log adding the user to a group

app/services/discourse_donations/rewards.rb

@@ -2,6 +2,8 @@
 
 module DiscourseDonations
   class Rewards
+    attr_reader :user
+
     def initialize(user)
       @user = user
     end
@@ -9,13 +11,19 @@ module DiscourseDonations
     def add_to_group(name)
       grp = ::Group.find_by_name(name)
       return if grp.nil?
-      grp.add(@user)
+      log_group_add(grp)
+      grp.add(user)
     end
 
     def grant_badge(name)
       badge = ::Badge.find_by_name(name)
       return if badge.nil?
-      BadgeGranter.grant(badge, @user)
+      BadgeGranter.grant(badge, user)
+    end
+
+    def log_group_add(grp)
+      system_user = User.find(-1)
+      GroupActionLogger.new(system_user, grp).log_add_user_to_group(user)
     end
   end
 end