/*
 * Copyright (c) 2020-2022, Andreas Kling <andreas@ladybird.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibWeb/CSS/ComputedProperties.h>
#include <LibWeb/CSS/StyleValues/AnchorStyleValue.h>
#include <LibWeb/CSS/StyleValues/KeywordStyleValue.h>
#include <LibWeb/CSS/StyleValues/PercentageStyleValue.h>
#include <LibWeb/DOM/Document.h>
#include <LibWeb/DOM/Element.h>
#include <LibWeb/DOM/ShadowRoot.h>
#include <LibWeb/Dump.h>
#include <LibWeb/HTML/HTMLInputElement.h>
#include <LibWeb/Layout/BlockFormattingContext.h>
#include <LibWeb/Layout/Box.h>
#include <LibWeb/Layout/FlexFormattingContext.h>
#include <LibWeb/Layout/FormattingContext.h>
#include <LibWeb/Layout/GridFormattingContext.h>
#include <LibWeb/Layout/InlineNode.h>
#include <LibWeb/Layout/ReplacedBox.h>
#include <LibWeb/Layout/ReplacedWithChildrenFormattingContext.h>
#include <LibWeb/Layout/SVGFormattingContext.h>
#include <LibWeb/Layout/SVGSVGBox.h>
#include <LibWeb/Layout/TableFormattingContext.h>
#include <LibWeb/Layout/TextInputBox.h>
#include <LibWeb/Layout/TextNode.h>
#include <LibWeb/Layout/Viewport.h>

namespace Web::Layout {

enum class SizeDimension {
    Width,
    Height,
};

// https://drafts.csswg.org/css-sizing-3/#intrinsic-sizes
static Optional<CSSPixels> max_content_size_for_replaced_element_without_natural_size(Box const& box, CSS::SizeWithAspectRatio const& natural_size, SizeDimension dimension, Optional<CSSPixels> definite_opposite_size = {})
{
    // the intrinsic sizes of replaced elements without natural sizes are defined below:
    auto is_width = dimension == SizeDimension::Width;
    if (!box.is_replaced_box() || (is_width ? natural_size.has_width() : natural_size.has_height()))
        return {};

    // SVG Integration says that a non-top-level <svg> starts with auto width/height, and that with a viewBox, missing
    // width/height attributes "keep" their auto value. The resulting width, height, and aspect ratio are then
    // "used in CSS sizing as intrinsic element size properties".
    //
    // CSS Sizing defines max-content as the size the box would have "if it was a float" with an auto preferred size.
    // CSS2 replaced sizing then resolves auto width from "(used height) * (intrinsic ratio)", and auto height from
    // "(used width) / (intrinsic ratio)". Keep this SVG specific bridge before falling through to CSS Sizing's fallback
    // for replaced elements without natural sizes.
    //  - https://svgwg.org/specs/integration/#svg-css-sizing
    //  - https://drafts.csswg.org/css-sizing-3/#intrinsic-sizes
    //  - https://drafts.csswg.org/css2/#inline-replaced-width
    //  - https://drafts.csswg.org/css2/#inline-replaced-height
    if (box.is_svg_svg_box() && natural_size.has_aspect_ratio()) {
        if (is_width && natural_size.has_height())
            return natural_size.height.value() * natural_size.aspect_ratio.value();
        if (!is_width && natural_size.has_width())
            return natural_size.width.value() / natural_size.aspect_ratio.value();
    }

    // For the max-content size:
    // If it has a preferred aspect ratio:
    if (natural_size.has_aspect_ratio()) {
        auto aspect_ratio = natural_size.aspect_ratio.value();

        // If the available space is definite in the inline axis, use the stretch fit into that size for the inline size
        // and calculate the block size using the aspect ratio.
        //
        // NB: This helper is only for the max-content size, which has no definite available inline size. Callers may
        //     still know a definite used size in the opposite axis when the box lacks a natural size in that axis.
        if (definite_opposite_size.has_value()) {
            auto opposite_size = definite_opposite_size.value();
            return is_width ? opposite_size * aspect_ratio : opposite_size / aspect_ratio;
        }

