text: /*
   * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
   * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
   * Copyright (c) 2021, Luke Wilde <lukew@serenityos.org>
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #include <AK/IDAllocator.h>
  #include <AK/StringBuilder.h>
  #include <LibJS/AST.h>
  #include <LibJS/Runtime/FunctionObject.h>
  #include <LibWeb/Bindings/EventWrapper.h>
  #include <LibWeb/Bindings/NodeWrapper.h>
  #include <LibWeb/Bindings/NodeWrapperFactory.h>
  #include <LibWeb/DOM/Comment.h>
  #include <LibWeb/DOM/DocumentType.h>
  #include <LibWeb/DOM/Element.h>
  #include <LibWeb/DOM/ElementFactory.h>
  #include <LibWeb/DOM/Event.h>
  #include <LibWeb/DOM/EventDispatcher.h>
  #include <LibWeb/DOM/IDLEventListener.h>
  #include <LibWeb/DOM/LiveNodeList.h>
  #include <LibWeb/DOM/Node.h>
  #include <LibWeb/DOM/ProcessingInstruction.h>
  #include <LibWeb/DOM/ShadowRoot.h>
  #include <LibWeb/HTML/BrowsingContextContainer.h>
  #include <LibWeb/HTML/HTMLAnchorElement.h>
  #include <LibWeb/HTML/Parser/HTMLParser.h>
  #include <LibWeb/Layout/InitialContainingBlock.h>
  #include <LibWeb/Layout/Node.h>
  #include <LibWeb/Layout/TextNode.h>
  #include <LibWeb/Origin.h>
  
  namespace Web::DOM {
  
  static IDAllocator s_node_id_allocator;
  static HashMap<i32, Node*> s_node_directory;
  
  static i32 allocate_node_id(Node* node)
  {
      i32 id = s_node_id_allocator.allocate();
      s_node_directory.set(id, node);
      return id;
  }
  
  static void deallocate_node_id(i32 node_id)
  {
      if (!s_node_directory.remove(node_id))
          VERIFY_NOT_REACHED();
      s_node_id_allocator.deallocate(node_id);
  }
  
  Node* Node::from_id(i32 node_id)
  {
      return s_node_directory.get(node_id).value_or(nullptr);
  }
  
  Node::Node(Document& document, NodeType type)
      : EventTarget()
      , m_document(&document)
      , m_type(type)
      , m_id(allocate_node_id(this))
  {
      if (!is_document())
          m_document->ref_from_node({});
  }
  
  Node::~Node()
  {
      VERIFY(m_deletion_has_begun);
      if (layout_node() && layout_node()->parent())
          layout_node()->parent()->remove_child(*layout_node());
  
      if (!is_document())
          m_document->unref_from_node({});
  
      deallocate_node_id(m_id);
  }
  
  const HTML::HTMLAnchorElement* Node::enclosing_link_element() const
  {
      for (auto* node = this; node; node = node->parent()) {
          if (is<HTML::HTMLAnchorElement>(*node) && verify_cast<HTML::HTMLAnchorElement>(*node).has_attribute(HTML::AttributeNames::href))
              return verify_cast<HTML::HTMLAnchorElement>(node);
      }
      return nullptr;
  }
  
  const HTML::HTMLElement* Node::enclosing_html_element() const
  {
      return first_ancestor_of_type<HTML::HTMLElement>();
  }
  
  const HTML::HTMLElement* Node::enclosing_html_element_with_attribute(const FlyString& attribute) const
  {
      for (auto* node = this; node; node = node->parent()) {
          if (is<HTML::HTMLElement>(*node) && verify_cast<HTML::HTMLElement>(*node).has_attribute(attribute))
              return verify_cast<HTML::HTMLElement>(node);
      }
      return nullptr;
  }
  
  // https://dom.spec.whatwg.org/#concept-descendant-text-content
  String Node::descendant_text_content() const
  {
      StringBuilder builder;
      for_each_in_subtree_of_type<Text>([&](auto& text_node) {
          builder.append(text_node.data());
          return IterationDecision::Continue;
      });
      return builder.to_string();
  }
  
  // https://dom.spec.whatwg.org/#dom-node-textcontent
  String Node::text_content() const
  {
      if (is<DocumentFragment>(this) || is<Element>(this))
          return descendant_text_content();
      else if (is<CharacterData>(this))
          return verify_cast<CharacterData>(this)->data();
  
      // FIXME: Else if this is an Attr node, return this's value.
  
