusterIcon {
    constructor(cluster, styles) {
      cluster.getMarkerClusterer().extend(ClusterIcon, google.maps.OverlayView);
  
      this.cluster_ = cluster;
      this.className_ = cluster.getMarkerClusterer().getClusterClass();
      this.styles_ = styles;
      this.center_ = null;
      this.div_ = null;
      this.sums_ = null;
      this.visible_ = false;
  
      this.setMap(cluster.getMap()); // Note: this causes onAdd to be called
    }
  
    /**
     * Adds the icon to the DOM.
     */
    onAdd() {
      var cClusterIcon = this;
      var cMouseDownInCluster;
      var cDraggingMapByCluster;
      var gmVersion = google.maps.version.split(".");
  
      gmVersion = parseInt(gmVersion[0] * 100, 10) + parseInt(gmVersion[1], 10);
  
      this.div_ = document.createElement("div");
      this.div_.className = this.className_;
      if (this.visible_) {
        this.show();
      }
  
      this.getPanes().overlayMouseTarget.appendChild(this.div_);
  
      // Fix for Issue 157
      this.boundsChangedListener_ = google.maps.event.addListener(
        this.getMap(),
        "bounds_changed",
        function() {
          cDraggingMapByCluster = cMouseDownInCluster;
        }
      );
  
      google.maps.event.addDomListener(this.div_, "mousedown", function() {
        cMouseDownInCluster = true;
        cDraggingMapByCluster = false;
      });
  
      // March 1, 2018: Fix for this 3.32 exp bug, https://issuetracker.google.com/issues/73571522
      // But it doesn't work with earlier releases so do a version check.
      if (gmVersion >= 332) {
        // Ugly version-dependent code
        google.maps.event.addDomListener(this.div_, "touchstart", function(e) {
          e.stopPropagation();
        });
      }
  
      google.maps.event.addDomListener(this.div_, "click", function(e) {
        cMouseDownInCluster = false;
        if (!cDraggingMapByCluster) {
          var theBounds;
          var mz;
          var mc = cClusterIcon.cluster_.getMarkerClusterer();
          /**
           * This event is fired when a cluster marker is clicked.
           * @name MarkerClusterer#click
           * @param {Cluster} c The cluster that was clicked.
           * @event
           */
          google.maps.event.trigger(mc, "click", cClusterIcon.cluster_);
          google.maps.event.trigger(mc, "clusterclick", cClusterIcon.cluster_); // deprecated name
  
          // The default click handler follows. Disable it by setting
          // the zoomOnClick property to false.
          if (mc.getZoomOnClick()) {
            // Zoom into the cluster.
            mz = mc.getMaxZoom();
            theBounds = cClusterIcon.cluster_.getBounds();
            mc.getMap().fitBounds(theBounds);
            // There is a fix for Issue 170 here:
            setTimeout(function() {
              mc.getMap().fitBounds(theBounds);
              // Don't zoom beyond the max zoom level
              if (mz !== null && mc.getMap().getZoom() > mz) {
                mc.getMap().setZoom(mz + 1);
              }
            }, 100);
          }
  
          // Prevent event propagation to the map:
          e.cancelBubble = true;
          if (e.stopPropagation) {
            e.stopPropagation();
          }
        }
      });
  
      google.maps.event.addDomListener(this.div_, "mouseover", function() {
        var mc = cClusterIcon.cluster_.getMarkerClusterer();
        /**
         * This event is fired when the mouse moves over a cluster marker.
         * @name MarkerClusterer#mouseover
         * @param {Cluster} c The cluster that the mouse moved over.
         * @event
         */
        google.maps.event.trigger(mc, "mouseover", cClusterIcon.cluster_);
      });
  
      google.maps.event.addDomListener(this.div_, "mouseout", function() {
        var mc = cClusterIcon.cluster_.getMarkerClusterer();
        /**
         * This event is fired when the mouse moves out of a cluster marker.
         * @name MarkerClusterer#mouseout
         * @param {Cluster} c The cluster that the mouse moved out of.
         * @event
         */
        google.maps.event.trigger(mc, "mouseout", cClusterIcon.cluster_);
      });
    }
  
    /**
     * Removes the icon from the DOM.
     */
    onRemove() {
      if (this.div_ && this.div_.parentNode) {
        this.hide();
        google.maps.event.removeListener(this.boundsChangedListener_);
        google.maps.event.clearInstanceListeners(this.div_);
        this.div_.parentNode.removeChild(this.div_);
        this.div_ = null;
      }
    }
  
    /**
     * Draws the icon.
     */
    draw() {
      if (this.visible_) {
        var pos = this.getPosFromLatLng_(this.center_);
        this.div_.style.top = pos.y + "px";
        this.div_.style.left = pos.x + "px";
        this.div_.style.zIndex = google.maps.Marker.MAX_ZINDEX + 1; // Put above all unclustered markers
      }
    }
  
    /**
     * Hides the icon.
     */
    hide() {
      if (this.div_) {
        this.div_.style.display = "none";
      }
      this.visible_ = false;
    }
  
