path: root/Userland/Libraries/LibWeb/DOM/Range.cpp

/*
 * Copyright (c) 2020, the SerenityOS developers.
 * Copyright (c) 2022, Luke Wilde <lukew@serenityos.org>
 * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibWeb/DOM/Document.h>
#include <LibWeb/DOM/DocumentFragment.h>
#include <LibWeb/DOM/DocumentType.h>
#include <LibWeb/DOM/Node.h>
#include <LibWeb/DOM/Range.h>
#include <LibWeb/DOM/Text.h>
#include <LibWeb/HTML/Window.h>

namespace Web::DOM {

NonnullRefPtr<Range> Range::create(HTML::Window& window)
{
    return Range::create(window.associated_document());
}

NonnullRefPtr<Range> Range::create(Document& document)
{
    return adopt_ref(*new Range(document));
}

NonnullRefPtr<Range> Range::create(Node& start_container, u32 start_offset, Node& end_container, u32 end_offset)
{
    return adopt_ref(*new Range(start_container, start_offset, end_container, end_offset));
}

NonnullRefPtr<Range> Range::create_with_global_object(Bindings::WindowObject& window)
{
    return Range::create(window.impl());
}

Range::Range(Document& document)
    : Range(document, 0, document, 0)
{
}

Range::Range(Node& start_container, u32 start_offset, Node& end_container, u32 end_offset)
    : AbstractRange(start_container, start_offset, end_container, end_offset)
{
}

// https://dom.spec.whatwg.org/#concept-range-root
Node& Range::root()
{
    // The root of a live range is the root of its start node.
    return m_start_container->root();
}

Node const& Range::root() const
{
    return m_start_container->root();
}

enum class RelativeBoundaryPointPosition {
    Equal,
    Before,
    After,
};

// https://dom.spec.whatwg.org/#concept-range-bp-position
static RelativeBoundaryPointPosition position_of_boundary_point_relative_to_other_boundary_point(Node const& node_a, u32 offset_a, Node const& node_b, u32 offset_b)
{
    // 1. Assert: nodeA and nodeB have the same root.
    VERIFY(&node_a.root() == &node_b.root());

    // 2. If nodeA is nodeB, then return equal if offsetA is offsetB, before if offsetA is less than offsetB, and after if offsetA is greater than offsetB.
    if (&node_a == &node_b) {
        if (offset_a == offset_b)
            return RelativeBoundaryPointPosition::Equal;

        if (offset_a < offset_b)
            return RelativeBoundaryPointPosition::Before;

        return RelativeBoundaryPointPosition::After;
    }

    // 3. If nodeA is following nodeB, then if the position of (nodeB, offsetB) relative to (nodeA, offsetA) is before, return after, and if it is after, return before.
    if (node_a.is_following(node_b)) {
        auto relative_position = position_of_boundary_point_relative_to_other_boundary_point(node_b, offset_b, node_a, offset_a);

        if (relative_position == RelativeBoundaryPointPosition::Before)
            return RelativeBoundaryPointPosition::After;

        if (relative_position == RelativeBoundaryPointPosition::After)
            return RelativeBoundaryPointPosition::Before;
    }

    // 4. If nodeA is an ancestor of nodeB:
    if (node_a.is_ancestor_of(node_b)) {
        // 1. Let child be nodeB.
        NonnullRefPtr<Node> child = node_b;

        // 2. While child is not a child of nodeA, set child to its parent.
        while (!node_a.is_parent_of(child)) {
            auto* parent = child->parent();
            VERIFY(parent);
            child = *parent;
        }

        // 3. If child’s index is less than offsetA, then return after.
        if (child->index() < offset_a)
            return RelativeBoundaryPointPosition::After;
    }

    // 5. Return before.
    return RelativeBoundaryPointPosition::Before;
}

ExceptionOr<void> Range::set_start_or_end(Node& node, u32 offset, StartOrEnd start_or_end)
{
    // To set the start or end of a range to a boundary point (node, offset), run these steps:

    // 1. If node is a doctype, then throw an "InvalidNodeTypeError" DOMException.
    if (is<DocumentType>(node))
        return InvalidNodeTypeError::create("Node cannot be a DocumentType.");

