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: random_topic_selector.rb
    path of file: ./repos/discourse/app/services
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class RandomTopicSelector
  BACKFILL_SIZE = 3000
  BACKFILL_LOW_WATER_MARK = 500

  def self.backfill(category = nil)
    exclude = category&.topic_i
    
  def self.next(count, category = nil)
    key = cache_key(category)

    results = []

    return results if count < 1

    results =
      Discourse.redis.multi do |transaction|
        transaction.lrange(key, 0, count - 1)
        transaction.ltrim(key, count, -1)
      end

    if !results.is_a?(Array) # Redis is in readonly mode
      results = Discourse.redis.lrange(key, 0, count - 1)
    else
      results = results[0]
    end