[+date+] placeholder to output 'Today', 'Yesterday', '2 wks ago' - how to do it?

<?php
if (!function_exists('timeSince'))
{
	function timeSince($timestamp)
	{
		if ($timestamp >= time())
		{
			$timeago = '0 seconds ago.';
			return $timeago;
		}
		$seconds = time()-$timestamp;
		$units = array(
			'year' => 31556926,
			'month' => 2629743,
			'day' => 86400,
			'hour' => 3600,
			'minute' => 60,
//			'second' => 1
		);
		$timeago = '';
		foreach ($units as $key => $val)
		{
			if ($seconds >= $val)
			{
				$results = floor($seconds/$val);
				$seconds = ($seconds-($results*$val));
				$timeago .= ($results >= 2) ? $results . ' ' . $key .  's, ' : $results . ' ' . $key .  ', ';
			}
		}	
		return rtrim($timeago, ', ') . ' ago';
	}
}
return timeSince($output);
?>

/**
     * Gets a proper array of time since a timestamp
     */
    public function timesince($input) {
        $output = '';
        $uts['start'] = strtotime($input);
        $uts['end'] = time();
        if( $uts['start']!==-1 && $uts['end']!==-1 ) {
            if( $uts['end'] >= $uts['start'] ) {
                $diff = $uts['end'] - $uts['start'];
                $days = intval((floor($diff/86400)));
                if ($days) $diff = $diff % 86400;
                $hours = intval((floor($diff/3600)));
                if ($hours) $diff = $diff % 3600;
                $minutes = intval((floor($diff/60)));
                if ($minutes) $diff = $diff % 60;

                $diff = intval($diff);
                $output = array(
                    'days' => $days
                    ,'hours' => $hours
                    ,'minutes' => $minutes
                    ,'seconds' => $diff
                );
            }
        }
        return $output;
    }