switch locale + rack::locale

Gemfile

@@ -30,6 +30,7 @@ gem 'kaminari'
 gem 'octokit'
 gem 'front_matter_parser'
 gem 'two_factor_authentication', git: 'https://github.com/lespoupeesrusses/two_factor_authentication.git'
+gem 'rack-contrib'
 
 # Front
 gem 'jquery-rails'

Gemfile.lock

@@ -240,6 +240,8 @@ GEM
       nio4r (~> 2.0)
     racc (1.5.2)
     rack (2.2.3)
+    rack-contrib (2.3.0)
+      rack (~> 2.0)
     rack-mini-profiler (2.3.3)
       rack (>= 1.2.0)
     rack-protection (2.1.0)
@@ -386,6 +388,7 @@ DEPENDENCIES
   octokit
   pg (~> 1.1)
   puma
+  rack-contrib
   rack-mini-profiler (~> 2.0)
   rails
   rails-i18n

app/controllers/admin/application_controller.rb

@@ -2,7 +2,7 @@ class Admin::ApplicationController < ApplicationController
   layout 'admin/layouts/application'
 
   before_action :authenticate_user!
-  before_action :set_locale
+  around_action :switch_locale
 
   protected
 
@@ -22,9 +22,8 @@ class Admin::ApplicationController < ApplicationController
                       : add_breadcrumb('Créer')
   end
 
-  def set_locale
-    return unless current_user
-    return unless current_user.language
-    I18n.locale = current_user.language.iso_code
+  def switch_locale(&action)
+    locale = LocaleService.locale(current_user, request.env['HTTP_ACCEPT_LANGUAGE'])
+    I18n.with_locale(locale, &action)
   end
 end

app/services/locale_service.rb

+class LocaleService
+
+  ## Get best locale for a user
+  def self.locale(user, accept_language_header)
+    user&.language.nil? ? self.preferred_language(accept_language_header) : user.language.iso_code.to_sym
+  end
+
+  def self.preferred_language(brand_languages, accept_language_header)
+    # browser_language > french
+    browser_languages = accept_language_header&.scan(/\*|([a-z]{1,8}(?:-[A-Z0-9]{1,8})*)/i)&.flatten&.compact&.reject { |v| v == "q" }
+
+    browser_languages&.each do |code|
+      symbol = self.get_symbol(code)
+      return symbol unless symbol.nil?
+    end
+
+    I18n.default_locale
+  end
+
+  def self.get_symbol(code)
+    if Language.where(iso_code: code).any?
+      symbol = code.to_sym
+    elsif code.include?('-')
+      # safari returns only "fr-fr", so if we only have "fr" active it fallbacks to english
+      root_code = code.split('-').first
+      symbol = root_code.to_sym if Language.where(iso_code: root_code).any?
+    end
+    symbol
+  end
+end

config/application.rb

@@ -23,6 +23,8 @@ module Osuny
   class Application < Rails::Application
     config.load_defaults 6.1
 
+    config.middleware.insert_before Warden::Manager, Rack::Locale
+
     config.time_zone = 'Europe/Paris'
 
     config.active_job.queue_adapter = :delayed_job