wiki/_includes/link-previews.html

<!-- That file is not particularly elegant. This will need a refactor at some point. -->
<style>
  content a.internal-link {
    border-color: #8b88e6;
    background-color: #efefff;
  }

  #tooltip-wrapper {
    background: white;
    padding: 1em;
    border: 1px solid #ddd;
    border-radius: 4px;
    overflow: hidden;
    position: absolute;
    width: 400px;
    height: 250px;
    font-size: 0.8em;
    box-shadow: 0 5px 10px rgba(0,0,0,0.1);
    opacity: 0;
    transition: opacity 100ms;
  }

  #tooltip-wrapper:after {
		content: "";
		position: absolute;
		z-index: 1;
		bottom: 0;
		left: 0;
		pointer-events: none;
		background-image: linear-gradient(to bottom, rgba(255,255,255, 0), rgba(255,255,255, 1) 90%);
		width: 100%;
		height: 75px;
  }
</style>

<div style="opacity: 0; display: none;" id='tooltip-wrapper'>
  <div id='tooltip-content'>
  </div>
</div>

<iframe style="display: none; height: 0; width: 0;" id='link-preview-iframe' src="">
</iframe>

<script>
  var opacityTimeout;
  var contentTimeout;
  var transitionDurationMs = 100;

  var iframe = document.getElementById('link-preview-iframe')
  var tooltipWrapper = document.getElementById('tooltip-wrapper')
  var tooltipContent = document.getElementById('tooltip-content')

  var linkHistories = {};

  function hideTooltip() {
    opacityTimeout = setTimeout(function() {
      tooltipWrapper.style.opacity = 0;
      contentTimeout = setTimeout(function() {
        tooltipContent.innerHTML = '';
        tooltipWrapper.style.display = 'none';
      }, transitionDurationMs + 1);
    }, transitionDurationMs)
  }

  function showTooltip(event) {
    var elem = event.target;
    var elem_props = elem.getClientRects()[elem.getClientRects().length - 1];
    var top = window.pageYOffset || document.documentElement.scrollTop

    if (event.target.host === window.location.host) {
      if (!linkHistories[event.target.href]) {
        iframe.src = event.target.href
        iframe.onload = function() {
          tooltipContentHtml = ''
          tooltipContentHtml += '<div style="font-weight: bold;">' + iframe.contentWindow.document.querySelector('h1').innerHTML + '</div>'
          tooltipContentHtml += iframe.contentWindow.document.querySelector('content').innerHTML

          tooltipContent.innerHTML = tooltipContentHtml
          linkHistories[event.target.href] = tooltipContentHtml

          tooltipWrapper.style.display = 'block';
          setTimeout(function() {
            tooltipWrapper.style.opacity = 1;
          }, 1)
        } 
      } else {
        tooltipContent.innerHTML = linkHistories[event.target.href]
        tooltipWrapper.style.display = 'block';
        setTimeout(function() {
          tooltipWrapper.style.opacity = 1;
        }, 1)
      }


      tooltipWrapper.style.left = elem_props.left - (tooltipWrapper.offsetWidth / 2) + (elem_props.width / 2) + "px";
      if ((window.innerHeight - elem_props.top) < (tooltipWrapper.offsetHeight)) {
          tooltipWrapper.style.top = elem_props.top + top - tooltipWrapper.offsetHeight - 10 + "px";
      } else if ((window.innerHeight - elem_props.top) > (tooltipWrapper.offsetHeight)) {
          tooltipWrapper.style.top = elem_props.top + top + 35 + "px";
      }

      if ((elem_props.left + (elem_props.width / 2)) < (tooltipWrapper.offsetWidth / 2)) {
          tooltipWrapper.style.left = "10px";
      } else if ((document.body.clientWidth - elem_props.left - (elem_props.width / 2)) < (tooltipWrapper.offsetWidth / 2)) {
          tooltipWrapper.style.left = document.body.clientWidth - tooltipWrapper.offsetWidth - 20 + "px";
      }
    }
  }

  function setupListeners(linkElement) {
    linkElement.addEventListener('mouseleave', function(_event) {
      hideTooltip();
    });

    tooltipWrapper.addEventListener('mouseleave', function(_event) {
      hideTooltip();
    });

    linkElement.addEventListener('touchend', function(_event) {
      hideTooltip();
    });

    tooltipWrapper.addEventListener('touchend', function(_event) {
      hideTooltip();
    });

    linkElement.addEventListener('mouseenter', function(event) {
      clearTimeout(opacityTimeout);
      clearTimeout(contentTimeout);
      showTooltip(event);
    });

    tooltipWrapper.addEventListener('mouseenter', function(event) {
      clearTimeout(opacityTimeout);
      clearTimeout(contentTimeout);
    });
  }

  document.querySelectorAll('{{ include.wrapperQuerySelector }} a').forEach(setupListeners);
</script>