<?php

/*
 * This file is part of the Carbon package.
 *
 * (c) Brian Nesbitt <brian@nesbot.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Carbon;

use Carbon\Exceptions\InvalidDateException;
use Closure;
use DatePeriod;
use DateTime;
use DateTimeZone;
use InvalidArgumentException;
use Symfony\Component\Translation\Loader\ArrayLoader;
use Symfony\Component\Translation\Translator;
use Symfony\Component\Translation\TranslatorInterface;

/**
 * A simple API extension for DateTime
 *
 * @property      int $year
 * @property      int $yearIso
 * @property      int $month
 * @property      int $day
 * @property      int $hour
 * @property      int $minute
 * @property      int $second
 * @property      int $timestamp seconds since the Unix Epoch
 * @property      \DateTimeZone $timezone the current timezone
 * @property      \DateTimeZone $tz alias of timezone
 * @property-read int $micro
 * @property-read int $dayOfWeek 0 (for Sunday) through 6 (for Saturday)
 * @property-read int $dayOfYear 0 through 365
 * @property-read int $weekOfMonth 1 through 5
 * @property-read int $weekOfYear ISO-8601 week number of year, weeks starting on Monday
 * @property-read int $daysInMonth number of days in the given month
 * @property-read int $age does a diffInYears() with default parameters
 * @property-read int $quarter the quarter of this instance, 1 - 4
 * @property-read int $offset the timezone offset in seconds from UTC
 * @property-read int $offsetHours the timezone offset in hours from UTC
 * @property-read bool $dst daylight savings time indicator, true if DST, false otherwise
 * @property-read bool $local checks if the timezone is local, true if local, false otherwise
 * @property-read bool $utc checks if the timezone is UTC, true if UTC, false otherwise
 * @property-read string $timezoneName
 * @property-read string $tzName
 */
class Carbon extends DateTime
{
	/**
	 * The day constants.
	 */
	const SUNDAY = 0;
	const MONDAY = 1;
	const TUESDAY = 2;
	const WEDNESDAY = 3;
	const THURSDAY = 4;
	const FRIDAY = 5;
	const SATURDAY = 6;

	/**
	 * Names of days of the week.
	 *
	 * @var array
	 */
	protected static $days = array(
		self::SUNDAY => 'Sunday',
		self::MONDAY => 'Monday',
		self::TUESDAY => 'Tuesday',
		self::WEDNESDAY => 'Wednesday',
		self::THURSDAY => 'Thursday',
		self::FRIDAY => 'Friday',
		self::SATURDAY => 'Saturday',
	);

	/**
	 * Terms used to detect if a time passed is a relative date.
	 *
	 * This is here for testing purposes.
	 *
	 * @var array
	 */
	protected static $relativeKeywords = array(
		'+',
		'-',
		'ago',
		'first',
		'last',
		'next',
		'this',
		'today',
		'tomorrow',
		'yesterday',
	);

	/**
	 * Number of X in Y.
	 */
	const YEARS_PER_CENTURY = 100;
	const YEARS_PER_DECADE = 10;
	const MONTHS_PER_YEAR = 12;
	const MONTHS_PER_QUARTER = 3;
	const WEEKS_PER_YEAR = 52;
	const DAYS_PER_WEEK = 7;
	const HOURS_PER_DAY = 24;
	const MINUTES_PER_HOUR = 60;
	const SECONDS_PER_MINUTE = 60;

	/**
	 * Default format to use for __toString method when type juggling occurs.
	 *
	 * @var string
	 */
	const DEFAULT_TO_STRING_FORMAT = 'Y-m-d H:i:s';

	/**
	 * Format to use for __toString method when type juggling occurs.
	 *
	 * @var string
	 */
	protected static $toStringFormat = self::DEFAULT_TO_STRING_FORMAT;

	/**
	 * First day of week.
	 *
	 * @var int
	 */
	protected static $weekStartsAt = self::MONDAY;

	/**
	 * Last day of week.
	 *
	 * @var int
	 */
	protected static $weekEndsAt = self::SUNDAY;

	/**
	 * Days of weekend.
	 *
	 * @var array
	 */
	protected static $weekendDays = array(
		self::SATURDAY,
		self::SUNDAY,
	);

	/**
	 * A test Carbon instance to be returned when now instances are created.
	 *
	 * @var \Carbon\Carbon
	 */
	protected static $testNow;

	/**
	 * A translator to ... er ... translate stuff.
	 *
	 * @var \Symfony\Component\Translation\TranslatorInterface
	 */
	protected static $translator;

	/**
	 * The errors that can occur.
	 *
	 * @var array
	 */
	protected static $lastErrors;

	/**
	 * Will UTF8 encoding be used to print localized date/time ?
	 *
	 * @var bool
	 */
	protected static $utf8 = false;

	/*
	 * Indicates if months should be calculated with overflow.
	 *
	 * @var bool
	 */
	protected static $monthsOverflow = true;

	/**
	 * Indicates if months should be calculated with overflow.
	 *
	 * @param bool $monthsOverflow
	 *
	 * @return void
	 */
	public static function useMonthsOverflow($monthsOverflow = true)
	{
		static::$monthsOverflow = $monthsOverflow;
	}

	/**
	 * Reset the month overflow behavior.
	 *
	 * @return void
	 */
	public static function resetMonthsOverflow()
	{
		static::$monthsOverflow = true;
	}

	/**
	 * Get the month overflow behavior.
	 *
	 * @return bool
	 */
	public static function shouldOverflowMonths()
	{
		return static::$monthsOverflow;
	}

	/**
	 * Creates a DateTimeZone from a string, DateTimeZone or integer offset.
	 *
	 * @param \DateTimeZone|string|int|null $object
	 *
	 * @throws \InvalidArgumentException
	 *
	 * @return \DateTimeZone
	 */
	protected static function safeCreateDateTimeZone($object)
	{
		if ($object === null) {
			// Don't return null... avoid Bug #52063 in PHP <5.3.6
			return new DateTimeZone(date_default_timezone_get());
		}

		if ($object instanceof DateTimeZone) {
			return $object;
		}

		if (is_numeric($object)) {
			$tzName = timezone_name_from_abbr(null, $object * 3600, true);

			if ($tzName === false) {
				throw new InvalidArgumentException('Unknown or bad timezone ('.$object.')');
			}

			$object = $tzName;
		}

		$tz = @timezone_open((string) $object);

		if ($tz === false) {
			throw new InvalidArgumentException('Unknown or bad timezone ('.$object.')');
		}

		return $tz;
	}

	///////////////////////////////////////////////////////////////////
	//////////////////////////// CONSTRUCTORS /////////////////////////
	///////////////////////////////////////////////////////////////////

	/**
	 * Create a new Carbon instance.
	 *
	 * Please see the testing aids section (specifically static::setTestNow())
	 * for more on the possibility of this constructor returning a test instance.
	 *
	 * @param string|null               $time
	 * @param \DateTimeZone|string|null $tz
	 */
	public function __construct($time = null, $tz = null)
	{
		// If the class has a test now set and we are trying to create a now()
		// instance then override as required
		if (static::hasTestNow() && (empty($time) || $time === 'now' || static::hasRelativeKeywords($time))) {
			$testInstance = clone static::getTestNow();
			if (static::hasRelativeKeywords($time)) {
				$testInstance->modify($time);
			}

			//shift the time according to the given time zone
			if ($tz !== null && $tz !== static::getTestNow()->getTimezone()) {
				$testInstance->setTimezone($tz);
			} else {
				$tz = $testInstance->getTimezone();
			}

			$time = $testInstance->toDateTimeString();
		}

		parent::__construct($time, static::safeCreateDateTimeZone($tz));
	}

	/**
	 * Create a Carbon instance from a DateTime one.
	 *
	 * @param \DateTime $dt
	 *
	 * @return static
	 */
	public static function instance(DateTime $dt)
	{
		if ($dt instanceof static) {
			return clone $dt;
		}

		return new static($dt->format('Y-m-d H:i:s.u'), $dt->getTimezone());
	}

	/**
	 * Create a carbon instance from a string.
	 *
	 * This is an alias for the constructor that allows better fluent syntax
	 * as it allows you to do Carbon::parse('Monday next week')->fn() rather
	 * than (new Carbon('Monday next week'))->fn().
	 *
	 * @param string|null               $time
	 * @param \DateTimeZone|string|null $tz
	 *
	 * @return static
	 */
	public static function parse($time = null, $tz = null)
	{
		return new static($time, $tz);
	}

	/**
	 * Get a Carbon instance for the current date and time.
	 *
	 * @param \DateTimeZone|string|null $tz
	 *
	 * @return static
	 */
	public static function now($tz = null)
	{
		return new static(null, $tz);
	}

	/**
	 * Create a Carbon instance for today.
	 *
	 * @param \DateTimeZone|string|null $tz
	 *
	 * @return static
	 */
	public static function today($tz = null)
	{
		return static::now($tz)->startOfDay();
	}

