/* Credit: gist.github.com/andrewmwilson */

function sendEmailsToSlack() {
  var label = GmailApp.getUserLabelByName('ToSlack');
  var messages = [];
  var threads = label.getThreads();

  for (var i = 0; i < threads.length; i++) {
    messages = messages.concat(threads[i].getMessages());
  }

  for (var i = 0; i < messages.length; i++) {
    var message = messages[i];
    Logger.log(message);

    var output = '*New Email*';
    output += '\n*from:* ' + message.getFrom();
    output += '\n*to:* ' + message.getTo();
    output += '\n*cc:* ' + message.getCc();
    output += '\n*date:* ' + message.getDate();
    output += '\n*subject:* ' + message.getSubject();
    output += '\n*body:* ' + message.getPlainBody();
    Logger.log(output);

    var payload = {
      username: 'gmail-bot',
      text: output,
      channel: '#some-channel',
      icon_emoji: ':hear_no_evil:',
    };

    var options = {
      method: 'post',
      payload: Utilities.jsonStringify(payload),
    };

    // replace this with your own Slack webhook URL
    // https://crowdscores.slack.com/services
    var webhookUrl = 'https://hooks.slack.com/services/****/****/****';
    UrlFetchApp.fetch(webhookUrl, options);
  }

  // remove the label from these threads so we don't send them to
  // slack again next time the script is run
  label.removeFromThreads(threads);
}