    // 2. If offset is greater than node’s length, then throw an "IndexSizeError" DOMException.
    if (offset > node.length())
        return IndexSizeError::create(String::formatted("Node does not contain a child at offset {}", offset));

    // 3. Let bp be the boundary point (node, offset).

    if (start_or_end == StartOrEnd::Start) {
        // -> If these steps were invoked as "set the start"

        // 1. If range’s root is not equal to node’s root, or if bp is after the range’s end, set range’s end to bp.
        if (&root() != &node.root() || position_of_boundary_point_relative_to_other_boundary_point(node, offset, m_end_container, m_end_offset) == RelativeBoundaryPointPosition::After) {
            m_end_container = node;
            m_end_offset = offset;
        }

        // 2. Set range’s start to bp.
        m_start_container = node;
        m_start_offset = offset;
    } else {
        // -> If these steps were invoked as "set the end"
        VERIFY(start_or_end == StartOrEnd::End);

        // 1. If range’s root is not equal to node’s root, or if bp is before the range’s start, set range’s start to bp.
        if (&root() != &node.root() || position_of_boundary_point_relative_to_other_boundary_point(node, offset, m_start_container, m_start_offset) == RelativeBoundaryPointPosition::Before) {
            m_start_container = node;
            m_start_offset = offset;
        }

        // 2. Set range’s end to bp.
        m_end_container = node;
        m_end_offset = offset;
    }

    return {};
}

// https://dom.spec.whatwg.org/#concept-range-bp-set
ExceptionOr<void> Range::set_start(Node& node, u32 offset)
{
    // The setStart(node, offset) method steps are to set the start of this to boundary point (node, offset).
    return set_start_or_end(node, offset, StartOrEnd::Start);
}

ExceptionOr<void> Range::set_end(Node& node, u32 offset)
{
    // The setEnd(node, offset) method steps are to set the end of this to boundary point (node, offset).
    return set_start_or_end(node, offset, StartOrEnd::End);
}

// https://dom.spec.whatwg.org/#dom-range-setstartbefore
ExceptionOr<void> Range::set_start_before(Node& node)
{
    // 1. Let parent be node’s parent.
    auto* parent = node.parent();

    // 2. If parent is null, then throw an "InvalidNodeTypeError" DOMException.
    if (!parent)
        return InvalidNodeTypeError::create("Given node has no parent.");

    // 3. Set the start of this to boundary point (parent, node’s index).
    return set_start_or_end(*parent, node.index(), StartOrEnd::Start);
}

// https://dom.spec.whatwg.org/#dom-range-setstartafter
ExceptionOr<void> Range::set_start_after(Node& node)
{
    // 1. Let parent be node’s parent.
    auto* parent = node.parent();

    // 2. If parent is null, then throw an "InvalidNodeTypeError" DOMException.
    if (!parent)
        return InvalidNodeTypeError::create("Given node has no parent.");

    // 3. Set the start of this to boundary point (parent, node’s index plus 1).
    return set_start_or_end(*parent, node.index() + 1, StartOrEnd::Start);
}

// https://dom.spec.whatwg.org/#dom-range-setendbefore
ExceptionOr<void> Range::set_end_before(Node& node)
{
    // 1. Let parent be node’s parent.
    auto* parent = node.parent();

    // 2. If parent is null, then throw an "InvalidNodeTypeError" DOMException.
    if (!parent)
        return InvalidNodeTypeError::create("Given node has no parent.");

    // 3. Set the end of this to boundary point (parent, node’s index).
    return set_start_or_end(*parent, node.index(), StartOrEnd::End);
}

// https://dom.spec.whatwg.org/#dom-range-setendafter
ExceptionOr<void> Range::set_end_after(Node& node)
{
    // 1. Let parent be node’s parent.
    auto* parent = node.parent();

    // 2. If parent is null, then throw an "InvalidNodeTypeError" DOMException.
    if (!parent)
        return InvalidNodeTypeError::create("Given node has no parent.");

    // 3. Set the end of this to boundary point (parent, node’s index plus 1).
    return set_start_or_end(*parent, node.index() + 1, StartOrEnd::End);
}