    /**
     * Positions and shows the icon.
     */
    show() {
      if (this.div_) {
        var mc = this.cluster_.markerClusterer_;
        var ariaLabel = mc.ariaLabelFn(this.sums_.text);
        var img = "";
        // NOTE: values must be specified in px units
        var bp = this.backgroundPosition_.split(" ");
        var spriteH = parseInt(bp[0].replace(/^\s+|\s+$/g, ""), 10);
        var spriteV = parseInt(bp[1].replace(/^\s+|\s+$/g, ""), 10);
        var pos = this.getPosFromLatLng_(this.center_);
        this.div_.style.cssText = this.createCss(pos);
        img =
          "<img aria-hidden='true' src='" +
          this.url_ +
          "' style='position: absolute; top: " +
          spriteV +
          "px; left: " +
          spriteH +
          "px; ";
        if (this.cluster_.getMarkerClusterer().enableRetinaIcons_) {
          img += "width: " + this.width_ + "px; height: " + this.height_ + "px;";
        } else {
          img +=
            "clip: rect(" +
            -1 * spriteV +
            "px, " +
            (-1 * spriteH + this.width_) +
            "px, " +
            (-1 * spriteV + this.height_) +
            "px, " +
            -1 * spriteH +
            "px);";
        }
        img += "'>";
        this.div_.innerHTML =
          img +
          "<div " +
          "aria-label='" +
          ariaLabel +
          "' " +
          "tabindex='0' " +
          "style='" +
          "position: absolute;" +
          "top: " +
          this.anchorText_[0] +
          "px;" +
          "left: " +
          this.anchorText_[1] +
          "px;" +
          "color: " +
          this.textColor_ +
          ";" +
          "font-size: " +
          this.textSize_ +
          "px;" +
          "font-family: " +
          this.fontFamily_ +
          ";" +
          "font-weight: " +
          this.fontWeight_ +
          ";" +
          "font-style: " +
          this.fontStyle_ +
          ";" +
          "text-decoration: " +
          this.textDecoration_ +
          ";" +
          "text-align: center;" +
          "width: " +
          this.width_ +
          "px;" +
          "line-height:" +
          this.height_ +
          "px;" +
          "'>" +
          "<span aria-hidden='true'>" +
          this.sums_.text +
          "</span>" +
          "</div>";
        if (typeof this.sums_.title === "undefined" || this.sums_.title === "") {
          this.div_.title = this.cluster_.getMarkerClusterer().getTitle();
        } else {
          this.div_.title = this.sums_.title;
        }
        this.div_.style.display = "";
      }
      this.visible_ = true;
    }
  
    /**
     * Sets the icon styles to the appropriate element in the styles array.
     *
     * @param {ClusterIconInfo} sums The icon label text and styles index.
     */
    useStyle(sums) {
      this.sums_ = sums;
      var index = Math.max(0, sums.index - 1);
      index = Math.min(this.styles_.length - 1, index);
      var style = this.styles_[index];
      this.url_ = style.url;
      this.height_ = style.height;
      this.width_ = style.width;
      this.anchorText_ = style.anchorText || [0, 0];
      this.anchorIcon_ = style.anchorIcon || [
        parseInt(this.height_ / 2, 10),
        parseInt(this.width_ / 2, 10)
      ];
      this.textColor_ = style.textColor || "black";
      this.textSize_ = style.textSize || 11;
      this.textDecoration_ = style.textDecoration || "none";
      this.fontWeight_ = style.fontWeight || "bold";
      this.fontStyle_ = style.fontStyle || "normal";
      this.fontFamily_ = style.fontFamily || "Arial,sans-serif";
      this.backgroundPosition_ = style.backgroundPosition || "0 0";
    }
  
    /**
     * Sets the position at which to center the icon.
     *
     * @param {google.maps.LatLng} center The latlng to set as the center.
     */
    setCenter(center) {
      this.center_ = center;
    }
  
    /**
     * Creates the cssText style parameter based on the position of the icon.
     *
     * @param {google.maps.Point} pos The position of the icon.
     * @return {string} The CSS style text.
     */
    createCss(pos) {
      var style = [];
      style.push("cursor: pointer;");
      style.push(
        "position: absolute; top: " + pos.y + "px; left: " + pos.x + "px;"
      );
      style.push("width: " + this.width_ + "px; height: " + this.height_ + "px;");
      style.push("-webkit-user-select: none;");
      style.push("-khtml-user-select: none;");
      style.push("-moz-user-select: none;");
      style.push("-o-user-select: none;");
      style.push("user-select: none;");
      return style.join("");
    }
  
    /**
     * Returns the position at which to place the DIV depending on the latlng.
     *
     * @param {google.maps.LatLng} latlng The position in latlng.
     * @return {google.maps.Point} The position in pixels.
     */
    getPosFromLatLng_(latlng) {
      var pos = this.getProjection().fromLatLngToDivPixel(latlng);
      pos.x -= this.anchorIcon_[1];
      pos.y -= this.anchorIcon_[0];
      pos.x = parseInt(pos.x, 10);
      pos.y = parseInt(pos.y, 10);
      return pos;
    }
  }
  
  /**
   * Creates a single cluster that manages a group of proximate markers.
   *  Used internally, do not call this constructor directly.
   * @constructor
   * @param {MarkerClusterer} mc The <code>MarkerClusterer</code> object with which this
   *  cluster is associated.
   */
  class Cluster {
    constructor(mc) {
      this.markerClusterer_ = mc;
      this.map_ = mc.getMap();
      this.gridSize_ = mc.getGridSize();
      this.minClusterSize_ = mc.getMinimumClusterSize();
      this.averageCenter_ = mc.getAverageCenter();
      this.markers_ = [];
      this.center_ = null;
      this.bounds_ = null;
      this.clusterIcon_ = new ClusterIcon(this, mc.getStyles());
    }
  
    /**
     * Returns the number of markers managed by the cluster. You can call this from
     * a <code>click</code>, <code>mouseover</code>, or <code>mouseout</code> event handler
     * for the <code>MarkerClusterer</code> object.
     *
     * @return {number} The number of markers in the cluster.
     */
    getSize() {
      return this.markers_.length;
    }
  
    /**
     * Returns the array of markers managed by the cluster. You can call this from
     * a <code>click</code>, <code>mouseover</code>, or <code>mouseout</code> event handler
     * for the <code>MarkerClusterer</code> object.
     *
     * @return {google.maps.Marker[]} The array of markers in the cluster.
     */
    getMarkers() {
      return this.markers_;
    }
  
    /**
     * Returns the center of the cluster. You can call this from
     * a <code>click</code>, <code>mouseover</code>, or <code>mouseout</code> event handler
     * for the <code>MarkerClusterer</code> object.
     *
     * @return {google.maps.LatLng} The center of the cluster.
     */
    getCenter() {
      return this.center_;
    }
  
    /**
     * Returns the map with which the cluster is associated.
     *
     * @return {google.maps.Map} The map.
     * @ignore
     */
    getMap() {
      return this.map_;
    }
  
    /**
     * Returns the <code>MarkerClusterer</code> object with which the cluster is associated.
     *
     * @return {MarkerClusterer} The associated marker clusterer.
     * @ignore
     */
    getMarkerClusterer() {
      return this.markerClusterer_;
    }
  
