public final class OAuthYahooService extends AbstractService
{
    
    
    static final Consumer __consumer = Consumer.getInstance();
    static final Endpoint __yahooEndpoint = __consumer.getEndpoint("api.login.yahoo.com");

    @Override
    protected void init()
    {
        
    }
    
    @HttpResource(location="/oauth/yahoo/contacts")
    @Get
    public void service(RequestContext rc) throws IOException
    {
        HttpServletRequest request = rc.getRequest();
        HttpServletResponse response = rc.getResponse();
        
        Token token = __consumer.getToken(__yahooEndpoint.getConsumerKey(), request);
        switch(token.getState())
        {
            case Token.UNITIALIZED:
                String requestUrl = request.getRequestURL().toString();
                UrlEncodedParameterMap params = new UrlEncodedParameterMap()
                    .add(Constants.OAUTH_CALLBACK, requestUrl);
                    
                Response r = __consumer.fetchToken(__yahooEndpoint, params, 
                        TokenExchange.REQUEST_TOKEN, token);                
                if(r.getStatus()==200 && token.getState()==Token.UNAUTHORIZED)
                {
                    // unauthorized request token
                    __consumer.saveToken(token, request, response);
                    StringBuilder urlBuffer = Transport.buildAuthUrl(
                            __yahooEndpoint.getAuthorizationUrl(), token, requestUrl);
                    response.sendRedirect(urlBuffer.toString());
                }
                break;
                
            case Token.UNAUTHORIZED:
                String verifier = request.getParameter(Constants.OAUTH_VERIFIER);
                if(verifier==null)
                {
                    // the user has possibly pressed the back button and retried
                    // so we redirect and let the user authenticate
                    StringBuilder urlBuffer = Transport.buildAuthUrl(
                            __yahooEndpoint.getAuthorizationUrl(), token, 
                            request.getRequestURL().toString());
                    Transport.appendToUrl("hd", "default", urlBuffer);
                    response.sendRedirect(urlBuffer.toString());
                }
                else if(token.authorize(request.getParameter(Constants.OAUTH_TOKEN), verifier))
                {
                    if(fetchAccessToken(token, request, response))
                        queryContacts(token, request, response);
                    else
                        __consumer.saveToken(token, request, response);
                }
                break;
                
            case Token.AUTHORIZED:
                if(fetchAccessToken(token, request, response))
                    queryContacts(token, request, response);
                break;
                
            case Token.ACCESS_TOKEN:
                queryContacts(token, request, response);
                break;
                
            default:
                response.sendRedirect(request.getContextPath() + "/oauth/yahoo");
        }
        System.err.println("token: " + token.getState() + " | " + token.getAttributes());
    }
    
    public boolean fetchAccessToken(Token token, HttpServletRequest request, 
            HttpServletResponse response) throws IOException
    {
        // authorized request token
        UrlEncodedParameterMap params = new UrlEncodedParameterMap();
        
        Response r = __consumer.fetchToken(__yahooEndpoint, params, TokenExchange.ACCESS_TOKEN, 
                token);
        if(r.getStatus()==200 && token.getState()==Token.ACCESS_TOKEN)
        {
            // access token
            __consumer.saveToken(token, request, response);
            return true;
        }
        return false;
    }
    
    void queryContacts(Token token, HttpServletRequest request, 
            HttpServletResponse response) throws IOException
    {
        String guid = (String)token.getAttribute("xoauth_yahoo_guid");
        String contactsUrl = "http://social.yahooapis.com/v1/user/" + guid+ "/contacts";
        Response r = serviceGET(contactsUrl, __consumer.getConsumerContext(), __yahooEndpoint, 
                token, request, response);
        
        BufferedReader br = new BufferedReader(new InputStreamReader(r.getInputStream(), "UTF-8"));
        response.setContentType("text/xml");
        PrintWriter pw = response.getWriter();
        for(String line=null; (line=br.readLine())!=null;)
            pw.append(line);
    }
    
    public static Response serviceGET(String serviceUrl, ConsumerContext context, Endpoint ep, 
            Token token, HttpServletRequest request, HttpServletResponse response) 
            throws IOException
    {
        HttpConnector connector = context.getHttpConnector();
        UrlEncodedParameterMap params = new UrlEncodedParameterMap(serviceUrl);
        context.getNonceAndTimestamp().put(params, token.getCk());
        Parameter authorization = new Parameter("Authorization", 
                HttpAuthTransport.getAuthHeaderValue(params, ep, token, 
                context.getNonceAndTimestamp(),  ep.getSignature()));
        return connector.doGET(params.getUrl(), authorization);
        
    }

}