// https://dom.spec.whatwg.org/#dom-range-compareboundarypoints
ExceptionOr<i16> Range::compare_boundary_points(u16 how, Range const& source_range) const
{
    // 1. If how is not one of
    //      - START_TO_START,
    //      - START_TO_END,
    //      - END_TO_END, and
    //      - END_TO_START,
    //    then throw a "NotSupportedError" DOMException.
    if (how != HowToCompareBoundaryPoints::START_TO_START && how != HowToCompareBoundaryPoints::START_TO_END && how != HowToCompareBoundaryPoints::END_TO_END && how != HowToCompareBoundaryPoints::END_TO_START)
        return NotSupportedError::create(String::formatted("Expected 'how' to be one of START_TO_START (0), START_TO_END (1), END_TO_END (2) or END_TO_START (3), got {}", how));

    // 2. If this’s root is not the same as sourceRange’s root, then throw a "WrongDocumentError" DOMException.
    if (&root() != &source_range.root())
        return WrongDocumentError::create("This range is not in the same tree as the source range.");

    RefPtr<Node> this_point_node;
    u32 this_point_offset = 0;

    RefPtr<Node> other_point_node;
    u32 other_point_offset = 0;

    // 3. If how is:
    switch (how) {
    case HowToCompareBoundaryPoints::START_TO_START:
        // -> START_TO_START:
        //    Let this point be this’s start. Let other point be sourceRange’s start.
        this_point_node = m_start_container;
        this_point_offset = m_start_offset;

        other_point_node = source_range.m_start_container;
        other_point_offset = source_range.m_start_offset;
        break;
    case HowToCompareBoundaryPoints::START_TO_END:
        // -> START_TO_END:
        //    Let this point be this’s end. Let other point be sourceRange’s start.
        this_point_node = m_end_container;
        this_point_offset = m_end_offset;

        other_point_node = source_range.m_start_container;
        other_point_offset = source_range.m_start_offset;
        break;
    case HowToCompareBoundaryPoints::END_TO_END:
        // -> END_TO_END:
        //    Let this point be this’s end. Let other point be sourceRange’s end.
        this_point_node = m_end_container;
        this_point_offset = m_end_offset;

        other_point_node = source_range.m_end_container;
        other_point_offset = source_range.m_end_offset;
        break;
    case HowToCompareBoundaryPoints::END_TO_START:
        // -> END_TO_START:
        //    Let this point be this’s start. Let other point be sourceRange’s end.
        this_point_node = m_start_container;
        this_point_offset = m_start_offset;

        other_point_node = source_range.m_end_container;
        other_point_offset = source_range.m_end_offset;
        break;
    default:
        VERIFY_NOT_REACHED();
    }

    VERIFY(this_point_node);
    VERIFY(other_point_node);

    // 4. If the position of this point relative to other point is
    auto relative_position = position_of_boundary_point_relative_to_other_boundary_point(*this_point_node, this_point_offset, *other_point_node, other_point_offset);
    switch (relative_position) {
    case RelativeBoundaryPointPosition::Before:
        // -> before
        //    Return −1.
        return -1;
    case RelativeBoundaryPointPosition::Equal:
        // -> equal
        //    Return 0.
        return 0;
    case RelativeBoundaryPointPosition::After:
        // -> after
        //    Return 1.
        return 1;
    default:
        VERIFY_NOT_REACHED();
    }
}

// https://dom.spec.whatwg.org/#concept-range-select
ExceptionOr<void> Range::select(Node& node)
{
    // 1. Let parent be node’s parent.
    auto* parent = node.parent();

    // 2. If parent is null, then throw an "InvalidNodeTypeError" DOMException.
    if (!parent)
        return InvalidNodeTypeError::create("Given node has no parent.");

    // 3. Let index be node’s index.
    auto index = node.index();

    // 4. Set range’s start to boundary point (parent, index).
    m_start_container = *parent;
    m_start_offset = index;

    // 5. Set range’s end to boundary point (parent, index plus 1).
    m_end_container = *parent;
    m_end_offset = index + 1;

    return {};
}

// https://dom.spec.whatwg.org/#dom-range-selectnode
ExceptionOr<void> Range::select_node(Node& node)
{
    // The selectNode(node) method steps are to select node within this.
    return select(node);
}

