$expect_verbose = false

class IO
  # Reads ios until pattern matches or the timeout is over. It returns
  # an array with the read buffer, followed by the matches. If a block is given,
  # the result is yielded to the block and returns nil. The optional timeout parameter defines,
  # in seconds, the total time to wait for pattern. If it is over of eof is found, it 
  # returns/yields nil. However, the buffer in a timeout session is kept for the next expect call.
  # The default timeout is 9999999 seconds.
  def expect(pat,timeout=9999999)
    buf = ''
    case pat
    when String
      e_pat = Regexp.new(Regexp.quote(pat))
    when Regexp
      e_pat = pat
    else
      raise TypeError, "unsupported pattern class: #{pattern.class}"
    end
    @unusedBuf ||= ''
    while true
      if not @unusedBuf.empty?
        c = @unusedBuf.slice!(0).chr
      elsif !IO.select([self],nil,nil,timeout) or eof? then
        result = nil
        @unusedBuf = buf
        break
      else
        c = getc.chr
      end
      buf << c
      if $expect_verbose
        STDOUT.print c
        STDOUT.flush
      end
      if mat=e_pat.match(buf) then
        result = [buf,*mat.to_a[1..-1]]
        break
      end
    end
    if block_given? then
      yield result
    else
      return result
    end
    nil
  end
end

