FEATURE: Basic backend support for muted and watched categories

app/models/category_user.rb

@@ -0,0 +1,49 @@
+class CategoryUser < ActiveRecord::Base
+  belongs_to :category
+  belongs_to :user
+
+  # same for now
+  def self.notification_levels
+    TopicUser.notification_levels
+  end
+
+  def self.auto_watch_new_topic(topic)
+    apply_default_to_topic(
+                           topic,
+                           TopicUser.notification_levels[:watching],
+                           TopicUser.notification_reasons[:auto_watch_category]
+                          )
+  end
+
+  def self.auto_mute_new_topic(topic)
+    apply_default_to_topic(
+                           topic,
+                           TopicUser.notification_levels[:muted],
+                           TopicUser.notification_reasons[:auto_mute_category]
+                          )
+  end
+
+  private
+
+  def self.apply_default_to_topic(topic, level, reason)
+    # Can not afford to slow down creation of topics when a pile of users are watching new topics, reverting to SQL for max perf here
+    sql = <<SQL
+    INSERT INTO topic_users(user_id, topic_id, notification_level, notifications_reason_id)
+    SELECT user_id, :topic_id, :level, :reason
+    FROM category_users
+    WHERE notification_level = :level AND
+          category_id = :category_id AND
+          NOT EXISTS(SELECT 1 FROM topic_users WHERE topic_id = :topic_id AND user_id = category_users.user_id)
+SQL
+
+    exec_sql(
+        sql,
+                  topic_id: topic.id,
+                  category_id: topic.category_id,
+                  level: level,
+                  reason: reason
+
+            )
+  end
+
+end

app/models/topic_user.rb

@@ -20,7 +20,15 @@ class TopicUser < ActiveRecord::Base
     end
 
     def notification_reasons
-      @notification_reasons ||= Enum.new(:created_topic, :user_changed, :user_interacted, :created_post, :auto_watch)
+      @notification_reasons ||= Enum.new(
+        :created_topic,
+        :user_changed,
+        :user_interacted,
+        :created_post,
+        :auto_watch,
+        :auto_watch_category,
+        :auto_mute_category
+      )
     end
 
     def auto_track(user_id, topic_id, reason)