fixes for editing calendar

src/Bundle/ChillCalendarBundle/Entity/Calendar.php

@@ -23,6 +23,7 @@ use Chill\MainBundle\Entity\User;
 use Chill\PersonBundle\Entity\AccompanyingPeriod;
 use Chill\PersonBundle\Entity\Person;
 use Chill\ThirdPartyBundle\Entity\ThirdParty;
+use DateInterval;
 use DateTimeImmutable;
 use Doctrine\Common\Collections\ArrayCollection;
 use Doctrine\Common\Collections\Collection;
@@ -30,8 +31,8 @@ use Doctrine\ORM\Mapping as ORM;
 use LogicException;
 use Symfony\Component\Serializer\Annotation as Serializer;
 use Symfony\Component\Validator\Constraints\NotBlank;
-use Symfony\Component\Validator\Constraints\Range;
 
+use Symfony\Component\Validator\Constraints\Range;
 use Symfony\Component\Validator\Mapping\ClassMetadata;
 use function in_array;
 
@@ -219,6 +220,15 @@ class Calendar implements TrackCreationInterface, TrackUpdateInterface
         return $this->comment;
     }
 
+    public function getDuration(): ?DateInterval
+    {
+        if ($this->getStartDate() === null || $this->getEndDate() === null) {
+            return null;
+        }
+
+        return $this->getStartDate()->diff($this->getEndDate());
+    }
+
     public function getEndDate(): ?DateTimeImmutable
     {
         return $this->endDate;