        // Otherwise if the box has a <length> as its computed value for min-width or min-height, use that size and
        // calculate the other dimension using the aspect ratio; if both dimensions have a <length> minimum, choose the
        // one that results in the larger overall size.
        //
        // NOTE: This case was previous calculated from a 300x150 default size, rather than the box’s min size. This is
        //       believed to be a better behavior, and likely to be Web-compatible, but please send feedback to the CSSWG
        //       if there are any problems.
        Optional<CSSPixels> size_from_min_width;
        auto const& min_width = box.computed_values().min_width();
        if (min_width.is_length()) {
            auto inline_size = min_width.to_px(box, 0);
            size_from_min_width = is_width ? inline_size : inline_size / aspect_ratio;
        }

        Optional<CSSPixels> size_from_min_height;
        auto const& min_height = box.computed_values().min_height();
        if (min_height.is_length()) {
            auto block_size = min_height.to_px(box, 0);
            size_from_min_height = is_width ? block_size * aspect_ratio : block_size;
        }

        if (size_from_min_width.has_value() && size_from_min_height.has_value())
            return max(size_from_min_width.value(), size_from_min_height.value());
        if (size_from_min_width.has_value())
            return size_from_min_width.value();
        if (size_from_min_height.has_value())
            return size_from_min_height.value();

        // Otherwise use an inline size matching the corresponding dimension of the initial containing block and calculate
        // the other dimension using the aspect ratio.
        //
        // NOTE: This author-controllable behavior is made possible by the new auto value for the min size properties.
        //       This is believed to be a better behavior, but it is not yet clear if it is Web-compatible, so please
        //       send feedback to the CSSWG if there are any problems.
        auto inline_size = box.document().viewport_rect().width();
        return is_width ? inline_size : inline_size / aspect_ratio;
    }

    // If it has no preferred aspect ratio:
    // For both the min-content size and max-content size:
    // If the box has a <length> as its computed minimum size (min-width/min-height) in that dimension, use that size.
    auto const& min_size = is_width ? box.computed_values().min_width() : box.computed_values().min_height();
    if (min_size.is_length())
        return min_size.to_px(box, 0);

    // Otherwise, use 300px for the width and/or 150px for the height as needed.
    return is_width ? CSSPixels(300) : CSSPixels(150);
}

static bool is_text_control_input(HTML::HTMLInputElement const& input_element)
{
    switch (input_element.type_state()) {
    case HTML::HTMLInputElement::TypeAttributeState::Text:
    case HTML::HTMLInputElement::TypeAttributeState::Search:
    case HTML::HTMLInputElement::TypeAttributeState::URL:
    case HTML::HTMLInputElement::TypeAttributeState::Telephone:
    case HTML::HTMLInputElement::TypeAttributeState::Email:
    case HTML::HTMLInputElement::TypeAttributeState::Password:
    case HTML::HTMLInputElement::TypeAttributeState::Number:
        return true;
    default:
        return false;
    }
}

static Optional<CSS::SizeWithAspectRatio> appearance_none_text_input_auto_content_box_size(Box const& box)
{
    if (box.computed_values().appearance() != CSS::Appearance::None)
        return {};

    auto const* input_element = as_if<HTML::HTMLInputElement>(box.dom_node());
    if (!input_element || !is_text_control_input(*input_element))
        return {};

    // https://drafts.csswg.org/css-ui/#appearance-switching
    // "Widgets must not have their native appearance, and instead must have their primitive appearance."
    //
    // https://html.spec.whatwg.org/multipage/input.html#the-size-attribute
    // "The size attribute gives the number of characters that, in a visual rendering, the user agent is to allow the
    // user to see while editing the element's value."
    return TextInputBox::auto_content_box_size_for_text_control(*input_element, box);
}

FormattingContext::FormattingContext(Type type, LayoutMode layout_mode, LayoutState& state, Box const& context_box, FormattingContext* parent)
    : m_type(type)
    , m_layout_mode(layout_mode)
    , m_parent(parent)
    , m_context_box(context_box)
    , m_state(state)
{
}

FormattingContext::~FormattingContext() = default;

bool FormattingContext::computed_height_establishes_definite_containing_block_height(CSS::Size const& computed_height)
{
    // A resolved used height is not always a definite containing block height.
    // Intrinsic sizing keywords like fit-content still depend on child layout,
    // so percentage-height descendants must continue to treat them as indefinite.
    return !computed_height.is_intrinsic_sizing_constraint();
}

// https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Block_formatting_context
bool FormattingContext::creates_block_formatting_context(Box const& box)
{
    // NOTE: Replaced elements never create a BFC.
    if (box.is_replaced_box())
        return false;

    // AD-HOC: We create a BFC for SVG foreignObject.
    if (box.is_svg_foreign_object_box())
        return true;

    // display: table
    if (box.display().is_table_inside()) {
        return false;
    }

    // display: flex
    if (box.display().is_flex_inside()) {
        return false;
    }

    // display: grid
    if (box.display().is_grid_inside()) {
        return false;
    }

    // NOTE: This function uses MDN as a reference, not because it's authoritative,
    //       but because they've gathered all the conditions in one convenient location.

