Wordpress Vkontakte new comment email notifier

functions.php

<?php
/**
 * Theme Native Code
 **/

add_action('wp_ajax_vk_comment_mail', 'vk_comment_mail');
add_action('wp_ajax_nopriv_vk_comment_mail', 'vk_comment_mail');
function vk_comment_mail()
{
    if (!isset($_POST['last_comment'])){
		return;
	}
	
	$api_secret = 'VK_APP_SECRET_CODE'; //Change this string
	
	$comment_text = htmlspecialchars_decode($_POST['last_comment'], ENT_NOQUOTES);//Yes, decode text before sign checking. Why? Because! (under my umbrella...)
	
	$comment_encoding = mb_detect_encoding($comment_text, 'utf-8,cp1251');
	$comment_encoded = iconv($comment_encoding, 'cp1251//TRANSLIT', $comment_text);
	
	if (md5($api_secret . $_POST['date'] . $_POST['num'] . $comment_encoded) !== $_POST['sign'])
	{
		status_header(403);
		echo print_r($_POST, true), PHP_EOL;
		die('Invalid Sign');
	}
	
	$mail_text = '';
	$mail_text .= $comment_text . PHP_EOL;
	$mail_text .= '<br /><br />' . $_SERVER['HTTP_REFERER'];
	
    	//Comment text is a HTML (<br />, <p />, etc)
	add_filter('wp_mail_content_type', function(){
		return 'text/html';
	});
	
	$responce = wp_mail('moderator-email@example.com', 'New Comment on site ' . get_bloginfo('name'), $mail_text);
	
	exit;
}

new-comment-added.js

;(function(){
    /**
     * Openapi code in body:
     * VK.init({apiId: 12345678, onlyWidgets: true});
     * VK.Widgets.Comments('vk_comments', {limit: 10, width: '610', attach: '*'})
     **/
	
	VK.Observer.subscribe('widgets.comments.new_comment', notify_comment)
	
	function notify_comment(num, last_comment, date, sign) {
		jQuery.ajax({
			type: 'post',
			url: (window.siteurl || '') + '/wp-admin/admin-ajax.php',
			data: {
				action: 'vk_comment_mail',
				num: num,
				last_comment: last_comment,
				date: date,
				sign: sign
			}
		})
	}
})();