<?php

/*
 * Modified for slx-admin to support streaming, some functions removed that are not needed,
 * Carbon removed, Honor window size when calculating recurring events, ...
 */

/**
 * This PHP class will read an ICS (`.ics`, `.ical`, `.ifb`) file, parse it and return an
 * array of its contents.
 *
 * PHP 5 (≥ 5.3.9)
 *
 * @author  Jonathan Goode <https://github.com/u01jmg3>
 * @license https://opensource.org/licenses/mit-license.php MIT License
 * @version 2.1.20
 */
class ICalParser
{
	// phpcs:disable Generic.Arrays.DisallowLongArraySyntax

	const DATE_TIME_FORMAT = 'Ymd\THis';
	const ICAL_DATE_TIME_TEMPLATE = 'TZID=%s:';
	const ISO_8601_WEEK_START = 'MO';
	const RECURRENCE_EVENT = 'Generated recurrence event';
	const TIME_FORMAT = 'His';
	const TIME_ZONE_UTC = 'UTC';
	const UNIX_FORMAT = 'U';

	/**
	 * Tracks the number of alarms in the current iCal feed
	 *
	 * @var integer
	 */
	public $alarmCount = 0;

	/**
	 * Tracks the number of events in the current iCal feed
	 *
	 * @var integer
	 */
	public $eventCount = 0;

	/**
	 * Tracks the free/busy count in the current iCal feed
	 *
	 * @var integer
	 */
	public $freeBusyCount = 0;

	/**
	 * Tracks the number of todos in the current iCal feed
	 *
	 * @var integer
	 */
	public $todoCount = 0;

	/**
	 * The value in years to use for indefinite, recurring events
	 *
	 * @var integer
	 */
	public $defaultSpan = 2;

	/**
	 * Enables customisation of the default time zone
	 *
	 * @var string
	 */
	public $defaultTimeZone;

	/**
	 * The two letter representation of the first day of the week
	 *
	 * @var string
	 */
	public $defaultWeekStart = self::ISO_8601_WEEK_START;

	/**
	 * Toggles whether to skip the parsing of recurrence rules
	 *
	 * @var boolean
	 */
	public $skipRecurrence = false;

	/**
	 * With this being non-null the parser will ignore all events more than roughly this many days after now.
	 *
	 * @var integer
	 */
	public $filterDaysBefore;

	/**
	 * With this being non-null the parser will ignore all events more than roughly this many days before now.
	 *
	 * @var integer
	 */
	public $filterDaysAfter;

	/**
	 * @var string Which object type we're currently handling while parsing.
	 */
	private $parseStateComponent = '';

	/**
	 * @var string Current line being read (in case of continuation).
	 */
	private $currentLineBuffer = '';

	/**
	 * @var string Chunk of data currently being handled - might stop mid-line.
	 */
	private $feedBuffer = '';

	/**
	 * @var bool whether we ever saw a BEGIN:VCALENDAR in the data
	 */
	private $hasSeenStart = false;

	/**
	 * The parsed calendar
	 *
	 * @var array
	 */
	public $cal = array();

	/**
	 * Tracks the VFREEBUSY component
	 *
	 * @var integer
	 */
	protected $freeBusyIndex = 0;

	/**
	 * Variable to track the previous keyword
	 *
	 * @var string
	 */
	protected $lastKeyword;

	/**
	 * Cache valid IANA time zone IDs to avoid unnecessary lookups
	 *
	 * @var array
	 */
	protected $validIanaTimeZones = array();

	/**
	 * Event recurrence instances that have been altered
	 *
	 * @var array
	 */
	protected $alteredRecurrenceInstances = array();

	/**
	 * An associative array containing weekday conversion data
	 *
	 * The order of the days in the array follow the ISO-8601 specification of a week.
	 *
	 * @var array
	 */
	protected $weekdays = array(
		'MO' => 'monday',
		'TU' => 'tuesday',
		'WE' => 'wednesday',
		'TH' => 'thursday',
		'FR' => 'friday',
		'SA' => 'saturday',
		'SU' => 'sunday',
	);

	/**
	 * An associative array containing frequency conversion terms
	 *
	 * @var array
	 */
	protected $frequencyConversion = array(
		'DAILY' => 'day',
		'WEEKLY' => 'week',
		'MONTHLY' => 'month',
		'YEARLY' => 'year',
	);

	/**
	 * Define which variables can be configured
	 *
	 * @var array
	 */
	private static $configurableOptions = array(
		'defaultSpan',
		'defaultTimeZone',
		'defaultWeekStart',
		'filterDaysAfter',
		'filterDaysBefore',
		'skipRecurrence',
	);

	/**
	 * CLDR time zones mapped to IANA time zones.
	 *
	 * @var array
	 */
	private static $cldrTimeZonesMap = array(
		'(UTC-12:00) International Date Line West' => 'Etc/GMT+12',
		'(UTC-11:00) Coordinated Universal Time-11' => 'Etc/GMT+11',
		'(UTC-10:00) Hawaii' => 'Pacific/Honolulu',
		'(UTC-09:00) Alaska' => 'America/Anchorage',
		'(UTC-08:00) Pacific Time (US & Canada)' => 'America/Los_Angeles',
		'(UTC-07:00) Arizona' => 'America/Phoenix',
		'(UTC-07:00) Chihuahua, La Paz, Mazatlan' => 'America/Chihuahua',
		'(UTC-07:00) Mountain Time (US & Canada)' => 'America/Denver',
		'(UTC-06:00) Central America' => 'America/Guatemala',
		'(UTC-06:00) Central Time (US & Canada)' => 'America/Chicago',
		'(UTC-06:00) Guadalajara, Mexico City, Monterrey' => 'America/Mexico_City',
		'(UTC-06:00) Saskatchewan' => 'America/Regina',
		'(UTC-05:00) Bogota, Lima, Quito, Rio Branco' => 'America/Bogota',
		'(UTC-05:00) Chetumal' => 'America/Cancun',
		'(UTC-05:00) Eastern Time (US & Canada)' => 'America/New_York',
		'(UTC-05:00) Indiana (East)' => 'America/Indianapolis',
		'(UTC-04:00) Asuncion' => 'America/Asuncion',
		'(UTC-04:00) Atlantic Time (Canada)' => 'America/Halifax',
		'(UTC-04:00) Caracas' => 'America/Caracas',
		'(UTC-04:00) Cuiaba' => 'America/Cuiaba',
		'(UTC-04:00) Georgetown, La Paz, Manaus, San Juan' => 'America/La_Paz',
		'(UTC-04:00) Santiago' => 'America/Santiago',
		'(UTC-03:30) Newfoundland' => 'America/St_Johns',
		'(UTC-03:00) Brasilia' => 'America/Sao_Paulo',
		'(UTC-03:00) Cayenne, Fortaleza' => 'America/Cayenne',
		'(UTC-03:00) City of Buenos Aires' => 'America/Buenos_Aires',
		'(UTC-03:00) Greenland' => 'America/Godthab',
		'(UTC-03:00) Montevideo' => 'America/Montevideo',
		'(UTC-03:00) Salvador' => 'America/Bahia',
		'(UTC-02:00) Coordinated Universal Time-02' => 'Etc/GMT+2',
		'(UTC-01:00) Azores' => 'Atlantic/Azores',
		'(UTC-01:00) Cabo Verde Is.' => 'Atlantic/Cape_Verde',
		'(UTC) Coordinated Universal Time' => 'Etc/GMT',
		'(UTC+00:00) Casablanca' => 'Africa/Casablanca',
		'(UTC+00:00) Dublin, Edinburgh, Lisbon, London' => 'Europe/London',
		'(UTC+00:00) Monrovia, Reykjavik' => 'Atlantic/Reykjavik',
		'(UTC+01:00) Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna' => 'Europe/Berlin',
		'(UTC+01:00) Belgrade, Bratislava, Budapest, Ljubljana, Prague' => 'Europe/Budapest',
		'(UTC+01:00) Brussels, Copenhagen, Madrid, Paris' => 'Europe/Paris',
		'(UTC+01:00) Sarajevo, Skopje, Warsaw, Zagreb' => 'Europe/Warsaw',
		'(UTC+01:00) West Central Africa' => 'Africa/Lagos',
		'(UTC+02:00) Amman' => 'Asia/Amman',
		'(UTC+02:00) Athens, Bucharest' => 'Europe/Bucharest',
		'(UTC+02:00) Beirut' => 'Asia/Beirut',
		'(UTC+02:00) Cairo' => 'Africa/Cairo',
		'(UTC+02:00) Chisinau' => 'Europe/Chisinau',
		'(UTC+02:00) Damascus' => 'Asia/Damascus',
		'(UTC+02:00) Harare, Pretoria' => 'Africa/Johannesburg',
		'(UTC+02:00) Helsinki, Kyiv, Riga, Sofia, Tallinn, Vilnius' => 'Europe/Kiev',
		'(UTC+02:00) Jerusalem' => 'Asia/Jerusalem',
		'(UTC+02:00) Kaliningrad' => 'Europe/Kaliningrad',
		'(UTC+02:00) Tripoli' => 'Africa/Tripoli',
		'(UTC+02:00) Windhoek' => 'Africa/Windhoek',
		'(UTC+03:00) Baghdad' => 'Asia/Baghdad',
		'(UTC+03:00) Istanbul' => 'Europe/Istanbul',
		'(UTC+03:00) Kuwait, Riyadh' => 'Asia/Riyadh',
		'(UTC+03:00) Minsk' => 'Europe/Minsk',
		'(UTC+03:00) Moscow, St. Petersburg, Volgograd' => 'Europe/Moscow',
		'(UTC+03:00) Nairobi' => 'Africa/Nairobi',
		'(UTC+03:30) Tehran' => 'Asia/Tehran',
		'(UTC+04:00) Abu Dhabi, Muscat' => 'Asia/Dubai',
		'(UTC+04:00) Baku' => 'Asia/Baku',
		'(UTC+04:00) Izhevsk, Samara' => 'Europe/Samara',
		'(UTC+04:00) Port Louis' => 'Indian/Mauritius',
		'(UTC+04:00) Tbilisi' => 'Asia/Tbilisi',
		'(UTC+04:00) Yerevan' => 'Asia/Yerevan',
		'(UTC+04:30) Kabul' => 'Asia/Kabul',
		'(UTC+05:00) Ashgabat, Tashkent' => 'Asia/Tashkent',
		'(UTC+05:00) Ekaterinburg' => 'Asia/Yekaterinburg',
		'(UTC+05:00) Islamabad, Karachi' => 'Asia/Karachi',
		'(UTC+05:30) Chennai, Kolkata, Mumbai, New Delhi' => 'Asia/Calcutta',
		'(UTC+05:30) Sri Jayawardenepura' => 'Asia/Colombo',
		'(UTC+05:45) Kathmandu' => 'Asia/Katmandu',
		'(UTC+06:00) Astana' => 'Asia/Almaty',
		'(UTC+06:00) Dhaka' => 'Asia/Dhaka',
		'(UTC+06:30) Yangon (Rangoon)' => 'Asia/Rangoon',
		'(UTC+07:00) Bangkok, Hanoi, Jakarta' => 'Asia/Bangkok',
		'(UTC+07:00) Krasnoyarsk' => 'Asia/Krasnoyarsk',
		'(UTC+07:00) Novosibirsk' => 'Asia/Novosibirsk',
		'(UTC+08:00) Beijing, Chongqing, Hong Kong, Urumqi' => 'Asia/Shanghai',
		'(UTC+08:00) Irkutsk' => 'Asia/Irkutsk',
		'(UTC+08:00) Kuala Lumpur, Singapore' => 'Asia/Singapore',
		'(UTC+08:00) Perth' => 'Australia/Perth',
		'(UTC+08:00) Taipei' => 'Asia/Taipei',
		'(UTC+08:00) Ulaanbaatar' => 'Asia/Ulaanbaatar',
		'(UTC+09:00) Osaka, Sapporo, Tokyo' => 'Asia/Tokyo',
		'(UTC+09:00) Pyongyang' => 'Asia/Pyongyang',
		'(UTC+09:00) Seoul' => 'Asia/Seoul',
		'(UTC+09:00) Yakutsk' => 'Asia/Yakutsk',
		'(UTC+09:30) Adelaide' => 'Australia/Adelaide',
		'(UTC+09:30) Darwin' => 'Australia/Darwin',
		'(UTC+10:00) Brisbane' => 'Australia/Brisbane',
		'(UTC+10:00) Canberra, Melbourne, Sydney' => 'Australia/Sydney',
		'(UTC+10:00) Guam, Port Moresby' => 'Pacific/Port_Moresby',
		'(UTC+10:00) Hobart' => 'Australia/Hobart',
		'(UTC+10:00) Vladivostok' => 'Asia/Vladivostok',
		'(UTC+11:00) Chokurdakh' => 'Asia/Srednekolymsk',
		'(UTC+11:00) Magadan' => 'Asia/Magadan',
		'(UTC+11:00) Solomon Is., New Caledonia' => 'Pacific/Guadalcanal',
		'(UTC+12:00) Anadyr, Petropavlovsk-Kamchatsky' => 'Asia/Kamchatka',
		'(UTC+12:00) Auckland, Wellington' => 'Pacific/Auckland',
		'(UTC+12:00) Coordinated Universal Time+12' => 'Etc/GMT-12',
		'(UTC+12:00) Fiji' => 'Pacific/Fiji',
		"(UTC+13:00) Nuku'alofa" => 'Pacific/Tongatapu',
		'(UTC+13:00) Samoa' => 'Pacific/Apia',
		'(UTC+14:00) Kiritimati Island' => 'Pacific/Kiritimati',
	);