    // The root element of the document (<html>).
    if (box.is_root_element())
        return true;

    // Floats (elements where float isn't none).
    if (box.is_floating())
        return true;

    // Absolutely positioned elements (elements where position is absolute or fixed).
    if (box.is_absolutely_positioned())
        return true;

    // Inline-blocks (elements with display: inline-block).
    if (box.display().is_inline_block())
        return true;

    // Table cells (elements with display: table-cell, which is the default for HTML table cells).
    if (box.display().is_table_cell())
        return true;

    // Table captions (elements with display: table-caption, which is the default for HTML table captions).
    if (box.display().is_table_caption())
        return true;

    // FIXME: Anonymous table cells implicitly created by the elements with display: table, table-row, table-row-group, table-header-group, table-footer-group
    //        (which is the default for HTML tables, table rows, table bodies, table headers, and table footers, respectively), or inline-table.

    // Block elements where overflow has a value other than visible and clip.
    CSS::Overflow overflow_x = box.computed_values().overflow_x();
    if ((overflow_x != CSS::Overflow::Visible) && (overflow_x != CSS::Overflow::Clip))
        return true;
    CSS::Overflow overflow_y = box.computed_values().overflow_y();
    if ((overflow_y != CSS::Overflow::Visible) && (overflow_y != CSS::Overflow::Clip))
        return true;

    // display: flow-root.
    if (box.display().is_flow_root_inside())
        return true;

    // https://drafts.csswg.org/css-contain-2/#containment-types
    // 1. The layout containment box establishes an independent formatting context.
    // 4. The paint containment box establishes an independent formatting context.
    if (box.has_layout_containment() || box.has_paint_containment())
        return true;

    // https://drafts.csswg.org/css-conditional-5/#valdef-container-type-size
    // Applies style containment and size containment to the principal box, and establishes an independent formatting
    // context.
    if (box.computed_values().container_type().is_size_container || box.computed_values().container_type().is_inline_size_container)
        return true;

    if (box.parent()) {
        auto parent_display = box.parent()->display();

        // Flex items (direct children of the element with display: flex or inline-flex) if they are neither flex nor grid nor table containers themselves.
        if (parent_display.is_flex_inside())
            return true;
        // Grid items (direct children of the element with display: grid or inline-grid) if they are neither flex nor grid nor table containers themselves.
        if (parent_display.is_grid_inside())
            return true;
    }

    // https://drafts.csswg.org/css-multicol-2/#the-multi-column-model
    // An element whose 'column-width', 'column-count', or 'column-height' property is not 'auto' establishes a multi-
    // column container (or multicol container for short), and therefore acts as a container for multi-column layout.
    // FIXME: Maybe add column-height, depending on the resolution for https://github.com/w3c/csswg-drafts/issues/12688
    if (!box.computed_values().column_width().is_auto() || !box.computed_values().column_count().is_auto())
        return true;

    // FIXME: column-span: all should always create a new formatting context, even when the column-span: all element isn't contained by a multicol container (Spec change, Chrome bug).

    // https://html.spec.whatwg.org/multipage/rendering.html#the-fieldset-and-legend-elements
    if (box.is_fieldset_box())
        // The fieldset element, when it generates a CSS box, is expected to act as follows:
        // The element is expected to establish a new block formatting context.
        return true;

    return false;
}

Optional<FormattingContext::Type> FormattingContext::formatting_context_type_created_by_box(Box const& box)
{
    if (is<SVGSVGBox>(box))
        return Type::SVG;

    if (box.is_replaced_box_with_children())
        return Type::ReplacedWithChildren;

    if (box.is_replaced_box())
        return Type::InternalReplaced;

    if (!box.can_have_children())
        return {};

    auto display = box.display();

    if (display.is_flex_inside())
        return Type::Flex;

    if (display.is_table_inside())
        return Type::Table;

    if (display.is_grid_inside())
        return Type::Grid;

    if (display.is_math_inside())
        // FIXME: We should create a MathML-specific formatting context here, but for now use a BFC, so _something_ is displayed
        return Type::Block;

    if (creates_block_formatting_context(box))
        return Type::Block;

    if (box.children_are_inline())
        return {};

    if (display.is_table_column() || display.is_table_row_group() || display.is_table_header_group() || display.is_table_footer_group() || display.is_table_row() || display.is_table_column_group())
        return {};

