// Note: The content from here upto '// End scroll test' is duplicated at:
//       - talos/page_load_test/scroll/scroll-test.js
//       - inside talos/pageloader/chrome/tscroll.js
//
// - Please keep these copies in sync.
// - Pleace make sure that any changes apply cleanly to all use cases.

function testScroll(target, stepSize, opt_reportFunc, opt_numSteps)
{
  var win;
  if (target == "content") {
    target = content.wrappedJSObject;
    win = content;
  } else {
    win = window;
  }

  function rAF(fn) {
    return content.requestAnimationFrame(fn);
  }


  function myNow() {
    return (win.performance && win.performance.now) ?
            win.performance.now() :
            Date.now();
  };

  var isWindow = target.self === target;

  var getPos =       isWindow ? function() { return target.pageYOffset; }
                              : function() { return target.scrollTop; };

  var gotoTop =      isWindow ? function() { target.scroll(0, 0);  ensureScroll(); }
                              : function() { target.scrollTop = 0; ensureScroll(); };

  var doScrollTick = isWindow ? function() { target.scrollBy(0, stepSize); ensureScroll(); }
                              : function() { target.scrollTop += stepSize; ensureScroll(); };

  function ensureScroll() { // Ensure scroll by reading computed values. screenY is for X11.
    if (!this.dummyEnsureScroll) {
      this.dummyEnsureScroll = 1;
    }
    this.dummyEnsureScroll += win.screenY + getPos();
  }

  // For reference, rAF should fire on vsync, but Gecko currently doesn't use vsync.
  // Instead, it uses 1000/layout.frame_rate
  // (with 60 as default value when layout.frame_rate == -1).
  function startTest()
  {
    // We should be at the top of the page now.
    var start = myNow();
    var lastScrollPos = getPos();
    var lastScrollTime = start;
    var durations = [];
    var report = opt_reportFunc || tpRecordTime;
    if (report == 'PageLoader:RecordTime') {
      report = function(duration) {
        var msg = { time: duration, startTime: '', testName: '' };
        sendAsyncMessage('PageLoader:RecordTime', msg);
      }
    }

    function tick() {
      var now = myNow();
      var duration = now - lastScrollTime;
      lastScrollTime = now;

      durations.push(duration);
      doScrollTick();

      /* stop scrolling if we can't scroll more, or if we've reached requested number of steps */
      if ((getPos() == lastScrollPos) || (opt_numSteps && (durations.length >= (opt_numSteps + 2)))) {
        if (typeof(Profiler) !== "undefined") {
          Profiler.pause();
        }

        // Note: The first (1-5) intervals WILL be longer than the rest.
        // First interval might include initial rendering and be extra slow.
        // Also requestAnimationFrame needs to sync (optimally in 1 frame) after long frames.
        // Suggested: Ignore the first 5 intervals.

        durations.pop(); // Last step was 0.
        durations.pop(); // and the prev one was shorter and with end-of-page logic, ignore both.

        if (win.talosDebug)
          win.talosDebug.displayData = true; // In a browser: also display all data points.

        // For analysis (otherwise, it's too many data points for talos):
        var sum = 0;
        for (var i = 0; i < durations.length; i++)
          sum += Number(durations[i]);

        // Report average interval or (failsafe) 0 if no intervls were recorded
        report(durations.length ? sum / durations.length : 0);
        return;
      }

      lastScrollPos = getPos();
      rAF(tick);
    }

    if (typeof(Profiler) !== "undefined") {
      Profiler.resume();
    }
    rAF(tick);
  }

  // Not part of the test and does nothing if we're within talos,
  // But provides an alternative tpRecordTime (with some stats display) if running in a browser
  // If a callback is provided, then we don't need this debug reporting.
  if(!opt_reportFunc && document.head) {
    var imported = document.createElement('script');
    imported.src = '../../scripts/talos-debug.js?dummy=' + Date.now(); // For some browsers to re-read
    document.head.appendChild(imported);
  }

  setTimeout(function(){
    gotoTop();
    rAF(startTest);
  }, 260);
}
// End scroll test - End duplicated code
