<?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);

		if (isset($this->end)) {
			$eventEnd = stripTime($this->end); // normalize
		}
		else {
			$eventEnd = $eventStart; // consider this a zero-duration event
		}

		// Check if the two whole-day 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'));
}