require 'open3'
require 'fileutils'
require 'pdf-reader'
require_relative '../pdfs2pdf'
module Pdfs2Pdf
  module Utils
    class << self
      # Create the 'pdfmarks' file for use with 'gs' utility
      #
      # @param [Array<String>] pdf_files the input file list (pdf)
      # @param [String] output_file the output filename default to 'pdfmarks'
      # @param [String] base_dir the base directory (TODO: review this code!)
      def create_pdfmarks(pdf_files, pdfmarks_file = 'pdfmarks', base_dir = Dir.pwd)
        File.open(pdfmarks_file, 'w') do |out_file|
          out_file.write(title)
          current_page = 1
          pdf_files.each do |pdf_file|
            filename = if base_dir
                         # remove the base_directory from the full path
                         pdf_file.gsub(base_dir, File.basename(pdf_file))
                       else
                         pdf_file
                       end
            out_file.write "[ /Page #{current_page} /Title (#{filename}) /OUT pdfmark\n"
            current_page += Pdfs2Pdf::Utils.page_count(pdf_file)
          end
        end
      end

      # Simple title for use in 'pdfmarks' file
      #
      # @todo allow the customization.
      def title
        <<-END.gsub(/^\s+\|/, '')
          |[ /Title (My Sample Book)
          |  /Author (Agile Creativity)
          |  /Keywords (fun, witty, interesting)
          |  /DOCINFO pdfmark
        END
      end

      # Merge list of files using 'gs' command
      #
      # @param [Array<String>] list input file list
      # @param [String] pdfmarks the pdfmarks file default to 'pdfmarks'
      # @param [String] output_file the output pdf file
      def merge_pdfs(list, pdfmarks = 'pdfmarks', output_file = 'output.pdf')
        _stdin, _stderr, status = Open3.capture3(
          'gs',
          '-q',
          '-dNOPAUSE',
          '-dBATCH',
          '-sDEVICE=pdfwrite',
          '-sPAPERSIZE=a4',
          "-sOutputFile=#{output_file}",
          *list,
          pdfmarks)
        fail 'Problem in merge_pdfs' unless status.success?
      end

      # Extract pdf page count using pdf-reader
      #
      # @return [Fixnum] the page count of the given pdf file
      def page_count(pdf_file)
        File.open(pdf_file, 'rb') do |io|
          reader = PDF::Reader.new(io)
          return reader.page_count
        end
        fail "Problem getting the page count for #{pdf_file}"
      end
    end
  end
end