Refactor to use amphp and event-store v8

[prolic]

[WIP] knitted with a hot needle - some changes / bugfixes may be required before merge

• This makes prooph/micro even smaller (only 2 files with less than 200 LOC combined).
• 100% async using amphp
• compatible with event-store v8 (async)
• Support async aggregate handlers

How to use this?

• extend a class from CommandSpecification, see f.e. UserSpecification in the examples dir
• add a command map and create dispatcher, see f.e. register_and_change_username.php in the examples dir

Todos:

• Write Tests
• Support Snapshots (see Add snapshot support #53)
• Support Event Publishing
• Documentation (see Update Documentation #52)

ping @codeliner @enumag

As the kernel returns an immutable list of all emitted events, you can simply publish them yourself however you like, that's event a dedicated event publisher will not be part of this. Also in most cases you would rely on event store projections to be running anyway.

[enumag]

Shouldn't this return Promise<bool> now?

[prolic]

yes

[enumag]

I like that these functions are now async and as such can use async guards. But I'm slightly doubtful about it resolving to an ImmList of event. In my project I let them return an asynchronous Iterator instead. What is your thought about that?

Note: Code examples assume that UniqueEmailGuard returns a Promise. Also I highly prefer to use the convention of handling error cases first with early return, leaving the happy scenario as main branch so I negated the condition.

function registerUser(callable $stateResolver, RegisterUser $command, UniqueEmailGuard $guard): Iterator
{
    return new Producer(function (callable $emit) use ($command, $guard): Generator {
        if (! yield $guard->isUnique($command->email())) {
             yield $emit(new UserRegisteredWithDuplicateEmail($command->payload()));
             return;
        }
        
        yield $emit(new UserRegistered($command->payload()));
    });
}

Admittedly while pure code should return Amp\Iterator here, I later decided that I don't like the Producer + $emit syntax so I actually let these functions return Generator<Promise|EventInterface>. Then there is a wrapper function that transforms it into \Amp\Iterator<EventInterface>. I consider such syntactic improvement as acceptable over code purity for my project although not sure if it's suitable for an example like this... But I'll show it to you anyway for comparison:

function registerUser(callable $stateResolver, RegisterUser $command, UniqueEmailGuard $guard): Generator
{
    if (! yield $guard->isUnique($command->email())) {
         yield new UserRegisteredWithDuplicateEmail($command->payload());
         return;
    }

    yield new UserRegistered($command->payload());
}

The wrapper function looks something like this:

function transform(Generator $generator): Iterator
{
    return new Producer(function (callable $emit) use ($generator) {
        foreach ($generator as $eventOrPromise) {
            if ($eventOrPromise instanceof Promise) {
                yield $eventOrPromise;
            } else {
                yield $emit($eventOrPromise);
            }
        }
    });
}

[prolic]

awesome, thanks !!

[prolic]

@enumag I ran into issues with this. On yield $eventOrPromise; the promises is yielded, but not assigned to the variable in the handler function.
$state = yield $stateResolver(); results in $state = null.

[enumag]

Ah yeah... sorry, I copy pasted a wrong function. I'll post the correct one tomorrow.

[prolic]

thanks

[prolic]

maybe can you directly submit a PR to this branch?

[prolic]

@enumag changes done

[codeliner]

@prolic the implementation looks really great. Hopefully I find some time to try it out. I'd also look at a way to connect Event Engine Cockpit to it.

[enumag]

Suggested change

	foreach ($specification->handle(stateResolver($eventStore, $specification, $readBatchSize)) as $eventOrPromise) {
	if ($eventOrPromise instanceof Promise) {
	yield $eventOrPromise;
	} else {
	yield $emit($eventOrPromise);
	}
	}
	$generator = $specification->handle(stateResolver($eventStore, $specification, $readBatchSize));
	while ($generator->valid()) {
	$eventOrPromise = $generator->current();
	if ($eventOrPromise instanceof Promise) {
	$generator->send(yield $eventOrPromise);
	} else {
	yield $emit($eventOrPromise);
	$generator->next();
	}
	}

[enumag]

@prolic This should work I think. ;-)

[prolic]

Awesome, thank you.

[prolic]

I added new issues for snapshot support and documentation. I'll merge this to master.