Add ability to permanently delete workflow

[MAILPOET-4540]

mailpoet/lib/Automation/Engine/Endpoints/Workflows/WorkflowsDeleteEndpoint.php

@@ -0,0 +1,42 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Endpoints\Workflows;
+
+use MailPoet\API\REST\Request;
+use MailPoet\API\REST\Response;
+use MailPoet\Automation\Engine\API\Endpoint;
+use MailPoet\Automation\Engine\Data\Workflow;
+use MailPoet\Automation\Engine\Exceptions\InvalidStateException;
+use MailPoet\Automation\Engine\Storage\WorkflowStorage;
+use MailPoet\Validator\Builder;
+
+class WorkflowsDeleteEndpoint extends Endpoint {
+  /** @var WorkflowStorage */
+  private $workflowStorage;
+
+  public function __construct(
+    WorkflowStorage $workflowStorage
+  ) {
+    $this->workflowStorage = $workflowStorage;
+  }
+
+  public function handle(Request $request): Response {
+    $workflowId = $request->getParam('id');
+    if (!is_int($workflowId)) {
+      throw InvalidStateException::create();
+    }
+    $existingWorkflow = $this->workflowStorage->getWorkflow($workflowId);
+    if (!$existingWorkflow instanceof Workflow) {
+      throw InvalidStateException::create();
+    }
+    $this->workflowStorage->deleteWorkflow($existingWorkflow);
+
+    return new Response(null);
+  }
+
+  public static function getRequestSchema(): array {
+    return [
+      'id' => Builder::integer()->required(),
+    ];
+  }
+}