/**
* @name MarkerManager v3
* @version 1.0
* @copyright (c) 2007 Google Inc.
* @author Doug Ricket, Bjorn Brala (port to v3), others,
*
* @fileoverview Marker manager is an interface between the map and the user,
* designed to manage adding and removing many points when the viewport changes.
* <br /><br />
* <b>How it Works</b>:<br/> 
* The MarkerManager places its markers onto a grid, similar to the map tiles.
* When the user moves the viewport, it computes which grid cells have
* entered or left the viewport, and shows or hides all the markers in those
* cells.
* (If the users scrolls the viewport beyond the markers that are loaded,
* no markers will be visible until the <code>EVENT_moveend</code> 
* triggers an update.)
* In practical consequences, this allows 10,000 markers to be distributed over
* a large area, and as long as only 100-200 are visible in any given viewport,
* the user will see good performance corresponding to the 100 visible markers,
* rather than poor performance corresponding to the total 10,000 markers.
* Note that some code is optimized for speed over space,
* with the goal of accommodating thousands of markers.
*/

/*
* 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 MarkerManagerOptions
* @class This class represents optional arguments to the {@link MarkerManager}
*     constructor.
* @property {Number} maxZoom Sets the maximum zoom level monitored by a
*     marker manager. If not given, the manager assumes the maximum map zoom
*     level. This value is also used when markers are added to the manager
*     without the optional {@link maxZoom} parameter.
* @property {Number} borderPadding Specifies, in pixels, the extra padding
*     outside the map's current viewport monitored by a manager. Markers that
*     fall within this padding are added to the map, even if they are not fully
*     visible.
* @property {Boolean} trackMarkers=false Indicates whether or not a marker
*     manager should track markers' movements. If you wish to move managed
*     markers using the {@link setPoint}/{@link setLatLng} methods, 
*     this option should be set to {@link true}.
*/

/**
* Creates a new MarkerManager that will show/hide markers on a map.
*
* Events:
* @event changed (Parameters: shown bounds, shown markers) Notify listeners when the state of what is displayed changes.
* @event loaded MarkerManager has succesfully been initialized.
*
* @constructor
* @param {Map} map The map to manage.
* @param {Object} opt_opts A container for optional arguments:
*   {Number} maxZoom The maximum zoom level for which to create tiles.
*   {Number} borderPadding The width in pixels beyond the map border,
*                   where markers should be display.
*   {Boolean} trackMarkers Whether or not this manager should track marker
*                   movements.
*/
function MarkerManager(map, opt_opts) {
    var me = this;
    me.map_ = map;
    me.mapZoom_ = map.getZoom();

    me.projectionHelper_ = new ProjectionHelperOverlay(map);
    google.maps.event.addListener(me.projectionHelper_, 'ready', function () {
        me.projection_ = this.getProjection();
        me.initialize(map, opt_opts);
    });
}


MarkerManager.prototype.initialize = function (map, opt_opts) {
    var me = this;

    opt_opts = opt_opts || {};
    me.tileSize_ = MarkerManager.DEFAULT_TILE_SIZE_;

    var mapTypes = map.mapTypes;

    // Find max zoom level
    var mapMaxZoom = 1;
    for (var sType in mapTypes) {
        if (typeof map.mapTypes.get(sType) === 'object' && typeof map.mapTypes.get(sType).maxZoom === 'number') {
            var mapTypeMaxZoom = map.mapTypes.get(sType).maxZoom;
            if (mapTypeMaxZoom > mapMaxZoom) {
                mapMaxZoom = mapTypeMaxZoom;
            }
        }
    }

    me.maxZoom_ = opt_opts.maxZoom || 19;

    me.trackMarkers_ = opt_opts.trackMarkers;
    me.show_ = opt_opts.show || true;