	/**
	 * Maps Windows (non-CLDR) time zone ID to IANA ID. This is pragmatic but not 100% precise as one Windows zone ID
	 * maps to multiple IANA IDs (one for each territory). For all practical purposes this should be good enough, though.
	 *
	 * Source: http://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml
	 *
	 * @var array
	 */
	private static $windowsTimeZonesMap = array(
		'AUS Central Standard Time' => 'Australia/Darwin',
		'AUS Eastern Standard Time' => 'Australia/Sydney',
		'Afghanistan Standard Time' => 'Asia/Kabul',
		'Alaskan Standard Time' => 'America/Anchorage',
		'Aleutian Standard Time' => 'America/Adak',
		'Altai Standard Time' => 'Asia/Barnaul',
		'Arab Standard Time' => 'Asia/Riyadh',
		'Arabian Standard Time' => 'Asia/Dubai',
		'Arabic Standard Time' => 'Asia/Baghdad',
		'Argentina Standard Time' => 'America/Buenos_Aires',
		'Astrakhan Standard Time' => 'Europe/Astrakhan',
		'Atlantic Standard Time' => 'America/Halifax',
		'Aus Central W. Standard Time' => 'Australia/Eucla',
		'Azerbaijan Standard Time' => 'Asia/Baku',
		'Azores Standard Time' => 'Atlantic/Azores',
		'Bahia Standard Time' => 'America/Bahia',
		'Bangladesh Standard Time' => 'Asia/Dhaka',
		'Belarus Standard Time' => 'Europe/Minsk',
		'Bougainville Standard Time' => 'Pacific/Bougainville',
		'Canada Central Standard Time' => 'America/Regina',
		'Cape Verde Standard Time' => 'Atlantic/Cape_Verde',
		'Caucasus Standard Time' => 'Asia/Yerevan',
		'Cen. Australia Standard Time' => 'Australia/Adelaide',
		'Central America Standard Time' => 'America/Guatemala',
		'Central Asia Standard Time' => 'Asia/Almaty',
		'Central Brazilian Standard Time' => 'America/Cuiaba',
		'Central Europe Standard Time' => 'Europe/Budapest',
		'Central European Standard Time' => 'Europe/Warsaw',
		'Central Pacific Standard Time' => 'Pacific/Guadalcanal',
		'Central Standard Time (Mexico)' => 'America/Mexico_City',
		'Central Standard Time' => 'America/Chicago',
		'Chatham Islands Standard Time' => 'Pacific/Chatham',
		'China Standard Time' => 'Asia/Shanghai',
		'Cuba Standard Time' => 'America/Havana',
		'Dateline Standard Time' => 'Etc/GMT+12',
		'E. Africa Standard Time' => 'Africa/Nairobi',
		'E. Australia Standard Time' => 'Australia/Brisbane',
		'E. Europe Standard Time' => 'Europe/Chisinau',
		'E. South America Standard Time' => 'America/Sao_Paulo',
		'Easter Island Standard Time' => 'Pacific/Easter',
		'Eastern Standard Time (Mexico)' => 'America/Cancun',
		'Eastern Standard Time' => 'America/New_York',
		'Egypt Standard Time' => 'Africa/Cairo',
		'Ekaterinburg Standard Time' => 'Asia/Yekaterinburg',
		'FLE Standard Time' => 'Europe/Kiev',
		'Fiji Standard Time' => 'Pacific/Fiji',
		'GMT Standard Time' => 'Europe/London',
		'GTB Standard Time' => 'Europe/Bucharest',
		'Georgian Standard Time' => 'Asia/Tbilisi',
		'Greenland Standard Time' => 'America/Godthab',
		'Greenwich Standard Time' => 'Atlantic/Reykjavik',
		'Haiti Standard Time' => 'America/Port-au-Prince',
		'Hawaiian Standard Time' => 'Pacific/Honolulu',
		'India Standard Time' => 'Asia/Calcutta',
		'Iran Standard Time' => 'Asia/Tehran',
		'Israel Standard Time' => 'Asia/Jerusalem',
		'Jordan Standard Time' => 'Asia/Amman',
		'Kaliningrad Standard Time' => 'Europe/Kaliningrad',
		'Korea Standard Time' => 'Asia/Seoul',
		'Libya Standard Time' => 'Africa/Tripoli',
		'Line Islands Standard Time' => 'Pacific/Kiritimati',
		'Lord Howe Standard Time' => 'Australia/Lord_Howe',
		'Magadan Standard Time' => 'Asia/Magadan',
		'Magallanes Standard Time' => 'America/Punta_Arenas',
		'Marquesas Standard Time' => 'Pacific/Marquesas',
		'Mauritius Standard Time' => 'Indian/Mauritius',
		'Middle East Standard Time' => 'Asia/Beirut',
		'Montevideo Standard Time' => 'America/Montevideo',
		'Morocco Standard Time' => 'Africa/Casablanca',
		'Mountain Standard Time (Mexico)' => 'America/Chihuahua',
		'Mountain Standard Time' => 'America/Denver',
		'Myanmar Standard Time' => 'Asia/Rangoon',
		'N. Central Asia Standard Time' => 'Asia/Novosibirsk',
		'Namibia Standard Time' => 'Africa/Windhoek',
		'Nepal Standard Time' => 'Asia/Katmandu',
		'New Zealand Standard Time' => 'Pacific/Auckland',
		'Newfoundland Standard Time' => 'America/St_Johns',
		'Norfolk Standard Time' => 'Pacific/Norfolk',
		'North Asia East Standard Time' => 'Asia/Irkutsk',
		'North Asia Standard Time' => 'Asia/Krasnoyarsk',
		'North Korea Standard Time' => 'Asia/Pyongyang',
		'Omsk Standard Time' => 'Asia/Omsk',
		'Pacific SA Standard Time' => 'America/Santiago',
		'Pacific Standard Time (Mexico)' => 'America/Tijuana',
		'Pacific Standard Time' => 'America/Los_Angeles',
		'Pakistan Standard Time' => 'Asia/Karachi',
		'Paraguay Standard Time' => 'America/Asuncion',
		'Romance Standard Time' => 'Europe/Paris',
		'Russia Time Zone 10' => 'Asia/Srednekolymsk',
		'Russia Time Zone 11' => 'Asia/Kamchatka',
		'Russia Time Zone 3' => 'Europe/Samara',
		'Russian Standard Time' => 'Europe/Moscow',
		'SA Eastern Standard Time' => 'America/Cayenne',
		'SA Pacific Standard Time' => 'America/Bogota',
		'SA Western Standard Time' => 'America/La_Paz',
		'SE Asia Standard Time' => 'Asia/Bangkok',
		'Saint Pierre Standard Time' => 'America/Miquelon',
		'Sakhalin Standard Time' => 'Asia/Sakhalin',
		'Samoa Standard Time' => 'Pacific/Apia',
		'Sao Tome Standard Time' => 'Africa/Sao_Tome',
		'Saratov Standard Time' => 'Europe/Saratov',
		'Singapore Standard Time' => 'Asia/Singapore',
		'South Africa Standard Time' => 'Africa/Johannesburg',
		'Sri Lanka Standard Time' => 'Asia/Colombo',
		'Sudan Standard Time' => 'Africa/Tripoli',
		'Syria Standard Time' => 'Asia/Damascus',
		'Taipei Standard Time' => 'Asia/Taipei',
		'Tasmania Standard Time' => 'Australia/Hobart',
		'Tocantins Standard Time' => 'America/Araguaina',
		'Tokyo Standard Time' => 'Asia/Tokyo',
		'Tomsk Standard Time' => 'Asia/Tomsk',
		'Tonga Standard Time' => 'Pacific/Tongatapu',
		'Transbaikal Standard Time' => 'Asia/Chita',
		'Turkey Standard Time' => 'Europe/Istanbul',
		'Turks And Caicos Standard Time' => 'America/Grand_Turk',
		'US Eastern Standard Time' => 'America/Indianapolis',
		'US Mountain Standard Time' => 'America/Phoenix',
		'UTC' => 'Etc/GMT',
		'UTC+12' => 'Etc/GMT-12',
		'UTC+13' => 'Etc/GMT-13',
		'UTC-02' => 'Etc/GMT+2',
		'UTC-08' => 'Etc/GMT+8',
		'UTC-09' => 'Etc/GMT+9',
		'UTC-11' => 'Etc/GMT+11',
		'Ulaanbaatar Standard Time' => 'Asia/Ulaanbaatar',
		'Venezuela Standard Time' => 'America/Caracas',
		'Vladivostok Standard Time' => 'Asia/Vladivostok',
		'W. Australia Standard Time' => 'Australia/Perth',
		'W. Central Africa Standard Time' => 'Africa/Lagos',
		'W. Europe Standard Time' => 'Europe/Berlin',
		'W. Mongolia Standard Time' => 'Asia/Hovd',
		'West Asia Standard Time' => 'Asia/Tashkent',
		'West Bank Standard Time' => 'Asia/Hebron',
		'West Pacific Standard Time' => 'Pacific/Port_Moresby',
		'Yakutsk Standard Time' => 'Asia/Yakutsk',
	);

