<?php

namespace Acme\FooBundle\Hateoas;

use Doctrine\ORM\EntityManager;
use Hateoas\Configuration\Metadata\ClassMetadataInterface;
use Hateoas\Configuration as Hateoas;
use Symfony\Component\Routing\Route;
use Symfony\Component\Routing\RouterInterface;

class DoctrineRelationProvider
{

    protected $entityManager;

    protected $router;

    public function __construct(EntityManager $entityManager, RouterInterface $router)
    {
        $this->entityManager = $entityManager;
        $this->router = $router;
    }

    public function addRelations($object, ClassMetadataInterface $classMetadata)
    {

        $relations = array();

        $parts = explode('\\', $classMetadata->getName());
        $self_route = 'get_' . strtolower(array_pop($parts));

        if ($this->routeExists($self_route) ) {
            $relations[] = new Hateoas\Relation(
                'self',
                new Hateoas\Route(
                    $self_route,
                    array('id' => 'expr(object.getId())')
                )
            );
        }

        $metadata = $this->entityManager->getClassMetadata($classMetadata->getName());

        foreach($metadata->getAssociationMappings() as $mapping) {
            $route_name = $self_route . '_' . strtolower($mapping['fieldName']);
            if ($this->routeExists($route_name)) {
                $relations[] = new Hateoas\Relation(
                    $mapping['fieldName'],
                    new Hateoas\Route(
                        $route_name,
                        array('id' => 'expr(object.getId())')
                    )
                );
            }
        }

        // You need to return the relations
        // Adding the relations to the $classMetadata won't work
        return $relations;
    }

    protected function routeExists($name) {
        return $this->router->getRouteCollection()->get($name) instanceof Route;
    }
}