Merged in feature/from-pantheon (pull request #16)

code from pantheon

* code from pantheon

wp/wp-content/plugins/wordpress-seo/inc/date-helper.php

@@ -0,0 +1,61 @@
+<?php
+/**
+ * Date helper class.
+ *
+ * @package WPSEO\Internals
+ */
+
+/**
+ * Class WPSEO_Date_Helper
+ *
+ * Note: Move this class with namespace to the src/helpers directory and add a class_alias for BC.
+ */
+class WPSEO_Date_Helper {
+
+	/**
+	 * Formats a given date in UTC TimeZone format.
+	 *
+	 * @param string $date   String representing the date / time.
+	 * @param string $format The format that the passed date should be in.
+	 *
+	 * @return string The formatted date.
+	 */
+	public function format( $date, $format = DATE_W3C ) {
+		return YoastSEO()->helpers->date->format( $date, $format );
+	}
+
+	/**
+	 * Formats the given timestamp to the needed format.
+	 *
+	 * @param int    $timestamp The timestamp to use for the formatting.
+	 * @param string $format    The format that the passed date should be in.
+	 *
+	 * @return string The formatted date.
+	 */
+	public function format_timestamp( $timestamp, $format = DATE_W3C ) {
+		return YoastSEO()->helpers->date->format_timestamp( $timestamp, $format );
+	}
+
+	/**
+	 * Formats a given date in UTC TimeZone format and translate it to the set language.
+	 *
+	 * @param string $date   String representing the date / time.
+	 * @param string $format The format that the passed date should be in.
+	 *
+	 * @return string The formatted and translated date.
+	 */
+	public function format_translated( $date, $format = DATE_W3C ) {
+		return YoastSEO()->helpers->date->format_translated( $date, $format );
+	}
+
+	/**
+	 * Check if a string is a valid datetime.
+	 *
+	 * @param string $datetime String input to check as valid input for DateTime class.
+	 *
+	 * @return bool True when datatime is valid.
+	 */
+	public function is_valid_datetime( $datetime ) {
+		return YoastSEO()->helpers->date->is_valid_datetime( $datetime );
+	}
+}