/* eslint no-param-reassign: 0 */

/**
 * JavaScript implementation of W3 DOM4 TreeWalker interface.
 *
 * See also:
 * - https://dom.spec.whatwg.org/#interface-treewalker
 *
 * Attributes like "read-only" and "private" are ignored in this implementation
 * due to ECMAScript 3 (as opposed to ES5) not supporting creation of such properties.
 * There are workarounds, but under "keep it simple" and "don't do stupid things" they
 * are ignored in this implementation.
 */
 (function(window, factory) {
     var lazySizes = factory(window, window.document);
     window.lazySizes = lazySizes;
     if(typeof module == 'object' && module.exports){
         module.exports = lazySizes;
     } else if (typeof define == 'function' && define.amd) {
         define(lazySizes);
     }
}(window, function l(win, doc) {
    var TreeWalker, NodeFilter, create, toString, is, mapChild, mapSibling,
        nodeFilter, traverseChildren, traverseSiblings, nextSkippingChildren;

    // Cross-browser polyfill for these constants
    NodeFilter = {
        // Constants for acceptNode()
        FILTER_ACCEPT: 1,
        FILTER_REJECT: 2,
        FILTER_SKIP: 3,

        // Constants for whatToShow
        SHOW_ALL: 0xFFFFFFFF,
        SHOW_ELEMENT: 0x1,
        SHOW_ATTRIBUTE: 0x2, // historical
        SHOW_TEXT: 0x4,
        SHOW_CDATA_SECTION: 0x8, // historical
        SHOW_ENTITY_REFERENCE: 0x10, // historical
        SHOW_ENTITY: 0x20, // historical
        SHOW_PROCESSING_INSTRUCTION: 0x40,
        SHOW_COMMENT: 0x80,
        SHOW_DOCUMENT: 0x100,
        SHOW_DOCUMENT_TYPE: 0x200,
        SHOW_DOCUMENT_FRAGMENT: 0x400,
        SHOW_NOTATION: 0x800 // historical
    };

    /* Local utilities */

    create = Object.create || function (proto) {
        function Empty() {}
        Empty.prototype = proto;
        return new Empty();
    };

    mapChild = {
        first: 'firstChild',
        last: 'lastChild',
        next: 'firstChild',
        previous: 'lastChild'
    };

    mapSibling = {
        next: 'nextSibling',
        previous: 'previousSibling'
    };

    toString = mapChild.toString;

    is = function (x, type) {
        return toString.call(x).toLowerCase() === '[object ' + type.toLowerCase() + ']';
    };

    /* Private methods and helpers */

    /**
     * See https://dom.spec.whatwg.org/#concept-node-filter
     *
     * @private
     * @method
     * @param {TreeWalker} tw
     * @param {Node} node
     */
    nodeFilter = function (tw, node) {
        // Maps nodeType to whatToShow
        if (!(((1 << (node.nodeType - 1)) & tw.whatToShow))) {
            return NodeFilter.FILTER_SKIP;
        }

        if (tw.filter === null) {
            return NodeFilter.FILTER_ACCEPT;
        }

        return tw.filter.acceptNode(node);
    };

    /**
     * See https://dom.spec.whatwg.org/#concept-traverse-children
     *
     * @private
     * @method
     * @param {TreeWalker} tw
     * @param {string} type One of 'first' or 'last'.
     * @return {Node|null}
     */
    traverseChildren = function (tw, type) {
        var child, node, parent, result, sibling;
        node = tw.currentNode[ mapChild[ type ] ];
        while (node !== null) {
            result = nodeFilter(tw, node);
            if (result === NodeFilter.FILTER_ACCEPT) {
                tw.currentNode = node;
                return node;
            }
            if (result === NodeFilter.FILTER_SKIP) {
                child = node[ mapChild[ type ] ];
                if (child !== null) {
                    node = child;
                    continue;
                }
            }
            while (node !== null) {
                sibling = node[ mapChild[ type ] ];
                if (sibling !== null) {
                    node = sibling;
                    break;
                }
                parent = node.parentNode;
                if (parent === null || parent === tw.root || parent === tw.currentNode) {
                    return null;
                } else {
                    node = parent;
                }
            }
        }
        return null;
    };

