pdf_generator.rb

require 'fileutils'
require 'logger'
require 'erb'

# Pdf generation service based on wkhtmltopdf.

class PdfGenerator
  class WkhtmltopdfError < RuntimeError; end

  DPI = 96 # Pixels in inch
  DPC = (DPI / 2.54) # = 37.795 Pixels in centimeter

  # See http://madalgo.au.dk/~jakobt/wkhtmltoxdoc/wkhtmltopdf-0.9.9-doc.html
  #
  # Options without argument just take true, rest should have string as value.
  # To disable option set it to false.
  PDF_OPTIONS = {
    'quiet'         => true,

    # Header is disabled.
    # 'header-html' => 'header.html',
    # 'footer-html' => 'footer.html',

    'print-media-type' => true,
    # 'disable-smart-shrinking' => true,

    'page-size'     => 'A4',
    'margin-top'    => '0.5cm',
    'margin-right'  => '0.5cm',
    'margin-bottom' => '1cm',
    'margin-left'   => '0.5cm',
    'encoding'      => "UTF-8",
  }

  PDF_DIR = 'pdfs'
  FileUtils.mkdir_p(PDF_DIR)

  attr_accessor :error_message
  attr_accessor :note

  def logger
    defined?(Rails) ? Rails.logger : (@logger ||= Logger.new($stdout))
  end

  def pdf_options
    PDF_OPTIONS
  end

  def note_url
    'index.html'
  end

  def pdf_path
    File.join(PDF_DIR, "ramki.pdf")
  end

  def wkhtmltopdf
    @wkhtmltopdf ||= begin
      pdf_command = [
        `ls -1 bin/wkhtmltopdf* 2>/dev/null`.split("\n").last,
        `which wkhtmltopdf`
      ].detect{|c| !c.nil? }

      raise("Cannot locate wkhtmltopdf in #{Dir.pwd} or $PATH") if pdf_command.nil?

      pdf_command.strip
    end
  end

  def xvfb_wrapper
    "" #'xvfb-run -s "-screen 0, 1600x1200x24"'
  end

  # wkhtmltopdf [OPTIONS]... <input file> [More input files] <output file>
  def pdf_command
    normalized_options = pdf_options.map{|k, v|
      v ? "--#{k} #{v == true ? "" : v}" : nil
    }.compact.join(" ")

    "#{xvfb_wrapper} #{wkhtmltopdf} #{normalized_options} #{note_url} #{pdf_path}"
  end

  def render
    File.open('index.html', 'w') do |f|
      f.write ERB.new(File.read('index.html.erb')).result
    end
  end

  # Generates a pdf.
  def generate
    render
    perform
  end

  # Performs a pdf generation.
  def perform
    logger.debug "Running: " + pdf_command

    # See http://mentalized.net/journal/2010/03/08/5_ways_to_run_commands_from_ruby/
    redirection = " 2>&1"
    @out = IO.popen(pdf_command + redirection, "wb+") do |pdf|
      pdf.close_write
      pdf.gets(nil)
    end
    
    unless $? == 0
      self.error_message = "Failed to generate pdf via: #{wkhtmltopdf}. Exit code: #{$?}."
      raise(WkhtmltopdfError, error_message, caller[1..-1])
    end
  end
end

if __FILE__ == $0
  PdfGenerator.new.generate
end