Category.php

<?php

namespace Category\Command;

use Category\CategoryId;
use Message\AbstractMessage;
use Message\Message;
use Message\MessageId;
use Message\MessageTrait;
use Product\Command\ProductsCommandTrait;

interface Command extends Message
{
    public function categoryId();
}

class CommandId extends MessageId
{
    const ADD_PRODUCTS_TO_CATEGORY      = 'AddProductsToCategory';
    const REMOVE_PRODUCTS_FROM_CATEGORY = 'RemoveProductsFromCategory';
    
    protected static $validNames = [
        self::ADD_PRODUCTS_TO_CATEGORY,
        self::REMOVE_PRODUCTS_FROM_CATEGORY
    ];
}

abstract class AbstractCommand extends AbstractMessage implements Command
{
    use MessageTrait {
        setAggregateRootId as private setCategoryId;
        aggregateRootId as categoryId;
    }
    
    public function __construct(CategoryId $categoryId)
    {
        parent::__construct(new CommandId(static::$messageName));
        $this->setCategoryId($categoryId);
    }
    
    public function __toString()
    {
        return sprintf(
            '%s [categoryId: %s, timestamp: %s]',
            $this->messageName(),
            $this->aggregateRootId ?: 'N/A',
            $this->messageTime()->format('Y-m-d\TH:i:s.u')
        );
    }
}

abstract class AbstractProductsCommand extends AbstractCommand
{
    use ProductsCommandTrait;
    
    protected $productIds;
    
    public function __construct(CategoryId $categoryId, array $productIds)
    {
        parent::__construct($categoryId);
        $this->setProductIds($productIds);
    }
}

class AddProductsToCategoryCommand extends AbstractProductsCommand
{
    final protected static $messageName = CommandId::ADD_PRODUCTS_TO_CATEGORY;
}

class RemoveProductsFromCategoryCommand extends AbstractProductsCommand
{
    final protected static $messageName = CommandId::REMOVE_PRODUCTS_FROM_CATEGORY;
}

Controller.php

<?php

namespace Category\Controller;

use Category\CategoryId;
use Category\Command\CommandId;
use Http\Status;
use Product\ProductId;

class ProductsController
{
    use ControllerTrait;
    
    public function put($id, array $data)
    {
        $categoryId = CategoryId::fromString($id);
        $productIds = $this->getProductIds($data['productIds']);
        $commandId  = $this->commandCenter->issue(
            new AddProductsToCategoryCommand($categoryId, $productIds)
        );
        
        return Status::202(compact('commandId'));
    }
    
    public function delete(array $data)
    {
        $categoryId = CategoryId::fromString($data['categoryId']);
        $productIds = $this->getProductIds($data['productIds']);
        $commandId  = $this->commandCenter->issue(
            new RemoveProductsFromCategoryCommand($categoryId, $productIds)
        );
        
        return Status::202(compact('commandId'));
    }
    
    private function getProductIds(array $dataIds)
    {
        return array_map(function($productId) {
            return ProductId::fromString($productId);
        }, $dataIds);
    }
}

Message.php

<?php

namespace Message;

use DateTime;
use DomainException;

interface Message
{
    public function messageId();
    public function messageName();
    public function messageTime();
}

/**
 * A rich and expressive unique identifier that forms the heart of every message.
 */
class MessageId
{
    protected static $partSeperator = '_';
    protected static $hashAlgorithm = 'crc32';
    protected static $validNames    = [];
    protected $name;
    protected $time;
    protected $hash;
    
    public function __construct($name)
    {
        $this->time = microtime(true);
        $this->name = trim($name);
        $this->hash = hash(static::$hashAlgorithm, rand(0, $this->time));

        if (empty($this->name)) {
            throw new DomainException('Name must not be empty');
        }
        if (!in_array($this->name, static::$validNames)) {
            throw new DomainException("Invalid name [$name]");
        }
    }

    public static function fromString($idString)
    {
        $parts = explode(static::$partSeperator, $idString);
        if (count($parts) != 3) {
            throw new DomainException("Unexpected format [$idString]");
        }
        return static::fromParts($parts[0], $parts[1], $parts[2]);
    }
    
    public static function fromParts($name, $time, $hash)
    {
        $id 	  = new static($name);
        $id->time = floatval($time);
        $id->hash = strval($hash);

        return $id;
    }
    
    public function name()
    {
        return $this->name;
    }
    
    public function time()
    {
        return $this->time;
    }

    public function equals(self $other)
    {
        return ((string) $this == (string) $other);
    }
    
    public function __toString()
    {
        return implode(static::$partSeperator, (array) $this);
    }
}

trait MessageTrait
{
    private function setAggregateRootId($aggregateRootId)
    {
        $this->aggregateRootId = $aggregateRootId;
    }
    
    public function aggregateRootId()
    {
        return $this->aggregateRootId;
    }
    
    public function messageId()
    {
        return $this->messageId;
    }
    
    public function messageName()
    {
        return $this->messageId->name();
    }
    
    public function messageTime()
    {
        return DateTime::createFromFormat('U.u', $this->messageId->time());
    }
}

abstract class AbstractMessage implements Message
{
    protected static $messageName;
    protected $aggregateRootId;
    protected $messageId;
    
    public function __construct(MessageId $messageId = null)
    {
        $this->messageId = $messageId ?: new MessageId(static::$messageName);
    }
    
    public function equals(self $other)
    {
        return $this->messageId->equals($other->messageId);
    }
}

interface MessageBus
{
    public function append(Message $aMessage);
    public function clear();
    public function deliver(Dispatcher $withDispatcher);
}

interface Dispatcher
{
    public function dispatch(Message $aMessage);
}

Product.php

<?php

namespace Product\Command;

use DomainException;
use Product\ProductId;

trait ProductsCommandTrait
{
    public function productIds()
    {
        return $this->productIds;
    }
    
    private function setProductIds(array $productIds)
    {
        $this->productIds = [];
        foreach (array_unique($productIds) as $productId) {
            $this->assertProductId($productId);
            $this->productIds[] = $productId;
        }
    }
    
    private function assertProductId($value)
    {
        if (!($value instanceof ProductId)) {
            $message = sprintf(
                'Expected ProductId, not %s',
                is_object($value) ? get_class($value) : gettype($value)
            );
            throw new DomainException($message);
        }
    }
}