Add event-sourcing Events

[stevenvegt]

To introduce tracibility we introduce event logs which can be used for event sourcing. The Nuts Event Octopus will provide the generic infrastructure. Specific engines will provide the data types used for encoding engine events.

A generic event-souring event consists fo the following fields: Field name	type	comment
EventID	string	sha1 of the byte value of the subsequent fields
AggregateID	string
AggregateType	string
Timestamp	int	Time in seconds since unix epoch
CausedBy	string	Nuts identity
Data	string	JSON Object with which has meaning for the subscribed party

The current primary use-case is the consent store.

• The store can subscribe to events of the aggregateType Consent
• The store can replay/fetch all events for a specific AggregateID
• The vendor can subscribe to get informed when a new consent has been created
• The vendor can subscribe to get informed when a new consent must be signed

Event Octopus should be able to

• Broadcast an event
• Let clients subscribe to an event stream based on an AggregateType
• Store the events on disk or in memory
• Replay a set of events for a certain AggregateID

[woutslakhorst]

Replaying from an AggregateID might be difficult todo with Nats. It's more sort-of a by type replay...

[stevenvegt]

Octpus needs a extra datastore like reddis for that. Than its just an array per aggregateId.

[woutslakhorst]

Octpus needs a extra datastore like reddis for that. Than its just an array per aggregateId.

that would mean you have to implement the event sourcing yourself with reddis as backend on aggregateId level. Nats would only be able to replay on type level?