/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "ContentIterator.h"

#include "mozilla/Assertions.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/RangeBoundary.h"
#include "mozilla/RangeUtils.h"
#include "mozilla/Result.h"
#include "mozilla/dom/HTMLSlotElement.h"
#include "mozilla/dom/ShadowRoot.h"
#include "nsContentUtils.h"
#include "nsElementTable.h"
#include "nsIContent.h"
#include "nsRange.h"

namespace mozilla {

using namespace dom;

#define NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(aResultType, aMethodName, ...) \
  template aResultType ContentIteratorBase<RefPtr<nsINode>>::aMethodName(      \
      __VA_ARGS__);                                                            \
  template aResultType ContentIteratorBase<nsINode*>::aMethodName(__VA_ARGS__)

static bool ComparePostMode(const RawRangeBoundary& aStart,
                            const RawRangeBoundary& aEnd, nsINode& aNode) {
  nsINode* parent = aNode.GetParentNode();
  if (!parent) {
    return false;
  }

  // aNode should always be content, as we have a parent, but let's just be
  // extra careful and check.
  nsIContent* content =
      NS_WARN_IF(!aNode.IsContent()) ? nullptr : aNode.AsContent();

  // Post mode: start < node <= end.
  RawRangeBoundary afterNode(parent, content);
  const auto isStartLessThanAfterNode = [&]() {
    const Maybe<int32_t> startComparedToAfterNode =
        nsContentUtils::ComparePoints(aStart, afterNode);
    return !NS_WARN_IF(!startComparedToAfterNode) &&
           (*startComparedToAfterNode < 0);
  };

  const auto isAfterNodeLessOrEqualToEnd = [&]() {
    const Maybe<int32_t> afterNodeComparedToEnd =
        nsContentUtils::ComparePoints(afterNode, aEnd);
    return !NS_WARN_IF(!afterNodeComparedToEnd) &&
           (*afterNodeComparedToEnd <= 0);
  };

  return isStartLessThanAfterNode() && isAfterNodeLessOrEqualToEnd();
}

static bool ComparePreMode(const RawRangeBoundary& aStart,
                           const RawRangeBoundary& aEnd, nsINode& aNode) {
  nsINode* parent = aNode.GetParentNode();
  if (!parent) {
    return false;
  }

  // Pre mode: start <= node < end.
  RawRangeBoundary beforeNode(parent, aNode.GetPreviousSibling());

  const auto isStartLessOrEqualToBeforeNode = [&]() {
    const Maybe<int32_t> startComparedToBeforeNode =
        nsContentUtils::ComparePoints(aStart, beforeNode);
    return !NS_WARN_IF(!startComparedToBeforeNode) &&
           (*startComparedToBeforeNode <= 0);
  };

  const auto isBeforeNodeLessThanEndNode = [&]() {
    const Maybe<int32_t> beforeNodeComparedToEnd =
        nsContentUtils::ComparePoints(beforeNode, aEnd);
    return !NS_WARN_IF(!beforeNodeComparedToEnd) &&
           (*beforeNodeComparedToEnd < 0);
  };

  return isStartLessOrEqualToBeforeNode() && isBeforeNodeLessThanEndNode();
}

///////////////////////////////////////////////////////////////////////////
// NodeIsInTraversalRange: returns true if content is visited during
// the traversal of the range in the specified mode.
//
static bool NodeIsInTraversalRange(nsINode* aNode, bool aIsPreMode,
                                   const RawRangeBoundary& aStart,
                                   const RawRangeBoundary& aEnd) {
  if (NS_WARN_IF(!aStart.IsSet()) || NS_WARN_IF(!aEnd.IsSet()) ||
      NS_WARN_IF(!aNode)) {
    return false;
  }

  // If a leaf node contains an end point of the traversal range, it is
  // always in the traversal range.
  if (aNode == aStart.GetContainer() || aNode == aEnd.GetContainer()) {
    if (aNode->IsCharacterData()) {
      return true;  // text node or something
    }
    if (!aNode->HasChildren()) {
      MOZ_ASSERT(
          aNode != aStart.GetContainer() || aStart.IsStartOfContainer(),
          "aStart.GetContainer() doesn't have children and not a data node, "
          "aStart should be at the beginning of its container");
      MOZ_ASSERT(
          aNode != aEnd.GetContainer() || aEnd.IsStartOfContainer(),
          "aEnd.GetContainer() doesn't have children and not a data node, "
          "aEnd should be at the beginning of its container");
      return true;
    }
  }

  if (aIsPreMode) {
    return ComparePreMode(aStart, aEnd, *aNode);
  }

  return ComparePostMode(aStart, aEnd, *aNode);
}

void ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
                                 PostContentIterator& aField, const char* aName,
                                 uint32_t aFlags = 0) {
  ImplCycleCollectionTraverse(
      aCallback, static_cast<SafeContentIteratorBase&>(aField), aName, aFlags);
}

void ImplCycleCollectionUnlink(PostContentIterator& aField) {
  ImplCycleCollectionUnlink(static_cast<SafeContentIteratorBase&>(aField));
}

void ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
                                 PreContentIterator& aField, const char* aName,
                                 uint32_t aFlags = 0) {
  ImplCycleCollectionTraverse(
      aCallback, static_cast<SafeContentIteratorBase&>(aField), aName, aFlags);
}

void ImplCycleCollectionUnlink(PreContentIterator& aField) {
  ImplCycleCollectionUnlink(static_cast<SafeContentIteratorBase&>(aField));
}

void ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
                                 ContentSubtreeIterator& aField,
                                 const char* aName, uint32_t aFlags = 0) {
  ImplCycleCollectionTraverse(aCallback, aField.mRange, aName, aFlags);
  ImplCycleCollectionTraverse(
      aCallback, static_cast<SafeContentIteratorBase&>(aField), aName, aFlags);
}

void ImplCycleCollectionUnlink(ContentSubtreeIterator& aField) {
  ImplCycleCollectionUnlink(aField.mRange);
  ImplCycleCollectionUnlink(static_cast<SafeContentIteratorBase&>(aField));
}

/******************************************************
 * ContentIteratorBase
 ******************************************************/

NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(, ContentIteratorBase, Order);

template <typename NodeType>
ContentIteratorBase<NodeType>::ContentIteratorBase(Order aOrder)
    : mOrder(aOrder) {}

template ContentIteratorBase<RefPtr<nsINode>>::~ContentIteratorBase();
template ContentIteratorBase<nsINode*>::~ContentIteratorBase();

template <typename NodeType>
ContentIteratorBase<NodeType>::~ContentIteratorBase() {
  MOZ_DIAGNOSTIC_ASSERT_IF(mMutationGuard.isSome(),
                           !mMutationGuard->Mutated(0));
}

