Plugin to set unpub_date automatically one year after pubdate

<?php

// Only execute when there is no unpub_date set
if ($resource->get('unpub_date') == 0)
	{

	// All children of 765 will be kept 1 year
	if ($resource->get('parent') == 765)
		{
		$publishedon = $resource->get('publishedon');

		//Substract time from publishedon
		$publishedon = substr($publishedon, 0, -9);
		$date = new DateTime($publishedon);

		// Add 1 year
		$date->add(new DateInterval('P1Y'));
		$resource->set('unpub_date', $date->format('Y-m-d'));
		$resource->save();
		}

	// All children of 767 will be kept 2 years
	elseif ($resource->get('parent') == 767)
		{
		$publishedon = $resource->get('publishedon');

		//Substract time from publishedon
		$publishedon = substr($publishedon, 0, -9);
		$date = new DateTime($publishedon);

		// Add 2 years
		$date->add(new DateInterval('P2Y'));
		$resource->set('unpub_date', $date->format('Y-m-d'));
		$resource->save();
		}
	}

$t = strtotime('+1 year', $resource->get('publishedon'));
$resource->set('unpub_date', $strftime('Y-m-d', $t));

$t = strtotime('+1 year');
$resource->set('unpub_date', $strftime('Y-m-d', $t));