module Api
  module ReadinglistController
    extend ActiveSupport::Concern

    INDEX_REACTIONS_ATTRIBUTES_FOR_SERIALIZATION = %i[id reactable_id created_at status].freeze
    private_constant :INDEX_REACTIONS_ATTRIBUTES_FOR_SERIALIZATION

    PER_PAGE_MAX = 100
    private_constant :PER_PAGE_MAX

    def index
      per_page = (params[:per_page] || 30).to_i
      num = [per_page, PER_PAGE_MAX].min

      @readinglist = Reaction
        .select(INDEX_REACTIONS_ATTRIBUTES_FOR_SERIALIZATION)
        .readinglist
        .where(user_id: @user.id)
        .where.not(status: "archived")
        .order(created_at: :desc)
        .page(params[:page])
        .per(num)

      articles = Article
        .includes(:organization)
        .select(ArticlesController::INDEX_ATTRIBUTES_FOR_SERIALIZATION)
        .where(id: @readinglist.map(&:reactable_id))
        .decorate

      @users_by_id = User
        .joins(:profile)
        .select(UsersController::SHOW_ATTRIBUTES_FOR_SERIALIZATION)
        .find(articles.map(&:user_id))
        .index_by(&:id)

      articles_by_id = articles.index_by(&:id)

      @articles_by_reaction_ids = @readinglist.each_with_object({}) do |reaction, result|
        result[reaction.id] = articles_by_id[reaction.reactable_id]
      end
    end
  end
end