/**
 * Provides stackable (z-index) support for Widgets through an extension.
 *
 * @module widget-stack
 */
    var L = Y.Lang,
        UA = Y.UA,
        Node = Y.Node,
        Widget = Y.Widget,

        ZINDEX = "zIndex",
        SHIM = "shim",
        VISIBLE = "visible",

        BOUNDING_BOX = "boundingBox",

        RENDER_UI = "renderUI",
        BIND_UI = "bindUI",
        SYNC_UI = "syncUI",

        OFFSET_WIDTH = "offsetWidth",
        OFFSET_HEIGHT = "offsetHeight",
        PARENT_NODE = "parentNode",
        FIRST_CHILD = "firstChild",
        OWNER_DOCUMENT = "ownerDocument",

        WIDTH = "width",
        HEIGHT = "height",
        PX = "px",

        // HANDLE KEYS
        SHIM_DEFERRED = "shimdeferred",
        SHIM_RESIZE = "shimresize",

        // Events
        VisibleChange = "visibleChange",
        WidthChange = "widthChange",
        HeightChange = "heightChange",
        ShimChange = "shimChange",
        ZIndexChange = "zIndexChange",
        ContentUpdate = "contentUpdate",

        // CSS
        STACKED = "stacked";

    /**
     * Widget extension, which can be used to add stackable (z-index) support to the
     * base Widget class along with a shimming solution, through the
     * <a href="Base.html#method_build">Base.build</a> method.
     *
     * @class WidgetStack
     * @param {Object} User configuration object
     */
    function Stack(config) {
        this._stackNode = this.get(BOUNDING_BOX);
        this._stackHandles = {};

        // WIDGET METHOD OVERLAP
        Y.after(this._renderUIStack, this, RENDER_UI);
        Y.after(this._syncUIStack, this, SYNC_UI);
        Y.after(this._bindUIStack, this, BIND_UI);
    }

    // Static Properties
    /**
     * Static property used to define the default attribute
     * configuration introduced by WidgetStack.
     *
     * @property ATTRS
     * @type Object
     * @static
     */
    Stack.ATTRS = {
        /**
         * @attribute shim
         * @type boolean
         * @default false, for all browsers other than IE6, for which a shim is enabled by default.
         *
         * @description Boolean flag to indicate whether or not a shim should be added to the Widgets
         * boundingBox, to protect it from select box bleedthrough.
         */
        shim: {
            value: (UA.ie == 6)
        },

        /**
         * @attribute zIndex
         * @type number
         * @default 0
         * @description The z-index to apply to the Widgets boundingBox. Non-numerical values for
         * zIndex will be converted to 0
         */
        zIndex: {
            value : 0,
            setter: '_setZIndex'
        }
    };

    /**
     * The HTML parsing rules for the WidgetStack class.
     *
     * @property HTML_PARSER
     * @static
     * @type Object
     */
    Stack.HTML_PARSER = {
        zIndex: function (srcNode) {
            return this._parseZIndex(srcNode);
        }
    };

    /**
     * Default class used to mark the shim element
     *
     * @property SHIM_CLASS_NAME
     * @type String
     * @static
     * @default "yui3-widget-shim"
     */
    Stack.SHIM_CLASS_NAME = Widget.getClassName(SHIM);

    /**
     * Default class used to mark the boundingBox of a stacked widget.
     *
     * @property STACKED_CLASS_NAME
     * @type String
     * @static
     * @default "yui3-widget-stacked"
     */
    Stack.STACKED_CLASS_NAME = Widget.getClassName(STACKED);

    /**
     * Default markup template used to generate the shim element.
     *
     * @property SHIM_TEMPLATE
     * @type String
     * @static
     */
    Stack.SHIM_TEMPLATE = '<iframe class="' + Stack.SHIM_CLASS_NAME + '" frameborder="0" title="Widget Stacking Shim" src="javascript:false" tabindex="-1" role="presentation"></iframe>';

    Stack.prototype = {

        /**
         * Synchronizes the UI to match the Widgets stack state. This method in
         * invoked after syncUI is invoked for the Widget class using YUI's aop infrastructure.
         *
         * @method _syncUIStack
         * @protected
         */
        _syncUIStack: function() {
            this._uiSetShim(this.get(SHIM));
            this._uiSetZIndex(this.get(ZINDEX));
        },

