class Lazily::Prefetcher

def each(&block)
  return @source.each(&block) if @buffer_size <= 0
  buffered_elements = []
  i = 0
  @source.each do |element|
    slot = i % @buffer_size
    if i >= @buffer_size
      yield buffered_elements[slot]
    end
    buffered_elements[slot] = element
    i += 1
  end
  buffered_elements.size.times do
    slot = i % buffered_elements.size
    yield buffered_elements[slot]
    i += 1
  end
end

def initialize(source, buffer_size)
  @source = source.to_enum
  @buffer_size = buffer_size
end