feat(core): Implement DDD, CQRS, and Event Sourcing architecture

- Add project README and Composer configuration with PSR-4 autoloading
- Implement domain layer with AggregateRoot base class for event sourcing
- Create Carrier aggregate with CarrierRegistered domain event
- Add application layer with RegisterCarrierCommand and RegisterCarrierHandler
- Implement infrastructure layer with EventStore interface and CassandraEventStore
- Add CommandBus and Router for request handling and routing
- Create demo test file to showcase carrier registration workflow
- Establish foundation for event-driven architecture with Cassandra persistence

README.md

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+# Distributing Carriers
+
+Distributing Carriers Application.

composer.json

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+{
+    "name": "mamad/distributing-carriers",
+    "description": "Distributing Carriers Application with DDD, CQRS, and Event Sourcing",
+    "type": "project",
+    "require": {
+        "php": "^8.0",
+        "ext-cassandra": "*"
+    },
+    "autoload": {
+        "psr-4": {
+            "DistributingCarriers\\": "src/"
+        }
+    },
+    "authors": [
+        {
+            "name": "Mamad",
+            "email": "mamad@example.com"
+        }
+    ]
+}

src/Application/Commands/RegisterCarrierCommand.php

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+<?php
+
+namespace DistributingCarriers\Application\Commands;
+
+class RegisterCarrierCommand
+{
+    public $name;
+    public $email;
+
+    public function __construct(string $name, string $email)
+    {
+        $this->name = $name;
+        $this->email = $email;
+    }
+}

src/Application/Handlers/RegisterCarrierHandler.php

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+<?php
+
+namespace DistributingCarriers\Application\Handlers;
+
+use DistributingCarriers\Application\Commands\RegisterCarrierCommand;
+use DistributingCarriers\Domain\Carrier;
+use DistributingCarriers\Infrastructure\EventStore;
+
+class RegisterCarrierHandler
+{
+    private $eventStore;
+
+    public function __construct(EventStore $eventStore)
+    {
+        $this->eventStore = $eventStore;
+    }
+
+    public function __invoke(RegisterCarrierCommand $command): void
+    {
+        $carrierId = uniqid('carrier_');
+        $carrier = Carrier::register($carrierId, $command->name, $command->email);
+
+        $this->eventStore->save($carrier->getId(), $carrier->getUncommittedChanges(), $carrier->getVersion());
+        $carrier->markChangesAsCommitted();
+
+        echo "Carrier registered with ID: " . $carrierId . "\n";
+    }
+}

src/Domain/AggregateRoot.php

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+<?php
+
+namespace DistributingCarriers\Domain;
+
+abstract class AggregateRoot
+{
+    protected $id;
+    protected $version = 0;
+    protected $changes = [];
+
+    public function getId(): string
+    {
+        return $this->id;
+    }
+
+    public function getVersion(): int
+    {
+        return $this->version;
+    }
+
+    public function getUncommittedChanges(): array
+    {
+        return $this->changes;
+    }
+
+    public function markChangesAsCommitted(): void
+    {
+        $this->changes = [];
+    }
+
+    protected function recordThat(object $event): void
+    {
+        $this->apply($event);
+        $this->changes[] = $event;
+    }
+
+    protected function apply(object $event): void
+    {
+        $method = 'apply' . (new \ReflectionClass($event))->getShortName();
+        if (method_exists($this, $method)) {
+            $this->$method($event);
+        }
+        $this->version++;
+    }
+
+    public function loadFromHistory(array $history): void
+    {
+        foreach ($history as $event) {
+            $this->apply($event);
+        }
+    }
+}

src/Domain/Carrier.php

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+<?php
+
+namespace DistributingCarriers\Domain;
+
+use DistributingCarriers\Domain\Events\CarrierRegistered;
+
+class Carrier extends AggregateRoot
+{
+    private $name;
+    private $email;
+
+    public static function register(string $carrierId, string $name, string $email): self
+    {
+        $carrier = new self();
+        $carrier->recordThat(new CarrierRegistered([
+            'carrierId' => $carrierId,
+            'name' => $name,
+            'email' => $email
+        ]));
+        return $carrier;
+    }
+
+    protected function applyCarrierRegistered(CarrierRegistered $event): void
+    {
+        $this->id = $event->carrierId;
+        $this->name = $event->name;
+        $this->email = $event->email;
+    }
+}

