ENGCOM-7155: Refactor datetime class #26538

 - Merge Pull Request #26538 from Tjitse-E/magento2:refactor-datetime-class
 - Merged commits:
   1. 13890db
   2. 6289916
   3. 1140cb7

Author: magento-engcom-team

lib/internal/Magento/Framework/Stdlib/DateTime/DateTime.php

@@ -13,13 +13,6 @@
  */
 class DateTime
 {
-    /**
-     * Current config offset in seconds
-     *
-     * @var int
-     */
-    private $_offset = 0;
-
     /**
      * @var TimezoneInterface
      */
@@ -31,7 +24,6 @@ class DateTime
     public function __construct(TimezoneInterface $localeDate)
     {
         $this->_localeDate = $localeDate;
-        $this->_offset = $this->calculateOffset($this->_localeDate->getConfigTimezone());
     }
 
     /**
@@ -78,8 +70,7 @@ public function gmtDate($format = null, $input = null)
     }
 
     /**
-     * Converts input date into date with timezone offset
-     * Input date must be in GMT timezone
+     * Converts input date into date with timezone offset. Input date must be in GMT timezone.
      *
      * @param  string $format
      * @param  int|string $input date in GMT timezone
@@ -122,8 +113,7 @@ public function gmtTimestamp($input = null)
     }
 
     /**
-     * Converts input date into timestamp with timezone offset
-     * Input date must be in GMT timezone
+     * Converts input date into timestamp with timezone offset. Input date must be in GMT timezone.
      *
      * @param  int|string $input date in GMT timezone
      * @return int
@@ -157,18 +147,18 @@ public function timestamp($input = null)
      */
     public function getGmtOffset($type = 'seconds')
     {
-        $result = $this->_offset;
+        $offset = $this->calculateOffset($this->_localeDate->getConfigTimezone());
         switch ($type) {
             case 'seconds':
             default:
                 break;
             case 'minutes':
-                $result = $result / 60;
+                $offset = $offset / 60;
                 break;
             case 'hours':
-                $result = $result / 60 / 60;
+                $offset = $offset / 60 / 60;
                 break;
         }
-        return $result;
+        return $offset;
     }
 }

lib/internal/Magento/Framework/Stdlib/Test/Unit/DateTime/DateTimeTest.php

@@ -46,6 +46,21 @@ public function testTimestamp($input)
         $this->assertEquals($expected, (new DateTime($timezone))->timestamp($input));
     }
 
+    public function testGtmOffset()
+    {
+        /** @var TimezoneInterface|\PHPUnit_Framework_MockObject_MockObject $timezone */
+        $timezone = $this->getMockBuilder(TimezoneInterface::class)->getMock();
+        $timezone->method('getConfigTimezone')->willReturn('Europe/Amsterdam');
+
+        /** @var DateTime|\PHPUnit_Framework_MockObject_MockObject $dateTime */
+        $dateTime = $this->getMockBuilder(DateTime::class)
+            ->setConstructorArgs([$timezone])
+            ->setMethods(null)
+            ->getMock();
+
+        $this->assertEquals(3600, $dateTime->getGmtOffset());
+    }
+
     /**
      * @return array
      */