/* Copyright © 2011-2012 by Neil Jenkins. Licensed under the MIT license. */

/*global document, window */

/*
    Native TreeWalker is buggy in IE and Opera:
    * IE9/10 sometimes throw errors when calling TreeWalker#nextNode or
      TreeWalker#previousNode. No way to feature detect this.
    * Some versions of Opera have a bug in TreeWalker#previousNode which makes
      it skip to the wrong node.

    Rather than risk further bugs, it's easiest just to implement our own
    (subset) of the spec in all browsers.
*/

var DOMTreeWalker = (function () {

    "use strict";

    var typeToBitArray = {
        // ELEMENT_NODE
        1: 1,
        // ATTRIBUTE_NODE
        2: 2,
        // TEXT_NODE
        3: 4,
        // COMMENT_NODE
        8: 128,
        // DOCUMENT_NODE
        9: 256,
        // DOCUMENT_FRAGMENT_NODE
        11: 1024
    };

    var FILTER_ACCEPT = 1;

    var TreeWalker = function ( root, nodeType, filter ) {
        this.root = this.currentNode = root;
        this.nodeType = nodeType;
        this.filter = filter;
    };

    TreeWalker.prototype.nextNode = function () {
        var current = this.currentNode,
            root = this.root,
            nodeType = this.nodeType,
            filter = this.filter,
            node;
        while ( true ) {
            node = current.firstChild;
            while ( !node && current ) {
                if ( current === root ) {
                    break;
                }
                node = current.nextSibling;
                if ( !node ) { current = current.parentNode; }
            }
            if ( !node ) {
                return null;
            }
            if ( ( typeToBitArray[ node.nodeType ] & nodeType ) &&
                    filter( node ) === FILTER_ACCEPT ) {
                this.currentNode = node;
                return node;
            }
            current = node;
        }
    };

    TreeWalker.prototype.previousNode = function () {
        var current = this.currentNode,
            root = this.root,
            nodeType = this.nodeType,
            filter = this.filter,
            node;
        while ( true ) {
            if ( current === root ) {
                return null;
            }
            node = current.previousSibling;
            if ( node ) {
                while ( current = node.lastChild ) {
                    node = current;
                }
            } else {
                node = current.parentNode;
            }
            if ( !node ) {
                return null;
            }
            if ( ( typeToBitArray[ node.nodeType ] & nodeType ) &&
                    filter( node ) === FILTER_ACCEPT ) {
                this.currentNode = node;
                return node;
            }
            current = node;
        }
    };

    return TreeWalker;

})();