Event listener filenames

[sldblog]

Short problem statement; why is this a problem?

We have a few strategies to name our listeners. We should explicitly pick one or guide when to pick one or the other.

The typical "find" pattern is "what happens after {event}", so naming should probably support that use case.

Link to different approaches

1. One file per multiple listeners listening to the same event; the file is named after the event:

   hmpps-interventions-service/src/main/kotlin/uk/gov/justice/digital/hmpps/hmppsinterventionsservice/service/listeners/ReferralConcludedListener.kt

   Lines 19 to 22 in d1f7c15

   	@Service
   	class ReferralConcludedListener(
   	private val snsPublisher: SNSPublisher,
   	) : ApplicationListener<ReferralConcludedEvent>, SNSService {

   hmpps-interventions-service/src/main/kotlin/uk/gov/justice/digital/hmpps/hmppsinterventionsservice/service/listeners/ReferralConcludedListener.kt

   Lines 63 to 70 in d1f7c15

   	@Service
   	class ReferralConcludedIntegrationListener(
   	@Value("\${interventions-ui.baseurl}") private val interventionsUIBaseURL: String,
   	@Value("\${interventions-ui.locations.probation-practitioner.end-of-service-report}") private val ppEndOfServiceReportLocation: String,
   	@Value("\${community-api.locations.notification-request}") private val communityAPINotificationLocation: String,
   	@Value("\${community-api.integration-context}") private val integrationContext: String,
   	private val communityAPIClient: CommunityAPIClient,
   	) : ApplicationListener<ReferralConcludedEvent>, CommunityAPIService {

2. One file per listener; the file is named after what it is doing:

   hmpps-interventions-service/src/main/kotlin/uk/gov/justice/digital/hmpps/hmppsinterventionsservice/service/listeners/ReferralMetricsListener.kt

   Lines 18 to 22 in d1f7c15

   	@Service
   	class ReferralMetricsListener(
   	val registry: MeterRegistry,
   	val repository: ReferralRepository,
   	) : ApplicationListener<ReferralEvent> {

3. One huge service file, with several @Service classes for doing similar things; the file is named after the "similar thing":

   hmpps-interventions-service/src/main/kotlin/uk/gov/justice/digital/hmpps/hmppsinterventionsservice/service/SNSService.kt

   Lines 22 to 25 in d1f7c15

   	@Service
   	class SNSActionPlanService(
   	private val snsPublisher: SNSPublisher,
   	) : ApplicationListener<ActionPlanEvent>, SNSService {

   hmpps-interventions-service/src/main/kotlin/uk/gov/justice/digital/hmpps/hmppsinterventionsservice/service/SNSService.kt

   Lines 54 to 57 in d1f7c15

   	@Service
   	class SNSReferralService(
   	private val snsPublisher: SNSPublisher,
   	) : ApplicationListener<ReferralEvent>, SNSService {

   hmpps-interventions-service/src/main/kotlin/uk/gov/justice/digital/hmpps/hmppsinterventionsservice/service/SNSService.kt

   Lines 88 to 91 in d1f7c15

   	@Service
   	class SNSActionPlanAppointmentService(
   	private val snsPublisher: SNSPublisher,
   	) : ApplicationListener<ActionPlanAppointmentEvent>, SNSService {

Do you have a proposed solution? Why?

Looking back, working with SNSService.kt was weird. Changes in events rippled over to several listener files.

Working with enums within the events probably does not help, as switches would start adding new warnings for not covering all cases or default to not doing anything. Using ReferralSentEvent would be better than ReferralEvent(type=SENT, ...).

In general, though, we should pick one and stick to it.