/******************************************************
 * Init routines
 ******************************************************/

NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(nsresult, Init, nsINode*);

template <typename NodeType>
nsresult ContentIteratorBase<NodeType>::Init(nsINode* aRoot) {
  if (NS_WARN_IF(!aRoot)) {
    return NS_ERROR_NULL_POINTER;
  }

  if (mOrder == Order::Pre) {
    mFirst = aRoot;
    mLast = ContentIteratorBase::GetDeepLastChild(aRoot);
    NS_WARNING_ASSERTION(mLast, "GetDeepLastChild returned null");
  } else {
    mFirst = ContentIteratorBase::GetDeepFirstChild(aRoot);
    NS_WARNING_ASSERTION(mFirst, "GetDeepFirstChild returned null");
    mLast = aRoot;
  }

  mClosestCommonInclusiveAncestor = aRoot;
  mCurNode = mFirst;
  return NS_OK;
}

NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(nsresult, Init, AbstractRange*);

template <typename NodeType>
nsresult ContentIteratorBase<NodeType>::Init(AbstractRange* aRange) {
  if (NS_WARN_IF(!aRange)) {
    return NS_ERROR_INVALID_ARG;
  }

  if (NS_WARN_IF(!aRange->IsPositioned())) {
    return NS_ERROR_INVALID_ARG;
  }

  return InitInternal(aRange->StartRef().AsRaw(), aRange->EndRef().AsRaw());
}

NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(nsresult, Init, nsINode*, uint32_t,
                                        nsINode*, uint32_t);

template <typename NodeType>
nsresult ContentIteratorBase<NodeType>::Init(nsINode* aStartContainer,
                                             uint32_t aStartOffset,
                                             nsINode* aEndContainer,
                                             uint32_t aEndOffset) {
  if (NS_WARN_IF(!RangeUtils::IsValidPoints(aStartContainer, aStartOffset,
                                            aEndContainer, aEndOffset))) {
    return NS_ERROR_INVALID_ARG;
  }

  return InitInternal(RawRangeBoundary(aStartContainer, aStartOffset),
                      RawRangeBoundary(aEndContainer, aEndOffset));
}

NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(nsresult, Init, const RawRangeBoundary&,
                                        const RawRangeBoundary&);

template <typename NodeType>
nsresult ContentIteratorBase<NodeType>::Init(const RawRangeBoundary& aStart,
                                             const RawRangeBoundary& aEnd) {
  if (NS_WARN_IF(!RangeUtils::IsValidPoints(aStart, aEnd))) {
    return NS_ERROR_INVALID_ARG;
  }

  return InitInternal(aStart, aEnd);
}

template <typename NodeType>
nsresult ContentIteratorBase<NodeType>::InitWithoutValidatingPoints(
    const RawRangeBoundary& aStart, const RawRangeBoundary& aEnd) {
  MOZ_DIAGNOSTIC_ASSERT(RangeUtils::IsValidPoints(aStart, aEnd));
  return InitInternal(aStart, aEnd);
}

template <typename NodeType>
class MOZ_STACK_CLASS ContentIteratorBase<NodeType>::Initializer final {
 public:
  Initializer(ContentIteratorBase<NodeType>& aIterator,
              const RawRangeBoundary& aStart, const RawRangeBoundary& aEnd)
      : mIterator{aIterator},
        mStart{aStart},
        mEnd{aEnd},
        mStartIsCharacterData{mStart.GetContainer()->IsCharacterData()} {
    MOZ_ASSERT(mStart.IsSetAndValid());
    MOZ_ASSERT(mEnd.IsSetAndValid());
  }

  nsresult Run();

 private:
  /**
   * @return may be nullptr.
   */
  nsINode* DetermineFirstNode() const;

  /**
   * @return may be nullptr.
   */
  [[nodiscard]] Result<nsINode*, nsresult> DetermineLastNode() const;

  bool IsCollapsedNonCharacterRange() const;
  bool IsSingleNodeCharacterRange() const;

  ContentIteratorBase& mIterator;
  const RawRangeBoundary& mStart;
  const RawRangeBoundary& mEnd;
  const bool mStartIsCharacterData;
};

template <>
nsresult ContentIteratorBase<RefPtr<nsINode>>::InitInternal(
    const RawRangeBoundary& aStart, const RawRangeBoundary& aEnd) {
  Initializer initializer{*this, aStart, aEnd};
  return initializer.Run();
}

template <>
nsresult ContentIteratorBase<nsINode*>::InitInternal(
    const RawRangeBoundary& aStart, const RawRangeBoundary& aEnd) {
  Initializer initializer{*this, aStart, aEnd};
  nsresult rv = initializer.Run();
  if (NS_FAILED(rv)) {
    return rv;
  }
  mMutationGuard.emplace();
  mAssertNoGC.emplace();
  return NS_OK;
}

template <typename NodeType>
bool ContentIteratorBase<NodeType>::Initializer::IsCollapsedNonCharacterRange()
    const {
  return !mStartIsCharacterData && mStart == mEnd;
}

template <typename NodeType>
bool ContentIteratorBase<NodeType>::Initializer::IsSingleNodeCharacterRange()
    const {
  return mStartIsCharacterData && mStart.GetContainer() == mEnd.GetContainer();
}

template <typename NodeType>
nsresult ContentIteratorBase<NodeType>::Initializer::Run() {
  // get common content parent
  mIterator.mClosestCommonInclusiveAncestor =
      nsContentUtils::GetClosestCommonInclusiveAncestor(mStart.GetContainer(),
                                                        mEnd.GetContainer());
  if (NS_WARN_IF(!mIterator.mClosestCommonInclusiveAncestor)) {
    return NS_ERROR_FAILURE;
  }

  // Check to see if we have a collapsed range, if so, there is nothing to
  // iterate over.
  //
  // XXX: CharacterDataNodes (text nodes) are currently an exception, since
  //      we always want to be able to iterate text nodes at the end points
  //      of a range.

