Defer Event (de)normalization

[bwaidelich]

Currently events are converted to an EventEnvelope instance (with RawEvent and the denormalized DomainEventInterface instance) when iterating an event stream.

Instead the denormalization should only happen when actually required (i.e. when invoking the corresponding when*() method).

[bwaidelich]

Some more thoughts I had on this one:
IMO the notion of DomainEvent should be removed completely from the Event Store "sub package" so that it can be simplified to sth like:

final class Event {
    public function __construct(string $identifier, string $type, array $data, array $metadata)
}

(currently WriteableEvent)
when committing events, and:

final class EventEnvelope {
    public function __construct(Event $event, StreamName $streamName, int $version, int $sequenceNumber, \DateTimeInterface $recordedAt)
}

when reading events.

The conversion from and to DomainEventInterface instances would happen outside of the Event Store part (and only as soon as required, if at all)

[bwaidelich]

As for the reasoning:

• Increase performance
• Allow Event Store part to be used for different (low level) purposes that don't require Domain Event instances
• Simplify ES code

[bwaidelich]

An additional reason:

It's a major design flaw that EventStorageInterface::load() returns an EventStream (https://github.com/neos/Neos.EventSourcing/blob/master/Classes/EventStore/Storage/EventStorageInterface.php#L32) since the event stream requires an instance of the EventNormalizer (https://github.com/neos/Neos.EventSourcing/blob/master/Classes/EventStore/EventStream.php#L43)

=> for custom event type converters etc. we always have to create a dedicated EventStorage instance and the factory won't support that out of the box