Refactor #set_locale in applicaiton_controller

by dividing the method to 3 methods each decides locales from given conditions.

app/controllers/application_controller.rb

@@ -75,28 +75,38 @@ class ApplicationController < ActionController::Base
   end
 
   def set_locale
-    available = I18n.available_locales.map(&:to_s)
-    if params[:lang] && available.include?(params[:lang])
-      session[:prefer_lang] = params[:lang]
-      I18n.locale = params[:lang]
-      return
-    end
-    if session[:prefer_lang]
-      I18n.locale = session[:prefer_lang]
-      return
+    # NOTE: ignoring q=xxx in request header for now
+    I18n.locale = locale_from_params || locale_from_session || locale_from_http_accept_lang || I18n.default_locale
   end
 
-    # NOTE: ignoring q=xxx in request header for now
-    return if request.env["HTTP_ACCEPT_LANGUAGE"].blank?
+  def locale_from_params
+    if params[:lang] && available_locales.include?(params[:lang])
+      session[:prefer_lang] = params[:lang]
+      params[:lang]
+    else
+      nil
+    end
+  end
+
+  def locale_from_session
+    session[:prefer_lang]
+  end
+
+  def locale_from_http_accept_lang
+    return nil if request.env["HTTP_ACCEPT_LANGUAGE"].blank?
+
     langs = request.env["HTTP_ACCEPT_LANGUAGE"].gsub(/q=[0-9.]+/, "").gsub(";","").split(",")
-    prefer = langs.find {|lang| available.include?(lang) }
+    prefer = langs.find { |lang| available_locales.include?(lang) }
+
     unless prefer
-      if langs.find{|lang| lang.match(/^en/)}
-        I18n.locale = :en
-        return
+      prefer = :en if langs.find{ |lang| lang.match(/^en/) }
     end
+
+    prefer
   end
-    I18n.locale = prefer
+
+  def available_locales
+    @available_locales ||= I18n.available_locales.map(&:to_s)
   end
 
   def file_tail(path, limit = 10)

spec/controllers/application_controller_spec.rb

@@ -0,0 +1,86 @@
+require 'spec_helper'
+
+class DummyController < ApplicationController; end
+
+describe DummyController do
+  controller DummyController do
+    skip_before_action :login_required
+    def index
+      render :text => "Hello World"
+    end
+  end
+
+  describe '#set_locale' do
+    let!(:default_locale) { :en }
+    before do
+      I18n.stub(:default_locale).and_return(default_locale)
+      I18n.stub(:available_locales).and_return([:en, :ja])
+
+      I18n.locale = I18n.default_locale #initialize
+    end
+
+    context 'with params[:lang]' do
+      before do
+        get 'index', lang: param_lang
+      end
+
+      context 'and in available_locales' do
+        let(:param_lang) { :ja }
+
+        it 'params[:lang] will be set as locale' do
+          expect(I18n.locale).to eq :ja
+        end
+      end
+
+      context 'and out of available_locales' do
+        let(:param_lang) { :ka }
+
+        it 'defalut locale will be set as locale' do
+          expect(I18n.locale).to eq default_locale
+        end
+      end
+    end
+
+    context 'with session[:prefer_lang]' do
+      before do
+        controller.session[:prefer_lang] = :ja
+      end
+
+      it 'session[:prefer_lang] will be set as locale' do
+        get 'index'
+        expect(I18n.locale).to eq :ja
+      end
+    end
+
+    context 'with request.env["HTTP_ACCEPT_LANGUAGE"]' do
+      before do
+        request.stub(:env).and_return({ "HTTP_ACCEPT_LANGUAGE" => accept_language })
+        get 'index'
+      end
+
+      context 'accept_language is available' do
+        let(:accept_language) { 'ja' }
+
+        it 'session[:prefer_lang] will be set as locale' do
+          expect(I18n.locale).to eq :ja
+        end
+      end
+
+      context 'accept_language is not available but start with en' do
+        let(:accept_language) { 'en-us' }
+
+        it ':en will be set as locale' do
+          expect(I18n.locale).to eq :en
+        end
+      end
+
+      context 'accept_language is not available' do
+        let(:accept_language) { 'ka' }
+
+        it 'default_locale will be set as locale' do
+          expect(I18n.locale).to eq default_locale
+        end
+      end
+    end
+  end
+end