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<?php

/**

 * @file

 * Parse iCal data.

 *

 * This file must be included when these functions are needed.

 */

/**

 * Return an array of iCalendar information from an iCalendar file.

 *

 * No timezone adjustment is performed in the import since the timezone

 * conversion needed will vary depending on whether the value is being

 * imported into the database (when it needs to be converted to UTC), is being

 * viewed on a site that has user-configurable timezones (when it needs to be

 * converted to the user's timezone), if it needs to be converted to the site

 * timezone, or if it is a date without a timezone which should not have any

 * timezone conversion applied.

 *

 * Properties that have dates and times are converted to sub-arrays like:

 * 'datetime' => Date in YYYY-MM-DD HH:MM format, not timezone adjusted.

 * 'all_day'  => Whether this is an all-day event.

 * 'tz'       => The timezone of the date, could be blank for absolute times

 *               that should get no timezone conversion.

 *

 * Exception dates can have muliple values and are returned as arrayslike the

 * above for each exception date.

 *

 * Most other properties are returned as PROPERTY => VALUE.

 *

 * Each item in the VCALENDAR will return an array like:

 * [0] => Array (

 *   [TYPE] => VEVENT

 *   [UID] => 104

 *   [SUMMARY] => An example event

 *   [URL] => http://example.com/node/1

 *   [DTSTART] => Array (

 *     [datetime] => 1997-09-07 09:00:00

 *     [all_day] => 0

 *     [tz] => US/Eastern

 *   )

 *   [DTEND] => Array (

 *     [datetime] => 1997-09-07 11:00:00

 *     [all_day] => 0

 *     [tz] => US/Eastern

 *   )

 *   [RRULE] => Array (

 *     [FREQ] => Array (

 *       [0] => MONTHLY

 *     )

 *     [BYDAY] => Array (

 *       [0] => 1SU

 *       [1] => -1SU

 *     )

 *   )

 *   [EXDATE] => Array (

 *     [0] = Array (

 *       [datetime] => 1997-09-21 09:00:00

 *       [all_day] => 0

 *       [tz] => US/Eastern

 *     )

 *     [1] = Array (

 *       [datetime] => 1997-10-05 09:00:00

 *       [all_day] => 0

 *       [tz] => US/Eastern

 *     )

 *   )

 *   [RDATE] => Array (

 *     [0] = Array (

 *       [datetime] => 1997-09-21 09:00:00

 *       [all_day] => 0

 *       [tz] => US/Eastern

 *     )

 *     [1] = Array (

 *       [datetime] => 1997-10-05 09:00:00

 *       [all_day] => 0

 *       [tz] => US/Eastern

 *     )

 *   )

 * )

 *

 * @todo

 *   figure out how to handle this if subgroups are nested,

 *   like a VALARM nested inside a VEVENT.

 *

 * @param string $filename

 *   Location (local or remote) of a valid iCalendar file.

 *

 * @return array

 *   An array with all the elements from the ical.

 */

function date_ical_import($filename) {

  // Fetch the iCal data. If file is a URL, use drupal_http_request. fopen

  // isn't always configured to allow network connections.

  if (substr($filename, 0, 4) == 'http') {

    // Fetch the ical data from the specified network location.

    $icaldatafetch = drupal_http_request($filename);

    // Check the return result.

    if ($icaldatafetch->error) {

      watchdog('date ical', 'HTTP Request Error importing %filename: @error', array('%filename' => $filename, '@error' => $icaldatafetch->error));

      return FALSE;

    }

    // Break the return result into one array entry per lines.

    $icaldatafolded = explode("\n", $icaldatafetch->data);

  }

  else {

    $icaldatafolded = @file($filename, FILE_IGNORE_NEW_LINES);

    if ($icaldatafolded === FALSE) {

      watchdog('date ical', 'Failed to open file: %filename', array('%filename' => $filename));

      return FALSE;

    }

  }

  // Verify this is iCal data.

  if (trim($icaldatafolded[0]) != 'BEGIN:VCALENDAR') {

    watchdog('date ical', 'Invalid calendar file: %filename', array('%filename' => $filename));

    return FALSE;

  }

  return date_ical_parse($icaldatafolded);

}

/**

 * Returns an array of iCalendar information from an iCalendar file.

 *

 * As date_ical_import() but different param.

 *

 * @param array $icaldatafolded

 *   An array of lines from an ical feed.

