Basic "Also, there are x new topics" text for the digest

app/mailers/user_notifications.rb

@@ -45,9 +45,15 @@ class UserNotifications < ActionMailer::Base
 
     # Don't send email unless there is content in it
     if @featured_topics.present?
+      @new_topics_since_seen = Topic.listable_topics
+                                    .where("created_at > ?", min_date).count - @featured_topics.length
+
+      @new_topics_since_seen = 0 if @new_topics_since_seen < 0
       @featured_topics, @new_topics = @featured_topics[0..4], @featured_topics[5..-1]
 
       @markdown_linker = MarkdownLinker.new(Discourse.base_url)
+
+
       build_email user.email,
                   from_alias: I18n.t('user_notifications.digest.from', site_name: SiteSetting.title),
                   subject: I18n.t('user_notifications.digest.subject_template',

app/views/user_notifications/digest.html.erb

@@ -44,6 +44,10 @@
 
     <%- end -%>
 
+    <%- if @new_topics_since_seen > 0 %>
+      <p><%= t('user_notifications.digest.more_topics', last_seen_at: @last_seen_at, new_topics_since_seen: @new_topics_since_seen) %></p>
+    <%- end -%>
+
   <span class='footer-notice'>
     <%=raw(t :'user_notifications.digest.unsubscribe',
        site_link: html_site_link,

config/locales/server.en.yml

@@ -1360,6 +1360,7 @@ en:
       click_here: "click here"
       from: "%{site_name} digest"
       read_more: "Read More"
+      more_topics: "Also, since we last saw you on %{last_seen_at} there have been %{new_topics_since_seen} new topics posted."
 
       posts:
         one: "1 post"