Collect all step error types instead of terminating on the first one

[MAILPOET-4659]

mailpoet/lib/Automation/Engine/Validation/WorkflowRules/ValidStepRule.php

@@ -0,0 +1,54 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Validation\WorkflowRules;
+
+use MailPoet\Automation\Engine\Data\Workflow;
+use MailPoet\Automation\Engine\Exceptions;
+use MailPoet\Automation\Engine\Exceptions\UnexpectedValueException;
+use MailPoet\Automation\Engine\Validation\WorkflowGraph\WorkflowNode;
+use MailPoet\Automation\Engine\Validation\WorkflowGraph\WorkflowNodeVisitor;
+use Throwable;
+
+class ValidStepRule implements WorkflowNodeVisitor {
+  /** @var WorkflowNodeVisitor[] */
+  private $rules;
+
+  /** @var array<string, array{step_id: string, message: string}> */
+  private $errors = [];
+
+  /** @param WorkflowNodeVisitor[] $rules */
+  public function __construct(
+    array $rules
+  ) {
+    $this->rules = $rules;
+  }
+
+  public function initialize(Workflow $workflow): void {
+    foreach ($this->rules as $rule) {
+      $rule->initialize($workflow);
+    }
+  }
+
+  public function visitNode(Workflow $workflow, WorkflowNode $node): void {
+    foreach ($this->rules as $rule) {
+      $stepId = $node->getStep()->getId();
+      try {
+        $rule->visitNode($workflow, $node);
+      } catch (UnexpectedValueException $e) {
+        $this->errors[$stepId] = ['step_id' => $stepId, 'message' => $e->getMessage()];
+      } catch (Throwable $e) {
+        $this->errors[$stepId] = ['step_id' => $stepId, 'message' => __('Unknown error.', 'mailpoet')];
+      }
+    }
+  }
+
+  public function complete(Workflow $workflow): void {
+    foreach ($this->rules as $rule) {
+      $rule->complete($workflow);
+    }
+
+    if ($this->errors) {
+      throw Exceptions::workflowNotValid(__('Some steps are not valid', 'mailpoet'), $this->errors);
+    }
+  }
+}