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<?php // phpcs:ignore WordPress.Files.FileName.InvalidClassFileName
/**
 * Get and render iCal feeds.
 * Used by the Upcoming Events widget and the [upcomingevents] shortcode.
 *
 * @package automattic/jetpack
 */

// phpcs:disable Universal.Files.SeparateFunctionsFromOO.Mixed -- TODO: Move classes to appropriately-named class files.

/**
 * Calendar utilities class.
 *
 * phpcs:disable PEAR.NamingConventions.ValidClassName.StartWithCapital
 */
class iCalendarReader {
	// phpcs:enable PEAR.NamingConventions.ValidClassName.StartWithCapital
	// phpcs:disable WordPress.DateTime.RestrictedFunctions.date_date -- we manually handle timezones all over the file.
	// @todo Verify that we're manually handling timezones *correctly*. We probably need more `DateTime` with `$this->timezone` and maybe `wp_date()` and less `strtotime()` and `date()` and `date_i18n()`.
	/**
	 * Count To Do events in calendar.
	 *
	 * @var int
	 */
	public $todo_count = 0;

/**
	 * How many events can be found in calendar.
	 *
	 * @var int
	 */
	public $event_count = 0;

/**
	 * Details about our calendar.
	 *
	 * @var array
	 */
	public $cal = array();

/**
	 * Timezone parsed from the iCalendar feed, if any.
	 *
	 * @var null|DateTimeZone
	 */
	public $timezone = null;

/**
	 * Last iCalendar keyword parsed.
	 *
	 * @var string
	 */
	public $last_keyword;

/**
	 * Class constructor
	 *
	 * @return void
	 */
	public function __construct() {}

/**
	 * Return an array of events
	 *
	 * @param string $url   (default: '') URL of the iCal feed.
	 * @param int    $count Count the number of events.
	 *
	 * @return array | false on failure
	 */
	public function get_events( $url = '', $count = 5 ) {
		$count        = (int) $count;
		$transient_id = 'icalendar_vcal_' . md5( $url ) . '_' . $count;

$vcal = get_transient( $transient_id );
		if ( ! empty( $vcal ) ) {
			if ( isset( $vcal['TIMEZONE'] ) ) {
				$this->timezone = $this->timezone_from_string( $vcal['TIMEZONE'] );
			}

if ( isset( $vcal['VEVENT'] ) ) {
				$vevent = $vcal['VEVENT'];

if ( $count > 0 ) {
					$vevent = array_slice( $vevent, 0, $count );
				}

$this->cal['VEVENT'] = $vevent;

return $this->cal['VEVENT'];
			}
		}

if ( ! $this->parse( $url ) ) {
			return false;
		}

$vcal = array();

if ( $this->timezone ) {
			$vcal['TIMEZONE'] = $this->timezone->getName();
		} else {
			$this->timezone = $this->timezone_from_string( '' );
		}

if ( ! empty( $this->cal['VEVENT'] ) ) {
			$vevent = $this->cal['VEVENT'];

// check for recurring events.
			// $vevent = $this->add_recurring_events( $vevent );.

// remove before caching - no sense in hanging onto the past.
			$vevent = $this->filter_past_and_recurring_events( $vevent );

// order by soonest start date.
			$vevent = $this->sort_by_recent( $vevent );

$vcal['VEVENT'] = $vevent;
		}

set_transient( $transient_id, $vcal, HOUR_IN_SECONDS );

if ( ! isset( $vcal['VEVENT'] ) ) {
			return false;
		}

if ( $count > 0 ) {
			return array_slice( $vcal['VEVENT'], 0, $count );
		}

return $vcal['VEVENT'];
	}

/**
	 * Adjust event's time based on site's timezone.
	 *
	 * @param array $events Array of events.
	 *
	 * @return array
	 */
	public function apply_timezone_offset( $events ) {
		if ( ! $events ) {
			return $events;
		}

// get timezone offset from the timezone name.
		$timezone = wp_timezone();

$offsetted_events = array();

foreach ( $events as $event ) {
			// Don't handle all-day events.
			if ( 8 < strlen( $event['DTSTART'] ) ) {
				$start_time = preg_replace( '/Z$/', '', $event['DTSTART'] );
				$start_time = new DateTime( $start_time, $this->timezone );
				$start_time->setTimeZone( $timezone );
				$event['DTSTART'] = $start_time->format( 'YmdHis\Z' );
				if ( isset( $event['DTEND'] ) ) {
					$end_time = preg_replace( '/Z$/', '', $event['DTEND'] );
					$end_time = new DateTime( $end_time, $this->timezone );
					$end_time->setTimeZone( $timezone );
					$event['DTEND'] = $end_time->format( 'YmdHis\Z' );
				}
			}