 *

 * @return array

 *   An array with all the elements from the ical.

 */

function date_ical_parse(array $icaldatafolded = array()) {

  $items = array();

  // Verify this is iCal data.

  if (trim($icaldatafolded[0]) != 'BEGIN:VCALENDAR') {

    watchdog('date ical', 'Invalid calendar file.');

    return FALSE;

  }

  // "Unfold" wrapped lines.

  $icaldata = array();

  foreach ($icaldatafolded as $line) {

    $out = array();

    // See if this looks like the beginning of a new property or value. If not,

    // it is a continuation of the previous line. The regex is to ensure that

    // wrapped QUOTED-PRINTABLE data is kept intact.

    if (!preg_match('/([A-Z]+)[:;](.*)/', $line, $out)) {

      // Trim up to 1 leading space from wrapped line per iCalendar standard.

      $line = array_pop($icaldata) . (ltrim(substr($line, 0, 1)) . substr($line, 1));

    }

    $icaldata[] = $line;

  }

  unset($icaldatafolded);

  // Parse the iCal information.

  $parents = array();

  $subgroups = array();

  $vcal = '';

  foreach ($icaldata as $line) {

    $line = trim($line);

    $vcal .= $line . "\n";

    // Deal with begin/end tags separately.

    if (preg_match('/(BEGIN|END):V(\S+)/', $line, $matches)) {

      $closure = $matches[1];

      $type = 'V' . $matches[2];

      if ($closure == 'BEGIN') {

        array_push($parents, $type);

        array_push($subgroups, array());

      }

      elseif ($closure == 'END') {

        end($subgroups);

        $subgroup = &$subgroups[key($subgroups)];

        switch ($type) {

          case 'VCALENDAR':

            if (prev($subgroups) == FALSE) {

              $items[] = array_pop($subgroups);

            }

            else {

              $parent[array_pop($parents)][] = array_pop($subgroups);

            }

            break;

          // Add the timezones in with their index their TZID.

          case 'VTIMEZONE':

            $subgroup = end($subgroups);

            $id = $subgroup['TZID'];

            unset($subgroup['TZID']);

            // Append this subgroup onto the one above it.

            prev($subgroups);

            $parent = &$subgroups[key($subgroups)];

            $parent[$type][$id] = $subgroup;

            array_pop($subgroups);

            array_pop($parents);

            break;

          // Do some fun stuff with durations and all_day events and then append

          // to parent.

          case 'VEVENT':

          case 'VALARM':

          case 'VTODO':

          case 'VJOURNAL':

          case 'VVENUE':

          case 'VFREEBUSY':

          default:

            // Can't be sure whether DTSTART is before or after DURATION, so

            // parse DURATION at the end.

            if (isset($subgroup['DURATION'])) {

              date_ical_parse_duration($subgroup, 'DURATION');

            }

            // Add a top-level indication for the 'All day' condition. Leave it

            // in the individual date components, too, so it is always available

            // even when you are working with only a portion of the VEVENT

            // array, like in Feed API parsers.

            $subgroup['all_day'] = FALSE;

            // iCal spec states 'The "DTEND" property for a "VEVENT" calendar

            // component specifies the non-inclusive end of the event'. Adjust

            // multi-day events to remove the extra day because the Date code

            // assumes the end date is inclusive.

            if (!empty($subgroup['DTEND']) && (!empty($subgroup['DTEND']['all_day']))) {

              // Make the end date one day earlier.

              $date = new DateObject($subgroup['DTEND']['datetime'] . ' 00:00:00', $subgroup['DTEND']['tz']);

              date_modify($date, '-1 day');

              $subgroup['DTEND']['datetime'] = date_format($date, 'Y-m-d');

            }

            // If a start datetime is defined AND there is no definition for

            // the end datetime THEN make the end datetime equal the start

            // datetime and if it is an all day event define the entire event

            // as a single all day event.

            if (!empty($subgroup['DTSTART']) &&

               (empty($subgroup['DTEND']) && empty($subgroup['RRULE']) && empty($subgroup['RRULE']['COUNT']))) {

              $subgroup['DTEND'] = $subgroup['DTSTART'];

            }

            // Add this element to the parent as an array under the component

            // name.

            if (!empty($subgroup['DTSTART']['all_day'])) {

              $subgroup['all_day'] = TRUE;

            }

            // Add this element to the parent as an array under the.

            prev($subgroups);

