socket.js

var debug = require('debug')('scc:socket');
var backoff = require('backoff');
var processTweet = require('./util/process-tweet');
var topic = process.env.TWITTER_TOPIC || '<topic>';
var preloadedTweets = [];

module.exports = function(io, twitter) {
  // existing sessions
  var sessions = {};

  var connectTwitter = function() {
    twitter.stream({ track: topic, filter_level: 'medium', language: 'en' }, function(stream) {
      debug('Connected to twitter.stream, topic: %s', topic);
      stream.on('data', function(tweet) {
        fibonacciBackoff.reset();
        processTweet(tweet, function (error, processedTweet) {
          if (error) {
            debug(error);
            debug('Ignore tweet: %s', tweet.text);
            return;
          }
          preloadedTweets.push(processedTweet);
          if(preloadedTweets.length > 5) {
            preloadedTweets.shift();
          }
          Object.keys(sessions).forEach(function(id) {
            sessions[id].socket.emit('message', processedTweet);
          });
        });
      });
      stream.on('error', function(error) {
        debug('Error connecting to twitter.stream: %s', error);
        fibonacciBackoff.backoff();
      });

      stream.on('close', function(error) {
        debug('Error connecting to twitter.stream: %s', error);
        fibonacciBackoff.backoff();
      });
    });
  };

  // Create a session on socket connection
  io.use(function(socket, next) {
    sessions[socket.id] = { socket: socket };
    debug('Total sessions: %s sessions', Object.keys(sessions).length);
    socket.emit('session', socket.id);
    next();
  });

  io.on('connection', function(socket) {
    preloadedTweets.forEach(function(tweet){
      socket.emit('message', tweet);
    });
    socket.on('message', function() {
      // send initial tweets
      socket.emit('message', 'hello!');
    });

    // Delete the session on disconnect
    socket.on('disconnect', function() {
      delete sessions[socket.id];
      debug('Disconnect: %s', socket.id);
    });
  });

  var fibonacciBackoff = backoff.fibonacci({
    randomisationFactor: 0,
    initialDelay: 10,
    maxDelay: 30000
  });

  fibonacciBackoff.failAfter(10);

  fibonacciBackoff.on('backoff', function(number, delay) {
      // Do something when backoff starts, e.g. show to the
      // user the delay before next reconnection attempt.
    debug('Attempting to reconect to twitter. Attempts: ' + number + ' ' + delay + 'ms');
  });

  fibonacciBackoff.on('ready', function() {
    connectTwitter();
  });

  fibonacciBackoff.on('fail', function() {
    debug('Failed to connect to twitter after multiple attempts.');
  });

  fibonacciBackoff.backoff();
};