Extract locale file digest logic to a separate class and add tests

app/helpers/application_helper.rb

@@ -76,12 +76,6 @@ module ApplicationHelper
   end
 
   def cache_key_with_locale(key, locale)
-    Array.wrap(key) + [locale.to_s, locale_digest(locale)]
-  end
-
-  private
-
-  def locale_digest(locale)
-    Rails.application.config.x.i18n_digests[locale]
+    Array.wrap(key) + [locale.to_s, I18nDigests.for_locale(locale)]
   end
 end

config/application.rb

@@ -23,6 +23,7 @@ end
 require_relative "../lib/open_food_network/i18n_config"
 require_relative '../lib/spree/core/environment'
 require_relative '../lib/spree/core/mail_interceptor'
+require_relative "../lib/i18n_digests"
 
 if defined?(Bundler)
   # If you precompile assets before deploying to production, use this line
@@ -185,10 +186,7 @@ module Openfoodnetwork
     I18n.locale = config.i18n.locale = config.i18n.default_locale
 
     # Calculate digests for locale files so we can know when they change
-    config.i18n.available_locales.each do |locale|
-      (config.x.i18n_digests ||= {})[locale.to_sym] =
-        Digest::MD5.hexdigest(File.read(Rails.root.join("config/locales/#{locale}.yml")))
-    end
+    I18nDigests.build_digests config.i18n.available_locales
 
     # Setting this to true causes a performance regression in Rails 3.2.17
     # When we're on a version with the fix below, we can set it to true

lib/i18n_digests.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+class I18nDigests
+  class << self
+    def build_digests(available_locales)
+      available_locales.each do |locale|
+        i18n_digests[locale.to_sym] = locale_file_digest(locale)
+      end
+    end
+
+    def for_locale(locale)
+      i18n_digests[locale.to_sym]
+    end
+
+    private
+
+    def i18n_digests
+      Rails.application.config.x.i18n_digests
+    end
+
+    def locale_file_digest(locale)
+      Digest::MD5.hexdigest(Rails.root.join("config/locales/#{locale}.yml").read)
+    end
+  end
+end

spec/helpers/application_helper_spec.rb

@@ -42,4 +42,51 @@ describe ApplicationHelper, type: :helper do
       end
     end
   end
+
+  describe "#cache_with_locale" do
+    let(:available_locales) { ["en", "es"] }
+    let(:current_locale) { "es" }
+    let(:locale_digest) { "8a7s5dfy28u0as9du" }
+    let(:options) { { expires_in: 10.seconds } }
+
+    before do
+      allow(I18n).to receive(:available_locales) { available_locales }
+      allow(I18n).to receive(:locale) { current_locale }
+      allow(I18nDigests).to receive(:for_locale) { locale_digest }
+    end
+
+    it "passes key, options, and block to #cache method with locale and locale digest appended" do
+      expect(helper).to receive(:cache_key_with_locale).
+        with("test-key", current_locale).and_return(["test-key", current_locale, locale_digest])
+
+      expect(helper).to receive(:cache).
+        with(["test-key", current_locale, locale_digest], options) do |&block|
+          expect(block.call).to eq("cached content")
+        end
+
+      helper.cache_with_locale "test-key", options do
+        "cached content"
+      end
+    end
+  end
+
+  describe "#cache_key_with_locale" do
+    let(:en_digest) { "asd689asy0239" }
+    let(:es_digest) { "9d8tu23oirhad" }
+
+    before { allow(I18nDigests).to receive(:for_locale).with("en") { en_digest } }
+    before { allow(I18nDigests).to receive(:for_locale).with("es") { es_digest } }
+
+    it "appends locale and digest to a single key" do
+      expect(
+        helper.cache_key_with_locale("single-key", "en")
+      ).to eq(["single-key", "en", en_digest])
+    end
+
+    it "appends locale and digest to multiple keys" do
+      expect(
+        helper.cache_key_with_locale(["array", "of", "keys"], "es")
+      ).to eq(["array", "of", "keys", "es", es_digest])
+    end
+  end
 end

spec/lib/i18n_digests_spec.rb

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe I18nDigests do
+  describe "#build_digests" do
+    let(:available_locales) { ["en", "es"] }
+    let(:md5_hex_regex) { /([a-f0-9]){10}/ }
+
+    around do |example|
+      original = Rails.application.config.x.i18n_digests
+      example.run
+      Rails.application.config.x.i18n_digests = original
+    end
+
+    it "computes and stores digests for each locale file" do
+      Rails.application.config.x.i18n_digests = {}
+      I18nDigests.build_digests(available_locales)
+
+      expect(Rails.application.config.x.i18n_digests.keys).to eq [:en, :es]
+      expect(Rails.application.config.x.i18n_digests.values).to all match(md5_hex_regex)
+
+      expect(
+        Rails.application.config.x.i18n_digests[:en]
+      ).to eq(Digest::MD5.hexdigest(Rails.root.join("config/locales/en.yml").read))
+
+      expect(
+        Rails.application.config.x.i18n_digests[:es]
+      ).to eq(Digest::MD5.hexdigest(Rails.root.join("config/locales/es.yml").read))
+    end
+  end
+
+  describe "#for_locale" do
+    let(:digests) { { en: "as8d7a9sdh", es: "iausyd9asdh" } }
+
+    before do
+      allow(Rails).to receive_message_chain(:application, :config, :x, :i18n_digests) { digests }
+    end
+
+    it "returns the digest for a given locale" do
+      expect(I18nDigests.for_locale("en")).to eq "as8d7a9sdh"
+    end
+  end
+end