    var padding;
    if (typeof opt_opts.borderPadding === 'number') {
        padding = opt_opts.borderPadding;
    } else {
        padding = MarkerManager.DEFAULT_BORDER_PADDING_;
    }
    // The padding in pixels beyond the viewport, where we will pre-load markers.
    me.swPadding_ = new google.maps.Size(-padding, padding);
    me.nePadding_ = new google.maps.Size(padding, -padding);
    me.borderPadding_ = padding;

    me.gridWidth_ = {};

    me.grid_ = {};
    me.grid_[me.maxZoom_] = {};
    me.numMarkers_ = {};
    me.numMarkers_[me.maxZoom_] = 0;


    google.maps.event.addListener(map, 'dragend', function () {
        me.onMapMoveEnd_();
    });
    google.maps.event.addListener(map, 'zoom_changed', function () {
        me.onMapMoveEnd_();
    });



    /**
    * This closure provide easy access to the map.
    * They are used as callbacks, not as methods.
    * @param GMarker marker Marker to be removed from the map
    * @private
    */
    me.removeOverlay_ = function (marker) {
        marker.setMap(null);
        me.shownMarkers_--;
    };

    /**
    * This closure provide easy access to the map.
    * They are used as callbacks, not as methods.
    * @param GMarker marker Marker to be added to the map
    * @private
    */
    me.addOverlay_ = function (marker) {
        if (me.show_) {
            marker.setMap(me.map_);
            me.shownMarkers_++;
        }
    };

    me.resetManager_();
    me.shownMarkers_ = 0;

    me.shownBounds_ = me.getMapGridBounds_();

    google.maps.event.trigger(me, 'loaded');

};

/**
*  Default tile size used for deviding the map into a grid.
*/
MarkerManager.DEFAULT_TILE_SIZE_ = 1024;

/*
*  How much extra space to show around the map border so
*  dragging doesn't result in an empty place.
*/
MarkerManager.DEFAULT_BORDER_PADDING_ = 100;

/**
*  Default tilesize of single tile world.
*/
MarkerManager.MERCATOR_ZOOM_LEVEL_ZERO_RANGE = 256;


/**
* Initializes MarkerManager arrays for all zoom levels
* Called by constructor and by clearAllMarkers
*/
MarkerManager.prototype.resetManager_ = function () {
    var mapWidth = MarkerManager.MERCATOR_ZOOM_LEVEL_ZERO_RANGE;
    for (var zoom = 0; zoom <= this.maxZoom_; ++zoom) {
        this.grid_[zoom] = {};
        this.numMarkers_[zoom] = 0;
        this.gridWidth_[zoom] = Math.ceil(mapWidth / this.tileSize_);
        mapWidth <<= 1;
    }

};

/**
* Removes all markers in the manager, and
* removes any visible markers from the map.
*/
MarkerManager.prototype.clearMarkers = function () {
    this.processAll_(this.shownBounds_, this.removeOverlay_);
    this.resetManager_();
};


/**
* Gets the tile coordinate for a given latlng point.
*
* @param {LatLng} latlng The geographical point.
* @param {Number} zoom The zoom level.
* @param {google.maps.Size} padding The padding used to shift the pixel coordinate.
*               Used for expanding a bounds to include an extra padding
*               of pixels surrounding the bounds.
* @return {GPoint} The point in tile coordinates.
*
*/
MarkerManager.prototype.getTilePoint_ = function (latlng, zoom, padding) {

    var pixelPoint = this.projectionHelper_.LatLngToPixel(latlng, zoom);

    var point = new google.maps.Point(
    Math.floor((pixelPoint.x + padding.width) / this.tileSize_),
    Math.floor((pixelPoint.y + padding.height) / this.tileSize_)
  );

    return point;
};


/**
* Finds the appropriate place to add the marker to the grid.
* Optimized for speed; does not actually add the marker to the map.
* Designed for batch-processing thousands of markers.
*
* @param {Marker} marker The marker to add.
* @param {Number} minZoom The minimum zoom for displaying the marker.
* @param {Number} maxZoom The maximum zoom for displaying the marker.
*/
MarkerManager.prototype.addMarkerBatch_ = function (marker, minZoom, maxZoom) {
    var me = this;

    var mPoint = marker.getPosition();
    marker.MarkerManager_minZoom = minZoom;