$offsetted_events[] = $event;
		}

return $offsetted_events;
	}

/**
	 * Reorganize events into an array of events with standardized data.
	 *
	 * @param array $events Array of events.
	 *
	 * @return array
	 */
	protected function filter_past_and_recurring_events( $events ) {
		$upcoming             = array();
		$set_recurring_events = array();
		/**
		 * This filter allows any time to be passed in for testing or changing timezones, etc...
		 *
		 * @module widgets
		 *
		 * @since 3.4.0
		 *
		 * @param object time() A time object.
		 */
		$current = apply_filters( 'ical_get_current_time', time() );

foreach ( $events as $event ) {

$date_from_ics = strtotime( $event['DTSTART'] );
			if ( isset( $event['DTEND'] ) ) {
				$duration = strtotime( $event['DTEND'] ) - strtotime( $event['DTSTART'] );
			} else {
				$duration = 0;
			}

if ( isset( $event['RRULE'] ) && $this->timezone->getName() && 8 !== strlen( $event['DTSTART'] ) ) {
				try {
					$adjusted_time = new DateTime( $event['DTSTART'], new DateTimeZone( 'UTC' ) );
					$adjusted_time->setTimeZone( new DateTimeZone( $this->timezone->getName() ) );
					$event['DTSTART'] = $adjusted_time->format( 'Ymd\THis' );
					$date_from_ics    = strtotime( $event['DTSTART'] );

if ( isset( $event['EXDATE'] ) ) {
					$exdates = array();
					foreach ( (array) $event['EXDATE'] as $exdate ) {
						try {
							$adjusted_time = new DateTime( $exdate, new DateTimeZone( 'UTC' ) );
							$adjusted_time->setTimeZone( new DateTimeZone( $this->timezone->getName() ) );
							if ( 8 === strlen( $event['DTSTART'] ) ) {
								$exdates[] = $adjusted_time->format( 'Ymd' );
							} else {
								$exdates[] = $adjusted_time->format( 'Ymd\THis' );
							}
						} catch ( Exception $e ) { // phpcs:ignore Generic.CodeAnalysis.EmptyStatement.DetectedCatch
							// Invalid argument to DateTime.
						}
					}
					$event['EXDATE'] = $exdates;
				} else {
					$event['EXDATE'] = array();
				}
			}

if ( ! isset( $event['DTSTART'] ) ) {
				continue;
			}

// Process events with RRULE before other events.
			$rrule = $event['RRULE'] ?? false;
			$uid   = $event['UID'] ?? false;

if ( $rrule && $uid && ! in_array( $uid, $set_recurring_events, true ) ) {

// Break down the RRULE into digestible chunks.
				$rrule_array = array();

foreach ( explode( ';', $event['RRULE'] ) as $rline ) {
					list( $rkey, $rvalue ) = explode( '=', $rline, 2 );
					$rrule_array[ $rkey ]  = $rvalue;
				}

$interval    = $rrule_array['INTERVAL'] ?? 1;
				$rrule_count = $rrule_array['COUNT'] ?? 0;
				$until       = ( isset( $rrule_array['UNTIL'] ) ) ? strtotime( $rrule_array['UNTIL'] ) : strtotime( '+1 year', $current );

// Used to bound event checks.
				$echo_limit = 10;
				$noop       = false;

// Set bydays for the event.
				$weekdays = array( 'SU', 'MO', 'TU', 'WE', 'TH', 'FR', 'SA' );
				$bydays   = $weekdays;

// Calculate a recent start date for incrementing depending on the frequency and interval.
				switch ( $rrule_array['FREQ'] ) {

case 'DAILY':
						$frequency  = 'day';
						$echo_limit = 10;

if ( $date_from_ics >= $current ) {
							$recurring_event_date_start = date( 'Ymd\THis', strtotime( $event['DTSTART'] ) );
						} else {
							// Interval and count.
							$catchup = floor( ( $current - strtotime( $event['DTSTART'] ) ) / ( $interval * DAY_IN_SECONDS ) );
							if ( $rrule_count && $catchup > 0 ) {
								if ( $catchup < $rrule_count ) {
									$rrule_count               -= $catchup;
									$recurring_event_date_start = date(
										'Ymd',
										strtotime(
											'+ ' . ( $interval * $catchup ) . ' days',
											strtotime( $event['DTSTART'] )
										)
									) . date(
										'\THis',
										strtotime( $event['DTSTART'] )
									);
								} else {
									$noop = true;
								}
							} else {
								$recurring_event_date_start = date(
									'Ymd',
									strtotime(
										'+ ' . ( $interval * $catchup ) . ' days',
										strtotime( $event['DTSTART'] )
									)
								) . date(
									'\THis',
									strtotime( $event['DTSTART'] )
								);
							}
						}
						break;

case 'WEEKLY':
						$frequency  = 'week';
						$echo_limit = 4;

