<script>
const kEntityMap = new Map([
  ['\u00a0', '&nbsp;'],
  ['&', '&amp;'],
  ['<', '&lt;'],
  ['>', '&gt;'],
  ['"', '&quot;'],
]);

const kTextEscapePattern = /&|<|>|"|\u00a0/g;
const kAttributeEscapePattern = /&|>|"|\u00a0/g;

function escapeText(value, pattern) {
  return (value || '').replace(pattern, function(match) {
    return kEntityMap.get(match);
  });
}

function serializeAttributes(element) {
  var buffer = "";
  var attributes = element.getAttributes();

  for (var i = 0; i < attributes.length; ++i) {
    var attribute = attributes[i];
    buffer += ' ';
    buffer += attribute.name;
    buffer += '="';
    buffer += escapeText(attribute.value, kAttributeEscapePattern);
    buffer += '"';
  }

  return buffer;
}

function getFirstChild(element) {
  if (element.tagName === 'template')
    return element.content.firstChild;
  return element.firstChild;
}

function serializeElementChildren(element) {
  if (element.tagName == "script" || element.tagName == "style")
    return element.textContent;
  return serializeChildren(getFirstChild(element));
}

function serializeChildren(firstChild) {
  var buffer = "";
  for (var child = firstChild; child; child = child.nextSibling)
    buffer += serializeNode(child);
  return buffer;
}

function serializeElement(element) {
  var buffer = '<' + element.tagName + serializeAttributes(element) + '>';
  buffer += serializeElementChildren(element);
  buffer += '</' + element.tagName + '>';
  return buffer;
}

function serializeNode(node) {
  if (node instanceof Text)
    return escapeText(node.data, kTextEscapePattern);
  if (node instanceof Element)
    return serializeElement(node);
  if (node instanceof Document || node instanceof ShadowRoot)
    return serializeChildren(node.firstChild);
  throw new Error("Cannot serialize node");
}

module.exports = {
  serializeNode: serializeNode,
};
</script>