FEATURE: set notification levels when added to a group (#10378)

* FEATURE: set notification levels when added to a group

This feature allows admins and group owners to define default
category and tag tracking levels that will be applied to user
preferences automatically at the time when users are added to the
group. Users are free to change those preferences afterwards.
When removed from a group, the user's notification preferences aren't
changed.

app/models/group_user.rb

@@ -12,6 +12,8 @@ class GroupUser < ActiveRecord::Base
 
   before_create :set_notification_level
   after_save :grant_trust_level
+  after_save :set_category_notifications
+  after_save :set_tag_notifications
 
   def self.notification_levels
     NotificationLevels.all
@@ -64,6 +66,70 @@ class GroupUser < ActiveRecord::Base
 
     Promotion.recalculate(user)
   end
+
+  def set_category_notifications
+    self.class.set_category_notifications(group, user)
+  end
+
+  def self.set_category_notifications(group, user)
+    group_levels = group.group_category_notification_defaults.each_with_object({}) do |r, h|
+      h[r.notification_level] ||= []
+      h[r.notification_level] << r.category_id
+    end
+
+    return if group_levels.empty?
+
+    user_levels = CategoryUser.where(user_id: user.id).each_with_object({}) do |r, h|
+      h[r.notification_level] ||= []
+      h[r.notification_level] << r.category_id
+    end
+
+    higher_level_category_ids = user_levels.values.flatten
+
+    [:muted, :tracking, :watching_first_post, :watching].each do |level|
+      level_num = NotificationLevels.all[level]
+      higher_level_category_ids -= (user_levels[level_num] || [])
+      if group_category_ids = group_levels[level_num]
+        CategoryUser.batch_set(
+          user,
+          level,
+          group_category_ids + (user_levels[level_num] || []) - higher_level_category_ids
+        )
+      end
+    end
+  end
+
+  def set_tag_notifications
+    self.class.set_tag_notifications(group, user)
+  end
+
+  def self.set_tag_notifications(group, user)
+    group_levels = group.group_tag_notification_defaults.each_with_object({}) do |r, h|
+      h[r.notification_level] ||= []
+      h[r.notification_level] << r.tag_id
+    end
+
+    return if group_levels.empty?
+
+    user_levels = TagUser.where(user_id: user.id).each_with_object({}) do |r, h|
+      h[r.notification_level] ||= []
+      h[r.notification_level] << r.tag_id
+    end
+
+    higher_level_tag_ids = user_levels.values.flatten
+
+    [:muted, :tracking, :watching_first_post, :watching].each do |level|
+      level_num = NotificationLevels.all[level]
+      higher_level_tag_ids -= (user_levels[level_num] || [])
+      if group_tag_ids = group_levels[level_num]
+        TagUser.batch_set(
+          user,
+          level,
+          group_tag_ids + (user_levels[level_num] || []) - higher_level_tag_ids
+        )
+      end
+    end
+  end
 end
 
 # == Schema Information