zhishi-engine/zhishi-backend

module Queries
  class StatisticsQuery
    class << self
      delegate :call, to: :new
    end

    attr_reader :relation

    def initialize(relation = User.all)
      @relation = relation
    end

    def call
      relation.joins(join_associations).select(user_data, questions_asked, answers_given).group("users.id")
    end

    private
      def user_table
        User.arel_table
      end

      def questions_table
        Question.arel_table
      end

      def answers_table
        Answer.arel_table
      end

      def join_associations
        user_table.outer_join(questions_table).on(user_table[:id].eq(questions_table[:user_id])).
        outer_join(answers_table).on(user_table[:id].eq(answers_table[:user_id])).join_sources
      end

      def questions_asked
        questions_table.project(Arel.star.count).where(questions_table[:user_id].eq(user_table[:id])).as("questions_asked")
      end

      def answers_given
        answers_table.project(Arel.star.count).where(answers_table[:user_id].eq(user_table[:id])).as("answers_given")
      end

      def user_data
        user_table[Arel.star]
      end
  end
end