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<?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'));

}