	/**
	 * If `$filterDaysBefore` or `$filterDaysAfter` are set then the events are filtered according to the window defined
	 * by this field and `$windowMaxTimestamp`.
	 *
	 * @var integer
	 */
	private $windowMinTimestamp;

	/**
	 * If `$filterDaysBefore` or `$filterDaysAfter` are set then the events are filtered according to the window defined
	 * by this field and `$windowMinTimestamp`.
	 *
	 * @var integer
	 */
	private $windowMaxTimestamp;

	/**
	 * `true` if either `$filterDaysBefore` or `$filterDaysAfter` are set.
	 *
	 * @var boolean
	 */
	private $shouldFilterByWindow;

	/**
	 * Creates the ICal object
	 *
	 * @param mixed $files
	 * @param array $options
	 * @return void
	 * @throws Exception
	 */
	public function __construct(array $options = array())
	{
		ini_set('auto_detect_line_endings', '1');

		foreach ($options as $option => $value) {
			if (in_array($option, self::$configurableOptions)) {
				$this->{$option} = $value;
			}
		}

		// Fallback to use the system default time zone
		if (!isset($this->defaultTimeZone) || !$this->isValidTimeZoneId($this->defaultTimeZone)) {
			$this->defaultTimeZone = date_default_timezone_get();
		}

		// Ideally you would use `PHP_INT_MIN` from PHP 7
		$php_int_min = -2147483648;

		$this->windowMinTimestamp = is_null($this->filterDaysBefore) ? $php_int_min : (new DateTime('now'))->sub(new DateInterval('P' . $this->filterDaysBefore . 'D'))->getTimestamp();
		$this->windowMaxTimestamp = is_null($this->filterDaysAfter) ? PHP_INT_MAX : (new DateTime('now'))->add(new DateInterval('P' . $this->filterDaysAfter . 'D'))->getTimestamp();

		$this->shouldFilterByWindow = !is_null($this->filterDaysBefore) || !is_null($this->filterDaysAfter);
	}

	/**
	 * Feed more data to the parser. This can be a chunk of arbitrary length, it
	 * is not required to end on a line break.
	 *
	 * @param string $data
	 */
	public function feedData($data)
	{
		$this->feedBuffer .= $data;
		$start = 0;
		$bufferLen = strlen($this->feedBuffer);
		while (($newLine = strcspn($this->feedBuffer, "\r\n", $start) + $start) !== $bufferLen) {
			$length = $newLine - $start;
			if ($length > 1) {
				if ($this->feedBuffer[$start] === ' ' || $this->feedBuffer[$start] === '\t') {
					// Continuation of previous line
					$this->currentLineBuffer .= substr($this->feedBuffer, $start + 1, $length - 1);
				} else {
					// New line, flush previous one
					$this->handleLine($this->currentLineBuffer);
					$this->currentLineBuffer = substr($this->feedBuffer, $start, $length);
				}
			}
			$start = $newLine + 1;
		}
		$this->feedBuffer = substr($this->feedBuffer, $start);
	}

	/**
	 * Finish feeding more data to the parser, process the data.
	 */
	public function finish()
	{
		// Flush
		$this->feedData("\n*\n");
		$this->currentLineBuffer = '';
		$this->feedBuffer = '';
		$this->processEvents();

		if (!$this->skipRecurrence) {
			$this->processRecurrences();

			// Apply changes to altered recurrence instances
			if (!empty($this->alteredRecurrenceInstances)) {
				$events = $this->cal['VEVENT'];

				foreach ($this->alteredRecurrenceInstances as $alteredRecurrenceInstance) {
					if (isset($alteredRecurrenceInstance['altered-event'])) {
						$alteredEvent = $alteredRecurrenceInstance['altered-event'];
						$key = key($alteredEvent);
						$events[$key] = $alteredEvent[$key];
					}
				}

				$this->cal['VEVENT'] = $events;
			}
		}

		if ($this->shouldFilterByWindow) {
			$this->reduceEventsToMinMaxRange();
		}

		$this->processDateConversions();
	}

	/**
	 * True if this resembles a calendar, i.e. we've seen the
	 * BEGIN:VCALENDAR line at some point.
	 *
	 * @return bool
	 */
	public function isValid()
	{
		return $this->hasSeenStart;
	}

	/**
	 * Process next completed line from file
	 *
	 * @param string $line
	 */
	protected function handleLine($line)
	{
		$line = rtrim($line); // Trim trailing whitespace
		$line = $this->removeUnprintableChars($line);

		if (empty($line)) {
			return;
		}

		$add = $this->keyValueFromString($line);

		if ($add === false) {
			return;
		}

		$keyword = $add[0];
		$values = $add[1]; // May be an array containing multiple values

		if (!is_array($values)) {
			if (!empty($values)) {
				$values = array($values); // Make an array as not already
				$blankArray = array(); // Empty placeholder array
				array_push($values, $blankArray);
			} else {
				$values = array(); // Use blank array to ignore this line
			}
		} elseif (empty($values[0])) {
			$values = array(); // Use blank array to ignore this line
		}

		// Reverse so that our array of properties is processed first
		$values = array_reverse($values);

		foreach ($values as $value) {
			switch ($line) {
				// https://www.kanzaki.com/docs/ical/vtodo.html
			case 'BEGIN:VTODO':
				if (!is_array($value)) {
					$this->todoCount++;
				}

