/*
 * Post to Twitter from Google Apps Script
 * Code by @rcknr
 */

function postTweet(message) {
  var method = 'POST';
  var baseUrl = 'https://api.twitter.com/1.1/statuses/update.json';
  var props = PropertiesService.getScriptProperties();

  var oauthParameters = {
    oauth_consumer_key: props.getProperty('CONSUMER_KEY'),
    oauth_token: props.getProperty('ACCESS_TOKEN'),
    oauth_timestamp: Math.floor(new Date().getTime() / 1000).toString(),
    oauth_signature_method: 'HMAC-SHA1',
    oauth_version: '1.0',
  };

  oauthParameters.oauth_nonce = oauthParameters.oauth_timestamp + Math.floor(Math.random() * 100000000);

  var payload = {
    status: message,
  };

  var queryKeys = Object.keys(oauthParameters).concat(Object.keys(payload)).sort();

  var baseString = queryKeys.reduce(function (acc, key, idx) {
    if (idx) acc += encodeURIComponent('&');
    if (oauthParameters.hasOwnProperty(key)) acc += encode(key + '=' + oauthParameters[key]);
    else if (payload.hasOwnProperty(key)) acc += encode(key + '=' + encode(payload[key]));
    return acc;
  }, method.toUpperCase() + '&' + encode(baseUrl) + '&');

  oauthParameters.oauth_signature = Utilities.base64Encode(
    Utilities.computeHmacSignature(
      Utilities.MacAlgorithm.HMAC_SHA_1,
      baseString,
      props.getProperty('CONSUMER_SECRET') + '&' + props.getProperty('ACCESS_SECRET')
    )
  );

  var options = {
    method: method,
    headers: {
      authorization:
        'OAuth ' +
        Object.keys(oauthParameters)
          .sort()
          .reduce(function (acc, key) {
            acc.push(key + '="' + encode(oauthParameters[key]) + '"');
            return acc;
          }, [])
          .join(', '),
    },
    payload: Object.keys(payload)
      .reduce(function (acc, key) {
        acc.push(key + '=' + encode(payload[key]));
        return acc;
      }, [])
      .join('&'),
    muteHttpExceptions: true,
  };

  var response = UrlFetchApp.fetch(baseUrl, options);
  var responseHeader = response.getHeaders();
  var responseText = response.getContentText();
  Logger.log(responseText);
}

function encode(string) {
  return encodeURIComponent(string)
    .replace('!', '%21')
    .replace('*', '%2A')
    .replace('(', '%28')
    .replace(')', '%29')
    .replace("'", '%27');
}