Milestone 3: Middleware Pipeline (The Onion) with Telemetry

src/MiddlewarePipeline.php

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+<?php
+
+declare(strict_types=1);
+
+namespace Phred\Beacon;
+
+use Phred\BeaconContracts\DispatchMiddlewareInterface;
+
+/**
+ * MiddlewarePipeline
+ *
+ * Coordinates the execution of global middleware before listeners are called.
+ * Uses a recursive "Onion" style closure chain.
+ */
+class MiddlewarePipeline
+{
+    /**
+     * @var array<DispatchMiddlewareInterface> The list of global middleware.
+     */
+    private array $middlewares = [];
+
+    /**
+     * Adds a middleware to the pipeline.
+     *
+     * @param DispatchMiddlewareInterface $middleware
+     * @return void
+     */
+    public function add(DispatchMiddlewareInterface $middleware): void
+    {
+        $this->middlewares[] = $middleware;
+    }
+
+    /**
+     * Executes the middleware pipeline, wrapping the final action.
+     *
+     * @param object $event The event object.
+     * @param callable $finalAction The final action (typically listener execution).
+     * @return object The potentially modified event object.
+     */
+    public function execute(object $event, callable $finalAction): object
+    {
+        $pipeline = array_reverse($this->middlewares);
+        
+        $runner = array_reduce(
+            $pipeline,
+            fn(callable $next, DispatchMiddlewareInterface $middleware) => 
+                fn(object $event) => $middleware->handle($event, $next),
+            $finalAction
+        );
+
+        return $runner($event);
+    }
+}

src/TelemetryMiddleware.php

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+<?php
+
+declare(strict_types=1);
+
+namespace Phred\Beacon;
+
+use Phred\BeaconContracts\DispatchMiddlewareInterface;
+
+/**
+ * TelemetryMiddleware
+ *
+ * A middleware that records execution time and memory usage for a dispatch.
+ * In a real-world scenario, this would push data to a Telemetry system.
+ * For now, it provides a basic structure for performance tracking.
+ */
+class TelemetryMiddleware implements DispatchMiddlewareInterface
+{
+    /**
+     * @var array<string, array{time: float, memory: int}> Recorded telemetry data.
+     */
+    private array $data = [];
+
+    /**
+     * Handles the event and records telemetry.
+     *
+     * @param object $event
+     * @param callable $next
+     * @return object
+     */
+    public function handle(object $event, callable $next): object
+    {
+        $start = microtime(true);
+        $mem = memory_get_usage();
+
+        $result = $next($event);
+
+        $this->data[$event::class] = [
+            'time' => microtime(true) - $start,
+            'memory' => memory_get_usage() - $mem,
+        ];
+
+        return $result;
+    }
+
+    /**
+     * Returns the recorded telemetry data.
+     *
+     * @return array<string, array{time: float, memory: int}>
+     */
+    public function getData(): array
+    {
+        return $this->data;
+    }
+}

tests/Integration/MiddlewarePipelineTest.php

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+<?php
+
+declare(strict_types=1);
+
+namespace Phred\Beacon\Tests\Integration;
+
+use PHPUnit\Framework\TestCase;
+use Phred\Beacon\EventDispatcher;
+use Phred\Beacon\ListenerProvider;
+use Phred\Beacon\TelemetryMiddleware;
+use Phred\BeaconContracts\DispatchMiddlewareInterface;
+
+class MiddlewarePipelineTest extends TestCase
+{
+    public function test_it_executes_middleware_in_order(): void
+    {
+        $provider = new ListenerProvider();
+        $dispatcher = new EventDispatcher($provider);
+        $order = [];
+
+        $middleware1 = new class($order) implements DispatchMiddlewareInterface {
+            public function __construct(private array &$order) {}
+            public function handle(object $event, callable $next): object {
+                $this->order[] = 'm1_before';
+                $result = $next($event);
+                $this->order[] = 'm1_after';
+                return $result;
+            }
+        };
+
+        $middleware2 = new class($order) implements DispatchMiddlewareInterface {
+            public function __construct(private array &$order) {}
+            public function handle(object $event, callable $next): object {
+                $this->order[] = 'm2_before';
+                $result = $next($event);
+                $this->order[] = 'm2_after';
+                return $result;
+            }
+        };
+
+        $dispatcher->addMiddleware($middleware1);
+        $dispatcher->addMiddleware($middleware2);
+
+        $provider->addListener('stdClass', function() use (&$order) {
+            $order[] = 'listener';
+        });
+
+        $dispatcher->dispatch(new \stdClass());
+
+        $expected = [
+            'm1_before',
+            'm2_before',
+            'listener',
+            'm2_after',
+            'm1_after'
+        ];
+
+        $this->assertEquals($expected, $order);
+    }
+
+    public function test_middleware_can_modify_event(): void
+    {
+        $provider = new ListenerProvider();
+        $dispatcher = new EventDispatcher($provider);
+
+        $middleware = new class implements DispatchMiddlewareInterface {
+            public function handle(object $event, callable $next): object {
+                $event->modified = true;
+                return $next($event);
+            }
+        };
+
+        $dispatcher->addMiddleware($middleware);
+
+        $event = new \stdClass();
+        $event->modified = false;
+
+        $dispatcher->dispatch($event);
+
+        $this->assertTrue($event->modified);
+    }
+
+    public function test_telemetry_middleware_records_data(): void
+    {
+        $provider = new ListenerProvider();
+        $dispatcher = new EventDispatcher($provider);
+        $telemetry = new TelemetryMiddleware();
+
+        $dispatcher->addMiddleware($telemetry);
+
+        $provider->addListener('stdClass', function() {
+            usleep(1000); // 1ms
+        });
+
+        $event = new \stdClass();
+        $dispatcher->dispatch($event);
+
+        $data = $telemetry->getData();
+        
+        $this->assertArrayHasKey('stdClass', $data);
+        $this->assertGreaterThan(0, $data['stdClass']['time']);
+    }
+}