discourse/app/models/topic_posters_summary.rb

# frozen_string_literal: true

# This is used in topic lists
class TopicPostersSummary
  # localization is fast, but this allows us to avoid
  # calling it in a loop which adds up
  def self.translations
    {
      original_poster: I18n.t(:original_poster),
      most_recent_poster: I18n.t(:most_recent_poster),
      frequent_poster: I18n.t(:frequent_poster),
      joiner: I18n.t(:poster_description_joiner),
    }
  end

  attr_reader :topic, :options

  def initialize(topic, options = {})
    @topic = topic
    @options = options
    @translations = options[:translations] || TopicPostersSummary.translations
  end

  def summary
    sorted_top_posters.compact.map(&method(:new_topic_poster_for))
  end

  private

  def new_topic_poster_for(user)
    topic_poster = TopicPoster.new
    topic_poster.user = user
    topic_poster.description = descriptions_for(user)
    topic_poster.primary_group = user_lookup.primary_groups[user.id]
    topic_poster.flair_group = user_lookup.flair_groups[user.id]
    if topic.last_post_user_id == user.id
      topic_poster.extras = +"latest"
      topic_poster.extras << " single" if user_ids.uniq.size == 1
    end
    topic_poster
  end

  def descriptions_by_id(ids: nil)
    @descriptions_by_id ||=
      begin
        result = {}
        ids = ids || user_ids

        if id = ids.shift
          result[id] ||= []
          result[id] << @translations[:original_poster]
        end

        if id = ids.shift
          result[id] ||= []
          result[id] << @translations[:most_recent_poster]
        end

        while id = ids.shift
          result[id] ||= []
          result[id] << @translations[:frequent_poster]
        end

        result
      end
  end

  def descriptions_for(user)
    descriptions_by_id[user.id].join(@translations[:joiner])
  end

  def shuffle_last_poster_to_back_in(summary)
    unless last_poster_is_topic_creator?
      summary.reject! { |u| u.id == topic.last_post_user_id }
      summary << user_lookup[topic.last_post_user_id]
    end
    summary
  end

  def last_poster_is_topic_creator?
    topic.user_id == topic.last_post_user_id
  end

  def sorted_top_posters
    shuffle_last_poster_to_back_in top_posters
  end

  def top_posters
    user_ids.map { |id| user_lookup[id] }.compact.uniq.take(5)
  end

  def user_ids
    [topic.user_id, topic.last_post_user_id, *topic.featured_user_ids]
  end

  def user_lookup
    @user_lookup ||= options[:user_lookup] || UserLookup.new(user_ids)
  end
end