Transfer date to solr date time.

solr_date2tdate.php

<?php
// need to set a valid timezone.
date_default_timezone_set('Asia/Taipei');

/**
 * @param
 *   $string: date string, '2013-12-12 01:23:44'
 * 
 * @return:
 *   string type => '2013-12-12T01:23:44Z'
 */
function date_to_tdate($string) {
    $millis = strtotime($string);
    $timezone = new DateTimeZone(date_default_timezone_get());
    $offset = $timezone->getOffset(new DateTime($string));
    $offsetHours = round(abs($offset)/3600);
    $offsetMinutes = round((abs($offset) - $offsetHours * 3600) / 60);
    $offsetString = ($offset < 0 ? '-' : '+')
                    . ($offsetHours < 10 ? '0' : '') . $offsetHours
                    . ':'
                    . ($offsetMinutes < 10 ? '0' : '') . $offsetMinutes;

    return ('' . date('Y-m-d\TH:i:s', $millis) . 'Z'. '');
}
?>