      return {};
  }
  
  // https://dom.spec.whatwg.org/#ref-for-dom-node-textcontent%E2%91%A0
  void Node::set_text_content(String const& content)
  {
      if (is<DocumentFragment>(this) || is<Element>(this)) {
          string_replace_all(content);
      } else if (is<CharacterData>(this)) {
          // FIXME: CharacterData::set_data is not spec compliant. Make this match the spec when set_data becomes spec compliant.
          //        Do note that this will make this function able to throw an exception.
  
          auto* character_data_node = verify_cast<CharacterData>(this);
          character_data_node->set_data(content);
      } else {
          // FIXME: Else if this is an Attr node, set an existing attribute value with this and the given value.
  
          return;
      }
  
      set_needs_style_update(true);
  }
  
  void Node::invalidate_style()
  {
      for_each_in_inclusive_subtree_of_type<Element>([&](auto& element) {
          element.set_needs_style_update(true);
          return IterationDecision::Continue;
      });
      document().schedule_style_update();
  }
  
  bool Node::is_link() const
  {
      return enclosing_link_element();
  }
  
  String Node::child_text_content() const
  {
      if (!is<ParentNode>(*this))
          return String::empty();
  
      StringBuilder builder;
      verify_cast<ParentNode>(*this).for_each_child([&](auto& child) {
          if (is<Text>(child))
              builder.append(verify_cast<Text>(child).text_content());
      });
      return builder.build();
  }
  
  // https://dom.spec.whatwg.org/#concept-tree-root
  Node& Node::root()
  {
      Node* root = this;
      while (root->parent())
          root = root->parent();
      return *root;
  }
  
  // https://dom.spec.whatwg.org/#concept-shadow-including-root
  Node& Node::shadow_including_root()
  {
      auto& node_root = root();
      if (is<ShadowRoot>(node_root))
          return verify_cast<ShadowRoot>(node_root).host()->shadow_including_root();
      return node_root;
  }
  
  // https://dom.spec.whatwg.org/#connected
  bool Node::is_connected() const
  {
      return shadow_including_root().is_document();
  }
  
  Element* Node::parent_element()
  {
      if (!parent() || !is<Element>(parent()))
          return nullptr;
      return verify_cast<Element>(parent());
  }
  
  const Element* Node::parent_element() const
  {
      if (!parent() || !is<Element>(parent()))
          return nullptr;
      return verify_cast<Element>(parent());
  }
  
  // https://dom.spec.whatwg.org/#concept-node-ensure-pre-insertion-validity
  ExceptionOr<void> Node::ensure_pre_insertion_validity(NonnullRefPtr<Node> node, RefPtr<Node> child) const
  {
      if (!is<Document>(this) && !is<DocumentFragment>(this) && !is<Element>(this))
          return DOM::HierarchyRequestError::create("Can only insert into a document, document fragment or element");
  
      if (node->is_host_including_inclusive_ancestor_of(*this))
          return DOM::HierarchyRequestError::create("New node is an ancestor of this node");
  
      if (child && child->parent() != this)
          return DOM::NotFoundError::create("This node is not the parent of the given child");
  
      // FIXME: All the following "Invalid node type for insertion" messages could be more descriptive.
  
      if (!is<DocumentFragment>(*node) && !is<DocumentType>(*node) && !is<Element>(*node) && !is<Text>(*node) && !is<Comment>(*node) && !is<ProcessingInstruction>(*node))
          return DOM::HierarchyRequestError::create("Invalid node type for insertion");
  
      if ((is<Text>(*node) && is<Document>(this)) || (is<DocumentType>(*node) && !is<Document>(this)))
          return DOM::HierarchyRequestError::create("Invalid node type for insertion");
  
      if (is<Document>(this)) {
          if (is<DocumentFragment>(*node)) {
              auto node_element_child_count = verify_cast<DocumentFragment>(*node).child_element_count();
              if ((node_element_child_count > 1 || node->has_child_of_type<Text>())
                  || (node_element_child_count == 1 && (has_child_of_type<Element>() || is<DocumentType>(child.ptr()) || (child && child->has_following_node_of_type_in_tree_order<DocumentType>())))) {
                  return DOM::HierarchyRequestError::create("Invalid node type for insertion");
              }
          } else if (is<Element>(*node)) {
              if (has_child_of_type<Element>() || is<DocumentType>(child.ptr()) || (child && child->has_following_node_of_type_in_tree_order<DocumentType>()))
                  return DOM::HierarchyRequestError::create("Invalid node type for insertion");
          } else if (is<DocumentType>(*node)) {
              if (has_child_of_type<DocumentType>() || (child && child->has_preceding_node_of_type_in_tree_order<Element>()) || (!child && has_child_of_type<Element>()))
                  return DOM::HierarchyRequestError::create("Invalid node type for insertion");
          }
      }
  
