gistfile1.rb

# controller
class MyController < ApplicationController
  TEMPLATE_ID = "TEMPLATE_ID"

  def create
    authorize ...

    if send_email
      redirect_to @referer, success: success_message
    else
      redirect_to @referer, error: error_message
    end
  end

  private

  def set_case_attachable
    ...
  end

  def send_email
    ...
    Notify::Email.new(
      client_email: "email@email.com",
      template_id: TEMPLATE_ID,
      ...
    ).deliver_now
  end

  def magic_link_url(name, gid)
    ...
  end

  def success_message
    ...
  end

  def error_message
    ...
  end
end

# PORO
module Notify
  class Email
    include PoroAttributes

    NOTIFY_API_KEY = SOME_KEY

    attribute :client_email
    attribute :template_id
    attribute :personalisation, default: -> {}

    def deliver_now
      send_email
    rescue Notifications::Client::RequestError
      raise # Retry elsewhere
    end

    private

    def send_email
      notify.send_email(...)
    end

    def notify
      @notify ||=
        ExternalLibrary::Client.new(SOME_API_KEY)
    end
  end
end