            $parent = &$subgroups[key($subgroups)];

            $parent[$type][] = $subgroup;

            array_pop($subgroups);

            array_pop($parents);

        }

      }

    }

    // Handle all other possibilities.

    else {

      // Grab current subgroup.

      end($subgroups);

      $subgroup = &$subgroups[key($subgroups)];

      // Split up the line into nice pieces for PROPERTYNAME,

      // PROPERTYATTRIBUTES, and PROPERTYVALUE.

      preg_match('/([^;:]+)(?:;([^:]*))?:(.+)/', $line, $matches);

      $name = !empty($matches[1]) ? strtoupper(trim($matches[1])) : '';

      $field = !empty($matches[2]) ? $matches[2] : '';

      $data = !empty($matches[3]) ? $matches[3] : '';

      $parse_result = '';

      switch ($name) {

        // Keep blank lines out of the results.

        case '':

          break;

        // Lots of properties have date values that must be parsed out.

        case 'CREATED':

        case 'LAST-MODIFIED':

        case 'DTSTART':

        case 'DTEND':

        case 'DTSTAMP':

        case 'FREEBUSY':

        case 'DUE':

        case 'COMPLETED':

          $parse_result = date_ical_parse_date($field, $data);

          break;

        case 'EXDATE':

        case 'RDATE':

          $parse_result = date_ical_parse_exceptions($field, $data);

          break;

        case 'TRIGGER':

          // A TRIGGER can either be a date or in the form -PT1H.

          if (!empty($field)) {

            $parse_result = date_ical_parse_date($field, $data);

          }

          else {

            $parse_result = array('DATA' => $data);

          }

          break;

        case 'DURATION':

          // Can't be sure whether DTSTART is before or after DURATION in

          // the VEVENT, so store the data and parse it at the end.

          $parse_result = array('DATA' => $data);

          break;

        case 'RRULE':

        case 'EXRULE':

          $parse_result = date_ical_parse_rrule($field, $data);

          break;

        case 'STATUS':

        case 'SUMMARY':

        case 'DESCRIPTION':

          $parse_result = date_ical_parse_text($field, $data);

          break;

        case 'LOCATION':

          $parse_result = date_ical_parse_location($field, $data);

          break;

        // For all other properties, just store the property and the value.

        // This can be expanded on in the future if other properties should

        // be given special treatment.

        default:

          $parse_result = $data;

      }

      // Store the result of our parsing.

      $subgroup[$name] = $parse_result;

    }

  }

  return $items;

}

/**

 * Parses a ical date element.

 *

 * Possible formats to parse include:

 * - PROPERTY:YYYYMMDD[T][HH][MM][SS][Z]

 * - PROPERTY;VALUE=DATE:YYYYMMDD[T][HH][MM][SS][Z]

 * - PROPERTY;VALUE=DATE-TIME:YYYYMMDD[T][HH][MM][SS][Z]

 * - PROPERTY;TZID=XXXXXXXX;VALUE=DATE:YYYYMMDD[T][HH][MM][SS]

 * - PROPERTY;TZID=XXXXXXXX:YYYYMMDD[T][HH][MM][SS]

 *

 * The property and the colon before the date are removed in the import

 * process above and we are left with $field and $data.

 *

 * @param string $field

 *   The text before the colon and the date, i.e.

 *   ';VALUE=DATE:', ';VALUE=DATE-TIME:', ';TZID='

 * @param string $data

 *   The date itself, after the colon, in the format YYYYMMDD[T][HH][MM][SS][Z]

 *   'Z', if supplied, means the date is in UTC.

 *

 * @return array

 *   Consisting of:

 *   'datetime' => Date in YYYY-MM-DD HH:MM format, not timezone adjusted.

 *   'all_day'  => Whether this is an all-day event with no time.

 *   'tz'       => The timezone of the date, could be blank if the iCal has no

 *                 timezone; the ical specs say no timezone conversion should be

 *                 done if no timezone info is supplied.

 *

 * @todo Another option for dates is the format PROPERTY;VALUE=PERIOD:XXXX. The

 *   period may include a duration, or a date and a duration, or two dates, so

 *   would have to be split into parts and run through date_ical_parse_date()

 *   and date_ical_parse_duration(). This is not commonly used, so ignored for

 *   now. It will take more work to figure how to support that.

 */

function date_ical_parse_date($field, $data) {

  $items = array('datetime' => '', 'all_day' => '', 'tz' => '');

  if (empty($data)) {

    return $items;

  }

  // Make this a little more whitespace independent.

