Undo feature based on event history

[graste]

Implementing some sort of generic undo feature is imho feasible. First ideas:

1. Listen to events extending AggregateRootModifiedEvent
2. Deliver those events via server-sent events or similar to web clients
3. Let a widget act upon the event depending on the context the user is currently in by displaying a "Undo this?" activity
4. Trigger building and dispatching a compensating undo command based upon the event

Instead of delivering the events via server-sent events or websockets it's maybe more advisable to have a widget that works e.g. with localstorage and pulls recent events and displays those on click and allows to undo certain events of those.

The undo command needs to be based on the modified event and should e.g. revert a value change.

An extension of the above clientside javascript based stuff could be to improve the history view for ARs and implement e.g. a "rollback to this revision" or "merge changes of this revision onto head revision". Giving a UI to only pick certain attributes or values would probably be overkill for most applications.