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Chronos

Chronos provides a zero-dependency collection of extensions to the DateTime object. In addition to convenience methods, Chronos provides:

  • ChronosDate objects for representing calendar dates.

  • Immutable date and datetime objects.

  • A pluggable translation system. Only English translations are included in the library. However, cakephp/i18n can be used for full language support.

Installation

To install Chronos, you should use composer. From your application’s ROOT directory (where composer.json file is located) run the following:

php composer.phar require "cakephp/chronos:^2.0"

Overview

Chronos provides a number of extensions to the DateTime objects provided by PHP. Chronos provides 5 classes that cover mutable and immutable date/time variants and extensions to DateInterval.

  • Cake\Chronos\Chronos is an immutable date and time object.

  • Cake\Chronos\ChronosDate is a immutable date object.

  • Cake\Chronos\MutableDateTime is a mutable date and time object.

  • Cake\Chronos\MutableDate is a mutable date object.

Lastly, if you want to typehint against Chronos-provided date/time objects you should use Cake\Chronos\ChronosInterface. All of the date and time objects implement this interface.

Creating Instances

There are many ways to get an instance of Chronos or Date. There are a number of factory methods that work with different argument sets:

use Cake\Chronos\Chronos;

$now = Chronos::now();
$today = Chronos::today();
$yesterday = Chronos::yesterday();
$tomorrow = Chronos::tomorrow();

// Parse relative expressions
$date = Chronos::parse('+2 days, +3 hours');

// Date and time integer values.
$date = Chronos::create(2015, 12, 25, 4, 32, 58);

// Date or time integer values.
$date = Chronos::createFromDate(2015, 12, 25);
$date = Chronos::createFromTime(11, 45, 10);

// Parse formatted values.
$date = Chronos::createFromFormat('m/d/Y', '06/15/2015');

Working with Immutable Objects

If you’ve used PHP’s DateTime objects, you’re comfortable with mutable objects. Chronos offers mutable objects, but it also provides immutable objects. Immutable objects create copies of objects each time an object is modified. Because modifier methods around datetimes are not always transparent, data can be modified accidentally or without the developer knowing. Immutable objects prevent accidental changes to data, and make code free of order-based dependency issues. Immutability does mean that you will need to remember to replace variables when using modifiers:

// This code doesn't work with immutable objects
$time->addDay(1);
doSomething($time);
return $time;

// This works like you'd expect
$time = $time->addDay(1);
$time = doSomething($time);
return $time;

By capturing the return value of each modification your code will work as expected. If you ever have an immutable object, and want to create a mutable one, you can use toMutable():

$inplace = $time->toMutable();

Date Objects

PHP only provides a single DateTime object. Representing calendar dates can be a bit awkward with this class as it includes timezones, and time components that don’t really belong in the concept of a ‘day’. Chronos provides a ChronosDate object that allows you to represent dates. The time for date objects is always fixed to 00:00:00, and the timezone is set to the server local timezone. All formatting/difference methods operate at the day resolution:

use Cake\Chronos\ChronosDate;

$today = ChronosDate::today();

// Changes to the time/timezone are ignored.
$today->modify('+1 hours');

// Outputs '2015-12-20'
echo $today;

Although ChronosDate uses a fixed time zone internally, you can specify which time zone to use for current time such as now() or today():

use Cake\Chronos\ChronosDate;

// Takes the current date from Asia/Tokyo time zone
$today = ChronosDate::today('Asia/Tokyo');

Modifier Methods

Chronos objects provide modifier methods that let you modify the value in a granular way:

// Set components of the datetime value.
$halloween = Chronos::create()
    ->year(2015)
    ->month(10)
    ->day(31)
    ->hour(20)
    ->minute(30);

You can also modify parts of the datetime relatively:

$future = Chronos::create()
    ->addYear(1)
    ->subMonth(2)
    ->addDays(15)
    ->addHours(20)
    ->subMinutes(2);

It is also possible to make big jumps to defined points in time:

$time = Chronos::create();
$time->startOfDay();
$time->endOfDay();
$time->startOfMonth();
$time->endOfMonth();
$time->startOfYear();
$time->endOfYear();
$time->startOfWeek();
$time->endOfWeek();

Or jump to specific days of the week:

$time->next(ChronosInterface::TUESDAY);
$time->previous(ChronosInterface::MONDAY);

When modifying dates/times across DST transitions your operations may gain/lose an additional hours resulting in hour values that don’t add up. You can avoid these issues by first changing your timezone to UTC, modifying the time:

// Additional hour gained.
$time = new Chronos('2014-03-30 00:00:00', 'Europe/London');
debug($time->modify('+24 hours')); // 2014-03-31 01:00:00

// First switch to UTC, and modify
$time = $time->setTimezone('UTC')
    ->modify('+24 hours');

Once you are done modifying the time you can add the original timezone to get the localized time.