    // Tracking markers is expensive, so we do this only if the
    // user explicitly requested it when creating marker manager.
    if (this.trackMarkers_) {
        google.maps.event.addListener(marker, 'changed', function (a, b, c) {
            me.onMarkerMoved_(a, b, c);
        });
    }

    var gridPoint = this.getTilePoint_(mPoint, maxZoom, new google.maps.Size(0, 0, 0, 0));

    for (var zoom = maxZoom; zoom >= minZoom; zoom--) {
        var cell = this.getGridCellCreate_(gridPoint.x, gridPoint.y, zoom);
        cell.push(marker);

        gridPoint.x = gridPoint.x >> 1;
        gridPoint.y = gridPoint.y >> 1;
    }
};


/**
* Returns whether or not the given point is visible in the shown bounds. This
* is a helper method that takes care of the corner case, when shownBounds have
* negative minX value.
*
* @param {Point} point a point on a grid.
* @return {Boolean} Whether or not the given point is visible in the currently
* shown bounds.
*/
MarkerManager.prototype.isGridPointVisible_ = function (point) {
    var vertical = this.shownBounds_.minY <= point.y &&
      point.y <= this.shownBounds_.maxY;
    var minX = this.shownBounds_.minX;
    var horizontal = minX <= point.x && point.x <= this.shownBounds_.maxX;
    if (!horizontal && minX < 0) {
        // Shifts the negative part of the rectangle. As point.x is always less
        // than grid width, only test shifted minX .. 0 part of the shown bounds.
        var width = this.gridWidth_[this.shownBounds_.z];
        horizontal = minX + width <= point.x && point.x <= width - 1;
    }
    return vertical && horizontal;
};


/**
* Reacts to a notification from a marker that it has moved to a new location.
* It scans the grid all all zoom levels and moves the marker from the old grid
* location to a new grid location.
*
* @param {Marker} marker The marker that moved.
* @param {LatLng} oldPoint The old position of the marker.
* @param {LatLng} newPoint The new position of the marker.
*/
MarkerManager.prototype.onMarkerMoved_ = function (marker, oldPoint, newPoint) {
    // NOTE: We do not know the minimum or maximum zoom the marker was
    // added at, so we start at the absolute maximum. Whenever we successfully
    // remove a marker at a given zoom, we add it at the new grid coordinates.
    var zoom = this.maxZoom_;
    var changed = false;
    var oldGrid = this.getTilePoint_(oldPoint, zoom, new google.maps.Size(0, 0, 0, 0));
    var newGrid = this.getTilePoint_(newPoint, zoom, new google.maps.Size(0, 0, 0, 0));
    while (zoom >= 0 && (oldGrid.x !== newGrid.x || oldGrid.y !== newGrid.y)) {
        var cell = this.getGridCellNoCreate_(oldGrid.x, oldGrid.y, zoom);
        if (cell) {
            if (this.removeFromArray_(cell, marker)) {
                this.getGridCellCreate_(newGrid.x, newGrid.y, zoom).push(marker);
            }
        }
        // For the current zoom we also need to update the map. Markers that no
        // longer are visible are removed from the map. Markers that moved into
        // the shown bounds are added to the map. This also lets us keep the count
        // of visible markers up to date.
        if (zoom === this.mapZoom_) {
            if (this.isGridPointVisible_(oldGrid)) {
                if (!this.isGridPointVisible_(newGrid)) {
                    this.removeOverlay_(marker);
                    changed = true;
                }
            } else {
                if (this.isGridPointVisible_(newGrid)) {
                    this.addOverlay_(marker);
                    changed = true;
                }
            }
        }
        oldGrid.x = oldGrid.x >> 1;
        oldGrid.y = oldGrid.y >> 1;
        newGrid.x = newGrid.x >> 1;
        newGrid.y = newGrid.y >> 1;
        --zoom;
    }
    if (changed) {
        this.notifyListeners_();
    }
};


