Merge pull request #11 from shouze/introduce-aggregate-root-and-change-classes

💄 Introduce AggregateRoot & Change classes.

Author: shouze

src/Domain/Vehicle.php

@@ -3,7 +3,7 @@
 
 namespace Shouze\ParkedLife\Domain;
 
-class Vehicle
+final class Vehicle
 {
     private $platenumber;
 

src/Domain/VehicleFleet.php

@@ -3,15 +3,16 @@
 
 namespace Shouze\ParkedLife\Domain;
 
-class VehicleFleet
-{
-    private $userId;
+use Shouze\ParkedLife\EventSourcing\AggregateRoot;
+use Shouze\ParkedLife\EventSourcing\Change;
 
+final class VehicleFleet extends AggregateRoot
+{
     private $vehicles = [];
 
     public function __construct(UserId $userId)
     {
-        $this->userId = $userId;
+        parent::__construct((string)$userId);
     }
 
     public static function ofUser(UserId $userId): VehicleFleet
@@ -21,30 +22,23 @@ public static function ofUser(UserId $userId): VehicleFleet
 
     public function registerVehicle(string $platenumber, string $description)
     {
-        $changes = [
-            new VehicleWasRegistered($platenumber, (string)$this->userId),
-            new VehicleWasDescribed($platenumber, $description)
-        ];
-
-        foreach ($changes as $change) {
-            $handler = sprintf('when%s', implode('', array_slice(explode('\\', get_class($change)), -1)));
-            $this->{$handler}($change);
-        }
+        $this->record(new VehicleWasRegistered($this->getAggregateId(), $platenumber));
+        $this->record(new VehicleWasDescribed($this->getAggregateId(), $platenumber, $description));
 
         return $this->vehicleWithPlatenumber($platenumber);
     }
 
-    public function whenVehicleWasRegistered($change)
+    public function whenVehicleWasRegistered(VehicleWasRegistered $change)
     {
-        $this->vehicles[] = Vehicle::register($change->getPlatenumber(), new UserId($change->getUserId()));
+        $this->vehicles[] = Vehicle::register($change->getPlatenumber(), new UserId($change->getAggregateId()));
     }
 
     public function describeVehicle(string $platenumber, string $description)
     {
-        $this->whenVehicleWasDescribed(new VehicleWasDescribed($platenumber, $description));
+        $this->record(new VehicleWasDescribed($this->getAggregateId(), $platenumber, $description));
     }
 
-    public function whenVehicleWasDescribed($change)
+    public function whenVehicleWasDescribed(VehicleWasDescribed $change)
     {
         $vehicle = $this->vehicleWithPlatenumber($change->getPlatenumber());
         $vehicle->describe($change->getDescription());
@@ -93,7 +87,7 @@ function ($carry, Vehicle $v) use ($platenumber) {
         );
 
         if (null === $vehicle) {
-            throw new \LogicException(sprintf('Vehicle with plate number %s is unknown in fleet #%s', $platenumber, $this->userId));
+            throw new \LogicException(sprintf('Vehicle with plate number %s is unknown in fleet #%s', $platenumber, $this->getAggregateId()));
         }
 
         return $vehicle;

src/Domain/VehicleWasDescribed.php

@@ -3,18 +3,28 @@
 
 namespace Shouze\ParkedLife\Domain;
 
-final class VehicleWasDescribed
+use Shouze\ParkedLife\EventSourcing\Change;
+
+final class VehicleWasDescribed implements Change
 {
+    private $userId;
+
     private $platenumber;
 
     private $description;
 
-    public function __construct(string $platenumber, string $description)
+    public function __construct(string $userId, string $platenumber, string $description)
     {
+        $this->userId = $userId;
         $this->platenumber = $platenumber;
         $this->description = $description;
     }
 
+    public function getAggregateId(): string
+    {
+        return $this->userId;
+    }
+
     public function getPlatenumber(): string
     {
         return $this->platenumber;

src/Domain/VehicleWasRegistered.php

@@ -3,25 +3,27 @@
 
 namespace Shouze\ParkedLife\Domain;
 
-final class VehicleWasRegistered
-{
-    private $platenumber;
+use Shouze\ParkedLife\EventSourcing\Change;
 
+final class VehicleWasRegistered implements Change
+{
     private $userId;
 
-    public function __construct(string $platenumber, string $userId)
+    private $platenumber;
+
+    public function __construct(string $userId, string $platenumber)
     {
-        $this->platenumber = $platenumber;
         $this->userId = $userId;
+        $this->platenumber = $platenumber;
     }
 
-    public function getPlatenumber(): string
+    public function getAggregateId(): string
     {
-        return $this->platenumber;
+        return $this->userId;
     }
 
-    public function getUserId(): string
+    public function getPlatenumber(): string
     {
-        return $this->userId;
+        return $this->platenumber;
     }
 }

src/EventSourcing/AggregateRoot.php

@@ -0,0 +1,70 @@
+<?php
+
+namespace Shouze\ParkedLife\EventSourcing;
+
+abstract class AggregateRoot
+{
+    private $aggregateId;
+
+    private $recordedChanges = [];
+
+    protected function __construct(string $aggregateId)
+    {
+        // Use named constructor as it made event sourcing and ubiquitous language easier
+        $this->aggregateId = $aggregateId;
+    }
+
+    public function getAggregateId(): string
+    {
+        return $this->aggregateId;
+    }
+
+    public static function reconstituteFromHistory(\Iterator $history)
+    {
+        $aggregateRoot = new static($history->getAggregateId());
+
+        foreach ($history as $change) {
+            $aggregateRoot->apply($change);
+        }
+
+        return $aggregateRoot;
+    }
+
+    public function popRecordedChanges(): \Iterator
+    {
+        $pendingChanges = $this->recordedChanges;
+
+        $this->recordedChanges = [];
+
+        return $pendingChanges;
+    }
+
+    protected function record(Change $change)
+    {
+        $this->recordedChanges[] = $change;
+        $this->apply($change);
+    }
+
+    private function apply(Change $change)
+    {
+        $handler = $this->resolveEventHandlerMethodFor($change);
+
+        if (false === method_exists($this, $handler)) {
+            throw new \RuntimeException(sprintf(
+                "Missing event handler method %s for aggregate root %s",
+                $handler,
+                get_class($this)
+            ));
+        }
+
+        $this->{$handler}($change);
+    }
+
+    /**
+     * For an event named ProductWasRegistered will look for method `whenProductWasRegistered`
+     */
+    private function resolveEventHandlerMethodFor(Change $change)
+    {
+        return 'when' . implode('', array_slice(explode('\\', get_class($change)), -1));
+    }
+}

src/EventSourcing/Change.php

@@ -0,0 +1,9 @@
+<?php
+declare(strict_types=1);
+
+namespace Shouze\ParkedLife\EventSourcing;
+
+interface Change
+{
+    public function getAggregateId();
+}