  $data = trim($data);

  // Turn the properties into a nice indexed array of

  // array(PROPERTYNAME => PROPERTYVALUE);

  $field_parts = preg_split('/[;:]/', $field);

  $properties = array();

  foreach ($field_parts as $part) {

    if (strpos($part, '=') !== FALSE) {

      $tmp = explode('=', $part);

      $properties[$tmp[0]] = $tmp[1];

    }

  }

  // Make this a little more whitespace independent.

  $data = trim($data);

  // Record if a time has been found.

  $has_time = FALSE;

  // If a format is specified, parse it according to that format.

  if (isset($properties['VALUE'])) {

    switch ($properties['VALUE']) {

      case 'DATE':

        preg_match(DATE_REGEX_ICAL_DATE, $data, $regs);

        // Date.

        $datetime = date_pad($regs[1]) . '-' . date_pad($regs[2]) . '-' . date_pad($regs[3]);

        break;

      case 'DATE-TIME':

        preg_match(DATE_REGEX_ICAL_DATETIME, $data, $regs);

        // Date.

        $datetime = date_pad($regs[1]) . '-' . date_pad($regs[2]) . '-' . date_pad($regs[3]);

        // Time.

        $datetime .= ' ' . date_pad($regs[4]) . ':' . date_pad($regs[5]) . ':' . date_pad($regs[6]);

        $has_time = TRUE;

        break;

    }

  }

  // If no format is specified, attempt a loose match.

  else {

    preg_match(DATE_REGEX_LOOSE, $data, $regs);

    if (!empty($regs) && count($regs) > 2) {

      // Date.

      $datetime = date_pad($regs[1]) . '-' . date_pad($regs[2]) . '-' . date_pad($regs[3]);

      if (isset($regs[4])) {

        $has_time = TRUE;

        // Time.

        $datetime .= ' ' . (!empty($regs[5]) ? date_pad($regs[5]) : '00') .

         ':' . (!empty($regs[6]) ? date_pad($regs[6]) : '00') .

         ':' . (!empty($regs[7]) ? date_pad($regs[7]) : '00');

      }

    }

  }

  // Use timezone if explicitly declared.

  if (isset($properties['TZID'])) {

    $tz = $properties['TZID'];

    // Fix alternatives like US-Eastern which should be US/Eastern.

    $tz = str_replace('-', '/', $tz);

    // Unset invalid timezone names.

    module_load_include('inc', 'date_api', 'date_api.admin');

    $tz = _date_timezone_replacement($tz);

    if (!date_timezone_is_valid($tz)) {

      $tz = '';

    }

  }

  // If declared as UTC with terminating 'Z', use that timezone.

  elseif (strpos($data, 'Z') !== FALSE) {

    $tz = 'UTC';

  }

  // Otherwise this date is floating.

  else {

    $tz = '';

  }

  $items['datetime'] = $datetime;

  $items['all_day'] = $has_time ? FALSE : TRUE;

  $items['tz'] = $tz;

  return $items;

}

/**

 * Parse an ical repeat rule.

 *

 * @return array

 *   A nested array in the form of 'PROPERTY' => array(VALUES) where

 *   'PROPERTIES' includes 'FREQ', 'INTERVAL', 'COUNT', 'BYDAY', 'BYMONTH',

 *   'BYYEAR', 'UNTIL'.

 */

function date_ical_parse_rrule($field, $data) {

  $data = preg_replace("/RRULE.*:/", '', $data);

  $items = array('DATA' => $data);

  $rrule = explode(';', $data);

  foreach ($rrule as $key => $value) {

    $param = explode('=', $value);

    // Must be some kind of invalid data.

    if (count($param) != 2) {

      continue;

    }

    if ($param[0] == 'UNTIL') {

      $values = date_ical_parse_date('', $param[1]);

    }

    else {

      $values = explode(',', $param[1]);

    }

    // Treat items differently if they have multiple or single values.

    if (in_array($param[0], array('FREQ', 'INTERVAL', 'COUNT', 'WKST'))) {

      $items[$param[0]] = $param[1];

    }

    else {

      $items[$param[0]] = $values;

    }

  }

  return $items;

}

/**

 * Parse exception dates (can be multiple values).

 *

 * @return array

 *   An array of date value arrays.

