/*
 * google map marker cluster
 */
 /**
 * @name MarkerClustererPlus for Google Maps V3
 * @version 2.1.1 [November 4, 2013]
 * @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
 * <a href="http://gmaps-utility-library-dev.googlecode.com/svn/tags/markerclusterer/"
 * >V2 MarkerClusterer</a> by Xiaoxi Wu. It is based on the
 * <a href="http://google-maps-utility-library-v3.googlecode.com/svn/tags/markerclusterer/"
 * >V3 MarkerClusterer</a> 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.
 */

/**
 * 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 ClusterIconStyle
 * @class This class 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 {Array} [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 {Array} [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.
 */
/**
 * @name ClusterIconInfo
 * @class This class 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 {Array} [styles] An array of {@link ClusterIconStyle} defining the cluster icons
 *  to use for various cluster sizes.
 * @private
 */
function ClusterIcon(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.
 */
ClusterIcon.prototype.onAdd = function () {
  var cClusterIcon = this;
  var cMouseDownInCluster;
  var cDraggingMapByCluster;

  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;
  });

  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);
          }
          // getting the type the map is and what the zoom is set to
        var mapType = mc.getMap().getMapTypeId();
        var mapZoomLvl = mc.getMap().getZoom();

        //if the zoom is set to the highest zoom we could have a cluster that is unbreakable.
        // To make sure the cluster does not disappear repaint() is used. The repaint()
        //function does a recalculation of all clusters and reprints them, thus if it did not
        //break it will re print our cluster.
        if ((mapZoomLvl == 21 && mapType == "roadmap") ||
            (mapZoomLvl==20 && mapType == "hybrid"))
        {
            mc.repaint();//The Sites can not be broken repaint it on the screen
        }
        }, 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.
 */
ClusterIcon.prototype.onRemove = function () {
  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.
 */
ClusterIcon.prototype.draw = function () {
  if (this.visible_) {
    var pos = this.getPosFromLatLng_(this.center_);
    this.div_.style.top = pos.y + "px";
    this.div_.style.left = pos.x + "px";
  }
};


/**
 * Hides the icon.
 */
ClusterIcon.prototype.hide = function () {
  if (this.div_) {
    this.div_.style.display = "none";
  }
  this.visible_ = false;
};


/**
 * Positions and shows the icon.
 */
ClusterIcon.prototype.show = function () {
  if (this.div_) {
    var img = "";
    // NOTE: values must be specified in px units
    var bp = this.backgroundPosition_.split(" ");
    var spriteH = parseInt(bp[0].trim(), 10);
    var spriteV = parseInt(bp[1].trim(), 10);
    var pos = this.getPosFromLatLng_(this.center_);
    this.div_.style.cssText = this.createCss(pos);
    img = "<img src='" + this.url_ + "' style='position: absolute; top: " + spriteV + "px; left: " + spriteH + "px; ";
    if (!this.cluster_.getMarkerClusterer().enableRetinaIcons_) {
      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 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;" +
        "'>" + this.sums_.text + "</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.
 */
ClusterIcon.prototype.useStyle = function (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.
 */
ClusterIcon.prototype.setCenter = function (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.
 */
ClusterIcon.prototype.createCss = function (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;");
  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.
 */
ClusterIcon.prototype.getPosFromLatLng_ = function (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.
 */
function Cluster(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.
 */
Cluster.prototype.getSize = function () {
  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 {Array} The array of markers in the cluster.
 */
Cluster.prototype.getMarkers = function () {
  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.
 */
Cluster.prototype.getCenter = function () {
  return this.center_;
};


/**
 * Returns the map with which the cluster is associated.
 *
 * @return {google.maps.Map} The map.
 * @ignore
 */
Cluster.prototype.getMap = function () {
  return this.map_;
};


/**
 * Returns the <code>MarkerClusterer</code> object with which the cluster is associated.
 *
 * @return {MarkerClusterer} The associated marker clusterer.
 * @ignore
 */
Cluster.prototype.getMarkerClusterer = function () {
  return this.markerClusterer_;
};