        /**
         * Binds event listeners responsible for updating the UI state in response to
         * Widget stack related state changes.
         * <p>
         * This method is invoked after bindUI is invoked for the Widget class
         * using YUI's aop infrastructure.
         * </p>
         * @method _bindUIStack
         * @protected
         */
        _bindUIStack: function() {
            this.after(ShimChange, this._afterShimChange);
            this.after(ZIndexChange, this._afterZIndexChange);
        },

        /**
         * Creates/Initializes the DOM to support stackability.
         * <p>
         * This method in invoked after renderUI is invoked for the Widget class
         * using YUI's aop infrastructure.
         * </p>
         * @method _renderUIStack
         * @protected
         */
        _renderUIStack: function() {
            this._stackNode.addClass(Stack.STACKED_CLASS_NAME);
        },

        /**
        Parses a `zIndex` attribute value from this widget's `srcNode`.

        @method _parseZIndex
        @param {Node} srcNode The node to parse a `zIndex` value from.
        @return {Mixed} The parsed `zIndex` value.
        @protected
        **/
        _parseZIndex: function (srcNode) {
            var zIndex;

            // Prefers how WebKit handles `z-index` which better matches the
            // spec:
            //
            // * http://www.w3.org/TR/CSS2/visuren.html#z-index
            // * https://bugs.webkit.org/show_bug.cgi?id=15562
            //
            // When a node isn't rendered in the document, and/or when a
            // node is not positioned, then it doesn't have a context to derive
            // a valid `z-index` value from.
            if (!srcNode.inDoc() || srcNode.getStyle('position') === 'static') {
                zIndex = 'auto';
            } else {
                // Uses `getComputedStyle()` because it has greater accuracy in
                // more browsers than `getStyle()` does for `z-index`.
                zIndex = srcNode.getComputedStyle('zIndex');
            }

            // This extension adds a stacking context to widgets, therefore a
            // `srcNode` witout a stacking context (i.e. "auto") will return
            // `null` from this DOM parser. This way the widget's default or
            // user provided value for `zIndex` will be used.
            return zIndex === 'auto' ? null : zIndex;
        },

        /**
         * Default setter for zIndex attribute changes. Normalizes zIndex values to
         * numbers, converting non-numerical values to 0.
         *
         * @method _setZIndex
         * @protected
         * @param {String | Number} zIndex
         * @return {Number} Normalized zIndex
         */
        _setZIndex: function(zIndex) {
            if (L.isString(zIndex)) {
                zIndex = parseInt(zIndex, 10);
            }
            if (!L.isNumber(zIndex)) {
                zIndex = 0;
            }
            return zIndex;
        },

        /**
         * Default attribute change listener for the shim attribute, responsible
         * for updating the UI, in response to attribute changes.
         *
         * @method _afterShimChange
         * @protected
         * @param {EventFacade} e The event facade for the attribute change
         */
        _afterShimChange : function(e) {
            this._uiSetShim(e.newVal);
        },

        /**
         * Default attribute change listener for the zIndex attribute, responsible
         * for updating the UI, in response to attribute changes.
         *
         * @method _afterZIndexChange
         * @protected
         * @param {EventFacade} e The event facade for the attribute change
         */
        _afterZIndexChange : function(e) {
            this._uiSetZIndex(e.newVal);
        },

        /**
         * Updates the UI to reflect the zIndex value passed in.
         *
         * @method _uiSetZIndex
         * @protected
         * @param {number} zIndex The zindex to be reflected in the UI
         */
        _uiSetZIndex: function (zIndex) {
            this._stackNode.setStyle(ZINDEX, zIndex);
        },

        /**
         * Updates the UI to enable/disable the shim. If the widget is not currently visible,
         * creation of the shim is deferred until it is made visible, for performance reasons.
         *
         * @method _uiSetShim
         * @protected
         * @param {boolean} enable If true, creates/renders the shim, if false, removes it.
         */
        _uiSetShim: function (enable) {
            if (enable) {
                // Lazy creation
                if (this.get(VISIBLE)) {
                    this._renderShim();
                } else {
                    this._renderShimDeferred();
                }

