The point of this function is to convert between UTC (what we expect all times to start with.). If we're coming from the the database or a time() function, it's UTC. The "end_timezone_string" should be the user's preferred timezone.

if end_timezone_string == null, then we will use the user's selected timezone. If that isn't set, we use they system's.

As a convenenience, if the data_format we will get back a formatted date. Otherwise we'll get back a timestamp.

File

includes/misc.inc, line 275

This file contains misc functions for FlightPath

Code

function convert_time($time_to_convert = 0, $start_timezone_string = "UTC", $end_timezone_string = NULL, $date_format = null) {

  // We require a start time
  if (empty($time_to_convert)) {
    return false;
  }

  if ($end_timezone_string == NULL) {
    $end_timezone_string = fp_get_user_timezone();
  }

  // If the two timezones are different, find the offset
  if ($start_timezone_string != $end_timezone_string) {
    // Create two timezone objects, one for the start and one for
    // the end
    $dateTimeZoneStart = new DateTimeZone($start_timezone_string);
    $dateTimeZoneEnd = new DateTimeZone($end_timezone_string);

    // Create two DateTime objects that will contain the same Unix timestamp, but
    // have different timezones attached to them.
    $dateTimeStart = new DateTime("now", $dateTimeZoneStart);
    $dateTimeEnd = new DateTime("now", $dateTimeZoneEnd);

    // Calculate the UTC offset for the date/time contained in the $dateTimeStart
    // object, but using the timezone rules as defined for the end timezone ($dateTimeEnd)
    $timeOffset = $dateTimeZoneEnd->getOffset($dateTimeStart);

    // If we are converting FROM non-utc TO UTC, then this logic doesn't work!
    // We need to basically grab the reverse logic...
    if ($start_timezone_string != 'UTC' && $end_timezone_string == 'UTC') {
      $x = $dateTimeZoneStart->getOffset($dateTimeEnd);
      $timeOffset = -$x;
    }

  }
  else {
    // If the timezones are the same, there is no offset    
    $timeOffset = 0;
  }

  // Convert the time by the offset
  $converted_time = $time_to_convert + $timeOffset;

  // If we have no given format, just return the time
  if (empty($date_format)) {
    return $converted_time;
  }

  // Convert to the given date format
  return date($date_format, $converted_time);
}