    /**
     * Returns the bounds of the cluster.
     *
     * @return {google.maps.LatLngBounds} the cluster bounds.
     * @ignore
     */
    getBounds() {
      var i;
      var bounds = new google.maps.LatLngBounds(this.center_, this.center_);
      var markers = this.getMarkers();
      for (i = 0; i < markers.length; i++) {
        bounds.extend(markers[i].getPosition());
      }
      return bounds;
    }
  
    /**
     * Removes the cluster from the map.
     *
     * @ignore
     */
    remove() {
      this.clusterIcon_.setMap(null);
      this.markers_ = [];
      delete this.markers_;
    }
  
    /**
     * Adds a marker to the cluster.
     *
     * @param {google.maps.Marker} marker The marker to be added.
     * @return {boolean} True if the marker was added.
     * @ignore
     */
    addMarker(marker) {
      var i;
      var mCount;
      var mz;
  
      if (this.isMarkerAlreadyAdded_(marker)) {
        return false;
      }
  
      if (!this.center_) {
        this.center_ = marker.getPosition();
        this.calculateBounds_();
      } else {
        if (this.averageCenter_) {
          var l = this.markers_.length + 1;
          var lat =
            (this.center_.lat() * (l - 1) + marker.getPosition().lat()) / l;
          var lng =
            (this.center_.lng() * (l - 1) + marker.getPosition().lng()) / l;
          this.center_ = new google.maps.LatLng(lat, lng);
          this.calculateBounds_();
        }
      }
  
      marker.isAdded = true;
      this.markers_.push(marker);
  
      mCount = this.markers_.length;
      mz = this.markerClusterer_.getMaxZoom();
      if (mz !== null && this.map_.getZoom() > mz) {
        // Zoomed in past max zoom, so show the marker.
        if (marker.getMap() !== this.map_) {
          marker.setMap(this.map_);
        }
      } else if (mCount < this.minClusterSize_) {
        // Min cluster size not reached so show the marker.
        if (marker.getMap() !== this.map_) {
          marker.setMap(this.map_);
        }
      } else if (mCount === this.minClusterSize_) {
        // Hide the markers that were showing.
        for (i = 0; i < mCount; i++) {
          this.markers_[i].setMap(null);
        }
      } else {
        marker.setMap(null);
      }
  
      this.updateIcon_();
      return true;
    }
  
    /**
     * Determines if a marker lies within the cluster's bounds.
     *
     * @param {google.maps.Marker} marker The marker to check.
     * @return {boolean} True if the marker lies in the bounds.
     * @ignore
     */
    isMarkerInClusterBounds(marker) {
      return this.bounds_.contains(marker.getPosition());
    }
  
    /**
     * Calculates the extended bounds of the cluster with the grid.
     */
    calculateBounds_() {
      var bounds = new google.maps.LatLngBounds(this.center_, this.center_);
      this.bounds_ = this.markerClusterer_.getExtendedBounds(bounds);
    }
  
    /**
     * Updates the cluster icon.
     */
    updateIcon_() {
      var mCount = this.markers_.length;
      var mz = this.markerClusterer_.getMaxZoom();
  
      if (mz !== null && this.map_.getZoom() > mz) {
        this.clusterIcon_.hide();
        return;
      }
  
      if (mCount < this.minClusterSize_) {
        // Min cluster size not yet reached.
        this.clusterIcon_.hide();
        return;
      }
  
      var numStyles = this.markerClusterer_.getStyles().length;
      var sums = this.markerClusterer_.getCalculator()(this.markers_, numStyles);
      this.clusterIcon_.setCenter(this.center_);
      this.clusterIcon_.useStyle(sums);
      this.clusterIcon_.show();
    }
  
    /**
     * Determines if a marker has already been added to the cluster.
     *
     * @param {google.maps.Marker} marker The marker to check.
     * @return {boolean} True if the marker has already been added.
     */
    isMarkerAlreadyAdded_(marker) {
      var i;
      if (this.markers_.indexOf) {
        return this.markers_.indexOf(marker) !== -1;
      } else {
        for (i = 0; i < this.markers_.length; i++) {
          if (marker === this.markers_[i]) {
            return true;
          }
        }
      }
      return false;
    }
  }
  
  /**
   * @callback {Function} ariaLabelFnType
   * @param {string} text The text attribute of the cluster
   * @returns {string}
   */
  
