    /**
     * @class Ext.dd.ScrollManager
     * <p>Provides automatic scrolling of overflow regions in the page during drag operations.</p>
     * <p>The ScrollManager configs will be used as the defaults for any scroll container registered with it,
     * but you can also override most of the configs per scroll container by adding a
     * <tt>ddScrollConfig</tt> object to the target element that contains these properties: {@link #hthresh},
     * {@link #vthresh}, {@link #increment} and {@link #frequency}.  Example usage:
     * <pre><code>
    var el = Ext.get('scroll-ct');
    el.ddScrollConfig = {
        vthresh: 50,
        hthresh: -1,
        frequency: 100,
        increment: 200
    };
    Ext.dd.ScrollManager.register(el);
    </code></pre>
     * <b>Note: This class uses "Point Mode" and is untested in "Intersect Mode".</b>
     * @singleton
     */
    Ext.define('Ext.dd.ScrollManager', {
        singleton: true,
        requires: [
            'Ext.dd.DragDropManager'
        ],

        constructor: function() {
            var ddm = Ext.dd.DragDropManager;
            ddm.fireEvents = Ext.Function.createSequence(ddm.fireEvents, this.onFire, this);
            ddm.stopDrag = Ext.Function.createSequence(ddm.stopDrag, this.onStop, this);
            this.doScroll = Ext.Function.bind(this.doScroll, this);
            this.ddmInstance = ddm;
            this.els = {};
            this.dragEl = null;
            this.proc = {};
        },

        onStop: function(e){
            var sm = Ext.dd.ScrollManager;
            sm.dragEl = null;
            sm.clearProc();
        },

        triggerRefresh: function() {
            if (this.ddmInstance.dragCurrent) {
                this.ddmInstance.refreshCache(this.ddmInstance.dragCurrent.groups);
            }
        },

        doScroll: function() {
            if (this.ddmInstance.dragCurrent) {
                var proc   = this.proc,
                    procEl = proc.el,
                    ddScrollConfig = proc.el.ddScrollConfig,
                    inc = ddScrollConfig ? ddScrollConfig.increment : this.increment;

                if (!this.animate) {
                    if (procEl.scroll(proc.dir, inc)) {
                        this.triggerRefresh();
                    }
                } else {
                    procEl.scroll(proc.dir, inc, true, this.animDuration, this.triggerRefresh);
                }
            }
        },

        clearProc: function() {
            var proc = this.proc;
            if (proc.id) {
                clearInterval(proc.id);
            }
            proc.id = 0;
            proc.el = null;
            proc.dir = "";
        },

        startProc: function(el, dir) {
            this.clearProc();
            this.proc.el = el;
            this.proc.dir = dir;
            var group = el.ddScrollConfig ? el.ddScrollConfig.ddGroup : undefined,
                freq  = (el.ddScrollConfig && el.ddScrollConfig.frequency)
                      ? el.ddScrollConfig.frequency
                      : this.frequency;

            if (group === undefined || this.ddmInstance.dragCurrent.ddGroup == group) {
                this.proc.id = setInterval(this.doScroll, freq);
            }
        },

        onFire: function(e, isDrop) {
            if (isDrop || !this.ddmInstance.dragCurrent) {
                return;
            }
            if (!this.dragEl || this.dragEl != this.ddmInstance.dragCurrent) {
                this.dragEl = this.ddmInstance.dragCurrent;
                // refresh regions on drag start
                this.refreshCache();
            }

            var xy = e.getXY(),
                pt = e.getPoint(),
                proc = this.proc,
                els = this.els;

            for (var id in els) {
                var el = els[id], r = el._region;
                var c = el.ddScrollConfig ? el.ddScrollConfig : this;
                if (r && r.contains(pt) && el.isScrollable()) {
                    if (r.bottom - pt.y <= c.vthresh) {
                        if(proc.el != el){
                            this.startProc(el, "down");
                        }
                        return;
                    }else if (r.right - pt.x <= c.hthresh) {
                        if (proc.el != el) {
                            this.startProc(el, "left");
                        }
                        return;
                    } else if(pt.y - r.top <= c.vthresh) {
                        if (proc.el != el) {
                            this.startProc(el, "up");
                        }
                        return;
                    } else if(pt.x - r.left <= c.hthresh) {
                        if (proc.el != el) {
                            this.startProc(el, "right");
                        }
                        return;
                    }
                }
            }
            this.clearProc();
        },

        /**
         * Registers new overflow element(s) to auto scroll
         * @param {Mixed/Array} el The id of or the element to be scrolled or an array of either
         */
        register : function(el){
            if (Ext.isArray(el)) {
                for(var i = 0, len = el.length; i < len; i++) {
                        this.register(el[i]);
                }
            } else {
                el = Ext.get(el);
                this.els[el.id] = el;
            }
        },

        /**
         * Unregisters overflow element(s) so they are no longer scrolled
         * @param {Mixed/Array} el The id of or the element to be removed or an array of either
         */
        unregister : function(el){
            if(Ext.isArray(el)){
                for (var i = 0, len = el.length; i < len; i++) {
                    this.unregister(el[i]);
                }
            }else{
                el = Ext.get(el);
                delete this.els[el.id];
            }
        },

        /**
         * The number of pixels from the top or bottom edge of a container the pointer needs to be to
         * trigger scrolling (defaults to 25)
         * @type Number
         */
        vthresh : 25,
        /**
         * The number of pixels from the right or left edge of a container the pointer needs to be to
         * trigger scrolling (defaults to 25)
         * @type Number
         */
        hthresh : 25,

        /**
         * The number of pixels to scroll in each scroll increment (defaults to 100)
         * @type Number
         */
        increment : 100,

        /**
         * The frequency of scrolls in milliseconds (defaults to 500)
         * @type Number
         */
        frequency : 500,

        /**
         * True to animate the scroll (defaults to true)
         * @type Boolean
         */
        animate: true,

        /**
         * The animation duration in seconds -
         * MUST BE less than Ext.dd.ScrollManager.frequency! (defaults to .4)
         * @type Number
         */
        animDuration: 0.4,

        /**
         * The named drag drop {@link Ext.dd.DragSource#ddGroup group} to which this container belongs (defaults to undefined).
         * If a ddGroup is specified, then container scrolling will only occur when a dragged object is in the same ddGroup.
         * @type String
         */
        ddGroup: undefined,

        /**
         * Manually trigger a cache refresh.
         */
        refreshCache : function(){
            var els = this.els,
                id;
            for (id in els) {
                if(typeof els[id] == 'object'){ // for people extending the object prototype
                    els[id]._region = els[id].getRegion();
                }
            }
        }
    });