github_notification_filter.js

////// Easily customizable stuff
// Step zero: have a filter that sorts all notifications@github.com mail into _github_incoming & archives it
var incomingLabel = '_github_incoming';  // You can hide this in the sidebar.
// github sends to "me", and I want less of that pollution
var toMeLabel = 'asf';

// labels for various conditions:
var meLabel = 'github';
var teamMentionLabel = 'github/team_mention';
///// End of the easily customizable stuff


// The main entry and trigger point for the post-hoc filter:
function processIncoming() {
  processMessages(true);
}

// Run this manually from the scripts console to backfill your github labels without filling your inbox:
function processIncomingBackfill() {
  processMessages(false);
}

function processMessages(putIntoInbox) {
  var incoming = getOrCreateLabel(incomingLabel);
  var threads = incoming.getThreads();
  
  for (var i = 0; i < threads.length; i++) {
    var thread = threads[i];
    var messages = thread.getMessages();
    // We consider only the last message, as you might have unsubscribed from github threads, or situations may have otherwise changed:
    sortMessage(messages[messages.length-1], thread, putIntoInbox);
    thread.removeLabel(incoming);
  }
}

function getOrCreateLabel(name) {
  var label = GmailApp.getUserLabelByName(name);  
  if(label == null){
    label = GmailApp.createLabel(name);
  }
  return label
}

function sortMessage(message, thread, putIntoInbox) {
  var headers = messageHeaders(message.getRawContent());
  if (isMessageRelevant(headers)) {
    Logger.log("Thread with message subject %s is relevant", headers['Subject']);
    markAsMine(thread, putIntoInbox);
  } else {
    Logger.log("Thread with subject %s is not relevant", headers['Subject']);
    markAsNonRelevant(thread);
  }
}

function isMessageRelevant(headers) {
  var isIt = (headers['X-GitHub-Reason'] === 'author') ||
    (headers['X-GitHub-Reason'] === 'comment') ||
      (headers['X-GitHub-Reason'] === 'assign') ||
        (headers['X-GitHub-Reason'] === 'mention');
  return isIt;
}

function markAsMine(thread, putIntoInbox) {
  thread.addLabel(getOrCreateLabel(meLabel));
  if (putIntoInbox) {
    thread.moveToInbox();
  }
}

function markAsNonRelevant(thread) {
  thread.addLabel(getOrCreateLabel(teamMentionLabel));
  
  var messages = thread.getMessages();
  var wasEverRelevant = false;
  for(var i=0; i < messages.length; i++) {
    var body = messages[i].getRawContent();
    var headers = messageHeaders(body);
    if (isMessageRelevant(headers)) {
      wasEverRelevant = true;
    }
  }
  if (!wasEverRelevant && toMeLabel !== null) {
    thread.removeLabel(GmailApp.getUserLabelByName(toMeLabel));
  }
}

/* Takes a raw message and returns a dictionary of header=>header values.
 * Note: This handles only "simple"&short (non-continued) headers, so any
 * continuation lines aren't going to be processed - only the first line
 * will be considered a value.
 */
function messageHeaders(body) {
  var lines = body.split(/\r?\n/);
  var headers = [], wasNewline = false;
  // Determine the empty line & split there:
  for(var i=0; i < lines.length && !wasNewline; i++) {
    var line = lines[i];
    if (line === '') {
      wasNewline = true;
    } else {
      headers.push(line);
    }
  }
  var headerDict = {}
  for (var i=0; i < headers.length; i++) {
    var headerSplit = headers[i].split(": ");
    var key = headerSplit.shift();
    if (!key.match(/^\s/)) {
      // it's a not header continuation, so add it as a new key
      headerDict[key] = headerSplit.join(": ");
    }
  }
  return headerDict;
}