/**
* Removes marker from the manager and from the map
* (if it's currently visible).
* @param {GMarker} marker The marker to delete.
*/
MarkerManager.prototype.removeMarker = function (marker) {
    var zoom = this.maxZoom_;
    var changed = false;
    var point = marker.getPosition();
    var grid = this.getTilePoint_(point, zoom, new google.maps.Size(0, 0, 0, 0));
    while (zoom >= 0) {
        var cell = this.getGridCellNoCreate_(grid.x, grid.y, zoom);

        if (cell) {
            this.removeFromArray_(cell, marker);
        }
        // For the current zoom we also need to update the map. Markers that no
        // longer are visible are removed from the map. This also lets us keep the count
        // of visible markers up to date.
        if (zoom === this.mapZoom_) {
            if (this.isGridPointVisible_(grid)) {
                this.removeOverlay_(marker);
                changed = true;
            }
        }
        grid.x = grid.x >> 1;
        grid.y = grid.y >> 1;
        --zoom;
    }
    if (changed) {
        this.notifyListeners_();
    }
    this.numMarkers_[marker.MarkerManager_minZoom]--;
};


/**
* Add many markers at once.
* Does not actually update the map, just the internal grid.
*
* @param {Array of Marker} markers The markers to add.
* @param {Number} minZoom The minimum zoom level to display the markers.
* @param {Number} opt_maxZoom The maximum zoom level to display the markers.
*/
MarkerManager.prototype.addMarkers = function (markers, minZoom, opt_maxZoom) {
    var maxZoom = this.getOptMaxZoom_(opt_maxZoom);
    for (var i = markers.length - 1; i >= 0; i--) {
        this.addMarkerBatch_(markers[i], minZoom, maxZoom);
    }

    this.numMarkers_[minZoom] += markers.length;
};


/**
* Returns the value of the optional maximum zoom. This method is defined so
* that we have just one place where optional maximum zoom is calculated.
*
* @param {Number} opt_maxZoom The optinal maximum zoom.
* @return The maximum zoom.
*/
MarkerManager.prototype.getOptMaxZoom_ = function (opt_maxZoom) {
    return opt_maxZoom || this.maxZoom_;
};


/**
* Calculates the total number of markers potentially visible at a given
* zoom level.
*
* @param {Number} zoom The zoom level to check.
*/
MarkerManager.prototype.getMarkerCount = function (zoom) {
    var total = 0;
    for (var z = 0; z <= zoom; z++) {
        total += this.numMarkers_[z];
    }
    return total;
};

/** 
* Returns a marker given latitude, longitude and zoom. If the marker does not 
* exist, the method will return a new marker. If a new marker is created, 
* it will NOT be added to the manager. 
* 
* @param {Number} lat - the latitude of a marker. 
* @param {Number} lng - the longitude of a marker. 
* @param {Number} zoom - the zoom level 
* @return {GMarker} marker - the marker found at lat and lng 
*/
MarkerManager.prototype.getMarker = function (lat, lng, zoom) {
    var mPoint = new google.maps.LatLng(lat, lng);
    var gridPoint = this.getTilePoint_(mPoint, zoom, new google.maps.Size(0, 0, 0, 0));

    var marker = new google.maps.Marker({ position: mPoint });

    var cellArray = this.getGridCellNoCreate_(gridPoint.x, gridPoint.y, zoom);
    if (cellArray !== undefined) {
        for (var i = 0; i < cellArray.length; i++) {
            if (lat === cellArray[i].getLatLng().lat() && lng === cellArray[i].getLatLng().lng()) {
                marker = cellArray[i];
            }
        }
    }
    return marker;
};