				$this->parseStateComponent = 'VTODO';

				break;

				// https://www.kanzaki.com/docs/ical/vevent.html
			case 'BEGIN:VEVENT':
				if (!is_array($value)) {
					$this->eventCount++;
				}

				$this->parseStateComponent = 'VEVENT';

				break;

				// https://www.kanzaki.com/docs/ical/vfreebusy.html
			case 'BEGIN:VFREEBUSY':
				if (!is_array($value)) {
					$this->freeBusyIndex++;
				}

				$this->parseStateComponent = 'VFREEBUSY';

				break;

			case 'BEGIN:VALARM':
				if (!is_array($value)) {
					$this->alarmCount++;
				}

				$this->parseStateComponent = 'VALARM';

				break;

			case 'END:VALARM':
				$this->parseStateComponent = 'VEVENT';

				break;

			case 'BEGIN:DAYLIGHT':
			case 'BEGIN:STANDARD':
			case 'BEGIN:VTIMEZONE':
				$this->parseStateComponent = $value;

				break;

			case 'END:DAYLIGHT':
			case 'END:STANDARD':
			case 'END:VFREEBUSY':
			case 'END:VTIMEZONE':
			case 'END:VTODO':
				$this->parseStateComponent = 'VCALENDAR';

				break;

			case 'BEGIN:VCALENDAR':
				$this->hasSeenStart = true;
				$this->parseStateComponent = $value;

				break;

			case 'END:VCALENDAR':
				$this->parseStateComponent = '';

				break;

			case 'END:VEVENT':
				if ($this->shouldFilterByWindow) {
					$this->removeLastEventIfOutsideWindowAndNonRecurring();
				}

				$this->parseStateComponent = 'VCALENDAR';

				break;

			default:
				if (!empty($this->parseStateComponent)) {
					$this->addCalendarComponentWithKeyAndValue($this->parseStateComponent, $keyword, $value);
				}
				break;
			}
		}
	}

	/**
	 * Removes the last event (i.e. most recently parsed) if its start date is outside the window spanned by
	 * `$windowMinTimestamp` / `$windowMaxTimestamp`.
	 *
	 * @return void
	 */
	protected function removeLastEventIfOutsideWindowAndNonRecurring()
	{
		$events = $this->cal['VEVENT'];

		if (!empty($events)) {
			$lastIndex = count($events) - 1;
			$lastEvent = $events[$lastIndex];

			if (empty($lastEvent['RRULE']) && $this->doesEventStartOutsideWindow($lastEvent)) {
				$this->eventCount--;

				unset($events[$lastIndex]);
			}

			$this->cal['VEVENT'] = $events;
		}
	}

	/**
	 * Reduces the number of events to the defined minimum and maximum range
	 *
	 * @return void
	 */
	protected function reduceEventsToMinMaxRange()
	{
		$events = (isset($this->cal['VEVENT'])) ? $this->cal['VEVENT'] : array();

		if (!empty($events)) {
			foreach ($events as $key => $anEvent) {
				if ($anEvent === null) {
					unset($events[$key]);

					continue;
				}

				if ($this->doesEventStartOutsideWindow($anEvent)) {
					$this->eventCount--;

					unset($events[$key]);

					continue;
				}
			}

			$this->cal['VEVENT'] = $events;
		}
	}

	/**
	 * Determines whether the event start date is outside `$windowMinTimestamp` / `$windowMaxTimestamp`.
	 * Returns `true` for invalid dates.
	 *
	 * @param array $event
	 * @return boolean
	 */
	protected function doesEventStartOutsideWindow(array $event)
	{
		return !isset($event['DTSTART']) || !$this->isValidDate($event['DTSTART'])
			|| $this->isOutOfRange($event['DTSTART'], $this->windowMinTimestamp, $this->windowMaxTimestamp);
	}

	/**
	 * Determines whether a valid iCalendar date is within a given range
	 *
	 * @param string $calendarDate
	 * @param integer $minTimestamp
	 * @param integer $maxTimestamp
	 * @return boolean
	 */
	protected function isOutOfRange($calendarDate, $minTimestamp, $maxTimestamp)
	{
		$timestamp = strtotime(explode('T', $calendarDate)[0]);

		return $timestamp < $minTimestamp || $timestamp > $maxTimestamp;
	}

	/**
	 * Unfolds an iCal file in preparation for parsing
	 * (https://icalendar.org/iCalendar-RFC-5545/3-1-content-lines.html)
	 *
	 * @param array $lines
	 * @return array
	 */
	protected function unfold(array $lines)
	{
		$string = implode(PHP_EOL, $lines);
		$string = preg_replace('/' . PHP_EOL . '[ \t]/', '', $string);

		$lines = explode(PHP_EOL, $string);

		return $lines;
	}

	/**
	 * Add one key and value pair to the `$this->cal` array
	 *
	 * @param string $component
	 * @param string|boolean $keyword
	 * @param string $value
	 * @return void
	 */
	protected function addCalendarComponentWithKeyAndValue($component, $keyword, $value)
	{
		if ($keyword == false) {
			$keyword = $this->lastKeyword;
		}

		switch ($component) {
		case 'VALARM':
			$key1 = 'VEVENT';
			$key2 = ($this->eventCount - 1);
			$key3 = $component;

			if (!isset($this->cal[$key1][$key2][$key3]["{$keyword}_array"])) {
				$this->cal[$key1][$key2][$key3]["{$keyword}_array"] = array();
			}

			if (is_array($value)) {
				// Add array of properties to the end
				array_push($this->cal[$key1][$key2][$key3]["{$keyword}_array"], $value);
			} else {
				if (!isset($this->cal[$key1][$key2][$key3][$keyword])) {
					$this->cal[$key1][$key2][$key3][$keyword] = $value;
				}

				if ($this->cal[$key1][$key2][$key3][$keyword] !== $value) {
					$this->cal[$key1][$key2][$key3][$keyword] .= ',' . $value;
				}
			}
			break;

		case 'VEVENT':
			$key1 = $component;
			$key2 = ($this->eventCount - 1);

			if (!isset($this->cal[$key1][$key2]["{$keyword}_array"])) {
				$this->cal[$key1][$key2]["{$keyword}_array"] = array();
			}

			if (is_array($value)) {
				// Add array of properties to the end
				array_push($this->cal[$key1][$key2]["{$keyword}_array"], $value);
			} else {
				if (!isset($this->cal[$key1][$key2][$keyword])) {
					$this->cal[$key1][$key2][$keyword] = $value;
				}

				if ($keyword === 'EXDATE') {
					if (trim($value) === $value) {
						$array = array_filter(explode(',', $value));
						$this->cal[$key1][$key2]["{$keyword}_array"][] = $array;
					} else {
						$value = explode(',', implode(',', $this->cal[$key1][$key2]["{$keyword}_array"][1]) . trim($value));
						$this->cal[$key1][$key2]["{$keyword}_array"][1] = $value;
					}
				} else {
					$this->cal[$key1][$key2]["{$keyword}_array"][] = $value;

					if ($keyword === 'DURATION') {
						try {
							$duration = new DateInterval($value);
							array_push($this->cal[$key1][$key2]["{$keyword}_array"], $duration);
						} catch (Exception $e) {
							error_log('Ignoring invalid duration ' . $value);
						}
					}
				}

				if ($this->cal[$key1][$key2][$keyword] !== $value) {
					$this->cal[$key1][$key2][$keyword] .= ',' . $value;
				}
			}
			break;

		case 'VFREEBUSY':
			$key1 = $component;
			$key2 = ($this->freeBusyIndex - 1);
			$key3 = $keyword;

			if ($keyword === 'FREEBUSY') {
				if (is_array($value)) {
					$this->cal[$key1][$key2][$key3][][] = $value;
				} else {
					$this->freeBusyCount++;

					end($this->cal[$key1][$key2][$key3]);
					$key = key($this->cal[$key1][$key2][$key3]);

					$value = explode('/', $value);
					$this->cal[$key1][$key2][$key3][$key][] = $value;
				}
			} else {
				$this->cal[$key1][$key2][$key3][] = $value;
			}
			break;

		case 'VTODO':
			$this->cal[$component][$this->todoCount - 1][$keyword] = $value;

			break;

		default:
			$this->cal[$component][$keyword] = $value;

			break;
		}

		$this->lastKeyword = $keyword;
	}

	/**
	 * Gets the key value pair from an iCal string
	 *
	 * @param string $text
	 * @return array|boolean
	 */
	protected function keyValueFromString($text)
	{
		$text = htmlspecialchars($text, ENT_NOQUOTES, 'UTF-8');

		$colon = strpos($text, ':');
		$quote = strpos($text, '"');
		if ($colon === false) {
			$matches = array();
		} elseif ($quote === false || $colon < $quote) {
			list($before, $after) = explode(':', $text, 2);
			$matches = array($text, $before, $after);
		} else {
			list($before, $text) = explode('"', $text, 2);
			$text = '"' . $text;
			$matches = str_getcsv($text, ':');
			$combinedValue = '';

			foreach (array_keys($matches) as $key) {
				if ($key === 0) {
					if (!empty($before)) {
						$matches[$key] = $before . '"' . $matches[$key] . '"';
					}
				} else {
					if ($key > 1) {
						$combinedValue .= ':';
					}

					$combinedValue .= $matches[$key];
				}
			}

			$matches = array_slice($matches, 0, 2);
			$matches[1] = $combinedValue;
			array_unshift($matches, $before . $text);
		}

