    /**
     * @class Ext.grid.plugin.HeaderResizer
     * @extends Ext.util.Observable
     *
     * Plugin to add header resizing functionality to a HeaderContainer.
     * Always resizing header to the left of the splitter you are resizing.
     */
    Ext.define('Ext.grid.plugin.HeaderResizer', {
        extend: 'Ext.util.Observable',
        requires: ['Ext.dd.DragTracker', 'Ext.util.Region'],
        alias: 'plugin.gridheaderresizer',

        disabled: false,

        /**
         * @cfg {Boolean} dynamic
         * Set to true to resize on the fly rather than using a proxy marker. Defaults to false.
         */
        configs: {
            dynamic: true
        },

        colHeaderCls: Ext.baseCSSPrefix + 'column-header',

        minColWidth: 40,
        maxColWidth: 1000,
        wResizeCursor: 'col-resize',
        eResizeCursor: 'col-resize',
        // not using w and e resize bc we are only ever resizing one
        // column
        //wResizeCursor: Ext.isWebKit ? 'w-resize' : 'col-resize',
        //eResizeCursor: Ext.isWebKit ? 'e-resize' : 'col-resize',

        init: function(headerCt) {
            this.headerCt = headerCt;
            headerCt.on('render', this.afterHeaderRender, this, {single: true});
        },

        /**
         * @private
         * AbstractComponent calls destroy on all its plugins at destroy time.
         */
        destroy: function() {
            if (this.tracker) {
                this.tracker.destroy();
            }
        },

        afterHeaderRender: function() {
            var headerCt = this.headerCt,
                el = headerCt.el;

            headerCt.mon(el, 'mousemove', this.onHeaderCtMouseMove, this);

            this.tracker = Ext.create('Ext.dd.DragTracker', {
                disabled: this.disabled,
                onBeforeStart: Ext.Function.bind(this.onBeforeStart, this),
                onStart: Ext.Function.bind(this.onStart, this),
                onDrag: Ext.Function.bind(this.onDrag, this),
                onEnd: Ext.Function.bind(this.onEnd, this),
                tolerance: 3,
                autoStart: 300,
                el: el
            });
        },

        // As we mouse over individual headers, change the cursor to indicate
        // that resizing is available, and cache the resize target header for use
        // if/when they mousedown.
        onHeaderCtMouseMove: function(e, t) {
            if (this.headerCt.dragging) {
                if (this.activeHd) {
                    this.activeHd.el.dom.style.cursor = '';
                    delete this.activeHd;
                }
            } else {
                var headerEl = e.getTarget('.' + this.colHeaderCls, 3, true),
                    overHeader, resizeHeader;

                if (headerEl){
                    overHeader = Ext.getCmp(headerEl.id);

                    // On left edge, go back to the previous non-hidden header.
                    if (overHeader.isOnLeftEdge(e)) {
                        resizeHeader = overHeader.previousNode('gridcolumn:not([hidden])');

                    }
                    // Else, if on the right edge, we're resizing the column we are over
                    else if (overHeader.isOnRightEdge(e)) {
                        resizeHeader = overHeader;
                    }
                    // Between the edges: we are not resizing
                    else {
                        resizeHeader = null;
                    }

                    // We *are* resizing
                    if (resizeHeader) {
                        // If we're attempting to resize a group header, that cannot be resized,
                        // so find its last visible leaf header; Group headers are sized
                        // by the size of their child headers.
                        if (resizeHeader.isGroupHeader) {
                            resizeHeader = resizeHeader.down(':not([isGroupHeader]):not([hidden]):last');
                        }

                        // Check if the header is resizable. Continue checking the old "fixed" property, bug also
                        // check whether the resizablwe property is set to false.
                        if (resizeHeader && !(resizeHeader.fixed || (resizeHeader.resizable === false) || this.disabled)) {
                            this.activeHd = resizeHeader;
                            overHeader.el.dom.style.cursor = this.eResizeCursor;
                        }
                    // reset
                    } else {
                        overHeader.el.dom.style.cursor = '';
                        delete this.activeHd;
                    }
                }
            }
        },

        // only start when there is an activeHd
        onBeforeStart : function(e){
            var t = e.getTarget();
            // cache the activeHd because it will be cleared.
            this.dragHd = this.activeHd;

            if (!!this.dragHd && !Ext.fly(t).hasCls('x-column-header-trigger') && !this.headerCt.dragging) {
                //this.headerCt.dragging = true;
                this.tracker.constrainTo = this.getConstrainRegion();
                return true;
            } else {
                this.headerCt.dragging = false;
                return false;
            }
        },

