Prevent deleting lists with emails that are being sent

[MAILPOET-3417]

lib/Newsletter/Segment/NewsletterSegmentRepository.php

@@ -53,4 +53,23 @@ class NewsletterSegmentRepository extends Repository {
     }
     return $nameMap;
   }
+
+  public function getSendingEmailSubjectsBySegmentIds(array $segmentIds): array {
+    $results = $this->doctrineRepository->createQueryBuilder('ns')
+      ->select('IDENTITY(ns.segment) AS segment_id, n.subject')
+      ->join('ns.newsletter', 'n')
+      ->join('n.queues', 'q')
+      ->join('q.task', 't')
+      ->where('t.status IS NULL')
+      ->andWhere('ns.segment IN (:segmentIds)')
+      ->setParameter('segmentIds', $segmentIds)
+      ->getQuery()
+      ->getResult();
+
+    $nameMap = [];
+    foreach ($results as $result) {
+      $nameMap[(string)$result['segment_id']][] = $result['subject'];
+    }
+    return $nameMap;
+  }
 }