  if (IsCollapsedNonCharacterRange()) {
    mIterator.SetEmpty();
    return NS_OK;
  }

  if (IsSingleNodeCharacterRange()) {
    mIterator.mFirst = mStart.GetContainer()->AsContent();
    mIterator.mLast = mIterator.mFirst;
    mIterator.mCurNode = mIterator.mFirst;

    return NS_OK;
  }

  mIterator.mFirst = DetermineFirstNode();

  if (Result<nsINode*, nsresult> lastNode = DetermineLastNode();
      NS_WARN_IF(lastNode.isErr())) {
    return lastNode.unwrapErr();
  } else {
    mIterator.mLast = lastNode.unwrap();
  }

  // If either first or last is null, they both have to be null!
  if (!mIterator.mFirst || !mIterator.mLast) {
    mIterator.SetEmpty();
  }

  mIterator.mCurNode = mIterator.mFirst;

  return NS_OK;
}

template <typename NodeType>
nsINode* ContentIteratorBase<NodeType>::Initializer::DetermineFirstNode()
    const {
  nsIContent* cChild = nullptr;

  // Try to get the child at our starting point. This might return null if
  // mStart is immediately after the last node in mStart.GetContainer().
  if (!mStartIsCharacterData) {
    cChild = mStart.GetChildAtOffset();
  }

  if (!cChild) {
    // No children (possibly a <br> or text node), or index is after last child.

    if (mIterator.mOrder == Order::Pre) {
      // XXX: In the future, if start offset is after the last
      //      character in the cdata node, should we set mFirst to
      //      the next sibling?

      // Normally we would skip the start node because the start node is outside
      // of the range in pre mode. However, if aStartOffset == 0, and the node
      // is a non-container node (e.g. <br>), we don't skip the node in this
      // case in order to address bug 1215798.
      bool startIsContainer = true;
      if (mStart.GetContainer()->IsHTMLElement()) {
        nsAtom* name = mStart.GetContainer()->NodeInfo()->NameAtom();
        startIsContainer =
            nsHTMLElement::IsContainer(nsHTMLTags::AtomTagToId(name));
      }
      if (!mStartIsCharacterData &&
          (startIsContainer || !mStart.IsStartOfContainer())) {
        nsINode* const result =
            ContentIteratorBase::GetNextSibling(mStart.GetContainer());
        NS_WARNING_ASSERTION(result, "GetNextSibling returned null");

        // Does mFirst node really intersect the range?  The range could be
        // 'degenerate', i.e., not collapsed but still contain no content.
        if (result &&
            NS_WARN_IF(!NodeIsInTraversalRange(
                result, mIterator.mOrder == Order::Pre, mStart, mEnd))) {
          return nullptr;
        }

        return result;
      }
      return mStart.GetContainer()->AsContent();
    }

    // post-order
    if (NS_WARN_IF(!mStart.GetContainer()->IsContent())) {
      // What else can we do?
      return nullptr;
    }
    return mStart.GetContainer()->AsContent();
  }

  if (mIterator.mOrder == Order::Pre) {
    return cChild;
  }

  // post-order
  nsINode* const result = ContentIteratorBase::GetDeepFirstChild(cChild);
  NS_WARNING_ASSERTION(result, "GetDeepFirstChild returned null");

  // Does mFirst node really intersect the range?  The range could be
  // 'degenerate', i.e., not collapsed but still contain no content.
  if (result && !NodeIsInTraversalRange(result, mIterator.mOrder == Order::Pre,
                                        mStart, mEnd)) {
    return nullptr;
  }

  return result;
}

template <typename NodeType>
Result<nsINode*, nsresult>
ContentIteratorBase<NodeType>::Initializer::DetermineLastNode() const {
  const bool endIsCharacterData = mEnd.GetContainer()->IsCharacterData();

  if (endIsCharacterData || !mEnd.GetContainer()->HasChildren() ||
      mEnd.IsStartOfContainer()) {
    if (mIterator.mOrder == Order::Pre) {
      if (NS_WARN_IF(!mEnd.GetContainer()->IsContent())) {
        // Not much else to do here...
        return nullptr;
      }

      // If the end node is a non-container element and the end offset is 0,
      // the last element should be the previous node (i.e., shouldn't
      // include the end node in the range).
      bool endIsContainer = true;
      if (mEnd.GetContainer()->IsHTMLElement()) {
        nsAtom* name = mEnd.GetContainer()->NodeInfo()->NameAtom();
        endIsContainer =
            nsHTMLElement::IsContainer(nsHTMLTags::AtomTagToId(name));
      }
      if (!endIsCharacterData && !endIsContainer && mEnd.IsStartOfContainer()) {
        nsINode* const result = mIterator.PrevNode(mEnd.GetContainer());
        NS_WARNING_ASSERTION(result, "PrevNode returned null");
        if (result && result != mIterator.mFirst &&
            NS_WARN_IF(!NodeIsInTraversalRange(
                result, mIterator.mOrder == Order::Pre,
                RawRangeBoundary(mIterator.mFirst, 0u), mEnd))) {
          return nullptr;
        }

        return result;
      }

      return mEnd.GetContainer()->AsContent();
    }

    // post-order
    //
    // XXX: In the future, if end offset is before the first character in the
    //      cdata node, should we set mLast to the prev sibling?

    if (!endIsCharacterData) {
      nsINode* const result =
          ContentIteratorBase::GetPrevSibling(mEnd.GetContainer());
      NS_WARNING_ASSERTION(result, "GetPrevSibling returned null");

      if (!NodeIsInTraversalRange(result, mIterator.mOrder == Order::Pre,
                                  mStart, mEnd)) {
        return nullptr;
      }
      return result;
    }
    return mEnd.GetContainer()->AsContent();
  }

  nsIContent* cChild = mEnd.Ref();

  if (NS_WARN_IF(!cChild)) {
    // No child at offset!
    MOZ_ASSERT_UNREACHABLE("ContentIterator::ContentIterator");
    return Err(NS_ERROR_FAILURE);
  }

  if (mIterator.mOrder == Order::Pre) {
    nsINode* const result = ContentIteratorBase::GetDeepLastChild(cChild);
    NS_WARNING_ASSERTION(result, "GetDeepLastChild returned null");

    if (NS_WARN_IF(!NodeIsInTraversalRange(
            result, mIterator.mOrder == Order::Pre, mStart, mEnd))) {
      return nullptr;
    }

    return result;
  }

  // post-order
  return cChild;
}

NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(void, SetEmpty);

template <typename NodeType>
void ContentIteratorBase<NodeType>::SetEmpty() {
  mCurNode = nullptr;
  mFirst = nullptr;
  mLast = nullptr;
  mClosestCommonInclusiveAncestor = nullptr;
}