// BYDAY exception to current date.
						$day = false;
						if ( ! isset( $rrule_array['BYDAY'] ) ) {
							$rrule_array['BYDAY'] = strtoupper( substr( date( 'D', strtotime( $event['DTSTART'] ) ), 0, 2 ) );
							$day                  = $rrule_array['BYDAY'];
						}
						$bydays = explode( ',', $rrule_array['BYDAY'] );

if ( $date_from_ics >= $current ) {
							$recurring_event_date_start = date( 'Ymd\THis', strtotime( $event['DTSTART'] ) );
						} else {
							// Interval and count.
							$catchup = floor( ( $current - strtotime( $event['DTSTART'] ) ) / ( $interval * WEEK_IN_SECONDS ) );
							if ( $rrule_count && $catchup > 0 ) {
								if ( ( $catchup * count( $bydays ) ) < $rrule_count ) {
									$rrule_count               -= $catchup * count( $bydays ); // Estimate current event count.
									$recurring_event_date_start = date( 'Ymd', strtotime( '+ ' . ( $interval * $catchup ) . ' weeks', strtotime( $event['DTSTART'] ) ) ) . date( '\THis', strtotime( $event['DTSTART'] ) );
								} else {
									$noop = true;
								}
							} else {
								$recurring_event_date_start = date( 'Ymd', strtotime( '+ ' . ( $interval * $catchup ) . ' weeks', strtotime( $event['DTSTART'] ) ) ) . date( '\THis', strtotime( $event['DTSTART'] ) );
							}
						}

// Set to Sunday start.
						if ( ! $noop && 'SU' !== strtoupper( substr( date( 'D', strtotime( $recurring_event_date_start ) ), 0, 2 ) ) ) {
							$recurring_event_date_start = date( 'Ymd', strtotime( 'last Sunday', strtotime( $recurring_event_date_start ) ) ) . date( '\THis', strtotime( $event['DTSTART'] ) );
						}
						break;

case 'MONTHLY':
						$frequency  = 'month';
						$echo_limit = 1;

if ( $date_from_ics >= $current ) {
							$recurring_event_date_start = date( 'Ymd\THis', strtotime( $event['DTSTART'] ) );
						} else {
							// Describe the date in the month.
							if ( isset( $rrule_array['BYDAY'] )
								&& preg_match( '/^(-?\d)([A-Z]{2})/', $rrule_array['BYDAY'], $matches )
							) {
								$day_number = $matches[1];
								$week_day   = $matches[2];

$day_cardinals = array(
									-3 => 'third to last',
									-2 => 'second to last',
									-1 => 'last',
									1  => 'first',
									2  => 'second',
									3  => 'third',
									4  => 'fourth',
									5  => 'fifth',
								);
								$weekdays      = array(
									'SU' => 'Sunday',
									'MO' => 'Monday',
									'TU' => 'Tuesday',
									'WE' => 'Wednesday',
									'TH' => 'Thursday',
									'FR' => 'Friday',
									'SA' => 'Saturday',
								);

$day_cardinal    = $day_cardinals[ $day_number ] ?? '';
								$weekday         = $weekdays[ $week_day ] ?? '';
								$event_date_desc = "$day_cardinal $weekday of ";
							} else {
								$event_date_desc = date( 'd ', strtotime( $event['DTSTART'] ) );
							}

// Interval only.
							if ( $interval > 1 ) {
								$catchup = 0;
								$maybe   = strtotime( $event['DTSTART'] );
								while ( $maybe < $current ) {
									$maybe = strtotime( '+ ' . ( $interval * $catchup ) . ' months', strtotime( $event['DTSTART'] ) );
									++$catchup;
								}
								$recurring_event_date_start = date( 'Ymd', strtotime( $event_date_desc . date( 'F Y', strtotime( '+ ' . ( $interval * ( $catchup - 1 ) ) . ' months', strtotime( $event['DTSTART'] ) ) ) ) ) . date( '\THis', strtotime( $event['DTSTART'] ) );
							} else {
								$recurring_event_date_start = date( 'Ymd', strtotime( $event_date_desc . date( 'F Y', $current ) ) ) . date( '\THis', strtotime( $event['DTSTART'] ) );
							}

