namespace oauth {

    /// <summary>
    /// Used to authenticate OAuth to Yahoo Services
    /// </summary>
    public class YahooOAuth {

        /// <summary>
        /// Encoding to use for talking to services
        /// </summary>
        private static Encoding m_encoding;

        /// <summary>
        /// Initialize Static Members
        /// </summary>
        static YahooOAuth() {
            m_encoding = Encoding.ASCII;
        }

        /// <summary>
        /// Consumer Context, generated / updated by responses from yahoo services
        /// </summary>
        public class consumer_context {

            /// <summary>
            /// initialize request qoken response
            /// </summary>
            /// <param name="source">Output from service response</param>
            public consumer_context(string source) {
                refresh(source);
                return;
            }

            /// <summary>
            /// Update Parameters from service response
            /// </summary>
            /// <param name="source">Output from service response</param>
            public void refresh(string source) {
                string[] strTok = source.Split(new string[] { "&" }, StringSplitOptions.RemoveEmptyEntries);
                foreach (string parameter in strTok) {
                    string[] pair = parameter.Split(new string[] { "=" }, StringSplitOptions.RemoveEmptyEntries);
                    typeof(consumer_context).GetProperty(pair[0]) //member names conveniently named from responses
                        .SetValue(this, HttpUtility.UrlDecode(pair[1]), null);
                }
            }

            public string oauth_token { get; set; }

            public string oauth_token_secret { get; set; }

            public string oauth_expires_in { get; set; }

            public string xoauth_request_auth_url { get; set; }

            public string oauth_callback_confirmed { get; set; }

            public string oauth_session_handle { get; set; }

            public string xoauth_yahoo_guid { get; set; }

            public string oauth_authorization_expires_in { get; set; }

        }

        /// <summary>
        /// Step 1: Get Request Token,
        /// 
        /// </summary>
        /// <param name="consumer_key">Yahoo Application Consumer Key</param>
        /// <param name="consumer_secret">Yahoo Application Consumer Secret</param>
        /// <returns>Token response</returns>
        public static consumer_context get_request_token(string consumer_key, string consumer_secret) {
            OAuthBase oauth = new OAuthBase();
            string url = Resources.url_get_request_token;
            string token_response;
            string timestamp = oauth.GenerateTimeStamp();
            string nonce = oauth.GenerateNonce();

            //Build parameters to post to get_request_token
            StringBuilder parameters = new StringBuilder();
            parameters.Append("oauth_consumer_key="); parameters.Append(consumer_key);
            parameters.Append("&oauth_signature="); parameters.Append(consumer_secret); parameters.Append("%26");   //%26 must be appended for plaintext
            parameters.Append("&oauth_nonce="); parameters.Append(nonce);
            parameters.Append("&oauth_signature_method="); parameters.Append("PLAINTEXT");
            parameters.Append("&oauth_timestamp="); parameters.Append(timestamp);
            parameters.Append("&oauth_version="); parameters.Append("1.0");
            parameters.Append("&oauth_callback="); parameters.Append("oob");
            byte[] data = m_encoding.GetBytes(parameters.ToString());

            //Post Parameters to get_request_token
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.ContentLength = data.Length;
            using (Stream request_stream = request.GetRequestStream()) {
                request_stream.Write(data, 0, data.Length);
                request_stream.Flush();
            }
            //Grab response from service
            using (WebResponse response = request.GetResponse()) {
                using (StreamReader reader = new StreamReader(response.GetResponseStream())) {
                    token_response = reader.ReadToEnd();
                }
            }
           
            return new consumer_context(token_response);
        }

        /// <summary>
        /// Get/Refresh Access Token
        /// </summary>
        /// <param name="consumer_key">Yahoo Application Consumer Key</param>
        /// <param name="consumer_secret">Yahoo Application Consumer Secret</param>
        /// <param name="get_request_token">Request Token Obtained</param>
        /// <param name="verifier_token">verifier token manually obtained, may be null</param>
        /// <returns></returns>
        public static consumer_context get_access_token(string consumer_key, string consumer_secret, consumer_context context, string verifier_token) {
            OAuthBase oauth = new OAuthBase();
            string url = Resources.url_get_access_token;
            string token_response;
            string timestamp = oauth.GenerateTimeStamp();
            string nonce = oauth.GenerateNonce();

            string normal_url, normal_parameters,

            signature = oauth.GenerateSignature(
                new Uri(url),
                consumer_key,
                consumer_secret,
                context.oauth_token,
                context.oauth_token_secret,
                "POST",
                timestamp,
                nonce, OAuthBase.SignatureTypes.PLAINTEXT,
                out normal_url,
                out normal_parameters);

            //Build parameters to post to get_request_token
            StringBuilder parameters = new StringBuilder();
            parameters.Append("oauth_consumer_key="); parameters.Append(consumer_key);
            parameters.Append("&oauth_signature_method="); parameters.Append("PLAINTEXT");
            parameters.Append("&oauth_signature="); parameters.Append(signature);
            parameters.Append("&oauth_version="); parameters.Append("1.0");
            if (verifier_token != null) {
                parameters.Append("&oauth_verifier="); parameters.Append(verifier_token);
            } else {
                parameters.Append("&oauth_session_handle="); parameters.Append(context.oauth_session_handle);
            }
            parameters.Append("&oauth_token="); parameters.Append(context.oauth_token);
            parameters.Append("&oauth_timestamp="); parameters.Append(timestamp);
            parameters.Append("&oauth_nonce="); parameters.Append(nonce);
            
            byte[] data = m_encoding.GetBytes(parameters.ToString());

            //Post Parameters to get_request_token
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.ContentLength = data.Length;
            using (Stream request_stream = request.GetRequestStream()) {
                request_stream.Write(data, 0, data.Length);
                request_stream.Flush();
            }
            //Grab response from service
            using (WebResponse response = request.GetResponse()) {
                using (StreamReader reader = new StreamReader(response.GetResponseStream())) {
                    token_response = reader.ReadToEnd();
                }
            }
            //Update Consumer Context
            context.refresh(token_response);
            return context;
        }

    }
}