<?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 = []; // 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, ['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'));
}
