background.js

var musicDiaryListener = (function() {
  var bg = {}
  var rdioUrl = "http://www.rdio.com/api/1/addStartEvent";

  chrome.webRequest.onCompleted.addListener(function(details) {
    if (details.url == rdioUrl) {
      chrome.tabs.query({url: "http://www.rdio.com/*"}, bg.getSongUrlFromTab);
    }
  }, {urls: ["http://www.rdio.com/*"]}, []);

  chrome.tabs.onActivated.addListener(function(info) {
    chrome.tabs.query({ url: "http://www.rdio.com/*"}, bg.toggleIcon);
  });

  bg.getSongUrlFromTab = function(tabs) {
    if(tabs.length > 0) {
      chrome.tabs.sendMessage(tabs[0].id, {name: "getSongUrl"}, bg.sendSongPlayed);
    }
  };

  chrome.extension.onMessage.addListener(function(request, sender, sendResponse) {
    switch (request.name) {
      case "popup-click":
        chrome.tabs.query({ url: "http://www.rdio.com/*"}, bg.toggleIcon);
    }
  });

  bg.sendSongPlayed = function(response) {
    var songUrl = response.songUrl;
    if(songUrl) {
      console.log(songUrl);

      body = {};
      body["service"] = "rdio";
      body["url"] = songUrl;

      var xhr = new XMLHttpRequest();
      xhr.open("POST", bg.getServer() + "/log", true);
      xhr.setRequestHeader("Content-type", "application/json");
      xhr.send(JSON.stringify(body));
    }
  }

  bg.toggleIcon = function(tabs) {
    if(tabs.length > 0) {
      chrome.tabs.sendMessage(tabs[0].id, {
        name: "getAuthed",
        server: bg.getServer()
      }, function(response) {
        if(response.authenticated) {
          chrome.browserAction.setIcon({ path: '/images/diary-blue.png' });
        }
        else {
          chrome.browserAction.setIcon({ path: '/images/diary-gray.png' });
        }
      });
    }
    else {
      chrome.browserAction.setIcon({ path: '/images/diary-gray.png' });
    }
  }

  bg.getServer = function() {
    return chrome.app.getDetails().homepage_url;
  }

  return bg;
}());