    /**
     * This is a layout that manages multiple Panels in an expandable accordion style such that only
     * **one Panel can be expanded at any given time**. Each Panel has built-in support for expanding and collapsing.
     *
     * Note: Only Ext Panels and all subclasses of Ext.panel.Panel may be used in an accordion layout Container.
     *
     *     @example
     *     Ext.create('Ext.panel.Panel', {
     *         title: 'Accordion Layout',
     *         width: 300,
     *         height: 300,
     *         defaults: {
     *             // applied to each contained panel
     *             bodyStyle: 'padding:15px'
     *         },
     *         layout: {
     *             // layout-specific configs go here
     *             type: 'accordion',
     *             titleCollapse: false,
     *             animate: true,
     *             activeOnTop: true
     *         },
     *         items: [{
     *             title: 'Panel 1',
     *             html: 'Panel content!'
     *         },{
     *             title: 'Panel 2',
     *             html: 'Panel content!'
     *         },{
     *             title: 'Panel 3',
     *             html: 'Panel content!'
     *         }],
     *         renderTo: Ext.getBody()
     *     });
     */
    Ext.define('Ext.layout.container.Accordion', {
        extend: 'Ext.layout.container.VBox',
        alias: ['layout.accordion'],
        alternateClassName: 'Ext.layout.AccordionLayout',

        itemCls: [Ext.baseCSSPrefix + 'box-item', Ext.baseCSSPrefix + 'accordion-item'],

        align: 'stretch',

        /**
         * @cfg {Boolean} fill
         * True to adjust the active item's height to fill the available space in the container, false to use the
         * item's current height, or auto height if not explicitly set.
         */
        fill : true,

        /**
         * @cfg {Boolean} autoWidth
         * Child Panels have their width actively managed to fit within the accordion's width.
         * @removed This config is ignored in ExtJS 4
         */

        /**
         * @cfg {Boolean} titleCollapse
         * True to allow expand/collapse of each contained panel by clicking anywhere on the title bar, false to allow
         * expand/collapse only when the toggle tool button is clicked.  When set to false,
         * {@link #hideCollapseTool} should be false also.
         */
        titleCollapse : true,

        /**
         * @cfg {Boolean} hideCollapseTool
         * True to hide the contained Panels' collapse/expand toggle buttons, false to display them.
         * When set to true, {@link #titleCollapse} is automatically set to true.
         */
        hideCollapseTool : false,

        /**
         * @cfg {Boolean} collapseFirst
         * True to make sure the collapse/expand toggle button always renders first (to the left of) any other tools
         * in the contained Panels' title bars, false to render it last.
         */
        collapseFirst : false,

        /**
         * @cfg {Boolean} animate
         * True to slide the contained panels open and closed during expand/collapse using animation, false to open and
         * close directly with no animation. Note: The layout performs animated collapsing
         * and expanding, *not* the child Panels.
         */
        animate : true,
        /**
         * @cfg {Boolean} activeOnTop
         * Only valid when {@link #multi} is `false` and {@link #animate} is `false`.
         *
         * True to swap the position of each panel as it is expanded so that it becomes the first item in the container,
         * false to keep the panels in the rendered order.
         */
        activeOnTop : false,
        /**
         * @cfg {Boolean} multi
         * Set to true to enable multiple accordion items to be open at once.
         */
        multi: false,

        defaultAnimatePolicy: {
            y: true,
            height: true
        },

        constructor: function() {
            var me = this;

            me.callParent(arguments);

            if (me.animate) {
                me.animatePolicy = Ext.apply({}, me.defaultAnimatePolicy);
            } else {
                me.animatePolicy = null;
            }
        },

        beforeRenderItems: function (items) {
            var me = this,
                ln = items.length,
                i = 0,
                comp;

            for (; i < ln; i++) {
                comp = items[i];
                if (!comp.rendered) {
                    // Set up initial properties for Panels in an accordion.
                    if (me.collapseFirst) {
                        comp.collapseFirst = me.collapseFirst;
                    }
                    if (me.hideCollapseTool) {
                        comp.hideCollapseTool = me.hideCollapseTool;
                        comp.titleCollapse = true;
                    }
                    else if (me.titleCollapse) {
                        comp.titleCollapse = me.titleCollapse;
                    }

                    delete comp.hideHeader;
                    delete comp.width;
                    comp.collapsible = true;
                    comp.title = comp.title || '&#160;';
                    comp.addBodyCls(Ext.baseCSSPrefix + 'accordion-body');

