FEATURE: Allow List for PMs (#10270)

* FEATURE: Allow List for PMs

This feature adds a new user setting that is disabled by default that
allows them to specify a list of users that are allowed to send them
private messages. This way they don't have to maintain a large list of
users they don't want to here from and instead just list the people they
know they do want. Staff will still always be able to send messages to
the user.

* Update PR based on feedback

lib/post_creator.rb

@@ -110,7 +110,7 @@ class PostCreator
         return false
       end
 
-      # Make sure none of the users have muted the creator
+      # Make sure none of the users have muted or ignored the creator
       users = User.where(username_lower: names).pluck(:id, :username).to_h
 
       User
@@ -128,6 +128,23 @@ class PostCreator
         errors.add(:base, I18n.t(:not_accepting_pms, username: users[m]))
       end
 
+      # Is Allowed PM users list enabled for any recipients?
+      users_with_allowed_pms = allowed_pms_enabled(users).pluck(:id).uniq
+
+      # If any of the users has allowed_pm_users enabled check to see if the creator
+      # is in their list
+      if users_with_allowed_pms.any?
+        users_sender_can_pm = allowed_pms_enabled(users)
+          .where("allowed_pm_users.allowed_pm_user_id" => @user.id.to_i)
+          .pluck(:id).uniq
+
+        # If not in the list add an error
+        users_not_allowed = users_with_allowed_pms - users_sender_can_pm
+        users_not_allowed.each do |id|
+          errors.add(:base, I18n.t(:not_accepting_pms, username: users[id]))
+        end
+      end
+
       return false if errors[:base].present?
     end
 
@@ -430,6 +447,17 @@ class PostCreator
 
   private
 
+  def allowed_pms_enabled(users)
+    User
+      .joins("LEFT JOIN user_options ON user_options.user_id = users.id")
+      .joins("LEFT JOIN allowed_pm_users ON allowed_pm_users.user_id = users.id")
+      .where("
+        user_options.user_id IS NOT NULL AND
+        user_options.user_id IN (:user_ids) AND
+        user_options.enable_allowed_pm_users
+      ", user_ids: users.keys)
+  end
+
   def create_topic
     return if @topic
     begin