	/**
	 * Create a Carbon instance for tomorrow.
	 *
	 * @param \DateTimeZone|string|null $tz
	 *
	 * @return static
	 */
	public static function tomorrow($tz = null)
	{
		return static::today($tz)->addDay();
	}

	/**
	 * Create a Carbon instance for yesterday.
	 *
	 * @param \DateTimeZone|string|null $tz
	 *
	 * @return static
	 */
	public static function yesterday($tz = null)
	{
		return static::today($tz)->subDay();
	}

	/**
	 * Create a Carbon instance for the greatest supported date.
	 *
	 * @return static
	 */
	public static function maxValue()
	{
		if (PHP_INT_SIZE === 4) {
			// 32 bit (and additionally Windows 64 bit)
			return static::createFromTimestamp(PHP_INT_MAX);
		}

		// 64 bit
		return static::create(9999, 12, 31, 23, 59, 59);
	}

	/**
	 * Create a Carbon instance for the lowest supported date.
	 *
	 * @return static
	 */
	public static function minValue()
	{
		if (PHP_INT_SIZE === 4) {
			// 32 bit (and additionally Windows 64 bit)
			return static::createFromTimestamp(~PHP_INT_MAX);
		}

		// 64 bit
		return static::create(1, 1, 1, 0, 0, 0);
	}

	/**
	 * Create a new Carbon instance from a specific date and time.
	 *
	 * If any of $year, $month or $day are set to null their now() values will
	 * be used.
	 *
	 * If $hour is null it will be set to its now() value and the default
	 * values for $minute and $second will be their now() values.
	 *
	 * If $hour is not null then the default values for $minute and $second
	 * will be 0.
	 *
	 * @param int|null                  $year
	 * @param int|null                  $month
	 * @param int|null                  $day
	 * @param int|null                  $hour
	 * @param int|null                  $minute
	 * @param int|null                  $second
	 * @param \DateTimeZone|string|null $tz
	 *
	 * @return static
	 */
	public static function create($year = null, $month = null, $day = null, $hour = null, $minute = null, $second = null, $tz = null)
	{
		$now = static::hasTestNow() ? static::getTestNow()->getTimestamp() : time();

		$defaults = array_combine(array(
			'year',
			'month',
			'day',
			'hour',
			'minute',
			'second',
		), explode('-', date('Y-n-j-G-i-s', $now)));

		$year = $year === null ? $defaults['year'] : $year;
		$month = $month === null ? $defaults['month'] : $month;
		$day = $day === null ? $defaults['day'] : $day;

		if ($hour === null) {
			$hour = $defaults['hour'];
			$minute = $minute === null ? $defaults['minute'] : $minute;
			$second = $second === null ? $defaults['second'] : $second;
		} else {
			$minute = $minute === null ? 0 : $minute;
			$second = $second === null ? 0 : $second;
		}

		$fixYear = null;

		if ($year < 0) {
			$fixYear = $year;
			$year = 0;
		} elseif ($year > 9999) {
			$fixYear = $year - 9999;
			$year = 9999;
		}

		$instance = static::createFromFormat('Y-n-j G:i:s', sprintf('%s-%s-%s %s:%02s:%02s', $year, $month, $day, $hour, $minute, $second), $tz);

		if ($fixYear !== null) {
			$instance->addYears($fixYear);
		}

		return $instance;
	}

	/**
	 * Create a new safe Carbon instance from a specific date and time.
	 *
	 * If any of $year, $month or $day are set to null their now() values will
	 * be used.
	 *
	 * If $hour is null it will be set to its now() value and the default
	 * values for $minute and $second will be their now() values.
	 *
	 * If $hour is not null then the default values for $minute and $second
	 * will be 0.
	 *
	 * If one of the set values is not valid, an \InvalidArgumentException
	 * will be thrown.
	 *
	 * @param int|null                  $year
	 * @param int|null                  $month
	 * @param int|null                  $day
	 * @param int|null                  $hour
	 * @param int|null                  $minute
	 * @param int|null                  $second
	 * @param \DateTimeZone|string|null $tz
	 *
	 * @throws \Carbon\Exceptions\InvalidDateException
	 *
	 * @return static
	 */
	public static function createSafe($year = null, $month = null, $day = null, $hour = null, $minute = null, $second = null, $tz = null)
	{
		$fields = array(
			'year' => array(0, 9999),
			'month' => array(0, 12),
			'day' => array(0, 31),
			'hour' => array(0, 24),
			'minute' => array(0, 59),
			'second' => array(0, 59),
		);

		foreach ($fields as $field => $range) {
			if ($$field !== null && (!is_int($$field) || $$field < $range[0] || $$field > $range[1])) {
				throw new InvalidDateException($field, $$field);
			}
		}

		$instance = static::create($year, $month, 1, $hour, $minute, $second, $tz);

		if ($day !== null && $day > $instance->daysInMonth) {
			throw new InvalidDateException('day', $day);
		}

		return $instance->day($day);
	}

	/**
	 * Create a Carbon instance from just a date. The time portion is set to now.
	 *
	 * @param int|null                  $year
	 * @param int|null                  $month
	 * @param int|null                  $day
	 * @param \DateTimeZone|string|null $tz
	 *
	 * @return static
	 */
	public static function createFromDate($year = null, $month = null, $day = null, $tz = null)
	{
		return static::create($year, $month, $day, null, null, null, $tz);
	}

	/**
	 * Create a Carbon instance from just a time. The date portion is set to today.
	 *
	 * @param int|null                  $hour
	 * @param int|null                  $minute
	 * @param int|null                  $second
	 * @param \DateTimeZone|string|null $tz
	 *
	 * @return static
	 */
	public static function createFromTime($hour = null, $minute = null, $second = null, $tz = null)
	{
		return static::create(null, null, null, $hour, $minute, $second, $tz);
	}

	/**
	 * Create a Carbon instance from a specific format.
	 *
	 * @param string                    $format
	 * @param string                    $time
	 * @param \DateTimeZone|string|null $tz
	 *
	 * @throws \InvalidArgumentException
	 *
	 * @return static
	 */
	public static function createFromFormat($format, $time, $tz = null)
	{
		if ($tz !== null) {
			$dt = parent::createFromFormat($format, $time, static::safeCreateDateTimeZone($tz));
		} else {
			$dt = parent::createFromFormat($format, $time);
		}

		static::setLastErrors($lastErrors = parent::getLastErrors());

		if ($dt instanceof DateTime) {
			return static::instance($dt);
		}

		throw new InvalidArgumentException(implode(PHP_EOL, $lastErrors['errors']));
	}

	/**
	 * Set last errors.
	 *
	 * @param array $lastErrors
	 *
	 * @return void
	 */
	private static function setLastErrors(array $lastErrors)
	{
		static::$lastErrors = $lastErrors;
	}

	/**
	 * {@inheritdoc}
	 */
	public static function getLastErrors()
	{
		return static::$lastErrors;
	}

	/**
	 * Create a Carbon instance from a timestamp.
	 *
	 * @param int                       $timestamp
	 * @param \DateTimeZone|string|null $tz
	 *
	 * @return static
	 */
	public static function createFromTimestamp($timestamp, $tz = null)
	{
		return static::now($tz)->setTimestamp($timestamp);
	}

	/**
	 * Create a Carbon instance from an UTC timestamp.
	 *
	 * @param int $timestamp
	 *
	 * @return static
	 */
	public static function createFromTimestampUTC($timestamp)
	{
		return new static('@'.$timestamp);
	}

	/**
	 * Get a copy of the instance.
	 *
	 * @return static
	 */
	public function copy()
	{
		return clone $this;
	}

	///////////////////////////////////////////////////////////////////
	///////////////////////// GETTERS AND SETTERS /////////////////////
	///////////////////////////////////////////////////////////////////

	/**
	 * Get a part of the Carbon object
	 *
	 * @param string $name
	 *
	 * @throws \InvalidArgumentException
	 *
	 * @return string|int|\DateTimeZone
	 */
	public function __get($name)
	{
		switch (true) {
			case array_key_exists($name, $formats = array(
				'year' => 'Y',
				'yearIso' => 'o',
				'month' => 'n',
				'day' => 'j',
				'hour' => 'G',
				'minute' => 'i',
				'second' => 's',
				'micro' => 'u',
				'dayOfWeek' => 'w',
				'dayOfYear' => 'z',
				'weekOfYear' => 'W',
				'daysInMonth' => 't',
				'timestamp' => 'U',
			)):
				return (int) $this->format($formats[$name]);

			case $name === 'weekOfMonth':
				return (int) ceil($this->day / static::DAYS_PER_WEEK);

			case $name === 'age':
				return $this->diffInYears();

			case $name === 'quarter':
				return (int) ceil($this->month / static::MONTHS_PER_QUARTER);

			case $name === 'offset':
				return $this->getOffset();

			case $name === 'offsetHours':
				return $this->getOffset() / static::SECONDS_PER_MINUTE / static::MINUTES_PER_HOUR;

			case $name === 'dst':
				return $this->format('I') === '1';

			case $name === 'local':
				return $this->getOffset() === $this->copy()->setTimezone(date_default_timezone_get())->getOffset();

			case $name === 'utc':
				return $this->getOffset() === 0;

			case $name === 'timezone' || $name === 'tz':
				return $this->getTimezone();

			case $name === 'timezoneName' || $name === 'tzName':
				return $this->getTimezone()->getName();

			default:
				throw new InvalidArgumentException(sprintf("Unknown getter '%s'", $name));
		}
	}

