/**
    Sends an email notification of a new post
    */
    function publish($post, $preview = '') {
        if ( !$post ) { return $post; }

        if ( $this->s2_mu && !apply_filters('s2_allow_site_switching', $this->site_switching) ) {
            global $switched;
            if ( $switched ) { return; }
        }

        if ( $preview == '' ) {
            // we aren't sending a Preview to the current user so carry out checks
            $s2mail = get_post_meta($post->ID, '_s2mail', true);
            if ( (isset($_POST['s2_meta_field']) && $_POST['s2_meta_field'] == 'no') || strtolower(trim($s2mail)) == 'no' ) { return $post; }

            // are we doing daily digests? If so, don't send anything now
            if ( $this->subscribe2_options['email_freq'] != 'never' ) { return $post; }

            // is the current post of a type that should generate a notification email?
            // uses s2_post_types filter to allow for custom post types in WP 3.0
            if ( $this->subscribe2_options['pages'] == 'yes' ) {
                $s2_post_types = array('page', 'post');
            } else {
                $s2_post_types = array('post');
            }
            $s2_post_types = apply_filters('s2_post_types', $s2_post_types);
            if ( !in_array($post->post_type, $s2_post_types) ) {
                return $post;
            }

            // Are we sending notifications for password protected posts?
            if ( $this->subscribe2_options['password'] == "no" && $post->post_password != '' ) {
                    return $post;
            }

            // Is the post assigned to a format for which we should not be sending posts
            $post_format = get_post_format($post->ID);
            $excluded_formats = explode(',', $this->subscribe2_options['exclude_formats']);
            if ( $post_format !== false && in_array($post_format, $excluded_formats) ) {
                return $post;
            }

            $s2_taxonomies = apply_filters('s2_taxonomies', array('category'));
            $post_cats = wp_get_object_terms($post->ID, $s2_taxonomies, array('fields' => 'ids'));
            $check = false;
            // is the current post assigned to any categories
            // which should not generate a notification email?
            foreach ( explode(',', $this->subscribe2_options['exclude']) as $cat ) {
                if ( in_array($cat, $post_cats) ) {
                    $check = true;
                }
            }

            if ( $check ) {
                // hang on -- can registered users subscribe to
                // excluded categories?
                if ( '0' == $this->subscribe2_options['reg_override'] ) {
                    // nope? okay, let's leave
                    return $post;
                }
            }

            // Are we sending notifications for Private posts?
            // Action is added if we are, but double check option and post status
            if ( $this->subscribe2_options['private'] == "yes" && $post->post_status == 'private' ) {
                // don't send notification to public users
                $check = true;
            }

            // lets collect our subscribers
            $public = array();
            if ( !$check ) {
                // if this post is assigned to an excluded
                // category, or is a private post then
                // don't send public subscribers a notification
                $public = $this->get_public();
            }
            if ( $post->post_type == 'page' ) {
                $post_cats_string = implode(',', get_all_category_ids());
            } else {
                $post_cats_string = implode(',', $post_cats);
            }
            $registered = $this->get_registered("cats=$post_cats_string");

            // do we have subscribers?
            if ( empty($public) && empty($registered) ) {
                // if not, no sense doing anything else
                return $post;
            }
        } else {
            // make sure we prime the taxonomy variable for preview posts
            $s2_taxonomies = apply_filters('s2_taxonomies', array('category'));
        }

        // we set these class variables so that we can avoid
        // passing them in function calls a little later
        $this->post_title = "<a href=\"" . get_permalink($post->ID) . "\">" . html_entity_decode($post->post_title, ENT_QUOTES) . "</a>";
        $this->permalink = get_permalink($post->ID);
        $this->post_date = get_the_time(get_option('date_format'), $post);
        $this->post_time = get_the_time('', $post);

        $author = get_userdata($post->post_author);
        $this->authorname = html_entity_decode(apply_filters('the_author', $author->display_name), ENT_QUOTES);

