S-Flow - Event sourcing example

Order.php

<?php
declare(strict_types=1);

final class Order
{
    /** @var Event */
    private $events;
    /** @var State */
    private $state;

    public function __construct(Events $events)
    {
        $this->events = $events;
        $this->state = $this->buildState($events);
    }

    public function getEvents(): Events
    {
        return $this->events;
    }

    public function getState(): State
    {
        return $this->state;
    }

    private function buildState(Events $events): State
    {
        $transitionOp = $this->fsm()->run(new S\NoItems, $events);

        if ($transitionOp->isSuccess() === false) {
            throw new RuntimeException(
                sprintf(
                    'Invalid transition: from %s via %s',
                    $transitionOp->getState()::name()->unWrap(),
                    $transitionOp->getLastEvent()::name()->unWrap()
                )
            );
        }

        return $transitionOp->getState();
    }

    private function fsm(): FSM
    {
        $labels = [
            S\NoItems::name(),
            S\HasItems::name(),
            S\NoCard::name(),
            S\CardSelected::name(),
            S\CardConfirmed::name(),
            S\OrderPlaced::name(),
        ];

        $arrows = [
            (new Arrow(E\Select::name()))->from(S\NoItems::name())->via(new T\AddFirstItem),
            (new Arrow(E\Select::name()))->from(S\HasItems::name())->via(new T\AddItem),
            (new Arrow(E\Checkout::name()))->from(S\HasItems::name())->via(new T\DoCheckout),
            (new Arrow(E\SelectCard::name()))->from(S\NoCard::name())->via(new T\DoSelectCard),
            (new Arrow(E\Confirm::name()))->from(S\CardSelected::name())->via(new T\ConfirmCard),
            (new Arrow(E\PlaceOrder::name()))->from(S\CardConfirmed::name())->via(new T\DoPlaceOrder),
            (new Arrow(E\Cancel::name()))->from(S\NoCard::name())->via(new T\DoCancel),
            (new Arrow(E\Cancel::name()))->from(S\CardSelected::name())->via(new T\DoCancel),
            (new Arrow(E\Cancel::name()))->from(S\CardConfirmed::name())->via(new T\DoCancel),
        ];

        return new FSM((new Graph(...$labels))->drawArrows(...$arrows));
    }
}

run.php

<?php
declare(strict_types=1);

// Get the events (eg. from the DB)
$events = new Events(
    new E\Select(new Item('foo')),
    new E\Select(new Item('bar')),
    new E\Select(new Item('baz')),
    new E\Checkout,
    new E\SelectCard(new Card('Visa', '1234567812345678')),
    new E\Confirm,
    new E\PlaceOrder
);

// Build the entity
$order = new Order($events);

\assert($order->getState() instanceof S\OrderPlaced); // true