      return {};
  }
  
  // https://dom.spec.whatwg.org/#concept-node-insert
  void Node::insert_before(NonnullRefPtr<Node> node, RefPtr<Node> child, bool suppress_observers)
  {
      NonnullRefPtrVector<Node> nodes;
      if (is<DocumentFragment>(*node))
          nodes = verify_cast<DocumentFragment>(*node).children_as_vector();
      else
          nodes.append(node);
  
      auto count = nodes.size();
      if (count == 0)
          return;
  
      if (is<DocumentFragment>(*node)) {
          node->remove_all_children(true);
          // FIXME: Queue a tree mutation record for node with « », nodes, null, and null.
      }
  
      if (child) {
          // FIXME: For each live range whose start node is parent and start offset is greater than child’s index, increase its start offset by count.
          // FIXME: For each live range whose end node is parent and end offset is greater than child’s index, increase its end offset by count.
      }
  
      // FIXME: Let previousSibling be child’s previous sibling or parent’s last child if child is null. (Currently unused so not included)
  
      for (auto& node_to_insert : nodes) { // FIXME: In tree order
          document().adopt_node(node_to_insert);
  
          if (!child)
              TreeNode<Node>::append_child(node_to_insert);
          else
              TreeNode<Node>::insert_before(node_to_insert, child);
  
          // FIXME: If parent is a shadow host and node is a slottable, then assign a slot for node.
          // FIXME: If parent’s root is a shadow root, and parent is a slot whose assigned nodes is the empty list, then run signal a slot change for parent.
          // FIXME: Run assign slottables for a tree with node’s root.
  
          // FIXME: This should be shadow-including.
          node_to_insert.for_each_in_inclusive_subtree([&](Node& inclusive_descendant) {
              inclusive_descendant.inserted();
              if (inclusive_descendant.is_connected()) {
                  // FIXME: If inclusiveDescendant is custom, then enqueue a custom element callback reaction with inclusiveDescendant,
                  //        callback name "connectedCallback", and an empty argument list.
  
                  // FIXME: Otherwise, try to upgrade inclusiveDescendant.
              }
  
              return IterationDecision::Continue;
          });
      }
  
      if (!suppress_observers) {
          // FIXME: queue a tree mutation record for parent with nodes, « », previousSibling, and child.
      }
  
      children_changed();
  }
  
  // https://dom.spec.whatwg.org/#concept-node-pre-insert
  ExceptionOr<NonnullRefPtr<Node>> Node::pre_insert(NonnullRefPtr<Node> node, RefPtr<Node> child)
  {
      auto validity_result = ensure_pre_insertion_validity(node, child);
      if (validity_result.is_exception())
          return validity_result.exception();
  
      auto reference_child = child;
      if (reference_child == node)
          reference_child = node->next_sibling();
  
      insert_before(node, reference_child);
      return node;
  }
  
  // https://dom.spec.whatwg.org/#concept-node-pre-remove
  ExceptionOr<NonnullRefPtr<Node>> Node::pre_remove(NonnullRefPtr<Node> child)
  {
      if (child->parent() != this)
          return DOM::NotFoundError::create("Child does not belong to this node");
  
      child->remove();
  
      return child;
  }
  
  // https://dom.spec.whatwg.org/#concept-node-append
  ExceptionOr<NonnullRefPtr<Node>> Node::append_child(NonnullRefPtr<Node> node)
  {
      return pre_insert(node, nullptr);
  }
  
  // https://dom.spec.whatwg.org/#concept-node-remove
  void Node::remove(bool suppress_observers)
  {
      auto* parent = TreeNode<Node>::parent();
      VERIFY(parent);
  
      // FIXME: Let index be node’s index. (Currently unused so not included)
  
      // FIXME: For each live range whose start node is an inclusive descendant of node, set its start to (parent, index).
      // FIXME: For each live range whose end node is an inclusive descendant of node, set its end to (parent, index).
      // FIXME: For each live range whose start node is parent and start offset is greater than index, decrease its start offset by 1.
      // FIXME: For each live range whose end node is parent and end offset is greater than index, decrease its end offset by 1.
  