// Add one interval if necessary.
							if ( strtotime( $recurring_event_date_start ) < $current ) {
								if ( $interval > 1 ) {
									$recurring_event_date_start = date( 'Ymd', strtotime( $event_date_desc . date( 'F Y', strtotime( '+ ' . ( $interval * $catchup ) . ' months', strtotime( $event['DTSTART'] ) ) ) ) ) . date( '\THis', strtotime( $event['DTSTART'] ) );
								} else {
									try {
										$adjustment = new DateTime( date( 'Y-m-d', $current ) );
										$adjustment->modify( 'first day of next month' );
										$recurring_event_date_start = date( 'Ymd', strtotime( $event_date_desc . $adjustment->format( 'F Y' ) ) ) . date( '\THis', strtotime( $event['DTSTART'] ) );
									} catch ( Exception $e ) { // phpcs:ignore Generic.CodeAnalysis.EmptyStatement.DetectedCatch
										// Invalid argument to DateTime.
									}
								}
							}
						}
						break;

case 'YEARLY':
						$frequency  = 'year';
						$echo_limit = 1;

if ( $date_from_ics >= $current ) {
							$recurring_event_date_start = date( 'Ymd\THis', strtotime( $event['DTSTART'] ) );
						} else {
							$recurring_event_date_start = date( 'Y', $current ) . date( 'md\THis', strtotime( $event['DTSTART'] ) );
							if ( strtotime( $recurring_event_date_start ) < $current ) {
								try {
									$next = new DateTime( date( 'Y-m-d', $current ) );
									$next->modify( 'first day of next year' );
									$recurring_event_date_start = $next->format( 'Y' ) . date( 'md\THis', strtotime( $event['DTSTART'] ) );
								} catch ( Exception $e ) { // phpcs:ignore Generic.CodeAnalysis.EmptyStatement.DetectedCatch
									// Invalid argument to DateTime.
								}
							}
						}
						break;

default:
						$frequency = false;
				}

if ( false !== $frequency && ! $noop ) {
					$count_counter = 1;

// If no COUNT limit, go to 10.
					if ( empty( $rrule_count ) ) {
						$rrule_count = 10;
					}

// Set up EXDATE handling for the event.
					$exdates = $event['EXDATE'] ?? array();

for ( $i = 1; $i <= $echo_limit; $i++ ) {

// Weeks need a daily loop and must check for inclusion in BYDAYS.
						if ( 'week' === $frequency ) {
							$byday_event_date_start = strtotime( $recurring_event_date_start );

foreach ( $weekdays as $day ) {

$event_start_timestamp = $byday_event_date_start;
								$start_time            = date( 'His', $event_start_timestamp );
								$event_end_timestamp   = $event_start_timestamp + $duration;
								$end_time              = date( 'His', $event_end_timestamp );
								if ( 8 === strlen( $event['DTSTART'] ) ) {
									$exdate_compare = date( 'Ymd', $event_start_timestamp );
								} else {
									$exdate_compare = date( 'Ymd\THis', $event_start_timestamp );
								}

if (
									in_array( $day, $bydays, true )
									&& $event_end_timestamp > $current
									&& $event_start_timestamp < $until
									&& $count_counter <= $rrule_count
									&& $event_start_timestamp >= $date_from_ics
									&& ! in_array( $exdate_compare, $exdates, true )
								) {
									if ( 8 === strlen( $event['DTSTART'] ) ) {
										$event['DTSTART'] = date( 'Ymd', $event_start_timestamp );
										$event['DTEND']   = date( 'Ymd', $event_end_timestamp );
									} else {
										$event['DTSTART'] = date( 'Ymd\THis', $event_start_timestamp );
										$event['DTEND']   = date( 'Ymd\THis', $event_end_timestamp );
									}
									if ( $this->timezone->getName() && 8 !== strlen( $event['DTSTART'] ) ) {
										try {
											$adjusted_time = new DateTime( $event['DTSTART'], new DateTimeZone( $this->timezone->getName() ) );
											$adjusted_time->setTimeZone( new DateTimeZone( 'UTC' ) );
											$event['DTSTART'] = $adjusted_time->format( 'Ymd\THis' );

$event['DTEND'] = date( 'Ymd\THis', strtotime( $event['DTSTART'] ) + $duration );
										} catch ( Exception $e ) { // phpcs:ignore Generic.CodeAnalysis.EmptyStatement.DetectedCatch
											// Invalid argument to DateTime.
										}
									}
									$upcoming[] = $event;
									++$count_counter;
								}

// Move forward one day.
								$byday_event_date_start = strtotime( date( 'Ymd\T', strtotime( '+ 1 day', $event_start_timestamp ) ) . $start_time );
							}

// Restore first event timestamp.
							$event_start_timestamp = strtotime( $recurring_event_date_start );

