gistfile1.rb

require 'mini_magick'

class InvalidInputFileError < Exception; end

class Converter
  def initialize(input, output = nil)
    raise InvalidInputFileError unless html_file?(input)
    @input = input
    if @output
      @ouput = output
    else
      @output = output_filename_from @input
    end
  end

  def convert_file
    system(Dir.pwd+"/wkhtmltopdf-amd64",@input, "temporary.pdf")
    image = MiniMagick::Image.open("temporary.pdf")
    image.format "png"
    image.write Dir.pwd+"/"+@output + ".png"
    File.delete("temporary.pdf")
  end

  protected

  def html_file?(filename)
    filename.match(/\.html$/)
  end

  def output_filename_from(filename)
    File.basename(filename, File.extname(filename))
  end
end

conv = Converter.new("faktura.html")
conv.convert_file