      // FIXME: For each NodeIterator object iterator whose root’s node document is node’s node document, run the NodeIterator pre-removing steps given node and iterator.
  
      // FIXME: Let oldPreviousSibling be node’s previous sibling. (Currently unused so not included)
      // FIXME: Let oldNextSibling be node’s next sibling. (Currently unused so not included)
  
      parent->remove_child(*this);
  
      // FIXME: If node is assigned, then run assign slottables for node’s assigned slot.
  
      // FIXME: If parent’s root is a shadow root, and parent is a slot whose assigned nodes is the empty list, then run signal a slot change for parent.
  
      // FIXME: If node has an inclusive descendant that is a slot, then:
      //          Run assign slottables for a tree with parent’s root.
      //          Run assign slottables for a tree with node.
  
      removed_from(parent);
  
      // FIXME: Let isParentConnected be parent’s connected. (Currently unused so not included)
  
      // FIXME: If node is custom and isParentConnected is true, then enqueue a custom element callback reaction with node,
      //        callback name "disconnectedCallback", and an empty argument list.
  
      // FIXME: This should be shadow-including.
      for_each_in_subtree([&](Node& descendant) {
          descendant.removed_from(nullptr);
  
          // FIXME: If descendant is custom and isParentConnected is true, then enqueue a custom element callback reaction with descendant,
          //        callback name "disconnectedCallback", and an empty argument list.
  
          return IterationDecision::Continue;
      });
  
      if (!suppress_observers) {
          // FIXME: queue a tree mutation record for parent with « », « node », oldPreviousSibling, and oldNextSibling.
      }
  
      parent->children_changed();
  }
  
  // https://dom.spec.whatwg.org/#concept-node-replace
  ExceptionOr<NonnullRefPtr<Node>> Node::replace_child(NonnullRefPtr<Node> node, NonnullRefPtr<Node> child)
  {
      // NOTE: This differs slightly from ensure_pre_insertion_validity.
      if (!is<Document>(this) && !is<DocumentFragment>(this) && !is<Element>(this))
          return DOM::HierarchyRequestError::create("Can only insert into a document, document fragment or element");
  
      if (node->is_host_including_inclusive_ancestor_of(*this))
          return DOM::HierarchyRequestError::create("New node is an ancestor of this node");
  
      if (child->parent() != this)
          return DOM::NotFoundError::create("This node is not the parent of the given child");
  
      // FIXME: All the following "Invalid node type for insertion" messages could be more descriptive.
  
      if (!is<DocumentFragment>(*node) && !is<DocumentType>(*node) && !is<Element>(*node) && !is<Text>(*node) && !is<Comment>(*node) && !is<ProcessingInstruction>(*node))
          return DOM::HierarchyRequestError::create("Invalid node type for insertion");
  
      if ((is<Text>(*node) && is<Document>(this)) || (is<DocumentType>(*node) && !is<Document>(this)))
          return DOM::HierarchyRequestError::create("Invalid node type for insertion");
  
      if (is<Document>(this)) {
          if (is<DocumentFragment>(*node)) {
              auto node_element_child_count = verify_cast<DocumentFragment>(*node).child_element_count();
              if ((node_element_child_count > 1 || node->has_child_of_type<Text>())
                  || (node_element_child_count == 1 && (first_child_of_type<Element>() != child || child->has_following_node_of_type_in_tree_order<DocumentType>()))) {
                  return DOM::HierarchyRequestError::create("Invalid node type for insertion");
              }
          } else if (is<Element>(*node)) {
              if (first_child_of_type<Element>() != child || child->has_following_node_of_type_in_tree_order<DocumentType>())
                  return DOM::HierarchyRequestError::create("Invalid node type for insertion");
          } else if (is<DocumentType>(*node)) {
              if (first_child_of_type<DocumentType>() != node || child->has_preceding_node_of_type_in_tree_order<Element>())
                  return DOM::HierarchyRequestError::create("Invalid node type for insertion");
          }
      }
  
      auto reference_child = child->next_sibling();
      if (reference_child == node)
          reference_child = node->next_sibling();
  
      // FIXME: Let previousSibling be child’s previous sibling. (Currently unused so not included)
      // FIXME: Let removedNodes be the empty set. (Currently unused so not included)
  
      if (child->parent()) {
          // FIXME: Set removedNodes to « child ».
          child->remove(true);
      }
  
      // FIXME: Let nodes be node’s children if node is a DocumentFragment node; otherwise « node ». (Currently unused so not included)
  
      insert_before(node, reference_child, true);
  