  /**
   * @typedef {Object} MarkerClustererOptions
   * This represents the optional parameter passed to
   *  the {@link MarkerClusterer} constructor.
   * @property {number} [gridSize=60] The grid size of a cluster in pixels. The grid is a square.
   * @property {number} [maxZoom=null] The maximum zoom level at which clustering is enabled or
   *  <code>null</code> if clustering is to be enabled at all zoom levels.
   * @property {boolean} [zoomOnClick=true] Whether to zoom the map when a cluster marker is
   *  clicked. You may want to set this to <code>false</code> if you have installed a handler
   *  for the <code>click</code> event and it deals with zooming on its own.
   * @property {boolean} [averageCenter=false] Whether the position of a cluster marker should be
   *  the average position of all markers in the cluster. If set to <code>false</code>, the
   *  cluster marker is positioned at the location of the first marker added to the cluster.
   * @property {number} [minimumClusterSize=2] The minimum number of markers needed in a cluster
   *  before the markers are hidden and a cluster marker appears.
   * @property {boolean} [ignoreHidden=false] Whether to ignore hidden markers in clusters. You
   *  may want to set this to <code>true</code> to ensure that hidden markers are not included
   *  in the marker count that appears on a cluster marker (this count is the value of the
   *  <code>text</code> property of the result returned by the default <code>calculator</code>).
   *  If set to <code>true</code> and you change the visibility of a marker being clustered, be
   *  sure to also call <code>MarkerClusterer.repaint()</code>.
   * @property {string} [title=""] The tooltip to display when the mouse moves over a cluster
   *  marker. (Alternatively, you can use a custom <code>calculator</code> function to specify a
   *  different tooltip for each cluster marker.)
   * @property {function} [calculator=MarkerClusterer.CALCULATOR] The function used to determine
   *  the text to be displayed on a cluster marker and the index indicating which style to use
   *  for the cluster marker. The input parameters for the function are (1) the array of markers
   *  represented by a cluster marker and (2) the number of cluster icon styles. It returns a
   *  {@link ClusterIconInfo} object. The default <code>calculator</code> returns a
   *  <code>text</code> property which is the number of markers in the cluster and an
   *  <code>index</code> property which is one higher than the lowest integer such that
   *  <code>10^i</code> exceeds the number of markers in the cluster, or the size of the styles
   *  array, whichever is less. The <code>styles</code> array element used has an index of
   *  <code>index</code> minus 1. For example, the default <code>calculator</code> returns a
   *  <code>text</code> value of <code>"125"</code> and an <code>index</code> of <code>3</code>
   *  for a cluster icon representing 125 markers so the element used in the <code>styles</code>
   *  array is <code>2</code>. A <code>calculator</code> may also return a <code>title</code>
   *  property that contains the text of the tooltip to be used for the cluster marker. If
   *   <code>title</code> is not defined, the tooltip is set to the value of the <code>title</code>
   *   property for the MarkerClusterer.
   * @property {string} [clusterClass="cluster"] The name of the CSS class defining general styles
   *  for the cluster markers. Use this class to define CSS styles that are not set up by the code
   *  that processes the <code>styles</code> array.
   * @property {ClusterIconStyle[]} [styles] An array of {@link ClusterIconStyle} elements defining the styles
   *  of the cluster markers to be used. The element to be used to style a given cluster marker
   *  is determined by the function defined by the <code>calculator</code> property.
   *  The default is an array of {@link ClusterIconStyle} elements whose properties are derived
   *  from the values for <code>imagePath</code>, <code>imageExtension</code>, and
   *  <code>imageSizes</code>.
   * @property {boolean} [enableRetinaIcons=false] Whether to allow the use of cluster icons that
   * have sizes that are some multiple (typically double) of their actual display size. Icons such
   * as these look better when viewed on high-resolution monitors such as Apple's Retina displays.
   * Note: if this property is <code>true</code>, sprites cannot be used as cluster icons.
   * @property {number} [batchSize=MarkerClusterer.BATCH_SIZE] Set this property to the
   *  number of markers to be processed in a single batch when using a browser other than
   *  Internet Explorer (for Internet Explorer, use the batchSizeIE property instead).
   * @property {number} [batchSizeIE=MarkerClusterer.BATCH_SIZE_IE] When Internet Explorer is
   *  being used, markers are processed in several batches with a small delay inserted between
   *  each batch in an attempt to avoid Javascript timeout errors. Set this property to the
   *  number of markers to be processed in a single batch; select as high a number as you can
   *  without causing a timeout error in the browser. This number might need to be as low as 100
   *  if 15,000 markers are being managed, for example.
   * @property {string} [imagePath=MarkerClusterer.IMAGE_PATH]
   *  The full URL of the root name of the group of image files to use for cluster icons.
   *  The complete file name is of the form <code>imagePath</code>n.<code>imageExtension</code>
   *  where n is the image file number (1, 2, etc.).
   * @property {string} [imageExtension=MarkerClusterer.IMAGE_EXTENSION]
   *  The extension name for the cluster icon image files (e.g., <code>"png"</code> or
   *  <code>"jpg"</code>).
   * @property {number[]} [imageSizes=MarkerClusterer.IMAGE_SIZES]
   *  An array of numbers containing the widths of the group of
   *  <code>imagePath</code>n.<code>imageExtension</code> image files.
   *  (The images are assumed to be square.)
   * @property {ariaLabelFnType} [ariaLabelFn]
   *  A function to take the text attribute associated with the cluster and output a string to attach an
   *  ariaLabel to the cluter
   */
  
  /**
   * @class
   * @extends google.maps.OverlayView
   */
  class MarkerClusterer {
    /**
     * Creates a MarkerClusterer object with the options specified in {@link MarkerClustererOptions}.
     * @constructor
     * @param {google.maps.Map} map The Google map to attach to.
     * @param {google.maps.Marker[]} [opt_markers] The markers to be added to the cluster.
     * @param {MarkerClustererOptions} [opt_options] The optional parameters.
     */
    constructor(map, opt_markers, opt_options) {
      // MarkerClusterer implements google.maps.OverlayView interface. We use the
      // extend function to extend MarkerClusterer with google.maps.OverlayView
      // because it might not always be available when the code is defined so we
      // look for it at the last possible moment. If it doesn't exist now then
      // there is no point going ahead :)
      this.extend(MarkerClusterer, google.maps.OverlayView);
  
      opt_markers = opt_markers || [];
      opt_options = opt_options || {};
  
      /**
       * The number of markers to process in one batch.
       *
       * @type {number}
       * @constant
       */
      this.BATCH_SIZE = 2000;
  
      /**
       * The number of markers to process in one batch (IE only).
       *
       * @type {number}
       * @constant
       */
      this.BATCH_SIZE_IE = 500;
  
      /**
       * The default root name for the marker cluster images.
       *
       * @type {string}
       * @constant
       */
      this.IMAGE_PATH = "../images/m";
  
      /**
       * The default extension name for the marker cluster images.
       *
       * @type {string}
       * @constant
       */
      this.IMAGE_EXTENSION = "png";
  
      /**
       * The default array of sizes for the marker cluster images.
       *
       * @type {number[]}
       * @constant
       */
      this.IMAGE_SIZES = [53, 56, 66, 78, 90];
      this.markers_ = [];
      this.clusters_ = [];
      this.listeners_ = [];
      this.activeMap_ = null;
      this.ready_ = false;
      this.ariaLabelFn =
        opt_options.ariaLabelFn ||
        function() {
          return "";
        };
  
