Calculate the last <blank> of the month

MyDateTime.php

<?php

class MyDateTime extends DateTime
{

	protected $_daysOfTheWeek = array('sunday', 'monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday');

	public function lastDayOfTheMonth()
	{
		$lastDayOfTheMonth = new MyDateTime($this->format('Y-m-t'), $this->getTimezone());
		return $lastDayOfTheMonth;
	}

	public function lastWeekdayOfTheMonth($weekday)
	{
		if (false === ($weekdayIndex = array_search(strtolower($weekday), $this->_daysOfTheWeek))) {
			throw new Exception("Unknown weekday: " . $weekday);
		}

		$lastDayOfTheMonth = $this->lastDayOfTheMonth();
		$lastWeekday = clone $lastDayOfTheMonth;

		if ($lastDayOfTheMonth->format('w') < $weekdayIndex) {
			$lastWeekday->sub(new DateInterval('P7D'));
			$daysUntil = $weekdayIndex - $lastDayOfTheMonth->format('w');
			$lastWeekday->add(new DateInterval(sprintf('P%dD', $daysUntil)));
		} else if ($lastDayOfTheMonth->format('w') > $weekdayIndex) {
			$daysSince = $lastDayOfTheMonth->format('w') - $weekdayIndex;
			$lastWeekday->sub(new DateInterval(sprintf("P%dD", $daysSince)));
		}

		return $lastWeekday;
	}
}

$today = new MyDateTime(null, new DateTimeZone('America/Toronto'));
$lastWednesday = $today->lastWeekdayOfTheMonth('wednesday');
echo $lastWednesday->format('Y-m-d') . "\n";

$april = new MyDateTime('2012-04-01', new DateTimeZone('America/Toronto'));
$lastWednesday = $april->lastWeekdayOfTheMonth('wednesday');
echo $lastWednesday->format('Y-m-d') . "\n";

$october = new MyDateTime('2012-10-01', new DateTimeZone('America/Toronto'));
$lastWednesday = $october->lastWeekdayOfTheMonth('wednesday');
echo $lastWednesday->format('Y-m-d') . "\n";

$september = new MyDateTime('2012-09-01', new DateTimeZone('America/Toronto'));
$lastSunday = $september->lastWeekdayOfTheMonth('sunday');
echo $lastSunday->format('Y-m-d') . "\n";

format('Y-m-d'); //Of course this is only good if you just want to get the last date of a month. //You'd have to muck about with some cloning, etc if you wanted to go from a start date to the last date of the month. //The following works if you want to work backwards in time: $date = new DateTime('1st April 2012', new DateTimeZone('America/Toronto')); $date->modify('Last Wednesday'); echo $date->format('Y-m-d');

Abracadabra!

You're right, what you've got there works, but for me, and this is just my opinion, it's got way too much black magic going on. I'm just not a fan of using relative dates like 'yesterday' or 'tomorrow' with strtotime. I just prefer to explicitly modify datetime objects with add() and sub().

Fair enough-I understand where you're coming from. I'll just keep performing my black magic. :)