    // The box is a block container that doesn't create its own BFC.
    // It will be formatted by the containing BFC.
    if (!display.is_flow_inside()) {
        // HACK: Instead of crashing, create a dummy formatting context that does nothing.
        // FIXME: We need this for <math> elements
        return Type::InternalDummy;
    }
    return {};
}

// FIXME: This is a hack. Get rid of it.
struct ReplacedFormattingContext : public FormattingContext {
    ReplacedFormattingContext(LayoutState& state, LayoutMode layout_mode, Box const& box)
        : FormattingContext(Type::InternalReplaced, layout_mode, state, box)
    {
    }
    virtual CSSPixels automatic_content_width() const override { return 0; }
    virtual CSSPixels automatic_content_height() const override { return 0; }
    virtual void run(AvailableSpace const&) override { }
};

// FIXME: This is a hack. Get rid of it.
struct DummyFormattingContext : public FormattingContext {
    DummyFormattingContext(LayoutState& state, LayoutMode layout_mode, Box const& box)
        : FormattingContext(Type::InternalDummy, layout_mode, state, box)
    {
    }
    virtual CSSPixels automatic_content_width() const override { return 0; }
    virtual CSSPixels automatic_content_height() const override { return 0; }
    virtual void run(AvailableSpace const&) override { }
};

OwnPtr<FormattingContext> FormattingContext::create_independent_formatting_context_if_needed(LayoutState& state, LayoutMode layout_mode, Box const& child_box)
{
    auto type = formatting_context_type_created_by_box(child_box);
    if (!type.has_value())
        return nullptr;

    switch (type.value()) {
    case Type::Block:
        return make<BlockFormattingContext>(state, layout_mode, as<BlockContainer>(child_box), this);
    case Type::SVG:
        return make<SVGFormattingContext>(state, layout_mode, child_box, this);
    case Type::Flex:
        return make<FlexFormattingContext>(state, layout_mode, child_box, this);
    case Type::Grid:
        return make<GridFormattingContext>(state, layout_mode, child_box, this);
    case Type::Table:
        return make<TableFormattingContext>(state, layout_mode, child_box, this);
    case Type::ReplacedWithChildren:
        return make<ReplacedWithChildrenFormattingContext>(state, layout_mode, child_box, this);
    case Type::InternalReplaced:
        return make<ReplacedFormattingContext>(state, layout_mode, child_box);
    case Type::InternalDummy:
        return make<DummyFormattingContext>(state, layout_mode, child_box);
    case Type::Inline:
        // IFC should always be created by a parent BFC directly.
        VERIFY_NOT_REACHED();
        break;
    default:
        VERIFY_NOT_REACHED();
    }
}

NonnullOwnPtr<FormattingContext> FormattingContext::create_independent_formatting_context(LayoutState& state, LayoutMode layout_mode, Box const& child_box)
{
    if (auto context = create_independent_formatting_context_if_needed(state, layout_mode, child_box))
        return context.release_nonnull();

    if (auto child_block_container = as_if<BlockContainer>(child_box))
        return make<BlockFormattingContext>(state, layout_mode, *child_block_container, nullptr);

    // HACK: Instead of crashing in scenarios that assume the formatting context can be created, create a dummy formatting context that does nothing.
    dbgln("FIXME: An independent formatting context was requested from a Box that does not have a formatting context type. A dummy formatting context will be created instead.");
    return make<DummyFormattingContext>(state, layout_mode, child_box);
}

