<?php



/*

 * This file is part of Xerxes.

 *

 * (c) California State University <library@calstate.edu>

 *

 * For the full copyright and license information, please view the LICENSE

 * file that was distributed with this source code.

 */



namespace Xerxes\Lti;



use Xerxes\Utility\Parser;



require_once __DIR__ . '/../OAuth/OAuth.php'; // @todo: make this not hardwired



/**

 * Convenience class for verifying and accessing properties of basic lti launch request

 *

 * @author David Walker <dwalker@calstate.edu>

 */



class Basic 

{

	/**

	 * @var OAuthRequest

	 */

	

	protected $request;

	

	/**

	 * Create new Basic LTI access object

	 * 

	 * @param string $key

	 * @param string $secret

	 * 

	 * @throws \Exception

	 */

	

	public function __construct( $key, $secret )

	{

		$request = \OAuthRequest::from_request();

	

		$oauth_consumer_key = $request->get_parameter("oauth_consumer_key");

	

		// ensure the key in the request matches the locally supplied one

	

		if ( $oauth_consumer_key == null)

		{

			throw new \Exception("Missing oauth_consumer_key in request");

		}

		

		if ( $oauth_consumer_key != $key )

		{

			throw new \Exception("oauth_consumer_key doesn't match supplied key");

		}

		

		// verify the message signature

		

		$store = new TrivialOAuthDataStore( $oauth_consumer_key, $secret );

		$server = new \OAuthServer( $store );

		

		$method = new \OAuthSignatureMethod_HMAC_SHA1();

		$server->add_signature_method( $method );



		$server->verify_request( $request );

		

		$this->request = $request;

	}

	

	/**

	 * Get request parameter

	 * 

	 * @param string $name

	 */

	

	public function getParam($name)

	{

		return $this->request->get_parameter($name);

	}

	

	/**

	 * Create a unique identifier for this LTI context

	 * 

	 * oauth_consumer_key + context_id + resource_link_id

	 * 

	 * @return string

	 */

	

	public function getID()

	{

		return $this->getParam("oauth_consumer_key") . "-" 

			. $this->getParam('context_id') . "-" 

			. $this->getParam('resource_link_id');		

	}

	

	/**

	 * User ID

	 * 

	 * @return string

	 */

	

	public function getUserID()

	{

		return $this->getParam('user_id');

	}

	

	/**

	 * Whether the user is an Instructor

	 * 

	 * @return bool

	 */

	

	public function isInstructor()

	{

		$roles = explode(',', $this->getParam('roles'));

		

		if ( in_array('Instructor', $roles) )

		{

			return true;

		}

		else

		{

			return false;

		}

	}

	

	/**

	 * Serialize the objet to XML

	 */

	

	public function toXML()

	{

		$xml = Parser::convertToDOMDocument("<lti />");

		

		$this->appendElement($xml, "id", $this->getID());

		$this->appendElement($xml, "instructor", $this->isInstructor());

		

		foreach ( $this->request->get_parameters() as $id => $value )

		{

			$this->appendElement($xml, $id, $value);

		}

		

		return $xml;

	}

	

	/**

	 * Append an item to the xml

	 * 

	 * @param DOMDocument $xml

	 * @param string $id

	 * @param mixed $value

	 */

	

	private function appendElement(&$xml, $id, $value)

	{

		$new = $xml->createElement($id, Parser::escapeXml($value));

		$xml->documentElement->appendChild($new);

	}

}



/**

 * A Trivial memory-based store - no support for tokens

 */



class TrivialOAuthDataStore extends \OAuthDataStore

{

    private $consumers = array();



    public function __construct($consumer_key, $consumer_secret) 

    {

        $this->consumers[$consumer_key] = $consumer_secret;

    }



    public function lookup_consumer($consumer_key) 

    {

        if ( strpos($consumer_key, "http://" ) === 0 )

        {

            $consumer = new \OAuthConsumer($consumer_key,"secret", NULL);

            return $consumer;

        }

        

        if ( $this->consumers[$consumer_key] )

        {

            $consumer = new \OAuthConsumer($consumer_key,$this->consumers[$consumer_key], NULL);

            return $consumer;

        }

        return NULL;

    }



    public function lookup_token($consumer, $token_type, $token) 

    {

        return new \OAuthToken($consumer, "");

    }



    public function lookup_nonce($consumer, $token, $nonce, $timestamp) 

    {

        // Should add some clever logic to keep nonces from

        // being reused - for no we are really trusting

		// that the timestamp will save us

        return NULL;

    }



    public function new_request_token($consumer) 

    {

        return NULL;

    }



    public function new_access_token($token, $consumer) 

    {

        return NULL;

    }

}