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

		if (preg_match('/^([A-Z-]+)([;][\w\W]*)?$/', $matches[1])) {
			$matches = array_splice($matches, 1, 2); // Remove first match and re-align ordering

			// Process properties
			if (preg_match('/([A-Z-]+)[;]([\w\W]*)/', $matches[0], $properties)) {
				// Remove first match
				array_shift($properties);
				// Fix to ignore everything in keyword after a ; (e.g. Language, TZID, etc.)
				$matches[0] = $properties[0];
				array_shift($properties); // Repeat removing first match

				$formatted = array();
				foreach ($properties as $property) {
					// Match semicolon separator outside of quoted substrings
					preg_match_all('~[^' . PHP_EOL . '";]+(?:"[^"\\\]*(?:\\\.[^"\\\]*)*"[^' . PHP_EOL . '";]*)*~', $property, $attributes);
					// Remove multi-dimensional array and use the first key
					$attributes = (count($attributes) === 0) ? array($property) : reset($attributes);

					if (is_array($attributes)) {
						foreach ($attributes as $attribute) {
							// Match equals sign separator outside of quoted substrings
							preg_match_all(
								'~[^' . PHP_EOL . '"=]+(?:"[^"\\\]*(?:\\\.[^"\\\]*)*"[^' . PHP_EOL . '"=]*)*~',
								$attribute,
								$values
							);
							// Remove multi-dimensional array and use the first key
							$value = (count($values) === 0) ? null : reset($values);

							if (is_array($value) && isset($value[1])) {
								// Remove double quotes from beginning and end only
								$formatted[$value[0]] = trim($value[1], '"');
							}
						}
					}
				}

				// Assign the keyword property information
				$properties[0] = $formatted;

				// Add match to beginning of array
				array_unshift($properties, $matches[1]);
				$matches[1] = $properties;
			}

			return $matches;
		} else {
			return false; // Ignore this match
		}
	}

	/**
	 * Returns a `DateTime` object from an iCal date time format
	 *
	 * @param string $icalDate
	 * @return DateTime
	 */
	public function iCalDateToDateTime($icalDate)
	{
		/**
		 * iCal times may be in 3 formats, (https://www.kanzaki.com/docs/ical/dateTime.html)
		 *
		 * UTC:      Has a trailing 'Z'
		 * Floating: No time zone reference specified, no trailing 'Z', use local time
		 * TZID:     Set time zone as specified
		 *
		 * Use DateTime class objects to get around limitations with `mktime` and `gmmktime`.
		 * Must have a local time zone set to process floating times.
		 */
		$pattern = '/^(?:TZID=)?([^:]*|".*")'; // [1]: Time zone
		$pattern .= ':?';                       //      Time zone delimiter
		$pattern .= '([0-9]{8})';               // [2]: YYYYMMDD
		$pattern .= 'T?';                       //      Time delimiter
		$pattern .= '(?(?<=T)([0-9]{6}))';      // [3]: HHMMSS (filled if delimiter present)
		$pattern .= '(Z?)/';                    // [4]: UTC flag

		preg_match($pattern, $icalDate, $date);

		if (empty($date)) {
			error_log('Invalid iCal date format: ' . $icalDate);
			return new Datetime('1970-08-08'); // Return something far in the past
		}

		// A Unix timestamp usually cannot represent a date prior to 1 Jan 1970.
		// PHP, on the other hand, uses negative numbers for that. Thus we don't
		// need to special case them.

		if ($date[4] === 'Z') {
			$dateTimeZone = new DateTimeZone(self::TIME_ZONE_UTC);
		} elseif (!empty($date[1])) {
			$dateTimeZone = $this->timeZoneStringToDateTimeZone($date[1]);
		} else {
			$dateTimeZone = new DateTimeZone($this->defaultTimeZone);
		}

		// The exclamation mark at the start of the format string indicates that if a
		// time portion is not included, the time in the returned DateTime should be
		// set to 00:00:00. Without it, the time would be set to the current system time.
		$dateFormat = '!Ymd';
		$dateBasic = $date[2];
		if (!empty($date[3])) {
			$dateBasic .= "T{$date[3]}";
			$dateFormat .= '\THis';
		}

		return DateTime::createFromFormat($dateFormat, $dateBasic, $dateTimeZone);
	}

	/**
	 * Returns a Unix timestamp from an iCal date time format
	 *
	 * @param string $icalDate
	 * @return integer
	 */
	public function iCalDateToUnixTimestamp($icalDate)
	{
		return $this->iCalDateToDateTime($icalDate)->getTimestamp();
	}

	/**
	 * Returns a date adapted to the calendar time zone depending on the event `TZID`
	 *
	 * @param array $event
	 * @param string $key
	 * @param string $format
	 * @return string|boolean
	 */
	public function iCalDateWithTimeZone(array $event, $key, $format = self::DATE_TIME_FORMAT)
	{
		if (!isset($event["{$key}_array"]) || !isset($event[$key])) {
			return false;
		}

		$dateArray = $event["{$key}_array"];

		if ($key === 'DURATION') {
			$dateTime = $this->parseDuration($event['DTSTART'], $dateArray[2], null);
		} else {
			// When constructing from a Unix Timestamp, no time zone needs passing.
			$dateTime = new DateTime("@{$dateArray[2]}");
		}

		// Set the time zone we wish to use when running `$dateTime->format`.
		$dateTime->setTimezone(new DateTimeZone($this->calendarTimeZone()));

		if (is_null($format)) {
			return $dateTime;
		}

		return $dateTime->format($format);
	}

	/**
	 * Performs admin tasks on all events as read from the iCal file.
	 * Adds a Unix timestamp to all `{DTSTART|DTEND|RECURRENCE-ID}_array` arrays
	 * Tracks modified recurrence instances
	 *
	 * @return void
	 */
	protected function processEvents()
	{
		if (empty($this->cal['VEVENT']))
			return;
		$events =& $this->cal['VEVENT'];
		$checks = null;

		foreach ($events as $key => $anEvent) {
			foreach (array('DTSTART', 'DTEND', 'RECURRENCE-ID') as $type) {
				if (isset($anEvent[$type])) {
					$date = $anEvent["{$type}_array"][1];

					if (isset($anEvent["{$type}_array"][0]['TZID'])) {
						$timeZone = $this->escapeParamText($anEvent["{$type}_array"][0]['TZID']);
						$date = sprintf(self::ICAL_DATE_TIME_TEMPLATE, $timeZone) . $date;
					}

					$anEvent["{$type}_array"][2] = $this->iCalDateToUnixTimestamp($date);
					$anEvent["{$type}_array"][3] = $date;
				}
			}

			if (isset($anEvent['RECURRENCE-ID'])) {
				$uid = $anEvent['UID'];

				if (!isset($this->alteredRecurrenceInstances[$uid])) {
					$this->alteredRecurrenceInstances[$uid] = array();
				}

				$recurrenceDateUtc = $this->iCalDateToUnixTimestamp($anEvent['RECURRENCE-ID_array'][3]);
				$this->alteredRecurrenceInstances[$uid][$key] = $recurrenceDateUtc;
			}

			$events[$key] = $anEvent;
		}

		$eventKeysToRemove = array();

		foreach ($events as $key => $event) {
			$checks[] = !isset($event['RECURRENCE-ID']);
			$checks[] = isset($event['UID']);
			$checks[] = isset($event['UID']) && isset($this->alteredRecurrenceInstances[$event['UID']]);

			if ((bool)array_product($checks)) {
				$eventDtstartUnix = $this->iCalDateToUnixTimestamp($event['DTSTART_array'][3]);

				// phpcs:ignore CustomPHPCS.ControlStructures.AssignmentInCondition
				if (($alteredEventKey = array_search($eventDtstartUnix, $this->alteredRecurrenceInstances[$event['UID']])) !== false) {
					$eventKeysToRemove[] = $alteredEventKey;

					$alteredEvent = array_replace_recursive($events[$key], $events[$alteredEventKey]);
					$this->alteredRecurrenceInstances[$event['UID']]['altered-event'] = array($key => $alteredEvent);
				}
			}

			unset($checks);
		}

		foreach ($eventKeysToRemove as $eventKeyToRemove) {
			$events[$eventKeyToRemove] = null;
		}
	}

	/**
	 * Processes recurrence rules
	 *
	 * @return void
	 */
	protected function processRecurrences()
	{
		// If there are no events, then we have nothing to process.
		if (empty($this->cal['VEVENT']))
			return;
		$events =& $this->cal['VEVENT'];

		$allEventRecurrences = array();
		$eventKeysToRemove = array();

		foreach ($events as $key => $anEvent) {
			if (!isset($anEvent['RRULE']) || $anEvent['RRULE'] === '') {
				continue;
			}

			// Tag as generated by a recurrence rule
			$anEvent['RRULE_array'][2] = self::RECURRENCE_EVENT;

			// Create new initial starting point.
			$initialEventDate = $this->icalDateToDateTime($anEvent['DTSTART_array'][3]);

			// Separate the RRULE stanzas, and explode the values that are lists.
			$rrules = array();
			foreach (explode(';', $anEvent['RRULE']) as $s) {
				list($k, $v) = explode('=', $s);
				if (in_array($k, array('BYSETPOS', 'BYDAY', 'BYMONTHDAY', 'BYMONTH'))) {
					$rrules[$k] = explode(',', $v);
				} else {
					$rrules[$k] = $v;
				}
			}

