sage.ex

defmodule SageExample do
  import Sage
  require Logger

  # It is better to build Saga struct in a module attribute, 
  # we don't need to spend resources each time we want to execute it
  @create_and_subscribe_user_sage 
    new()
    |> run(:user, &create_user/2)
    |> run(:plans, &fetch_subscription_plans/2)
    |> run(:subscription, &create_subscription/2, &delete_subscription/3)
    |> run_async(:delivery, &schedule_delivery/2, &delete_delivery_from_schedule/3)
    |> run_async(:receipt, &send_email_receipt/2, &send_excuse_for_email_receipt/3)
    |> run(:update_user, &set_plan_for_a_user/2)
    |> finally(&acknowledge_job/2)

  def create_and_subscribe_user(attrs) do
    Sage.transaction(@create_and_subscribe_user_sage, Repo, attrs)
  end

  # Transaction callback receives previously created effects 
  # and attributes passed to `execute/2` or `transaction/3`
  def create_user(_effects, attrs) do
    # We can use raw insert if we expect Sage to be wrapped in a transaction,
    # because DB-related effects would be compensated on transaction rollback
    Repo.insert(%SageExample.User{login: attrs["login"], password: attrs["password"]})
  end
  
  # .. other transaction callbacks

  # Steps have access to effects created on previous steps
  def create_subscription(%{user: user}, attrs) do
    BillingAPI.subscribe_user(user, plan: attrs["plan"])
  end

  # If we failed on this step because of timeout of external service, let's keep retrying
  def delete_subscription(nil, {:subscription, _reason}, _attrs) do
    {:retry, retry_limit: 5}
  end

  # Cleanup effect created by create_subscription/2
  def delete_subscription(_subscription_or_nil, _errorred_step_name_and_reason, _attrs) do
    Logger.error("Failed to create subscription because of #{inspect(reason)}")
    # We must delete all subscriptions for a newly created user,
    # because we don't know if it was actually created on third-party service or not
    BillingAPI.Subscription.delete_all_by_email(attrs["email"])
  end

  # .. other transaction callbacks

  def acknowledge_job(:ok, attrs) do
    Logger.info("Successfully created user #{attrs["email"]}")
  end

  def acknowledge_job(_error, attrs) do
    Logger.warn("Failed to create user #{attrs["email"]}")
  end
end