Relative date/time format support

Thanks to @srizzling for getting this started in
https://github.com/silverstripe/silverstripe-cms/pull/896

README.md

@@ -595,6 +595,16 @@ It's based on the `vendor/bin/behat -di @cms` output.
 	    - Example: Given a "group" "Admin" with permissions "Access to 'Pages' section" and "Access to 'Files' section"
 	    # SilverStripe\Cms\Test\Behaviour\FixtureContext::stepCreateGroupWithPermissions()
 
+### Transformations
+
+Behat [transformations](http://docs.behat.org/guides/2.definitions.html#step-argument-transformations)
+have the ability to change step arguments based on their original value,
+for example to cast any argument matching the `\d` regex into an actual PHP integer.
+
+ * `/^(?:(the|a)) time of (?<val>.*)$/`: Transforms relative time statements compatible with [strtotime()](http://www.php.net/manual/en/datetime.formats.relative.php). Example: "the time of 1 hour ago" might return "22:00:00" if its currently "23:00:00".
+ * `/^(?:(the|a)) date of (?<val>.*)$/`: Transforms relative date statements compatible with [strtotime()](http://www.php.net/manual/en/datetime.formats.relative.php). Example: "the date of 2 days ago" might return "2013-10-10" if its currently the 12th of October 2013. 
+ * `/^(?:(the|a)) datetime of (?<val>.*)$/`: Transforms relative date and time statements compatible with [strtotime()](http://www.php.net/manual/en/datetime.formats.relative.php). Example: "the datetime of 2 days ago" might return "2013-10-10 23:00:00" if its currently the 12th of October 2013. 
+
 ## Useful resources
 
 * [SilverStripe CMS architecture](http://doc.silverstripe.org/sapphire/en/trunk/reference/cms-architecture)

src/SilverStripe/BehatExtension/Context/BasicContext.php

@@ -29,6 +29,24 @@ class BasicContext extends BehatContext
 {
     protected $context;
 
+    /**
+	 * Date format in date() syntax
+	 * @var String
+	 */
+	protected $dateFormat = 'Y-m-d';
+
+	/**
+	 * Time format in date() syntax
+	 * @var String
+	 */
+	protected $timeFormat = 'H:i:s';
+
+	/**
+	 * Date/time format in date() syntax
+	 * @var String
+	 */
+	protected $datetimeFormat = 'Y-m-d H:i:s';
+
     /**
      * Initializes context.
      * Every scenario gets it's own context object.
@@ -373,4 +391,82 @@ JS;
 
         return new Step\Given(sprintf('I attach the file "%s" to "%s"', $path, $field));
     }
+
+    /**
+	 * Transforms relative time statements compatible with strtotime().
+	 * Example: "time of 1 hour ago" might return "22:00:00" if its currently "23:00:00".
+	 * Customize through {@link setTimeFormat()}.
+	 * 
+	 * @Transform /^(?:(the|a)) time of (?<val>.*)$/
+	 */
+	public function castRelativeToAbsoluteTime($prefix, $val) {
+		$timestamp = strtotime($val);
+		if(!$timestamp) {
+			throw new \InvalidArgumentException(sprintf(
+				"Can't resolve '%s' into a valid datetime value",
+				$val
+			));
+		}
+		return date($this->timeFormat, $timestamp);
+	}
+
+	/**
+	 * Transforms relative date and time statements compatible with strtotime().
+	 * Example: "datetime of 2 days ago" might return "2013-10-10 22:00:00" if its currently 
+	 * the 12th of October 2013. Customize through {@link setDatetimeFormat()}.
+	 * 
+	 * @Transform /^(?:(the|a)) datetime of (?<val>.*)$/
+	 */
+	public function castRelativeToAbsoluteDatetime($prefix, $val) {
+		$timestamp = strtotime($val);
+		if(!$timestamp) {
+			throw new \InvalidArgumentException(sprintf(
+				"Can't resolve '%s' into a valid datetime value",
+				$val
+			));
+		}
+		return date($this->datetimeFormat, $timestamp);
+	}
+
+	/**
+	 * Transforms relative date statements compatible with strtotime().
+	 * Example: "date 2 days ago" might return "2013-10-10" if its currently 
+	 * the 12th of October 2013. Customize through {@link setDateFormat()}.
+	 * 
+	 * @Transform /^(?:(the|a)) date of (?<val>.*)$/
+	 */
+	public function castRelativeToAbsoluteDate($prefix, $val) {
+		$timestamp = strtotime($val);
+		if(!$timestamp) {
+			throw new \InvalidArgumentException(sprintf(
+				"Can't resolve '%s' into a valid datetime value",
+				$val
+			));
+		}
+		return date($this->dateFormat, $timestamp);
+	}
+
+	public function getDateFormat() {
+		return $this->dateFormat;
+	}
+
+	public function setDateFormat($format) {
+		$this->dateFormat = $format;
+	}
+
+	public function getTimeFormat() {
+		return $this->timeFormat;
+	}
+
+	public function setTimeFormat($format) {
+		$this->timeFormat = $format;
+	}
+
+	public function getDatetimeFormat() {
+		return $this->datetimeFormat;
+	}
+
+	public function setDatetimeFormat($format) {
+		$this->datetimeFormat = $format;
+	}
 }