app.js

var crypto = require("crypto")
  , request = require("request")
  , Parser = require("feedparser")
  , Firebase = require("firebase");

var feeds = {};
var feedContent = {};

var REFRESH_INTERVAL = 600000;

var ref = new Firebase("https://feedthefire.firebaseio.com/persona");
ref.auth(process.env.SECRET, function(err) {
  if (err) {
    console.error("Firebase authentication failed!", err);
  } else {
    setupHandlers();
    setInterval(parseFeeds, REFRESH_INTERVAL);
  }
});

function getHash(value) {
  var shasum = crypto.createHash("sha1");
  shasum.update(value);
  return shasum.digest("hex");
}

function sanitizeObject(obj) {
  if (typeof obj != typeof {}) {
    return obj;
  }

  var newObj = {};
  var special = [".", "$", "/", "[", "]"];
  for (var key in obj) {
    var sum = -1;
    for (var i in special) {
      sum += (key.indexOf(special[i])) + 1;
    }
    if (sum < 0) {
      if (key == "date" || key == "pubdate" || key == "pubDate") {
        if (obj[key]) {
          newObj[key] = obj[key].toString();
        }
      } else if (key == "#") {
        newObj["value"] = sanitizeObject(obj[key]);
      } else if (key.indexOf("#") >= 0) {
        newObj["@" + key.replace("#", "")] = sanitizeObject(obj[key]);
      } else if (sanitizeObject(obj[key]) && key != "") {
        newObj[key] = sanitizeObject(obj[key]);
      }
    }
  }
  return newObj;
}

function writeStatus(url, data) {
  writeToFirebase(url, data, process.env.SECRET, function(err) {
    if (err) {
      console.error(err);
    }
  });
}

function writeToFirebase(url, data, secret, cb) {
  var options = {url: url + ".json", method: "PUT", json: data};
  if (secret) {
    options.qs = {auth: secret};
  }

  request(options, function(err, resp, body) {
    if (!resp || !resp.statusCode) {
      code = "500";
    } else {
      code = resp.statusCode;
    }

    if (!err && code == 200) {
      if (cb) {
        cb(null);
      }
    } else {
      var msg;
      if (code == 403) {
        msg = "Error: permission denied while writing to " + url + " (did you specify a secret?)";
      } else if (code == 417) {
        msg = "Error: the specified Firebase " + url + " does not exist.";
      } else {
        msg = "Error: could not write to " + url + ", received status code " + code;
      }
      if (err) {
        msg = url + ": " + err.toString();
      }
      if (cb) {
        cb(msg);
      } else {
        console.error(msg);
      }
    }
  });
}

function setupHandlers() {
  var self = this;
  ref.on("child_added", function(snap) {
    var userid = snap.name();
    if (!feeds[userid]) {
      feeds[userid] = {};
    }
    var childRef = ref.child(userid).child("feeds");
    childRef.on("child_added", editUserFeed.bind(self, userid));
    childRef.on("child_changed", editUserFeed.bind(self, userid));
    childRef.on("child_removed", function(childSnap) {
      delete feeds[userid][childSnap.name()];
    });
  });
  ref.on("child_removed", function(remSnap) {
    var childRef = ref.child(remSnap.name()).child("feeds");
    childRef.off();
  });
}

function editUserFeed(userid, snap) {
  var id = snap.name();
  var entry = feeds[userid][id] = {
    statusURL: new Firebase(
      snap.ref().toString()
    ).parent().parent().child("status/" + id).toString(),
    value: snap.val()
  };
  parseFeed(entry);
}

function parseFeeds() {
  for (var uid in feeds) {
    var user = feeds[uid];
    for (var index in user) {
      parseFeed(user[index]);
    }
  }
}

function parseFeed(feed) {
  try {
    var url = feed.value.url;
    var statusURL = new Firebase(feed.statusURL).toString();

    if (!url || url.indexOf("http") < 0) {
      writeStatus(statusURL, "Error: Invalid feed URL specified: " + url);
      return;
    }
    if (!feed.value.firebase || feed.value.firebase.indexOf("https") < 0) {
      writeStatus(statusURL, "Error: Invalid Firebase URL specified, did you include the https prefix?");
      return;
    }

    var fbURL = new Firebase(feed.value.firebase).toString();
    var secret = feed.value.secret;
    var urlHash = getHash(url);

    if (feedContent[urlHash]) {
      if (new Date().getTime() - feedContent[urlHash].lastSync > REFRESH_INTERVAL) {
        getAndSet(url, urlHash, statusURL, fbURL, secret);
      } else {
        setFeed(feedContent[urlHash].content, statusURL, fbURL, secret);
      }
    } else {
      getAndSet(url, urlHash, statusURL, fbURL, secret);
    }
  } catch(e) {
    writeStatus(statusURL, e.toString());
  }
}

function getAndSet(url, hash, statusURL, fbURL, secret) {
  request(url, function(err, resp, body) {
    if (!err && resp.statusCode == 200) {
      feedContent[hash] = {time: new Date().getTime(), content: body};
      setFeed(body, statusURL, fbURL, secret);
    } else {
      if (err) {
        writeStatus(statusURL, err.toString());
      } else {
        writeStatus(statusURL, "Error: got status " + resp.statusCode + " when fetching feed.");
      }
    }
  });
}

function setFeed(feed, statusURL, fbURL, secret) {
  Parser.parseString(feed, {addmeta: false}, function(err, meta, articles) {
    if (err) {
      writeStatus(statusURL, err.toString());
      return;
    }
    try {
      writeToFirebase(fbURL + "/meta", sanitizeObject(meta), secret, function(err) {
        if (err) {
          writeStatus(statusURL, err.toString());
          return;
        }
        setArticles(articles, 0, articles.length, statusURL, fbURL, secret);
      });
    } catch(e) {
      writeStatus(statusURL, e.toString());
    }
  });
}

function setArticles(articles, done, total, statusURL, fbURL, secret) {
  if (total <= 0) {
    writeStatus(statusURL, "Last Sync: " + new Date().toString());
    return;
  }

  var article = articles[done];
  var id = getHash(article.guid || article.link || article.title);
  var date = article.pubDate || article.pubdate || article.date ||
    article["rss:pubdate"] || new Date().toString();
  var timestamp = Date.parse(date);

  var arURL = fbURL + "/articles/" + id;
  var articleObj = sanitizeObject(article);
  articleObj[".priority"] = timestamp;

  writeToFirebase(arURL, articleObj, secret, function(err) {
    if (err) {
      writeStatus(statusURL, err);
    } else {
      done++;
      if (done == total - 1) {
        writeStatus(statusURL, "Last Sync: " + new Date().toString());
      } else {
        setArticles(articles, done, total, statusURL, fbURL, secret);
      }
    }
  });
}