Use "automation" instead of "workflow"

[MAILPOET-4793]

mailpoet/lib/Automation/Engine/Validation/AutomationRules/ValidStepOrderRule.php

@@ -0,0 +1,71 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Validation\AutomationRules;
+
+use MailPoet\Automation\Engine\Data\Automation;
+use MailPoet\Automation\Engine\Data\Step;
+use MailPoet\Automation\Engine\Exceptions;
+use MailPoet\Automation\Engine\Registry;
+use MailPoet\Automation\Engine\Validation\AutomationGraph\AutomationNode;
+use MailPoet\Automation\Engine\Validation\AutomationGraph\AutomationNodeVisitor;
+
+class ValidStepOrderRule implements AutomationNodeVisitor {
+  /** @var Registry */
+  private $registry;
+
+  public function __construct(
+    Registry $registry
+  ) {
+    $this->registry = $registry;
+  }
+
+  public function initialize(Automation $automation): void {
+  }
+
+  public function visitNode(Automation $automation, AutomationNode $node): void {
+    $step = $node->getStep();
+    $registryStep = $this->registry->getStep($step->getKey());
+    if (!$registryStep) {
+      return;
+    }
+
+    // triggers don't require any subjects (they provide them)
+    if ($step->getType() === Step::TYPE_TRIGGER) {
+      return;
+    }
+
+    $requiredSubjectKeys = $registryStep->getSubjectKeys();
+    if (!$requiredSubjectKeys) {
+      return;
+    }
+
+    $subjectKeys = $this->collectSubjectKeys($automation, $node->getParents());
+    $missingSubjectKeys = array_diff($requiredSubjectKeys, $subjectKeys);
+    if (count($missingSubjectKeys) > 0) {
+      throw Exceptions::missingRequiredSubjects($step, $missingSubjectKeys);
+    }
+  }
+
+  public function complete(Automation $automation): void {
+  }
+
+  /**
+   * @param Step[] $parents
+   * @return string[]
+   */
+  private function collectSubjectKeys(Automation $automation, array $parents): array {
+    $triggers = array_filter($parents, function (Step $step) {
+      return $step->getType() === Step::TYPE_TRIGGER;
+    });
+
+    $subjectKeys = [];
+    foreach ($triggers as $trigger) {
+      $registryTrigger = $this->registry->getTrigger($trigger->getKey());
+      if (!$registryTrigger) {
+        throw Exceptions::automationTriggerNotFound($automation->getId(), $trigger->getKey());
+      }
+      $subjectKeys = array_merge($subjectKeys, $registryTrigger->getSubjectKeys());
+    }
+    return array_unique($subjectKeys);
+  }
+}