def prepare_and_send_mail(student)
      return unless enabled_for?(student)

      email_params = Serializers::PremiumFiveDaysSerializer.new(student).data
      return unless email_params['total_completed_cards_count'] > 10

      subj_count = 0
      ['math', 'eng', 'env', 'rus'].each do |subject|
        subj_count += 1 if email_params["prem5#{subject}left"].nil? || email_params["prem5#{subject}left"] > 10
      end
      return unless subj_count == 4

      send_mail(email_params)
    end