			// Get frequency
			$frequency = $rrules['FREQ'];

			// Reject RRULE if BYDAY stanza is invalid:
			// > The BYDAY rule part MUST NOT be specified with a numeric value
			// > when the FREQ rule part is not set to MONTHLY or YEARLY.
			if (isset($rrules['BYDAY']) && !in_array($frequency, array('MONTHLY', 'YEARLY'))) {
				$allByDayStanzasValid = array_reduce($rrules['BYDAY'], function ($carry, $weekday) {
					return $carry && substr($weekday, -2) === $weekday;
				}, true);

				if (!$allByDayStanzasValid) {
					error_log("ICal::ProcessRecurrences: A \"{$frequency}\" RRULE should not contain BYDAY values with numeric prefixes");

					continue;
				}
			}

			// Get Interval
			$interval = (empty($rrules['INTERVAL'])) ? 1 : $rrules['INTERVAL'];

			// Throw an error if this isn't an integer.
			if (!is_int($this->defaultSpan)) {
				trigger_error('ICal::defaultSpan: User defined value is not an integer', E_USER_NOTICE);
			}

			// Compute EXDATEs
			$exdates = $this->parseExdates($anEvent);

			// Determine if the initial date is also an EXDATE
			$initialDateIsExdate = array_reduce($exdates, function ($carry, $exdate) use ($initialEventDate) {
				return $carry || $exdate->getTimestamp() === $initialEventDate->getTimestamp();
			}, false);

			if ($initialDateIsExdate) {
				$eventKeysToRemove[] = $key;
			}

			/**
			 * Determine at what point we should stop calculating recurrences
			 * by looking at the UNTIL or COUNT rrule stanza, or, if neither
			 * if set, using a fallback.
			 *
			 * If the initial date is also an EXDATE, it shouldn't be included
			 * in the count.
			 *
			 * Syntax:
			 *   UNTIL={enddate}
			 *   COUNT=<positive integer>
			 *
			 * Where:
			 *   enddate = <icalDate> || <icalDateTime>
			 */
			$count = 1;
			$countLimit = (isset($rrules['COUNT'])) ? intval($rrules['COUNT']) : 0;
			$until = date_create()->modify("{$this->defaultSpan} years")->setTime(23, 59, 59)->getTimestamp();

			if (isset($rrules['UNTIL'])) {
				$until = min($until, $this->iCalDateToUnixTimestamp($rrules['UNTIL']));
			}
			$until = min($until, $this->windowMaxTimestamp);

			$eventRecurrences = array();

			$frequencyRecurringDateTime = clone $initialEventDate;
			while ($frequencyRecurringDateTime->getTimestamp() <= $until) {
				$candidateDateTimes = array();

				// phpcs:ignore Squiz.ControlStructures.SwitchDeclaration.MissingDefault
				switch ($frequency) {
				case 'DAILY':
					$candidateDateTimes[] = clone $frequencyRecurringDateTime;

					break;

				case 'WEEKLY':
					$initialDayOfWeek = $frequencyRecurringDateTime->format('N');
					$matchingDays = array($initialDayOfWeek);

					if (!empty($rrules['BYDAY'])) {
						// setISODate() below uses the ISO-8601 specification of weeks: start on
						// a Monday, end on a Sunday. However, RRULEs (or the caller of the
						// parser) may state an alternate WeeKSTart.
						$wkstTransition = 7;

						if (empty($rrules['WKST'])) {
							if ($this->defaultWeekStart !== self::ISO_8601_WEEK_START) {
								$wkstTransition = array_search($this->defaultWeekStart, array_keys($this->weekdays));
							}
						} elseif ($rrules['WKST'] !== self::ISO_8601_WEEK_START) {
							$wkstTransition = array_search($rrules['WKST'], array_keys($this->weekdays));
						}

						$matchingDays = array_map(
							function ($weekday) use ($initialDayOfWeek, $wkstTransition, $interval) {
								$day = array_search($weekday, array_keys($this->weekdays));

								if ($day < $initialDayOfWeek) {
									$day += 7;
								}

								if ($day >= $wkstTransition) {
									$day += 7 * ($interval - 1);
								}

								// Ignoring alternate week starts, $day at this point will have a
								// value between 0 and 6. But setISODate() expects a value of 1 to 7.
								// Even with alternate week starts, we still need to +1 to set the
								// correct weekday.
								$day++;

								return $day;
							},
							$rrules['BYDAY']
						);
					}

					sort($matchingDays);

					foreach ($matchingDays as $day) {
						$clonedDateTime = clone $frequencyRecurringDateTime;
						$candidateDateTimes[] = $clonedDateTime->setISODate(
							$frequencyRecurringDateTime->format('o'),
							$frequencyRecurringDateTime->format('W'),
							$day
						);
					}
					break;

				case 'MONTHLY':
					$matchingDays = array();

					if (!empty($rrules['BYMONTHDAY'])) {
						$matchingDays = $rrules['BYMONTHDAY'];
					} elseif (!empty($rrules['BYDAY'])) {
						$matchingDays = $this->getDaysOfMonthMatchingByDayRRule($rrules['BYDAY'], $frequencyRecurringDateTime);
					}

					if (!empty($rrules['BYSETPOS'])) {
						$matchingDays = $this->filterValuesUsingBySetPosRRule($rrules['BYSETPOS'], $matchingDays);
					}

					foreach ($matchingDays as $day) {
						// Skip invalid dates (e.g. 30th February)
						if ($day > $frequencyRecurringDateTime->format('t')) {
							continue;
						}

						$clonedDateTime = clone $frequencyRecurringDateTime;
						$candidateDateTimes[] = $clonedDateTime->setDate(
							$frequencyRecurringDateTime->format('Y'),
							$frequencyRecurringDateTime->format('m'),
							$day
						);
					}
					break;

				case 'YEARLY':
					if (!empty($rrules['BYMONTH'])) {
						foreach ($rrules['BYMONTH'] as $byMonth) {
							$clonedDateTime = clone $frequencyRecurringDateTime;
							$bymonthRecurringDatetime = $clonedDateTime->setDate(
								$frequencyRecurringDateTime->format('Y'),
								$byMonth,
								$frequencyRecurringDateTime->format('d')
							);

							if (!empty($rrules['BYDAY'])) {
								// Get all days of the month that match the BYDAY rule.
								$matchingDays = $this->getDaysOfMonthMatchingByDayRRule($rrules['BYDAY'], $bymonthRecurringDatetime);

								// And add each of them to the list of recurrences
								foreach ($matchingDays as $day) {
									$clonedDateTime = clone $bymonthRecurringDatetime;
									$candidateDateTimes[] = $clonedDateTime->setDate(
										$frequencyRecurringDateTime->format('Y'),
										$bymonthRecurringDatetime->format('m'),
										$day
									);
								}
							} else {
								$candidateDateTimes[] = clone $bymonthRecurringDatetime;
							}
						}
					} else {
						$candidateDateTimes[] = clone $frequencyRecurringDateTime;
					}
					break;
				}

				foreach ($candidateDateTimes as $candidate) {
					$timestamp = $candidate->getTimestamp();
					if ($timestamp <= $initialEventDate->getTimestamp()) {
						continue;
					}

					if ($timestamp > $until) {
						break;
					}

					// Exclusions
					$isExcluded = ($this->shouldFilterByWindow && $timestamp + 160000 < $this->windowMinTimestamp);

					if (!$isExcluded) {
						$isExcluded = array_filter($exdates, function ($exdate) use ($timestamp) {
							return $exdate->getTimestamp() == $timestamp;
						});
					}

					if (!$isExcluded && isset($this->alteredRecurrenceInstances[$anEvent['UID']])) {
						if (in_array($timestamp, $this->alteredRecurrenceInstances[$anEvent['UID']])) {
							$isExcluded = true;
						}
					}

					if (!$isExcluded) {
						$eventRecurrences[] = $candidate;
						$this->eventCount++;
					}

					// Count all evaluated candidates including excluded ones
					if (isset($rrules['COUNT'])) {
						$count++;

						// If RRULE[COUNT] is reached then break
						if ($count >= $countLimit) {
							break 2;
						}
					}
				}

				// Move forwards $interval $frequency.
				$monthPreMove = $frequencyRecurringDateTime->format('m');
				$frequencyRecurringDateTime->modify("{$interval} {$this->frequencyConversion[$frequency]}");

				// As noted in Example #2 on https://www.php.net/manual/en/datetime.modify.php,
				// there are some occasions where adding months doesn't give the month you might
				// expect. For instance: January 31st + 1 month == March 3rd (March 2nd on a leap
				// year.) The following code crudely rectifies this.
				if ($frequency === 'MONTHLY') {
					$monthDiff = $frequencyRecurringDateTime->format('m') - $monthPreMove;

					if (($monthDiff > 0 && $monthDiff > $interval) || ($monthDiff < 0 && $monthDiff > $interval - 12)) {
						$frequencyRecurringDateTime->modify('-1 month');
					}
				}
			}

			// Determine event length
			$eventLength = 0;
			if (isset($anEvent['DURATION'])) {
				$clonedDateTime = clone $initialEventDate;
				$endDate = $clonedDateTime->add($anEvent['DURATION_array'][2]);
				$eventLength = $endDate->getTimestamp() - $anEvent['DTSTART_array'][2];
			} elseif (isset($anEvent['DTEND_array'])) {
				$eventLength = $anEvent['DTEND_array'][2] - $anEvent['DTSTART_array'][2];
			}

