class Pipeline
  def initialize(file)
    @op = lambda { |nxt| File.open(file) { |fp| nxt.call(fp) }}
  end

  def transform(&transformation)
    old_op = @op
    @op = lambda {|nxt| old_op.call(lambda {|fp| 
      IO.pipe {|r, w|
        transformation.call(fp, w)
        w.close_write
        nxt.call(r)
      }
    })}
  end

  def transform_all(&transformation)
    old_op = @op
    @op = lambda {|nxt| old_op.call(lambda {|fp| 
      IO.pipe {|r, w|
        w.write(transformation.call(fp.read))
        w.close_write
        nxt.call(r)
      }
    })}
  end

  def skip_to(n)
    old_op = @op
    @op = lambda {|nxt| old_op.call(lambda {|fp| fp.pos = n; nxt.call(fp) })}
  end

  def consume_all
    ret = nil
    @op.call(lambda {|fp| ret = fp.read })
    ret
  end

  def consume(&consumer)
    @op.call(lambda {|fp| consumer.call(fp) })
  end

  def pipe_to(out_fp)
    @op.call(lambda { |fp|
      until fp.eof? do
        data = fp.read(nil)
        out_fp.write(data) unless data.nil?
      end
    })
  end

end