Add CachedProductsRenderer - wraps ProductsRenderer using Rails cache

lib/open_food_network/cached_products_renderer.rb

@@ -0,0 +1,35 @@
+require 'open_food_network/products_renderer'
+
+# Wrapper for ProductsRenderer that caches the JSON output.
+# ProductsRenderer::NoProducts is represented in the cache as nil,
+# but re-raised to provide the same interface as ProductsRenderer.
+
+module OpenFoodNetwork
+  class CachedProductsRenderer
+    def initialize(distributor, order_cycle)
+      @distributor = distributor
+      @order_cycle = order_cycle
+    end
+
+    def products_json
+      products_json = Rails.cache.fetch("products-json-#{@distributor.id}-#{@order_cycle.id}") do
+        begin
+          uncached_products_json
+        rescue ProductsRenderer::NoProducts
+          nil
+        end
+      end
+
+      raise ProductsRenderer::NoProducts.new if products_json.nil?
+
+      products_json
+    end
+
+
+    private
+
+    def uncached_products_json
+      ProductsRenderer.new(@distributor, @order_cycle).products_json
+    end
+  end
+end

spec/lib/open_food_network/cached_products_renderer_spec.rb

@@ -0,0 +1,80 @@
+require 'spec_helper'
+require 'open_food_network/cached_products_renderer'
+require 'open_food_network/products_renderer'
+
+module OpenFoodNetwork
+  describe CachedProductsRenderer do
+    let(:distributor) { double(:distributor, id: 123) }
+    let(:order_cycle) { double(:order_cycle, id: 456) }
+    let(:cpr) { CachedProductsRenderer.new(distributor, order_cycle) }
+
+    describe "when the products JSON is already cached" do
+      before do
+        Rails.cache.write "products-json-#{distributor.id}-#{order_cycle.id}", 'products'
+      end
+
+      it "returns the cached JSON" do
+        expect(cpr.products_json).to eq 'products'
+      end
+
+      it "raises an exception when there are no products" do
+        Rails.cache.write "products-json-#{distributor.id}-#{order_cycle.id}", nil
+        expect { cpr.products_json }.to raise_error ProductsRenderer::NoProducts
+      end
+    end
+
+    describe "when the products JSON is not cached" do
+      let(:cached_json) { Rails.cache.read "products-json-#{distributor.id}-#{order_cycle.id}" }
+      let(:cache_present) { Rails.cache.exist? "products-json-#{distributor.id}-#{order_cycle.id}" }
+
+      before do
+        Rails.cache.clear
+        cpr.stub(:uncached_products_json) { 'fresh products' }
+      end
+
+      describe "when there are products" do
+        it "returns products as JSON" do
+          expect(cpr.products_json).to eq 'fresh products'
+        end
+
+        it "caches the JSON" do
+          cpr.products_json
+          expect(cached_json).to eq 'fresh products'
+        end
+      end
+
+      describe "when there are no products" do
+        before { cpr.stub(:uncached_products_json).and_raise ProductsRenderer::NoProducts }
+
+        it "raises an error" do
+          expect { cpr.products_json }.to raise_error ProductsRenderer::NoProducts
+        end
+
+        it "caches the products as nil" do
+          expect { cpr.products_json }.to raise_error ProductsRenderer::NoProducts
+          expect(cache_present).to be
+          expect(cached_json).to be_nil
+        end
+      end
+
+      describe "logging a warning" do
+        it "logs a warning when in production"
+        it "logs a warning when in staging"
+        it "does not log a warning in development"
+        it "does not log a warning in test"
+      end
+    end
+
+    describe "fetching uncached products from ProductsRenderer" do
+      let(:pr) { double(:products_renderer, products_json: 'uncached products') }
+
+      before do
+        ProductsRenderer.stub(:new) { pr }
+      end
+
+      it "returns the uncached products" do
+        expect(cpr.send(:uncached_products_json)).to eq 'uncached products'
+      end
+    end
+  end
+end