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Chronos

Chronos provides a zero-dependency DateTimeImmutable extension, Date-only and Time-only classes:

  • Cake\Chronos\Chronos extends DateTimeImmutable and provides many helpers.

  • Cake\Chronos\ChronosDate represents calendar dates unaffected by time or time zones.

  • Cake\Chronos\ChronosTime represents clock times independent of date or time zones.

  • Only safe, immutable objects.

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

The Chronos class extends DateTimeImmutable and implements DateTimeInterface which allows users to use type declarations that support either.

ChronosDate and ChronosTime do not extend DateTimeImmutable and do not share an interface. However, they can be converted to a DateTimeImmutable instance using toDateTimeImmutable().

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:^3.0"

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

Chronos provides only immutable objects.

If you’ve used PHP DateTimeImmutable and DateTime classes, then you understand the difference between mutable and immutable objects.

Immutable objects create copies of an object each time a change is made. Because modifier methods around datetimes are not always easy to identify, 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
$chronos->addDay(1);
doSomething($chronos);
return $chronos;

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

By capturing the return value of each modification your code will work as expected.

Date Objects

PHP provides only date-time classes that combines both dates and time parts. Representing calendar dates can be a bit awkward with DateTimeImmutable as it includes time and timezones, which aren’t part of a ‘date’. Chronos provides ChronosDate that allows you to represent dates. The time these objects these objects is always fixed to 00:00:00 and not affeced by the server time zone or modify helpers:

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()
    ->addYears(1)
    ->subMonths(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(Chronos::TUESDAY);
$time->previous(Chronos::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

  • half

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());
ChronosDate::setTestNow(ChronosDate::parse(Chronos::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.