booklet-pdf.rb

require 'combine_pdf' # https://github.com/boazsegev/combine_pdf

input_filename = ARGV[0]

if input_filename.empty?
  puts 'ERROR:'
  puts 'Enter filename'
  return
end

pdf = CombinePDF.load(input_filename)
booklet_pdf = CombinePDF.new
total_pages_count = pdf.pages.size

if (total_pages_count % 4).nonzero?
  puts 'ERROR:'
  puts "Pages count #{total_pages_count} should be divisible by 4"
  puts 'Add pages to the pdf file'
  return
end

page_nums = (1..total_pages_count).to_a[0..((total_pages_count / 2) - 1)]
page_nums_rev = (1..total_pages_count).to_a[(total_pages_count / 2)..-1].reverse
res_page_nums = []
page_nums.each.with_index do |num, index|
  pair = [num, page_nums_rev[index]]
  res_page_nums << (index.odd? ? pair : pair.reverse)
end
res_page_nums.flatten!

res_page_nums.each do |page_num|
  booklet_pdf << pdf.pages[page_num - 1]
end

output_filename = File.basename(input_filename, '.pdf') + '_booklet.pdf'
booklet_pdf.save(output_filename)
puts "See #{output_filename} file"