create_subscription_nested.ex

def create_subscription(email, plan_id, payment_method_id) do
  case Repo.get_by(User, email: email) do
    %User{customer_id: nil, name: name} = user ->
      params = %{
        name: name,
        email: email,
        payment_method: payment_method_id,
        invoice_settings: %{
          default_payment_method: payment_method_id
        }
      }

      case Stripe.Customer.create(params) do
        {:ok, %Stripe.Customer{id: customer_id}} ->
          case Stripe.Subscription.create(%{
                 customer: customer_id,
                 items: [%{plan: plan_id}]
               }) do
            {:ok, %Stripe.Subscription{id: subscription_id}} ->
              case User.update(user, %{
                     customer_id: customer_id,
                     subscription_id: subscription_id
                   }) do
                {:ok, %User{}} ->
                  {:ok, :subscription_created}

                {:error, _} ->
                  {:ok, :user_update_error}
              end

            {:error, %Stripe.Error{}} ->
              {:error, :create_subscription_error}
          end

        {:error, %Stripe.Error{}} ->
          {:error, :create_customer_error}
      end

    %User{customer_id: customer_id} when is_binary(customer_id) and customer_id != "" ->
      {:error, :customer_exists_error}

    nil ->
      {:error, :unknown_user_error}

    _ ->
      {:error, :user_lookup_error}
  end
end