      this.gridSize_ = opt_options.gridSize || 60;
      this.minClusterSize_ = opt_options.minimumClusterSize || 2;
      this.maxZoom_ = opt_options.maxZoom || null;
      this.styles_ = opt_options.styles || [];
      this.title_ = opt_options.title || "";
      this.zoomOnClick_ = true;
      if (opt_options.zoomOnClick !== undefined) {
        this.zoomOnClick_ = opt_options.zoomOnClick;
      }
      this.averageCenter_ = false;
      if (opt_options.averageCenter !== undefined) {
        this.averageCenter_ = opt_options.averageCenter;
      }
      this.ignoreHidden_ = false;
      if (opt_options.ignoreHidden !== undefined) {
        this.ignoreHidden_ = opt_options.ignoreHidden;
      }
      this.enableRetinaIcons_ = false;
      if (opt_options.enableRetinaIcons !== undefined) {
        this.enableRetinaIcons_ = opt_options.enableRetinaIcons;
      }
      this.imagePath_ = opt_options.imagePath || this.IMAGE_PATH;
      this.imageExtension_ = opt_options.imageExtension || this.IMAGE_EXTENSION;
      this.imageSizes_ = opt_options.imageSizes || this.IMAGE_SIZES;
      this.calculator_ = opt_options.calculator || this.CALCULATOR;
      this.batchSize_ = opt_options.batchSize || this.BATCH_SIZE;
      this.batchSizeIE_ = opt_options.batchSizeIE || this.BATCH_SIZE_IE;
      this.clusterClass_ = opt_options.clusterClass || "cluster";
  
      if (navigator.userAgent.toLowerCase().indexOf("msie") !== -1) {
        // Try to avoid IE timeout when processing a huge number of markers:
        this.batchSize_ = this.batchSizeIE_;
      }
  
      this.setupStyles_();
  
      this.addMarkers(opt_markers, true);
      this.setMap(map); // Note: this causes onAdd to be called
    }
  
    /**
     * Implementation of the onAdd interface method.
     * @ignore
     */
    onAdd() {
      var cMarkerClusterer = this;
  
      this.activeMap_ = this.getMap();
      this.ready_ = true;
  
      this.repaint();
  
      this.prevZoom_ = this.getMap().getZoom();
  
      // Add the map event listeners
      this.listeners_ = [
        google.maps.event.addListener(
          this.getMap(),
          "zoom_changed",
          function() {
            // Fix for bug #407
            // Determines map type and prevents illegal zoom levels
            var zoom = this.getMap().getZoom();
            var minZoom = this.getMap().minZoom || 0;
            var maxZoom = Math.min(
              this.getMap().maxZoom || 100,
              this.getMap().mapTypes[this.getMap().getMapTypeId()].maxZoom
            );
            zoom = Math.min(Math.max(zoom, minZoom), maxZoom);
  
            if (this.prevZoom_ != zoom) {
              this.prevZoom_ = zoom;
              this.resetViewport_(false);
            }
          }.bind(this)
        ),
        google.maps.event.addListener(this.getMap(), "idle", function() {
          cMarkerClusterer.redraw_();
        })
      ];
    }
  
    /**
     * Implementation of the onRemove interface method.
     * Removes map event listeners and all cluster icons from the DOM.
     * All managed markers are also put back on the map.
     * @ignore
     */
    onRemove() {
      var i;
  
      // Put all the managed markers back on the map:
      for (i = 0; i < this.markers_.length; i++) {
        if (this.markers_[i].getMap() !== this.activeMap_) {
          this.markers_[i].setMap(this.activeMap_);
        }
      }
  
      // Remove all clusters:
      for (i = 0; i < this.clusters_.length; i++) {
        this.clusters_[i].remove();
      }
      this.clusters_ = [];
  
      // Remove map event listeners:
      for (i = 0; i < this.listeners_.length; i++) {
        google.maps.event.removeListener(this.listeners_[i]);
      }
      this.listeners_ = [];
  
      this.activeMap_ = null;
      this.ready_ = false;
    }
  
    /**
     * Implementation of the draw interface method.
     * @ignore
     */
    draw() {}
  
    /**
     * Sets up the styles object.
     */
    setupStyles_() {
      var i, size;
      if (this.styles_.length > 0) {
        return;
      }
  
      for (i = 0; i < this.imageSizes_.length; i++) {
        size = this.imageSizes_[i];
        this.styles_.push({
          url: this.imagePath_ + (i + 1) + "." + this.imageExtension_,
          height: size,
          width: size
        });
      }
    }
  
    /**
     *  Fits the map to the bounds of the markers managed by the clusterer.
     */
    fitMapToMarkers() {
      var i;
      var markers = this.getMarkers();
      var bounds = new google.maps.LatLngBounds();
      for (i = 0; i < markers.length; i++) {
        // March 3, 2018: Bug fix -- honor the ignoreHidden property
        if (markers[i].getVisible() || !this.getIgnoreHidden()) {
          bounds.extend(markers[i].getPosition());
        }
      }
  
      this.getMap().fitBounds(bounds);
    }
  
    /**
     * Returns the value of the <code>gridSize</code> property.
     *
     * @return {number} The grid size.
     */
    getGridSize() {
      return this.gridSize_;
    }
  
    /**
     * Sets the value of the <code>gridSize</code> property.
     *
     * @param {number} gridSize The grid size.
     */
    setGridSize(gridSize) {
      this.gridSize_ = gridSize;
    }
  
    /**
     * Returns the value of the <code>minimumClusterSize</code> property.
     *
     * @return {number} The minimum cluster size.
     */
    getMinimumClusterSize() {
      return this.minClusterSize_;
    }
  
    /**
     * Sets the value of the <code>minimumClusterSize</code> property.
     *
     * @param {number} minimumClusterSize The minimum cluster size.
     */
    setMinimumClusterSize(minimumClusterSize) {
      this.minClusterSize_ = minimumClusterSize;
    }
  
    /**
     *  Returns the value of the <code>maxZoom</code> property.
     *
     *  @return {number} The maximum zoom level.
     */
    getMaxZoom() {
      return this.maxZoom_;
    }
  
    /**
     *  Sets the value of the <code>maxZoom</code> property.
     *
     *  @param {number} maxZoom The maximum zoom level.
     */
    setMaxZoom(maxZoom) {
      this.maxZoom_ = maxZoom;
    }
  
    /**
     *  Returns the value of the <code>styles</code> property.
     *
     *  @return {ClusterIconStyle[]} The array of styles defining the cluster markers to be used.
     */
    getStyles() {
      return this.styles_;
    }
  
    /**
     *  Sets the value of the <code>styles</code> property.
     *
     *  @param {ClusterIconStyle[]} styles The array of styles to use.
     */
    setStyles(styles) {
      this.styles_ = styles;
    }
  