			// Whether or not the initial date was UTC
			$initialDateWasUTC = substr($anEvent['DTSTART'], -1) === 'Z';

			// Build the param array
			$dateParamArray = array();
			if (
				!$initialDateWasUTC
				&& isset($anEvent['DTSTART_array'][0]['TZID'])
				&& $this->isValidTimeZoneId($anEvent['DTSTART_array'][0]['TZID'])
			) {
				$dateParamArray['TZID'] = $anEvent['DTSTART_array'][0]['TZID'];
			}

			// Populate the `DT{START|END}[_array]`s
			$eventRecurrences = array_map(
				function ($recurringDatetime) use ($anEvent, $eventLength, $initialDateWasUTC, $dateParamArray) {
					$tzidPrefix = (isset($dateParamArray['TZID'])) ? 'TZID=' . $this->escapeParamText($dateParamArray['TZID']) . ':' : '';

					foreach (array('DTSTART', 'DTEND') as $dtkey) {
						$anEvent[$dtkey] = $recurringDatetime->format(self::DATE_TIME_FORMAT) . (($initialDateWasUTC) ? 'Z' : '');

						$anEvent["{$dtkey}_array"] = array(
							$dateParamArray,                    // [0] Array of params (incl. TZID)
							$anEvent[$dtkey],                   // [1] ICalDateTime string w/o TZID
							$recurringDatetime->getTimestamp(), // [2] Unix Timestamp
							"{$tzidPrefix}{$anEvent[$dtkey]}",  // [3] Full ICalDateTime string
						);

						if ($dtkey !== 'DTEND') {
							$recurringDatetime->modify("{$eventLength} seconds");
						}
					}

					return $anEvent;
				},
				$eventRecurrences
			);

			$allEventRecurrences = array_merge($allEventRecurrences, $eventRecurrences);
		}

		// Nullify the initial events that are also EXDATEs
		foreach ($eventKeysToRemove as $eventKeyToRemove) {
			$events[$eventKeyToRemove] = null;
		}

		$events = array_merge($events, $allEventRecurrences);
	}

	/**
	 * Find all days of a month that match the BYDAY stanza of an RRULE.
	 *
	 * With no {ordwk}, then return the day number of every {weekday}
	 * within the month.
	 *
	 * With a +ve {ordwk}, then return the {ordwk} {weekday} within the
	 * month.
	 *
	 * With a -ve {ordwk}, then return the {ordwk}-to-last {weekday}
	 * within the month.
	 *
	 * RRule Syntax:
	 *   BYDAY={bywdaylist}
	 *
	 * Where:
	 *   bywdaylist = {weekdaynum}[,{weekdaynum}...]
	 *   weekdaynum = [[+]{ordwk} || -{ordwk}]{weekday}
	 *   ordwk      = 1 to 53
	 *   weekday    = SU || MO || TU || WE || TH || FR || SA
	 *
	 * @param array $byDays
	 * @param DateTime $initialDateTime
	 * @return array
	 */
	protected function getDaysOfMonthMatchingByDayRRule(array $byDays, $initialDateTime)
	{
		$matchingDays = array();

		foreach ($byDays as $weekday) {
			$bydayDateTime = clone $initialDateTime;

			$ordwk = intval(substr($weekday, 0, -2));

			// Quantise the date to the first instance of the requested day in a month
			// (Or last if we have a -ve {ordwk})
			$bydayDateTime->modify(
				(($ordwk < 0) ? 'Last' : 'First')
				. ' '
				. $this->weekdays[substr($weekday, -2)]  // e.g. "Monday"
				. ' of ' . $initialDateTime->format('F') // e.g. "June"
			);

			if ($ordwk < 0) { // -ve {ordwk}
				$bydayDateTime->modify((++$ordwk) . ' week');
				$matchingDays[] = $bydayDateTime->format('j');
			} elseif ($ordwk > 0) { // +ve {ordwk}
				$bydayDateTime->modify((--$ordwk) . ' week');
				$matchingDays[] = $bydayDateTime->format('j');
			} else { // No {ordwk}
				while ($bydayDateTime->format('n') === $initialDateTime->format('n')) {
					$matchingDays[] = $bydayDateTime->format('j');
					$bydayDateTime->modify('+1 week');
				}
			}
		}

		// Sort into ascending order.
		sort($matchingDays);

		return $matchingDays;
	}

	/**
	 * Filters a provided values-list by applying a BYSETPOS RRule.
	 *
	 * Where a +ve {daynum} is provided, the {ordday} position'd value as
	 * measured from the start of the list of values should be retained.
	 *
	 * Where a -ve {daynum} is provided, the {ordday} position'd value as
	 * measured from the end of the list of values should be retained.
	 *
	 * RRule Syntax:
	 *   BYSETPOS={bysplist}
	 *
	 * Where:
	 *   bysplist  = {setposday}[,{setposday}...]
	 *   setposday = {daynum}
	 *   daynum    = [+ || -] {ordday}
	 *   ordday    = 1 to 366
	 *
	 * @param array $bySetPos
	 * @param array $valuesList
	 * @return array
	 */
	protected function filterValuesUsingBySetPosRRule(array $bySetPos, array $valuesList)
	{
		$filteredMatches = array();

		foreach ($bySetPos as $setPosition) {
			if ($setPosition < 0) {
				$setPosition = count($valuesList) + ++$setPosition;
			}

			// Positioning starts at 1, array indexes start at 0
			if (isset($valuesList[$setPosition - 1])) {
				$filteredMatches[] = $valuesList[$setPosition - 1];
			}
		}

		return $filteredMatches;
	}

	/**
	 * Processes date conversions using the time zone
	 *
	 * Add keys `DTSTART_tz` and `DTEND_tz` to each Event
	 * These keys contain dates adapted to the calendar
	 * time zone depending on the event `TZID`.
	 *
	 * @return void
	 */
	protected function processDateConversions()
	{
		if (empty($this->cal['VEVENT']))
			return;

		$events =& $this->cal['VEVENT'];
		foreach ($events as $key => $anEvent) {
			if (is_null($anEvent) || !$this->isValidDate($anEvent['DTSTART'])) {
				unset($events[$key]);
				$this->eventCount--;

				continue;
			}

			$events[$key]['DTSTART_tz'] = $this->iCalDateWithTimeZone($anEvent, 'DTSTART');

			if ($this->iCalDateWithTimeZone($anEvent, 'DTEND')) {
				$events[$key]['DTEND_tz'] = $this->iCalDateWithTimeZone($anEvent, 'DTEND');
			} elseif ($this->iCalDateWithTimeZone($anEvent, 'DURATION')) {
				$events[$key]['DTEND_tz'] = $this->iCalDateWithTimeZone($anEvent, 'DURATION');
			} else {
				$events[$key]['DTEND_tz'] = $events[$key]['DTSTART_tz'];
			}
		}
	}

	/**
	 * Returns an array of Events.
	 * Every event is a class with the event
	 * details being properties within it.
	 *
	 * @return ICalEvent[]
	 */
	public function events()
	{
		if (empty($this->cal) || empty($this->cal['VEVENT']))
			return [];

		$events = array();
		foreach ($this->cal['VEVENT'] as $event) {
			$events[] = new ICalEvent($event);
		}

		return $events;
	}

	/**
	 * Returns the calendar name
	 *
	 * @return string
	 */
	public function calendarName()
	{
		return isset($this->cal['VCALENDAR']['X-WR-CALNAME']) ? $this->cal['VCALENDAR']['X-WR-CALNAME'] : '';
	}

	/**
	 * Returns the calendar description
	 *
	 * @return string
	 */
	public function calendarDescription()
	{
		return isset($this->cal['VCALENDAR']['X-WR-CALDESC']) ? $this->cal['VCALENDAR']['X-WR-CALDESC'] : '';
	}

	/**
	 * Returns the calendar time zone
	 *
	 * @param boolean $ignoreUtc
	 * @return string
	 */
	public function calendarTimeZone($ignoreUtc = false)
	{
		if (isset($this->cal['VCALENDAR']['X-WR-TIMEZONE'])) {
			$timeZone = $this->cal['VCALENDAR']['X-WR-TIMEZONE'];
		} elseif (isset($this->cal['VTIMEZONE']['TZID'])) {
			$timeZone = $this->cal['VTIMEZONE']['TZID'];
		} else {
			$timeZone = $this->defaultTimeZone;
		}

		// Validate the time zone, falling back to the time zone set in the PHP environment.
		$timeZone = $this->timeZoneStringToDateTimeZone($timeZone)->getName();

		if ($ignoreUtc && strtoupper($timeZone) === self::TIME_ZONE_UTC) {
			return null;
		}

		return $timeZone;
	}

	/**
	 * Returns an array of arrays with all free/busy events.
	 * Every event is an associative array and each property
	 * is an element it.
	 *
	 * @return array
	 */
	public function freeBusyEvents()
	{
		$array = $this->cal;

		return isset($array['VFREEBUSY']) ? $array['VFREEBUSY'] : array();
	}

	/**
	 * Returns a sorted array of the events in a given range,
	 * or an empty array if no events exist in the range.
	 *
	 * Events will be returned if the start or end date is contained within the
	 * range (inclusive), or if the event starts before and end after the range.
	 *
	 * If a start date is not specified or of a valid format, then the start
	 * of the range will default to the current time and date of the server.
	 *
	 * If an end date is not specified or of a valid format, then the end of
	 * the range will default to the current time and date of the server,
	 * plus 20 years.
	 *
	 * Note that this function makes use of Unix timestamps. This might be a
	 * problem for events on, during, or after 29 Jan 2038.
	 * See https://en.wikipedia.org/wiki/Unix_time#Representing_the_number
	 *
	 * @param string|null $rangeStart
	 * @param string|null $rangeEnd
	 * @return array
	 * @throws Exception
	 */
	public function eventsFromRange($rangeStart = null, $rangeEnd = null)
	{
		// Sort events before processing range
		$events = $this->sortEventsWithOrder($this->events());

