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

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

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(node) {
  if (node.localName === 'template')
    return node.content.firstChild;
  return node.firstChild;
}

function getLastChild(node) {
  if (node.localName === 'template')
    return node.content.lastChild;
  return node.lastChild;
}

function serializeChildren(node, depth) {
  var buffer = '';
  var firstChild = getFirstChild(node);
  var lastChild = getLastChild(node);
  if (firstChild instanceof Element && depth)
    buffer += '\n' + kIndent.repeat(depth);
  for (var child = firstChild; child; child = child.nextSibling) {
    buffer += serializeNode(child, depth);
    if (child instanceof Element && child.nextSibling instanceof Element)
      buffer += '\n' + kIndent.repeat(depth);
  }
  if (lastChild instanceof Element) {
    buffer += '\n';
    if (depth)
      buffer += kIndent.repeat(depth - 1);
  }
  return buffer;
}

function serializeElement(element, depth) {
  var buffer = '<' + element.tagName + serializeAttributes(element) + '>';
  buffer += serializeChildren(element, depth + 1);
  buffer += '</' + element.tagName + '>';
  return buffer;
}

function serializeText(node) {
  var parent = node.parentNode;
  if (parent && (parent.tagName == 'script' || parent.tagName == 'style'))
    return node.data;
  return escapeText(node.data, kTextEscapePattern);
}

function serializeNode(node, depth) {
  if (node instanceof Text)
    return serializeText(node);
  if (node instanceof Element)
    return serializeElement(node, depth || 0);
  if (node instanceof Document || node instanceof ShadowRoot)
    return serializeChildren(node, depth || 0);
  throw new Error('Cannot serialize node');
}

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