#!/usr/bin/env ruby

#
# A ruby program to convert a file to images.
#
# author: Torsten Tränkner
# license: GPL version 3
#
class FileToImagesConverter

  require 'fileutils'
  require 'base64'
  require 'digest/sha1'

  VERSION="0.1"

  # returns the version
  def version
    return VERSION
  end

  # JPG header
  HEADER="FF D8 FF E0 00 10 4A 46 49 46 00 01 01 01 00 48 00 48 00 00"

  # JPG footer
  FOOTER="FF DB 00 43 00 03 02 02 03 02 02 03 03 03 03 04 03 03 04 05 08 05 05 04 04 05 0A 07 07 06 08 0C 0A 0C 0C 0B 0A 0B 0B 0D 0E 12 10 0D 0E 11 0E 0B 0B 10 16 10 11 13 14 15 15 15 0C 0F 17 18 16 14 18 12 14 15 14 FF DB 00 43 01 03 04 04 05 04 05 09 05 05 09 14 0D 0B 0D 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 FF C2 00 11 08 00 0A 00 0A 03 01 11 00 02 11 01 03 11 01 FF C4 00 16 00 01 01 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 03 08 FF C4 00 14 01 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 FF DA 00 0C 03 01 00 02 10 03 10 00 00 01 D4 85 40 3F FF C4 00 16 10 01 01 01 00 00 00 00 00 00 00 00 00 00 00 00 00 03 02 10 FF DA 00 08 01 01 00 01 05 02 22 80 2D FF C4 00 14 11 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 20 FF DA 00 08 01 03 01 01 3F 01 1F FF C4 00 14 11 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 20 FF DA 00 08 01 02 01 01 3F 01 1F FF C4 00 1A 10 00 03 00 03 01 00 00 00 00 00 00 00 00 00 00 00 01 02 03 11 12 20 51 FF DA 00 08 01 01 00 06 3F 02 49 CD 16 73 41 AA A2 8C 00 3C E3 FF C4 00 18 10 01 00 03 01 00 00 00 00 00 00 00 00 00 00 00 00 01 11 20 31 41 FF DA 00 08 01 01 00 01 3F 21 3C C5 14 31 00 0C 03 94 FF DA 00 0C 03 01 00 02 00 03 00 00 00 10 12 4F FF C4 00 14 11 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 20 FF DA 00 08 01 03 01 01 3F 10 1F FF C4 00 14 11 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 20 FF DA 00 08 01 02 01 01 3F 10 1F FF C4 00 15 10 01 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 20 FF DA 00 08 01 01 00 01 3F 10 07 EA CD 70 B0 00 00 00 00 23 FF D9"

  # maximum number of comments per image file
  MAXIMUM_COMMENTS = 30

  # size of one image comment
  CHUNK_SIZE = 65520

  #
  # converts a given file to (several) images
  # in the subdirectory "parts.filename"
  #
  def self.convert(filename)
    # puts "Creating images for: #{filename}"

    # create a directory for the images
    directory="parts.#{filename}"

    if File.directory?(directory)
      FileUtils.remove_dir(directory)
    end

    FileUtils.mkdir(directory)

    # get base64 encoded string of the file
    base64String=""
    File.open(filename, 'r') do |openedFile|
      base64String=Base64.strict_encode64(openedFile.read)
    end

    sha1sumOfBase64String = Digest::SHA1.hexdigest(base64String)

    imageIndex=0
    numberOfChunks=(Float(base64String.length) / CHUNK_SIZE).ceil
    numberOfImages=(Float(numberOfChunks) / MAXIMUM_COMMENTS).ceil

    # puts "#{base64String.length}, numberOfChunks: #{numberOfChunks}, numberOfImages: #{numberOfImages}"

    numberOfImages.times do |imageIndex|
      imageFilename="image%03i.jpg"%imageIndex
      #puts "imageFilename: #{imageFilename}"

      File.open(File.join(directory, imageFilename), 'w') do |openedFile|
        openedFile.write([HEADER.delete(" ")].pack("H*"))

        MAXIMUM_COMMENTS.times do |partIndex|
          partStart=(MAXIMUM_COMMENTS * CHUNK_SIZE * imageIndex) + partIndex * CHUNK_SIZE
          if partStart >= base64String.length
            next
          end

          partEnd=(MAXIMUM_COMMENTS * CHUNK_SIZE * imageIndex) + (partIndex + 1) * CHUNK_SIZE
          if partEnd >= base64String.length
            partEnd=base64String.length
          end
          #puts "partStart: #{partStart}, partEnd: #{partEnd}"
          commentSize = partEnd - partStart + 6

          # write the comment
          openedFile.write("\xff\xfe")
          # comment size as binary
          openedFile.write("%c"%(commentSize/256)+"%c"%(commentSize%256))
          openedFile.write("%%")
          openedFile.write(base64String[partStart..partEnd-1])
          openedFile.write("%%")

        end

        openedFile.write([FOOTER.delete(" ")].pack("H*"))
      end

      # prepare the link file
      File.open(File.join(directory, "linkfile.txt"), 'w') do |openedFile|

        openedFile.write("// put your upload links here:\n")

        numberOfImages.times do
          openedFile.write("l=\n")
        end

        openedFile.write("\nf=#{filename}\n\n")
        openedFile.write("// SHA1 checksum:\n")
        openedFile.write("c=#{sha1sumOfBase64String}\n")
        openedFile.write("a=\n")
      end
    end

  end

end

if __FILE__ == $0
  if ARGV.length == 1
    FileToImagesConverter.convert(ARGV[0])
  else
    puts "A script to convert a file to images."
    puts "Version #{FileToImagesConverter.version}\n\n"
    puts "Usage:\nruby #{$0} <filename>"
  end
end