    /**
     * Returns the value of the <code>title</code> property.
     *
     * @return {string} The content of the title text.
     */
    getTitle() {
      return this.title_;
    }
  
    /**
     *  Sets the value of the <code>title</code> property.
     *
     *  @param {string} title The value of the title property.
     */
    setTitle(title) {
      this.title_ = title;
    }
  
    /**
     * Returns the value of the <code>zoomOnClick</code> property.
     *
     * @return {boolean} True if zoomOnClick property is set.
     */
    getZoomOnClick() {
      return this.zoomOnClick_;
    }
  
    /**
     *  Sets the value of the <code>zoomOnClick</code> property.
     *
     *  @param {boolean} zoomOnClick The value of the zoomOnClick property.
     */
    setZoomOnClick(zoomOnClick) {
      this.zoomOnClick_ = zoomOnClick;
    }
  
    /**
     * Returns the value of the <code>averageCenter</code> property.
     *
     * @return {boolean} True if averageCenter property is set.
     */
    getAverageCenter() {
      return this.averageCenter_;
    }
  
    /**
     *  Sets the value of the <code>averageCenter</code> property.
     *
     *  @param {boolean} averageCenter The value of the averageCenter property.
     */
    setAverageCenter(averageCenter) {
      this.averageCenter_ = averageCenter;
    }
  
    /**
     * Returns the value of the <code>ignoreHidden</code> property.
     *
     * @return {boolean} True if ignoreHidden property is set.
     */
    getIgnoreHidden() {
      return this.ignoreHidden_;
    }
  
    /**
     *  Sets the value of the <code>ignoreHidden</code> property.
     *
     *  @param {boolean} ignoreHidden The value of the ignoreHidden property.
     */
    setIgnoreHidden(ignoreHidden) {
      this.ignoreHidden_ = ignoreHidden;
    }
  
    /**
     * Returns the value of the <code>enableRetinaIcons</code> property.
     *
     * @return {boolean} True if enableRetinaIcons property is set.
     */
    getEnableRetinaIcons() {
      return this.enableRetinaIcons_;
    }
  
    /**
     *  Sets the value of the <code>enableRetinaIcons</code> property.
     *
     *  @param {boolean} enableRetinaIcons The value of the enableRetinaIcons property.
     */
    setEnableRetinaIcons(enableRetinaIcons) {
      this.enableRetinaIcons_ = enableRetinaIcons;
    }
  
    /**
     * Returns the value of the <code>imageExtension</code> property.
     *
     * @return {string} The value of the imageExtension property.
     */
    getImageExtension() {
      return this.imageExtension_;
    }
  
    /**
     *  Sets the value of the <code>imageExtension</code> property.
     *
     *  @param {string} imageExtension The value of the imageExtension property.
     */
    setImageExtension(imageExtension) {
      this.imageExtension_ = imageExtension;
    }
  
    /**
     * Returns the value of the <code>imagePath</code> property.
     *
     * @return {string} The value of the imagePath property.
     */
    getImagePath() {
      return this.imagePath_;
    }
  
    /**
     *  Sets the value of the <code>imagePath</code> property.
     *
     *  @param {string} imagePath The value of the imagePath property.
     */
    setImagePath(imagePath) {
      this.imagePath_ = imagePath;
    }
  
    /**
     * Returns the value of the <code>imageSizes</code> property.
     *
     * @return {number[]} The value of the imageSizes property.
     */
    getImageSizes() {
      return this.imageSizes_;
    }
  
    /**
     *  Sets the value of the <code>imageSizes</code> property.
     *
     *  @param {number[]} imageSizes The value of the imageSizes property.
     */
    setImageSizes(imageSizes) {
      this.imageSizes_ = imageSizes;
    }
  
    /**
     * Returns the value of the <code>calculator</code> property.
     *
     * @return {function} the value of the calculator property.
     */
    getCalculator() {
      return this.calculator_;
    }
  
    /**
     * Sets the value of the <code>calculator</code> property.
     *
     * @param {function(google.maps.Marker[], number)} calculator The value
     *  of the calculator property.
     */
    setCalculator(calculator) {
      this.calculator_ = calculator;
    }
  
    /**
     * Returns the value of the <code>batchSizeIE</code> property.
     *
     * @return {number} the value of the batchSizeIE property.
     */
    getBatchSizeIE() {
      return this.batchSizeIE_;
    }
  
    /**
     * Sets the value of the <code>batchSizeIE</code> property.
     *
     *  @param {number} batchSizeIE The value of the batchSizeIE property.
     */
    setBatchSizeIE(batchSizeIE) {
      this.batchSizeIE_ = batchSizeIE;
    }
  
    /**
     * Returns the value of the <code>clusterClass</code> property.
     *
     * @return {string} the value of the clusterClass property.
     */
    getClusterClass() {
      return this.clusterClass_;
    }
  
    /**
     * Sets the value of the <code>clusterClass</code> property.
     *
     *  @param {string} clusterClass The value of the clusterClass property.
     */
    setClusterClass(clusterClass) {
      this.clusterClass_ = clusterClass;
    }
  
    /**
     *  Returns the array of markers managed by the clusterer.
     *
     *  @return {google.maps.Marker[]} The array of markers managed by the clusterer.
     */
    getMarkers() {
      return this.markers_;
    }
  
    /**
     *  Returns the number of markers managed by the clusterer.
     *
     *  @return {number} The number of markers.
     */
    getTotalMarkers() {
      return this.markers_.length;
    }
  
    /**
     * Returns the current array of clusters formed by the clusterer.
     *
     * @return {Cluster[]} The array of clusters formed by the clusterer.
     */
    getClusters() {
      return this.clusters_;
    }
  
    /**
     * Returns the number of clusters formed by the clusterer.
     *
     * @return {number} The number of clusters formed by the clusterer.
     */
    getTotalClusters() {
      return this.clusters_.length;
    }
  
    /**
     * Adds a marker to the clusterer. The clusters are redrawn unless
     *  <code>opt_nodraw</code> is set to <code>true</code>.
     *
     * @param {google.maps.Marker} marker The marker to add.
     * @param {boolean} [opt_nodraw] Set to <code>true</code> to prevent redrawing.
     */
    addMarker(marker, opt_nodraw) {
      this.pushMarkerTo_(marker);
      if (!opt_nodraw) {
        this.redraw_();
      }
    }
  
