Introduce subject entry to carry subject & payload data

[MAILPOET-4629]

mailpoet/lib/Automation/Engine/Data/SubjectEntry.php

@@ -0,0 +1,49 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Data;
+
+use MailPoet\Automation\Engine\Data\Subject as SubjectData;
+use MailPoet\Automation\Engine\Exceptions;
+use MailPoet\Automation\Engine\Workflows\Payload;
+use MailPoet\Automation\Engine\Workflows\Subject;
+use Throwable;
+
+/**
+ * @template-covariant S of Subject<Payload>
+ */
+class SubjectEntry {
+  /** @var S */
+  private $subject;
+
+  /** @var SubjectData */
+  private $subjectData;
+
+  /** @var Payload|null */
+  private $payloadCache;
+
+  /** @param S $subject */
+  public function __construct(
+    Subject $subject,
+    SubjectData $subjectData
+  ) {
+    $this->subject = $subject;
+    $this->subjectData = $subjectData;
+  }
+
+  /** @return S */
+  public function getSubject(): Subject {
+    return $this->subject;
+  }
+
+  /** @return Payload */
+  public function getPayload() {
+    if ($this->payloadCache === null) {
+      try {
+        $this->payloadCache = $this->subject->getPayload($this->subjectData);
+      } catch (Throwable $e) {
+        throw Exceptions::subjectLoadFailed($this->subject->getKey(), $this->subjectData->getArgs());
+      }
+    }
+    return $this->payloadCache;
+  }
+}