feat(cross-domain-redirect): redirect to APP_HOST when user is on APP_HOST_LEGACY

app/helpers/application_helper.rb

@@ -8,6 +8,14 @@ module ApplicationHelper
     Regexp.new(APP_HOST_LEGACY).match?(request.base_url)
   end
 
+  def auto_switch_domain?(request, user_signed_in)
+    switch_domain_enabled?(request) && !user_signed_in && app_host_legacy?(request)
+  end
+
+  def switch_domain_enabled?(request)
+    request.params.key?(:switch_domain) || Flipper.enabled?(:switch_domain)
+  end
+
   def html_lang
     I18n.locale.to_s
   end

app/views/layouts/_switch_domain_banner.html.haml

@@ -0,0 +1,7 @@
+- if auto_switch_domain?(request, user_signed_in?)
+  :javascript
+    const hintUrl = "#{image_url(FAVICONS_SRC["16px"])}"
+    fetch(hintUrl)
+      .then(function(){
+        window.location = window.location.href.replace("#{ApplicationHelper::APP_HOST_LEGACY}", "#{ApplicationHelper::APP_HOST}")
+      })

app/views/layouts/application.html.haml

@@ -36,6 +36,7 @@
 
     = yield(:invisible_captcha_styles)
     = render partial: 'layouts/setup_theme'
+    = render partial: 'layouts/switch_domain_banner'
 
   %body{ { id: content_for(:page_id), class: browser.platform.ios? ? 'ios' : nil, data: { controller: 'turbo number-input' } }.compact }
     = render partial: 'layouts/skiplinks'

spec/helpers/application_helper_spec.rb

@@ -11,17 +11,63 @@ describe ApplicationHelper do
 
     subject { app_host_legacy?(request) }
 
-    context 'request on ENV[APP_HOST_LEGACY]' do
+    context 'when request on ENV[APP_HOST_LEGACY]' do
       let(:request_base_url) { app_host_legacy }
       it { is_expected.to be_truthy }
     end
 
-    context 'request on ENV[APP_HOST]' do
+    context 'when request on ENV[APP_HOST]' do
       let(:request_base_url) { app_host }
       it { is_expected.to be_falsey }
     end
   end
 
+  describe 'auto_switch_domain?' do
+    subject { auto_switch_domain?(request, user_signed_in) }
+
+    context 'when user_signed_in? is true' do
+      let(:user_signed_in) { true }
+      let(:request) { instance_double(ActionDispatch::Request, base_url: 'osf', params: {}) }
+      it { is_expected.to be_falsey }
+    end
+
+    context 'when user_signed_in? is false' do
+      let(:user_signed_in) { false }
+      let(:params) { {} }
+      let(:request) { instance_double(ActionDispatch::Request, base_url: request_base_url, params:) }
+      let(:app_host_legacy) { 'legacy' }
+      let(:app_host) { 'host' }
+
+      before do
+        stub_const("ApplicationHelper::APP_HOST_LEGACY", app_host_legacy)
+        stub_const("ApplicationHelper::APP_HOST", app_host)
+      end
+
+      context 'request on ENV[APP_HOST_LEGACY] without feature or url' do
+        let(:request_base_url) { app_host_legacy }
+        it { is_expected.to be_falsey }
+      end
+
+      context 'request on ENV[APP_HOST_LEGACY] with switch_domain params' do
+        let(:params) { { switch_domain: '1' } }
+        let(:request_base_url) { app_host_legacy }
+        it { is_expected.to be_truthy }
+      end
+
+      context 'request on ENV[APP_HOST_LEGACY] with switch_domain params' do
+        before { Flipper.enable :switch_domain }
+        after { Flipper.disable :switch_domain }
+        let(:request_base_url) { app_host_legacy }
+        it { is_expected.to be_truthy }
+      end
+
+      context 'request on ENV[APP_HOST]' do
+        let(:request_base_url) { app_host }
+        it { is_expected.to be_falsey }
+      end
+    end
+  end
+
   describe "#flash_class" do
     it { expect(flash_class('notice')).to eq 'alert-success' }
     it { expect(flash_class('alert', sticky: true, fixed: true)).to eq 'alert-danger sticky alert-fixed' }