FEED_COUNT=30

  # get latest feed using reverse range lookup of sorted set
  # then decode raw JSON back into Ruby objects
  def feed(obj=true, count=FEED_COUNT)
    results=$redis.zrevrange key(:feed), 0, count
    if obj && results.size > 0
      results.collect {|r| Status.decode(r)}
    end
  end

  # get older statuses by using reverse range by score lookup
  def ofeed(max, obj=true, id=self.id_s, limit=FEED_COUNT, scores=false)
    results=$redis.zrevrangebyscore(key(:feed), "(#{max}", "-inf", :limit => [0, limit], :with_scores => scores)
    if obj && results.size > 0
      results.collect {|r| Status.decode(r)}
    end     
  end

  # push status to a specific feed
    def push(id, location="feed")
      $redis.zadd key(location, id), timestamp, encoded
    end

  # push to followers (assumes an array of follower ids)
  def push_to_followers
    @follower_ids.each do |follower_id|
      push(follower_id)
    end
  end

  # since most sorted set commands are a variation on O(log(N)) 
  # where N is the size of the set, in makes sense to trim the
  # feed when it gets beyond a certain length

  FEED_LENGTH=240

  # there may be a more efficient way to do this
  # but I check the length of the set
  # then I get the score of the last value I want to keep
  # then remove all keys with a lower score
  def trim_feed(id=self.id_s, location="feed", indx=FEED_LENGTH)
    k = key(:feed)
    if ($redis.zcard k) >= indx
      n = indx - 1
      if (r = $redis.zrevrange k, n, n, :with_scores => true)
        $redis.zremrangebyscore k, "-inf", "(#{r.last}"
      end
    end
  end