// static
template <typename NodeType>
nsINode* ContentIteratorBase<NodeType>::GetDeepFirstChild(nsINode* aRoot) {
  if (NS_WARN_IF(!aRoot) || !aRoot->HasChildren()) {
    return aRoot;
  }

  return ContentIteratorBase::GetDeepFirstChild(aRoot->GetFirstChild());
}

// static
template <typename NodeType>
nsIContent* ContentIteratorBase<NodeType>::GetDeepFirstChild(
    nsIContent* aRoot,
    AllowRangeCrossShadowBoundary aAllowCrossShadowBoundary) {
  if (NS_WARN_IF(!aRoot)) {
    return nullptr;
  }

  nsIContent* node = aRoot;
  nsIContent* child = nullptr;

  if (ShadowRoot* shadowRoot = ShadowDOMSelectionHelpers::GetShadowRoot(
          node, aAllowCrossShadowBoundary)) {
    // When finding the deepest child of node, if this node has a
    // web exposed shadow root, we use this shadow root to find the deepest
    // child.
    // If the first candidate should be a slotted content,
    // shadowRoot->GetFirstChild() should be able to return the <slot> element.
    // It's probably correct I think. Then it's up to the caller of this
    // iterator to decide whether to use the slot's assigned nodes or not.
    MOZ_ASSERT(aAllowCrossShadowBoundary == AllowRangeCrossShadowBoundary::Yes);
    child = shadowRoot->GetFirstChild();
  } else {
    child = node->GetFirstChild();
  }

  while (child) {
    node = child;
    if (ShadowRoot* shadowRoot = ShadowDOMSelectionHelpers::GetShadowRoot(
            node, aAllowCrossShadowBoundary)) {
      // When finding the deepest child of node, if this node has a
      // web exposed shadow root, we use this shadow root to find the deepest
      // child.
      // If the first candidate should be a slotted content,
      // shadowRoot->GetFirstChild() should be able to return the <slot>
      // element. It's probably correct I think. Then it's up to the caller of
      // this iterator to decide whether to use the slot's assigned nodes or
      // not.
      child = shadowRoot->GetFirstChild();
    } else {
      child = node->GetFirstChild();
    }
  }

  return node;
}

// static
template <typename NodeType>
nsINode* ContentIteratorBase<NodeType>::GetDeepLastChild(nsINode* aRoot) {
  if (NS_WARN_IF(!aRoot) || !aRoot->HasChildren()) {
    return aRoot;
  }

  return ContentIteratorBase::GetDeepLastChild(aRoot->GetLastChild());
}

// static
template <typename NodeType>
nsIContent* ContentIteratorBase<NodeType>::GetDeepLastChild(
    nsIContent* aRoot,
    AllowRangeCrossShadowBoundary aAllowCrossShadowBoundary) {
  if (NS_WARN_IF(!aRoot)) {
    return nullptr;
  }

  nsIContent* node = aRoot;

  while (HTMLSlotElement* slot = HTMLSlotElement::FromNode(node)) {
    // The deep last child of a slot should be the last slotted element of it
    if (!slot->AssignedNodes().IsEmpty()) {
      if (nsIContent* content =
              nsIContent::FromNode(slot->AssignedNodes().LastElement())) {
        node = content;
        continue;
      }
    }
    break;
  }

  ShadowRoot* shadowRoot =
      ShadowDOMSelectionHelpers::GetShadowRoot(node, aAllowCrossShadowBoundary);
  while (node->HasChildren() || (shadowRoot && shadowRoot->HasChildren())) {
    if (node->HasChildren()) {
      node = node->GetLastChild();
    } else {
      MOZ_ASSERT(shadowRoot);
      // If this node doesn't have a child, but it's also a shadow host
      // that can be selected, we go into this shadow tree.
      node = shadowRoot->GetLastChild();
    }
    shadowRoot = ShadowDOMSelectionHelpers::GetShadowRoot(
        node, aAllowCrossShadowBoundary);
  }
  return node;
}

// Get the next sibling, or parent's next sibling, or shadow host's next
// sibling (when aAllowCrossShadowBoundary is true), or grandpa's next
// sibling...
//
// static
//
template <typename NodeType>
nsIContent* ContentIteratorBase<NodeType>::GetNextSibling(
    nsINode* aNode, AllowRangeCrossShadowBoundary aAllowCrossShadowBoundary,
    nsTArray<AncestorInfo>* aInclusiveAncestorsOfEndContainer) {
  if (NS_WARN_IF(!aNode)) {
    return nullptr;
  }

  if (aNode->IsContent() &&
      aAllowCrossShadowBoundary == AllowRangeCrossShadowBoundary::Yes) {
    // Could have nested slots
    while (HTMLSlotElement* slot = aNode->AsContent()->GetAssignedSlot()) {
      if (!ShadowDOMSelectionHelpers::GetShadowRoot(
              slot->GetContainingShadowHost(), aAllowCrossShadowBoundary)) {
        // The corresponding shadow host isn't supported
        // by ContentSubtreeIterator, so let's skip this slot.
        break;
      }

      // Next sibling of a slotted node should be the next slotted node
      auto currentIndex = slot->AssignedNodes().IndexOf(aNode);
      if (currentIndex < slot->AssignedNodes().Length() - 1) {
        nsINode* nextSlottedNode =
            slot->AssignedNodes().ElementAt(currentIndex + 1);
        if (nextSlottedNode->IsContent()) {
          return nextSlottedNode->AsContent();
        }
      }
      // Move on to assigned slot's next sibling
      aNode = slot;
    }
  }

  if (nsIContent* next = aNode->GetNextSibling()) {
    return next;
  }

  nsINode* parent = ShadowDOMSelectionHelpers::GetParentNodeInSameSelection(
      *aNode, aAllowCrossShadowBoundary);
  if (NS_WARN_IF(!parent)) {
    return nullptr;
  }

  // We now have finished iterating descendants within this shadow root, and
  // reached to the shadow host.
  if (aAllowCrossShadowBoundary == AllowRangeCrossShadowBoundary::Yes &&
      aInclusiveAncestorsOfEndContainer && parent->GetShadowRoot() == aNode) {
    const int32_t i = aInclusiveAncestorsOfEndContainer->IndexOf(
        parent, 0, InclusiveAncestorComparator());

