refactor unwieldy Rack::Attack::StoreProxy.build method

lib/rack/attack/store_proxy.rb

@@ -2,25 +2,30 @@ module Rack
   class Attack
     module StoreProxy
       PROXIES = [DalliProxy, MemCacheProxy, RedisStoreProxy]
+      USE_BASE_CLIENT = ['Redis::Store', 'Dalli::Client', 'MemCache']
 
       def self.build(store)
         # RedisStore#increment needs different behavior, so detect that
         # (method has an arity of 2; must call #expire separately
-        if (defined?(::ActiveSupport::Cache::RedisStore) && store.is_a?(::ActiveSupport::Cache::RedisStore)) ||
-          (defined?(::ActiveSupport::Cache::MemCacheStore) && store.is_a?(::ActiveSupport::Cache::MemCacheStore))
+        client = fetch_client(store)
+        klass = PROXIES.find { |proxy| proxy.handle?(client) }
+        klass ? klass.new(client) : client
+      end
 
-          # ActiveSupport::Cache::RedisStore doesn't expose any way to set an expiry,
-          # so use the raw Redis::Store instead.
-          # We also want to use the underlying Dalli client instead of ::ActiveSupport::Cache::MemCacheStore,
-          # and the MemCache client if using Rails 3.x
-          client = store.instance_variable_get(:@data)
-          if (defined?(::Redis::Store) && client.is_a?(Redis::Store)) ||
-            (defined?(Dalli::Client) && client.is_a?(Dalli::Client)) || (defined?(MemCache) && client.is_a?(MemCache))
-            store = store.instance_variable_get(:@data)
-          end
+      def self.fetch_client(store)
+        client = store.instance_variable_get(:@data)
+        # RedisStore#increment needs different behavior, so detect that
+        # (method has an arity of 2; must call #expire separately
+        #
+        # ActiveSupport::Cache::RedisStore doesn't expose any way to set an expiry,
+        # so use the raw Redis::Store instead.
+        #
+        # We also want to use the underlying Dalli client instead of ::ActiveSupport::Cache::MemCacheStore,
+        # and the MemCache client if using Rails 3.x
+        USE_BASE_CLIENT.each do |klass|
+          return client if !client.nil? && Object.const_defined?(klass) && client.is_a?(Object.const_get(klass))
         end
-        klass = PROXIES.find { |proxy| proxy.handle?(store) }
-        klass ? klass.new(store) : store
+        return store
       end
 
     end