export.rb

require 'prawn'


arr = HallSession
        .joins(:check_in_sessions, :hall)
        .group('check_in_sessions.hall_session_id, auditorium_halls.name, hall_sessions.start_at, hall_sessions.end_at, hall_sessions.id')
        .select('auditorium_halls.name as hall_name, hall_sessions.start_at, hall_sessions.end_at, COUNT(*) as c')
        .order('hall_name, start_at, end_at')
        .map do |ci|
          [
            ci.hall_name,
            ci.start_at.strftime('%H:%M'),
            ci.end_at.strftime('%H:%M'),
            ci.c
          ]
        end

header = %w[Hall\ Name Session\ Start\ At Session\ End\ At Count]
pdf = Prawn::Document.new(page_size: 'A4')

pdf.font_size(20) { pdf.text 'Hall sessions check-ins' }
pdf.move_down 10

pdf.table(
  [header] + arr,
  width: pdf.bounds.width
)

pdf.render_file 'test.pdf'