class SplitIoClient::Observers::ImpressionObserver

def initialize
  @cache = LruRedux::TTL::ThreadSafeCache.new(LAST_SEEN_CACHE_SIZE)
  @impression_hasher = Hashers::ImpressionHasher.new
end

def test_and_set(impression)
  return if impression.nil?
  
  hash = @impression_hasher.process(impression)
  previous = @cache[hash]
  @cache[hash] = impression[:m]
  previous.nil? ? nil : [previous, impression[:m]].min
end