                // Eagerly attach resize handlers
                //
                // Required because of Event stack behavior, commit ref: cd8dddc
                // Should be revisted after Ticket #2531067 is resolved.
                if (UA.ie == 6) {
                    this._addShimResizeHandlers();
                }
            } else {
                this._destroyShim();
            }
        },

        /**
         * Sets up change handlers for the visible attribute, to defer shim creation/rendering
         * until the Widget is made visible.
         *
         * @method _renderShimDeferred
         * @private
         */
        _renderShimDeferred : function() {

            this._stackHandles[SHIM_DEFERRED] = this._stackHandles[SHIM_DEFERRED] || [];

            var handles = this._stackHandles[SHIM_DEFERRED],
                createBeforeVisible = function(e) {
                    if (e.newVal) {
                        this._renderShim();
                    }
                };

            handles.push(this.on(VisibleChange, createBeforeVisible));
            // Depending how how Ticket #2531067 is resolved, a reversal of
            // commit ref: cd8dddc could lead to a more elagent solution, with
            // the addition of this line here:
            //
            // handles.push(this.after(VisibleChange, this.sizeShim));
        },

        /**
         * Sets up event listeners to resize the shim when the size of the Widget changes.
         * <p>
         * NOTE: This method is only used for IE6 currently, since IE6 doesn't support a way to
         * resize the shim purely through CSS, when the Widget does not have an explicit width/height
         * set.
         * </p>
         * @method _addShimResizeHandlers
         * @private
         */
        _addShimResizeHandlers : function() {

            this._stackHandles[SHIM_RESIZE] = this._stackHandles[SHIM_RESIZE] || [];

            var sizeShim = this.sizeShim,
                handles = this._stackHandles[SHIM_RESIZE];

            handles.push(this.after(VisibleChange, sizeShim));
            handles.push(this.after(WidthChange, sizeShim));
            handles.push(this.after(HeightChange, sizeShim));
            handles.push(this.after(ContentUpdate, sizeShim));
        },

        /**
         * Detaches any handles stored for the provided key
         *
         * @method _detachStackHandles
         * @param String handleKey The key defining the group of handles which should be detached
         * @private
         */
        _detachStackHandles : function(handleKey) {
            var handles = this._stackHandles[handleKey],
                handle;

            if (handles && handles.length > 0) {
                while((handle = handles.pop())) {
                    handle.detach();
                }
            }
        },

        /**
         * Creates the shim element and adds it to the DOM
         *
         * @method _renderShim
         * @private
         */
        _renderShim : function() {
            var shimEl = this._shimNode,
                stackEl = this._stackNode;

            if (!shimEl) {
                shimEl = this._shimNode = this._getShimTemplate();
                stackEl.insertBefore(shimEl, stackEl.get(FIRST_CHILD));

                this._detachStackHandles(SHIM_DEFERRED);
                this.sizeShim();
            }
        },

        /**
         * Removes the shim from the DOM, and detaches any related event
         * listeners.
         *
         * @method _destroyShim
         * @private
         */
        _destroyShim : function() {
            if (this._shimNode) {
                this._shimNode.get(PARENT_NODE).removeChild(this._shimNode);
                this._shimNode = null;

                this._detachStackHandles(SHIM_DEFERRED);
                this._detachStackHandles(SHIM_RESIZE);
            }
        },

        /**
         * For IE6, synchronizes the size and position of iframe shim to that of
         * Widget bounding box which it is protecting. For all other browsers,
         * this method does not do anything.
         *
         * @method sizeShim
         */
        sizeShim: function () {
            var shim = this._shimNode,
                node = this._stackNode;

            if (shim && UA.ie === 6 && this.get(VISIBLE)) {
                shim.setStyle(WIDTH, node.get(OFFSET_WIDTH) + PX);
                shim.setStyle(HEIGHT, node.get(OFFSET_HEIGHT) + PX);
            }
        },

        /**
         * Creates a cloned shim node, using the SHIM_TEMPLATE html template, for use on a new instance.
         *
         * @method _getShimTemplate
         * @private
         * @return {Node} node A new shim Node instance.
         */
        _getShimTemplate : function() {
            return Node.create(Stack.SHIM_TEMPLATE, this._stackNode.get(OWNER_DOCUMENT));
        }
    };

    Y.WidgetStack = Stack;