function downloadTweets(searchTerm) {
  var twitterService = getTwitterService_();

  var props = PropertiesService.getUserProperties();
  var sinceID = props.getProperty('SINCEID') || '';

  var api = 'https://api.twitter.com/1.1/search/tweets.json?count=100&include_entities=false';
  api += '&result_type=recent&q=' + encodeString_(searchTerm) + '&since_id=' + sinceID;

  var result = twitterService.fetch(api);

  if (result.getResponseCode() == 200) {
    var json = JSON.parse(result.getContentText());

    var tweets = json.statuses;

    // SINCEID will store the ID of the last processed tweet

    for (var i = tweets.length - 1; i >= 0; i--) {
      logTweet_(tweets[i]);
      if (i == 0) {
        props.setProperty('SINCEID', tweets[0].id_str);
      }
    }
  }
}

/* Add the tweet details into the sheet */
function logTweet_(tweet) {
  var log = [];

  log.push(new Date(tweet.created_at));
  log.push(
    '=HYPERLINK("https://twitter.com/' +
      tweet.user.screen_name +
      '/status/' +
      tweet.id_str +
      '","' +
      tweet.user.name +
      '")'
  );
  log.push(tweet.user.followers_count);
  log.push(tweet.user.friends_count);
  log.push(tweet.retweet_count);
  log.push(tweet.favorite_count);
  log.push(tweet.text.replace(/\n|\r/g, ' '));

  SpreadsheetApp.getActiveSheet().appendRow(log);
}

function getTwitterService_() {
  var props = PropertiesService.getUserProperties();

  return OAuth1.createService('twitter')
    .setAccessTokenUrl('https://api.twitter.com/oauth/access_token')
    .setRequestTokenUrl('https://api.twitter.com/oauth/request_token')
    .setAuthorizationUrl('https://api.twitter.com/oauth/authorize')
    .setConsumerKey(props.getProperty('consumer_key'))
    .setConsumerSecret(props.getProperty('consumer_secret'))
    .setProjectKey(ScriptApp.getProjectKey())
    .setCallbackFunction('twitter')
    .setPropertyStore(props);
}

/* Properly encode the Twitter search query */
function encodeString_(q) {
  var str = encodeURIComponent(q);
  str = str.replace(/!/g, '%21');
  str = str.replace(/\*/g, '%2A');
  str = str.replace(/\(/g, '%28');
  str = str.replace(/\)/g, '%29');
  str = str.replace(/'/g, '%27');
  return str;
}