instance events

[matt-beanland]

As per #8 we want to support TMF Service and Resource events. These will be ash resources which will be related to the firing instance, and chained. They will render as json in TMF format.

We'll want a domain API to return the most recent event/s.

Eventually we will want an action which checks if an event should be fired, and if so fires it. It will do this using the most recently fired event, compared with the current state of the instance. Need to think about how this relates to the instance version. The version should be incremented if the json rendering of the instance changes, we could do by storing hash and/or serialised json.

Initially we can just create a method to fire an event and call it on create/state/value change actions.

TMF events must have:
eventId (we can use a uuid, would be good to use uuid7 since sortable in time order
eventTime
eventType
event

Where event is service: {}, resource: {}

eventType for service:
serviceCreateEvent
serviceStateChangeEvent
serviceAttributeValueChangeEvent
serviceDeleteEvent

where any state/status change causes serviceStateChangeEvent

resource is same except prefixed by resource, not service.

..DeleteEvent just includes the id/href, not the entire (ex) service/resource.

NaaS has serviceOperatingStateChangeEvent and serviceProcessStatusChangeEvent but these are non-standard.
We will make serviceCreateEvent on initial create, not on state change to target state.

[matt-beanland]

I'm not sure we need to be able to traverse from the Event back to the instance, since the Event is a snapshot of an instance and the instance may have been deleted.

[matt-beanland]

Did some work on this, need to write event_test.exs

[matt-beanland]

Wrote event_test, also did some work on outstanding and json implementations. Still need to implement event chaining mechanism. We want to be able to traverse chain from instance to earlier events, but we don't need to go the other way. We will something like change manage_relationships to manage the chaining, since we want to be able to create an event which inserts itself into the head of the instance event chain such that (n:Instance) -[FIRED]->(new:event)-[AFTER]-> (earlier:Event).

[matt-beanland]

AshNeo4j has Service|Resource FIRED Event however Service|Resource has_many events.
AshNeo4j also has a Chain resource, which implements a chain where each link has a head and tail link.
We'll want to find which event an instance has FIRED if any, then update that event_id to remove the instance. We'll want to create the new event with a tail_id of the original head_id, and with the instance_id. We need to update two things.

[matt-beanland]

Worked out how to use the builtin present validator with exactly to ensure that an event is linked to either an instance or a head event.
Added a chain method, ideally this would be called from the create, but acting on any event currently linked to the instance.

[matt-beanland]

Made the instance - event relationship exclusive on the instance by adding has_one relationship, rather than no relationship. Chain is now simpler as you don't need to pass in the instance to remove the relationship, since it is automatically removed. There is a warning here with Diffo.Test.Shelf and Diffo.Test.Card (fragments, instance extension, since they expect Diffo.Provider.Event to have shelf_id, card_id.

Would like to make chain not needed, since we can add the tail in the create by finding out if there is an existing event on the instance.

Also want to serialise the instance and store that on event creation, rather than take it from the linked instance, as later there will not be one.

[matt-beanland]

Worked on this some more, added fire_event to the instance so that it can create the event and do all the work of snapshotting and chaining. Will need to snap the instance Jason into a Jason.Fragment. The instance has_one event, and the event belongs_to the instance.
fire_event will need a custom change to do this using Ash.Changeset.manage_relationship/4

[matt-beanland]

Worked on this today, improved the Event.create to get the Jason.Fragment working.
Added Diffo.Changes.DetailEvent custom change which is called by BaseInstance fire_event action to populate the event in the changeset (it will have the event type and nothing else) with information from the Instance. Works well, fire event manage relationship does the rest, and the event is successfully fired, and if not the first it is chained at the head.