Data transformer for week data

LabourWeekTransformer.php

<?php

namespace Samson\TRSBundle\Form\DataTransformer;

use Symfony\Component\Form\DataTransformerInterface;
use Symfony\Component\Form\Exception\TransformationFailedException;

class LabourWeekTransformer implements DataTransformerInterface
{
    private $week;
    private $year;
    public function __construct($year, $week)
    {
        $this->week = $week;
        $this->year = $year;
    }

    public function transform($value)
    {
        // norm to client
        
        if (null === $value) {
            return;
        }

        $start = new \DateTime;
        $start->setISODate($this->year, $this->week, 0);
        $end = clone $start;
        $end->modify('next sunday 23:59');

        foreach($value as $labour) {
            if (null === $labour->getDate()) {
                throw new TransformationFailedException('The labour entity has no date!');
            }
            if ($labour->getDate() < $start || $labour->getDate() > $end) {
                throw new TransformationFailedException('The labour entity date '.$labour->getDate()->format('Y-m-d H:i:s').' is not in week '.$this->week.' of year '.$this->year);
            }
        }
        
        usort($value, function($a, $b) {
            return $a->getStart() < $b->getStart() ? -1 : ($a->getStart() == $b->getStart() ? 0 : 1);
        });
        
        $return = array(
            'Mon' => array(),
            'Tue' => array(),
            'Wed' => array(),
            'Thu' => array(),
            'Fri' => array(),
            'Sat' => array(),
            'Sun' => array(),
        );
        foreach($value as $labour) {
            $return[$labour->getDate()->format('D')][] = $labour;
        }
        
        return $return;
    }

    public function reverseTransform($value)
    {
        $labour = array();

        foreach ($value as $day => $dayLabour) {
            foreach($dayLabour as $labourEntity) {
                if (null !== $labourEntity->getDate()) {
                    $labour[] = $labourEntity;
                }
            }
        }

        return $labour;
    }
}