    // If parent is an ancestor of the end container, we return the parent so
    // that the caller (ContentSubtreeIterator::Next) can stop the iteration.
    //
    // This is only a special case for ShadowDOM selection where
    // the end container is in light DOM and we have to iterate
    // shadow DOM nodes first. We would have reached to mLast
    // already if this isn't the case.
    if (i != -1) {
      MOZ_ASSERT(!aInclusiveAncestorsOfEndContainer->ElementAt(i)
                      .mIsDescendantInShadowTree);
      return parent->AsContent();
    }
  }

  return ContentIteratorBase::GetNextSibling(parent, aAllowCrossShadowBoundary,
                                             aInclusiveAncestorsOfEndContainer);
}

// Get the prev sibling, or parent's prev sibling, or shadow host's prev sibling
// (when aAllowCrossShadowBoundary is true), or grandpa's prev sibling... static
template <typename NodeType>
nsIContent* ContentIteratorBase<NodeType>::GetPrevSibling(
    nsINode* aNode, AllowRangeCrossShadowBoundary aAllowCrossShadowBoundary) {
  if (NS_WARN_IF(!aNode)) {
    return nullptr;
  }

  if (aNode->IsContent() &&
      aAllowCrossShadowBoundary == AllowRangeCrossShadowBoundary::Yes) {
    // Could have nested slots.
    while (HTMLSlotElement* slot = aNode->AsContent()->GetAssignedSlot()) {
      if (!ShadowDOMSelectionHelpers::GetShadowRoot(
              slot->GetContainingShadowHost(), aAllowCrossShadowBoundary)) {
        // The corresponding shadow host isn't supported
        // by ContentSubtreeIterator, so let's skip this slot.
        break;
      }
      // prev sibling of a slotted node should be the prev slotted node
      auto currentIndex = slot->AssignedNodes().IndexOf(aNode);
      if (currentIndex > 0) {
        nsINode* prevSlottedNode =
            slot->AssignedNodes().ElementAt(currentIndex - 1);
        if (prevSlottedNode->IsContent()) {
          return prevSlottedNode->AsContent();
        }
      }
      aNode = slot;
    }
  }

  if (nsIContent* prev = aNode->GetPreviousSibling()) {
    return prev;
  }

  nsINode* parent = ShadowDOMSelectionHelpers::GetParentNodeInSameSelection(
      *aNode, aAllowCrossShadowBoundary);
  if (NS_WARN_IF(!parent)) {
    return nullptr;
  }

  return ContentIteratorBase::GetPrevSibling(parent, aAllowCrossShadowBoundary);
}

template <typename NodeType>
nsINode* ContentIteratorBase<NodeType>::NextNode(nsINode* aNode) {
  nsINode* node = aNode;

  // if we are a Pre-order iterator, use pre-order
  if (mOrder == Order::Pre) {
    // if it has children then next node is first child
    if (node->HasChildren()) {
      nsIContent* firstChild = node->GetFirstChild();
      MOZ_ASSERT(firstChild);

      return firstChild;
    }

    // else next sibling is next
    return ContentIteratorBase::GetNextSibling(node);
  }

  // post-order
  nsINode* parent = node->GetParentNode();
  if (NS_WARN_IF(!parent)) {
    MOZ_ASSERT(parent, "The node is the root node but not the last node");
    mCurNode = nullptr;
    return node;
  }

  if (nsIContent* sibling = node->GetNextSibling()) {
    // next node is sibling's "deep left" child
    return ContentIteratorBase::GetDeepFirstChild(sibling);
  }

  return parent;
}

template <typename NodeType>
nsINode* ContentIteratorBase<NodeType>::PrevNode(nsINode* aNode) {
  nsINode* node = aNode;

  // if we are a Pre-order iterator, use pre-order
  if (mOrder == Order::Pre) {
    nsINode* parent = node->GetParentNode();
    if (NS_WARN_IF(!parent)) {
      MOZ_ASSERT(parent, "The node is the root node but not the first node");
      mCurNode = nullptr;
      return aNode;
    }

    nsIContent* sibling = node->GetPreviousSibling();
    if (sibling) {
      return ContentIteratorBase::GetDeepLastChild(sibling);
    }

    return parent;
  }

  // post-order
  if (node->HasChildren()) {
    return node->GetLastChild();
  }

  // else prev sibling is previous
  return ContentIteratorBase::GetPrevSibling(node);
}

/******************************************************
 * ContentIteratorBase routines
 ******************************************************/

NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(void, First);

template <typename NodeType>
void ContentIteratorBase<NodeType>::First() {
  if (!mFirst) {
    MOZ_ASSERT(IsDone());
    mCurNode = nullptr;
    return;
  }

  mozilla::DebugOnly<nsresult> rv = PositionAt(mFirst);
  NS_ASSERTION(NS_SUCCEEDED(rv), "Failed to position iterator!");
}

NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(void, Last);

template <typename NodeType>
void ContentIteratorBase<NodeType>::Last() {
  // Note that mLast can be nullptr if SetEmpty() is called in Init()
  // since at that time, Init() returns NS_OK.
  if (!mLast) {
    MOZ_ASSERT(IsDone());
    mCurNode = nullptr;
    return;
  }

  mozilla::DebugOnly<nsresult> rv = PositionAt(mLast);
  NS_ASSERTION(NS_SUCCEEDED(rv), "Failed to position iterator!");
}

NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(void, Next);

template <typename NodeType>
void ContentIteratorBase<NodeType>::Next() {
  if (IsDone()) {
    return;
  }

  if (mCurNode == mLast) {
    mCurNode = nullptr;
    return;
  }

  mCurNode = NextNode(mCurNode);
}

NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(void, Prev);

template <typename NodeType>
void ContentIteratorBase<NodeType>::Prev() {
  if (IsDone()) {
    return;
  }

  if (mCurNode == mFirst) {
    mCurNode = nullptr;
    return;
  }

  mCurNode = PrevNode(mCurNode);
}

// Keeping arrays of indexes for the stack of nodes makes PositionAt
// interesting...
NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD(nsresult, PositionAt, nsINode*);

template <typename NodeType>
nsresult ContentIteratorBase<NodeType>::PositionAt(nsINode* aCurNode) {
  if (NS_WARN_IF(!aCurNode)) {
    return NS_ERROR_NULL_POINTER;
  }

  // take an early out if this doesn't actually change the position
  if (mCurNode == aCurNode) {
    return NS_OK;
  }
  mCurNode = aCurNode;

  // Check to see if the node falls within the traversal range.

