* Handles the addition of the comment form.

 * @output wp-includes/js/comment-reply.js

 *

 * @namespace addComment

window.addComment = ( function( window ) {

	// Avoid scope lookups on commonly used variables.

	var document = window.document;

	// Settings.

	var config = {

		commentReplyClass : 'comment-reply-link',

		cancelReplyId     : 'cancel-comment-reply-link',

		commentFormId     : 'commentform',

		temporaryFormId   : 'wp-temp-form-div',

		parentIdFieldId   : 'comment_parent',

		postIdFieldId     : 'comment_post_ID'

	};

	// Cross browser MutationObserver.

	var MutationObserver = window.MutationObserver || window.WebKitMutationObserver || window.MozMutationObserver;

	// Check browser cuts the mustard.

	var cutsTheMustard = 'querySelector' in document && 'addEventListener' in window;

	/*

	 * Check browser supports dataset.

	 * !! sets the variable to true if the property exists.

	 */

	var supportsDataset = !! document.documentElement.dataset;

	// For holding the cancel element.

	var cancelElement;

	// For holding the comment form element.

	var commentFormElement;

	// The respond element.

	var respondElement;

	// The mutation observer.

	var observer;

	if ( cutsTheMustard && document.readyState !== 'loading' ) {

		ready();

	} else if ( cutsTheMustard ) {

		window.addEventListener( 'DOMContentLoaded', ready, false );

	}

	 * Sets up object variables after the DOM is ready.

	 * @since 5.1.1

	 */

	function ready() {

		// Initialise the events.

		init();

		// Set up a MutationObserver to check for comments loaded late.

		observeChanges();

	}

	/**

	 * Add events to links classed .comment-reply-link.

	 *

	 * Searches the context for reply links and adds the JavaScript events

	 * required to move the comment form. To allow for lazy loading of

	 * comments this method is exposed as window.commentReply.init().

	 *

	 * @since 5.1.0

	 *

	 * @memberOf addComment

	 *

	 * @param {HTMLElement} context The parent DOM element to search for links.

	function init( context ) {

		if ( ! cutsTheMustard ) {

			return;

		}

		// Get required elements.

		cancelElement = getElementById( config.cancelReplyId );

		commentFormElement = getElementById( config.commentFormId );

		// No cancel element, no replies.

		if ( ! cancelElement ) {

			return;

		}

		cancelElement.addEventListener( 'touchstart', cancelEvent );

		cancelElement.addEventListener( 'click',      cancelEvent );

		var links = replyLinks( context );

		var element;

		for ( var i = 0, l = links.length; i < l; i++ ) {

			element = links[i];

			element.addEventListener( 'touchstart', clickEvent );

			element.addEventListener( 'click',      clickEvent );

		}

	}

	/**

	 * Return all links classed .comment-reply-link.

	 *

	 * @since 5.1.0

	 *

	 * @param {HTMLElement} context The parent DOM element to search for links.

	 *

	 * @return {HTMLCollection|NodeList|Array}

	 */

	function replyLinks( context ) {

		var selectorClass = config.commentReplyClass;

		var allReplyLinks;

		// childNodes is a handy check to ensure the context is a HTMLElement.

		if ( ! context || ! context.childNodes ) {

			context = document;

		}

		if ( document.getElementsByClassName ) {

			// Fastest.

			allReplyLinks = context.getElementsByClassName( selectorClass );

		}

		else {

			// Fast.

			allReplyLinks = context.querySelectorAll( '.' + selectorClass );

		}

		return allReplyLinks;

	}

	/**

	 * Cancel event handler.

	 *

	 * @since 5.1.0

	 *

	 * @param {Event} event The calling event.

	 */

	function cancelEvent( event ) {

		var cancelLink = this;

		var temporaryFormId  = config.temporaryFormId;

		var temporaryElement = getElementById( temporaryFormId );

		if ( ! temporaryElement || ! respondElement ) {

			// Conditions for cancel link fail.

		getElementById( config.parentIdFieldId ).value = '0';

		// Move the respond form back in place of the temporary element.

		temporaryElement.parentNode.replaceChild( respondElement ,temporaryElement );

		cancelLink.style.display = 'none';

		event.preventDefault();

	}

	/**

	 * Click event handler.

	 *

	 * @since 5.1.0

	 *

	 * @param {Event} event The calling event.

	 */

	function clickEvent( event ) {

		var replyLink = this,

			commId    = getDataAttribute( replyLink, 'belowelement'),

			parentId  = getDataAttribute( replyLink, 'commentid' ),

			respondId = getDataAttribute( replyLink, 'respondelement'),

			postId    = getDataAttribute( replyLink, 'postid'),

			follow;

		if ( ! commId || ! parentId || ! respondId || ! postId ) {

			/*

			 * Theme or plugin defines own link via custom `wp_list_comments()` callback

			 * and calls `moveForm()` either directly or via a custom event hook.