    /**
     * Adds an array of markers to the clusterer. The clusters are redrawn unless
     *  <code>opt_nodraw</code> is set to <code>true</code>.
     *
     * @param {google.maps.Marker[]} markers The markers to add.
     * @param {boolean} [opt_nodraw] Set to <code>true</code> to prevent redrawing.
     */
    addMarkers(markers, opt_nodraw) {
      var key;
      for (key in markers) {
        if (Object.prototype.hasOwnProperty.call(markers, key)) {
          this.pushMarkerTo_(markers[key]);
        }
      }
      if (!opt_nodraw) {
        this.redraw_();
      }
    }
  
    /**
     * Pushes a marker to the clusterer.
     *
     * @param {google.maps.Marker} marker The marker to add.
     */
    pushMarkerTo_(marker) {
      // If the marker is draggable add a listener so we can update the clusters on the dragend:
      if (marker.getDraggable()) {
        var cMarkerClusterer = this;
        google.maps.event.addListener(marker, "dragend", function() {
          if (cMarkerClusterer.ready_) {
            this.isAdded = false;
            cMarkerClusterer.repaint();
          }
        });
      }
      marker.isAdded = false;
      this.markers_.push(marker);
    }
  
    /**
     * Removes a marker from the cluster.  The clusters are redrawn unless
     *  <code>opt_nodraw</code> is set to <code>true</code>. Returns <code>true</code> if the
     *  marker was removed from the clusterer.
     *
     * @param {google.maps.Marker} marker The marker to remove.
     * @param {boolean} [opt_nodraw] Set to <code>true</code> to prevent redrawing.
     * @return {boolean} True if the marker was removed from the clusterer.
     */
    removeMarker(marker, opt_nodraw) {
      var removed = this.removeMarker_(marker);
  
      if (!opt_nodraw && removed) {
        this.repaint();
      }
  
      return removed;
    }
  
    /**
     * Removes an array of markers from the cluster. The clusters are redrawn unless
     *  <code>opt_nodraw</code> is set to <code>true</code>. Returns <code>true</code> if markers
     *  were removed from the clusterer.
     *
     * @param {google.maps.Marker[]} markers The markers to remove.
     * @param {boolean} [opt_nodraw] Set to <code>true</code> to prevent redrawing.
     * @return {boolean} True if markers were removed from the clusterer.
     */
    removeMarkers(markers, opt_nodraw) {
      var i, r;
      var removed = false;
  
      for (i = 0; i < markers.length; i++) {
        r = this.removeMarker_(markers[i]);
        removed = removed || r;
      }
  
      if (!opt_nodraw && removed) {
        this.repaint();
      }
  
      return removed;
    }
  
    /**
     * Removes a marker and returns true if removed, false if not.
     *
     * @param {google.maps.Marker} marker The marker to remove
     * @return {boolean} Whether the marker was removed or not
     */
    removeMarker_(marker) {
      var i;
      var index = -1;
      if (this.markers_.indexOf) {
        index = this.markers_.indexOf(marker);
      } else {
        for (i = 0; i < this.markers_.length; i++) {
          if (marker === this.markers_[i]) {
            index = i;
            break;
          }
        }
      }
  
      if (index === -1) {
        // Marker is not in our list of markers, so do nothing:
        return false;
      }
  
      marker.setMap(null);
      this.markers_.splice(index, 1); // Remove the marker from the list of managed markers
      return true;
    }
  
    /**
     * Removes all clusters and markers from the map and also removes all markers
     *  managed by the clusterer.
     */
    clearMarkers() {
      this.resetViewport_(true);
      this.markers_ = [];
    }
  
    /**
     * Recalculates and redraws all the marker clusters from scratch.
     *  Call this after changing any properties.
     */
    repaint() {
      var oldClusters = this.clusters_.slice();
      this.clusters_ = [];
      this.resetViewport_(false);
      this.redraw_();
  
      // Remove the old clusters.
      // Do it in a timeout to prevent blinking effect.
      setTimeout(function() {
        var i;
        for (i = 0; i < oldClusters.length; i++) {
          oldClusters[i].remove();
        }
      }, 0);
    }
  
    /**
     * Returns the current bounds extended by the grid size.
     *
     * @param {google.maps.LatLngBounds} bounds The bounds to extend.
     * @return {google.maps.LatLngBounds} The extended bounds.
     * @ignore
     */
    getExtendedBounds(bounds) {
      var projection = this.getProjection();
  
      // Turn the bounds into latlng.
      var tr = new google.maps.LatLng(
        bounds.getNorthEast().lat(),
        bounds.getNorthEast().lng()
      );
      var bl = new google.maps.LatLng(
        bounds.getSouthWest().lat(),
        bounds.getSouthWest().lng()
      );
  
      // Convert the points to pixels and the extend out by the grid size.
      var trPix = projection.fromLatLngToDivPixel(tr);
      trPix.x += this.gridSize_;
      trPix.y -= this.gridSize_;
  
      var blPix = projection.fromLatLngToDivPixel(bl);
      blPix.x -= this.gridSize_;
      blPix.y += this.gridSize_;
  
      // Convert the pixel points back to LatLng
      var ne = projection.fromDivPixelToLatLng(trPix);
      var sw = projection.fromDivPixelToLatLng(blPix);
  
      // Extend the bounds to contain the new bounds.
      bounds.extend(ne);
      bounds.extend(sw);
  
      return bounds;
    }
  
    /**
     * Redraws all the clusters.
     */
    redraw_() {
      this.createClusters_(0);
    }
  
    /**
     * Removes all clusters from the map. The markers are also removed from the map
     *  if <code>opt_hide</code> is set to <code>true</code>.
     *
     * @param {boolean} [opt_hide] Set to <code>true</code> to also remove the markers
     *  from the map.
     */
    resetViewport_(opt_hide) {
      var i, marker;
      // Remove all the clusters
      for (i = 0; i < this.clusters_.length; i++) {
        this.clusters_[i].remove();
      }
      this.clusters_ = [];
  
      // Reset the markers to not be added and to be removed from the map.
      for (i = 0; i < this.markers_.length; i++) {
        marker = this.markers_[i];
        marker.isAdded = false;
        if (opt_hide) {
          marker.setMap(null);
        }
      }
    }
  
