Extract all locale-setting logic to a service

app/controllers/spree/user_sessions_controller.rb

@@ -6,7 +6,6 @@ module Spree
     include Spree::Core::ControllerHelpers::Common
     include Spree::Core::ControllerHelpers::Order
     include Spree::Core::ControllerHelpers::SSL
-    include I18nHelper
 
     ssl_required :new, :create, :destroy, :update
     ssl_allowed :login_bar
@@ -54,9 +53,8 @@ module Spree
     def ensure_valid_locale_persisted
       # When creating a new user session we have to wait until after a successful
       # login to be able to persist a locale on the current user
-      return unless spree_current_user && !available_locale?(spree_current_user.locale)
 
-      spree_current_user.update!(locale: I18n.default_locale)
+      UserLocaleSetter.ensure_valid_locale_persisted(spree_current_user)
     end
   end
 end

app/helpers/i18n_helper.rb

@@ -1,49 +1,9 @@
 module I18nHelper
   def set_locale
-    save_locale_from_params
-
-    # After logging in, check if the user chose a locale before
-    if current_user_locale.nil? && cookies[:locale] && available_locale?(params[:locale])
-      spree_current_user&.update!(locale: params[:locale])
-    end
-
-    I18n.locale = valid_current_locale
+    UserLocaleSetter.new(spree_current_user, params[:locale], cookies).call
   end
 
   def valid_locale(user)
-    if user.present? &&
-       user.locale.present? &&
-       available_locale?(user.locale)
-      user.locale
-    else
-      I18n.default_locale
-    end
-  end
-
-  def available_locale?(locale)
-    Rails.application.config.i18n.available_locales.include?(locale)
-  end
-
-  private
-
-  def save_locale_from_params
-    return unless params[:locale] && available_locale?(params[:locale])
-
-    spree_current_user&.update!(locale: params[:locale])
-    cookies[:locale] = params[:locale]
-  end
-
-  def current_user_locale
-    spree_current_user.andand.locale
-  end
-
-  def valid_current_locale
-    if available_locale?(current_user_locale)
-      current_user_locale
-    elsif available_locale?(cookies[:locale])
-      cookies[:locale]
-    else
-      I18n.default_locale
-    end
+    UserLocaleSetter.valid_locale_for_user(user)
   end
 end

app/services/user_locale_setter.rb

@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+class UserLocaleSetter
+  def initialize(current_user, params_locale, cookies)
+    @current_user = current_user
+    @params_locale = params_locale
+    @cookies = cookies
+  end
+
+  def call
+    save_locale_from_params
+
+    # After logging in, check if the user chose a locale before
+    if current_user_locale.nil? && cookies[:locale] && available_locale?(params_locale)
+      current_user&.update!(locale: params_locale)
+    end
+
+    I18n.locale = valid_current_locale
+  end
+
+  def self.ensure_valid_locale_persisted(user)
+    return unless user && !available_locale?(user.locale)
+
+    user.update!(locale: I18n.default_locale)
+  end
+
+  def self.valid_locale_for_user(user)
+    if user.present? && user.locale.present? && available_locale?(user.locale)
+      user.locale
+    else
+      I18n.default_locale
+    end
+  end
+
+  def self.available_locale?(locale)
+    Rails.application.config.i18n.available_locales.include?(locale)
+  end
+
+  private
+
+  attr_reader :current_user, :params_locale, :cookies
+
+  def save_locale_from_params
+    return unless params_locale && available_locale?(params_locale)
+
+    current_user&.update!(locale: params_locale)
+    cookies[:locale] = params_locale
+  end
+
+  def available_locale?(locale)
+    self.class.available_locale?(locale)
+  end
+
+  def current_user_locale
+    current_user.andand.locale
+  end
+
+  def valid_current_locale
+    if available_locale?(current_user_locale)
+      current_user_locale
+    elsif available_locale?(cookies[:locale])
+      cookies[:locale]
+    else
+      I18n.default_locale
+    end
+  end
+end