/**
 * Returns the bounds of the cluster.
 *
 * @return {google.maps.LatLngBounds} the cluster bounds.
 * @ignore
 */
Cluster.prototype.getBounds = function () {
  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
 */
Cluster.prototype.remove = function () {
  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
 */
Cluster.prototype.addMarker = function (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
 */
Cluster.prototype.isMarkerInClusterBounds = function (marker) {
  return this.bounds_.contains(marker.getPosition());
};


/**
 * Calculates the extended bounds of the cluster with the grid.
 */
Cluster.prototype.calculateBounds_ = function () {
  var bounds = new google.maps.LatLngBounds(this.center_, this.center_);
  this.bounds_ = this.markerClusterer_.getExtendedBounds(bounds);
};


/**
 * Updates the cluster icon.
 */
Cluster.prototype.updateIcon_ = function () {
  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.
 */
Cluster.prototype.isMarkerAlreadyAdded_ = function (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;
};


/**
 * @name MarkerClustererOptions
 * @class This class 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 {Array} [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 {Array} [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.)
 */
/**
 * Creates a MarkerClusterer object with the options specified in {@link MarkerClustererOptions}.
 * @constructor
 * @extends google.maps.OverlayView
 * @param {google.maps.Map} map The Google map to attach to.
 * @param {Array.<google.maps.Marker>} [opt_markers] The markers to be added to the cluster.
 * @param {MarkerClustererOptions} [opt_options] The optional parameters.
 */
function MarkerClusterer(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 || {};

  this.markers_ = [];
  this.clusters_ = [];
  this.listeners_ = [];
  this.activeMap_ = null;
  this.ready_ = false;

  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 || MarkerClusterer.IMAGE_PATH;
  this.imageExtension_ = opt_options.imageExtension || MarkerClusterer.IMAGE_EXTENSION;
  this.imageSizes_ = opt_options.imageSizes || MarkerClusterer.IMAGE_SIZES;
  this.calculator_ = opt_options.calculator || MarkerClusterer.CALCULATOR;
  this.batchSize_ = opt_options.batchSize || MarkerClusterer.BATCH_SIZE;
  this.batchSizeIE_ = opt_options.batchSizeIE || MarkerClusterer.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
 */
MarkerClusterer.prototype.onAdd = function () {
  var cMarkerClusterer = this;

  this.activeMap_ = this.getMap();
  this.ready_ = true;

  this.repaint();

  // Add the map event listeners
  this.listeners_ = [
    google.maps.event.addListener(this.getMap(), "zoom_changed", function () {
      cMarkerClusterer.resetViewport_(false);
      // Workaround for this Google bug: when map is at level 0 and "-" of
      // zoom slider is clicked, a "zoom_changed" event is fired even though
      // the map doesn't zoom out any further. In this situation, no "idle"
      // event is triggered so the cluster markers that have been removed
      // do not get redrawn. Same goes for a zoom in at maxZoom.
      if (this.getZoom() === (this.get("minZoom") || 0) || this.getZoom() === this.get("maxZoom")) {
        google.maps.event.trigger(this, "idle");
      }
    }),
    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
 */
MarkerClusterer.prototype.onRemove = function () {
  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
 */
MarkerClusterer.prototype.draw = function () {};


/**
 * Sets up the styles object.
 */
MarkerClusterer.prototype.setupStyles_ = function () {
  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.
 */
MarkerClusterer.prototype.fitMapToMarkers = function () {
  var i;
  var markers = this.getMarkers();
  var bounds = new google.maps.LatLngBounds();
  for (i = 0; i < markers.length; i++) {
    bounds.extend(markers[i].getPosition());
  }

  this.getMap().fitBounds(bounds);
};


/**
 * Returns the value of the <code>gridSize</code> property.
 *
 * @return {number} The grid size.
 */
MarkerClusterer.prototype.getGridSize = function () {
  return this.gridSize_;
};


