function Start() {

  var props = PropertiesService.getScriptProperties();

  props.setProperties({
    TWITTER_CONSUMER_KEY: TWITTER_CONSUMER_KEY,
    TWITTER_CONSUMER_SECRET: TWITTER_CONSUMER_SECRET,
    TWITTER_ACCESS_TOKEN: TWITTER_ACCESS_TOKEN,
    TWITTER_ACCESS_SECRET: TWITTER_ACCESS_SECRET,
    MAX_TWITTER_ID: 0
  });

  // Delete exiting triggers, if any

  var triggers = ScriptApp.getProjectTriggers();

  for (var i = 0; i < triggers.length; i++) {
    ScriptApp.deleteTrigger(triggers[i]);
  }

  // Setup a time-based trigger for the Bot to fetch and process incoming Tweets
  // every minute. If your Google Script is running out of quota, change the
  // time to 5 or 10 minutes though the bot won't offer real-time answers then.

  ScriptApp.newTrigger("labnol_twitterBot")
    .timeBased()
    .everyMinutes(1)
    .create();

}

/\* For help, email amit@labnol.org or visit http://ctrlq.org \*/

function labnol_twitterBot() {

  try {

    var props = PropertiesService.getScriptProperties(),
      twit = new Twitter.OAuth(props);

    // Are the Twitter access tokens are valid?
    if (twit.hasAccess()) {

      var tweets = twit.fetchTweets("to:" + TWITTER_HANDLE,
        function(tweet) {
          // Ignore tweets that are sensitive (NSFW content)
          if (!tweet.possibly_sensitive) {
            var question = tweet.text.toLowerCase().replace("@" + TWITTER_HANDLE, "").trim(),
              answer = askWolframAlpha_(question);
            if (answer) {
              return {
                answer: "@" + tweet.user.screen_name + " " + answer,
                id_str: tweet.id_str
              };
            }
          }
        }, {
          multi: true,
          lang: "en",  // Fetch only English tweets
          count: 5,    // Process 5 tweets in a batch
          since_id: props.getProperty("MAX_TWITTER_ID")
        });

      if (tweets.length) {

       // The MAX_TWITTER_ID property store the ID of the last tweet answered by the bot
        props.setProperty("MAX_TWITTER_ID", tweets[0].id_str);

        // Process the tweets in FIFO order
        for (var i = tweets.length - 1; i >= 0; i--) {

          // The bot replies with an answer
          twit.sendTweet(tweets[i].answer, {
            in_reply_to_status_id: tweets[i].id_str
          });

          // Wait a second to avoid hitting the rate limits
          Utilities.sleep(1000);
        }
      }
    }

  } catch (f) {
    // You can also use MailApp to get email notifications of errors.
    Logger.log("Error: " + f.toString());
  }

}

function askWolframAlpha_(q, app) {

  try {

    var api = "http://api.wolframalpha.com/v2/query?podindex=2&format=plaintext&appid="
                   + WOLFRAM_APP_ID + "&input=" + encodeURIComponent(q);
    var response = UrlFetchApp.fetch(api, {
      muteHttpException: true
    });

    // Parse the XML response
    if (response.getResponseCode() == 200) {
      var document = XmlService.parse(response.getContentText());
      var root = document.getRootElement();
      if (root.getAttribute("success").getValue() === "true") {
        return root.getChild("pod").getChild("subpod").getChild("plaintext").getText();
      }
    }
  } catch (f) {}
  return false;
}