  RawRangeBoundary first(mFirst, 0u);
  RawRangeBoundary last(mLast, 0u);

  if (mFirst && mLast) {
    if (mOrder == Order::Pre) {
      // In pre we want to record the point immediately before mFirst, which is
      // the point immediately after mFirst's previous sibling.
      first = {mFirst->GetParentNode(), mFirst->GetPreviousSibling()};

      // If mLast has no children, then we want to make sure to include it.
      if (!mLast->HasChildren()) {
        last = {mLast->GetParentNode(), mLast->AsContent()};
      }
    } else {
      // If the first node has any children, we want to be immediately after the
      // last. Otherwise we want to be immediately before mFirst.
      if (mFirst->HasChildren()) {
        first = {mFirst, mFirst->GetLastChild()};
      } else {
        first = {mFirst->GetParentNode(), mFirst->GetPreviousSibling()};
      }

      // Set the last point immediately after the final node.
      last = {mLast->GetParentNode(), mLast->AsContent()};
    }
  }

  NS_WARNING_ASSERTION(first.IsSetAndValid(), "first is not valid");
  NS_WARNING_ASSERTION(last.IsSetAndValid(), "last is not valid");

  // The end positions are always in the range even if it has no parent.  We
  // need to allow that or 'iter->Init(root)' would assert in Last() or First()
  // for example, bug 327694.
  if (mFirst != mCurNode && mLast != mCurNode &&
      (NS_WARN_IF(!first.IsSet()) || NS_WARN_IF(!last.IsSet()) ||
       NS_WARN_IF(!NodeIsInTraversalRange(mCurNode, mOrder == Order::Pre, first,
                                          last)))) {
    mCurNode = nullptr;
    return NS_ERROR_FAILURE;
  }

  return NS_OK;
}

/******************************************************
 * ContentSubtreeIterator init routines
 ******************************************************/

nsresult ContentSubtreeIterator::Init(nsINode* aRoot) {
  return NS_ERROR_NOT_IMPLEMENTED;
}

nsresult ContentSubtreeIterator::Init(AbstractRange* aRange) {
  MOZ_ASSERT(aRange);

  if (NS_WARN_IF(!aRange->IsPositioned())) {
    return NS_ERROR_INVALID_ARG;
  }

  mRange = aRange;

  return InitWithRange();
}

nsresult ContentSubtreeIterator::Init(nsINode* aStartContainer,
                                      uint32_t aStartOffset,
                                      nsINode* aEndContainer,
                                      uint32_t aEndOffset) {
  return Init(RawRangeBoundary(aStartContainer, aStartOffset),
              RawRangeBoundary(aEndContainer, aEndOffset));
}

nsresult ContentSubtreeIterator::Init(const RawRangeBoundary& aStartBoundary,
                                      const RawRangeBoundary& aEndBoundary) {
  RefPtr<nsRange> range =
      nsRange::Create(aStartBoundary, aEndBoundary, IgnoreErrors());
  if (NS_WARN_IF(!range) || NS_WARN_IF(!range->IsPositioned())) {
    return NS_ERROR_INVALID_ARG;
  }

  if (NS_WARN_IF(range->MayCrossShadowBoundaryStartRef() != aStartBoundary) ||
      NS_WARN_IF(range->MayCrossShadowBoundaryEndRef() != aEndBoundary)) {
    // Could happen if the above nsRange::Create decides to collapse
    // the range, like aStartBoundary is "after" aEndBoundary.
    return NS_ERROR_UNEXPECTED;
  }

  mRange = std::move(range);

  return InitWithRange();
}

nsresult ContentSubtreeIterator::InitWithAllowCrossShadowBoundary(
    AbstractRange* aRange) {
  MOZ_ASSERT(aRange);

  if (NS_WARN_IF(!aRange->IsPositioned())) {
    return NS_ERROR_INVALID_ARG;
  }

  mRange = aRange;

  if (StaticPrefs::dom_shadowdom_selection_across_boundary_enabled()) {
    mAllowCrossShadowBoundary = AllowRangeCrossShadowBoundary::Yes;
  }
  return InitWithRange();
}

void ContentSubtreeIterator::CacheInclusiveAncestorsOfEndContainer() {
  mInclusiveAncestorsOfEndContainer.Clear();
  nsINode* const endContainer = ShadowDOMSelectionHelpers::GetEndContainer(
      mRange, mAllowCrossShadowBoundary);
  nsIContent* endNode =
      endContainer->IsContent() ? endContainer->AsContent() : nullptr;

  AncestorInfo info{endNode, false};
  while (info.mAncestor) {
    const nsINode* child = info.mAncestor;
    mInclusiveAncestorsOfEndContainer.AppendElement(info);
    // Cross the boundary for contents in shadow tree.
    nsINode* parent = ShadowDOMSelectionHelpers::GetParentNodeInSameSelection(
        *child, mAllowCrossShadowBoundary);
    if (!parent || !parent->IsContent()) {
      break;
    }

    // `ShadowDOMSelectionHelpers::GetShadowRoot` would return non-null shadow
    // root if parent is a shadow host that we support cross boundary selection.
    const bool isChildAShadowRootForSelection =
        ShadowDOMSelectionHelpers::GetShadowRoot(
            parent, mAllowCrossShadowBoundary) == child;

    info.mAncestor = parent->AsContent();
    // mIsDescendantInShadowTree indicates that whether child is in the
    // shadow tree of parent or in the regular light DOM tree of parent.
    // So that later, when info.mAncestor is reached, we can decide whether
    // we should dive into the shadow tree.
    info.mIsDescendantInShadowTree =
        IterAllowCrossShadowBoundary() && isChildAShadowRootForSelection;
  }
}

nsIContent* ContentSubtreeIterator::DetermineCandidateForFirstContent() const {
  nsINode* startContainer = ShadowDOMSelectionHelpers::GetStartContainer(
      mRange, mAllowCrossShadowBoundary);
  nsIContent* firstCandidate = nullptr;
  // find first node in range
  nsINode* node = nullptr;
  if (!startContainer->GetChildCount()) {
    // no children, start at the node itself
    node = startContainer;
  } else {
    nsIContent* child =
        IterAllowCrossShadowBoundary()
            ? mRange->GetMayCrossShadowBoundaryChildAtStartOffset()
            : mRange->GetChildAtStartOffset();

