FIX: when the user is promoted to TL2 invite to advance training (#10752)

Invitation to advanced training should be sent as a separate private message instead of hooking into TL2 promotion message.

plugins/discourse-narrative-bot/config/locales/server.en.yml

@@ -24,10 +24,8 @@ en:
     bio: "Hi, I’m not a real person. I’m a bot that can teach you about this site. To interact with me, send me a message or mention **`@%{discobot_username}`** anywhere."
 
     tl2_promotion_message:
-      subject_template: "Congratulations on your trust level promotion!"
+      subject_template: "Now that you’ve been promoted, it’s time to learn about some advanced features!"
       text_body_template: |
-        Now that you’ve been promoted, it’s time to learn about some advanced features!
-
         Reply to this message with `@%{discobot_username} %{reset_trigger}` to find out more about what you can do.
 
     timeout:

plugins/discourse-narrative-bot/plugin.rb

@@ -293,12 +293,15 @@ after_initialize do
                   discobot_username: ::DiscourseNarrativeBot::Base.new.discobot_username,
                   reset_trigger: "#{::DiscourseNarrativeBot::TrackSelector.reset_trigger} #{::DiscourseNarrativeBot::AdvancedUserNarrative.reset_trigger}")
 
+      recipient = args[:post].topic.topic_users.where.not(user_id: args[:post].user_id).last.user
+
       PostCreator.create!(
         ::DiscourseNarrativeBot::Base.new.discobot_user,
         title: I18n.t("discourse_narrative_bot.tl2_promotion_message.subject_template"),
         raw: raw,
-        topic_id: args[:post].topic_id,
+        skip_validations: true,
-        skip_validations: true
+        archetype: Archetype.private_message,
+        target_usernames: recipient.username
       )
     end
   end

plugins/discourse-narrative-bot/spec/discourse_narrative_bot/advanced_user_narrative_spec.rb

@@ -732,4 +732,13 @@ RSpec.describe DiscourseNarrativeBot::AdvancedUserNarrative do
       end
     end
   end
+
+  it 'invites to advanced training when user is promoted to TL2' do
+    recipient = Fabricate(:user)
+    expect {
+      DiscourseEvent.trigger(:system_message_sent, post: Post.last, message_type: 'tl2_promotion_message')
+    }.to change { Topic.count }
+    expect(Topic.last.title).to eq(I18n.t("discourse_narrative_bot.tl2_promotion_message.subject_template"))
+    expect(Topic.last.topic_users.map(&:user_id).sort).to eq([DiscourseNarrativeBot::Base.new.discobot_user.id, recipient.id])
+  end
 end