/**
 * Sets the value of the <code>gridSize</code> property.
 *
 * @param {number} gridSize The grid size.
 */
MarkerClusterer.prototype.setGridSize = function (gridSize) {
  this.gridSize_ = gridSize;
};


/**
 * Returns the value of the <code>minimumClusterSize</code> property.
 *
 * @return {number} The minimum cluster size.
 */
MarkerClusterer.prototype.getMinimumClusterSize = function () {
  return this.minClusterSize_;
};

/**
 * Sets the value of the <code>minimumClusterSize</code> property.
 *
 * @param {number} minimumClusterSize The minimum cluster size.
 */
MarkerClusterer.prototype.setMinimumClusterSize = function (minimumClusterSize) {
  this.minClusterSize_ = minimumClusterSize;
};


/**
 *  Returns the value of the <code>maxZoom</code> property.
 *
 *  @return {number} The maximum zoom level.
 */
MarkerClusterer.prototype.getMaxZoom = function () {
  return this.maxZoom_;
};


/**
 *  Sets the value of the <code>maxZoom</code> property.
 *
 *  @param {number} maxZoom The maximum zoom level.
 */
MarkerClusterer.prototype.setMaxZoom = function (maxZoom) {
  this.maxZoom_ = maxZoom;
};


/**
 *  Returns the value of the <code>styles</code> property.
 *
 *  @return {Array} The array of styles defining the cluster markers to be used.
 */
MarkerClusterer.prototype.getStyles = function () {
  return this.styles_;
};


/**
 *  Sets the value of the <code>styles</code> property.
 *
 *  @param {Array.<ClusterIconStyle>} styles The array of styles to use.
 */
MarkerClusterer.prototype.setStyles = function (styles) {
  this.styles_ = styles;
};


/**
 * Returns the value of the <code>title</code> property.
 *
 * @return {string} The content of the title text.
 */
MarkerClusterer.prototype.getTitle = function () {
  return this.title_;
};


/**
 *  Sets the value of the <code>title</code> property.
 *
 *  @param {string} title The value of the title property.
 */
MarkerClusterer.prototype.setTitle = function (title) {
  this.title_ = title;
};


/**
 * Returns the value of the <code>zoomOnClick</code> property.
 *
 * @return {boolean} True if zoomOnClick property is set.
 */
MarkerClusterer.prototype.getZoomOnClick = function () {
  return this.zoomOnClick_;
};


/**
 *  Sets the value of the <code>zoomOnClick</code> property.
 *
 *  @param {boolean} zoomOnClick The value of the zoomOnClick property.
 */
MarkerClusterer.prototype.setZoomOnClick = function (zoomOnClick) {
  this.zoomOnClick_ = zoomOnClick;
};


/**
 * Returns the value of the <code>averageCenter</code> property.
 *
 * @return {boolean} True if averageCenter property is set.
 */
MarkerClusterer.prototype.getAverageCenter = function () {
  return this.averageCenter_;
};


/**
 *  Sets the value of the <code>averageCenter</code> property.
 *
 *  @param {boolean} averageCenter The value of the averageCenter property.
 */
MarkerClusterer.prototype.setAverageCenter = function (averageCenter) {
  this.averageCenter_ = averageCenter;
};


/**
 * Returns the value of the <code>ignoreHidden</code> property.
 *
 * @return {boolean} True if ignoreHidden property is set.
 */
MarkerClusterer.prototype.getIgnoreHidden = function () {
  return this.ignoreHidden_;
};


/**
 *  Sets the value of the <code>ignoreHidden</code> property.
 *
 *  @param {boolean} ignoreHidden The value of the ignoreHidden property.
 */
MarkerClusterer.prototype.setIgnoreHidden = function (ignoreHidden) {
  this.ignoreHidden_ = ignoreHidden;
};


