#!/usr/bin/env ruby
# UziMonkey <uzimonkey@gmail.com>

class HexDump < File
  alias :old_write :write

  def write(s)
    @bytes ||= 0   # Bytes written
    @line ||= 0    # Offset of current line

    s.each_byte do|b|
      new_line if @bytes % 16 == 0

      write_byte b
      write_ascii b
      @bytes += 1
    end
  end

  protected
  def new_line
    seek 0, IO::SEEK_END
    @line = tell

    old_write " " * 76
    old_write "\n"

    seek @line, IO::SEEK_SET
    old_write "%08x" % @bytes
  end

  # Write a hex byte
  def write_byte(b)
    seek @line + 8 + 1 + (3 * (@bytes % 16)), IO::SEEK_SET
    old_write "%02x" % b
  end

  # Write an ASCII byte
  def write_ascii(b)
    seek @line + 8 + (16 * 3) + 3 + (@bytes % 16), IO::SEEK_SET
    old_write (b.chr =~ /[[:print:]]/).nil? ? '.' : b.chr
  end
end

h = HexDump.new( 'output.txt', 'w' )
h.write ARGF.read