	/**
	 * Check if an attribute exists on the object
	 *
	 * @param string $name
	 *
	 * @return bool
	 */
	public function __isset($name)
	{
		try {
			$this->__get($name);
		} catch (InvalidArgumentException $e) {
			return false;
		}

		return true;
	}

	/**
	 * Set a part of the Carbon object
	 *
	 * @param string                   $name
	 * @param string|int|\DateTimeZone $value
	 *
	 * @throws \InvalidArgumentException
	 */
	public function __set($name, $value)
	{
		switch ($name) {
			case 'year':
			case 'month':
			case 'day':
			case 'hour':
			case 'minute':
			case 'second':
				list($year, $month, $day, $hour, $minute, $second) = explode('-', $this->format('Y-n-j-G-i-s'));
				$$name = $value;
				$this->setDateTime($year, $month, $day, $hour, $minute, $second);
				break;

			case 'timestamp':
				parent::setTimestamp($value);
				break;

			case 'timezone':
			case 'tz':
				$this->setTimezone($value);
				break;

			default:
				throw new InvalidArgumentException(sprintf("Unknown setter '%s'", $name));
		}
	}

	/**
	 * Set the instance's year
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function year($value)
	{
		$this->year = $value;

		return $this;
	}

	/**
	 * Set the instance's month
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function month($value)
	{
		$this->month = $value;

		return $this;
	}

	/**
	 * Set the instance's day
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function day($value)
	{
		$this->day = $value;

		return $this;
	}

	/**
	 * Set the instance's hour
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function hour($value)
	{
		$this->hour = $value;

		return $this;
	}

	/**
	 * Set the instance's minute
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function minute($value)
	{
		$this->minute = $value;

		return $this;
	}

	/**
	 * Set the instance's second
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function second($value)
	{
		$this->second = $value;

		return $this;
	}

	/**
	 * Sets the current date of the DateTime object to a different date.
	 * Calls modify as a workaround for a php bug
	 *
	 * @param int $year
	 * @param int $month
	 * @param int $day
	 *
	 * @return static
	 *
	 * @see https://github.com/briannesbitt/Carbon/issues/539
	 * @see https://bugs.php.net/bug.php?id=63863
	 */
	public function setDate($year, $month, $day)
	{
		$this->modify('+0 day');

		return parent::setDate($year, $month, $day);
	}

	/**
	 * Set the date and time all together
	 *
	 * @param int $year
	 * @param int $month
	 * @param int $day
	 * @param int $hour
	 * @param int $minute
	 * @param int $second
	 *
	 * @return static
	 */
	public function setDateTime($year, $month, $day, $hour, $minute, $second = 0)
	{
		return $this->setDate($year, $month, $day)->setTime($hour, $minute, $second);
	}

	/**
	 * Set the time by time string
	 *
	 * @param string $time
	 *
	 * @return static
	 */
	public function setTimeFromTimeString($time)
	{
		$time = explode(':', $time);

		$hour = $time[0];
		$minute = isset($time[1]) ? $time[1] : 0;
		$second = isset($time[2]) ? $time[2] : 0;

		return $this->setTime($hour, $minute, $second);
	}

	/**
	 * Set the instance's timestamp
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function timestamp($value)
	{
		return $this->setTimestamp($value);
	}

	/**
	 * Alias for setTimezone()
	 *
	 * @param \DateTimeZone|string $value
	 *
	 * @return static
	 */
	public function timezone($value)
	{
		return $this->setTimezone($value);
	}

	/**
	 * Alias for setTimezone()
	 *
	 * @param \DateTimeZone|string $value
	 *
	 * @return static
	 */
	public function tz($value)
	{
		return $this->setTimezone($value);
	}

	/**
	 * Set the instance's timezone from a string or object
	 *
	 * @param \DateTimeZone|string $value
	 *
	 * @return static
	 */
	public function setTimezone($value)
	{
		return parent::setTimezone(static::safeCreateDateTimeZone($value));
	}

	/**
	 * Get the days of the week
	 *
	 * @return array
	 */
	public static function getDays()
	{
		return static::$days;
	}

	///////////////////////////////////////////////////////////////////
	/////////////////////// WEEK SPECIAL DAYS /////////////////////////
	///////////////////////////////////////////////////////////////////

	/**
	 * Get the first day of week
	 *
	 * @return int
	 */
	public static function getWeekStartsAt()
	{
		return static::$weekStartsAt;
	}

	/**
	 * Set the first day of week
	 *
	 * @param int
	 */
	public static function setWeekStartsAt($day)
	{
		static::$weekStartsAt = $day;
	}

	/**
	 * Get the last day of week
	 *
	 * @return int
	 */
	public static function getWeekEndsAt()
	{
		return static::$weekEndsAt;
	}

	/**
	 * Set the last day of week
	 *
	 * @param int
	 */
	public static function setWeekEndsAt($day)
	{
		static::$weekEndsAt = $day;
	}

	/**
	 * Get weekend days
	 *
	 * @return array
	 */
	public static function getWeekendDays()
	{
		return static::$weekendDays;
	}

	/**
	 * Set weekend days
	 *
	 * @param array
	 */
	public static function setWeekendDays($days)
	{
		static::$weekendDays = $days;
	}

	///////////////////////////////////////////////////////////////////
	///////////////////////// TESTING AIDS ////////////////////////////
	///////////////////////////////////////////////////////////////////

	/**
	 * Set a Carbon instance (real or mock) to be returned when a "now"
	 * instance is created.  The provided instance will be returned
	 * specifically under the following conditions:
	 *   - A call to the static now() method, ex. Carbon::now()
	 *   - When a null (or blank string) is passed to the constructor or parse(), ex. new Carbon(null)
	 *   - When the string "now" is passed to the constructor or parse(), ex. new Carbon('now')
	 *   - When a string containing the desired time is passed to Carbon::parse().
	 *
	 * Note the timezone parameter was left out of the examples above and
	 * has no affect as the mock value will be returned regardless of its value.
	 *
	 * To clear the test instance call this method using the default
	 * parameter of null.
	 *
	 * @param \Carbon\Carbon|string|null $testNow
	 */
	public static function setTestNow($testNow = null)
	{
		static::$testNow = is_string($testNow) ? static::parse($testNow) : $testNow;
	}

	/**
	 * Get the Carbon instance (real or mock) to be returned when a "now"
	 * instance is created.
	 *
	 * @return static the current instance used for testing
	 */
	public static function getTestNow()
	{
		return static::$testNow;
	}

	/**
	 * Determine if there is a valid test instance set. A valid test instance
	 * is anything that is not null.
	 *
	 * @return bool true if there is a test instance, otherwise false
	 */
	public static function hasTestNow()
	{
		return static::getTestNow() !== null;
	}

	/**
	 * Determine if there is a relative keyword in the time string, this is to
	 * create dates relative to now for test instances. e.g.: next tuesday
	 *
	 * @param string $time
	 *
	 * @return bool true if there is a keyword, otherwise false
	 */
	public static function hasRelativeKeywords($time)
	{
		// skip common format with a '-' in it
		if (preg_match('/\d{4}-\d{1,2}-\d{1,2}/', $time) !== 1) {
			foreach (static::$relativeKeywords as $keyword) {
				if (stripos($time, $keyword) !== false) {
					return true;
				}
			}
		}

		return false;
	}

	///////////////////////////////////////////////////////////////////
	/////////////////////// LOCALIZATION //////////////////////////////
	///////////////////////////////////////////////////////////////////

	/**
	 * Initialize the translator instance if necessary.
	 *
	 * @return \Symfony\Component\Translation\TranslatorInterface
	 */
	protected static function translator()
	{
		if (static::$translator === null) {
			$translator = new Translator('en');
			$translator->addLoader('array', new ArrayLoader());
			static::$translator = $translator;
			static::setLocale('en');
		}

		return static::$translator;
	}

	/**
	 * Get the translator instance in use
	 *
	 * @return \Symfony\Component\Translation\TranslatorInterface
	 */
	public static function getTranslator()
	{
		return static::translator();
	}

	/**
	 * Set the translator instance to use
	 *
	 * @param \Symfony\Component\Translation\TranslatorInterface $translator
	 */
	public static function setTranslator(TranslatorInterface $translator)
	{
		static::$translator = $translator;
	}

	/**
	 * Get the current translator locale
	 *
	 * @return string
	 */
	public static function getLocale()
	{
		return static::translator()->getLocale();
	}