      // FIXME: Queue a tree mutation record for parent with nodes, removedNodes, previousSibling, and referenceChild.
  
      return child;
  }
  
  // https://dom.spec.whatwg.org/#concept-node-clone
  NonnullRefPtr<Node> Node::clone_node(Document* document, bool clone_children)
  {
      if (!document)
          document = m_document;
      RefPtr<Node> copy;
      if (is<Element>(this)) {
          auto& element = *verify_cast<Element>(this);
          auto element_copy = DOM::create_element(*document, element.local_name(), element.namespace_() /* FIXME: node’s namespace prefix, and node’s is value, with the synchronous custom elements flag unset */);
          element.for_each_attribute([&](auto& name, auto& value) {
              element_copy->set_attribute(name, value);
          });
          copy = move(element_copy);
      } else if (is<Document>(this)) {
          auto document_ = verify_cast<Document>(this);
          auto document_copy = Document::create(document_->url());
          document_copy->set_encoding(document_->encoding());
          document_copy->set_content_type(document_->content_type());
          document_copy->set_origin(document_->origin());
          document_copy->set_quirks_mode(document_->mode());
          // FIXME: Set type ("xml" or "html")
          copy = move(document_copy);
      } else if (is<DocumentType>(this)) {
          auto document_type = verify_cast<DocumentType>(this);
          auto document_type_copy = adopt_ref(*new DocumentType(*document));
          document_type_copy->set_name(document_type->name());
          document_type_copy->set_public_id(document_type->public_id());
          document_type_copy->set_system_id(document_type->system_id());
          copy = move(document_type_copy);
      } else if (is<Text>(this)) {
          auto text = verify_cast<Text>(this);
          auto text_copy = adopt_ref(*new Text(*document, text->data()));
          copy = move(text_copy);
      } else if (is<Comment>(this)) {
          auto comment = verify_cast<Comment>(this);
          auto comment_copy = adopt_ref(*new Comment(*document, comment->data()));
          copy = move(comment_copy);
      } else if (is<ProcessingInstruction>(this)) {
          auto processing_instruction = verify_cast<ProcessingInstruction>(this);
          auto processing_instruction_copy = adopt_ref(*new ProcessingInstruction(*document, processing_instruction->data(), processing_instruction->target()));
          copy = move(processing_instruction_copy);
      } else if (is<DocumentFragment>(this)) {
          auto document_fragment_copy = adopt_ref(*new DocumentFragment(*document));
          copy = move(document_fragment_copy);
      } else {
          dbgln("clone_node() not implemented for NodeType {}", (u16)m_type);
          TODO();
      }
      // FIXME: 4. Set copy’s node document and document to copy, if copy is a document, and set copy’s node document to document otherwise.
  
      cloned(*copy, clone_children);
  
      if (clone_children) {
          for_each_child([&](auto& child) {
              copy->append_child(child.clone_node(document, true));
          });
      }
      return copy.release_nonnull();
  }
  
  // https://dom.spec.whatwg.org/#dom-node-clonenode
  ExceptionOr<NonnullRefPtr<Node>> Node::clone_node_binding(bool deep)
  {
      if (is<ShadowRoot>(*this))
          return NotSupportedError::create("Cannot clone shadow root");
      return clone_node(nullptr, deep);
  }
  
  void Node::set_document(Badge<Document>, Document& document)
  {
      if (m_document == &document)
          return;
  
      document.ref_from_node({});
      m_document->unref_from_node({});
      m_document = &document;
  
      if (needs_style_update() || child_needs_style_update()) {
          // NOTE: We unset and reset the "needs style update" flag here.
          //       This ensures that there's a pending style update in the new document
          //       that will eventually assign some style to this node if needed.
          set_needs_style_update(false);
          set_needs_style_update(true);
      }
  }
  
  bool Node::is_editable() const
  {
      return parent() && parent()->is_editable();
  }
  
  JS::Object* Node::create_wrapper(JS::GlobalObject& global_object)
  {
      return wrap(global_object, *this);
  }
  
  void Node::removed_last_ref()
  {
      if (is<Document>(*this)) {
          verify_cast<Document>(*this).removed_last_ref();
          return;
      }
      m_deletion_has_begun = true;
      delete this;
  }
  
  void Node::set_layout_node(Badge<Layout::Node>, Layout::Node* layout_node) const
  {
      if (layout_node)
          m_layout_node = layout_node->make_weak_ptr();
      else
          m_layout_node = nullptr;
  }
  
