How can I tell if a string represents a valid date time format?

Question

I'm working on an object that validates date and times as part of a larger validation library.

Some of the functions take DateTime formats as one of their arguments. Is there a way to check that a string is a valid DateTime format?

The string should NOT be a date, the string should be a format that can be passed to Date::format() .

Here is the class:

<?php

namespace ArgumentValidator;

use DateTime;
use InvalidArgumentException;

class DateTimeValidationRule implements IValidationRule
{
    /** @var  string $defaultDateTimeFormat */
    private static $defaultDateTimeFormat = DATE_ATOM;
    /** @var  string $defaultDateFormat */
    private static $defaultDateFormat = 'Y-m-d';
    /** @var  string $defaultTimeFormat */
    private static $defaultTimeFormat = 'H:i:s';

    /** @var  string $dateTimeFormat */
    private $dateTimeFormat;

    public function __construct($dateTimeFormat = '') {
        $this->dateTimeFormat = $dateTimeFormat != '' ? $dateTimeFormat : self::$defaultDateTimeFormat;
    }

    /** @return string */
    public static function getDefaultDateTimeFormat() {
        return self::$defaultDateTimeFormat;
    }
    /** @param string $defaultDateTimeFormat */
    public static function setDefaultDateTimeFormat($defaultDateTimeFormat) {
        self::$defaultDateTimeFormat = $defaultDateTimeFormat;
    }
    /** @return string */
    public static function getDefaultDateFormat() {
        return self::$defaultDateFormat;
    }
    /** @param string $defaultDateFormat */
    public static function setDefaultDateFormat($defaultDateFormat) {
        self::$defaultDateFormat = $defaultDateFormat;
    }
    /** @return string */
    public static function getDefaultTimeFormat() {
        return self::$defaultTimeFormat;
    }
    /** @param string $defaultTimeFormat */
    public static function setDefaultTimeFormat($defaultTimeFormat) {
        self::$defaultTimeFormat = $defaultTimeFormat;
    }

    /**
     * @param string $value        The value to validate
     * @param bool   $throwOnError Should throw an exception if it is invalid?
     * @return ValidationResult
     */
    public function validate($value, $throwOnError = true) {
        $isValid = boolval(DateTime::createFromFormat($this->dateTimeFormat, $value));
        if(!$isValid && $throwOnError) {
            throw new InvalidArgumentException("Expected value to be in dateTime format: {$this->dateTimeFormat}");
        }
        return $isValid ? ValidationResult::makeSuccessResult() : ValidationResult::makeFailResult($this);
    }

    public function __toString() {
        return "DateTime-{$this->dateTimeFormat}";
    }
}

I need to validate the argument in the constructor and in all the static setters.

Answer 1

I would imagine that validating a string as a valid date format will be an exercise in futility, there are probably thousands of possible strings that will result in a valid date time format. I guess you're trying to avoid the stupid things that DateTime::createFromFormat() does .

It will be much easier to verify that a given format string produces the expected date. I use this function quite a lot (so much so that I turned it into a factory I can install with composer ):-

function validateDate($dateString, $format = 'Y-m-d H:i:s')
{
    $d = \DateTime::createFromFormat($format, $dateString);
    return $d && $d->format($format) == $dateString;
}

This function was shamelessly stolen from php.net .