	/**
	 * Set the current translator locale and indicate if the source locale file exists
	 *
	 * @param string $locale
	 *
	 * @return bool
	 */
	public static function setLocale($locale)
	{
		$locale = preg_replace_callback('/\b([a-z]{2})[-_](?:([a-z]{4})[-_])?([a-z]{2})\b/', function ($matches) {
			return $matches[1].'_'.(!empty($matches[2]) ? ucfirst($matches[2]).'_' : '').strtoupper($matches[3]);
		}, strtolower($locale));

		if (file_exists($filename = __DIR__.'/Lang/'.$locale.'.php')) {
			$translator = static::translator();
			$translator->setLocale($locale);

			if ($translator instanceof Translator) {
				// Ensure the locale has been loaded.
				$translator->addResource('array', require $filename, $locale);
			}

			return true;
		}

		return false;
	}

	///////////////////////////////////////////////////////////////////
	/////////////////////// STRING FORMATTING /////////////////////////
	///////////////////////////////////////////////////////////////////

	/**
	 * Set if UTF8 will be used for localized date/time
	 *
	 * @param bool $utf8
	 */
	public static function setUtf8($utf8)
	{
		static::$utf8 = $utf8;
	}

	/**
	 * Format the instance with the current locale.  You can set the current
	 * locale using setlocale() http://php.net/setlocale.
	 *
	 * @param string $format
	 *
	 * @return string
	 */
	public function formatLocalized($format)
	{
		// Check for Windows to find and replace the %e
		// modifier correctly
		if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {
			$format = preg_replace('#(?<!%)((?:%%)*)%e#', '\1%#d', $format);
		}

		$formatted = strftime($format, strtotime($this));

		return static::$utf8 ? utf8_encode($formatted) : $formatted;
	}

	/**
	 * Reset the format used to the default when type juggling a Carbon instance to a string
	 */
	public static function resetToStringFormat()
	{
		static::setToStringFormat(static::DEFAULT_TO_STRING_FORMAT);
	}

	/**
	 * Set the default format used when type juggling a Carbon instance to a string
	 *
	 * @param string $format
	 */
	public static function setToStringFormat($format)
	{
		static::$toStringFormat = $format;
	}

	/**
	 * Format the instance as a string using the set format
	 *
	 * @return string
	 */
	public function __toString()
	{
		return $this->format(static::$toStringFormat);
	}

	/**
	 * Format the instance as date
	 *
	 * @return string
	 */
	public function toDateString()
	{
		return $this->format('Y-m-d');
	}

	/**
	 * Format the instance as a readable date
	 *
	 * @return string
	 */
	public function toFormattedDateString()
	{
		return $this->format('M j, Y');
	}

	/**
	 * Format the instance as time
	 *
	 * @return string
	 */
	public function toTimeString()
	{
		return $this->format('H:i:s');
	}

	/**
	 * Format the instance as date and time
	 *
	 * @return string
	 */
	public function toDateTimeString()
	{
		return $this->format('Y-m-d H:i:s');
	}

	/**
	 * Format the instance with day, date and time
	 *
	 * @return string
	 */
	public function toDayDateTimeString()
	{
		return $this->format('D, M j, Y g:i A');
	}

	/**
	 * Format the instance as ATOM
	 *
	 * @return string
	 */
	public function toAtomString()
	{
		return $this->format(static::ATOM);
	}

	/**
	 * Format the instance as COOKIE
	 *
	 * @return string
	 */
	public function toCookieString()
	{
		return $this->format(static::COOKIE);
	}

	/**
	 * Format the instance as ISO8601
	 *
	 * @return string
	 */
	public function toIso8601String()
	{
		return $this->toAtomString();
	}

	/**
	 * Format the instance as RFC822
	 *
	 * @return string
	 */
	public function toRfc822String()
	{
		return $this->format(static::RFC822);
	}

	/**
	 * Format the instance as RFC850
	 *
	 * @return string
	 */
	public function toRfc850String()
	{
		return $this->format(static::RFC850);
	}

	/**
	 * Format the instance as RFC1036
	 *
	 * @return string
	 */
	public function toRfc1036String()
	{
		return $this->format(static::RFC1036);
	}

	/**
	 * Format the instance as RFC1123
	 *
	 * @return string
	 */
	public function toRfc1123String()
	{
		return $this->format(static::RFC1123);
	}

	/**
	 * Format the instance as RFC2822
	 *
	 * @return string
	 */
	public function toRfc2822String()
	{
		return $this->format(static::RFC2822);
	}

	/**
	 * Format the instance as RFC3339
	 *
	 * @return string
	 */
	public function toRfc3339String()
	{
		return $this->format(static::RFC3339);
	}

	/**
	 * Format the instance as RSS
	 *
	 * @return string
	 */
	public function toRssString()
	{
		return $this->format(static::RSS);
	}

	/**
	 * Format the instance as W3C
	 *
	 * @return string
	 */
	public function toW3cString()
	{
		return $this->format(static::W3C);
	}

	///////////////////////////////////////////////////////////////////
	////////////////////////// COMPARISONS ////////////////////////////
	///////////////////////////////////////////////////////////////////

	/**
	 * Determines if the instance is equal to another
	 *
	 * @param Carbon $dt
	 *
	 * @return bool
	 */
	public function eq(Carbon $dt)
	{
		return $this == $dt;
	}

	/**
	 * Determines if the instance is equal to another
	 *
	 * @param Carbon $dt
	 *
	 * @see eq()
	 *
	 * @return bool
	 */
	public function equalTo(Carbon $dt)
	{
		return $this->eq($dt);
	}

	/**
	 * Determines if the instance is not equal to another
	 *
	 * @param Carbon $dt
	 *
	 * @return bool
	 */
	public function ne(Carbon $dt)
	{
		return !$this->eq($dt);
	}

	/**
	 * Determines if the instance is not equal to another
	 *
	 * @param Carbon $dt
	 *
	 * @see ne()
	 *
	 * @return bool
	 */
	public function notEqualTo(Carbon $dt)
	{
		return $this->ne($dt);
	}

	/**
	 * Determines if the instance is greater (after) than another
	 *
	 * @param Carbon $dt
	 *
	 * @return bool
	 */
	public function gt(Carbon $dt)
	{
		return $this > $dt;
	}

	/**
	 * Determines if the instance is greater (after) than another
	 *
	 * @param Carbon $dt
	 *
	 * @see gt()
	 *
	 * @return bool
	 */
	public function greaterThan(Carbon $dt)
	{
		return $this->gt($dt);
	}

	/**
	 * Determines if the instance is greater (after) than or equal to another
	 *
	 * @param Carbon $dt
	 *
	 * @return bool
	 */
	public function gte(Carbon $dt)
	{
		return $this >= $dt;
	}

	/**
	 * Determines if the instance is greater (after) than or equal to another
	 *
	 * @param Carbon $dt
	 *
	 * @see gte()
	 *
	 * @return bool
	 */
	public function greaterThanOrEqualTo(Carbon $dt)
	{
		return $this->gte($dt);
	}

	/**
	 * Determines if the instance is less (before) than another
	 *
	 * @param Carbon $dt
	 *
	 * @return bool
	 */
	public function lt(Carbon $dt)
	{
		return $this < $dt;
	}

	/**
	 * Determines if the instance is less (before) than another
	 *
	 * @param Carbon $dt
	 *
	 * @see lt()
	 *
	 * @return bool
	 */
	public function lessThan(Carbon $dt)
	{
		return $this->lt($dt);
	}

	/**
	 * Determines if the instance is less (before) or equal to another
	 *
	 * @param Carbon $dt
	 *
	 * @return bool
	 */
	public function lte(Carbon $dt)
	{
		return $this <= $dt;
	}

	/**
	 * Determines if the instance is less (before) or equal to another
	 *
	 * @param Carbon $dt
	 *
	 * @see lte()
	 *
	 * @return bool
	 */
	public function lessThanOrEqualTo(Carbon $dt)
	{
		return $this->lte($dt);
	}

	/**
	 * Determines if the instance is between two others
	 *
	 * @param Carbon $dt1
	 * @param Carbon $dt2
	 * @param bool   $equal Indicates if a > and < comparison should be used or <= or >=
	 *
	 * @return bool
	 */
	public function between(Carbon $dt1, Carbon $dt2, $equal = true)
	{
		if ($dt1->gt($dt2)) {
			$temp = $dt1;
			$dt1 = $dt2;
			$dt2 = $temp;
		}

		if ($equal) {
			return $this->gte($dt1) && $this->lte($dt2);
		}

		return $this->gt($dt1) && $this->lt($dt2);
	}

	/**
	 * Get the closest date from the instance.
	 *
	 * @param Carbon $dt1
	 * @param Carbon $dt2
	 *
	 * @return static
	 */
	public function closest(Carbon $dt1, Carbon $dt2)
	{
		return $this->diffInSeconds($dt1) < $this->diffInSeconds($dt2) ? $dt1 : $dt2;
	}

