trait TimeStampItemNormalizerTrait

trait TimeStampItemNormalizerTrait {
    
    /**
     * Allowed timestamps formats for the denormalizer.
     *
     * The denormalizer allows deserialization to timestamps from three
     * different formats. Validation of the input data and creation of the
     * numerical timestamp value is handled with \DateTime::createFromFormat().
     * The list is chosen to be unambiguous and language neutral, but also common
     * for data interchange.
     *
     * @var string[]
     *
     * @see http://php.net/manual/datetime.createfromformat.php
     */
    protected $allowedFormats = [
        'UNIX timestamp' => 'U',
        'ISO 8601' => \DateTime::ISO8601,
        'RFC 3339' => \DateTime::RFC3339,
    ];
    
    /**
     * Processes normalized timestamp values to add a formatted date and format.
     *
     * @param array $normalized
     *   The normalized field data to process.
     *
     * @return array
     *   The processed data.
     */
    protected function processNormalizedValues(array $normalized) {
        // Use a RFC 3339 timestamp with the time zone set to UTC to replace the
        // timestamp value.
        $date = new \DateTime();
        $date->setTimestamp($normalized['value']);
        $date->setTimezone(new \DateTimeZone('UTC'));
        $normalized['value'] = $date->format(\DateTime::RFC3339);
        // 'format' is not a property on TimestampItem fields. This is present to
        // assist consumers of this data.
        $normalized['format'] = \DateTime::RFC3339;
        return $normalized;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function constructValue($data, $context) {
        // Loop through the allowed formats and create a TimestampItem from the
        // input data if it matches the defined pattern. Since the formats are
        // unambiguous (i.e., they reference an absolute time with a defined time
        // zone), only one will ever match.
        $timezone = new \DateTimeZone('UTC');
        // First check for a provided format.
        if (!empty($data['format']) && in_array($data['format'], $this->allowedFormats)) {
            $date = \DateTime::createFromFormat($data['format'], $data['value'], $timezone);
            return [
                'value' => $date->getTimestamp(),
            ];
        }
        else {
            foreach ($this->allowedFormats as $format) {
                if (($date = \DateTime::createFromFormat($format, $data['value'], $timezone)) !== FALSE) {
                    return [
                        'value' => $date->getTimestamp(),
                    ];
                }
            }
        }
        $format_strings = [];
        foreach ($this->allowedFormats as $label => $format) {
            $format_strings[] = "\"{$format}\" ({$label})";
        }
        $formats = implode(', ', $format_strings);
        throw new UnexpectedValueException(sprintf('The specified date "%s" is not in an accepted format: %s.', $data['value'], $formats));
    }

}