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

		$extendedEvents = array();

		if (!is_null($rangeStart)) {
			try {
				$rangeStart = new DateTime($rangeStart, new DateTimeZone($this->defaultTimeZone));
			} catch (Exception $exception) {
				error_log("ICal::eventsFromRange: Invalid date passed ({$rangeStart})");
				$rangeStart = false;
			}
		} else {
			$rangeStart = new DateTime('now', new DateTimeZone($this->defaultTimeZone));
		}

		if (!is_null($rangeEnd)) {
			try {
				$rangeEnd = new DateTime($rangeEnd, new DateTimeZone($this->defaultTimeZone));
			} catch (Exception $exception) {
				error_log("ICal::eventsFromRange: Invalid date passed ({$rangeEnd})");
				$rangeEnd = false;
			}
		} else {
			$rangeEnd = new DateTime('now', new DateTimeZone($this->defaultTimeZone));
			$rangeEnd->modify('+20 years');
		}

		// If start and end are identical and are dates with no times...
		if ($rangeEnd->format('His') == 0 && $rangeStart->getTimestamp() === $rangeEnd->getTimestamp()) {
			$rangeEnd->modify('+1 day');
		}

		$rangeStart = $rangeStart->getTimestamp();
		$rangeEnd = $rangeEnd->getTimestamp();

		foreach ($events as $anEvent) {
			$eventStart = $anEvent->dtstart_array[2];
			$eventEnd = (isset($anEvent->dtend_array[2])) ? $anEvent->dtend_array[2] : null;

			if (
				($eventStart >= $rangeStart && $eventStart < $rangeEnd)         // Event start date contained in the range
				|| ($eventEnd !== null
					&& (
						($eventEnd > $rangeStart && $eventEnd <= $rangeEnd)     // Event end date contained in the range
						|| ($eventStart < $rangeStart && $eventEnd > $rangeEnd) // Event starts before and finishes after range
					)
				)
			) {
				$extendedEvents[] = $anEvent;
			}
		}

		if (empty($extendedEvents)) {
			return array();
		}

		return $extendedEvents;
	}

	/**
	 * Sorts events based on a given sort order
	 *
	 * @param array $events
	 * @param integer $sortOrder Either SORT_ASC, SORT_DESC, SORT_REGULAR, SORT_NUMERIC, SORT_STRING
	 * @return array
	 */
	public function sortEventsWithOrder(array $events, $sortOrder = SORT_ASC)
	{
		$extendedEvents = array();
		$timestamp = array();

		foreach ($events as $key => $anEvent) {
			$extendedEvents[] = $anEvent;
			$timestamp[$key] = $anEvent->dtstart_array[2];
		}

		array_multisort($timestamp, $sortOrder, $extendedEvents);

		return $extendedEvents;
	}

	/**
	 * Checks if a time zone is valid (IANA, CLDR, or Windows)
	 *
	 * @param string $timeZone
	 * @return boolean
	 */
	protected function isValidTimeZoneId($timeZone)
	{
		return $this->isValidIanaTimeZoneId($timeZone) !== false
			|| $this->isValidCldrTimeZoneId($timeZone) !== false
			|| $this->isValidWindowsTimeZoneId($timeZone) !== false;
	}

	/**
	 * Checks if a time zone is a valid IANA time zone
	 *
	 * @param string $timeZone
	 * @return boolean
	 */
	protected function isValidIanaTimeZoneId($timeZone)
	{
		if (in_array($timeZone, $this->validIanaTimeZones)) {
			return true;
		}

		$valid = array();
		$tza = timezone_abbreviations_list();

		foreach ($tza as $zone) {
			foreach ($zone as $item) {
				$valid[$item['timezone_id']] = true;
			}
		}

		unset($valid['']);

		if (isset($valid[$timeZone]) || in_array($timeZone, timezone_identifiers_list(DateTimeZone::ALL_WITH_BC))) {
			$this->validIanaTimeZones[] = $timeZone;

			return true;
		}

		return false;
	}

	/**
	 * Checks if a time zone is a valid CLDR time zone
	 *
	 * @param string $timeZone
	 * @return boolean
	 */
	public function isValidCldrTimeZoneId($timeZone)
	{
		return array_key_exists(html_entity_decode($timeZone), self::$cldrTimeZonesMap);
	}

	/**
	 * Checks if a time zone is a recognised Windows (non-CLDR) time zone
	 *
	 * @param string $timeZone
	 * @return boolean
	 */
	public function isValidWindowsTimeZoneId($timeZone)
	{
		return array_key_exists(html_entity_decode($timeZone), self::$windowsTimeZonesMap);
	}

	/**
	 * Parses a duration and applies it to a date
	 *
	 * @param string $date
	 * @param DateInterval $duration
	 * @param string $format
	 * @return integer|DateTime
	 */
	protected function parseDuration($date, $duration, $format = self::UNIX_FORMAT)
	{
		$dateTime = date_create($date);
		$dateTime->modify("{$duration->y} year");
		$dateTime->modify("{$duration->m} month");
		$dateTime->modify("{$duration->d} day");
		$dateTime->modify("{$duration->h} hour");
		$dateTime->modify("{$duration->i} minute");
		$dateTime->modify("{$duration->s} second");

		if (is_null($format)) {
			$output = $dateTime;
		} elseif ($format === self::UNIX_FORMAT) {
			$output = $dateTime->getTimestamp();
		} else {
			$output = $dateTime->format($format);
		}

		return $output;
	}

	/**
	 * Removes unprintable ASCII and UTF-8 characters
	 *
	 * @param string $data
	 * @return string
	 */
	protected function removeUnprintableChars($data)
	{
		return preg_replace('/[\x00-\x1F\x7F\xA0]/u', '', $data);
	}

	/**
	 * Places double-quotes around texts that have characters not permitted
	 * in parameter-texts, but are permitted in quoted-texts.
	 *
	 * @param string $candidateText
	 * @return string
	 */
	protected function escapeParamText($candidateText)
	{
		if (strpbrk($candidateText, ':;,') !== false) {
			return '"' . $candidateText . '"';
		}

		return $candidateText;
	}

	/**
	 * Parses a list of excluded dates
	 * to be applied to an Event
	 *
	 * @param array $event
	 * @return array
	 */
	public function parseExdates(array $event)
	{
		if (empty($event['EXDATE_array'])) {
			return array();
		} else {
			$exdates = $event['EXDATE_array'];
		}

		$output = array();
		$currentTimeZone = $this->defaultTimeZone;

		foreach ($exdates as $subArray) {
			end($subArray);
			$finalKey = key($subArray);

			foreach (array_keys($subArray) as $key) {
				if ($key === 'TZID') {
					$currentTimeZone = $subArray[$key];
				} elseif (is_numeric($key)) {
					$icalDate = $subArray[$key];

					if (substr($icalDate, -1) === 'Z') {
						$currentTimeZone = self::TIME_ZONE_UTC;
					}

					$output[] = new DateTimeImmutable($icalDate, $this->timeZoneStringToDateTimeZone($currentTimeZone));

					if ($key === $finalKey) {
						// Reset to default
						$currentTimeZone = $this->defaultTimeZone;
					}
				}
			}
		}

		return $output;
	}

	/**
	 * Checks if a date string is a valid date
	 *
	 * @param string $value
	 * @return boolean
	 */
	public function isValidDate($value)
	{
		if (!$value) {
			return false;
		}

		try {
			new DateTime($value);

			return true;
		} catch (Exception $exception) {
			return false;
		}
	}

	/**
	 * Returns a `DateTimeZone` object based on a string containing a time zone name.
	 * Falls back to the default time zone if string passed not a recognised time zone.
	 *
	 * @param string $timeZoneString
	 * @return DateTimeZone
	 */
	public function timeZoneStringToDateTimeZone($timeZoneString)
	{
		if ($timeZoneString instanceof DateTimeZone)
			return $timeZoneString;
		// Some time zones contain characters that are not permitted in param-texts,
		// but are within quoted texts. We need to remove the quotes as they're not
		// actually part of the time zone.
		$timeZoneString = trim($timeZoneString, '"');
		$timeZoneString = html_entity_decode($timeZoneString);

		if ($this->isValidIanaTimeZoneId($timeZoneString)) {
			return new DateTimeZone($timeZoneString);
		}

		if ($this->isValidCldrTimeZoneId($timeZoneString)) {
			return new DateTimeZone(self::$cldrTimeZonesMap[$timeZoneString]);
		}

		if ($this->isValidWindowsTimeZoneId($timeZoneString)) {
			return new DateTimeZone(self::$windowsTimeZonesMap[$timeZoneString]);
		}

		return new DateTimeZone($this->defaultTimeZone);
	}
}