/**
* Add a single marker to the map.
*
* @param {Marker} marker The marker to add.
* @param {Number} minZoom The minimum zoom level to display the marker.
* @param {Number} opt_maxZoom The maximum zoom level to display the marker.
*/
MarkerManager.prototype.addMarker = function (marker, minZoom, opt_maxZoom) {
    var maxZoom = this.getOptMaxZoom_(opt_maxZoom);
    this.addMarkerBatch_(marker, minZoom, maxZoom);
    var gridPoint = this.getTilePoint_(marker.getPosition(), this.mapZoom_, new google.maps.Size(0, 0, 0, 0));
    if (this.isGridPointVisible_(gridPoint) &&
      minZoom <= this.shownBounds_.z &&
      this.shownBounds_.z <= maxZoom) {
        this.addOverlay_(marker);
        this.notifyListeners_();
    }
    this.numMarkers_[minZoom]++;
};


/**
* Helper class to create a bounds of INT ranges.
* @param bounds Array.<Object.<string, number>> Bounds object.
* @constructor
*/
function GridBounds(bounds) {
    // [sw, ne]

    this.minX = Math.min(bounds[0].x, bounds[1].x);
    this.maxX = Math.max(bounds[0].x, bounds[1].x);
    this.minY = Math.min(bounds[0].y, bounds[1].y);
    this.maxY = Math.max(bounds[0].y, bounds[1].y);

}

/**
* Returns true if this bounds equal the given bounds.
* @param {GridBounds} gridBounds GridBounds The bounds to test.
* @return {Boolean} This Bounds equals the given GridBounds.
*/
GridBounds.prototype.equals = function (gridBounds) {
    if (this.maxX === gridBounds.maxX && this.maxY === gridBounds.maxY && this.minX === gridBounds.minX && this.minY === gridBounds.minY) {
        return true;
    } else {
        return false;
    }
};

/**
* Returns true if this bounds (inclusively) contains the given point.
* @param {Point} point  The point to test.
* @return {Boolean} This Bounds contains the given Point.
*/
GridBounds.prototype.containsPoint = function (point) {
    var outer = this;
    return (outer.minX <= point.x && outer.maxX >= point.x && outer.minY <= point.y && outer.maxY >= point.y);
};

/**
* Get a cell in the grid, creating it first if necessary.
*
* Optimization candidate
*
* @param {Number} x The x coordinate of the cell.
* @param {Number} y The y coordinate of the cell.
* @param {Number} z The z coordinate of the cell.
* @return {Array} The cell in the array.
*/
MarkerManager.prototype.getGridCellCreate_ = function (x, y, z) {
    var grid = this.grid_[z];
    if (x < 0) {
        x += this.gridWidth_[z];
    }
    var gridCol = grid[x];
    if (!gridCol) {
        gridCol = grid[x] = [];
        return (gridCol[y] = []);
    }
    var gridCell = gridCol[y];
    if (!gridCell) {
        return (gridCol[y] = []);
    }
    return gridCell;
};


/**
* Get a cell in the grid, returning undefined if it does not exist.
*
* NOTE: Optimized for speed -- otherwise could combine with getGridCellCreate_.
*
* @param {Number} x The x coordinate of the cell.
* @param {Number} y The y coordinate of the cell.
* @param {Number} z The z coordinate of the cell.
* @return {Array} The cell in the array.
*/
MarkerManager.prototype.getGridCellNoCreate_ = function (x, y, z) {
    var grid = this.grid_[z];

    if (x < 0) {
        x += this.gridWidth_[z];
    }
    var gridCol = grid[x];
    return gridCol ? gridCol[y] : undefined;
};


