require "stringio"

class Pipeline
  def initialize(source)

    source = { file:source } unless source.is_a? Hash

    if source.has_key? :file
      @op = lambda { |nxt| File.open(source[:file]) { |fp| nxt.call(fp) }}
    elsif source.has_key? :string
      data = source[:string]
      @op = lambda { |nxt| 
        IO.pipe { |r, w| 
          w.write(data)
          w.close_write
          nxt.call(r)
        }
      }
    end
  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| 
      data = transformation.call(fp.read)
      nxt.call(StringIO.new(data))
    })}
  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