    /**
     * See https://dom.spec.whatwg.org/#concept-traverse-siblings
     *
     * @private
     * @method
     * @param {TreeWalker} tw
     * @param {TreeWalker} type One of 'next' or 'previous'.
     * @return {Node|null}
     */
    traverseSiblings = function (tw, type) {
        var node, result, sibling;
        node = tw.currentNode;
        if (node === tw.root) {
            return null;
        }
        while (true) {
            sibling = node[ mapSibling[ type ] ];
            while (sibling !== null) {
                node = sibling;
                result = nodeFilter(tw, node);
                if (result === NodeFilter.FILTER_ACCEPT) {
                    tw.currentNode = node;
                    return node;
                }
                sibling = node[ mapChild[ type ] ];
                if (result === NodeFilter.FILTER_REJECT) {
                    sibling = node[ mapSibling[ type ] ];
                }
            }
            node = node.parentNode;
            if (node === null || node === tw.root) {
                return null;
            }
            if (nodeFilter(tw, node) === NodeFilter.FILTER_ACCEPT) {
                return null;
            }
        }
    };

    /**
     * Based on WebKit's NodeTraversal::nextSkippingChildren
     * https://trac.webkit.org/browser/trunk/Source/WebCore/dom/NodeTraversal.h?rev=137221#L103
     */
    nextSkippingChildren = function (node, stayWithin) {
        if (node === stayWithin) {
            return null;
        }
        if (node.nextSibling !== null) {
            return node.nextSibling;
        }

        /**
         * Based on WebKit's NodeTraversal::nextAncestorSibling
         * https://trac.webkit.org/browser/trunk/Source/WebCore/dom/NodeTraversal.cpp?rev=137221#L43
         */
        while (node.parentNode !== null) {
            node = node.parentNode;
            if (node === stayWithin) {
                return null;
            }
            if (node.nextSibling !== null) {
                return node.nextSibling;
            }
        }
        return null;
    };

    /**
     * See https://dom.spec.whatwg.org/#interface-treewalker
     *
     * @constructor
     * @param {Node} root
     * @param {number} [whatToShow]
     * @param {Function} [filter]
     * @throws Error
     */
    TreeWalker = function (root, whatToShow, filter) {
        var tw = this, active = false;

        if (!root || !root.nodeType) {
            throw new Error('DOMException: NOT_SUPPORTED_ERR');
        }

        tw.root = root;
        tw.whatToShow = Number(whatToShow) || 0;

        tw.currentNode = root;

        if (!is(filter, 'function')) {
            tw.filter = null;
        } else {
            tw.filter = create(win.NodeFilter.prototype);

            /**
             * See https://dom.spec.whatwg.org/#dom-nodefilter-acceptnode
             *
             * @method
             * @member NodeFilter
             * @param {Node} node
             * @return {number} Constant NodeFilter.FILTER_ACCEPT,
             *  NodeFilter.FILTER_REJECT or NodeFilter.FILTER_SKIP.
             */
            tw.filter.acceptNode = function (node) {
                var result;
                if (active) {
                    throw new Error('DOMException: INVALID_STATE_ERR');
                }

                active = true;
                result = filter(node);
                active = false;

                return result;
            };
        }
    };

    TreeWalker.prototype = {

        constructor: TreeWalker,

        /**
         * See https://dom.spec.whatwg.org/#ddom-treewalker-parentnode
         *
         * @method
         * @return {Node|null}
         */
        parentNode: function () {
            var node = this.currentNode;
            while (node !== null && node !== this.root) {
                node = node.parentNode;
                if (node !== null && nodeFilter(this, node) === NodeFilter.FILTER_ACCEPT) {
                    this.currentNode = node;
                    return node;
                }
            }
            return null;
        },

