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

src/Infrastructure/CassandraEventStore.php

@@ -0,0 +1,71 @@
+<?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

@@ -0,0 +1,24 @@
+<?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";
+    }
+}