You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: one_signal_notification_service.rb
    path of file: ./repos/kitsu-server/app/services
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class OneSignalNotificationService
  class OneSignalError < StandardErro
    
  def params_for(platform)
    params = {
      app_id:,
      contents: { en: notification.message },
      external_id: external_id_for(platform)
    }
    case platform
    when :mobile
      params[:ios_badgeType] = 'Increase'
      params[:ios_badgeCount] = 1
      params[:data] = notification.reference
    when :web
      params[:url] = notification.url
    end