hospital_booking.rb

class HospitalBooking
  def self.send_overtime_mail(user, bookings)
    OvertimeMailer.overtime_pdf(user, hospital_booking).deliver
  end
end

hospitalbooking_controller.rb

 def index 
    @hospital_bookings = HospitalBooking.scoped
    if params[:format] == 'pdf'
      @hospital_bookings = @hospital_bookings.where(:day => Date.today.beginning_of_month..Date.today.end_of_month)
      HospitalBooking.send_overtime_mail(current_user, @hospital_bookings)
    end
 
    respond_to do |format|
      format.html
      format.pdf do
        render :pdf => "#{Date.today.strftime('%B')} Overtime Report",
               :header => {:html => {:template => 'layouts/pdf.html.erb'}}
      end
    end
  end

scheduler.rake

task :overtime_report => :environment do
  if Date.today.day == 18
    user = User.where(:role => :administrator).first
    bookings = HospitalBooking.where(:day => Date.today.beginning_of_month..Date.today.end_of_month)
    HospitalBooking.send_overtime_mail(user, bookings)
  end
end