	/**
	 * Get the farthest date from the instance.
	 *
	 * @param Carbon $dt1
	 * @param Carbon $dt2
	 *
	 * @return static
	 */
	public function farthest(Carbon $dt1, Carbon $dt2)
	{
		return $this->diffInSeconds($dt1) > $this->diffInSeconds($dt2) ? $dt1 : $dt2;
	}

	/**
	 * Get the minimum instance between a given instance (default now) and the current instance.
	 *
	 * @param \Carbon\Carbon|null $dt
	 *
	 * @return static
	 */
	public function min(Carbon $dt = null)
	{
		$dt = $dt ?: static::now($this->getTimezone());

		return $this->lt($dt) ? $this : $dt;
	}

	/**
	 * Get the minimum instance between a given instance (default now) and the current instance.
	 *
	 * @param \Carbon\Carbon|null $dt
	 *
	 * @see min()
	 *
	 * @return static
	 */
	public function minimum(Carbon $dt = null)
	{
		return $this->min($dt);
	}

	/**
	 * Get the maximum instance between a given instance (default now) and the current instance.
	 *
	 * @param \Carbon\Carbon|null $dt
	 *
	 * @return static
	 */
	public function max(Carbon $dt = null)
	{
		$dt = $dt ?: static::now($this->getTimezone());

		return $this->gt($dt) ? $this : $dt;
	}

	/**
	 * Get the maximum instance between a given instance (default now) and the current instance.
	 *
	 * @param \Carbon\Carbon|null $dt
	 *
	 * @see max()
	 *
	 * @return static
	 */
	public function maximum(Carbon $dt = null)
	{
		return $this->max($dt);
	}

	/**
	 * Determines if the instance is a weekday
	 *
	 * @return bool
	 */
	public function isWeekday()
	{
		return !$this->isWeekend();
	}

	/**
	 * Determines if the instance is a weekend day
	 *
	 * @return bool
	 */
	public function isWeekend()
	{
		return in_array($this->dayOfWeek, static::$weekendDays);
	}

	/**
	 * Determines if the instance is yesterday
	 *
	 * @return bool
	 */
	public function isYesterday()
	{
		return $this->toDateString() === static::yesterday($this->getTimezone())->toDateString();
	}

	/**
	 * Determines if the instance is today
	 *
	 * @return bool
	 */
	public function isToday()
	{
		return $this->toDateString() === static::now($this->getTimezone())->toDateString();
	}

	/**
	 * Determines if the instance is tomorrow
	 *
	 * @return bool
	 */
	public function isTomorrow()
	{
		return $this->toDateString() === static::tomorrow($this->getTimezone())->toDateString();
	}

	/**
	 * Determines if the instance is within the next week
	 *
	 * @return bool
	 */
	public function isNextWeek()
	{
		return $this->weekOfYear === static::now($this->getTimezone())->addWeek()->weekOfYear;
	}

	/**
	 * Determines if the instance is within the last week
	 *
	 * @return bool
	 */
	public function isLastWeek()
	{
		return $this->weekOfYear === static::now($this->getTimezone())->subWeek()->weekOfYear;
	}

	/**
	 * Determines if the instance is within the next month
	 *
	 * @return bool
	 */
	public function isNextMonth()
	{
		return $this->month === static::now($this->getTimezone())->addMonthNoOverflow()->month;
	}

	/**
	 * Determines if the instance is within the last month
	 *
	 * @return bool
	 */
	public function isLastMonth()
	{
		return $this->month === static::now($this->getTimezone())->subMonthNoOverflow()->month;
	}

	/**
	 * Determines if the instance is within next year
	 *
	 * @return bool
	 */
	public function isNextYear()
	{
		return $this->year === static::now($this->getTimezone())->addYear()->year;
	}

	/**
	 * Determines if the instance is within the previous year
	 *
	 * @return bool
	 */
	public function isLastYear()
	{
		return $this->year === static::now($this->getTimezone())->subYear()->year;
	}

	/**
	 * Determines if the instance is in the future, ie. greater (after) than now
	 *
	 * @return bool
	 */
	public function isFuture()
	{
		return $this->gt(static::now($this->getTimezone()));
	}

	/**
	 * Determines if the instance is in the past, ie. less (before) than now
	 *
	 * @return bool
	 */
	public function isPast()
	{
		return $this->lt(static::now($this->getTimezone()));
	}

	/**
	 * Determines if the instance is a leap year
	 *
	 * @return bool
	 */
	public function isLeapYear()
	{
		return $this->format('L') === '1';
	}

	/**
	 * Determines if the instance is a long year
	 *
	 * @see https://en.wikipedia.org/wiki/ISO_8601#Week_dates
	 *
	 * @return bool
	 */
	public function isLongYear()
	{
		return static::create($this->year, 12, 28, 0, 0, 0, $this->tz)->weekOfYear === 53;
	}

	/*
	 * Compares the formatted values of the two dates.
	 *
	 * @param string              $format The date formats to compare.
	 * @param \Carbon\Carbon|null $dt     The instance to compare with or null to use current day.
	 *
	 * @return bool
	 */
	public function isSameAs($format, Carbon $dt = null)
	{
		$dt = $dt ?: static::now($this->tz);

		return $this->format($format) === $dt->format($format);
	}

	/**
	 * Determines if the instance is in the current year
	 *
	 * @return bool
	 */
	public function isCurrentYear()
	{
		return $this->isSameYear();
	}

	/**
	 * Checks if the passed in date is in the same year as the instance year.
	 *
	 * @param \Carbon\Carbon|null $dt The instance to compare with or null to use current day.
	 *
	 * @return bool
	 */
	public function isSameYear(Carbon $dt = null)
	{
		return $this->isSameAs('Y', $dt);
	}

	/**
	 * Determines if the instance is in the current month
	 *
	 * @return bool
	 */
	public function isCurrentMonth()
	{
		return $this->isSameMonth();
	}

	/**
	 * Checks if the passed in date is in the same month as the instance month (and year if needed).
	 *
	 * @param \Carbon\Carbon|null $dt         The instance to compare with or null to use current day.
	 * @param bool                $ofSameYear Check if it is the same month in the same year.
	 *
	 * @return bool
	 */
	public function isSameMonth(Carbon $dt = null, $ofSameYear = false)
	{
		$format = $ofSameYear ? 'Y-m' : 'm';

		return $this->isSameAs($format, $dt);
	}

	/**
	 * Checks if the passed in date is the same day as the instance current day.
	 *
	 * @param \Carbon\Carbon $dt
	 *
	 * @return bool
	 */
	public function isSameDay(Carbon $dt)
	{
		return $this->toDateString() === $dt->toDateString();
	}

	/**
	 * Checks if this day is a Sunday.
	 *
	 * @return bool
	 */
	public function isSunday()
	{
		return $this->dayOfWeek === static::SUNDAY;
	}

	/**
	 * Checks if this day is a Monday.
	 *
	 * @return bool
	 */
	public function isMonday()
	{
		return $this->dayOfWeek === static::MONDAY;
	}

	/**
	 * Checks if this day is a Tuesday.
	 *
	 * @return bool
	 */
	public function isTuesday()
	{
		return $this->dayOfWeek === static::TUESDAY;
	}

	/**
	 * Checks if this day is a Wednesday.
	 *
	 * @return bool
	 */
	public function isWednesday()
	{
		return $this->dayOfWeek === static::WEDNESDAY;
	}

	/**
	 * Checks if this day is a Thursday.
	 *
	 * @return bool
	 */
	public function isThursday()
	{
		return $this->dayOfWeek === static::THURSDAY;
	}

	/**
	 * Checks if this day is a Friday.
	 *
	 * @return bool
	 */
	public function isFriday()
	{
		return $this->dayOfWeek === static::FRIDAY;
	}

	/**
	 * Checks if this day is a Saturday.
	 *
	 * @return bool
	 */
	public function isSaturday()
	{
		return $this->dayOfWeek === static::SATURDAY;
	}

	///////////////////////////////////////////////////////////////////
	/////////////////// ADDITIONS AND SUBTRACTIONS ////////////////////
	///////////////////////////////////////////////////////////////////

	/**
	 * Add years to the instance. Positive $value travel forward while
	 * negative $value travel into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addYears($value)
	{
		return $this->modify((int) $value.' year');
	}

	/**
	 * Add a year to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addYear($value = 1)
	{
		return $this->addYears($value);
	}

	/**
	 * Remove a year from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subYear($value = 1)
	{
		return $this->subYears($value);
	}

	/**
	 * Remove years from the instance.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subYears($value)
	{
		return $this->addYears(-1 * $value);
	}

	/**
	 * Add quarters to the instance. Positive $value travels forward while
	 * negative $value travels into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addQuarters($value)
	{
		return $this->addMonths(static::MONTHS_PER_QUARTER * $value);
	}

	/**
	 * Add a quarter to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addQuarter($value = 1)
	{
		return $this->addQuarters($value);
	}

	/**
	 * Remove a quarter from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subQuarter($value = 1)
	{
		return $this->subQuarters($value);
	}

