background-script.js

var currentTab;
var pages = [];
var clacks = [];
var current_clacks;
var has_clacks;
var pos = 0;
var loop = 0;

function updateIcon() {
  browser.browserAction.setIcon({
    path: has_clacks ? {
			"16": "data/Clacks16/END.png",
			"32": "data/Clacks32/END.png",
			"64": "data/Clacks64/END.png"
    } : {
			"16": "data/Clacks16/BLANK.png",
			"32": "data/Clacks32/BLANK.png",
			"64": "data/Clacks64/BLANK.png"
    },
    tabId: currentTab.id
  });
  browser.browserAction.setTitle({
    // Screen readers can see the title
    title: has_clacks ? current_clacks : "Nothing in the overhead" ,
    tabId: currentTab.id
  }); 
}

function checkTime() {
  if (has_clacks == true) {
	loop = loop + 1;
	if (loop > 4) { loop = 0; }
	if (loop < 1) {
		browser.browserAction.setIcon({
			path: {
					"16": "data/Clacks16/BLANK.png",
					"32": "data/Clacks32/BLANK.png",
					"64": "data/Clacks64/BLANK.png"
					},
				tabId: currentTab.id
				});
		pos = pos + 1;
	} else {
		if (current_clacks.length-1 < pos) { pos = 0; };
		if (current_clacks.charAt(pos) == " ") {
				browser.browserAction.setIcon({
					path: {
						"16": "data/Clacks16/SPACE.png",
						"32": "data/Clacks32/SPACE.png",
						"64": "data/Clacks64/SPACE.png"
						},
					tabId: currentTab.id
				});
			} else {
				if (current_clacks.charAt(pos) == "+") {
				browser.browserAction.setIcon({
					path: {
						"16": "data/Clacks16/END.png",
						"32": "data/Clacks32/END.png",
						"64": "data/Clacks64/END.png"
					},
					tabId: currentTab.id
				});
			} else {
				try {
					browser.browserAction.setIcon({
						path: {
							"16": "data/Clacks16/"+current_clacks.charAt(pos).toUpperCase()+".png",
							"32": "data/Clacks32/"+current_clacks.charAt(pos).toUpperCase()+".png",
							"64": "data/Clacks64/"+current_clacks.charAt(pos).toUpperCase()+".png"
						},
						tabId: currentTab.id
					});
				} catch (ex4) {
					browser.browserAction.setIcon({
						path: {
							"16": "data/Clacks16/SPACE.png",
							"32": "data/Clacks32/SPACE.png",
							"64": "data/Clacks64/SPACE.png"
							},
						tabId: currentTab.id
					});
				}
			}
		}
	}
  }
}

function updateActiveTab(tabs) {

  function updateTab(tabs) {
    if (tabs[0]) {
      currentTab = tabs[0];
	  var l = pages.indexOf(currentTab.url);
      if (l == -1) {          
	    current_clacks = "Nothing in the overhead";
		has_clacks = false;
      } else {
        current_clacks = clacks[l];	  
		has_clacks = true;
	  }
	  updateIcon();
    }
  }

  var gettingActiveTab = browser.tabs.query({active: true, currentWindow: true});
  gettingActiveTab.then(updateTab);
}

function setGNU(e) {
  for (var header of e.responseHeaders) {
    if (header.name.toLowerCase() == "x-clacks-overhead") {
	  if (pages.indexOf(e.url) == -1) {
		pages.push(e.url);
		clacks.push("+"+header.value);
	  }
    }
  }
  return {responseHeaders: e.responseHeaders};
}

// Listen for onHeaderReceived for the target page.
// Set "blocking" and "responseHeaders".
browser.webRequest.onHeadersReceived.addListener(
  setGNU,
  {urls: ["<all_urls>"]},
  ["responseHeaders"]
);

function openPage() {
  browser.tabs.create({
    url: "http://www.gnuterrypratchett.com/"
  });
}
function notify(message) {
  if (pages.indexOf(message.url) == -1) {
		pages.push(message.url);
		clacks.push("+"+message.value);
	  }
	updateActiveTab();
}

browser.runtime.onMessage.addListener(notify);

browser.browserAction.onClicked.addListener(openPage);

// listen to tab URL changes
browser.tabs.onUpdated.addListener(updateActiveTab);

// listen to tab switching
browser.tabs.onActivated.addListener(updateActiveTab);

// listen for window switching
browser.windows.onFocusChanged.addListener(updateActiveTab);

browser.alarms.onAlarm.addListener(checkTime);
browser.alarms.create('checkTime', {periodInMinutes: 0.02});

// update when the extension loads initially
updateActiveTab();