  EventTarget* Node::get_parent(const Event&)
  {
      // FIXME: returns the node’s assigned slot, if node is assigned, and node’s parent otherwise.
      return parent();
  }
  
  void Node::set_needs_style_update(bool value)
  {
      if (m_needs_style_update == value)
          return;
      m_needs_style_update = value;
  
      if (m_needs_style_update) {
          for (auto* ancestor = parent(); ancestor; ancestor = ancestor->parent()) {
              ancestor->m_child_needs_style_update = true;
          }
          document().schedule_style_update();
      }
  }
  
  void Node::inserted()
  {
      set_needs_style_update(true);
  }
  
  ParentNode* Node::parent_or_shadow_host()
  {
      if (is<ShadowRoot>(*this))
          return verify_cast<ShadowRoot>(*this).host();
      return verify_cast<ParentNode>(parent());
  }
  
  NonnullRefPtr<NodeList> Node::child_nodes()
  {
      // FIXME: This should return the same LiveNodeList object every time,
      //        but that would cause a reference cycle since NodeList refs the root.
      return LiveNodeList::create(*this, [this](auto& node) {
          return is_parent_of(node);
      });
  }
  
  NonnullRefPtrVector<Node> Node::children_as_vector() const
  {
      NonnullRefPtrVector<Node> nodes;
  
      for_each_child([&](auto& child) {
          nodes.append(child);
      });
  
      return nodes;
  }
  
  void Node::remove_all_children(bool suppress_observers)
  {
      while (RefPtr<Node> child = first_child())
          child->remove(suppress_observers);
  }
  
  // https://dom.spec.whatwg.org/#dom-node-comparedocumentposition
  u16 Node::compare_document_position(RefPtr<Node> other)
  {
      enum Position : u16 {
          DOCUMENT_POSITION_EQUAL = 0,
          DOCUMENT_POSITION_DISCONNECTED = 1,
          DOCUMENT_POSITION_PRECEDING = 2,
          DOCUMENT_POSITION_FOLLOWING = 4,
          DOCUMENT_POSITION_CONTAINS = 8,
          DOCUMENT_POSITION_CONTAINED_BY = 16,
          DOCUMENT_POSITION_IMPLEMENTATION_SPECIFIC = 32,
      };
  
      if (this == other)
          return DOCUMENT_POSITION_EQUAL;
  
      Node* node1 = other.ptr();
      Node* node2 = this;
  
      // FIXME: Once LibWeb supports attribute nodes fix to follow the specification.
      VERIFY(node1->type() != NodeType::ATTRIBUTE_NODE && node2->type() != NodeType::ATTRIBUTE_NODE);
  
      if ((node1 == nullptr || node2 == nullptr) || (&node1->root() != &node2->root()))
          return DOCUMENT_POSITION_DISCONNECTED | DOCUMENT_POSITION_IMPLEMENTATION_SPECIFIC | (node1 > node2 ? DOCUMENT_POSITION_PRECEDING : DOCUMENT_POSITION_FOLLOWING);
  
      if (node1->is_ancestor_of(*node2))
          return DOCUMENT_POSITION_CONTAINS | DOCUMENT_POSITION_PRECEDING;
  
      if (node2->is_ancestor_of(*node1))
          return DOCUMENT_POSITION_CONTAINED_BY | DOCUMENT_POSITION_FOLLOWING;
  
      if (node1->is_before(*node2))
          return DOCUMENT_POSITION_PRECEDING;
      else
          return DOCUMENT_POSITION_FOLLOWING;
  }
  
  // https://dom.spec.whatwg.org/#concept-tree-host-including-inclusive-ancestor
  bool Node::is_host_including_inclusive_ancestor_of(const Node& other) const
  {
      return is_inclusive_ancestor_of(other) || (is<DocumentFragment>(other.root()) && verify_cast<DocumentFragment>(other.root()).host() && is_inclusive_ancestor_of(*verify_cast<DocumentFragment>(other.root()).host().ptr()));
  }
  
  // https://dom.spec.whatwg.org/#dom-node-ownerdocument
  RefPtr<Document> Node::owner_document() const
  {
      if (is_document())
          return nullptr;
      return m_document;
  }
  
