# Small cache proxy object to cache the index.
class Cache
  instance_methods.each { |id| id =~ /\A__/ or undef_method id }

  # Caches data returned by block, for _duration_ seconds.
  def initialize(duration = 3600, &block)
    @duration = duration
    @block = block
    fetch_data
  end

  def fetch_data
    @data = @block.call
    @last_fetch = Time.now
  end
  private :fetch_data

  def method_missing(id, *a, &b)
    fetch_data if @last_fetch + @duration < Time.now
    @data.__send__(id, *a, &b)
  end
end