Compose multiple pdf files into one content or file.

pdf_composer.rb

require 'tempfile'

# usage:
#  pc = PDFComposer.new(file_or_content1[, file_or_content2 ...])
#  content = pc.compose # compose all into content
#  pc.compose(to_file_path) # output to 'to_file_path' :-)

class PDFComposer
  def initialize(*args)
    @sources = args.flatten
    @tempfiles = []
  end
  def compose(path = nil)
    @content ||= compose_content
    if path
      File.open(path, 'wb') do |f|
        f.write @content
      end
    else
      @content
    end
  end

  private
  def compose_content
    source_files = files_from_sources
    tf = Tempfile.new(%w(pdf-composer-output .pdf), encoding: 'BINARY')
    tf.close
    cmd_args = [self.class.gs_path, '-q', '-dNOPAUSE', '-dBATCH',
                '-sDEVICE=pdfwrite', "-sOutputFile=#{tf.path}"]
    cmd_args += source_files
    success = system *cmd_args
    raise "Fail to exec #{cmd_args.inspect}." unless success
    content = tf.open.read
    tf.close(true)
    content
  end

  def files_from_sources
    @sources.map do |source|
      if source.is_a?(String)
        if source.encoding != Encoding::BINARY && File.exist?(source)
          source
        else
          tf = Tempfile.new(%w(pdf-composer .pdf), encoding: 'BINARY')
          tf.write(source)
          tf.close
          @tempfiles << tf
          tf.path
        end
      elsif source.is_a? Tempfile
        source.path
      end
    end
  end
  def self.gs_path
    @@gs_path ||= `which gs`.chomp
  end
end