ADR for Visit Notifications

docs/adr/0014-visits-notifications.md

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+# 0014 - Visit Notifications
+
+Decision date: 2025-03-04
+
+## Status
+
+Decision status: Accepted
+
+## Context
+
+Private prisons are now required to provide a copy of data they collect to the MoJ, 
+and this includes data on visits.
+
+HMPPS have a general preference for all visits to be booked through DPS, though with
+a recognition that this may not always be practical.
+
+A number of options were considered for implemented the integration points required to
+support this...
+
+1. DPS Visits Led - Nexus is a front end (get available slots from DPS and choose one of those)
+2. Nexus Led - send to DPS (DPS service accepts whatever visit Nexus provides)
+3. Nexus Led - send to NOMIS (Same but send visits into NOMIS)
+4. Nexus Led - send to other database (Same but send visits into a new data store)
+
+## Decision
+
+We will proceed with option 2 in the short term, and allow for implementation of option 1
+in future.
+
+A new API will be created that will receive a Visit notification, perform some basic
+synchronous validation, and then queue the notification for asynchronous processing by DPS. 
+
+### Rationale
+
+Options 3 and 4 were quickly rejected: #3 directly includes NOMIS integration which would need 
+to be replaced anyway, and #4 involves the creation of an entirely new, and unnecessary, component. 
+
+Option 1 is the overall MoJ architecture preference, but it is accepted that this is likely more
+development effort for all parties, and it is unlikely that we will be able to enforce it for
+all prisons anyway. 
+
+It will be challenging to implement option 1 in a manner that complies with our asynchronous
+writes policy. This would be a new integration pattern for HMPPS.
+
+It is anticipated that in the long run both #1 and #2 will be supported, with option #1 being
+the HMPPS preferred approach.
+
+Option 2 also offers the most flexibility for API clients, particularly if option 1 is added later.
+
+## Consequences
+
+* DPS will have to accept whatever visit information is sent, as long as it passes the initial
+  synchronous validation performed by the Integration API.
+* The prison provider system must not book the visit if the initial synchronous validation fails.
+* Any problems encountered when processing the notification after the initial synchronous 
+  validation and response will be the responsibility of HMPPS and not the prison provider.
+* It will be significantly harder for the private prison system and HMPPS to provide guarantees of 
+  capacity and lack of conflicts due visits being booked in multiple systems.
+* Does not stop private prisons implementing visits that go against national policy. 
+
+## Supporting Documentation
+
+* [Discussion Document, Google Docs](https://docs.google.com/document/d/1NA9OzNn6GEBQZCc1Ba4dllOZLwXK_NTM2uZdC607oJg/edit?tab=t.0#heading=h.exkvg6tmp7ez)
+* [Integration API schema for Visit](https://ministryofjustice.github.io/hmpps-integration-api/documentation/api/index.html#schema-dataresponsevisit)
+* [Visits implementation epic](https://dsdmoj.atlassian.net/browse/HMAI-2)