  // This function tells us whether a node is interesting enough to show up
  // in the DOM inspector. This hides two things:
  // - Non-rendered whitespace
  // - Rendered whitespace between block-level elements
  bool Node::is_uninteresting_whitespace_node() const
  {
      if (!is<Text>(*this))
          return false;
      if (!static_cast<Text const&>(*this).data().is_whitespace())
          return false;
      if (!layout_node())
          return true;
      if (layout_node()->parent()->is_anonymous())
          return true;
      return false;
  }
  
  void Node::serialize_tree_as_json(JsonObjectSerializer<StringBuilder>& object) const
  {
      object.add("name", node_name().view());
      object.add("id", id());
      if (is_document()) {
          object.add("type", "document");
      } else if (is_element()) {
          object.add("type", "element");
  
          auto const* element = static_cast<DOM::Element const*>(this);
          if (element->has_attributes()) {
              auto attributes = object.add_object("attributes");
              element->for_each_attribute([&attributes](auto& name, auto& value) {
                  attributes.add(name, value);
              });
          }
  
          if (element->is_browsing_context_container()) {
              auto const* container = static_cast<HTML::BrowsingContextContainer const*>(element);
              if (auto const* content_document = container->content_document()) {
                  auto children = object.add_array("children");
                  JsonObjectSerializer<StringBuilder> content_document_object = children.add_object();
                  content_document->serialize_tree_as_json(content_document_object);
              }
          }
      } else if (is_text()) {
          object.add("type", "text");
  
          auto text_node = static_cast<DOM::Text const*>(this);
          object.add("text", text_node->data());
      } else if (is_comment()) {
          object.add("type"sv, "comment"sv);
          object.add("data"sv, static_cast<DOM::Comment const&>(*this).data());
      }
  
      if (has_child_nodes()) {
          auto children = object.add_array("children");
          for_each_child([&children](DOM::Node& child) {
              if (child.is_uninteresting_whitespace_node())
                  return;
              JsonObjectSerializer<StringBuilder> child_object = children.add_object();
              child.serialize_tree_as_json(child_object);
          });
      }
  }
  
  // https://html.spec.whatwg.org/multipage/webappapis.html#concept-n-noscript
  bool Node::is_scripting_disabled() const
  {
      // FIXME: or when scripting is disabled for its relevant settings object.
      return !document().browsing_context();
  }
  
  // https://dom.spec.whatwg.org/#dom-node-contains
  bool Node::contains(RefPtr<Node> other) const
  {
      return other && other->is_inclusive_descendant_of(*this);
  }
  
  // https://dom.spec.whatwg.org/#concept-shadow-including-descendant
  bool Node::is_shadow_including_descendant_of(Node const& other) const
  {
      if (is_descendant_of(other))
          return true;
  
      if (!is<ShadowRoot>(root()))
          return false;
  
      auto& shadow_root = verify_cast<ShadowRoot>(root());
  
      // NOTE: While host is nullable because of inheriting from DocumentFragment, shadow roots always have a host.
      return shadow_root.host()->is_shadow_including_inclusive_descendant_of(other);
  }
  
  // https://dom.spec.whatwg.org/#concept-shadow-including-inclusive-descendant
  bool Node::is_shadow_including_inclusive_descendant_of(Node const& other) const
  {
      return &other == this || is_shadow_including_descendant_of(other);
  }
  
  // https://dom.spec.whatwg.org/#concept-shadow-including-ancestor
  bool Node::is_shadow_including_ancestor_of(Node const& other) const
  {
      return other.is_shadow_including_descendant_of(*this);
  }
  
  // https://dom.spec.whatwg.org/#concept-shadow-including-inclusive-ancestor
  bool Node::is_shadow_including_inclusive_ancestor_of(Node const& other) const
  {
      return other.is_shadow_including_inclusive_descendant_of(*this);
  }
  
  // https://dom.spec.whatwg.org/#concept-node-replace-all
  void Node::replace_all(RefPtr<Node> node)
  {
      // FIXME: Let removedNodes be parent’s children. (Current unused so not included)
      // FIXME: Let addedNodes be the empty set. (Currently unused so not included)
      // FIXME: If node is a DocumentFragment node, then set addedNodes to node’s children.
      // FIXME: Otherwise, if node is non-null, set addedNodes to « node ».
  
      remove_all_children(true);
  
      if (node)
          insert_before(*node, nullptr, true);
  
      // FIXME: If either addedNodes or removedNodes is not empty, then queue a tree mutation record for parent with addedNodes, removedNodes, null, and null.
  }
  
  // https://dom.spec.whatwg.org/#string-replace-all
  void Node::string_replace_all(String const& string)
  {
      RefPtr<Node> node;
  
      if (!string.is_empty())
          node = make_ref_counted<Text>(document(), string);
  
      replace_all(node);
  }
  
  // https://w3c.github.io/DOM-Parsing/#dfn-fragment-serializing-algorithm
  String Node::serialize_fragment(/* FIXME: Requires well-formed flag */) const
  {
      // FIXME: Let context document be the value of node's node document.
  
