Calculate when a cron job will be executed then next time

Here’s a PHP project that is based on dlamblin’s psuedo code.

It can calculate the next run date of a CRON expression, the previous run date of a CRON expression, and determine if a CRON expression matches a given time. You can skip This CRON expression parser fully implements CRON:

1. Increments of ranges (e.g. */12, 3-59/15)
2. Intervals (e.g. 1-4, MON-FRI, JAN-MAR )
3. Lists (e.g. 1,2,3 | JAN,MAR,DEC)
4. Last day of a month (e.g. L)
5. Last given weekday of a month (e.g. 5L)
6. Nth given weekday of a month (e.g. 3#2, 1#1, MON#4)
7. Closest weekday to a given day of the month (e.g. 15W, 1W, 30W)

https://github.com/mtdowling/cron-expression

Usage (PHP 5.3+):

<?php

// Works with predefined scheduling definitions
$cron = Cron\CronExpression::factory('@daily');
$cron->isDue();
$cron->getNextRunDate();
$cron->getPreviousRunDate();

// Works with complex expressions
$cron = Cron\CronExpression::factory('15 2,6-12 */15 1 2-5');
$cron->getNextRunDate();