src/Domain/Events/CarrierRegistered.php

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+<?php
+
+namespace DistributingCarriers\Domain\Events;
+
+class CarrierRegistered
+{
+    public $carrierId;
+    public $name;
+    public $email;
+
+    public function __construct(array $payload)
+    {
+        $this->carrierId = $payload['carrierId'] ?? null;
+        $this->name = $payload['name'] ?? null;
+        $this->email = $payload['email'] ?? null;
+    }
+}

src/Infrastructure/CassandraEventStore.php

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+<?php
+
+namespace DistributingCarriers\Infrastructure;
+
+use Cassandra;
+
+class CassandraEventStore implements EventStore
+{
+    private $session;
+
+    public function __construct($session)
+    {
+        $this->session = $session;
+    }
+
+    public function save(string $aggregateId, array $events, int $expectedVersion): void
+    {
+        // In a real implementation, we would check the version for concurrency control.
+        // For this example, we'll just append.
+
+        $statement = $this->session->prepare(
+            "INSERT INTO events (aggregate_id, version, event_type, payload, created_at) VALUES (?, ?, ?, ?, ?)"
+        );
+
+        foreach ($events as $event) {
+            $version = ++$expectedVersion;
+            $payload = json_encode($event);
+            $eventType = get_class($event);
+            $createdAt = new Cassandra\Timestamp();
+
+            $this->session->execute($statement, [
+                'arguments' => [
+                    $aggregateId,
+                    $version,
+                    $eventType,
+                    $payload,
+                    $createdAt
+                ]
+            ]);
+        }
+    }
+
+    public function getEventsForAggregate(string $aggregateId): array
+    {
+        $statement = $this->session->prepare(
+            "SELECT event_type, payload FROM events WHERE aggregate_id = ?"
+        );
+
+        $result = $this->session->execute($statement, ['arguments' => [$aggregateId]]);
+
+        $events = [];
+        foreach ($result as $row) {
+            $eventType = $row['event_type'];
+            $payload = json_decode($row['payload'], true);
+
+            // Assuming we can reconstruct the event object from payload
+            // This is a simplified version.
+            if (class_exists($eventType)) {
+                // In a real app, you might use a serializer/deserializer
+                // Here we assume the event has a static fromArray or similar, or just public properties
+                // For simplicity, let's assume we just return the data or a generic object if class doesn't handle it
+                // But for the plan, let's try to instantiate.
+                // We'll leave it as an array or basic object for now if complex reconstruction is needed.
+                // Let's assume the event class has a constructor that takes the payload.
+                $events[] = new $eventType($payload);
+            }
+        }
+
+        return $events;
+    }
+}

src/Infrastructure/CommandBus.php

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+<?php
+
+namespace DistributingCarriers\Infrastructure;
+
+class CommandBus
+{
+    private $handlers = [];
+
+    public function register(string $commandClass, callable $handler): void
+    {
+        $this->handlers[$commandClass] = $handler;
+    }
+
+    public function dispatch(object $command): void
+    {
+        $commandClass = get_class($command);
+        if (!isset($this->handlers[$commandClass])) {
+            throw new \Exception("No handler registered for command: " . $commandClass);
+        }
+
+        $handler = $this->handlers[$commandClass];
+        $handler($command);
+    }
+}

src/Infrastructure/EventStore.php

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+<?php
+
+namespace DistributingCarriers\Infrastructure;
+
+interface EventStore
+{
+    public function save(string $aggregateId, array $events, int $expectedVersion): void;
+    public function getEventsForAggregate(string $aggregateId): array;
+}

src/Infrastructure/Router.php

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+<?php
+
+namespace DistributingCarriers\Infrastructure;
+
+class Router
+{
+    private $routes = [];
+
+    public function add(string $method, string $path, callable $handler): void
+    {
+        $this->routes[] = [
+            'method' => $method,
+            'path' => $path,
+            'handler' => $handler
+        ];
+    }
+
+    public function dispatch(string $method, string $uri)
+    {
+        foreach ($this->routes as $route) {
+            if ($route['method'] === $method && $route['path'] === $uri) {
+                return call_user_func($route['handler']);
+            }
+        }
+
+        http_response_code(404);
+        echo "Not Found";
+    }
+}