// https://dom.spec.whatwg.org/#dom-range-collapse
void Range::collapse(bool to_start)
{
    // The collapse(toStart) method steps are to, if toStart is true, set end to start; otherwise set start to end.
    if (to_start) {
        m_end_container = m_start_container;
        m_end_offset = m_start_offset;
        return;
    }

    m_start_container = m_end_container;
    m_start_offset = m_end_offset;
}

// https://dom.spec.whatwg.org/#dom-range-selectnodecontents
ExceptionOr<void> Range::select_node_contents(Node const& node)
{
    // 1. If node is a doctype, throw an "InvalidNodeTypeError" DOMException.
    if (is<DocumentType>(node))
        return InvalidNodeTypeError::create("Node cannot be a DocumentType.");

    // 2. Let length be the length of node.
    auto length = node.length();

    // 3. Set start to the boundary point (node, 0).
    m_start_container = node;
    m_start_offset = 0;

    // 4. Set end to the boundary point (node, length).
    m_end_container = node;
    m_end_offset = length;

    return {};
}

NonnullRefPtr<Range> Range::clone_range() const
{
    return adopt_ref(*new Range(const_cast<Node&>(*m_start_container), m_start_offset, const_cast<Node&>(*m_end_container), m_end_offset));
}

NonnullRefPtr<Range> Range::inverted() const
{
    return adopt_ref(*new Range(const_cast<Node&>(*m_end_container), m_end_offset, const_cast<Node&>(*m_start_container), m_start_offset));
}

NonnullRefPtr<Range> Range::normalized() const
{
    if (m_start_container.ptr() == m_end_container.ptr()) {
        if (m_start_offset <= m_end_offset)
            return clone_range();

        return inverted();
    }

    if (m_start_container->is_before(m_end_container))
        return clone_range();

    return inverted();
}

// https://dom.spec.whatwg.org/#dom-range-commonancestorcontainer
NonnullRefPtr<Node> Range::common_ancestor_container() const
{
    // 1. Let container be start node.
    auto container = m_start_container;

    // 2. While container is not an inclusive ancestor of end node, let container be container’s parent.
    while (!container->is_inclusive_ancestor_of(m_end_container)) {
        VERIFY(container->parent());
        container = *container->parent();
    }

    // 3. Return container.
    return container;
}

// https://dom.spec.whatwg.org/#dom-range-intersectsnode
bool Range::intersects_node(Node const& node) const
{
    // 1. If node’s root is different from this’s root, return false.
    if (&node.root() != &root())
        return false;

    // 2. Let parent be node’s parent.
    auto* parent = node.parent();

    // 3. If parent is null, return true.
    if (!parent)
        return true;

    // 4. Let offset be node’s index.
    auto offset = node.index();

    // 5. If (parent, offset) is before end and (parent, offset plus 1) is after start, return true
    auto relative_position_to_end = position_of_boundary_point_relative_to_other_boundary_point(*parent, offset, m_end_container, m_end_offset);
    auto relative_position_to_start = position_of_boundary_point_relative_to_other_boundary_point(*parent, offset + 1, m_start_container, m_start_offset);
    if (relative_position_to_end == RelativeBoundaryPointPosition::Before && relative_position_to_start == RelativeBoundaryPointPosition::After)
        return true;

    // 6. Return false.
    return false;
}

// https://dom.spec.whatwg.org/#dom-range-ispointinrange
ExceptionOr<bool> Range::is_point_in_range(Node const& node, u32 offset) const
{
    // 1. If node’s root is different from this’s root, return false.
    if (&node.root() != &root())
        return false;

    // 2. If node is a doctype, then throw an "InvalidNodeTypeError" DOMException.
    if (is<DocumentType>(node))
        return InvalidNodeTypeError::create("Node cannot be a DocumentType.");

    // 3. If offset is greater than node’s length, then throw an "IndexSizeError" DOMException.
    if (offset > node.length())
        return IndexSizeError::create(String::formatted("Node does not contain a child at offset {}", offset));

    // 4. If (node, offset) is before start or after end, return false.
    auto relative_position_to_start = position_of_boundary_point_relative_to_other_boundary_point(node, offset, m_start_container, m_start_offset);
    auto relative_position_to_end = position_of_boundary_point_relative_to_other_boundary_point(node, offset, m_end_container, m_end_offset);
    if (relative_position_to_start == RelativeBoundaryPointPosition::Before || relative_position_to_end == RelativeBoundaryPointPosition::After)
        return false;

