{
  "manifest_version": 2,

  "name": "showigid",
  "description" : "Show Instagram Id on user page",
  "version": "0.1",

  "background": {
      "scripts": ["eventPage.js"]
  },

  "content_scripts": [
    {
      "matches": ["https://www.instagram.com/*"],
      "js": ["showid.js"]
    }
  ],

  "permissions": [
    "https://www.instagram.com/*",
    "tabs"
  ]
}

var reUrlUser = /^https:\/\/www\.instagram\.com\/([a-z0-9_.]+)\/$/;

function sendMsg(id, url) {
  chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
    chrome.tabs.sendMessage(
      tabs[0].id,
      {id: id, url: url}
    );
  });
}

function getId(url) {
  var jsonUrl = url + "?__a=1";
  var xhr = new XMLHttpRequest();
  xhr.open("GET", jsonUrl, true);
  xhr.onreadystatechange = function() {
    if (xhr.readyState == 4) {
      // JSON.parse does not evaluate the attacker's scripts.
      var resp = JSON.parse(xhr.responseText);
      sendMsg(resp["user"]["id"], jsonUrl);
    }
  }
  xhr.send();
}

chrome.tabs.onUpdated.addListener(function(tabId, changeInfo, tab) {
  if (changeInfo.hasOwnProperty('url')) {

    // check if URL is user page
    var result = changeInfo.url.match(reUrlUser);
    if (result) {
      getId(changeInfo.url);
    }
  }
});

function showId(elm, id, url) {
  var link = document.createElement("a");
  link.setAttribute("href", url);
  link.setAttribute("target", "_blank");
  link.setAttribute("class", "_fd86t");
  link.appendChild(document.createTextNode(id));

  elm.appendChild(document.createElement("br"));
  elm.appendChild(link);
}

chrome.runtime.onMessage.addListener(
  function(request, sender, sendResponse) {

    // wait page to be loaded
    var timerId = setInterval(function() {
      var n = document.querySelector("section._o6mpc");
      if (n != null) {
        showId(n, request.id, request.url);
        clearInterval(timerId);
      }
    }, 500);
  });