        // do we send as admin, or post author?
        if ( 'author' == $this->subscribe2_options['sender'] ) {
            // get author details
            $user = &$author;
            $this->myemail = $user->user_email;
            $this->myname = html_entity_decode($user->display_name, ENT_QUOTES);
        } elseif ( 'blogname' == $this->subscribe2_options['sender'] ) {
            $this->myemail = get_option('admin_email');
            $this->myname = html_entity_decode(get_option('blogname'), ENT_QUOTES);
        } else {
            // get admin details
            $user = $this->get_userdata($this->subscribe2_options['sender']);
            $this->myemail = $user->user_email;
            $this->myname = html_entity_decode($user->display_name, ENT_QUOTES);
        }

        $this->post_cat_names = implode(', ', wp_get_object_terms($post->ID, $s2_taxonomies, array('fields' => 'names')));
        $this->post_tag_names = implode(', ', wp_get_post_tags($post->ID, array('fields' => 'names')));

        // Get email subject
        $subject = html_entity_decode(stripslashes(wp_kses($this->substitute($this->subscribe2_options['notification_subject']), '')));
        // Get the message template
        $mailtext = apply_filters('s2_email_template', $this->subscribe2_options['mailtext']);
        $mailtext = stripslashes($this->substitute($mailtext));

        $plaintext = $post->post_content;
        $plaintext = strip_shortcodes($plaintext);

        $plaintext = preg_replace('|<s[^>]*>(.*)<\/s>|Ui','', $plaintext);
        $plaintext = preg_replace('|<strike[^>]*>(.*)<\/strike>|Ui','', $plaintext);
        $plaintext = preg_replace('|<del[^>]*>(.*)<\/del>|Ui','', $plaintext);
        $excerpttext = $plaintext;

        if ( strstr($mailtext, "{REFERENCELINKS}") ) {
            $mailtext = str_replace("{REFERENCELINKS}", '', $mailtext);
            $plaintext_links = '';
            $i = 0;
            while ( preg_match('|<a([^>]*)>(.*)<\/a>|Ui', $plaintext, $matches) ) {
                if ( preg_match('|href="([^"]*)"|', $matches[1], $link_matches) ){
                    $plaintext_links .= sprintf( "[%d] %s\r\n", ++$i, $link_matches[1] );
                    $link_replacement = sprintf( "%s [%d]", $matches[2], $i );
                } else {
                    $link_replacement = $matches[2];
                }
                $plaintext = preg_replace('|<a[^>]*>(.*)<\/a>|Ui', $link_replacement, $plaintext, 1);
            }
        }

        $plaintext = trim(strip_tags($plaintext));

        if ( strstr($mailtext, "{REFERENCELINKS}") && $plaintext_links != '' ) {
            $plaintext .= "\r\n\r\n" . trim($plaintext_links);
        }

        $gallid = '[gallery id="' . $post->ID . '"';
        $content = str_replace('[gallery', $gallid, $post->post_content);

        // remove the autoembed filter to remove iframes from notification emails
        if ( get_option('embed_autourls') ) {
            global $wp_embed;
            $priority = has_filter('the_content', array(&$wp_embed, 'autoembed'));
            if ( $priority !== false ) {
                remove_filter('the_content', array(&$wp_embed, 'autoembed'), $priority);
            }
        }

        $content = apply_filters('the_content', $content);
        $content = str_replace("]]>", "]]&gt", $content);