 */

function date_ical_parse_exceptions($field, $data) {

  $data = str_replace($field . ':', '', $data);

  $items = array('DATA' => $data);

  $ex_dates = explode(',', $data);

  foreach ($ex_dates as $ex_date) {

    $items[] = date_ical_parse_date('', $ex_date);

  }

  return $items;

}

/**

 * Parses the duration of the event.

 *

 * Example:

 * DURATION:PT1H30M

 * DURATION:P1Y2M.

 *

 * @param array $subgroup

 *   Array of other values in the vevent so we can check for DTSTART.

 * @param string $value_name

 *   The name of the value to process; defaults to 'DURATION'.

 */

function date_ical_parse_duration(array &$subgroup, $value_name = 'DURATION') {

  $items = $subgroup[$value_name];

  $data = $items['DATA'];

  preg_match('/^P(\d{1,4}[Y])?(\d{1,2}[M])?(\d{1,2}[W])?(\d{1,2}[D])?([T]{0,1})?(\d{1,2}[H])?(\d{1,2}[M])?(\d{1,2}[S])?/', $data, $duration);

  $items['year'] = isset($duration[1]) ? str_replace('Y', '', $duration[1]) : '';

  $items['month'] = isset($duration[2]) ? str_replace('M', '', $duration[2]) : '';

  $items['week'] = isset($duration[3]) ? str_replace('W', '', $duration[3]) : '';

  $items['day'] = isset($duration[4]) ? str_replace('D', '', $duration[4]) : '';

  $items['hour'] = isset($duration[6]) ? str_replace('H', '', $duration[6]) : '';

  $items['minute'] = isset($duration[7]) ? str_replace('M', '', $duration[7]) : '';

  $items['second'] = isset($duration[8]) ? str_replace('S', '', $duration[8]) : '';

  $start_date = array_key_exists('DTSTART', $subgroup) ? $subgroup['DTSTART']['datetime'] : date_format(date_now(), DATE_FORMAT_ISO);

  $timezone = array_key_exists('DTSTART', $subgroup) ? $subgroup['DTSTART']['tz'] : variable_get('date_default_timezone');

  if (empty($timezone)) {

    $timezone = 'UTC';

  }

  $date = new DateObject($start_date, $timezone);

  $date2 = clone $date;

  foreach ($items as $item => $count) {

    if ($count > 0) {

      date_modify($date2, '+' . $count . ' ' . $item);

    }

  }

  $format = isset($subgroup['DTSTART']['type']) && $subgroup['DTSTART']['type'] == 'DATE' ? 'Y-m-d' : 'Y-m-d H:i:s';

  $subgroup['DTEND'] = array(

    'datetime' => date_format($date2, DATE_FORMAT_DATETIME),

    'all_day' => isset($subgroup['DTSTART']['all_day']) ? $subgroup['DTSTART']['all_day'] : 0,

    'tz' => $timezone,

  );

  $duration = date_format($date2, 'U') - date_format($date, 'U');

  $subgroup['DURATION'] = array('DATA' => $data, 'DURATION' => $duration);

}

/**

 * Parse and clean up ical text elements.

 */

function date_ical_parse_text($field, $data) {

  if (strstr($field, 'QUOTED-PRINTABLE')) {

    $data = quoted_printable_decode($data);

  }

  // Strip line breaks within element.

  $data = str_replace(array("\r\n ", "\n ", "\r "), '', $data);

  // Put in line breaks where encoded.

  $data = str_replace(array("\\n", "\\N"), "\n", $data);

  // Remove other escaping.

  $data = stripslashes($data);

  return $data;

}

/**

 * Parse location elements.

 *

 * Catch situations like the upcoming.org feed that uses

 * LOCATION;VENUE-UID="http://upcoming.yahoo.com/venue/104/":111 First Street...

 * or more normal LOCATION;UID=123:111 First Street...

 * Upcoming feed would have been improperly broken on the ':' in http:// so we

 * paste the $field and $data back together first.

 *

 * Use non-greedy check for ':' in case there are more of them in the address.

 */

function date_ical_parse_location($field, $data) {

  if (preg_match('/UID=[?"](.+)[?"][*?:](.+)/', $field . ':' . $data, $matches)) {

    $location = array();

    $location['UID'] = $matches[1];

    $location['DESCRIPTION'] = stripslashes($matches[2]);

    return $location;

  }

  else {

    // Remove other escaping.

