Improve default language decision and spec (#3351)

* Improve default language decision

This change allows to takes account of accepted language determined by
the user agent even if the custom default locale of the instance is
configured.

* Cover Localized more

* Fix code style

1 files changed, 88 insertions, 0 deletions

diff --git a/spec/controllers/concerns/localized_spec.rb b/spec/controllers/concerns/localized_spec.rb
new file mode 100644
index 000000000..18fe508e4
--- /dev/null
+++ b/spec/controllers/concerns/localized_spec.rb
@@ -0,0 +1,88 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe ApplicationController, type: :controller do
+  controller do
+    include Localized
+
+    def success
+      head 200
+    end
+  end
+
+  before do
+    routes.draw { get 'success' => 'anonymous#success' }
+  end
+
+  shared_examples 'default locale' do
+    context 'when DEFAULT_LOCALE environment variable is set' do
+      around do |example|
+        ClimateControl.modify 'DEFAULT_LOCALE' => 'ca', &example.method(:run)
+      end
+
+      it 'sets language specified by ENV if preferred' do
+        request.headers['Accept-Language'] = 'ca, fa'
+        get 'success'
+        expect(I18n.locale).to eq :ca
+      end
+
+      it 'sets available and preferred language if language specified by ENV is not preferred' do
+        request.headers['Accept-Language'] = 'ca-ES, fa'
+        get 'success'
+        expect(I18n.locale).to eq :fa
+      end
+
+      it 'sets language specified by ENV if it is compatible and none of available languages are preferred' do
+        request.headers['Accept-Language'] = 'ca-ES, fa-IR'
+        get 'success'
+        expect(I18n.locale).to eq :ca
+      end
+
+      it 'sets available and compatible langauge if language specified by ENV is not compatible none of available languages are preferred' do
+        request.headers['Accept-Language'] = 'fa-IR'
+        get 'success'
+        expect(I18n.locale).to eq :fa
+      end
+
+      it 'sets language specified by ENV if none of available languages are compatible' do
+        request.headers['Accept-Language'] = ''
+        get 'success'
+        expect(I18n.locale).to eq :ca
+      end
+    end
+
+    context 'when DEFAULT_LOCALE environment variable is not set' do
+      it 'sets default locale if none of available languages are compatible' do
+        request.headers['Accept-Language'] = ''
+        get 'success'
+        expect(I18n.locale).to eq :en
+      end
+    end
+  end
+
+  context 'user with valid locale has signed in' do
+    it "sets user's locale" do
+      user = Fabricate(:user, locale: :ca)
+
+      sign_in(user)
+      get 'success'
+
+      expect(I18n.locale).to eq :ca
+    end
+  end
+
+  context 'user with invalid locale has signed in' do
+    before do
+      user = Fabricate.build(:user, locale: :invalid)
+      user.save!(validate: false)
+      sign_in(user)
+    end
+
+    include_examples 'default locale'
+  end
+
+  context 'user has not signed in' do
+    include_examples 'default locale'
+  end
+end