README

Installation

I've added this to Packagist, so you can use:

composer require chrisharrison/date-validator

Alternatively, you can clone the repository and run:

composer install

Running tests

Run tests with:

vendor/bin/phpunit

Usage

You can inject the date validator like this:

final class SomeOtherFunctionality
{
    private $dateValidator;
    
    public function __construct(DateValidator $dateValidator)
    {
        $this->dateValidator = $dateValidator;
    }
    
    public function doSomethingWithDate(string $date)
    {
        if ($this->dateValidator->validate()->isValid()) {
            return 'A valid historical date';
        }
    }
}

This package comes with a default implementation. The DefaultDateValidator requires a Clock in order for it to compare dates. A DefaultDateValidator should be initialised within an IoC container. It can be constructed like this:

$dateValidator = new DefaultDateValidator(new SystemClock);

The validate() method returns a DateValidatorResponse value object with the following methods:

• isValid(): bool Whether the date is a valid historical date or not.
• getMessage(): DateValidatorResponseMessage Returns an enum with the following options:
  • INVALID_DATE The input date is not a valid date (e.g. 32/13/1994)
  • NOT_A_DATE_IN_THE_PAST The input date is valid but it's not in the past (e.g. 01/01/3033)
  • INVALID_FORMAT The input is not a date at all (e.g. 'jibberish')
  • If the date is valid then the message is a null version of DateValidatorResponseMessage

This package also provides a singleton which can be used like this:

use ChrisHarrison\DateValidator\Singleton\DateValidator;

DateValidator::validateHistoricalDate('03/12/1999');

The singleton uses a DefaultDateValidator internally and validateHistoricalDate() works the same way as above.

My strategy

You can see the way that I approached this task my looking at my commit history.

Note on really historical dates

The solution I've written handles dates back to the year 1 CE. It doesn't handle dates BCE. And bizarrely thinks that there is a year zero. If I was to devote more time to this - and there was a business case for it - I'd investigate that. [OK I couldn't resist looking it up. It seems that PHP is using some implementation of ISO 8601 and not the Gregorian calendar]

Note on PHP date formats

The stipulation that the input date format should be DD/MM/YYYY reminded me of an interesting quirk of certain PHP functions which I discussed in a Stackoverflow answer many years ago. Just a mildly interesting titbit 😄