OwnPtr<FormattingContext> FormattingContext::layout_inside(Box const& child_box, LayoutMode layout_mode, AvailableSpace const& available_space)
{
    {
        // OPTIMIZATION: If we're doing intrinsic sizing and `child_box` has definite size in both axes,
        //               we don't need to layout its insides. The size is resolvable without learning
        //               the metrics of whatever's inside the box.
        auto const& used_values = m_state.get(child_box);
        if (layout_mode == LayoutMode::IntrinsicSizing
            && used_values.width_constraint == SizeConstraint::None
            && used_values.height_constraint == SizeConstraint::None
            && used_values.has_definite_width()
            && used_values.has_definite_height()) {
            return nullptr;
        }
    }

    if (!child_box.can_have_children())
        return {};

    auto independent_formatting_context = create_independent_formatting_context_if_needed(m_state, layout_mode, child_box);
    if (independent_formatting_context)
        independent_formatting_context->run(available_space);
    else
        run(available_space);

    return independent_formatting_context;
}

CSSPixels FormattingContext::greatest_child_width(Box const& box) const
{
    CSSPixels max_width = 0;
    if (box.children_are_inline()) {
        for (auto& line_box : m_state.get(box).line_boxes)
            max_width = max(max_width, line_box_physical_width(box, line_box));
    } else {
        box.for_each_child_of_type<Box>([&](Box const& child) {
            if (!child.is_absolutely_positioned())
                max_width = max(max_width, m_state.get(child).margin_box_width());
            return IterationDecision::Continue;
        });
    }
    return max_width;
}

CSSPixels FormattingContext::line_box_physical_width(Box const& box, LineBox const& line_box)
{
    if (box.computed_values().writing_mode() == CSS::WritingMode::HorizontalTb)
        return line_box.width();

    CSSPixels leftmost_fragment_x = 0;
    CSSPixels rightmost_fragment_x = 0;
    bool saw_fragment = false;
    for (auto const& fragment : line_box.fragments()) {
        auto fragment_left = fragment.offset().x();
        auto fragment_right = fragment_left + fragment.width();
        leftmost_fragment_x = saw_fragment ? min(leftmost_fragment_x, fragment_left) : fragment_left;
        rightmost_fragment_x = saw_fragment ? max(rightmost_fragment_x, fragment_right) : fragment_right;
        saw_fragment = true;
    }

    if (!saw_fragment)
        return 0;

    return rightmost_fragment_x - leftmost_fragment_x;
}

FormattingContext::ShrinkToFitResult FormattingContext::calculate_shrink_to_fit_widths(Box const& box)
{
    return {
        .preferred_width = calculate_max_content_width(box),
        .preferred_minimum_width = calculate_min_content_width(box),
    };
}

CSSPixelSize FormattingContext::solve_replaced_size_constraint(CSSPixels input_width, CSSPixels input_height, Box const& box, AvailableSpace const& available_space) const
{
    // 10.4 Minimum and maximum widths: 'min-width' and 'max-width'
    // https://www.w3.org/TR/CSS22/visudet.html#min-max-widths

    auto min_width = box.computed_values().min_width().is_auto() ? 0 : calculate_inner_width(box, available_space.width, box.computed_values().min_width());
    auto specified_max_width = should_treat_max_width_as_none(box, available_space.width) ? input_width : calculate_inner_width(box, available_space.width, box.computed_values().max_width());
    auto max_width = max(min_width, specified_max_width);

    auto min_height = box.computed_values().min_height().is_auto() ? 0 : calculate_inner_height(box, available_space, box.computed_values().min_height());
    auto specified_max_height = should_treat_max_height_as_none(box, available_space.height) ? input_height : calculate_inner_height(box, available_space, box.computed_values().max_height());
    auto max_height = max(min_height, specified_max_height);

    CSSPixelFraction aspect_ratio = *box.preferred_aspect_ratio();

    // These are from the "Constraint Violation" table in spec, but reordered so that each condition is
    // interpreted as mutually exclusive to any other.
    if (input_width < min_width && input_height > max_height)
        return { min_width, max_height };
    if (input_width > max_width && input_height < min_height)
        return { max_width, min_height };

    if (input_width > 0 && input_height > 0) {
        if (input_width > max_width && input_height > max_height && max_width / input_width <= max_height / input_height)
            return { max_width, max(min_height, max_width / aspect_ratio) };
        if (input_width > max_width && input_height > max_height && max_width / input_width > max_height / input_height)
            return { max(min_width, max_height * aspect_ratio), max_height };
        if (input_width < min_width && input_height < min_height && min_width / input_width <= min_height / input_height)
            return { min(max_width, min_height * aspect_ratio), min_height };
        if (input_width < min_width && input_height < min_height && min_width / input_width > min_height / input_height)
            return { min_width, min(max_height, min_width / aspect_ratio) };
    }