/**
 * Returns the value of the <code>enableRetinaIcons</code> property.
 *
 * @return {boolean} True if enableRetinaIcons property is set.
 */
MarkerClusterer.prototype.getEnableRetinaIcons = function () {
  return this.enableRetinaIcons_;
};


/**
 *  Sets the value of the <code>enableRetinaIcons</code> property.
 *
 *  @param {boolean} enableRetinaIcons The value of the enableRetinaIcons property.
 */
MarkerClusterer.prototype.setEnableRetinaIcons = function (enableRetinaIcons) {
  this.enableRetinaIcons_ = enableRetinaIcons;
};


/**
 * Returns the value of the <code>imageExtension</code> property.
 *
 * @return {string} The value of the imageExtension property.
 */
MarkerClusterer.prototype.getImageExtension = function () {
  return this.imageExtension_;
};


/**
 *  Sets the value of the <code>imageExtension</code> property.
 *
 *  @param {string} imageExtension The value of the imageExtension property.
 */
MarkerClusterer.prototype.setImageExtension = function (imageExtension) {
  this.imageExtension_ = imageExtension;
};


/**
 * Returns the value of the <code>imagePath</code> property.
 *
 * @return {string} The value of the imagePath property.
 */
MarkerClusterer.prototype.getImagePath = function () {
  return this.imagePath_;
};


/**
 *  Sets the value of the <code>imagePath</code> property.
 *
 *  @param {string} imagePath The value of the imagePath property.
 */
MarkerClusterer.prototype.setImagePath = function (imagePath) {
  this.imagePath_ = imagePath;
};


/**
 * Returns the value of the <code>imageSizes</code> property.
 *
 * @return {Array} The value of the imageSizes property.
 */
MarkerClusterer.prototype.getImageSizes = function () {
  return this.imageSizes_;
};


/**
 *  Sets the value of the <code>imageSizes</code> property.
 *
 *  @param {Array} imageSizes The value of the imageSizes property.
 */
MarkerClusterer.prototype.setImageSizes = function (imageSizes) {
  this.imageSizes_ = imageSizes;
};


/**
 * Returns the value of the <code>calculator</code> property.
 *
 * @return {function} the value of the calculator property.
 */
MarkerClusterer.prototype.getCalculator = function () {
  return this.calculator_;
};


/**
 * Sets the value of the <code>calculator</code> property.
 *
 * @param {function(Array.<google.maps.Marker>, number)} calculator The value
 *  of the calculator property.
 */
MarkerClusterer.prototype.setCalculator = function (calculator) {
  this.calculator_ = calculator;
};


/**
 * Returns the value of the <code>batchSizeIE</code> property.
 *
 * @return {number} the value of the batchSizeIE property.
 */
MarkerClusterer.prototype.getBatchSizeIE = function () {
  return this.batchSizeIE_;
};


/**
 * Sets the value of the <code>batchSizeIE</code> property.
 *
 *  @param {number} batchSizeIE The value of the batchSizeIE property.
 */
MarkerClusterer.prototype.setBatchSizeIE = function (batchSizeIE) {
  this.batchSizeIE_ = batchSizeIE;
};


/**
 * Returns the value of the <code>clusterClass</code> property.
 *
 * @return {string} the value of the clusterClass property.
 */
MarkerClusterer.prototype.getClusterClass = function () {
  return this.clusterClass_;
};


/**
 * Sets the value of the <code>clusterClass</code> property.
 *
 *  @param {string} clusterClass The value of the clusterClass property.
 */
MarkerClusterer.prototype.setClusterClass = function (clusterClass) {
  this.clusterClass_ = clusterClass;
};


/**
 *  Returns the array of markers managed by the clusterer.
 *
 *  @return {Array} The array of markers managed by the clusterer.
 */
MarkerClusterer.prototype.getMarkers = function () {
  return this.markers_;
};


/**
 *  Returns the number of markers managed by the clusterer.
 *
 *  @return {number} The number of markers.
 */
MarkerClusterer.prototype.getTotalMarkers = function () {
  return this.markers_.length;
};