/**
* Turns at geographical bounds into a grid-space bounds.
*
* @param {LatLngBounds} bounds The geographical bounds.
* @param {Number} zoom The zoom level of the bounds.
* @param {google.maps.Size} swPadding The padding in pixels to extend beyond the
* given bounds.
* @param {google.maps.Size} nePadding The padding in pixels to extend beyond the
* given bounds.
* @return {GridBounds} The bounds in grid space.
*/
MarkerManager.prototype.getGridBounds_ = function (bounds, zoom, swPadding, nePadding) {
    zoom = Math.min(zoom, this.maxZoom_);

    var bl = bounds.getSouthWest();
    var tr = bounds.getNorthEast();
    var sw = this.getTilePoint_(bl, zoom, swPadding);

    var ne = this.getTilePoint_(tr, zoom, nePadding);
    var gw = this.gridWidth_[zoom];

    // Crossing the prime meridian requires correction of bounds.
    if (tr.lng() < bl.lng() || ne.x < sw.x) {
        sw.x -= gw;
    }
    if (ne.x - sw.x + 1 >= gw) {
        // Computed grid bounds are larger than the world; truncate.
        sw.x = 0;
        ne.x = gw - 1;
    }

    var gridBounds = new GridBounds([sw, ne]);
    gridBounds.z = zoom;

    return gridBounds;
};


/**
* Gets the grid-space bounds for the current map viewport.
*
* @return {Bounds} The bounds in grid space.
*/
MarkerManager.prototype.getMapGridBounds_ = function () {
    return this.getGridBounds_(this.map_.getBounds(), this.mapZoom_, this.swPadding_, this.nePadding_);
};


/**
* Event listener for map:movend.
* NOTE: Use a timeout so that the user is not blocked
* from moving the map.
*
* Removed this because a a lack of a scopy override/callback function on events. 
*/
MarkerManager.prototype.onMapMoveEnd_ = function () {
    this.objectSetTimeout_(this, this.updateMarkers_, 0);
};


/**
* Call a function or evaluate an expression after a specified number of
* milliseconds.
*
* Equivalent to the standard window.setTimeout function, but the given
* function executes as a method of this instance. So the function passed to
* objectSetTimeout can contain references to this.
*    objectSetTimeout(this, function () { alert(this.x) }, 1000);
*
* @param {Object} object  The target object.
* @param {Function} command  The command to run.
* @param {Number} milliseconds  The delay.
* @return {Boolean}  Success.
*/
MarkerManager.prototype.objectSetTimeout_ = function (object, command, milliseconds) {
    return window.setTimeout(function () {
        command.call(object);
    }, milliseconds);
};


/**
* Is this layer visible?
*
* Returns visibility setting
*
* @return {Boolean} Visible
*/
MarkerManager.prototype.visible = function () {
    return this.show_ ? true : false;
};


/**
* Returns true if the manager is hidden.
* Otherwise returns false.
* @return {Boolean} Hidden
*/
MarkerManager.prototype.isHidden = function () {
    return !this.show_;
};


/**
* Shows the manager if it's currently hidden.
*/
MarkerManager.prototype.show = function () {
    this.show_ = true;
    this.refresh();
};


/**
* Hides the manager if it's currently visible
*/
MarkerManager.prototype.hide = function () {
    this.show_ = false;
    this.refresh();
};


/**
* Toggles the visibility of the manager.
*/
MarkerManager.prototype.toggle = function () {
    this.show_ = !this.show_;
    this.refresh();
};


/**
* Refresh forces the marker-manager into a good state.
* <ol>
*   <li>If never before initialized, shows all the markers.</li>
*   <li>If previously initialized, removes and re-adds all markers.</li>
* </ol>
*/
MarkerManager.prototype.refresh = function () {
    if (this.shownMarkers_ > 0) {
        this.processAll_(this.shownBounds_, this.removeOverlay_);
    }
    // An extra check on this.show_ to increase performance (no need to processAll_)
    if (this.show_) {
        this.processAll_(this.shownBounds_, this.addOverlay_);
    }
    this.notifyListeners_();
};


/**
* After the viewport may have changed, add or remove markers as needed.
*/
MarkerManager.prototype.updateMarkers_ = function () {
    this.mapZoom_ = this.map_.getZoom();
    var newBounds = this.getMapGridBounds_();

