Create local and network component resolvers

We need the option to use local components when using Slimmer in
static. This avoids network requests, excessive network stubbing and
i18n chain hacks.

Because static components have a `.raw.html.erb` filename, we can’t use
the default Rails component resolver. eg `govuk_component/title` can’t
find the `_title` partial – we need to load `title.raw.html.erb`.

* Split ComponentResolver into LocalComponentResolver and
NetworkComponentResolver
* Create new module for LocalGovukComponents which
govuk_publishing_components can use when included on static
* LocalGovukComponents don’t need a test version

lib/slimmer.rb

@@ -28,7 +28,10 @@ def fetch(*)
   autoload :HTTPClient, 'slimmer/http_client'
 
   autoload :GovukComponents, 'slimmer/govuk_components'
+  autoload :LocalGovukComponents, 'slimmer/local_govuk_components'
   autoload :ComponentResolver, 'slimmer/component_resolver'
+  autoload :NetworkComponentResolver, 'slimmer/network_component_resolver'
+  autoload :LocalComponentResolver, 'slimmer/local_component_resolver'
   autoload :I18nBackend, 'slimmer/i18n_backend'
 
   module Processors

lib/slimmer/component_resolver.rb

@@ -1,61 +1,26 @@
-require 'slimmer/govuk_request_id'
-require 'active_support/core_ext/string/inflections'
-
 module Slimmer
   class ComponentResolver < ::ActionView::Resolver
     TEST_TAG_NAME = 'test-govuk-component'
 
     def find_templates(name, prefix, partial, details, outside_app_allowed = false)
       return [] unless prefix == 'govuk_component'
-
       template_path = [prefix, name].join('/')
-      if test?
-        template_body = test_body(template_path)
-      else
-        template_body = Slimmer.cache.fetch(template_path, expires_in: Slimmer::CACHE_TTL) do
-          fetch(template_url(template_path))
-        end
-      end
-
       details = {
         :format => 'text/html',
         :updated_at => Time.now,
         :virtual_path => template_path
       }
 
-      [ActionView::Template.new(template_body, template_path, erb_handler, details)]
+      [ActionView::Template.new(template_body(template_path), template_path, erb_handler, details)]
     end
 
   private
-    def test?
-      defined?(Rails) && Rails.env.test?
-    end
-
     def erb_handler
       @erb_handler ||= ActionView::Template.registered_template_handler(:erb)
     end
 
-    def fetch(template_url)
-      HTTPClient.get(template_url)
-    rescue RestClient::Exception => e
-      raise TemplateNotFoundException, "Unable to fetch: '#{template_url}' because #{e}", caller
-    rescue Errno::ECONNREFUSED => e
-      raise CouldNotRetrieveTemplate, "Unable to fetch: '#{template_url}' because #{e}", caller
-    rescue SocketError => e
-      raise CouldNotRetrieveTemplate, "Unable to fetch: '#{template_url}' because #{e}", caller
-    end
-
-    def template_url(template_path)
-      path = template_path.sub(/\.raw(\.html\.erb)?$/, '')
-      [static_host, "templates", "#{path}.raw.html.erb"].join('/')
-    end
-
-    def static_host
-      @static_host ||= Plek.new.find('static')
-    end
-
-    def test_body(path)
-      %Q{<#{TEST_TAG_NAME} data-template="#{path.parameterize}"><%= JSON.dump(local_assigns) %></#{TEST_TAG_NAME}>}
+    def template_body(_template_path)
+      raise NotImplementedError, "Use NetworkComponentResolver or LocalComponentResolver"
     end
   end
 end

lib/slimmer/govuk_components.rb

@@ -50,7 +50,7 @@ def resolver
           @cache_last_reset = Time.now
         end
 