        // get the region to constrain to, takes into account max and min col widths
        getConstrainRegion: function() {
            var dragHdEl = this.dragHd.el,
                region   = Ext.util.Region.getRegion(dragHdEl);

            return region.adjust(
                0,
                this.maxColWidth - dragHdEl.getWidth(),
                0,
                this.minColWidth
            );
        },

        // initialize the left and right hand side markers around
        // the header that we are resizing
        onStart: function(e){
            var me       = this,
                dragHd   = me.dragHd,
                dragHdEl = dragHd.el,
                width    = dragHdEl.getWidth(),
                headerCt = me.headerCt,
                t        = e.getTarget();

            if (me.dragHd && !Ext.fly(t).hasCls('x-column-header-trigger')) {
                headerCt.dragging = true;
            }

            me.origWidth = width;

            // setup marker proxies
            if (!me.dynamic) {
                var xy           = dragHdEl.getXY(),
                    gridSection  = headerCt.up('[scrollerOwner]'),
                    dragHct      = me.dragHd.up(':not([isGroupHeader])'),
                    firstSection = dragHct.up(),
                    lhsMarker    = gridSection.getLhsMarker(),
                    rhsMarker    = gridSection.getRhsMarker(),
                    el           = rhsMarker.parent(),
                    offsetLeft   = el.getLeft(true),
                    offsetTop    = el.getTop(true),
                    topLeft      = el.translatePoints(xy),
                    markerHeight = firstSection.body.getHeight() + headerCt.getHeight(),
                    top = topLeft.top - offsetTop;

                lhsMarker.setTop(top);
                rhsMarker.setTop(top);
                lhsMarker.setHeight(markerHeight);
                rhsMarker.setHeight(markerHeight);
                lhsMarker.setLeft(topLeft.left - offsetLeft);
                rhsMarker.setLeft(topLeft.left + width - offsetLeft);
            }
        },

        // synchronize the rhsMarker with the mouse movement
        onDrag: function(e){
            if (!this.dynamic) {
                var xy          = this.tracker.getXY('point'),
                    gridSection = this.headerCt.up('[scrollerOwner]'),
                    rhsMarker   = gridSection.getRhsMarker(),
                    el          = rhsMarker.parent(),
                    topLeft     = el.translatePoints(xy),
                    offsetLeft  = el.getLeft(true);

                rhsMarker.setLeft(topLeft.left - offsetLeft);
            // Resize as user interacts
            } else {
                this.doResize();
            }
        },

        onEnd: function(e){
            this.headerCt.dragging = false;
            if (this.dragHd) {
                if (!this.dynamic) {
                    var dragHd      = this.dragHd,
                        gridSection = this.headerCt.up('[scrollerOwner]'),
                        lhsMarker   = gridSection.getLhsMarker(),
                        rhsMarker   = gridSection.getRhsMarker(),
                        currWidth   = dragHd.getWidth(),
                        offset      = this.tracker.getOffset('point'),
                        offscreen   = -9999;

                    // hide markers
                    lhsMarker.setLeft(offscreen);
                    rhsMarker.setLeft(offscreen);
                }
                this.doResize();
            }
        },

        doResize: function() {
            if (this.dragHd) {
                var dragHd = this.dragHd,
                    nextHd,
                    offset = this.tracker.getOffset('point');

                // resize the dragHd
                if (dragHd.flex) {
                    delete dragHd.flex;
                }

                this.headerCt.suspendLayout = true;
                dragHd.setWidth(this.origWidth + offset[0], false);

                // In the case of forceFit, change the following Header width.
                // Then apply the two width changes by laying out the owning HeaderContainer
                // If HeaderContainer is configured forceFit, inhibit upstream layout notification, so that
                // we can also shrink the following Header by an equal amount, and *then* inform the upstream layout.
                if (this.headerCt.forceFit) {
                    nextHd = dragHd.nextNode('gridcolumn:not([hidden]):not([isGroupHeader])');
                    if (nextHd) {
                        delete nextHd.flex;
                        nextHd.setWidth(nextHd.getWidth() - offset[0], false);
                    }
                }
                this.headerCt.suspendLayout = false;
                this.headerCt.doComponentLayout(this.headerCt.getFullWidth());
            }
        },

        disable: function() {
            this.disabled = true;
            if (this.tracker) {
                this.tracker.disable();
            }
        },

        enable: function() {
            this.disabled = false;
            if (this.tracker) {
                this.tracker.enable();
            }
        }
    });