plugin.rb

# name: Watch Category
# about: Watches a category for all the users in a particular group
# version: 0.2
# authors: Arpit Jalan, Thomas Purchas
# url: https://github.com/thomaspurchas/discourse-watch-category
enabled_site_setting :watching_enabled

module ::WatchCategory
  def self.watch_category!
    groups_cats = {
      "exec" => ["exec", "shadow-exec"],
      "duty_managers" => ["duty-managers"],
      "q_proj" => ["proj", "show-reports", "proj-meeting-minutes"],
      "t_proj" => ["show-reports", "proj-meeting-minutes"],
      "it_team" => ["it"],
    }

    groups_cats.each do |group_name, cats|
      cats.each do |cat_slug|

        category = Category.find_by_slug(cat_slug)
        group = Group.find_by_name(group_name)
        
        unless category.nil? || group.nil?
          group.users.each do |user|
            watched_categories = CategoryUser.lookup(user, :watching).pluck(:category_id)
            CategoryUser.set_notification_level_for_category(user, CategoryUser.notification_levels[:watching], category.id) unless watched_categories.include?(category.id)
          end
        end
      end
    end
  end
end

after_initialize do
  DiscourseEvent.on(:groups_synced) do
    if SiteSetting.watching_enabled
      Sidekiq::Client.enqueue(WatchCategory::WatchCategoryJob)
    end
  end

  module ::WatchCategory
    class WatchCategoryJob < ::Jobs::Scheduled
      every 1.day

      def execute(args)
        if SiteSetting.watching_enabled
          WatchCategory.watch_category!
        end
      end
    end
  end
end