        $excerpt = trim($post->post_excerpt);
        if ( '' == $excerpt ) {
            // no excerpt, is there a <!--more--> ?
            if ( false !== strpos($excerpttext, '<!--more-->') ) {
                list($excerpt, $more) = explode('<!--more-->', $excerpttext, 2);
                // strip tags and trailing whitespace
                $excerpt = trim(strip_tags($excerpt));
            } else {
                // no <!--more-->, so grab the first 55 words
                $excerpt = trim(strip_tags($excerpttext));
                $words = explode(' ', $excerpt, $this->excerpt_length + 1);
                if (count($words) > $this->excerpt_length) {
                    array_pop($words);
                    array_push($words, '[...]');
                    $excerpt = implode(' ', $words);
                }
            }
        }
        $html_excerpt = trim($post->post_excerpt);
        if ( '' == $html_excerpt ) {
            // no excerpt, is there a <!--more--> ?
            if ( false !== strpos($content, '<!--more-->') ) {
                list($html_excerpt, $more) = explode('<!--more-->', $content, 2);
                // balance HTML tags and then strip leading and trailing whitespace
                $html_excerpt = trim(balanceTags($html_excerpt, true));
            } else {
                // no <!--more-->, so grab the first 55 words
                $words = explode(' ', $content, $this->excerpt_length + 1);
                if (count($words) > $this->excerpt_length) {
                    array_pop($words);
                    array_push($words, '[...]');
                    $html_excerpt = implode(' ', $words);
                    // balance HTML tags and then strip leading and trailing whitespace
                    $html_excerpt = trim(balanceTags($html_excerpt, true));
                } else {
                    $html_excerpt = $content;
                }
            }
        }

        // maybe add social media sharing buttons
        $social = apply_filters('s2_social_links', array('facebook', 'twitter'));
        if ( !empty($social) ) {
            $social_buttons = $this->social_buttons($social);
            $content .= $social_buttons;
            $html_excerpt .= $social_buttons;
        }

        // remove excess white space from with $excerpt and $plaintext
        $excerpt = preg_replace('|[ ]+|', ' ', $excerpt);
        $plaintext = preg_replace('|[ ]+|', ' ', $plaintext);

        // prepare mail body texts
        $plain_excerpt_body = str_replace("{POST}", $excerpt, $mailtext);
        $plain_body = str_replace("{POST}", $plaintext, $mailtext);
        $html_body = str_replace("\r\n", "<br />\r\n", $mailtext);
        $html_body = str_replace("{POST}", $content, $html_body);
        $html_excerpt_body = str_replace("\r\n", "<br />\r\n", $mailtext);
        $html_excerpt_body = str_replace("{POST}", $html_excerpt, $html_excerpt_body);

        if ( $preview != '' ) {
            $this->myemail = $preview;
            $this->myname = __('Plain Text Excerpt Preview', 'subscribe2');
            $this->mail(array($preview), $subject, $plain_excerpt_body);
            $this->myname = __('Plain Text Full Preview', 'subscribe2');
            $this->mail(array($preview), $subject, $plain_body);
            $this->myname = __('HTML Excerpt Preview', 'subscribe2');
            $this->mail(array($preview), $subject, $html_excerpt_body, 'html');
            $this->myname = __('HTML Full Preview', 'subscribe2');
            $this->mail(array($preview), $subject, $html_body, 'html');
        } else {
            // Registered Subscribers first
            // first we send plaintext summary emails
            $recipients = $this->get_registered("cats=$post_cats_string&format=excerpt&author=$post->post_author");
            $recipients = apply_filters('s2_send_plain_excerpt_subscribers', $recipients, $post->ID);
            $this->mail($recipients, $subject, $plain_excerpt_body);

            // next we send plaintext full content emails
            $recipients = $this->get_registered("cats=$post_cats_string&format=post&author=$post->post_author");
            $recipients = apply_filters('s2_send_plain_fullcontent_subscribers', $recipients, $post->ID);
            $this->mail($recipients, $subject, $plain_body);

            // next we send html excerpt content emails
            $recipients = $this->get_registered("cats=$post_cats_string&format=html_excerpt&author=$post->post_author");
            $recipients = apply_filters('s2_send_html_excerpt_subscribers', $recipients, $post->ID);
            $this->mail($recipients, $subject, $html_excerpt_body, 'html');

            // next we send html full content emails
            $recipients = $this->get_registered("cats=$post_cats_string&format=html&author=$post->post_author");
            $recipients = apply_filters('s2_send_html_fullcontent_subscribers', $recipients, $post->ID);
            $this->mail($recipients, $subject, $html_body, 'html');

            // and finally we send to Public Subscribers
            $recipients = apply_filters('s2_send_public_subscribers', $public, $post->ID);
            $this->mail($recipients, $subject, $plain_excerpt_body, 'text');
        }
    } // end publish()