lib/determinator/cache/fetch_wrapper.rb in determinator-2.0.0 vs lib/determinator/cache/fetch_wrapper.rb in determinator-2.1.0

@@ -1,20 +1,58 @@
 module Determinator
   module Cache
     class FetchWrapper
-      # @param cache [#fetch] An instance of a cache class which implements #fetch like ActiveSupport::Cache does
-      def initialize(cache)
-        @cache = cache
+      # @param *caches [ActiveSupport::Cache] If a list then the head of the the
+      # list should will be checked before the  tail. If the head is empty but
+      # the tail is not then the head will be filled with the value of the tail.
+      def initialize(*caches)
+        @caches = caches
       end
 
+      # Call walks through each cache, returning a value if the item exists in
+      # any cache, otherwise popularing each cache with the value of yield.
       def call(feature_name)
-        @cache.fetch(key(feature_name)) { yield }
+        value = read_and_upfill(feature_name)
+        # nil is an acceptable value in the case of a missing feature definition
+        return nil if value.nil?
+        return value if value != false
+
+        value_to_write = yield
+        @caches.each do |cache|
+          cache.write(key(feature_name), value_to_write)
+        end
+        return value_to_write
       end
 
+      def expire(feature_name)
+        @caches.each{ |c| c.delete(key(feature_name)) }
+      end
+
       private
 
       def key(feature_name)
         "determinator:feature_cache:#{feature_name}"
+      end
+
+      # Walks through the list of caches, returning the first stored value.
+      #
+      # If a value is found in a cache after the first then all caches earlier
+      # in that list will be backfilled.
+      #
+      # @param url [String] a feature name
+      # @return [false, nil, Feature] false when no value is found, otherwise
+      # the value stored in the cache (including nil)
+      def read_and_upfill(feature_name)
+        @caches.each.with_index do |cache, index|
+          if cache.exist?(key(feature_name))
+            value = cache.read(key(feature_name))
+            @caches[0...index].each do |cache|
+              cache.write(key(feature_name), value)
+            end
+            return value
+          end
+        end
+        return false
       end
     end
   end
 end