Move automation engine code under "Engine" namespace

This is to separate the engine itself from "integrations" that will be
built on top of the engine.

[MAILPOET-4136]

mailpoet/lib/Automation/Engine/API/API.php

@@ -0,0 +1,77 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\API;
+
+use MailPoet\Automation\Engine\API\Endpoints\SystemDatabaseEndpoint;
+use MailPoet\Automation\Engine\API\Endpoints\WorkflowsEndpoint;
+use MailPoet\Automation\Engine\Exceptions\Exception;
+use MailPoet\Automation\Engine\WordPress;
+use ReflectionClass;
+use Throwable;
+
+class API {
+  private const PREFIX = 'mailpoet/v1/automation';
+  private const METHODS = ['get', 'post', 'put', 'delete'];
+  private const WP_REST_API_INIT_ACTION = 'rest_api_init';
+
+  /** @var EndpointFactory */
+  private $endpointFactory;
+
+  /** @var WordPress */
+  private $wordPress;
+
+  /** @var array<string, class-string<Endpoint>> */
+  private $routes = [
+    'system/database' => SystemDatabaseEndpoint::class,
+    'workflows' => WorkflowsEndpoint::class,
+  ];
+
+  public function __construct(
+    EndpointFactory $endpointFactory,
+    WordPress $wordPress
+  ) {
+    $this->endpointFactory = $endpointFactory;
+    $this->wordPress = $wordPress;
+  }
+
+  public function initialize(): void {
+    $this->wordPress->addAction(self::WP_REST_API_INIT_ACTION, function () {
+      foreach ($this->routes as $route => $endpoint) {
+        $reflection = new ReflectionClass($endpoint);
+        foreach (self::METHODS as $method) {
+          if ($reflection->hasMethod($method) && $reflection->getMethod($method)->class === $endpoint) {
+            $this->registerRoute($route, $endpoint, $method);
+          }
+        }
+      }
+    });
+  }
+
+  private function registerRoute(string $route, string $endpoint, string $method): void {
+    $this->wordPress->registerRestRoute(self::PREFIX, $route, [
+      'methods' => strtoupper($method),
+      'callback' => function ($wpRequest) use ($endpoint, $method) {
+        try {
+          $request = new Request($wpRequest);
+          return $this->endpointFactory->createEndpoint($endpoint)->$method($request);
+        } catch (Throwable $e) {
+          return $this->convertToErrorResponse($e);
+        }
+      },
+      'permission_callback' => function () {
+        return $this->wordPress->currentUserCan('administrator');
+      },
+    ]);
+  }
+
+  private function convertToErrorResponse(Throwable $e): ErrorResponse {
+    $response = $e instanceof Exception
+      ? new ErrorResponse($e->getStatusCode(), $e->getMessage(), $e->getErrorCode())
+      : new ErrorResponse(500, __('An unknown error occurred.', 'mailpoet'), 'mailpoet_automation_unknown_error');
+
+    if ($response->get_status() >= 500) {
+      error_log((string)$e); // phpcs:ignore Squiz.PHP.DiscouragedFunctions
+    }
+    return $response;
+  }
+}