class LaptopDrive < Drive
end


class DesktopComputer < Computer
  # Lots of interesting desktop details omitted...
end

class LaptopComputer < Computer
  def initialize( motherboard=Motherboard.new,  drives=[] )
    super(:lcd, motherboard, drives)
  end

  # Lots of interesting laptop details omitted...

end

class ComputerBuilder
  attr_reader :computer

  def turbo(has_turbo_cpu=true)
    @computer.motherboard.cpu = TurboCPU.new
  end

  def memory_size=(size_in_mb)
    @computer.motherboard.memory_size = size_in_mb
  end
end

class DesktopBuilder < ComputerBuilder
  def initialize
    @computer = DesktopComputer.new
  end

  def display=(display)
    @display = display
  end

  def add_cd(writer=false)
    @computer.drives << Drive.new(:cd, 760, writer)
  end

  def add_dvd(writer=false)
    @computer.drives << Drive.new(:dvd, 4000, writer)
  end

  def add_hard_disk(size_in_mb)
    @computer.drives << Drive.new(:hard_disk, size_in_mb, true)
  end  
end

class LaptopBuilder < ComputerBuilder
  def initialize
    @computer = LaptopComputer.new
  end

  def display=(display)
    raise "Laptop display must be lcd" unless display == :lcd
  end

  def add_cd(writer=false)
    @computer.drives << LaptopDrive.new(:cd, 760, writer)
  end

  def add_dvd(writer=false)
    @computer.drives << LaptopDrive.new(:dvd, 4000, writer)
  end

  def add_hard_disk(size_in_mb)
    @computer.drives << LaptopDrive.new(:hard_disk, size_in_mb, true)
  end  
end