<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <title> CSS Scroll Snap 2 Test: scroll-start interaction with anchor navigation</title>
  <link rel="help" href="https://drafts.csswg.org/css-scroll-snap-2/#scroll-start">
  <script src="/resources/testharness.js"></script>
  <script src="/resources/testharnessreport.js"></script>
  <script src="/html/browsers/browsing-the-web/resources/helpers.js"></script>
  <script src="/dom/events/scrolling/scroll_support.js"></script>
</head>

<body>
  <iframe id="frame" src="scroll-start-with-anchor-navigation-inner-frame.html" onload="runTest()"></iframe>
  <script>
    function runTest() {
      promise_test(async (t) => {
        let scroller = frame.contentDocument.scrollingElement;
        // anchor_target is at the bottom of the frame so the frame should be
        // fully scrolled down to bring it into view.
        let anchor_target_scrolltop = scroller.scrollHeight - scroller.clientHeight;
        let anchor_target_link = frame.contentDocument.getElementById("anchor_target_link");

        // Expect scroll offset of 100px per scroll-start.
        assert_equals(scroller.scrollTop, 100,
          "scroll-start sets initial scroll offset");

        // Scroll away from start position.
        scroller.scrollTop = 200;
        await waitForCompositorCommit();
        assert_equals(scroller.scrollTop, 200,
          "scroll-start sets initial scroll offset");

        anchor_target_link.click();
        await waitForHashchange(frame.contentWindow);
        assert_equals(frame.contentWindow.location.hash, "#anchor_target",
          "clicking anchor link navigates to target");

        // Expect page to be fully scrolled as anchor_target is at the bottom of
        // the document.
        assert_equals(scroller.scrollTop, anchor_target_scrolltop,
          "anchor navigation sets scroll offset");

        frame.contentWindow.history.back();
        await waitForHashchange(frame.contentWindow);
        assert_equals(frame.contentWindow.location.hash, "");

        scroller = frame.contentDocument.scrollingElement;
        assert_equals(scroller.scrollTop, 200,
          "scroller returns to previous scroll position, not " +
          "scroll-start");
      }, "scroll-start does not override anchor navigation.");
    }
  </script>
</body>