Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/datetime/src/DateTimeComputed.php

@@ -0,0 +1,75 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\datetime\DateTimeComputed.
+ */
+
+namespace Drupal\datetime;
+
+use Drupal\Core\Datetime\DrupalDateTime;
+use Drupal\Core\TypedData\DataDefinitionInterface;
+use Drupal\Core\TypedData\TypedDataInterface;
+use Drupal\Core\TypedData\TypedData;
+
+/**
+ * A computed property for dates of date time field items.
+ *
+ * Required settings (below the definition's 'settings' key) are:
+ *  - date source: The date property containing the to be computed date.
+ */
+class DateTimeComputed extends TypedData {
+
+  /**
+   * Cached computed date.
+   *
+   * @var \DateTime|null
+   */
+  protected $date = NULL;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(DataDefinitionInterface $definition, $name = NULL, TypedDataInterface $parent = NULL) {
+    parent::__construct($definition, $name, $parent);
+    if (!$definition->getSetting('date source')) {
+      throw new \InvalidArgumentException("The definition's 'date source' key has to specify the name of the date property to be computed.");
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getValue($langcode = NULL) {
+    if ($this->date !== NULL) {
+      return $this->date;
+    }
+
+    $item = $this->getParent();
+    $value = $item->{($this->definition->getSetting('date source'))};
+
+    $storage_format = $item->getFieldDefinition()->getSetting('datetime_type') == 'date' ? DATETIME_DATE_STORAGE_FORMAT : DATETIME_DATETIME_STORAGE_FORMAT;
+    try {
+      $date = DrupalDateTime::createFromFormat($storage_format, $value, DATETIME_STORAGE_TIMEZONE);
+      if ($date instanceOf DrupalDateTime && !$date->hasErrors()) {
+        $this->date = $date;
+      }
+    }
+    catch (\Exception $e) {
+      // @todo Handle this.
+    }
+    return $this->date;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setValue($value, $notify = TRUE) {
+    $this->date = $value;
+    // Notify the parent of any changes.
+    if ($notify && isset($this->parent)) {
+      $this->parent->onChange($this->name);
+    }
+  }
+
+}