date_convert.php

<?php

/**
 * Converts a date string to a date object with requested time zone
 *
 * @param $date
 *   Date String
 * @param $from_tz
 *   String of timezone to convert FROM
 * @param $to_tz
 *   String of timezone to convert TO
 * @param $return_type
 *   How should the result be returned.
 *   if NULL, date object is returned
 *   if it's an array of formats, the parts are returned in an array
 */
function _date_convert_tz($date, $from_tz = 'UTC', $to_tz = 'UTC', $return_type = NULL) {
  // make a date object, initialize with $from_tz
  $date = date_make_date($date, $from_tz, $type= DATE_ISO);
  // check if conversion is needed
  if ($from_tz != $to_tz) {
    date_timezone_set($date, timezone_open($to_tz));
  }
  // if the return type is null return date object
  if (is_null($return_type)) {
    return $date;
  }
  if (is_string($return_type)) {
    return date_format_date($date, 'custom', $return_type);
  }
  // otherwise return formatted array
  $return = array();
  foreach ($return_type as $key => $format) {
    $return[$key] = date_format_date($date, 'custom', $format);
  }
  return $return;
}