} else {

$event_start_timestamp = strtotime( $recurring_event_date_start );
							$start_time            = date( 'His', $event_start_timestamp );
							$event_end_timestamp   = $event_start_timestamp + $duration;
							$end_time              = date( 'His', $event_end_timestamp );
							if ( 8 === strlen( $event['DTSTART'] ) ) {
								$exdate_compare = date( 'Ymd', $event_start_timestamp );
							} else {
								$exdate_compare = date( 'Ymd\THis', $event_start_timestamp );
							}

if (
								$event_end_timestamp > $current
								&& $event_start_timestamp < $until
								&& $count_counter <= $rrule_count
								&& $event_start_timestamp >= $date_from_ics
								&& ! in_array( $exdate_compare, $exdates, true )
							) {
								if ( 8 === strlen( $event['DTSTART'] ) ) {
									$event['DTSTART'] = date( 'Ymd', $event_start_timestamp );
									$event['DTEND']   = date( 'Ymd', $event_end_timestamp );
								} else {
									$event['DTSTART'] = date( 'Ymd\T', $event_start_timestamp ) . $start_time;
									$event['DTEND']   = date( 'Ymd\T', $event_end_timestamp ) . $end_time;
								}
								if ( $this->timezone->getName() && 8 !== strlen( $event['DTSTART'] ) ) {
									try {
										$adjusted_time = new DateTime( $event['DTSTART'], new DateTimeZone( $this->timezone->getName() ) );
										$adjusted_time->setTimeZone( new DateTimeZone( 'UTC' ) );
										$event['DTSTART'] = $adjusted_time->format( 'Ymd\THis' );

$event['DTEND'] = date( 'Ymd\THis', strtotime( $event['DTSTART'] ) + $duration );
									} catch ( Exception $e ) { // phpcs:ignore Generic.CodeAnalysis.EmptyStatement.DetectedCatch
										// Invalid argument to DateTime.
									}
								}
								$upcoming[] = $event;
								++$count_counter;
							}
						}

// Set up next interval and reset $event['DTSTART'] and $event['DTEND'], keeping timestamps intact.
						$next_start_timestamp = strtotime( "+ {$interval} {$frequency}s", $event_start_timestamp );
						if ( 8 === strlen( $event['DTSTART'] ) ) {
							$event['DTSTART'] = date( 'Ymd', $next_start_timestamp );
							$event['DTEND']   = date( 'Ymd', strtotime( $event['DTSTART'] ) + $duration );
						} else {
							$event['DTSTART'] = date( 'Ymd\THis', $next_start_timestamp );
							$event['DTEND']   = date( 'Ymd\THis', strtotime( $event['DTSTART'] ) + $duration );
						}

// Move recurring event date forward.
						$recurring_event_date_start = $event['DTSTART'];
					}
					$set_recurring_events[] = $uid;

}
			} elseif ( strtotime( $event['DTEND'] ?? $event['DTSTART'] ) >= $current ) { // Process normal events.
				$upcoming[] = $event;
			}
		}
		return $upcoming;
	}

/**
	 * Parse events from an iCalendar feed
	 *
	 * @param string $url (default: '').
	 * @return array | false on failure
	 */
	public function parse( $url = '' ) {
		$cache_group     = 'icalendar_reader_parse';
		$disable_get_key = 'disable:' . md5( $url );

// Check to see if previous attempts have failed.
		if ( false !== wp_cache_get( $disable_get_key, $cache_group ) ) {
			return false;
		}

// rewrite webcal: URI scheme to HTTP.
		$url = preg_replace( '/^webcal/', 'http', $url );
		// try to fetch.
		$r = wp_safe_remote_get(
			$url,
			array(
				'timeout'   => 3,
				'sslverify' => false,
			)
		);
		if ( 200 !== wp_remote_retrieve_response_code( $r ) ) {
			// We were unable to fetch any content, so don't try again for another 60 seconds.
			wp_cache_set( $disable_get_key, 1, $cache_group, 60 );
			return false;
		}

$body = wp_remote_retrieve_body( $r );
		if ( empty( $body ) ) {
			return false;
		}

$body  = str_replace( "\r\n", "\n", $body );
		$lines = preg_split( "/\n(?=[A-Z])/", $body );

if ( empty( $lines ) ) {
			return false;
		}

if ( false === stristr( $lines[0], 'BEGIN:VCALENDAR' ) ) {
			return false;
		}

$type = '';
		foreach ( $lines as $line ) {
			$add = $this->key_value_from_string( $line );
			if ( ! $add ) {
				$this->add_component( $type, false, $line );
				continue;
			}
			list( $keyword, $value ) = $add;

