event-sourcing-example.php

<?php

interface DatabaseDriver {
    public function save(string $data);
}

abstract class AbstractPersistence {

    private $driver;

    public function setDriver(DatabaseDriver $driver) {
        $this->driver = $driver;
    }

    protected function saveEvent(EventInterface $event) {
        $this->driver->save($event->serialize());
    }

    protected function getByReference(array $where) {
        $this->driver->findBy($where);
    }
}

class Wallet extends AbstractPersistence
{

    private $id;

    private $value;

    public function __construct(int $id) {
        $this->id = $id;
        $this->value = 0.0;
    }

    public function handle(WalletEvent $event) {
        if ($event->getType() === WalletEvent::EVENT_DEPOSIT) {
            $this->addFunds($event->getValue());
        } else if ($event->getType() === WalletEvent::EVENT_WITHDRAW) {
            $this->removeFunds($event->getValue());
        }
    }

    public function handleAndSave(WalletEvent $event) {
        if ($event->getType() === WalletEvent::EVENT_DEPOSIT) {
            $this->saveEvent($event);
            $this->addFunds($event->getValue());
        } else if ($event->getType() === WalletEvent::EVENT_WITHDRAW) {
            $this->saveEvent($event);
            $this->removeFunds($event->getValue());
        }
    }

    private function addFunds(float $value) {
        $this->value += $value;
    }

    private function removeFunds(float $value) {
        $this->value -= $value;
    }

    public static function fromDatabase($walletId) {
        $data = $this->getByReference(['walletId' => $walletId]);
        $wallet = new self($walletId);
        foreach ($data as $event) {
            $wallet->handle($event);
        }
        
        return $wallet;
    }
}

interface EventInterface extends Serializable{}

interface WalletEvent extends EventInterface {

    public const EVENT_DEPOSIT = 'deposit';
    public const EVENT_WITHDRAW = 'withdraw';

    public function getType(): string;

    public function getValue(): float;
}