src/index.php

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+<?php
+
+require_once __DIR__ . '/../vendor/autoload.php';
+
+use DistributingCarriers\Infrastructure\CommandBus;
+use DistributingCarriers\Infrastructure\Router;
+use DistributingCarriers\Infrastructure\CassandraEventStore;
+use DistributingCarriers\Application\Commands\RegisterCarrierCommand;
+use DistributingCarriers\Application\Handlers\RegisterCarrierHandler;
+
+// Initialize Infrastructure
+// Note: In a real app, you'd configure the Cassandra session here.
+// For this demo, we'll mock it or assume it's passed in.
+// Since we don't have a running Cassandra instance we can connect to easily without extension,
+// we will assume the $session is created.
+// $cluster = Cassandra::cluster()->build();
+// $session = $cluster->connect('distributing_carriers');
+
+// Mocking session for demonstration if extension is missing, or just placeholder.
+$session = null; // Placeholder
+
+$eventStore = new CassandraEventStore($session);
+$commandBus = new CommandBus();
+
+// Register Handlers
+$commandBus->register(RegisterCarrierCommand::class, new RegisterCarrierHandler($eventStore));
+
+// Router
+$router = new Router();
+
+$router->add('POST', '/register-carrier', function () use ($commandBus) {
+    // In a real app, parse body.
+    // For demo, we'll just create a dummy command.
+    $command = new RegisterCarrierCommand("Test Carrier", "test@example.com");
+    $commandBus->dispatch($command);
+});
+
+
+$method = $_SERVER['REQUEST_METHOD'] ?? 'GET';
+$uri = $_SERVER['REQUEST_URI'] ?? '/';
+
+
+$router->dispatch($method, $uri);

tests/demo.php

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+<?php
+
+namespace Cassandra {
+    class Timestamp
+    {
+    }
+}
+
+namespace {
+    // Mock Cassandra Session
+    class MockCassandraSession
+    {
+        public $executedStatements = [];
+
+        public function prepare($cql)
+        {
+            return new MockStatement($cql);
+        }
+
+        public function execute($statement, $options)
+        {
+            $this->executedStatements[] = [
+                'statement' => $statement->cql,
+                'arguments' => $options['arguments']
+            ];
+            echo "Executed CQL: " . $statement->cql . "\n";
+            return [];
+        }
+    }
+
+    class MockStatement
+    {
+        public $cql;
+        public function __construct($cql)
+        {
+            $this->cql = $cql;
+        }
+    }
+
+    require_once __DIR__ . '/../src/Infrastructure/EventStore.php';
+    require_once __DIR__ . '/../src/Infrastructure/CassandraEventStore.php';
+    require_once __DIR__ . '/../src/Infrastructure/CommandBus.php';
+    require_once __DIR__ . '/../src/Domain/AggregateRoot.php';
+    require_once __DIR__ . '/../src/Domain/Events/CarrierRegistered.php';
+    require_once __DIR__ . '/../src/Domain/Carrier.php';
+    require_once __DIR__ . '/../src/Application/Commands/RegisterCarrierCommand.php';
+    require_once __DIR__ . '/../src/Application/Handlers/RegisterCarrierHandler.php';
+
+    use DistributingCarriers\Infrastructure\CommandBus;
+    use DistributingCarriers\Infrastructure\CassandraEventStore;
+    use DistributingCarriers\Application\Commands\RegisterCarrierCommand;
+    use DistributingCarriers\Application\Handlers\RegisterCarrierHandler;
+
+    echo "Starting Demo...\n";
+
+    $session = new MockCassandraSession();
+    $eventStore = new CassandraEventStore($session);
+    $commandBus = new CommandBus();
+
+    $commandBus->register(RegisterCarrierCommand::class, new RegisterCarrierHandler($eventStore));
+
+    $command = new RegisterCarrierCommand("Demo Carrier", "demo@example.com");
+    $commandBus->dispatch($command);
+
+    echo "Demo Completed.\n";
+}