#ifdef DEBUG
    const auto& startRef = IterAllowCrossShadowBoundary()
                               ? mRange->MayCrossShadowBoundaryStartRef()
                               : mRange->StartRef();
    const uint32_t startOffset = ShadowDOMSelectionHelpers::StartOffset(
        mRange, mAllowCrossShadowBoundary);
    MOZ_ASSERT(child ==
               (startRef.GetTreeKind() == TreeKind::Flat
                    ? startContainer->GetChildAtInFlatTree(startOffset)
                    : startContainer->GetChildAt_Deprecated(startOffset)));
#endif
    if (!child) {
      // offset after last child
      node = startContainer;
    } else {
      firstCandidate = child;
    }
  }

  if (!firstCandidate) {
    // then firstCandidate is next node after node
    firstCandidate =
        ContentIteratorBase::GetNextSibling(node, mAllowCrossShadowBoundary);
  }

  if (firstCandidate) {
    firstCandidate = ContentIteratorBase::GetDeepFirstChild(
        firstCandidate, mAllowCrossShadowBoundary);
  }

  return firstCandidate;
}

nsIContent* ContentSubtreeIterator::DetermineFirstContent() const {
  nsIContent* firstCandidate = DetermineCandidateForFirstContent();
  if (!firstCandidate) {
    return nullptr;
  }

  // confirm that this first possible contained node is indeed contained.  Else
  // we have a range that does not fully contain any node.
  const Maybe<bool> isNodeContainedInRange =
      IterAllowCrossShadowBoundary()
          ? RangeUtils::IsNodeContainedInRange<TreeKind::Flat>(*firstCandidate,
                                                               mRange)
          : RangeUtils::IsNodeContainedInRange<TreeKind::ShadowIncludingDOM>(
                *firstCandidate, mRange);
  MOZ_ALWAYS_TRUE(isNodeContainedInRange);
  if (!isNodeContainedInRange.value()) {
    return nullptr;
  }

  // cool, we have the first node in the range.  Now we walk up its ancestors
  // to find the most senior that is still in the range.  That's the real first
  // node.
  return GetTopAncestorInRange(firstCandidate);
}

nsIContent* ContentSubtreeIterator::DetermineCandidateForLastContent() const {
  nsIContent* lastCandidate{nullptr};
  nsINode* endContainer = ShadowDOMSelectionHelpers::GetEndContainer(
      mRange, mAllowCrossShadowBoundary);
  // now to find the last node
  int32_t offset =
      ShadowDOMSelectionHelpers::EndOffset(mRange, mAllowCrossShadowBoundary);

  int32_t numChildren = endContainer->GetChildCount();

  nsINode* node = nullptr;
  if (offset > numChildren) {
    // Can happen for text nodes
    offset = numChildren;
  }
  if (!offset || !numChildren) {
    node = endContainer;
  } else {
    lastCandidate = IterAllowCrossShadowBoundary()
                        ? mRange->MayCrossShadowBoundaryEndRef().Ref()
                        : mRange->EndRef().Ref();
#ifdef DEBUG
    const auto& endRef = IterAllowCrossShadowBoundary()
                             ? mRange->MayCrossShadowBoundaryEndRef()
                             : mRange->EndRef();
    MOZ_ASSERT(lastCandidate ==
               (endRef.GetTreeKind() == TreeKind::Flat
                    ? endContainer->GetChildAtInFlatTree(offset - 1)
                    : endContainer->GetChildAt_Deprecated(offset - 1)));
#endif
    NS_ASSERTION(lastCandidate,
                 "tree traversal trouble in ContentSubtreeIterator::Init");
  }

  if (!lastCandidate) {
    // then lastCandidate is prev node before node
    lastCandidate =
        ContentIteratorBase::GetPrevSibling(node, mAllowCrossShadowBoundary);
  }

  if (lastCandidate) {
    lastCandidate = ContentIteratorBase::GetDeepLastChild(
        lastCandidate, mAllowCrossShadowBoundary);
  }

  return lastCandidate;
}

nsresult ContentSubtreeIterator::InitWithRange() {
  MOZ_ASSERT(mRange);
  MOZ_ASSERT(mRange->IsPositioned());

  // get the start node and offset, convert to nsINode
  mClosestCommonInclusiveAncestor =
      mRange->GetClosestCommonInclusiveAncestor(mAllowCrossShadowBoundary);

  nsINode* startContainer = ShadowDOMSelectionHelpers::GetStartContainer(
      mRange, mAllowCrossShadowBoundary);
  const int32_t startOffset =
      ShadowDOMSelectionHelpers::StartOffset(mRange, mAllowCrossShadowBoundary);
  nsINode* endContainer = ShadowDOMSelectionHelpers::GetEndContainer(
      mRange, mAllowCrossShadowBoundary);
  const int32_t endOffset =
      ShadowDOMSelectionHelpers::EndOffset(mRange, mAllowCrossShadowBoundary);
  MOZ_ASSERT(mClosestCommonInclusiveAncestor && startContainer && endContainer);
  // Bug 767169
  MOZ_ASSERT(uint32_t(startOffset) <= startContainer->Length() &&
             uint32_t(endOffset) <= endContainer->Length());

  // short circuit when start node == end node
  if (startContainer == endContainer) {
    nsINode* child = startContainer->GetFirstChild();

    if (!child || startOffset == endOffset) {
      // Text node, empty container, or collapsed
      SetEmpty();
      return NS_OK;
    }
  }

  CacheInclusiveAncestorsOfEndContainer();

  mFirst = DetermineFirstContent();
  if (!mFirst) {
    SetEmpty();
    return NS_OK;
  }

  mLast = DetermineLastContent();
  if (!mLast) {
    SetEmpty();
    return NS_OK;
  }

  mCurNode = mFirst;

  return NS_OK;
}

nsIContent* ContentSubtreeIterator::DetermineLastContent() const {
  nsIContent* lastCandidate = DetermineCandidateForLastContent();
  if (!lastCandidate) {
    return nullptr;
  }

  // confirm that this last possible contained node is indeed contained.  Else
  // we have a range that does not fully contain any node.

  const Maybe<bool> isNodeContainedInRange =
      IterAllowCrossShadowBoundary()
          ? RangeUtils::IsNodeContainedInRange<TreeKind::Flat>(*lastCandidate,
                                                               mRange)
          : RangeUtils::IsNodeContainedInRange<TreeKind::ShadowIncludingDOM>(
                *lastCandidate, mRange);
  MOZ_ALWAYS_TRUE(isNodeContainedInRange);
  if (!isNodeContainedInRange.value()) {
    return nullptr;
  }

  // cool, we have the last node in the range.  Now we walk up its ancestors to
  // find the most senior that is still in the range.  That's the real first
  // node.
  return GetTopAncestorInRange(lastCandidate);
}

/****************************************************************
 * ContentSubtreeIterator overrides of ContentIterator routines
 ****************************************************************/