-        @resolver ||= Slimmer::ComponentResolver.new
+        @resolver ||= Slimmer::NetworkComponentResolver.new
       end
     end
   end

lib/slimmer/local_component_resolver.rb

@@ -0,0 +1,19 @@
+module Slimmer
+  class LocalComponentResolver < ComponentResolver
+  private
+
+    def template_body(template_path)
+      File.read(template_file(template_path))
+    end
+
+    def template_file(template_path)
+      path = template_path.sub(/\.raw(\.html\.erb)?$/, '')
+
+      if defined?(Rails)
+        Rails.root.join("app", "views", "#{path}.raw.html.erb")
+      else
+        "#{path}.raw.html.erb"
+      end
+    end
+  end
+end

lib/slimmer/local_govuk_components.rb

@@ -0,0 +1,49 @@
+module Slimmer
+  # @api public
+  #
+  # Include this module to avoid loading components over the network
+  # @example
+  #   class ApplicationController < ActionController::Base
+  #     include Slimmer::LocalGovukComponents
+  #   end
+  #
+  #   # In your views:
+  #
+  #   <%= render partial: 'govuk_component/example_component' %>
+  module LocalGovukComponents
+    def self.included into
+      into.before_action :add_govuk_components
+    end
+
+    # @private
+    def add_govuk_components
+      append_view_path LocalGovukComponents.expiring_resolver_cache.resolver
+    end
+
+    # @private
+    def self.expiring_resolver_cache
+      @expiring_resolver_cache ||= TimedExpirationResolverCache.new
+    end
+
+  private
+
+    # Slimmer::ComponentResolver instantiates a lot of large objects and leaks
+    # memory. This class will cache the resolver so that it doesn't have to
+    # create new ActionView::Template objects for each request. The cache is
+    # timed to allow frontends to pick up changes made to components in `static`.
+    class TimedExpirationResolverCache
+      def initialize
+        @cache_last_reset = Time.now
+      end
+
+      def resolver
+        if (@cache_last_reset + Slimmer::CACHE_TTL) < Time.now
+          @resolver = nil
+          @cache_last_reset = Time.now
+        end
+
+        @resolver ||= Slimmer::LocalComponentResolver.new
+      end
+    end
+  end
+end

lib/slimmer/network_component_resolver.rb

@@ -0,0 +1,45 @@
+require 'slimmer/govuk_request_id'
+require 'active_support/core_ext/string/inflections'
+
+module Slimmer
+  class NetworkComponentResolver < ComponentResolver
+  private
+
+    def template_body(template_path)
+      if test?
+        test_body(template_path)
+      else
+        Slimmer.cache.fetch(template_path, expires_in: Slimmer::CACHE_TTL) do
+          fetch(template_url(template_path))
+        end
+      end
+    end
+
+    def test?
+      defined?(Rails) && Rails.env.test?
+    end
+
+    def fetch(template_url)
+      HTTPClient.get(template_url)
+    rescue RestClient::Exception => e
+      raise TemplateNotFoundException, "Unable to fetch: '#{template_url}' because #{e}", caller
+    rescue Errno::ECONNREFUSED => e
+      raise CouldNotRetrieveTemplate, "Unable to fetch: '#{template_url}' because #{e}", caller
+    rescue SocketError => e
+      raise CouldNotRetrieveTemplate, "Unable to fetch: '#{template_url}' because #{e}", caller
+    end
+
+    def template_url(template_path)
+      path = template_path.sub(/\.raw(\.html\.erb)?$/, '')
+      [static_host, "templates", "#{path}.raw.html.erb"].join('/')
+    end
+
+    def static_host
+      @static_host ||= Plek.new.find('static')
+    end
+
+    def test_body(path)
+      %{<#{TEST_TAG_NAME} data-template="#{path.parameterize}"><%= JSON.dump(local_assigns) %></#{TEST_TAG_NAME}>}
+    end
+  end
+end

test/component_resolver_test.rb

@@ -10,32 +10,10 @@
       assert_equal [], @resolver.find_templates('name', 'prefix', false, {}, false)
     end
 