	/**
	 * Remove quarters from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subQuarters($value)
	{
		return $this->addQuarters(-1 * $value);
	}

	/**
	 * Add centuries to the instance. Positive $value travels forward while
	 * negative $value travels into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addCenturies($value)
	{
		return $this->addYears(static::YEARS_PER_CENTURY * $value);
	}

	/**
	 * Add a century to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addCentury($value = 1)
	{
		return $this->addCenturies($value);
	}

	/**
	 * Remove a century from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subCentury($value = 1)
	{
		return $this->subCenturies($value);
	}

	/**
	 * Remove centuries from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subCenturies($value)
	{
		return $this->addCenturies(-1 * $value);
	}

	/**
	 * Add months to the instance. Positive $value travels forward while
	 * negative $value travels into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addMonths($value)
	{
		if (static::shouldOverflowMonths()) {
			return $this->addMonthsWithOverflow($value);
		}

		return $this->addMonthsNoOverflow($value);
	}

	/**
	 * Add a month to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addMonth($value = 1)
	{
		return $this->addMonths($value);
	}

	/**
	 * Remove a month from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subMonth($value = 1)
	{
		return $this->subMonths($value);
	}

	/**
	 * Remove months from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subMonths($value)
	{
		return $this->addMonths(-1 * $value);
	}

	/**
	 * Add months to the instance. Positive $value travels forward while
	 * negative $value travels into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addMonthsWithOverflow($value)
	{
		return $this->modify((int) $value.' month');
	}

	/**
	 * Add a month to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addMonthWithOverflow($value = 1)
	{
		return $this->addMonthsWithOverflow($value);
	}

	/**
	 * Remove a month from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subMonthWithOverflow($value = 1)
	{
		return $this->subMonthsWithOverflow($value);
	}

	/**
	 * Remove months from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subMonthsWithOverflow($value)
	{
		return $this->addMonthsWithOverflow(-1 * $value);
	}

	/**
	 * Add months without overflowing to the instance. Positive $value
	 * travels forward while negative $value travels into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addMonthsNoOverflow($value)
	{
		$day = $this->day;

		$this->modify((int) $value.' month');

		if ($day !== $this->day) {
			$this->modify('last day of previous month');
		}

		return $this;
	}

	/**
	 * Add a month with no overflow to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addMonthNoOverflow($value = 1)
	{
		return $this->addMonthsNoOverflow($value);
	}

	/**
	 * Remove a month with no overflow from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subMonthNoOverflow($value = 1)
	{
		return $this->subMonthsNoOverflow($value);
	}

	/**
	 * Remove months with no overflow from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subMonthsNoOverflow($value)
	{
		return $this->addMonthsNoOverflow(-1 * $value);
	}

	/**
	 * Add days to the instance. Positive $value travels forward while
	 * negative $value travels into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addDays($value)
	{
		return $this->modify((int) $value.' day');
	}

	/**
	 * Add a day to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addDay($value = 1)
	{
		return $this->addDays($value);
	}

	/**
	 * Remove a day from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subDay($value = 1)
	{
		return $this->subDays($value);
	}

	/**
	 * Remove days from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subDays($value)
	{
		return $this->addDays(-1 * $value);
	}

	/**
	 * Add weekdays to the instance. Positive $value travels forward while
	 * negative $value travels into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addWeekdays($value)
	{
		// fix for https://bugs.php.net/bug.php?id=54909
		$t = $this->toTimeString();
		$this->modify((int) $value.' weekday');

		return $this->setTimeFromTimeString($t);
	}

	/**
	 * Add a weekday to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addWeekday($value = 1)
	{
		return $this->addWeekdays($value);
	}

	/**
	 * Remove a weekday from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subWeekday($value = 1)
	{
		return $this->subWeekdays($value);
	}

	/**
	 * Remove weekdays from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subWeekdays($value)
	{
		return $this->addWeekdays(-1 * $value);
	}

	/**
	 * Add weeks to the instance. Positive $value travels forward while
	 * negative $value travels into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addWeeks($value)
	{
		return $this->modify((int) $value.' week');
	}

	/**
	 * Add a week to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addWeek($value = 1)
	{
		return $this->addWeeks($value);
	}

	/**
	 * Remove a week from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subWeek($value = 1)
	{
		return $this->subWeeks($value);
	}

	/**
	 * Remove weeks to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subWeeks($value)
	{
		return $this->addWeeks(-1 * $value);
	}

	/**
	 * Add hours to the instance. Positive $value travels forward while
	 * negative $value travels into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addHours($value)
	{
		return $this->modify((int) $value.' hour');
	}

	/**
	 * Add an hour to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addHour($value = 1)
	{
		return $this->addHours($value);
	}

	/**
	 * Remove an hour from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subHour($value = 1)
	{
		return $this->subHours($value);
	}

	/**
	 * Remove hours from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subHours($value)
	{
		return $this->addHours(-1 * $value);
	}

	/**
	 * Add minutes to the instance. Positive $value travels forward while
	 * negative $value travels into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addMinutes($value)
	{
		return $this->modify((int) $value.' minute');
	}

	/**
	 * Add a minute to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addMinute($value = 1)
	{
		return $this->addMinutes($value);
	}

	/**
	 * Remove a minute from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subMinute($value = 1)
	{
		return $this->subMinutes($value);
	}

	/**
	 * Remove minutes from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subMinutes($value)
	{
		return $this->addMinutes(-1 * $value);
	}

	/**
	 * Add seconds to the instance. Positive $value travels forward while
	 * negative $value travels into the past.
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addSeconds($value)
	{
		return $this->modify((int) $value.' second');
	}

	/**
	 * Add a second to the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function addSecond($value = 1)
	{
		return $this->addSeconds($value);
	}

	/**
	 * Remove a second from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subSecond($value = 1)
	{
		return $this->subSeconds($value);
	}

	/**
	 * Remove seconds from the instance
	 *
	 * @param int $value
	 *
	 * @return static
	 */
	public function subSeconds($value)
	{
		return $this->addSeconds(-1 * $value);
	}

	///////////////////////////////////////////////////////////////////
	/////////////////////////// DIFFERENCES ///////////////////////////
	///////////////////////////////////////////////////////////////////

	/**
	 * Get the difference in years
	 *
	 * @param \Carbon\Carbon|null $dt
	 * @param bool                $abs Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffInYears(Carbon $dt = null, $abs = true)
	{
		$dt = $dt ?: static::now($this->getTimezone());

		return (int) $this->diff($dt, $abs)->format('%r%y');
	}

	/**
	 * Get the difference in months
	 *
	 * @param \Carbon\Carbon|null $dt
	 * @param bool                $abs Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffInMonths(Carbon $dt = null, $abs = true)
	{
		$dt = $dt ?: static::now($this->getTimezone());

		return $this->diffInYears($dt, $abs) * static::MONTHS_PER_YEAR + (int) $this->diff($dt, $abs)->format('%r%m');
	}

	/**
	 * Get the difference in weeks
	 *
	 * @param \Carbon\Carbon|null $dt
	 * @param bool                $abs Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffInWeeks(Carbon $dt = null, $abs = true)
	{
		return (int) ($this->diffInDays($dt, $abs) / static::DAYS_PER_WEEK);
	}

	/**
	 * Get the difference in days
	 *
	 * @param \Carbon\Carbon|null $dt
	 * @param bool                $abs Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffInDays(Carbon $dt = null, $abs = true)
	{
		$dt = $dt ?: static::now($this->getTimezone());

		return (int) $this->diff($dt, $abs)->format('%r%a');
	}

	/**
	 * Get the difference in days using a filter closure
	 *
	 * @param Closure             $callback
	 * @param \Carbon\Carbon|null $dt
	 * @param bool                $abs      Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffInDaysFiltered(Closure $callback, Carbon $dt = null, $abs = true)
	{
		return $this->diffFiltered(CarbonInterval::day(), $callback, $dt, $abs);
	}

	/**
	 * Get the difference in hours using a filter closure
	 *
	 * @param Closure             $callback
	 * @param \Carbon\Carbon|null $dt
	 * @param bool                $abs      Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffInHoursFiltered(Closure $callback, Carbon $dt = null, $abs = true)
	{
		return $this->diffFiltered(CarbonInterval::hour(), $callback, $dt, $abs);
	}

	/**
	 * Get the difference by the given interval using a filter closure
	 *
	 * @param CarbonInterval $ci       An interval to traverse by
	 * @param Closure        $callback
	 * @param Carbon|null    $dt
	 * @param bool           $abs      Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffFiltered(CarbonInterval $ci, Closure $callback, Carbon $dt = null, $abs = true)
	{
		$start = $this;
		$end = $dt ?: static::now($this->getTimezone());
		$inverse = false;

		if ($end < $start) {
			$start = $end;
			$end = $this;
			$inverse = true;
		}

		$period = new DatePeriod($start, $ci, $end);
		$vals = array_filter(iterator_to_array($period), function (DateTime $date) use ($callback) {
			return call_user_func($callback, Carbon::instance($date));
		});