Comparison Methods

Once you have 2 instances of Chronos date/time objects you can compare them in a variety of ways:

// Full suite of comparators exist
// ne, gt, lt, lte.
$first->eq($second);
$first->gte($second);

// See if the current object is between two others.
$now->between($start, $end);

// Find which argument is closest or farthest.
$now->closest($june, $november);
$now->farthest($june, $november);

You can also inquire about where a given value falls on the calendar:

$now->isToday();
$now->isYesterday();
$now->isFuture();
$now->isPast();

// Check the day of the week
$now->isWeekend();

// All other weekday methods exist too.
$now->isMonday();

You can also find out if a value was within a relative time period:

$time->wasWithinLast('3 days');
$time->isWithinNext('3 hours');

Generating Differences

In addition to comparing datetimes, calculating differences or deltas between two values is a common task:

// Get a DateInterval representing the difference
$first->diff($second);

// Get difference as a count of specific units.
$first->diffInHours($second);
$first->diffInDays($second);
$first->diffInWeeks($second);
$first->diffInYears($second);

You can generate human readable differences suitable for use in a feed or timeline:

// Difference from now.
echo $date->diffForHumans();

// Difference from another point in time.
echo $date->diffForHumans($other); // 1 hour ago;

Formatting Strings

Chronos provides a number of methods for displaying our outputting datetime objects:

// Uses the format controlled by setToStringFormat()
echo $date;

// Different standard formats
echo $time->toAtomString();      // 1975-12-25T14:15:16-05:00
echo $time->toCookieString();    // Thursday, 25-Dec-1975 14:15:16 EST
echo $time->toIso8601String();   // 1975-12-25T14:15:16-05:00
echo $time->toRfc822String();    // Thu, 25 Dec 75 14:15:16 -0500
echo $time->toRfc850String();    // Thursday, 25-Dec-75 14:15:16 EST
echo $time->toRfc1036String();   // Thu, 25 Dec 75 14:15:16 -0500
echo $time->toRfc1123String();   // Thu, 25 Dec 1975 14:15:16 -0500
echo $time->toRfc2822String();   // Thu, 25 Dec 1975 14:15:16 -0500
echo $time->toRfc3339String();   // 1975-12-25T14:15:16-05:00
echo $time->toRssString();       // Thu, 25 Dec 1975 14:15:16 -0500
echo $time->toW3cString();       // 1975-12-25T14:15:16-05:00

// Get the quarter/week
echo $time->toQuarter();         // 4
echo $time->toWeek();            // 52

// Generic formatting
echo $time->toTimeString();           // 14:15:16
echo $time->toDateString();           // 1975-12-25
echo $time->toDateTimeString();       // 1975-12-25 14:15:16
echo $time->toFormattedDateString();  // Dec 25, 1975
echo $time->toDayDateTimeString();    // Thu, Dec 25, 1975 2:15 PM

Extracting Date Components

Getting parts of a date object can be done by directly accessing properties:

$time = new Chronos('2015-12-31 23:59:58.123');
$time->year;    // 2015
$time->month;   // 12
$time->day;     // 31
$time->hour     // 23
$time->minute   // 59
$time->second   // 58
$time->micro    // 123

Other properties that can be accessed are:

  • timezone

  • timezoneName

  • dayOfWeek

  • dayOfMonth

  • dayOfYear

  • daysInMonth

  • timestamp

  • quarter

Testing Aids

When writing unit tests, it is helpful to fixate the current time. Chronos lets you fix the current time for each class. As part of your test suite’s bootstrap process you can include the following:

Chronos::setTestNow(Chronos::now());
MutableDateTime::setTestNow(MutableDateTime::now());
ChronosDate::setTestNow(ChronosDate::now());
MutableDate::setTestNow(MutableDate::now());

This will fix the current time of all objects to be the point at which the test suite started.

For example, if you fixate the Chronos to some moment in the past, any new instance of Chronos created with now or a relative time string, will be returned relative to the fixated time:

Chronos::setTestNow(new Chronos('1975-12-25 00:00:00'));

$time = new Chronos(); // 1975-12-25 00:00:00
$time = new Chronos('1 hour ago'); // 1975-12-24 23:00:00

To reset the fixation, simply call setTestNow() again with no parameter or with null as a parameter.