// we can't call PositionAt in a subtree iterator...
void ContentSubtreeIterator::First() { mCurNode = mFirst; }

// we can't call PositionAt in a subtree iterator...
void ContentSubtreeIterator::Last() { mCurNode = mLast; }

void ContentSubtreeIterator::Next() {
  if (IsDone()) {
    return;
  }

  if (mCurNode == mLast) {
    mCurNode = nullptr;
    return;
  }

  nsINode* nextNode = ContentIteratorBase::GetNextSibling(
      mCurNode, mAllowCrossShadowBoundary, &mInclusiveAncestorsOfEndContainer);

  NS_ASSERTION(nextNode, "No next sibling!?! This could mean deadlock!");

  int32_t i = mInclusiveAncestorsOfEndContainer.IndexOf(
      nextNode, 0, InclusiveAncestorComparator());

  while (i != -1) {
    // as long as we are finding ancestors of the endpoint of the range,
    // dive down into their children
    ShadowRoot* root = ShadowDOMSelectionHelpers::GetShadowRoot(
        nextNode, mAllowCrossShadowBoundary);
    if (mInclusiveAncestorsOfEndContainer[i].mIsDescendantInShadowTree) {
      MOZ_ASSERT(root);
      nextNode = root->GetFirstChild();
    } else if (auto* slot = HTMLSlotElement::FromNode(nextNode);
               slot && IterAllowCrossShadowBoundary() &&
               !slot->AssignedNodes().IsEmpty()) {
      // Ancestor is a slot, we start from the first assigned node within this
      // slot
      nextNode = slot->AssignedNodes()[0];
    } else {
      if (root) {
        // nextNode is a shadow host but the descendant in the light DOM
        // of it. There's no need to iterate light DOM elements for a
        // shadow tree. Stop here.
        mCurNode = nullptr;
        return;
      }
      nextNode = nextNode->GetFirstChild();
    }
    NS_ASSERTION(nextNode, "Iterator error, expected a child node!");

    // should be impossible to get a null pointer.  If we went all the way
    // down the child chain to the bottom without finding an interior node,
    // then the previous node should have been the last, which was
    // was tested at top of routine.
    i = mInclusiveAncestorsOfEndContainer.IndexOf(
        nextNode, 0, InclusiveAncestorComparator());
  }

  mCurNode = nextNode;
}

void ContentSubtreeIterator::Prev() {
  // Prev should be optimized to use the mStartNodes, just as Next
  // uses mInclusiveAncestorsOfEndContainer.
  if (IsDone()) {
    return;
  }

  if (mCurNode == mFirst) {
    mCurNode = nullptr;
    return;
  }

  // If any of these function calls return null, so will all succeeding ones,
  // so mCurNode will wind up set to null.
  nsINode* prevNode = ContentIteratorBase::GetDeepFirstChild(mCurNode);

  prevNode = PrevNode(prevNode);

  prevNode = ContentIteratorBase::GetDeepLastChild(prevNode);

  mCurNode = GetTopAncestorInRange(prevNode);
}

nsresult ContentSubtreeIterator::PositionAt(nsINode* aCurNode) {
  NS_ERROR("Not implemented!");
  return NS_ERROR_NOT_IMPLEMENTED;
}

/****************************************************************
 * ContentSubtreeIterator helper routines
 ****************************************************************/

nsIContent* ContentSubtreeIterator::GetTopAncestorInRange(
    nsINode* aNode) const {
  if (!aNode || !ShadowDOMSelectionHelpers::GetParentNodeInSameSelection(
                    *aNode, mAllowCrossShadowBoundary)) {
    return nullptr;
  }

  // aNode has a parent, so it must be content.
  nsIContent* content = aNode->AsContent();

  // sanity check: aNode is itself in the range
  Maybe<bool> isNodeContainedInRange =
      IterAllowCrossShadowBoundary()
          ? RangeUtils::IsNodeContainedInRange<TreeKind::Flat>(*aNode, mRange)
          : RangeUtils::IsNodeContainedInRange<TreeKind::ShadowIncludingDOM>(
                *aNode, mRange);

  NS_ASSERTION(isNodeContainedInRange && isNodeContainedInRange.value(),
               "aNode isn't in mRange, or something else weird happened");
  if (!isNodeContainedInRange || !isNodeContainedInRange.value()) {
    return nullptr;
  }

  nsIContent* lastContentInShadowTree = nullptr;
  while (content) {
    nsINode* parent = ShadowDOMSelectionHelpers::GetParentNodeInSameSelection(
        *content, mAllowCrossShadowBoundary);

    // content always has a parent.  If its parent is the root, however --
    // i.e., either it's not content, or it is content but its own parent is
    // null -- then we're finished, since we don't go up to the root.
    //
    // Caveat: If iteration crossing shadow boundary is allowed
    // and the root is a shadow root, we keep going up to the
    // shadow host and continue.
    //
    // We have to special-case this because CompareNodeToRange treats the root
    // node differently -- see bug 765205.
    if (!parent || !ShadowDOMSelectionHelpers::GetParentNodeInSameSelection(
                       *parent, mAllowCrossShadowBoundary)) {
      return content;
    }

    isNodeContainedInRange =
        IterAllowCrossShadowBoundary()
            ? RangeUtils::IsNodeContainedInRange<TreeKind::Flat>(*parent,
                                                                 mRange)
            : RangeUtils::IsNodeContainedInRange<TreeKind::ShadowIncludingDOM>(
                  *parent, mRange);

    MOZ_ALWAYS_TRUE(isNodeContainedInRange);
    if (!isNodeContainedInRange.value()) {
      if (IterAllowCrossShadowBoundary() && content->IsShadowRoot()) {
        MOZ_ASSERT(parent->GetShadowRoot() == content);
        // host element is not in range, the last content in tree
        // should be the ancestor.
        MOZ_ASSERT(lastContentInShadowTree);
        return lastContentInShadowTree;
      }
      return content;
    }

    // When we cross the boundary, we keep a reference to the
    // last content that is in tree, because if we later
    // find the shadow host element is not in the range, that means
    // the last content in the tree should be top ancestor in range.
    //
    // Using shadow root doesn't make sense here because it doesn't
    // represent a actual content.
    if (IterAllowCrossShadowBoundary() && parent->IsShadowRoot()) {
      lastContentInShadowTree = content;
    }

    content = parent->AsContent();
  }

  MOZ_CRASH("This should only be possible if aNode was null");
}

#undef NS_INSTANTIATE_CONTENT_ITER_BASE_METHOD

}  // namespace mozilla