To roll back a user (simple structure, could be way more complex)

rollback.go

// Handles the rollback to a previous document
func handleRollbackUser(ctx context.Context, e FirestoreEvent) error {
	// This can be grabbed from split of e.OldValue.Name
	clientDoc := client.Collection("users").Doc(strings.Split(e.OldValue.Name, "/")[6])

	// Again, you have to
	type NewUser struct {
		Username   string `json:"userId"`
		Email      string `json:"email"`
		DateEdited int64  `json:"date_edited"`
	}

	// Might crash on this
	newDate, err := strconv.Atoi(e.OldValue.Fields.DateEdited.IntegerValue)
	if err != nil {
		return err
	}

	translatedUser := NewUser{
		Username:   e.OldValue.Fields.Username.StringValue,
		Email:      e.OldValue.Fields.Email.StringValue,
		DateEdited: int64(newDate),
	}

	setter, err := clientDoc.Set(ctx, translatedUser)
	if err != nil {
		return err
	}

	log.Printf("Successfully updated document. Data: %#v", setter)
	return errors.New("Should have rolled back to a previous version")
}