(function() {
    // "Virtual elements" is an abstraction on top of the usual DOM API which understands the notion that comment nodes
    // may be used to represent hierarchy (in addition to the DOM's natural hierarchy).
    // If you call the DOM-manipulating functions on ko.virtualElements, you will be able to read and write the state
    // of that virtual hierarchy
    //
    // The point of all this is to support containerless templates (e.g., <!-- ko foreach:someCollection -->blah<!-- /ko -->)
    // without having to scatter special cases all over the binding and templating code.

    var startCommentRegex = /^\s*ko(?:\s+([\s\S]+))?\s*$/;
    var endCommentRegex =   /^\s*\/ko\s*$/;
    var htmlTagsWithOptionallyClosingChildren = { 'ul': true, 'ol': true };

    function isStartComment(node) {
        return (node.nodeType == 8) && startCommentRegex.test(node.nodeValue);
    }

    function isEndComment(node) {
        return (node.nodeType == 8) && endCommentRegex.test(node.nodeValue);
    }

    function isUnmatchedEndComment(node) {
        return isEndComment(node) && !(ko.utils.domData.get(node, matchedEndCommentDataKey));
    }

    var matchedEndCommentDataKey = "__ko_matchedEndComment__"

    function getVirtualChildren(startComment, allowUnbalanced) {
        var currentNode = startComment;
        var depth = 1;
        var children = [];
        while (currentNode = currentNode.nextSibling) {
            if (isEndComment(currentNode)) {
                ko.utils.domData.set(currentNode, matchedEndCommentDataKey, true);
                depth--;
                if (depth === 0)
                    return children;
            }

            children.push(currentNode);

            if (isStartComment(currentNode))
                depth++;
        }
        if (!allowUnbalanced)
            throw new Error("Cannot find closing comment tag to match: " + startComment.nodeValue);
        return null;
    }

    function getMatchingEndComment(startComment, allowUnbalanced) {
        var allVirtualChildren = getVirtualChildren(startComment, allowUnbalanced);
        if (allVirtualChildren) {
            if (allVirtualChildren.length > 0)
                return allVirtualChildren[allVirtualChildren.length - 1].nextSibling;
            return startComment.nextSibling;
        } else
            return null; // Must have no matching end comment, and allowUnbalanced is true
    }

    function getUnbalancedChildTags(node) {
        // e.g., from <div>OK</div><!-- ko blah --><span>Another</span>, returns: <!-- ko blah --><span>Another</span>
        //       from <div>OK</div><!-- /ko --><!-- /ko -->,             returns: <!-- /ko --><!-- /ko -->
        var childNode = node.firstChild, captureRemaining = null;
        if (childNode) {
            do {
                if (captureRemaining)                   // We already hit an unbalanced node and are now just scooping up all subsequent nodes
                    captureRemaining.push(childNode);
                else if (isStartComment(childNode)) {
                    var matchingEndComment = getMatchingEndComment(childNode, /* allowUnbalanced: */ true);
                    if (matchingEndComment)             // It's a balanced tag, so skip immediately to the end of this virtual set
                        childNode = matchingEndComment;
                    else
                        captureRemaining = [childNode]; // It's unbalanced, so start capturing from this point
                } else if (isEndComment(childNode)) {
                    captureRemaining = [childNode];     // It's unbalanced (if it wasn't, we'd have skipped over it already), so start capturing
                }
            } while (childNode = childNode.nextSibling);
        }
        return captureRemaining;
    }

    ko.virtualElements = {
        allowedBindings: {},

        childNodes: function(node) {
            return isStartComment(node) ? getVirtualChildren(node) : node.childNodes;
        },

        emptyNode: function(node) {
            if (!isStartComment(node))
                ko.utils.emptyDomNode(node);
            else {
                var virtualChildren = ko.virtualElements.childNodes(node);
                for (var i = 0, j = virtualChildren.length; i < j; i++)
                    ko.removeNode(virtualChildren[i]);
            }
        },

        setDomNodeChildren: function(node, childNodes) {
            if (!isStartComment(node))
                ko.utils.setDomNodeChildren(node, childNodes);
            else {
                ko.virtualElements.emptyNode(node);
                var endCommentNode = node.nextSibling; // Must be the next sibling, as we just emptied the children
                for (var i = 0, j = childNodes.length; i < j; i++)
                    endCommentNode.parentNode.insertBefore(childNodes[i], endCommentNode);
            }
        },

        prepend: function(containerNode, nodeToPrepend) {
            var insertBeforeNode;

            if (isStartComment(containerNode)) {
                // Start comments must always have a parent and at least one following sibling (the end comment)
                insertBeforeNode = containerNode.nextSibling;
                containerNode = containerNode.parentNode;
            } else {
                insertBeforeNode = containerNode.firstChild;
            }

            containerNode.insertBefore(nodeToPrepend, insertBeforeNode);
        },

        insertAfter: function(containerNode, nodeToInsert, insertAfterNode) {
            if (!insertAfterNode) {
                ko.virtualElements.prepend(containerNode, nodeToInsert);
            } else {
                // Children of start comments must always have a parent and at least one following sibling (the end comment)
                var insertBeforeNode = insertAfterNode.nextSibling;

                if (isStartComment(containerNode)) {
                    containerNode = containerNode.parentNode;
                }

                containerNode.insertBefore(nodeToInsert, insertBeforeNode);
            }
        },

        firstChild: function(node) {
            if (!isStartComment(node)) {
                if (node.firstChild && isEndComment(node.firstChild)) {
                    throw new Error("Found invalid end comment, as the first child of " + node);
                }
                return node.firstChild;
            } else if (!node.nextSibling || isEndComment(node.nextSibling)) {
                return null;
            } else {
                return node.nextSibling;
            }
        },

        nextSibling: function(node) {
            if (isStartComment(node)) {
                node = getMatchingEndComment(node);
            }

            if (node.nextSibling && isEndComment(node.nextSibling)) {
                if (isUnmatchedEndComment(node.nextSibling)) {
                    throw Error("Found end comment without a matching opening comment, as child of " + node);
                } else {
                    return null;
                }
            } else {
                return node.nextSibling;
            }
        },

        hasBindingValue: isStartComment,

        virtualNodeBindingValue: function(node) {
            var regexMatch = (node.nodeValue).match(startCommentRegex);
            return regexMatch ? regexMatch[1] : null;
        }
    };
})();
ko.exportSymbol('virtualElements', ko.virtualElements);
ko.exportSymbol('virtualElements.allowedBindings', ko.virtualElements.allowedBindings);
ko.exportSymbol('virtualElements.emptyNode', ko.virtualElements.emptyNode);
//ko.exportSymbol('virtualElements.firstChild', ko.virtualElements.firstChild);     // firstChild is not minified
ko.exportSymbol('virtualElements.insertAfter', ko.virtualElements.insertAfter);
//ko.exportSymbol('virtualElements.nextSibling', ko.virtualElements.nextSibling);   // nextSibling is not minified
ko.exportSymbol('virtualElements.prepend', ko.virtualElements.prepend);
ko.exportSymbol('virtualElements.setDomNodeChildren', ko.virtualElements.setDomNodeChildren);