		$diff = count($vals);

		return $inverse && !$abs ? -$diff : $diff;
	}

	/**
	 * Get the difference in weekdays
	 *
	 * @param \Carbon\Carbon|null $dt
	 * @param bool                $abs Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffInWeekdays(Carbon $dt = null, $abs = true)
	{
		return $this->diffInDaysFiltered(function (Carbon $date) {
			return $date->isWeekday();
		}, $dt, $abs);
	}

	/**
	 * Get the difference in weekend days using a filter
	 *
	 * @param \Carbon\Carbon|null $dt
	 * @param bool                $abs Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffInWeekendDays(Carbon $dt = null, $abs = true)
	{
		return $this->diffInDaysFiltered(function (Carbon $date) {
			return $date->isWeekend();
		}, $dt, $abs);
	}

	/**
	 * Get the difference in hours
	 *
	 * @param \Carbon\Carbon|null $dt
	 * @param bool                $abs Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffInHours(Carbon $dt = null, $abs = true)
	{
		return (int) ($this->diffInSeconds($dt, $abs) / static::SECONDS_PER_MINUTE / static::MINUTES_PER_HOUR);
	}

	/**
	 * Get the difference in minutes
	 *
	 * @param \Carbon\Carbon|null $dt
	 * @param bool                $abs Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffInMinutes(Carbon $dt = null, $abs = true)
	{
		return (int) ($this->diffInSeconds($dt, $abs) / static::SECONDS_PER_MINUTE);
	}

	/**
	 * Get the difference in seconds
	 *
	 * @param \Carbon\Carbon|null $dt
	 * @param bool                $abs Get the absolute of the difference
	 *
	 * @return int
	 */
	public function diffInSeconds(Carbon $dt = null, $abs = true)
	{
		$dt = $dt ?: static::now($this->getTimezone());
		$value = $dt->getTimestamp() - $this->getTimestamp();

		return $abs ? abs($value) : $value;
	}

	/**
	 * The number of seconds since midnight.
	 *
	 * @return int
	 */
	public function secondsSinceMidnight()
	{
		return $this->diffInSeconds($this->copy()->startOfDay());
	}

	/**
	 * The number of seconds until 23:23:59.
	 *
	 * @return int
	 */
	public function secondsUntilEndOfDay()
	{
		return $this->diffInSeconds($this->copy()->endOfDay());
	}

	/**
	 * Get the difference in a human readable format in the current locale.
	 *
	 * When comparing a value in the past to default now:
	 * 1 hour ago
	 * 5 months ago
	 *
	 * When comparing a value in the future to default now:
	 * 1 hour from now
	 * 5 months from now
	 *
	 * When comparing a value in the past to another value:
	 * 1 hour before
	 * 5 months before
	 *
	 * When comparing a value in the future to another value:
	 * 1 hour after
	 * 5 months after
	 *
	 * @param Carbon|null $other
	 * @param bool        $absolute removes time difference modifiers ago, after, etc
	 * @param bool        $short    displays short format of time units
	 *
	 * @return string
	 */
	public function diffForHumans(Carbon $other = null, $absolute = false, $short = false)
	{
		$isNow = $other === null;

		if ($isNow) {
			$other = static::now($this->getTimezone());
		}

		$diffInterval = $this->diff($other);

		switch (true) {
			case $diffInterval->y > 0:
				$unit = $short ? 'y' : 'year';
				$count = $diffInterval->y;
				break;

			case $diffInterval->m > 0:
				$unit = $short ? 'm' : 'month';
				$count = $diffInterval->m;
				break;

			case $diffInterval->d > 0:
				$unit = $short ? 'd' : 'day';
				$count = $diffInterval->d;

				if ($count >= static::DAYS_PER_WEEK) {
					$unit = $short ? 'w' : 'week';
					$count = (int) ($count / static::DAYS_PER_WEEK);
				}
				break;

			case $diffInterval->h > 0:
				$unit = $short ? 'h' : 'hour';
				$count = $diffInterval->h;
				break;

			case $diffInterval->i > 0:
				$unit = $short ? 'min' : 'minute';
				$count = $diffInterval->i;
				break;

			default:
				$count = $diffInterval->s;
				$unit = $short ? 's' : 'second';
				break;
		}

		if ($count === 0) {
			$count = 1;
		}

		$time = static::translator()->transChoice($unit, $count, array(':count' => $count));

		if ($absolute) {
			return $time;
		}

		$isFuture = $diffInterval->invert === 1;

		$transId = $isNow ? ($isFuture ? 'from_now' : 'ago') : ($isFuture ? 'after' : 'before');

		// Some langs have special pluralization for past and future tense.
		$tryKeyExists = $unit.'_'.$transId;
		if ($tryKeyExists !== static::translator()->transChoice($tryKeyExists, $count)) {
			$time = static::translator()->transChoice($tryKeyExists, $count, array(':count' => $count));
		}

		return static::translator()->trans($transId, array(':time' => $time));
	}

	///////////////////////////////////////////////////////////////////
	//////////////////////////// MODIFIERS ////////////////////////////
	///////////////////////////////////////////////////////////////////

	/**
	 * Resets the time to 00:00:00
	 *
	 * @return static
	 */
	public function startOfDay()
	{
		return $this->setTime(0, 0, 0);
	}

	/**
	 * Resets the time to 23:59:59
	 *
	 * @return static
	 */
	public function endOfDay()
	{
		return $this->setTime(23, 59, 59);
	}

	/**
	 * Resets the date to the first day of the month and the time to 00:00:00
	 *
	 * @return static
	 */
	public function startOfMonth()
	{
		return $this->setDateTime($this->year, $this->month, 1, 0, 0, 0);
	}

	/**
	 * Resets the date to end of the month and time to 23:59:59
	 *
	 * @return static
	 */
	public function endOfMonth()
	{
		return $this->setDateTime($this->year, $this->month, $this->daysInMonth, 23, 59, 59);
	}

	/**
	 * Resets the date to the first day of the quarter and the time to 00:00:00
	 *
	 * @return static
	 */
	public function startOfQuarter()
	{
		$month = ($this->quarter - 1) * static::MONTHS_PER_QUARTER + 1;

		return $this->setDateTime($this->year, $month, 1, 0, 0, 0);
	}

	/**
	 * Resets the date to end of the quarter and time to 23:59:59
	 *
	 * @return static
	 */
	public function endOfQuarter()
	{
		return $this->startOfQuarter()->addMonths(static::MONTHS_PER_QUARTER - 1)->endOfMonth();
	}

	/**
	 * Resets the date to the first day of the year and the time to 00:00:00
	 *
	 * @return static
	 */
	public function startOfYear()
	{
		return $this->setDateTime($this->year, 1, 1, 0, 0, 0);
	}

	/**
	 * Resets the date to end of the year and time to 23:59:59
	 *
	 * @return static
	 */
	public function endOfYear()
	{
		return $this->setDateTime($this->year, 12, 31, 23, 59, 59);
	}

	/**
	 * Resets the date to the first day of the decade and the time to 00:00:00
	 *
	 * @return static
	 */
	public function startOfDecade()
	{
		$year = $this->year - $this->year % static::YEARS_PER_DECADE;

		return $this->setDateTime($year, 1, 1, 0, 0, 0);
	}

	/**
	 * Resets the date to end of the decade and time to 23:59:59
	 *
	 * @return static
	 */
	public function endOfDecade()
	{
		$year = $this->year - $this->year % static::YEARS_PER_DECADE + static::YEARS_PER_DECADE - 1;

		return $this->setDateTime($year, 12, 31, 23, 59, 59);
	}

	/**
	 * Resets the date to the first day of the century and the time to 00:00:00
	 *
	 * @return static
	 */
	public function startOfCentury()
	{
		$year = $this->year - ($this->year - 1) % static::YEARS_PER_CENTURY;

		return $this->setDateTime($year, 1, 1, 0, 0, 0);
	}

	/**
	 * Resets the date to end of the century and time to 23:59:59
	 *
	 * @return static
	 */
	public function endOfCentury()
	{
		$year = $this->year - 1 - ($this->year - 1) % static::YEARS_PER_CENTURY + static::YEARS_PER_CENTURY;

		return $this->setDateTime($year, 12, 31, 23, 59, 59);
	}

	/**
	 * Resets the date to the first day of week (defined in $weekStartsAt) and the time to 00:00:00
	 *
	 * @return static
	 */
	public function startOfWeek()
	{
		while ($this->dayOfWeek !== static::$weekStartsAt) {
			$this->subDay();
		}

		return $this->startOfDay();
	}

	/**
	 * Resets the date to end of week (defined in $weekEndsAt) and time to 23:59:59
	 *
	 * @return static
	 */
	public function endOfWeek()
	{
		while ($this->dayOfWeek !== static::$weekEndsAt) {
			$this->addDay();
		}

		return $this->endOfDay();
	}

	/**
	 * Modify to the next occurrence of a given day of the week.
	 * If no dayOfWeek is provided, modify to the next occurrence
	 * of the current day of the week.  Use the supplied constants
	 * to indicate the desired dayOfWeek, ex. static::MONDAY.
	 *
	 * @param int|null $dayOfWeek
	 *
	 * @return static
	 */
	public function next($dayOfWeek = null)
	{
		if ($dayOfWeek === null) {
			$dayOfWeek = $this->dayOfWeek;
		}

		return $this->startOfDay()->modify('next '.static::$days[$dayOfWeek]);
	}

	/**
	 * Go forward or backward to the next week- or weekend-day.
	 *
	 * @param bool $weekday
	 * @param bool $forward
	 *
	 * @return $this
	 */
	private function nextOrPreviousDay($weekday = true, $forward = true)
	{
		$step = $forward ? 1 : -1;

		do {
			$this->addDay($step);
		} while ($weekday ? $this->isWeekend() : $this->isWeekday());

		return $this;
	}

	/**
	 * Go forward to the next weekday.
	 *
	 * @return $this
	 */
	public function nextWeekday()
	{
		return $this->nextOrPreviousDay();
	}