    // 5. Return true.
    return true;
}

// https://dom.spec.whatwg.org/#dom-range-comparepoint
ExceptionOr<i16> Range::compare_point(Node const& node, u32 offset) const
{
    // 1. If node’s root is different from this’s root, then throw a "WrongDocumentError" DOMException.
    if (&node.root() != &root())
        return WrongDocumentError::create("Given node is not in the same document as the range.");

    // 2. If node is a doctype, then throw an "InvalidNodeTypeError" DOMException.
    if (is<DocumentType>(node))
        return InvalidNodeTypeError::create("Node cannot be a DocumentType.");

    // 3. If offset is greater than node’s length, then throw an "IndexSizeError" DOMException.
    if (offset > node.length())
        return IndexSizeError::create(String::formatted("Node does not contain a child at offset {}", offset));

    // 4. If (node, offset) is before start, return −1.
    auto relative_position_to_start = position_of_boundary_point_relative_to_other_boundary_point(node, offset, m_start_container, m_start_offset);
    if (relative_position_to_start == RelativeBoundaryPointPosition::Before)
        return -1;

    // 5. If (node, offset) is after end, return 1.
    auto relative_position_to_end = position_of_boundary_point_relative_to_other_boundary_point(node, offset, m_end_container, m_end_offset);
    if (relative_position_to_end == RelativeBoundaryPointPosition::After)
        return 1;

    // 6. Return 0.
    return 0;
}

// https://dom.spec.whatwg.org/#dom-range-stringifier
String Range::to_string() const
{
    // 1. Let s be the empty string.
    StringBuilder builder;

    // 2. If this’s start node is this’s end node and it is a Text node,
    //    then return the substring of that Text node’s data beginning at this’s start offset and ending at this’s end offset.
    if (start_container() == end_container() && is<Text>(*start_container()))
        return static_cast<Text const&>(*start_container()).data().substring(start_offset(), end_offset());

    // 3. If this’s start node is a Text node, then append the substring of that node’s data from this’s start offset until the end to s.
    if (is<Text>(*start_container()))
        builder.append(static_cast<Text const&>(*start_container()).data().substring_view(start_offset()));

    // 4. Append the concatenation of the data of all Text nodes that are contained in this, in tree order, to s.
    for (Node const* node = start_container()->next_in_pre_order(); node && node != end_container(); node = node->next_in_pre_order()) {
        if (is<Text>(*node))
            builder.append(static_cast<Text const&>(*node).data());
    }

    // 5. If this’s end node is a Text node, then append the substring of that node’s data from its start until this’s end offset to s.
    if (is<Text>(*end_container()))
        builder.append(static_cast<Text const&>(*end_container()).data().substring_view(0, end_offset()));

    // 6. Return s.
    return builder.to_string();
}

// https://dom.spec.whatwg.org/#dom-range-extractcontents
ExceptionOr<NonnullRefPtr<DocumentFragment>> Range::extract_contents()
{
    return extract();
}

// https://dom.spec.whatwg.org/#concept-range-extract
ExceptionOr<NonnullRefPtr<DocumentFragment>> Range::extract()
{
    // 1. Let fragment be a new DocumentFragment node whose node document is range’s start node’s node document.
    auto fragment = adopt_ref(*new DocumentFragment(const_cast<Document&>(start_container()->document())));

    // 2. If range is collapsed, then return fragment.
    if (collapsed())
        return fragment;

    // 3. Let original start node, original start offset, original end node, and original end offset
    //    be range’s start node, start offset, end node, and end offset, respectively.
    NonnullRefPtr<Node> original_start_node = m_start_container;
    auto original_start_offset = m_start_offset;
    NonnullRefPtr<Node> original_end_node = m_end_container;
    auto original_end_offset = m_end_offset;

    // 4. If original start node is original end node and it is a CharacterData node, then:
    if (original_start_node.ptr() == original_end_node.ptr() && is<CharacterData>(*original_start_node)) {
        // 1. Let clone be a clone of original start node.
        auto clone = original_start_node->clone_node();