switch ( $keyword ) {
				case 'BEGIN':
				case 'END':
					switch ( $line ) {
						case 'BEGIN:VTODO':
							++$this->todo_count;
							$type = 'VTODO';
							break;
						case 'BEGIN:VEVENT':
							++$this->event_count;
							$type = 'VEVENT';
							break;
						case 'BEGIN:VCALENDAR':
						case 'BEGIN:DAYLIGHT':
						case 'BEGIN:VTIMEZONE':
						case 'BEGIN:STANDARD':
							$type = $value;
							break;
						case 'END:VTODO':
						case 'END:VEVENT':
						case 'END:VCALENDAR':
						case 'END:DAYLIGHT':
						case 'END:VTIMEZONE':
						case 'END:STANDARD':
							$type = 'VCALENDAR';
							break;
					}
					break;
				case 'TZID':
					if (
						'VTIMEZONE' === $type
						&& ! $this->timezone
					) {
						$this->timezone = $this->timezone_from_string( $value );
					}
					break;
				case 'X-WR-TIMEZONE':
					if ( ! $this->timezone ) {
						$this->timezone = $this->timezone_from_string( $value );
					}
					break;
				default:
					$this->add_component( $type, $keyword, $value );
					break;
			}
		}

// Filter for RECURRENCE-IDs.
		$recurrences = array();
		if ( array_key_exists( 'VEVENT', $this->cal ) ) {
			foreach ( $this->cal['VEVENT'] as $event ) {
				if ( isset( $event['RECURRENCE-ID'] ) ) {
					$recurrences[] = $event;
				}
			}
			foreach ( $recurrences as $recurrence ) {
				$count_vevent = count( $this->cal['VEVENT'] );
				for ( $i = 0; $i < $count_vevent; $i++ ) {
					if (
						$this->cal['VEVENT'][ $i ]['UID'] === $recurrence['UID']
						&& ! isset( $this->cal['VEVENT'][ $i ]['RECURRENCE-ID'] )
					) {
						$this->cal['VEVENT'][ $i ]['EXDATE'][] = $recurrence['RECURRENCE-ID'];
						break;
					}
				}
			}
		}

return $this->cal;
	}

/**
	 * Parse key:value from a string
	 *
	 * @param string $text (default: '').
	 * @return array
	 */
	public function key_value_from_string( $text = '' ) {
		preg_match( '/([^:]+)(;[^:]+)?[:]([\w\W]*)/', $text, $matches );

if ( 0 === count( $matches ) ) {
			return false;
		}

return array( $matches[1], $matches[3] );
	}

/**
	 * Convert a timezone name into a timezone object.
	 *
	 * @param string $text Timezone name. Example: America/Chicago.
	 * @return object|null A DateTimeZone object if the conversion was successful.
	 */
	private function timezone_from_string( $text ) {
		try {
			$timezone = new DateTimeZone( $text );
		} catch ( Exception $e ) {
			$blog_timezone = get_option( 'timezone_string' );
			if ( ! $blog_timezone ) {
				$blog_timezone = 'Etc/UTC';
			}

$timezone = new DateTimeZone( $blog_timezone );
		}

return $timezone;
	}

/**
	 * Add a component to the calendar array
	 *
	 * @param string      $component (default: '').
	 * @param bool|string $keyword (default: '').
	 * @param string      $value (default: '').
	 * @return void
	 */
	public function add_component( $component = '', $keyword = '', $value = '' ) {
		if ( ! $keyword ) {
			$keyword = $this->last_keyword;
			switch ( $component ) {
				case 'VEVENT':
					$value = $this->cal[ $component ][ $this->event_count - 1 ][ $keyword ] . $value;
					break;
				case 'VTODO':
					$value = $this->cal[ $component ][ $this->todo_count - 1 ][ $keyword ] . $value;
					break;
			}
		}

/*
		 * Some events have a specific timezone set in their start/end date,
		 * and it may or may not be different than the calendar timzeone.
		 * Valid formats include:
		 * DTSTART;TZID=Pacific Standard Time:20141219T180000
		 * DTEND;TZID=Pacific Standard Time:20141219T200000
		 * EXDATE:19960402T010000Z,19960403T010000Z,19960404T010000Z
		 * EXDATE;VALUE=DATE:2015050
		 * EXDATE;TZID=America/New_York:20150424T170000
		 * EXDATE;TZID=Pacific Standard Time:20120615T140000,20120629T140000,20120706T140000
		 */

// Always store EXDATE as an array.
		if ( stristr( $keyword, 'EXDATE' ) ) {
			$value = explode( ',', $value );
		}

// Adjust DTSTART, DTEND, and EXDATE according to their TZID if set.
		if ( strpos( $keyword, ';' ) && ( stristr( $keyword, 'DTSTART' ) || stristr( $keyword, 'DTEND' ) || stristr( $keyword, 'EXDATE' ) || stristr( $keyword, 'RECURRENCE-ID' ) ) ) {
			$keyword = explode( ';', $keyword );

$tzid = false;
			if ( 2 === count( $keyword ) ) {
				$tparam = $keyword[1];

if ( str_contains( $tparam, 'TZID' ) ) {
					$tzid = $this->timezone_from_string( str_replace( 'TZID=', '', $tparam ) );
				}
			}

