4.ts

const processUser = functions.firestore
  .document("accounts/{accountId}/users/{userId}")
  .onCreate(async (snapshot, context) => {
    try {
      await processTheUser(snapshot);
      const event = new UserProcessed(snapshot);
      await new Account(context.params.accountId).addEvent(event);
    } catch (error) {
      const event = new UserProcessingFailed(snapshot, error);
      await new Account(context.params.accountId).addEvent(event);
    }
  })