/**
 * Returns the current array of clusters formed by the clusterer.
 *
 * @return {Array} The array of clusters formed by the clusterer.
 */
MarkerClusterer.prototype.getClusters = function () {
  return this.clusters_;
};


/**
 * Returns the number of clusters formed by the clusterer.
 *
 * @return {number} The number of clusters formed by the clusterer.
 */
MarkerClusterer.prototype.getTotalClusters = function () {
  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.
 */
MarkerClusterer.prototype.addMarker = function (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 {Array.<google.maps.Marker>} markers The markers to add.
 * @param {boolean} [opt_nodraw] Set to <code>true</code> to prevent redrawing.
 */
MarkerClusterer.prototype.addMarkers = function (markers, opt_nodraw) {
  var key;
  for (key in markers) {
    if (markers.hasOwnProperty(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.
 */
MarkerClusterer.prototype.pushMarkerTo_ = function (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.
 */
MarkerClusterer.prototype.removeMarker = function (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 {Array.<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.
 */
MarkerClusterer.prototype.removeMarkers = function (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
 */
MarkerClusterer.prototype.removeMarker_ = function (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.
 */
MarkerClusterer.prototype.clearMarkers = function () {
  this.resetViewport_(true);
  this.markers_ = [];
};


/**
 * Recalculates and redraws all the marker clusters from scratch.
 *  Call this after changing any properties.
 */
MarkerClusterer.prototype.repaint = function () {
  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
 */
MarkerClusterer.prototype.getExtendedBounds = function (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.
 */
MarkerClusterer.prototype.redraw_ = function () {
  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.
 */
MarkerClusterer.prototype.resetViewport_ = function (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
*/
MarkerClusterer.prototype.distanceBetweenPoints_ = function (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.
 */
MarkerClusterer.prototype.isMarkerInBounds_ = function (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.
 */
MarkerClusterer.prototype.addToClosestCluster_ = function (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.
 */
MarkerClusterer.prototype.createClusters_ = function (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
 */
MarkerClusterer.prototype.extend = function (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 {Array.<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
 */
MarkerClusterer.CALCULATOR = function (markers, numStyles) {
  var index = 0;
  var title = "";
  var count = markers.length;

  // modified by John
  for(var i in markers) {
    if (markers[i].flGc > 1) {
        count += (parseInt(markers[i].flGc) - 1);
    }
  }
  // modified by John end

  var dv = count.toString();
  while (dv !== 0) {
    dv = parseInt(dv / 10, 10);
    index++;
  }

  index = Math.min(index, numStyles);
  return {
    text: count,
    index: index,
    title: title
  };
};


/**
 * The number of markers to process in one batch.
 *
 * @type {number}
 * @constant
 */
MarkerClusterer.BATCH_SIZE = 2000;


/**
 * The number of markers to process in one batch (IE only).
 *
 * @type {number}
 * @constant
 */
MarkerClusterer.BATCH_SIZE_IE = 500;


/**
 * The default root name for the marker cluster images.
 *
 * @type {string}
 * @constant
 */
MarkerClusterer.IMAGE_PATH = "http://google-maps-utility-library-v3.googlecode.com/svn/trunk/markerclustererplus/images/m";


/**
 * The default extension name for the marker cluster images.
 *
 * @type {string}
 * @constant
 */
MarkerClusterer.IMAGE_EXTENSION = "png";


/**
 * The default array of sizes for the marker cluster images.
 *
 * @type {Array.<number>}
 * @constant
 */
MarkerClusterer.IMAGE_SIZES = [53, 56, 66, 78, 90];

if (typeof String.prototype.trim !== 'function') {
  /**
   * IE hack since trim() doesn't exist in all browsers
   * @return {string} The string with removed whitespace
   */
  String.prototype.trim = function() {
    return this.replace(/^\s+|\s+$/g, ''); 
  }
}