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";

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