<?php



//--------------------------------------------------------------------------------------------------

// Utilities for our event-fetching scripts.

//

// Requires PHP 5.2.0 or higher.

//--------------------------------------------------------------------------------------------------



// PHP will fatal error if we attempt to use the DateTime class without this being set.

date_default_timezone_set('UTC');





class Event {



	// Tests whether the given ISO8601 string has a time-of-day or not

	const ALL_DAY_REGEX = '/^\d{4}-\d\d-\d\d$/'; // matches strings like "2013-12-29"



	public $title;

	public $allDay; // a boolean

	public $start; // a DateTime

	public $end; // a DateTime, or null

	public $properties = array(); // an array of other misc properties





	// Constructs an Event object from the given array of key=>values.

	// You can optionally force the timezone of the parsed dates.

	public function __construct($array, $timezone=null) {



		$this->title = $array['title'];



		if (isset($array['allDay'])) {

			// allDay has been explicitly specified

			$this->allDay = (bool)$array['allDay'];

		}

		else {

			// Guess allDay based off of ISO8601 date strings

			$this->allDay = preg_match(self::ALL_DAY_REGEX, $array['start']) &&

				(!isset($array['end']) || preg_match(self::ALL_DAY_REGEX, $array['end']));

		}



		if ($this->allDay) {

			// If dates are allDay, we want to parse them in UTC to avoid DST issues.

			$timezone = null;

		}



		// Parse dates

		$this->start = parseDateTime($array['start'], $timezone);

		$this->end = isset($array['end']) ? parseDateTime($array['end'], $timezone) : null;



		// Record misc properties

		foreach ($array as $name => $value) {

			if (!in_array($name, array('title', 'allDay', 'start', 'end'))) {

				$this->properties[$name] = $value;

			}

		}

	}





	// Returns whether the date range of our event intersects with the given all-day range.

	// $rangeStart and $rangeEnd are assumed to be dates in UTC with 00:00:00 time.

	public function isWithinDayRange($rangeStart, $rangeEnd) {



		// Normalize our event's dates for comparison with the all-day range.

		$eventStart = stripTime($this->start);

		$eventEnd = isset($this->end) ? stripTime($this->end) : null;



		if (!$eventEnd) {

			// No end time? Only check if the start is within range.

			return $eventStart < $rangeEnd && $eventStart >= $rangeStart;

		}

		else {

			// Check if the two ranges intersect.

			return $eventStart < $rangeEnd && $eventEnd > $rangeStart;

		}

	}





	// Converts this Event object back to a plain data array, to be used for generating JSON

	public function toArray() {



		// Start with the misc properties (don't worry, PHP won't affect the original array)

		$array = $this->properties;



		$array['title'] = $this->title;



		// Figure out the date format. This essentially encodes allDay into the date string.

		if ($this->allDay) {

			$format = 'Y-m-d'; // output like "2013-12-29"

		}

		else {

			$format = 'c'; // full ISO8601 output, like "2013-12-29T09:00:00+08:00"

		}



		// Serialize dates into strings

		$array['start'] = $this->start->format($format);

		if (isset($this->end)) {

			$array['end'] = $this->end->format($format);

		}



		return $array;

	}



}





// Date Utilities

//----------------------------------------------------------------------------------------------





// Parses a string into a DateTime object, optionally forced into the given timezone.

function parseDateTime($string, $timezone=null) {

	$date = new DateTime(

		$string,

		$timezone ? $timezone : new DateTimeZone('UTC')

			// Used only when the string is ambiguous.

			// Ignored if string has a timezone offset in it.

	);

	if ($timezone) {

		// If our timezone was ignored above, force it.

		$date->setTimezone($timezone);

	}

	return $date;

}





// Takes the year/month/date values of the given DateTime and converts them to a new DateTime,

// but in UTC.

function stripTime($datetime) {

	return new DateTime($datetime->format('Y-m-d'));

}

