web_i18n_locale.rb

module WebI18nLocale
  extend ActiveSupport::Concern

  included do
    prepend_before_action :digest_locale_params
    before_action :set_locale
    helper_method :set_locale_path
  end

  private

  def digest_locale_params
    return unless params[:locale] && request.get?

    session[:locale] = resolve_locale(params[:locale])
    redirect_to url_for(request.params.except(:locale).merge(only_path: true))
  end

  def set_locale_path(locale)
    url_for(request.params.merge(locale: locale, only_path: true))
  end

  def set_locale
    the_locale = session_locale || browser_locale
    I18n.locale = the_locale
    @pagy_locale = the_locale.to_s # for pagy i18n
  end

  def resolve_locale(str)
    locale = String(str).to_sym
    I18n.available_locales.include?(locale) ? locale : nil
  end

  def session_locale
    @session_locale ||= resolve_locale(session[:locale])
  end

  def browser_locale
    @browser_locale ||= compatible_language_from(I18n.available_locales)
  end

  # references http_accept_language gem
  def user_preferred_languages # rubocop:disable all
    @user_preferred_languages ||= begin
      header = request.env['HTTP_ACCEPT_LANGUAGE']
      locale_quality_array = header.to_s.gsub(/\s+/, '').split(',').map do |language|
        locale, quality = language.split(';q=')
        raise ArgumentError, 'Not correctly formatted' unless locale =~ /^[a-z\-0-9]+|\*$/i

        locale  = locale.downcase.gsub(/-[a-z0-9]+$/i, &:upcase) # Uppercase territory
        locale  = nil if locale == '*' # Ignore wildcards

        quality = quality ? quality.to_f : 1.0

        [locale, quality]
      end
      locale_quality_array.sort { |(_, left), (_, right)| right <=> left }.map(&:first).compact
    rescue ArgumentError # Just rescue anything if the browser messed up badly.
      []
    end
  end

  # references http_accept_language gem
  def compatible_language_from(available_languages)
    user_preferred_languages.map do |preferred| # en-US
      preferred = preferred.downcase
      preferred_language = preferred.split('-', 2).first

      available_languages.find do |available| # en
        available = available.to_s.downcase
        preferred == available || preferred_language == available.split('-', 2).first
      end
    end.compact.first
  end
end