Issue #3255666 by SyfJO: Wrong DateTime when a website is using timezone other than UTC

src/Plugin/Field/FieldFormatter/HijriFieldFormatter.php

@@ -122,12 +122,12 @@ class HijriFieldFormatter extends FormatterBase {
       $class = get_class($item);
       switch ($class) {
         case DateRangeItem::class:
-          $date[] = $this->hijriFormatManager->convertToHijri(strtotime($item->getValue()['value']), $format, $is_indian);
-          $date[] = $this->hijriFormatManager->convertToHijri(strtotime($item->getValue()['end_value']), $format, $is_indian);
+          $date[] = $this->hijriFormatManager->convertToHijri($this->getUTCTimestamp($item->getValue()['value']), $format, $is_indian);
+          $date[] = $this->hijriFormatManager->convertToHijri($this->getUTCTimestamp($item->getValue()['end_value']), $format, $is_indian);
           break;
 
         case DateTimeItem::class:
-          $value = strtotime($item->getValue()['value']);
+          $value = $this->getUTCTimestamp($item->getValue()['value']);
         default:
           $value = $value ?? $item->getValue()['value'];
           $date[] = $this->hijriFormatManager->convertToHijri($value, $format, $is_indian);
@@ -141,4 +141,18 @@ class HijriFieldFormatter extends FormatterBase {
     return $elements;
   }
 
+  /**
+   * Gets the timestamp using UTC timezone.
+   *
+   * @param string $date_time_string
+   *   DateTime string (e.g. 1996-04-24T12:00:00).
+   * @return int
+   *   Timestamp using UTC timezone.
+   */
+  private function getUTCTimestamp(string $date_time_string) {
+    $timezone = new \DateTimeZone('UTC');
+    $date_time_string = str_replace("T", " ", $date_time_string);
+    return \DateTime::createFromFormat('Y-m-d H:i:s', $date_time_string, $timezone)->getTimestamp();
+  }
+
 }