        // 2. Set the data of clone to the result of substringing data with node original start node,
        //    offset original start offset, and count original end offset minus original start offset.
        auto result = static_cast<CharacterData const&>(*original_start_node).substring_data(original_start_offset, original_end_offset - original_start_offset);
        if (result.is_exception())
            return result.exception();
        verify_cast<CharacterData>(*clone).set_data(result.release_value());

        // 3. Append clone to fragment.
        fragment->append_child(clone);

        // 4. Replace data with node original start node, offset original start offset, count original end offset minus original start offset, and data the empty string.
        static_cast<CharacterData&>(*original_start_node).replace_data(original_start_offset, original_end_offset - original_start_offset, "");

        // 5. Return fragment.
        return fragment;
    }

    // 5. Let common ancestor be original start node.
    NonnullRefPtr<Node> common_ancestor = original_start_node;

    // 6. While common ancestor is not an inclusive ancestor of original end node, set common ancestor to its own parent.
    while (!common_ancestor->is_inclusive_ancestor_of(original_end_node))
        common_ancestor = *common_ancestor->parent_node();

    // 7. Let first partially contained child be null.
    RefPtr<Node> first_partially_contained_child;

    // 8. If original start node is not an inclusive ancestor of original end node,
    //    set first partially contained child to the first child of common ancestor that is partially contained in range.
    if (!original_start_node->is_inclusive_ancestor_of(original_end_node)) {
        for (auto* child = common_ancestor->first_child(); child; child = child->next_sibling()) {
            if (partially_contains_node(*child)) {
                first_partially_contained_child = child;
                break;
            }
        }
    }

    // 9. Let last partially contained child be null.
    RefPtr<Node> last_partially_contained_child;

    // 10. If original end node is not an inclusive ancestor of original start node,
    //     set last partially contained child to the last child of common ancestor that is partially contained in range.
    if (!original_end_node->is_inclusive_ancestor_of(original_start_node)) {
        for (auto* child = common_ancestor->last_child(); child; child = child->previous_sibling()) {
            if (partially_contains_node(*child)) {
                last_partially_contained_child = child;
                break;
            }
        }
    }

    // 11. Let contained children be a list of all children of common ancestor that are contained in range, in tree order.
    Vector<NonnullRefPtr<Node>> contained_children;
    for (Node const* node = common_ancestor->first_child(); node; node = node->next_sibling()) {
        if (contains_node(*node))
            contained_children.append(*node);
    }

    // 12. If any member of contained children is a doctype, then throw a "HierarchyRequestError" DOMException.
    for (auto const& child : contained_children) {
        if (is<DocumentType>(*child))
            return DOM::HierarchyRequestError::create("Contained child is a DocumentType");
    }

    RefPtr<Node> new_node;
    size_t new_offset = 0;

    // 13. If original start node is an inclusive ancestor of original end node, set new node to original start node and new offset to original start offset.
    if (original_start_node->is_inclusive_ancestor_of(original_end_node)) {
        new_node = original_start_node;
        new_offset = original_start_offset;
    }
    // 14. Otherwise:
    else {
        // 1. Let reference node equal original start node.
        RefPtr<Node> reference_node = original_start_node;

        // 2. While reference node’s parent is not null and is not an inclusive ancestor of original end node, set reference node to its parent.
        while (reference_node->parent_node() && !reference_node->parent_node()->is_inclusive_ancestor_of(original_end_node))
            reference_node = reference_node->parent_node();

        // 3. Set new node to the parent of reference node, and new offset to one plus reference node’s index.
        new_node = reference_node->parent_node();
        new_offset = 1 + reference_node->index();
    }

    // 15. If first partially contained child is a CharacterData node, then:
    if (first_partially_contained_child && is<CharacterData>(*first_partially_contained_child)) {
        // 1. Let clone be a clone of original start node.
        auto clone = original_start_node->clone_node();

        // 2. Set the data of clone to the result of substringing data with node original start node, offset original start offset, and count original start node’s length minus original start offset.
        auto result = static_cast<CharacterData const&>(*original_start_node).substring_data(original_start_offset, original_end_offset - original_start_offset);
        if (result.is_exception())
            return result.exception();
        verify_cast<CharacterData>(*clone).set_data(result.release_value());

