function registerUser(UserEntity $user)
{
if ($this->usernameExists($user['username'])) {
throw new Exception("The username is already taken");
} elseif ($this->emailExists($user['email'])) {
throw new Exception("The email is already taken");
}
$user['created_at'] = new MongoDate();
$user['updated_at'] = new MongoDate();
$userToCommit = $user->toArray();
unset($userToCommit['_id']);
$status = $this->_collection->insert($userToCommit, array('safe' => true));
return new UserEntity($userToCommit);
}
