You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: forum_subscription.rb
    path of file: ./repos/e621ng/app/models
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class ForumSubscription < ApplicationRecord
  belongs_to :user
  belongs_to :forum_topic

  def self.prune!
    where("last_read_at < ?", 3.months.a
    
  def self.process_all!
    ForumSubscription.find_each do |subscription|
      forum_topic = subscription.forum_topic
      if forum_topic.updated_at > subscription.last_read_at
        CurrentUser.scoped(subscription.user) do
          forum_posts = forum_topic.posts.where("created_at > ?", subscription.last_read_at).order("id desc")
          begin
            UserMailer.forum_notice(subscription.user, forum_topic, forum_posts).deliver_now
          rescue Net::SMTPSyntaxError
          end
          subscription.update_attribute(:last_read_at, forum_topic.updated_at)
        end
      end