gistfile1.js

// @src
//   https://github.com/GoogleChrome/chrome-app-samples/tree/master/one-time-payment
// @output
//   "FULL" - Fully paid & properly licensed
//   "FREE_TRIAL" - Free trial, still within trial period
//   "FREE_TRIAL_EXPIRED" - Free trial, trial period expired
//   "NONE" - No license ever issued
var getLicense = function(callback) {
  var retry = true;
  var access_token = null

  var requestStart = function() {
    var xhr = new XMLHttpRequest();
    xhr.open("GET", "https://www.googleapis.com/chromewebstore/v1.1/userlicenses/" + chrome.runtime.id);
    xhr.setRequestHeader('Authorization', 'Bearer ' + access_token);
    xhr.onload = requestComplete;
   
    // If either Google server is down or user has no internet connection then assume trial mode 
    xhr.onerror = function(error) {
      callback("FREE_TRIAL");
    };
    
    xhr.send();
  };

  var requestComplete = function() {
    if (this.status == 401 && retry) {
      retry = false;
      chrome.identity.removeCachedAuthToken({ token: access_token }, getToken);
    }
    else {
      handleResponse(null, this.status, this.response);
    }
  };

  var getToken = function() {
    chrome.identity.getAuthToken({ interactive: true }, function(token) {
      if (chrome.runtime.lastError) {
        handleResponse(chrome.runtime.lastError);
      }
      else {
        access_token = token;
        requestStart();
      }
    });
  };

  var handleResponse = function(error, status, responseJSON) {
    var response = JSON.parse(responseJSON);
    var license;

    if (response.accessLevel === "FULL") {
      license = "FULL";
    }
    else if (response.accessLevel === "FREE_TRIAL") {
      var startedSellingTime = 1382871600000; // 2013-10-27 12:00
      var currentTime = Date.now();
      var firstInstallTime = parseInt(response.createdTime, 10);
      var daysSinceFirstInstall = (currentTime - firstInstallTime) / 1000 / 60 / 60 / 24;

      // Grant trial license to users who first installed the app less than 2 days ago
      if (daysSinceFirstInstall <= 2) {
        license = "FREE_TRIAL";
      }
      // Grant full license to users that first installed the app when it was still free
      else if (firstInstallTime < startedSellingTime) {
        license = "FULL";
      }
      else {
        license = "FREE_TRIAL_EXPIRED";
      }
    }
    else {
      license = "NONE";
    }

    callback(license);
  };

  getToken();
};