Twig filter that converts a datetime string to an "ago format", like "posted 9 months ago"

TimeAgoExtension.php

<?php

/*
 * Installation:
 * =============
 * # services.yml
 * services:
 * 	# ...
 *     acme.twig.time_ago:
 *         class: Acme\AcmeBundle\Twig\TimeAgoExtension
 *         tags:
 *           - { name: twig.extension }
 * 
 * Usage:
 * ======
 * {{ customer.birthday | date("Y-m-d H:i:s") | timeAgo }}
 */

namespace Acme\AcmeBundle\Twig;

class TimeAgoExtension extends \Twig_Extension
{
    public function getFilters()
    {
        return array(
            new \Twig_SimpleFilter("timeAgo", array($this, "timeAgo"))
        );
    }

    public function timeAgo($dateTime)
    {
        $now = new \DateTime();
        $ago = new \DateTime($dateTime);
        $diff = $now->diff($ago);

        $diff->w = \floor($diff->d / 7);
        $diff->d -= $diff->w * 7;

        $periods = array(
            "y" => "year",
            "m" => "month",
            "w" => "week",
            "d" => "day",
            "h" => "hour",
            "i" => "minute",
            "s" => "second"
        );
        
        foreach ($periods as $code => &$name) {
            if ($diff->$code) {
                $name = $diff->$code . " " . $name . ($diff->$code > 1 ? "s" : "");
            } else {
                unset($periods[$code]);
            }
        }

        // get only the most generic. Ex. from:
        // array("9 months", "4 weeks", "2 days", "21 hours", "27 minutes", "37 seconds")
        // return only array("9 months")
        $difference = \array_slice($periods, 0, 1);
        return $difference ? \implode(", ", $periods) . " ago" : "just now";
    }

    public function getName()
    {
        return "timeAgo_extension";
    }
}