    /**
     * Calculates the distance between two latlng locations in km.
     *
     * @param {google.maps.LatLng} p1 The first lat lng point.
     * @param {google.maps.LatLng} p2 The second lat lng point.
     * @return {number} The distance between the two points in km.
     * @see http://www.movable-type.co.uk/scripts/latlong.html
     */
    distanceBetweenPoints_(p1, p2) {
      var R = 6371; // Radius of the Earth in km
      var dLat = ((p2.lat() - p1.lat()) * Math.PI) / 180;
      var dLon = ((p2.lng() - p1.lng()) * Math.PI) / 180;
      var a =
        Math.sin(dLat / 2) * Math.sin(dLat / 2) +
        Math.cos((p1.lat() * Math.PI) / 180) *
          Math.cos((p2.lat() * Math.PI) / 180) *
          Math.sin(dLon / 2) *
          Math.sin(dLon / 2);
      var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
      var d = R * c;
      return d;
    }
  
    /**
     * Determines if a marker is contained in a bounds.
     *
     * @param {google.maps.Marker} marker The marker to check.
     * @param {google.maps.LatLngBounds} bounds The bounds to check against.
     * @return {boolean} True if the marker is in the bounds.
     */
    isMarkerInBounds_(marker, bounds) {
      return bounds.contains(marker.getPosition());
    }
  
    /**
     * Adds a marker to a cluster, or creates a new cluster.
     *
     * @param {google.maps.Marker} marker The marker to add.
     */
    addToClosestCluster_(marker) {
      var i, d, cluster, center;
      var distance = 40000; // Some large number
      var clusterToAddTo = null;
      for (i = 0; i < this.clusters_.length; i++) {
        cluster = this.clusters_[i];
        center = cluster.getCenter();
        if (center) {
          d = this.distanceBetweenPoints_(center, marker.getPosition());
          if (d < distance) {
            distance = d;
            clusterToAddTo = cluster;
          }
        }
      }
  
      if (clusterToAddTo && clusterToAddTo.isMarkerInClusterBounds(marker)) {
        clusterToAddTo.addMarker(marker);
      } else {
        cluster = new Cluster(this);
        cluster.addMarker(marker);
        this.clusters_.push(cluster);
      }
    }
  
    /**
     * Creates the clusters. This is done in batches to avoid timeout errors
     *  in some browsers when there is a huge number of markers.
     *
     * @param {number} iFirst The index of the first marker in the batch of
     *  markers to be added to clusters.
     */
    createClusters_(iFirst) {
      var i, marker;
      var mapBounds;
      var cMarkerClusterer = this;
      if (!this.ready_) {
        return;
      }
  
      // Cancel previous batch processing if we're working on the first batch:
      if (iFirst === 0) {
        /**
         * This event is fired when the <code>MarkerClusterer</code> begins
         *  clustering markers.
         * @name MarkerClusterer#clusteringbegin
         * @param {MarkerClusterer} mc The MarkerClusterer whose markers are being clustered.
         * @event
         */
        google.maps.event.trigger(this, "clusteringbegin", this);
  
        if (typeof this.timerRefStatic !== "undefined") {
          clearTimeout(this.timerRefStatic);
          delete this.timerRefStatic;
        }
      }
  
      // Get our current map view bounds.
      // Create a new bounds object so we don't affect the map.
      //
      // See Comments 9 & 11 on Issue 3651 relating to this workaround for a Google Maps bug:
      if (this.getMap().getZoom() > 3) {
        mapBounds = new google.maps.LatLngBounds(
          this.getMap()
            .getBounds()
            .getSouthWest(),
          this.getMap()
            .getBounds()
            .getNorthEast()
        );
      } else {
        mapBounds = new google.maps.LatLngBounds(
          new google.maps.LatLng(85.02070771743472, -178.48388434375),
          new google.maps.LatLng(-85.08136444384544, 178.00048865625)
        );
      }
      var bounds = this.getExtendedBounds(mapBounds);
  
      var iLast = Math.min(iFirst + this.batchSize_, this.markers_.length);
  
      for (i = iFirst; i < iLast; i++) {
        marker = this.markers_[i];
        if (!marker.isAdded && this.isMarkerInBounds_(marker, bounds)) {
          if (
            !this.ignoreHidden_ ||
            (this.ignoreHidden_ && marker.getVisible())
          ) {
            this.addToClosestCluster_(marker);
          }
        }
      }
  
      if (iLast < this.markers_.length) {
        this.timerRefStatic = setTimeout(function() {
          cMarkerClusterer.createClusters_(iLast);
        }, 0);
      } else {
        delete this.timerRefStatic;
  
        /**
         * This event is fired when the <code>MarkerClusterer</code> stops
         *  clustering markers.
         * @name MarkerClusterer#clusteringend
         * @param {MarkerClusterer} mc The MarkerClusterer whose markers are being clustered.
         * @event
         */
        google.maps.event.trigger(this, "clusteringend", this);
      }
    }
  
    /**
     * Extends an object's prototype by another's.
     *
     * @param {Object} obj1 The object to be extended.
     * @param {Object} obj2 The object to extend with.
     * @return {Object} The new extended object.
     * @ignore
     */
    extend(obj1, obj2) {
      return function(object) {
        var property;
        for (property in object.prototype) {
          this.prototype[property] = object.prototype[property];
        }
        return this;
      }.apply(obj1, [obj2]);
    }
  
    /**
     * The default function for determining the label text and style
     * for a cluster icon.
     *
     * @param {google.maps.Marker[]} markers The array of markers represented by the cluster.
     * @param {number} numStyles The number of marker styles available.
     * @return {ClusterIconInfo} The information resource for the cluster.
     * @constant
     * @ignore
     */
    CALCULATOR(markers, numStyles) {
      var index = 0;
      var title = "";
      var count = markers.length.toString();
  
      var dv = count;
      while (dv !== 0) {
        dv = parseInt(dv / 10, 10);
        index++;
      }
  
      index = Math.min(index, numStyles);
      return {
        text: count,
        index: index,
        title: title
      };
    }
  }
  
  export default MarkerClusterer;
  