    $location = stripslashes($data);

    return $location;

  }

}

/**

 * Return a date object for the ical date, adjusted to its local timezone.

 *

 * @param array $ical_date

 *   An array of ical date information created in the ical import.

 * @param string $to_tz

 *   The timezone to convert the date's value to.

 *

 * @return object

 *   A timezone-adjusted date object.

 */

function date_ical_date(array $ical_date, $to_tz = FALSE) {

  // If the ical date has no timezone, must assume it is stateless

  // so treat it as a local date.

  if (empty($ical_date['datetime'])) {

    return NULL;

  }

  elseif (empty($ical_date['tz'])) {

    $from_tz = date_default_timezone();

  }

  else {

    $from_tz = $ical_date['tz'];

  }

  if (strlen($ical_date['datetime']) < 11) {

    $ical_date['datetime'] .= ' 00:00:00';

  }

  $date = new DateObject($ical_date['datetime'], new DateTimeZone($from_tz));

  if ($to_tz && !empty($ical_date['tz']) && $to_tz != $ical_date['tz']) {

    date_timezone_set($date, timezone_open($to_tz));

  }

  return $date;

}

/**

 * Escape #text elements for safe iCal use.

 *

 * @param string $text

 *   Text to escape.

 *

 * @return string

 *   Escaped text

 */

function date_ical_escape_text($text) {

  $text = drupal_html_to_text($text);

  $text = trim($text);

  // @todo Per #38130 the iCal specs don't want : and " escaped but there was

  // some reason for adding this in. Need to watch this and see if anything

  // breaks.

  // $text = str_replace('"', '\"', $text);

  // $text = str_replace(":", "\:", $text);

  $text = preg_replace("/\\\b/", "\\\\", $text);

  $text = str_replace(",", "\,", $text);

  $text = str_replace(";", "\;", $text);

  $text = str_replace("\n", "\\n ", $text);

  return trim($text);

}

/**

 * Build an iCal RULE from $form_values.

 *

 * @param array $form_values

 *   An array constructed like the one created by date_ical_parse_rrule().

 *     [RRULE] => Array (

 *       [FREQ] => Array (

 *         [0] => MONTHLY

 *       )

 *       [BYDAY] => Array (

 *         [0] => 1SU

 *         [1] => -1SU

 *       )

 *       [UNTIL] => Array (

 *         [datetime] => 1997-21-31 09:00:00

 *         [all_day] => 0

 *         [tz] => US/Eastern

 *       )

 *     )

 *     [EXDATE] => Array (

 *       [0] = Array (

 *         [datetime] => 1997-09-21 09:00:00

 *         [all_day] => 0

 *         [tz] => US/Eastern

 *       )

 *       [1] = Array (

 *         [datetime] => 1997-10-05 09:00:00

 *         [all_day] => 0

 *         [tz] => US/Eastern

 *       )

 *     )

 *     [RDATE] => Array (

 *       [0] = Array (

 *         [datetime] => 1997-09-21 09:00:00

 *         [all_day] => 0

 *         [tz] => US/Eastern

 *       )

 *       [1] = Array (

 *         [datetime] => 1997-10-05 09:00:00

 *         [all_day] => 0

 *         [tz] => US/Eastern

 *       )

 *     )

 */

function date_api_ical_build_rrule(array $form_values) {

  $rrule = '';

  if (empty($form_values) || !is_array($form_values)) {

    return $rrule;

  }

  // Grab the RRULE data and put them into iCal RRULE format.

  $rrule .= 'RRULE:FREQ=' . (!array_key_exists('FREQ', $form_values) ? 'DAILY' : $form_values['FREQ']);

  $rrule .= ';INTERVAL=' . (!array_key_exists('INTERVAL', $form_values) ? 1 : $form_values['INTERVAL']);

  // Unset the empty 'All' values.

  if (array_key_exists('BYDAY', $form_values) && is_array($form_values['BYDAY'])) {

    unset($form_values['BYDAY']['']);

  }

  if (array_key_exists('BYMONTH', $form_values) && is_array($form_values['BYMONTH'])) {

    unset($form_values['BYMONTH']['']);

  }

  if (array_key_exists('BYMONTHDAY', $form_values) && is_array($form_values['BYMONTHDAY'])) {

    unset($form_values['BYMONTHDAY']['']);

  }

  if (array_key_exists('BYDAY', $form_values) && is_array($form_values['BYDAY']) && $byday = implode(",", $form_values['BYDAY'])) {