-    it "should request a valid template from the server" do
-      assert_valid_template_requested('name', 'name.raw.html.erb')
+    it "should raise when template_body is called directly from ComponentResolver" do
+      assert_raises NotImplementedError do
+        @resolver.find_templates('name', 'govuk_component', false, {}, false)
+      end
     end
-
-    it "should request a valid template from the server when a raw template is requested" do
-      assert_valid_template_requested('name.raw', 'name.raw.html.erb')
-    end
-
-    it "should request a valid template from the server when the full template filename is requested" do
-      assert_valid_template_requested('name.raw.html.erb', 'name.raw.html.erb')
-    end
-
-    it "should return a known template in test mode" do
-      @resolver.expects(:test?).returns(true)
-
-      templates = @resolver.find_templates('name', 'govuk_component', false, {}, false)
-      assert_match /<test-govuk-component data-template="govuk_component-name">/, templates.first.args[0]
-    end
-  end
-
-  def assert_valid_template_requested(requested, expected)
-    expected_url = "http://static.dev.gov.uk/templates/govuk_component/#{expected}"
-    stub_request(:get, expected_url).to_return body: "<foo />"
-
-    templates = @resolver.find_templates(requested, 'govuk_component', false, {}, false)
-    assert_requested :get, expected_url
-    assert_equal '<foo />', templates.first.args[0]
   end
 end

test/local_component_resolver_test.rb

@@ -0,0 +1,27 @@
+require_relative "test_helper"
+
+describe Slimmer::LocalComponentResolver do
+  describe "find_templates" do
+    before do
+      @resolver = Slimmer::LocalComponentResolver.new
+    end
+
+    it "should request a valid template" do
+      assert_valid_template_requested('name', 'name.raw.html.erb')
+    end
+
+    it "should request a valid template when a raw template is requested" do
+      assert_valid_template_requested('name.raw', 'name.raw.html.erb')
+    end
+
+    it "should request a valid template when the full template filename is requested" do
+      assert_valid_template_requested('name.raw.html.erb', 'name.raw.html.erb')
+    end
+  end
+
+  def assert_valid_template_requested(requested, expected)
+    File.expects(:read).with("govuk_component/#{expected}").returns('<foo />')
+    templates = @resolver.find_templates(requested, 'govuk_component', false, {}, false)
+    assert_equal '<foo />', templates.first.args[0]
+  end
+end

test/network_component_resolver_test.rb

@@ -0,0 +1,41 @@
+require_relative "test_helper"
+
+describe Slimmer::NetworkComponentResolver do
+  describe "find_templates" do
+    before do
+      @resolver = Slimmer::NetworkComponentResolver.new
+    end
+
+    it "should return nothing if the prefix doesn't match 'govuk_component'" do
+      assert_equal [], @resolver.find_templates('name', 'prefix', false, {}, false)
+    end
+
+    it "should request a valid template from the server" do
+      assert_valid_template_requested('name', 'name.raw.html.erb')
+    end
+
+    it "should request a valid template from the server when a raw template is requested" do
+      assert_valid_template_requested('name.raw', 'name.raw.html.erb')
+    end
+
+    it "should request a valid template from the server when the full template filename is requested" do
+      assert_valid_template_requested('name.raw.html.erb', 'name.raw.html.erb')
+    end
+
+    it "should return a known template in test mode" do
+      @resolver.expects(:test?).returns(true)
+
+      templates = @resolver.find_templates('name', 'govuk_component', false, {}, false)
+      assert_match(/<test-govuk-component data-template="govuk_component-name">/, templates.first.args[0])
+    end
+  end
+
+  def assert_valid_template_requested(requested, expected)
+    expected_url = "http://static.dev.gov.uk/templates/govuk_component/#{expected}"
+    stub_request(:get, expected_url).to_return body: "<foo />"
+
+    templates = @resolver.find_templates(requested, 'govuk_component', false, {}, false)
+    assert_requested :get, expected_url
+    assert_equal '<foo />', templates.first.args[0]
+  end
+end

test/test_helper.rb

@@ -40,7 +40,7 @@ def teardown
 require 'webmock/minitest'
 WebMock.disable_net_connect!
 
-# Including action_view is dificualt because it depends on rails and internal
+# Including action_view is difficult because it depends on rails and internal
 # ~*magic*~. To avoid depending on the whole of rails mock out the method we
 # need so we can tests the internal implementations which don't depend on rails
 module ActionView