Contents

module Determinator
  module Cache
    class FetchWrapper
      # @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)
        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

Version data entries

4 entries across 4 versions & 1 rubygems

Version	Path
determinator-2.3.0	lib/determinator/cache/fetch_wrapper.rb
determinator-2.2.1	lib/determinator/cache/fetch_wrapper.rb
determinator-2.2.0	lib/determinator/cache/fetch_wrapper.rb
determinator-2.1.0	lib/determinator/cache/fetch_wrapper.rb