<!DOCTYPE html>
<html>
<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">

<body>
  <style>
    :root {
      margin: 0px;
    }

    #spacer {
      height: 100vh;
      width: 100px;
    }

    #top_box {
      width: 100px;
      height: 60vh;
      background-color: blue;
    }
    #middle_box {
      width: 100px;
      height: 60vh;
      scroll-initial-target: nearest;
      background-color: purple;
    }
    #bottom_box {
      width: 100px;
      height: 60vh;
      background-color: yellow;
    }

    #fragment_target {
      width: 100px;
      height: 100px;
      background-color: red;
    }
  </style>
  <div id="top_box"></div>
  <div id="middle_box"></div>
  <div id="bottom_box"></div>
  <div id="spacer"></div>
  <div id="fragment_target">Target</div>
  <script>
    function stashResult(key, results) {
      fetch(`/css/css-scroll-snap/scroll-initial-target/stash.py?key=${key}`, {
        method: "POST",
        body: JSON.stringify(results)
      }).then(() => {
        window.close();
      });
    }
    function record() {
      let scroll_position = "UNKNOWN";
      // Expect page is scrolled all the way down as the text is at the bottom of
      // the page.
      const expected_scroll_top = document.scrollingElement.scrollHeight -
        document.scrollingElement.clientHeight;

      const scroll_start_target_top = Math.round(top_box.getBoundingClientRect().height);

      const actual_scroll_top = Math.round(document.scrollingElement.scrollTop);
      if (actual_scroll_top == scroll_start_target_top) {
        scroll_position = "AT_SCROLL_START_TARGET";
      } else if (actual_scroll_top == expected_scroll_top) {
        scroll_position = "AT_TEXT_FRAGMENT";
      }

      const result = {
        scroll_position: scroll_position
      };

      let key = (new URL(document.location)).searchParams.get("key");
      stashResult(key, result);
    }

    window.onload = () => {
      window.requestAnimationFrame(function () {
        window.requestAnimationFrame(record);
      })
    }
  </script>
</body>

</html>