			 */

			return;

		}

		/*

		 * Third party comments systems can hook into this function via the global scope,

		 * therefore the click event needs to reference the global scope.

		 */

		follow = window.addComment.moveForm(commId, parentId, respondId, postId);

		if ( false === follow ) {

			event.preventDefault();

		}

	}

	/**

	 * Creates a mutation observer to check for newly inserted comments.

	 *

	 * @since 5.1.0

	 */

	function observeChanges() {

		if ( ! MutationObserver ) {

			return;

		var observerOptions = {

			childList: true,

			subTree: true

		};

		observer = new MutationObserver( handleChanges );

		observer.observe( document.body, observerOptions );

	}

	/**

	 * Handles DOM changes, calling init() if any new nodes are added.

	 *

	 * @since 5.1.0

	 *

	 * @param {Array} mutationRecords Array of MutationRecord objects.

	 */

	function handleChanges( mutationRecords ) {

		var i = mutationRecords.length;

		while ( i-- ) {

			// Call init() once if any record in this set adds nodes.

			if ( mutationRecords[ i ].addedNodes.length ) {

				init();

		}

	}

	/**

	 * Backward compatible getter of data-* attribute.

	 *

	 * Uses element.dataset if it exists, otherwise uses getAttribute.

	 *

	 * @since 5.1.0

	 *

	 * @param {HTMLElement} Element DOM element with the attribute.

	 * @param {String}      Attribute the attribute to get.

	 *

	 * @return {String}

	 */

	function getDataAttribute( element, attribute ) {

		if ( supportsDataset ) {

			return element.dataset[attribute];

		}

		else {

			return element.getAttribute( 'data-' + attribute );

		}

	}

	/**

	 * Get element by ID.

	 *

	 * Local alias for document.getElementById.

	 *

	 * @since 5.1.0

	 *

	 * @param {HTMLElement} The requested element.

	 */

	function getElementById( elementId ) {

		return document.getElementById( elementId );

	}

	/**

	 * Moves the reply form from its current position to the reply location.

	 *

	 * @since 2.7.0

	 *

	 * @memberOf addComment

	 *

	 * @param {String} addBelowId HTML ID of element the form follows.

	 * @param {String} commentId  Database ID of comment being replied to.

	 * @param {String} respondId  HTML ID of 'respond' element.

	 * @param {String} postId     Database ID of the post.

	 */

	function moveForm( addBelowId, commentId, respondId, postId ) {

		// Get elements based on their IDs.

		var addBelowElement = getElementById( addBelowId );

		respondElement  = getElementById( respondId );

		// Get the hidden fields.

		var parentIdField   = getElementById( config.parentIdFieldId );

		var postIdField     = getElementById( config.postIdFieldId );

		var element, cssHidden, style;

		if ( ! addBelowElement || ! respondElement || ! parentIdField ) {

			// Missing key elements, fail.

			return;

		}

		addPlaceHolder( respondElement );

		// Set the value of the post.

		if ( postId && postIdField ) {

			postIdField.value = postId;

		}

		parentIdField.value = commentId;

		cancelElement.style.display = '';

		addBelowElement.parentNode.insertBefore( respondElement, addBelowElement.nextSibling );

		/*

		 * This is for backward compatibility with third party commenting systems

		 * hooking into the event using older techniques.

		 */

		cancelElement.onclick = function(){

		// Focus on the first field in the comment form.

			for ( var i = 0; i < commentFormElement.elements.length; i++ ) {

				element = commentFormElement.elements[i];

				// Get elements computed style.

					// Modern browsers.

					// IE 8.

		}

		catch(e) {

		}

		/*

		 * false is returned for backward compatibility with third party commenting systems

		 * hooking into this function.

		 */

	}

	 * Add placeholder element.

	 *

	 * Places a place holder element above the #respond element for

	 * the form to be returned to if needs be.

	 * @param {HTMLelement} respondElement the #respond element holding comment form.

	function addPlaceHolder( respondElement ) {

		var temporaryFormId  = config.temporaryFormId;

		var temporaryElement = getElementById( temporaryFormId );

		if ( temporaryElement ) {

			// The element already exists, no need to recreate.

			return;

		}

		temporaryElement = document.createElement( 'div' );

		temporaryElement.id = temporaryFormId;

		temporaryElement.style.display = 'none';

		respondElement.parentNode.insertBefore( temporaryElement, respondElement );