// Normalize all times to default UTC.
			if ( $tzid ) {
				$adjusted_times = array();
				foreach ( (array) $value as $v ) {
					try {
						$adjusted_time = new DateTime( $v, $tzid );
						$adjusted_time->setTimeZone( new DateTimeZone( 'UTC' ) );
						$adjusted_times[] = $adjusted_time->format( 'Ymd\THis' );
					} catch ( Exception $e ) {
						// Invalid argument to DateTime.
						return;
					}
				}
				$value = $adjusted_times;
			}

// Format for adding to event.
			$keyword = $keyword[0];
			if ( 'EXDATE' !== $keyword ) {
				$value = implode( (array) $value );
			}
		}

foreach ( (array) $value as $v ) {
			switch ( $component ) {
				case 'VTODO':
					if ( 'EXDATE' === $keyword ) {
						$this->cal[ $component ][ $this->todo_count - 1 ][ $keyword ][] = $v;
					} else {
						$this->cal[ $component ][ $this->todo_count - 1 ][ $keyword ] = $v;
					}
					break;
				case 'VEVENT':
					if ( 'EXDATE' === $keyword ) {
						$this->cal[ $component ][ $this->event_count - 1 ][ $keyword ][] = $v;
					} else {
						$this->cal[ $component ][ $this->event_count - 1 ][ $keyword ] = $v;
					}
					break;
				default:
					$this->cal[ $component ][ $keyword ] = $v;
					break;
			}
		}
		$this->last_keyword = $keyword;
	}

/**
	 * Escape strings with wp_kses, allow links
	 *
	 * @param string $string (default: '') The string to escape.
	 * @return string
	 */
	public function escape( $string = '' ) {
		// Unfold content lines per RFC 5545.
		$string = str_replace( "\n\t", '', $string );
		$string = str_replace( "\n ", '', $string );

$allowed_html = array(
			'a' => array(
				'href'  => array(),
				'title' => array(),
			),
		);

$allowed_tags = '';
		foreach ( array_keys( $allowed_html ) as $tag ) {
			$allowed_tags .= "<{$tag}>";
		}

// Running strip_tags() first with allowed tags to get rid of remaining gallery markup, etc
		// because wp_kses() would only htmlentity'fy that. Then still running wp_kses(), for extra
		// safety and good measure.
		return wp_kses( strip_tags( $string, $allowed_tags ), $allowed_html );
	}

/**
	 * Render the events
	 *
	 * @param string $url  (default: '') URL of the iCal feed.
	 * @param array  $args Event options.
	 *
	 * @return mixed bool|string false on failure, rendered HTML string on success.
	 */
	public function render( $url = '', $args = array() ) {

$args = wp_parse_args(
			$args,
			array(
				'context' => 'widget',
				'number'  => 5,
			)
		);

$events = $this->get_events( $url, $args['number'] );
		$events = $this->apply_timezone_offset( $events );

if ( empty( $events ) ) {
			return false;
		}

ob_start();

if ( 'widget' === $args['context'] ) : ?>
		<ul class="upcoming-events">
			<?php foreach ( $events as $event ) : ?>
			<li>
				<strong class="event-summary">
					<?php
					echo $this->escape( stripslashes( $event['SUMMARY'] ) ); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- this method is built to escape.
					?>
				</strong>
				<span class="event-when"><?php echo esc_html( $this->formatted_date( $event ) ); ?></span>
				<?php if ( ! empty( $event['LOCATION'] ) ) : ?>
					<span class="event-location">
						<?php
						echo $this->escape( stripslashes( $event['LOCATION'] ) ); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- this method is built to escape.
						?>
					</span>
				<?php endif; ?>
				<?php if ( ! empty( $event['DESCRIPTION'] ) ) : ?>
					<span class="event-description">
						<?php
						echo wp_trim_words( $this->escape( stripcslashes( $event['DESCRIPTION'] ) ) ); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- this method is built to escape.
						?>
						</span>
				<?php endif; ?>
			</li>
			<?php endforeach; ?>
		</ul>
			<?php
		endif;

