Set time_zone to London in all GOV.UK apps

README.md

@@ -8,6 +8,7 @@ Adds the basics of a GOV.UK application:
 - Statsd client for reporting stats (deprecated; use Prometheus instead)
 - Rails logging
 - Content Security Policy generation for frontend apps
+- Sets the time zone to London
 
 ## Installation
 
@@ -181,6 +182,9 @@ GovukContentSecurityPolicy.configure
 
 Some frontend apps support languages that are not defined in the i18n gem. This provides them with our own custom rules for these languages.
 
+## Time zone
+
+This gem sets `config.time_zone` to `"London"` - this cannot currently be overridden in application config.
 
 ## License
 

lib/govuk_app_config.rb

@@ -9,5 +9,6 @@
 if defined?(Rails)
   require "govuk_app_config/govuk_json_logging"
   require "govuk_app_config/govuk_content_security_policy"
+  require "govuk_app_config/govuk_timezone"
   require "govuk_app_config/railtie"
 end

lib/govuk_app_config/govuk_timezone.rb

@@ -0,0 +1,14 @@
+module GovukTimezone
+  def self.configure(config)
+    case config.time_zone
+    when "UTC"
+      Rails.logger.info "govuk_app_config changing time_zone from UTC (the default) to London"
+    when "London"
+      Rails.logger.info "govuk_app_config always sets time_zone to London - there is no need to set config.time_zone in your app"
+    else
+      raise "govuk_app_config prevents configuring time_zones other than London - config.time_zone was set to #{config.time_zone}"
+    end
+
+    config.time_zone = "London"
+  end
+end

lib/govuk_app_config/railtie.rb

@@ -14,6 +14,10 @@ class Railtie < Rails::Railtie
       end
     end
 
+    initializer "govuk_app_config.configure_timezone", before: "active_support.initialize_time_zone" do |app|
+      GovukTimezone.configure(app.config)
+    end
+
     config.before_initialize do
       GovukJsonLogging.configure if ENV["GOVUK_RAILS_JSON_LOGGING"]
     end

spec/lib/govuk_timezone_spec.rb

@@ -0,0 +1,32 @@
+require "spec_helper"
+require "govuk_app_config/govuk_timezone"
+
+RSpec.describe GovukError do
+  describe ".configure" do
+    let(:config) { Rails::Railtie::Configuration.new }
+    let(:logger) { instance_double("ActiveSupport::Logger") }
+
+    before do
+      allow(Rails).to receive(:logger).and_return(logger)
+    end
+
+    it "should override the default UTC time_zone to London" do
+      config.time_zone = "UTC"
+      expect(logger).to receive(:info)
+      GovukTimezone.configure(config)
+      expect(config.time_zone).to eq("London")
+    end
+
+    it "should leave time_zones set to London as London" do
+      config.time_zone = "London"
+      expect(logger).to receive(:info)
+      GovukTimezone.configure(config)
+      expect(config.time_zone).to eq("London")
+    end
+
+    it "should raise an error if configured with any other time zone" do
+      config.time_zone = "Shanghai"
+      expect { GovukTimezone.configure(config) }.to raise_error(/govuk_app_config prevents configuring time_zones/)
+    end
+  end
+end