        /**
         * See https://dom.spec.whatwg.org/#dom-treewalker-firstchild
         *
         * @method
         * @return {Node|null}
         */
        firstChild: function () {
            return traverseChildren(this, 'first');
        },

        /**
         * See https://dom.spec.whatwg.org/#dom-treewalker-lastchild
         *
         * @method
         * @return {Node|null}
         */
        lastChild: function () {
            return traverseChildren(this, 'last');
        },

        /**
         * See https://dom.spec.whatwg.org/#dom-treewalker-previoussibling
         *
         * @method
         * @return {Node|null}
         */
        previousSibling: function () {
            return traverseSiblings(this, 'previous');
        },

        /**
         * See https://dom.spec.whatwg.org/#dom-treewalker-nextsibling
         *
         * @method
         * @return {Node|null}
         */
        nextSibling: function () {
            return traverseSiblings(this, 'next');
        },

        /**
         * See https://dom.spec.whatwg.org/#dom-treewalker-previousnode
         *
         * @method
         * @return {Node|null}
         */
        previousNode: function () {
            var node, result, sibling;
            node = this.currentNode;
            while (node !== this.root) {
                sibling = node.previousSibling;
                while (sibling !== null) {
                    node = sibling;
                    result = nodeFilter(this, node);
                    while (result !== NodeFilter.FILTER_REJECT && node.lastChild !== null) {
                        node = node.lastChild;
                        result = nodeFilter(this, node);
                    }
                    if (result === NodeFilter.FILTER_ACCEPT) {
                        this.currentNode = node;
                        return node;
                    }
                }
                if (node === this.root || node.parentNode === null) {
                    return null;
                }
                node = node.parentNode;
                if (nodeFilter(this, node) === NodeFilter.FILTER_ACCEPT) {
                    this.currentNode = node;
                    return node;
                }
            }
            return null;
        },

        /**
         * See https://dom.spec.whatwg.org/#dom-treewalker-nextnode
         *
         * @method
         * @return {Node|null}
         */
        nextNode: function () {
            var node, result, following;
            node = this.currentNode;
            result = NodeFilter.FILTER_ACCEPT;

            while (true) {
                while (result !== NodeFilter.FILTER_REJECT && node.firstChild !== null) {
                    node = node.firstChild;
                    result = nodeFilter(this, node);
                    if (result === NodeFilter.FILTER_ACCEPT) {
                        this.currentNode = node;
                        return node;
                    }
                }
                following = nextSkippingChildren(node, this.root);
                if (following !== null) {
                    node = following;
                } else {
                    return null;
                }
                result = nodeFilter(this, node);
                if (result === NodeFilter.FILTER_ACCEPT) {
                    this.currentNode = node;
                    return node;
                }
            }
        }
    };

    /**
     * See http://www.w3.org/TR/dom/#dom-document-createtreewalker
     *
     * @param {Node} root
     * @param {number} [whatToShow=NodeFilter.SHOW_ALL]
     * @param {Function|Object} [filter=null]
     * @return {TreeWalker}
     */
    doc.createTreeWalker = function (root, whatToShow, filter) {
        whatToShow = whatToShow === undefined ? NodeFilter.SHOW_ALL : whatToShow;

        if (filter && is(filter.acceptNode, 'function')) {
            filter = filter.acceptNode;
        // Support Gecko-ism of filter being a function.
        // https://developer.mozilla.org/en-US/docs/DOM/document.createTreeWalker
        } else if (!is(filter, 'function')) {
            filter = null;
        }

        return new TreeWalker(root, whatToShow, filter);
    };

    if (!win.NodeFilter) {
        win.NodeFilter = NodeFilter.constructor = NodeFilter.prototype = NodeFilter;
    }

    if (!win.TreeWalker) {
        win.TreeWalker = TreeWalker;
    }
}));