Freelancer Savegame Encoder/Decoder

flcodec.rb

# This script is based on the C++ implementation by Sherlog <sherlog@t-online.de> and Jor <flcodec@jors.net>

require 'active_support/all'
require 'singleton'

class FLCodec
  include Singleton

  class << self
    delegate :encode, :decode, :load_file, :decode_file, :encode_file, to: :instance
  end

  class InvalidData < StandardError
    def initialize
      super "Stream contains invalid data"
    end
  end

  HEADER = 'FLS1'.freeze
  GENE = 'Gene'.freeze

  def load_file(filename)
    result = StringIO.new
    File.open(filename, 'r') do |file|
      self.decode(file, result)
    end
    result.string
  end

  def decode_file(src_path, dst_path = nil)
    convert_file(:decode, src_path, dst_path, '.ini')
  end

  def decode(src_io, dst_io)
    header = src_io.read(HEADER.length)
    raise InvalidData unless header == HEADER
    convert(src_io, dst_io)
  end

  def encode_file(src_path, dst_path = nil)
    convert_file(:encode, src_path, dst_path, '.fl')
  end

  def encode(src_io, dst_io)
    dst_io.write(HEADER)
    convert(src_io, dst_io)
  end

  private
  def convert(src_io, dst_io)
    buffer = src_io.read
    buffer.each_byte.with_index do |byte, index|
      key = (GENE[index % GENE.length].ord + index) % 256
      new_byte = byte ^ (key | 0x80)
      dst_io.write(new_byte.chr)
    end
    true
  end

  def convert_file(type, src_path, dst_path, default_ext)
    dst_path = src_path.chomp(File.extname(src_path)) + default_ext if dst_path.nil?
    File.open(src_path, 'r') do |src_file|
      File.open(dst_path, 'w') do |dst_file|
        self.public_send(type, src_file, dst_file)
      end
    end
    dst_path
  end
end