    // If the move does not include new grid sections,
    // we have no work to do:
    if (newBounds.equals(this.shownBounds_) && newBounds.z === this.shownBounds_.z) {
        return;
    }

    if (newBounds.z !== this.shownBounds_.z) {
        this.processAll_(this.shownBounds_, this.removeOverlay_);
        if (this.show_) { // performance
            this.processAll_(newBounds, this.addOverlay_);
        }
    } else {
        // Remove markers:
        this.rectangleDiff_(this.shownBounds_, newBounds, this.removeCellMarkers_);

        // Add markers:
        if (this.show_) { // performance
            this.rectangleDiff_(newBounds, this.shownBounds_, this.addCellMarkers_);
        }
    }
    this.shownBounds_ = newBounds;

    this.notifyListeners_();
};


/**
* Notify listeners when the state of what is displayed changes.
*/
MarkerManager.prototype.notifyListeners_ = function () {
    google.maps.event.trigger(this, 'changed', this.shownBounds_, this.shownMarkers_);
};


/**
* Process all markers in the bounds provided, using a callback.
*
* @param {Bounds} bounds The bounds in grid space.
* @param {Function} callback The function to call for each marker.
*/
MarkerManager.prototype.processAll_ = function (bounds, callback) {
    for (var x = bounds.minX; x <= bounds.maxX; x++) {
        for (var y = bounds.minY; y <= bounds.maxY; y++) {
            this.processCellMarkers_(x, y, bounds.z, callback);
        }
    }
};


/**
* Process all markers in the grid cell, using a callback.
*
* @param {Number} x The x coordinate of the cell.
* @param {Number} y The y coordinate of the cell.
* @param {Number} z The z coordinate of the cell.
* @param {Function} callback The function to call for each marker.
*/
MarkerManager.prototype.processCellMarkers_ = function (x, y, z, callback) {
    var cell = this.getGridCellNoCreate_(x, y, z);
    if (cell) {
        for (var i = cell.length - 1; i >= 0; i--) {
            callback(cell[i]);
        }
    }
};


/**
* Remove all markers in a grid cell.
*
* @param {Number} x The x coordinate of the cell.
* @param {Number} y The y coordinate of the cell.
* @param {Number} z The z coordinate of the cell.
*/
MarkerManager.prototype.removeCellMarkers_ = function (x, y, z) {
    this.processCellMarkers_(x, y, z, this.removeOverlay_);
};


/**
* Add all markers in a grid cell.
*
* @param {Number} x The x coordinate of the cell.
* @param {Number} y The y coordinate of the cell.
* @param {Number} z The z coordinate of the cell.
*/
MarkerManager.prototype.addCellMarkers_ = function (x, y, z) {
    this.processCellMarkers_(x, y, z, this.addOverlay_);
};


/**
* Use the rectangleDiffCoords_ function to process all grid cells
* that are in bounds1 but not bounds2, using a callback, and using
* the current MarkerManager object as the instance.
*
* Pass the z parameter to the callback in addition to x and y.
*
* @param {Bounds} bounds1 The bounds of all points we may process.
* @param {Bounds} bounds2 The bounds of points to exclude.
* @param {Function} callback The callback function to call
*                   for each grid coordinate (x, y, z).
*/
MarkerManager.prototype.rectangleDiff_ = function (bounds1, bounds2, callback) {
    var me = this;
    me.rectangleDiffCoords_(bounds1, bounds2, function (x, y) {
        callback.apply(me, [x, y, bounds1.z]);
    });
};


