Alternative refactor for https://avdi.codes/service-objects/

ipn.rb

class DbGateway
  def add_ipn(email, params)
    DB[:ipns].insert(email_address: email, data: Sequel.pg_json(params)
  end

  def generate_redemption_token(email)
    SecureRandom.hex.tap do |t|
      DB[:tokens].insert(email_address: email, value: t)
    end
  end
end

class MailService
  def send_claim_purchase_email(email, token)
    subject = "Claim your purchase!"
    redemption_url_template =
      Addressable::Template.new("#{request.base_url}/redeem?token={token}")
    email_template = Tilt.new("templates/welcome_email.txt.erb")
    contact_email  = "contact@example.com"
    redemption_url = redemption_url_template.expand("token" => token)
    body           = email_template.render(Object.new,
      login_url:     redemption_url,
      contact_email: contact_email)

    # Send the email
    Pony.mail(to: email,
      from: contact_email,
      subject: subject,
      body: body,
      via: :smtp,
      via_options: settings.email_options)
    end
  end
end

#######

set :db, DbGateway.new
set :mail_service, MailService.new

post "/ipn" do
  demand_basic_auth
  email = params.fetch("payer_email") { "<MISSING_EMAIL>" }
  settings.db.add_ipn(email, params)
  token = settings.db.generate_redemption_token(email)
  settings.mail_service.send_claim_purchase_email(email, token)
  [202, "Accepted"]
end