        // 3. Append clone to fragment.
        fragment->append_child(clone);

        // 4. Replace data with node original start node, offset original start offset, count original start node’s length minus original start offset, and data the empty string.
        static_cast<CharacterData&>(*original_start_node).replace_data(original_start_offset, original_start_node->length() - original_start_offset, "");
    }
    // 16. Otherwise, if first partially contained child is not null:
    else if (first_partially_contained_child) {
        // 1. Let clone be a clone of first partially contained child.
        auto clone = first_partially_contained_child->clone_node();

        // 2. Append clone to fragment.
        fragment->append_child(clone);

        // 3. Let subrange be a new live range whose start is (original start node, original start offset) and whose end is (first partially contained child, first partially contained child’s length).
        auto subrange = Range::create(original_start_node, original_start_offset, *first_partially_contained_child, first_partially_contained_child->length());

        // 4. Let subfragment be the result of extracting subrange.
        auto result = subrange->extract();
        if (result.is_exception())
            return result.exception();
        auto subfragment = result.release_value();

        // 5. Append subfragment to clone.
        clone->append_child(subfragment);
    }

    // 17. For each contained child in contained children, append contained child to fragment.
    for (auto& contained_child : contained_children) {
        fragment->append_child(contained_child);
    }

    // 18. If last partially contained child is a CharacterData node, then:
    if (last_partially_contained_child && is<CharacterData>(*last_partially_contained_child)) {
        // 1. Let clone be a clone of original end node.
        auto clone = original_end_node->clone_node();

        // 2. Set the data of clone to the result of substringing data with node original end node, offset 0, and count original end offset.
        auto result = static_cast<CharacterData const&>(*original_end_node).substring_data(0, original_end_offset);
        if (result.is_exception())
            return result.exception();
        verify_cast<CharacterData>(*clone).set_data(result.release_value());

        // 3. Append clone to fragment.
        fragment->append_child(clone);

        // 4. Replace data with node original end node, offset 0, count original end offset, and data the empty string.
        verify_cast<CharacterData>(*original_end_node).replace_data(0, original_end_offset, "");
    }
    // 19. Otherwise, if last partially contained child is not null:
    else if (last_partially_contained_child) {
        // 1. Let clone be a clone of last partially contained child.
        auto clone = last_partially_contained_child->clone_node();

        // 2. Append clone to fragment.
        fragment->append_child(clone);

        // 3. Let subrange be a new live range whose start is (last partially contained child, 0) and whose end is (original end node, original end offset).
        auto subrange = Range::create(*last_partially_contained_child, 0, original_end_node, original_end_offset);

        // 4. Let subfragment be the result of extracting subrange.
        auto result = subrange->extract();
        if (result.is_exception())
            return result.exception();
        auto subfragment = result.release_value();

        // 5. Append subfragment to clone.
        clone->append_child(subfragment);
    }

    // 20. Set range’s start and end to (new node, new offset).
    set_start(*new_node, new_offset);
    set_end(*new_node, new_offset);

    // 21. Return fragment.
    return fragment;
}

// https://dom.spec.whatwg.org/#contained
bool Range::contains_node(Node const& node) const
{
    // A node node is contained in a live range range if node’s root is range’s root,
    if (&node.root() != &root())
        return false;

    // and (node, 0) is after range’s start,
    if (position_of_boundary_point_relative_to_other_boundary_point(node, 0, m_start_container, m_start_offset) != RelativeBoundaryPointPosition::After)
        return false;

    // and (node, node’s length) is before range’s end.
    if (position_of_boundary_point_relative_to_other_boundary_point(node, node.length(), m_end_container, m_end_offset) != RelativeBoundaryPointPosition::Before)
        return false;

    return true;
}

// https://dom.spec.whatwg.org/#partially-contained
bool Range::partially_contains_node(Node const& node) const
{
    // A node is partially contained in a live range if it’s an inclusive ancestor of the live range’s start node but not its end node, or vice versa.
    if (node.is_inclusive_ancestor_of(m_start_container) && &node != m_end_container.ptr())
        return true;
    if (node.is_inclusive_ancestor_of(m_end_container) && &node != m_start_container.ptr())
        return true;
    return false;
}

}