/**
* Calls the function for all points in bounds1, not in bounds2
*
* @param {Bounds} bounds1 The bounds of all points we may process.
* @param {Bounds} bounds2 The bounds of points to exclude.
* @param {Function} callback The callback function to call
*                   for each grid coordinate.
*/
MarkerManager.prototype.rectangleDiffCoords_ = function (bounds1, bounds2, callback) {
    var minX1 = bounds1.minX;
    var minY1 = bounds1.minY;
    var maxX1 = bounds1.maxX;
    var maxY1 = bounds1.maxY;
    var minX2 = bounds2.minX;
    var minY2 = bounds2.minY;
    var maxX2 = bounds2.maxX;
    var maxY2 = bounds2.maxY;

    var x, y;
    for (x = minX1; x <= maxX1; x++) {  // All x in R1
        // All above:
        for (y = minY1; y <= maxY1 && y < minY2; y++) {  // y in R1 above R2
            callback(x, y);
        }
        // All below:
        for (y = Math.max(maxY2 + 1, minY1);  // y in R1 below R2
         y <= maxY1; y++) {
            callback(x, y);
        }
    }

    for (y = Math.max(minY1, minY2);
       y <= Math.min(maxY1, maxY2); y++) {  // All y in R2 and in R1
        // Strictly left:
        for (x = Math.min(maxX1 + 1, minX2) - 1;
         x >= minX1; x--) {  // x in R1 left of R2
            callback(x, y);
        }
        // Strictly right:
        for (x = Math.max(minX1, maxX2 + 1);  // x in R1 right of R2
         x <= maxX1; x++) {
            callback(x, y);
        }
    }
};


/**
* Removes value from array. O(N).
*
* @param {Array} array  The array to modify.
* @param {any} value  The value to remove.
* @param {Boolean} opt_notype  Flag to disable type checking in equality.
* @return {Number}  The number of instances of value that were removed.
*/
MarkerManager.prototype.removeFromArray_ = function (array, value, opt_notype) {
    var shift = 0;
    for (var i = 0; i < array.length; ++i) {
        if (array[i] === value || (opt_notype && array[i] === value)) {
            array.splice(i--, 1);
            shift++;
        }
    }
    return shift;
};







/**
*   Projection overlay helper. Helps in calculating
*   that markers get into the right grid.
*   @constructor
*   @param {Map} map The map to manage.
**/
function ProjectionHelperOverlay(map) {

    this.setMap(map);

    var TILEFACTOR = 8;
    var TILESIDE = 1 << TILEFACTOR;
    var RADIUS = 7;

    this._map = map;
    this._zoom = -1;
    this._X0 =
  this._Y0 =
  this._X1 =
  this._Y1 = -1;


}
ProjectionHelperOverlay.prototype = new google.maps.OverlayView();

/**
*  Helper function to convert Lng to X
*  @private
*  @param {float} lng
**/
ProjectionHelperOverlay.prototype.LngToX_ = function (lng) {
    return (1 + lng / 180);
};

/**
*  Helper function to convert Lat to Y
*  @private
*  @param {float} lat
**/
ProjectionHelperOverlay.prototype.LatToY_ = function (lat) {
    var sinofphi = Math.sin(lat * Math.PI / 180);
    return (1 - 0.5 / Math.PI * Math.log((1 + sinofphi) / (1 - sinofphi)));
};

/**
*   Old school LatLngToPixel
*   @param {LatLng} latlng google.maps.LatLng object
*   @param {Number} zoom Zoom level
*   @return {position} {x: pixelPositionX, y: pixelPositionY}
**/
ProjectionHelperOverlay.prototype.LatLngToPixel = function (latlng, zoom) {
    var map = this._map;
    var div = this.getProjection().fromLatLngToDivPixel(latlng);
    var abs = { x: ~ ~(0.5 + this.LngToX_(latlng.lng()) * (2 << (zoom + 6))), y: ~ ~(0.5 + this.LatToY_(latlng.lat()) * (2 << (zoom + 6))) };
    return abs;
};


/**
* Draw function only triggers a ready event for
* MarkerManager to know projection can proceed to
* initialize.
*/
ProjectionHelperOverlay.prototype.draw = function () {
    if (!this.ready) {
        this.ready = true;
        google.maps.event.trigger(this, 'ready');
    }
};