require 'tmpdir'
require 'pdftoimage/version'
require 'pdftoimage/image'
require 'iconv'

module PDFToImage
  class PDFError < RuntimeError; end
end

module PDFToImage
  # A class variable for storing the location of our temp folder
  @@pdf_temp_dir = File.join(Dir.tmpdir())

  begin
    tmp = `pdftoppm -v 2>&1`
    raise(PDFToImage::PDFError, "poppler_utils not installed") unless tmp.index('Poppler')
  rescue Errno::ENOENT
    raise PDFToImage::PDFError, "poppler_utils not installed"
  end

  begin
    tmp = `identify -version 2>&1`
    raise(PDFToImage::PDFError, "ImageMagick not installed") unless tmp.index('ImageMagick')
  rescue Errno::ENOENT
    raise PDFToImage::PDFError, "ImageMagick not installed"
  end

  class << self

    # Opens a PDF document and prepares it for splitting into images.
    #
    # @param [filename] The filename of the PDF to open
    # @return [Array] An array of images
    def open(filename, &block)
      if not File.exists?(filename)
        raise PDFError, "File '#{filename}' not found."
      end

      pages = page_count(filename)

      # Array of images
      images = []

      1.upto(pages) { |n|
        dimensions = page_size(filename, n)
        image = Image.new(filename, random_filename, n, dimensions, pages)
        images << image
      }

      images.each(&block) if block_given?

      return images

    end

    # Executes the specified command, returning the output.
    #
    # @param [cmd] The command to run
    # @return [String] The output of the command
    def exec(cmd, error = nil)
      output = `#{cmd}`
      if $? != 0
        if error == nil
          raise PDFError, "Error executing command: #{cmd}"
        else
          raise PDFError, error
        end
      end

      return output
    end

    private

    def page_size(filename, page)
      cmd = "pdfinfo -f #{page} -l #{page} #{filename} | grep Page"
      output = exec(cmd)

      matches = /^Page.*?size:.*?(\d+).*?(\d+)/.match(output)
      if matches.nil?
        raise PDFError, "Unable to determine page size."
      end

      scale = 2.08333333333333333
      dimension = {
        :width => (matches[1].to_i * scale).to_i,
        :height => (matches[2].to_i * scale).to_i
      }

      dimension
    end

    def page_count(filename)
      cmd = "pdfinfo #{filename} | grep Pages"
      output = exec(cmd)
      matches = /^Pages:.*?(\d+)$/.match(output)
      if matches.nil?
        raise PDFError, "Error determining page count."
      end

      return matches[1].to_i
    end

    # Generate a random file name in the system's tmp folder
    def random_filename
      File.join(@@pdf_temp_dir, random_name)
    end

    # Generate a random name of {#length} characters.
    def random_name(length = 15)
      @@chars ||= ("a".."z").to_a + ("A".."Z").to_a + ("1".."9").to_a
      return 'pdftoimage-' + Array.new(length, '').collect{@@chars[rand(@@chars.size)]}.join
    end

  end

end