      // FIXME: If context document is an HTML document, return an HTML serialization of node.
      //        (We currently always do this)
      return HTML::HTMLParser::serialize_html_fragment(*this);
  
      // FIXME: Otherwise, context document is an XML document; return an XML serialization of node passing the flag require well-formed.
  }
  
  // https://dom.spec.whatwg.org/#dom-node-issamenode
  bool Node::is_same_node(Node const* other_node) const
  {
      return this == other_node;
  }
  
  // https://dom.spec.whatwg.org/#dom-node-isequalnode
  bool Node::is_equal_node(Node const* other_node) const
  {
      // The isEqualNode(otherNode) method steps are to return true if otherNode is non-null and this equals otherNode; otherwise false.
      if (!other_node)
          return false;
  
      // Fast path for testing a node against itself.
      if (this == other_node)
          return true;
  
      // A node A equals a node B if all of the following conditions are true:
  
      // A and B implement the same interfaces.
      if (node_name() != other_node->node_name())
          return false;
  
      // The following are equal, switching on the interface A implements:
      switch (node_type()) {
      case (u16)NodeType::DOCUMENT_TYPE_NODE: {
          // Its name, public ID, and system ID.
          auto& this_doctype = verify_cast<DocumentType>(*this);
          auto& other_doctype = verify_cast<DocumentType>(*other_node);
          if (this_doctype.name() != other_doctype.name()
              || this_doctype.public_id() != other_doctype.public_id()
              || this_doctype.system_id() != other_doctype.system_id())
              return false;
          break;
      }
      case (u16)NodeType::ELEMENT_NODE: {
          // Its namespace, namespace prefix, local name, and its attribute list’s size.
          auto& this_element = verify_cast<Element>(*this);
          auto& other_element = verify_cast<Element>(*other_node);
          if (this_element.namespace_() != other_element.namespace_()
              || this_element.prefix() != other_element.prefix()
              || this_element.local_name() != other_element.local_name()
              || this_element.attribute_list_size() != other_element.attribute_list_size())
              return false;
          // If A is an element, each attribute in its attribute list has an attribute that equals an attribute in B’s attribute list.
          bool has_same_attributes = true;
          this_element.for_each_attribute([&](auto& name, auto& value) {
              if (other_element.get_attribute(name) != value)
                  has_same_attributes = false;
          });
          if (!has_same_attributes)
              return false;
          break;
      }
      case (u16)NodeType::COMMENT_NODE:
      case (u16)NodeType::TEXT_NODE: {
          // Its data.
          auto& this_cdata = verify_cast<CharacterData>(*this);
          auto& other_cdata = verify_cast<CharacterData>(*other_node);
          if (this_cdata.data() != other_cdata.data())
              return false;
          break;
      }
      case (u16)NodeType::PROCESSING_INSTRUCTION_NODE:
      case (u16)NodeType::ATTRIBUTE_NODE:
          TODO();
      default:
          break;
      }
  
      // A and B have the same number of children.
      size_t this_child_count = child_count();
      size_t other_child_count = other_node->child_count();
      if (this_child_count != other_child_count)
          return false;
  
      // Each child of A equals the child of B at the identical index.
      // FIXME: This can be made nicer. child_at_index() is O(n).
      for (size_t i = 0; i < this_child_count; ++i) {
          auto* this_child = child_at_index(i);
          auto* other_child = other_node->child_at_index(i);
          VERIFY(this_child);
          VERIFY(other_child);
          if (!this_child->is_equal_node(other_child))
              return false;
      }
  
      return true;
  }
  
  // https://dom.spec.whatwg.org/#in-a-document-tree
  bool Node::in_a_document_tree() const
  {
      // An element is in a document tree if its root is a document.
      return root().is_document();
  }
  
  // https://dom.spec.whatwg.org/#dom-node-getrootnode
  NonnullRefPtr<Node> Node::get_root_node(GetRootNodeOptions const& options)
  {
      // The getRootNode(options) method steps are to return this’s shadow-including root if options["composed"] is true; otherwise this’s root.
      if (options.composed)
          return shadow_including_root();
  
      return root();
  }
  
  }
  