Add cache_store adapter for caching via ActiveSupport::CacheStore

* Helpful adapter for Rails users that want to use their configured
cache.

lib/flipper/adapters/cache_store.rb

@@ -0,0 +1,103 @@
+module Flipper
+  module Adapters
+    # Public: Adapter that wraps another adapter with the ability to cache
+    # adapter calls in ActiveSupport::CacheStore caches.
+    #
+    class CacheStore
+      include ::Flipper::Adapter
+
+      Version = 'v1'.freeze
+      Namespace = "flipper/#{Version}".freeze
+      FeaturesKey = "#{Namespace}/features".freeze
+
+      # Private
+      def self.key_for(key)
+        "#{Namespace}/feature/#{key}"
+      end
+
+      # Internal
+      attr_reader :cache
+
+      # Public: The name of the adapter.
+      attr_reader :name
+
+      # Public
+      def initialize(adapter, cache, options = nil)
+        @adapter = adapter
+        @name = :cache_store
+        @cache = cache
+        @options = options
+      end
+
+      # Public
+      def features
+        @cache.fetch(FeaturesKey, @options) do
+          @adapter.features
+        end
+      end
+
+      # Public
+      def add(feature)
+        result = @adapter.add(feature)
+        @cache.delete(FeaturesKey, @options)
+        result
+      end
+
+      ## Public
+      def remove(feature)
+        result = @adapter.remove(feature)
+        @cache.delete(FeaturesKey, @options)
+        @cache.delete(key_for(feature.key), @options)
+        result
+      end
+
+      ## Public
+      def clear(feature)
+        result = @adapter.clear(feature)
+        @cache.delete(key_for(feature.key), @options)
+        result
+      end
+
+      ## Public
+      def get(feature)
+        @cache.fetch(key_for(feature.key), @options) do
+          @adapter.get(feature)
+        end
+      end
+
+      def get_multi(features)
+        keys = features.map { |feature| key_for(feature.key) }
+        result = @cache.read_multi(keys)
+        uncached_features = features.reject { |feature| result[feature.key] }
+        if uncached_features.any?
+          response = @adapter.get_multi(uncached_features)
+          response.each do |key, value|
+            @cache.write(key_for(key), value, @options)
+            result[key] = value
+          end
+        end
+        result
+      end
+
+      ## Public
+      def enable(feature, gate, thing)
+        result = @adapter.enable(feature, gate, thing)
+        @cache.delete(key_for(feature.key), @options)
+        result
+      end
+
+      ## Public
+      def disable(feature, gate, thing)
+        result = @adapter.disable(feature, gate, thing)
+        @cache.delete(key_for(feature.key), @options)
+        result
+      end
+
+      private
+
+      def key_for(key)
+        self.class.key_for(key)
+      end
+    end
+  end
+end

spec/flipper/adapters/cache_store_spec.rb

@@ -0,0 +1,50 @@
+require 'helper'
+require 'active_support/cache'
+require 'flipper/adapters/memory'
+require 'flipper/adapters/cache_store'
+require 'flipper/spec/shared_adapter_specs'
+
+RSpec.describe Flipper::Adapters::CacheStore do
+  let(:memory_adapter) { Flipper::Adapters::Memory.new }
+  let(:cache) { ActiveSupport::Cache::MemoryStore.new }
+  let(:adapter) { described_class.new(memory_adapter, cache) }
+  let(:flipper) { Flipper.new(adapter) }
+
+  subject { adapter }
+
+  it_should_behave_like 'a flipper adapter'
+
+  describe '#remove' do
+    it 'expires feature' do
+      feature = flipper[:stats]
+      adapter.get(feature)
+      adapter.remove(feature)
+      expect(cache.read(described_class.key_for(feature))).to be(nil)
+    end
+  end
+
+  describe '#get_multi' do
+    it 'warms uncached features' do
+      stats = flipper[:stats]
+      search = flipper[:search]
+      other = flipper[:other]
+      stats.enable
+      search.enable
+
+      adapter.get(stats)
+      expect(cache.read(described_class.key_for(search))).to be(nil)
+      expect(cache.read(described_class.key_for(other))).to be(nil)
+
+      adapter.get_multi([stats, search, other])
+
+      expect(cache.read(described_class.key_for(search))[:boolean]).to eq('true')
+      expect(cache.read(described_class.key_for(other))[:boolean]).to be(nil)
+    end
+  end
+
+  describe '#name' do
+    it 'is cache_store' do
+      expect(subject.name).to be(:cache_store)
+    end
+  end
+end