//
// Sends Cloudwatch Event notifications to Slack 
//


//
// Setup: See setup in the readme file
//


const SLACK_URL = 'https://<your organization>.slack.com/services/hooks/incoming-webhook'; // Replace
const SLACK_CHANNEL_NAME = "#ops"; // Replace with yout own channel name
const kmsEncyptedToken = 'Replace with your KMS token'; // Replace
const SLACK_USERNAME = "webhookbot";

console.log('Loading function');

const AWS = require('aws-sdk');
const url = require('url');
const https = require('https');
const qs = require('querystring');


exports.handler = function(event, context) {
  var token = null;
  var slackReqOpts = null;
  if (token) {
    // Container reuse, simply process the event with the key in memory
    processEvent(event, context, slackReqOpts);
  } else {
    const encryptedBuf = new Buffer(kmsEncyptedToken, 'base64');
    const cipherText = {CiphertextBlob: encryptedBuf};

    const kms = new AWS.KMS();
    kms.decrypt(cipherText, function (err, data) {
      if (err) {
        console.log("Decrypt error: " + err);
        context.fail(err);
      } else {
        token = data.Plaintext.toString('ascii');
        const slackUrl = SLACK_URL;
        slackReqOpts = url.parse(slackUrl + '?token=' + token);
        slackReqOpts.method = 'POST';
        slackReqOpts.headers = {'Content-Type': 'application/json'};
        processEvent(event, context, slackReqOpts);
      }
    });
  }
};

var processEvent = function(event, context, slackReqOpts) {
  var source = event.source;
  var region = event.region;
  var detail = event.detail;
  var instanceId = detail['instance-id'];
  var state = detail.state;
  var text = [];
  text.push(source);
  text.push(' (' + region + ')');
  text.push(': ');
  text.push(instanceId);
  text.push(' is ');
  text.push(state);


  var req = https.request(slackReqOpts, function (res) {
    if (res.statusCode === 200) {
      context.succeed('posted to slack');
    } else {
      context.fail('status code: ' + res.statusCode);
    }
  });

  req.on('error', function(e) {
    console.log('problem with request: ' + e.message);
    context.fail(e.message);
  });
  req.write(JSON.stringify({
      channel: SLACK_CHANNEL_NAME,
      username: SLACK_USERNAME,
      text: text.join(''),
      icon_emoji: ":ghost:"
  }));
  req.end();
}