                    // If only one child Panel is allowed to be expanded
                    // then collapse all except the first one found with collapsed:false
                    if (!me.multi) {
                        // If there is an expanded item, all others must be rendered collapsed.
                        if (me.expandedItem !== undefined) {
                            comp.collapsed = true;
                        }
                        // Otherwise expand the first item with collapsed explicitly configured as false
                        else if (comp.hasOwnProperty('collapsed') && comp.collapsed === false) {
                            me.expandedItem = i;
                        } else {
                            comp.collapsed = true;
                        }

                        // If only one child Panel may be expanded, then intercept expand/show requests.
                        me.owner.mon(comp, {
                            show: me.onComponentShow,
                            beforeexpand: me.onComponentExpand,
                            scope: me
                        });
                    }

                    // If we must fill available space, a collapse must be listened for and a sibling must
                    // be expanded.
                    if (me.fill) {
                        me.owner.mon(comp, {
                            beforecollapse: me.onComponentCollapse,
                            scope: me
                        });
                    }
                }
            }

            // If no collapsed:false Panels found, make the first one expanded.
            if (ln && me.expandedItem === undefined) {
                me.expandedItem = 0;
                items[0].collapsed = false;
            }
        },

        getItemsRenderTree: function(items) {
            this.beforeRenderItems(items);

            return this.callParent(arguments);
        },

        renderItems : function(items, target) {
            this.beforeRenderItems(items);

            this.callParent(arguments);
        },

        configureItem: function(item) {
            this.callParent(arguments);

            // We handle animations for the expand/collapse of items.
            // Items do not have individual borders
            item.animCollapse = item.border = false;

            // If filling available space, all Panels flex.
            if (this.fill) {
                item.flex = 1;
            }
        },

        onChildPanelRender: function(panel) {
            panel.header.addCls(Ext.baseCSSPrefix + 'accordion-hd');
        },

        beginLayout: function (ownerContext) {
            this.callParent(arguments);
            this.updatePanelClasses(ownerContext);
        },

        updatePanelClasses: function(ownerContext) {
            var children = ownerContext.visibleItems,
                ln = children.length,
                siblingCollapsed = true,
                i, child, header;

            for (i = 0; i < ln; i++) {
                child = children[i];
                header = child.header;
                header.addCls(Ext.baseCSSPrefix + 'accordion-hd');

                if (siblingCollapsed) {
                    header.removeCls(Ext.baseCSSPrefix + 'accordion-hd-sibling-expanded');
                } else {
                    header.addCls(Ext.baseCSSPrefix + 'accordion-hd-sibling-expanded');
                }

                if (i + 1 == ln && child.collapsed) {
                    header.addCls(Ext.baseCSSPrefix + 'accordion-hd-last-collapsed');
                } else {
                    header.removeCls(Ext.baseCSSPrefix + 'accordion-hd-last-collapsed');
                }

                siblingCollapsed = child.collapsed;
            }
        },

        // When a Component expands, adjust the heights of the other Components to be just enough to accommodate
        // their headers.
        // The expanded Component receives the only flex value, and so gets all remaining space.
        onComponentExpand: function(toExpand) {
            var me = this,
                owner = me.owner,
                expanded,
                expandedCount, i,
                previousValue;

            if (!me.processing) {
                me.processing = true;
                previousValue = owner.deferLayouts;
                owner.deferLayouts = true;
                expanded = me.multi ? [] : owner.query('>panel:not([collapsed])');
                expandedCount = expanded.length;

                // Collapse all other expanded child items (Won't loop if multi is true)
                for (i = 0; i < expandedCount; i++) {
                    expanded[i].collapse();
                }
                owner.deferLayouts = previousValue;
                me.processing = false;
            }
        },

        onComponentCollapse: function(comp) {
            var me = this,
                owner = me.owner,
                toExpand,
                expanded,
                previousValue;

            if (!me.processing) {
                me.processing = true;
                previousValue = owner.deferLayouts;
                owner.deferLayouts = true;
                toExpand = comp.next() || comp.prev();

                // If we are allowing multi, and the "toCollapse" component is NOT the only expanded Component,
                // then ask the box layout to collapse it to its header.
                if (me.multi) {
                    expanded = me.owner.query('>panel:not([collapsed])');

                    // If the collapsing Panel is the only expanded one, expand the following Component.
                    // All this is handling fill: true, so there must be at least one expanded,
                    if (expanded.length === 1) {
                        toExpand.expand();
                    }

                } else if (toExpand) {
                    toExpand.expand();
                }
                owner.deferLayouts = previousValue;
                me.processing = false;
            }
        },

        onComponentShow: function(comp) {
            // Showing a Component means that you want to see it, so expand it.
            this.onComponentExpand(comp);
        }
    });