if ( 'shortcode' === $args['context'] ) :
			?>
		<table class="upcoming-events">
			<thead>
				<tr>
					<th><?php esc_html_e( 'Location', 'jetpack' ); ?></th>
					<th><?php esc_html_e( 'When', 'jetpack' ); ?></th>
					<th><?php esc_html_e( 'Summary', 'jetpack' ); ?></th>
					<th><?php esc_html_e( 'Description', 'jetpack' ); ?></th>
				</tr>
			</thead>
			<tbody>
			<?php foreach ( $events as $event ) : ?>
				<tr>
					<td>
					<?php
					echo empty( $event['LOCATION'] )
						? '&nbsp;'
						: $this->escape( stripslashes( $event['LOCATION'] ) ); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- this method is built to escape.
					?>
					</td>
					<td><?php echo esc_html( $this->formatted_date( $event ) ); ?></td>
					<td>
					<?php
					echo empty( $event['SUMMARY'] )
						? '&nbsp;'
						: $this->escape( stripslashes( $event['SUMMARY'] ) ); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- this method is built to escape.
					?>
					</td>
					<td>
					<?php
					echo empty( $event['DESCRIPTION'] )
						? '&nbsp;'
						: wp_trim_words( $this->escape( stripcslashes( $event['DESCRIPTION'] ) ) ); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- this method is built to escape.
					?>
					</td>
				</tr>
			<?php endforeach; ?>
			</tbody>
		</table>
			<?php
		endif;

$rendered = ob_get_clean();

if ( empty( $rendered ) ) {
			return false;
		}

return $rendered;
	}

/**
	 * Return a localized string with information about the event's date and time,
	 * or starting date and end date.
	 *
	 * @param array $event Info about the event.
	 *
	 * @return string
	 */
	public function formatted_date( $event ) {
		$date_format = get_option( 'date_format' );
		$time_format = get_option( 'time_format' );
		$start       = strtotime( $event['DTSTART'] );
		$end         = isset( $event['DTEND'] ) ? strtotime( $event['DTEND'] ) : false;

$all_day = ( 8 === strlen( $event['DTSTART'] ) );

if ( ! $all_day && $this->timezone ) {
			try {
				$timezone_offset = $this->timezone->getOffset( new DateTime( $event['DTSTART'] ) );
				$start          += $timezone_offset;

if ( $end ) {
					$end += $timezone_offset;
				}
			} catch ( Exception $e ) {
				// Invalid argument to DateTime.
				return '';
			}
		}
		$single_day = $end ? ( $end - $start ) <= DAY_IN_SECONDS : true;

/* translators: Date and time */
		$date_with_time = __( '%1$s at %2$s', 'jetpack' );
		/* translators: Two dates with a separator */
		$two_dates = __( '%1$s &ndash; %2$s', 'jetpack' );

// we'll always have the start date. Maybe with time.
		if ( $all_day ) {
			$date = date_i18n( $date_format, $start );
		} else {
			$date = sprintf(
				$date_with_time,
				date_i18n( $date_format, $start ),
				date_i18n( $time_format, $start )
			);
		}

// single day, timed.
		if ( $single_day && ! $all_day && false !== $end ) {
			$date = sprintf( $two_dates, $date, date_i18n( $time_format, $end ) );
		}

// multi-day.
		if ( ! $single_day ) {

if ( $all_day ) {
				// DTEND for multi-day events represents "until", not "including", so subtract one minute.
				$end_date = date_i18n( $date_format, $end - 60 );
			} else {
				$end_date = sprintf( $date_with_time, date_i18n( $date_format, $end ), date_i18n( $time_format, $end ) );
			}

$date = sprintf( $two_dates, $date, $end_date );

}

return $date;
	}

/**
	 * Sort list of events by event date.
	 *
	 * @param array $list List of events.
	 *
	 * @return array
	 */
	protected function sort_by_recent( $list ) {
		$dates       = array();
		$sorted_list = array();

foreach ( $list as $key => $row ) {
			$date = $row['DTSTART'];
			// pad some time onto an all day date.
			if ( 8 === strlen( $date ) ) {
				$date .= 'T000000Z';
			}
			$dates[ $key ] = $date;
		}
		asort( $dates );
		foreach ( $dates as $key => $value ) {
			$sorted_list[ $key ] = $list[ $key ];
		}
		unset( $list );
		return $sorted_list;
	}

// phpcs:enable WordPress.DateTime.RestrictedFunctions.date_date
}

/**
 * Wrapper function for iCalendarReader->get_events()
 *
 * @param string $url   (default: '').
 * @param int    $count Number of events to fetch.
 * @return array
 */
function icalendar_get_events( $url = '', $count = 5 ) {
	/*
	 * Find your calendar's address
	 * https://support.google.com/calendar/bin/answer.py?hl=en&answer=37103
	 */
	return ( new iCalendarReader() )->get_events( $url, $count );
}

/**
 * Wrapper function for iCalendarReader->render()
 *
 * @param string $url (default: '').
 * @param array  $args Options when rendering events.
 *
 * @return mixed bool|string false on failure, rendered HTML string on success.
 */
function icalendar_render_events( $url = '', $args = array() ) {
	return ( new iCalendarReader() )->render( $url, $args );
}

Editing: icalendar-reader.php

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