	/**
	 * Go backward to the previous weekday.
	 *
	 * @return $this
	 */
	public function previousWeekday()
	{
		return $this->nextOrPreviousDay(true, false);
	}

	/**
	 * Go forward to the next weekend day.
	 *
	 * @return $this
	 */
	public function nextWeekendDay()
	{
		return $this->nextOrPreviousDay(false);
	}

	/**
	 * Go backward to the previous weekend day.
	 *
	 * @return $this
	 */
	public function previousWeekendDay()
	{
		return $this->nextOrPreviousDay(false, false);
	}

	/**
	 * Modify to the previous occurrence of a given day of the week.
	 * If no dayOfWeek is provided, modify to the previous occurrence
	 * of the current day of the week.  Use the supplied constants
	 * to indicate the desired dayOfWeek, ex. static::MONDAY.
	 *
	 * @param int|null $dayOfWeek
	 *
	 * @return static
	 */
	public function previous($dayOfWeek = null)
	{
		if ($dayOfWeek === null) {
			$dayOfWeek = $this->dayOfWeek;
		}

		return $this->startOfDay()->modify('last '.static::$days[$dayOfWeek]);
	}

	/**
	 * Modify to the first occurrence of a given day of the week
	 * in the current month. If no dayOfWeek is provided, modify to the
	 * first day of the current month.  Use the supplied constants
	 * to indicate the desired dayOfWeek, ex. static::MONDAY.
	 *
	 * @param int|null $dayOfWeek
	 *
	 * @return static
	 */
	public function firstOfMonth($dayOfWeek = null)
	{
		$this->startOfDay();

		if ($dayOfWeek === null) {
			return $this->day(1);
		}

		return $this->modify('first '.static::$days[$dayOfWeek].' of '.$this->format('F').' '.$this->year);
	}

	/**
	 * Modify to the last occurrence of a given day of the week
	 * in the current month. If no dayOfWeek is provided, modify to the
	 * last day of the current month.  Use the supplied constants
	 * to indicate the desired dayOfWeek, ex. static::MONDAY.
	 *
	 * @param int|null $dayOfWeek
	 *
	 * @return static
	 */
	public function lastOfMonth($dayOfWeek = null)
	{
		$this->startOfDay();

		if ($dayOfWeek === null) {
			return $this->day($this->daysInMonth);
		}

		return $this->modify('last '.static::$days[$dayOfWeek].' of '.$this->format('F').' '.$this->year);
	}

	/**
	 * Modify to the given occurrence of a given day of the week
	 * in the current month. If the calculated occurrence is outside the scope
	 * of the current month, then return false and no modifications are made.
	 * Use the supplied constants to indicate the desired dayOfWeek, ex. static::MONDAY.
	 *
	 * @param int $nth
	 * @param int $dayOfWeek
	 *
	 * @return mixed
	 */
	public function nthOfMonth($nth, $dayOfWeek)
	{
		$dt = $this->copy()->firstOfMonth();
		$check = $dt->format('Y-m');
		$dt->modify('+'.$nth.' '.static::$days[$dayOfWeek]);

		return $dt->format('Y-m') === $check ? $this->modify($dt) : false;
	}

	/**
	 * Modify to the first occurrence of a given day of the week
	 * in the current quarter. If no dayOfWeek is provided, modify to the
	 * first day of the current quarter.  Use the supplied constants
	 * to indicate the desired dayOfWeek, ex. static::MONDAY.
	 *
	 * @param int|null $dayOfWeek
	 *
	 * @return static
	 */
	public function firstOfQuarter($dayOfWeek = null)
	{
		return $this->setDate($this->year, $this->quarter * static::MONTHS_PER_QUARTER - 2, 1)->firstOfMonth($dayOfWeek);
	}

	/**
	 * Modify to the last occurrence of a given day of the week
	 * in the current quarter. If no dayOfWeek is provided, modify to the
	 * last day of the current quarter.  Use the supplied constants
	 * to indicate the desired dayOfWeek, ex. static::MONDAY.
	 *
	 * @param int|null $dayOfWeek
	 *
	 * @return static
	 */
	public function lastOfQuarter($dayOfWeek = null)
	{
		return $this->setDate($this->year, $this->quarter * static::MONTHS_PER_QUARTER, 1)->lastOfMonth($dayOfWeek);
	}

	/**
	 * Modify to the given occurrence of a given day of the week
	 * in the current quarter. If the calculated occurrence is outside the scope
	 * of the current quarter, then return false and no modifications are made.
	 * Use the supplied constants to indicate the desired dayOfWeek, ex. static::MONDAY.
	 *
	 * @param int $nth
	 * @param int $dayOfWeek
	 *
	 * @return mixed
	 */
	public function nthOfQuarter($nth, $dayOfWeek)
	{
		$dt = $this->copy()->day(1)->month($this->quarter * static::MONTHS_PER_QUARTER);
		$lastMonth = $dt->month;
		$year = $dt->year;
		$dt->firstOfQuarter()->modify('+'.$nth.' '.static::$days[$dayOfWeek]);

		return ($lastMonth < $dt->month || $year !== $dt->year) ? false : $this->modify($dt);
	}

	/**
	 * Modify to the first occurrence of a given day of the week
	 * in the current year. If no dayOfWeek is provided, modify to the
	 * first day of the current year.  Use the supplied constants
	 * to indicate the desired dayOfWeek, ex. static::MONDAY.
	 *
	 * @param int|null $dayOfWeek
	 *
	 * @return static
	 */
	public function firstOfYear($dayOfWeek = null)
	{
		return $this->month(1)->firstOfMonth($dayOfWeek);
	}

	/**
	 * Modify to the last occurrence of a given day of the week
	 * in the current year. If no dayOfWeek is provided, modify to the
	 * last day of the current year.  Use the supplied constants
	 * to indicate the desired dayOfWeek, ex. static::MONDAY.
	 *
	 * @param int|null $dayOfWeek
	 *
	 * @return static
	 */
	public function lastOfYear($dayOfWeek = null)
	{
		return $this->month(static::MONTHS_PER_YEAR)->lastOfMonth($dayOfWeek);
	}

	/**
	 * Modify to the given occurrence of a given day of the week
	 * in the current year. If the calculated occurrence is outside the scope
	 * of the current year, then return false and no modifications are made.
	 * Use the supplied constants to indicate the desired dayOfWeek, ex. static::MONDAY.
	 *
	 * @param int $nth
	 * @param int $dayOfWeek
	 *
	 * @return mixed
	 */
	public function nthOfYear($nth, $dayOfWeek)
	{
		$dt = $this->copy()->firstOfYear()->modify('+'.$nth.' '.static::$days[$dayOfWeek]);

		return $this->year === $dt->year ? $this->modify($dt) : false;
	}

	/**
	 * Modify the current instance to the average of a given instance (default now) and the current instance.
	 *
	 * @param \Carbon\Carbon|null $dt
	 *
	 * @return static
	 */
	public function average(Carbon $dt = null)
	{
		$dt = $dt ?: static::now($this->getTimezone());

		return $this->addSeconds((int) ($this->diffInSeconds($dt, false) / 2));
	}

	/**
	 * Check if its the birthday. Compares the date/month values of the two dates.
	 *
	 * @param \Carbon\Carbon|null $dt The instance to compare with or null to use current day.
	 *
	 * @return bool
	 */
	public function isBirthday(Carbon $dt = null)
	{
		return $this->isSameAs('md', $dt);
	}

	/**
	 * Return a serialized string of the instance.
	 *
	 * @return string
	 */
	public function serialize()
	{
		return serialize($this);
	}

	/**
	 * Create an instance form a serialized string.
	 *
	 * @param string $value
	 *
	 * @throws \InvalidArgumentException
	 *
	 * @return static
	 */
	public static function fromSerialized($value)
	{
		$instance = @unserialize($value);

		if (!$instance instanceof static) {
			throw new InvalidArgumentException('Invalid serialized value.');
		}

		return $instance;
	}
}
