zhishi-engine/zhishi-backend

module Queries
  class OrderBySubscriptionQuery < UserQuestionsQuery
    def call
      relation.joins(join_associations).order(case_statement, sort_by_date_created).group("tags_questions.id")
      # , sort_by_votes_sum, sort_by_views
    end

    private
      def sort_by_votes_sum
        "SUM(votes.value) DESC"
      end

      def sort_by_views
        "questions.views DESC"
      end

      def sort_by_date_created
        "questions.created_at DESC"
      end

      # def case_handler
      #   Arel::Nodes::Case.new
      # end

      def case_statement
        "CASE WHEN #{user_subscriptions.to_sql} THEN 0 ELSE 2 END"
        # NOTE below method call should be commented out if/when we switch to Rails 5
        # case_handler.when(user_subscriptions).then(0).else(2)
      end

      def question_table
        Question.arel_table
      end

      def join_associations
        question_table.outer_join(resource_tag_table).on(resource_tag_table[:taggable_id].eq(question_table[:id]).and(resource_tag_table[:taggable_type].eq('Question'))).
        outer_join(tag_table).on(tag_table[:id].eq(resource_tag_table[:tag_id])).join_sources
      end
  end
end