    $rrule .= ';BYDAY=' . $byday;

  }

  if (array_key_exists('BYMONTH', $form_values) && is_array($form_values['BYMONTH']) && $bymonth = implode(",", $form_values['BYMONTH'])) {

    $rrule .= ';BYMONTH=' . $bymonth;

  }

  if (array_key_exists('BYMONTHDAY', $form_values) && is_array($form_values['BYMONTHDAY']) && $bymonthday = implode(",", $form_values['BYMONTHDAY'])) {

    $rrule .= ';BYMONTHDAY=' . $bymonthday;

  }

  // The UNTIL date is supposed to always be expressed in UTC. The input date

  // values may already have been converted to a date object on a previous

  // pass, so check for that.

  if (array_key_exists('UNTIL', $form_values) && array_key_exists('datetime', $form_values['UNTIL']) && !empty($form_values['UNTIL']['datetime'])) {

    // We only collect a date for UNTIL, but we need it to be inclusive, so

    // force it to a full datetime element at the last second of the day.

    if (!is_object($form_values['UNTIL']['datetime'])) {

      // If this is a date without time, give it time.

      if (strlen($form_values['UNTIL']['datetime']) < 11) {

        $granularity_options = drupal_map_assoc(array(

          'year',

          'month',

          'day',

          'hour',

          'minute',

          'second',

        ));

        $form_values['UNTIL']['datetime'] .= ' 23:59:59';

        $form_values['UNTIL']['granularity'] = serialize($granularity_options);

        $form_values['UNTIL']['all_day'] = FALSE;

      }

      $until = date_ical_date($form_values['UNTIL'], 'UTC');

    }

    else {

      $until = $form_values['UNTIL']['datetime'];

    }

    $rrule .= ';UNTIL=' . date_format($until, DATE_FORMAT_ICAL) . 'Z';

  }

  // Our form doesn't allow a value for COUNT, but it may be needed by modules

  // using the API, so add it to the rule.

  if (array_key_exists('COUNT', $form_values)) {

    $rrule .= ';COUNT=' . $form_values['COUNT'];

  }

  // iCal rules presume the week starts on Monday unless otherwise specified,

  // so we'll specify it.

  if (array_key_exists('WKST', $form_values)) {

    $rrule .= ';WKST=' . $form_values['WKST'];

  }

  else {

    $rrule .= ';WKST=' . date_repeat_dow2day(variable_get('date_first_day', 0));

  }

  // Exceptions dates go last, on their own line. The input date values may

  // already have been converted to a date object on a previous pass, so check

  // for that.

  if (isset($form_values['EXDATE']) && is_array($form_values['EXDATE'])) {

    $ex_dates = array();

    foreach ($form_values['EXDATE'] as $value) {

      if (!empty($value['datetime'])) {

        $date = !is_object($value['datetime']) ? date_ical_date($value, 'UTC') : $value['datetime'];

        $ex_date = !empty($date) ? date_format($date, DATE_FORMAT_ICAL) . 'Z' : '';

        if (!empty($ex_date)) {

          $ex_dates[] = $ex_date;

        }

      }

    }

    if (!empty($ex_dates)) {

      sort($ex_dates);

      $rrule .= chr(13) . chr(10) . 'EXDATE:' . implode(',', $ex_dates);

    }

  }

  elseif (!empty($form_values['EXDATE'])) {

    $rrule .= chr(13) . chr(10) . 'EXDATE:' . $form_values['EXDATE'];

  }

  // Exceptions dates go last, on their own line.

  if (isset($form_values['RDATE']) && is_array($form_values['RDATE'])) {

    $ex_dates = array();

    foreach ($form_values['RDATE'] as $value) {

      $date = !is_object($value['datetime']) ? date_ical_date($value, 'UTC') : $value['datetime'];

      $ex_date = !empty($date) ? date_format($date, DATE_FORMAT_ICAL) . 'Z' : '';

      if (!empty($ex_date)) {

        $ex_dates[] = $ex_date;

      }

    }

    if (!empty($ex_dates)) {

      sort($ex_dates);

      $rrule .= chr(13) . chr(10) . 'RDATE:' . implode(',', $ex_dates);

    }

  }

  elseif (!empty($form_values['RDATE'])) {

    $rrule .= chr(13) . chr(10) . 'RDATE:' . $form_values['RDATE'];

  }

  return $rrule;

}