    if (input_width > max_width)
        return { max_width, max(max_width / aspect_ratio, min_height) };
    if (input_width < min_width)
        return { min_width, min(min_width / aspect_ratio, max_height) };
    if (input_height > max_height)
        return { max(max_height * aspect_ratio, min_width), max_height };
    if (input_height < min_height)
        return { min(min_height * aspect_ratio, max_width), min_height };

    return { input_width, input_height };
}

Optional<CSSPixels> FormattingContext::compute_auto_height_for_absolutely_positioned_element(Box const& box, AvailableSpace const& available_space, BeforeOrAfterInsideLayout before_or_after_inside_layout) const
{
    // NOTE: CSS 2.2 tells us to use the "auto height for block formatting context roots" here.
    //       That's fine as long as the box is a BFC root.
    if (creates_block_formatting_context(box)) {
        if (before_or_after_inside_layout == BeforeOrAfterInsideLayout::Before)
            return {};
        return compute_auto_height_for_block_formatting_context_root(box);
    }

    // NOTE: For anything else, we use the fit-content height.
    //       This should eventually be replaced by the new absolute positioning model:
    //       https://www.w3.org/TR/css-position-3/#abspos-layout
    return calculate_fit_content_height(box, m_state.get(box).available_inner_space_or_constraints_from(available_space));
}

// https://www.w3.org/TR/CSS22/visudet.html#root-height
CSSPixels FormattingContext::compute_auto_height_for_block_formatting_context_root(Box const& root) const
{
    // 10.6.7 'Auto' heights for block formatting context roots
    Optional<CSSPixels> top;
    Optional<CSSPixels> bottom;

    if (root.children_are_inline()) {
        // If it only has inline-level children, the height is the distance between
        // the top content edge and the bottom of the bottommost line box.
        auto const& line_boxes = m_state.get(root).line_boxes;
        top = 0;
        if (!line_boxes.is_empty())
            bottom = line_boxes.last().bottom();
    } else {
        // If it has block-level children, the height is the distance between
        // the top margin-edge of the topmost block-level child box
        // and the bottom margin-edge of the bottommost block-level child box.

        // NOTE: The top margin edge of the topmost block-level child box is the same as the top content edge of the root box.
        top = 0;

        root.for_each_child_of_type<Box>([&](Layout::Box& child_box) {
            // Absolutely positioned children are ignored,
            // and relatively positioned boxes are considered without their offset.
            // Note that the child box may be an anonymous block box.
            if (child_box.is_absolutely_positioned())
                return IterationDecision::Continue;

            // FIXME: This doesn't look right.
            if ((root.computed_values().overflow_y() == CSS::Overflow::Visible) && child_box.is_floating())
                return IterationDecision::Continue;

            auto const& child_box_state = m_state.get(child_box);

            CSSPixels child_box_bottom = child_box_state.offset.y() + child_box_state.content_height() + child_box_state.margin_box_bottom();

            if (!bottom.has_value() || child_box_bottom > bottom.value())
                bottom = child_box_bottom;

            return IterationDecision::Continue;
        });
    }

    // In addition, if the element has any floating descendants
    // whose bottom margin edge is below the element's bottom content edge,
    // then the height is increased to include those edges.
    for (auto floating_box : m_state.get(root).floating_descendants()) {
        // NOTE: Floating box coordinates are relative to their own containing block,
        //       which may or may not be the BFC root.
        auto margin_box = margin_box_rect_in_ancestor_coordinate_space(*floating_box, root);
        CSSPixels floating_box_bottom_margin_edge = margin_box.bottom();
        if (!bottom.has_value() || floating_box_bottom_margin_edge > bottom.value())
            bottom = floating_box_bottom_margin_edge;
    }

    return max(CSSPixels(0.0f), bottom.value_or(0) - top.value_or(0));
}

// 17.5.2 Table width algorithms: the 'table-layout' property
// https://www.w3.org/TR/CSS22/tables.html#width-layout
CSSPixels FormattingContext::compute_table_box_width_inside_table_wrapper(
    Box const& box,
    AvailableSpace const& available_space,
    Optional<CSSPixels> table_wrapper_containing_block_width,
    TableWrapperWidthMode table_wrapper_width_mode)
{
    // CSS 2 says the table wrapper width is the border-edge width of the table grid box inside it.

    auto const& computed_values = box.computed_values();

    auto width_of_containing_block = table_wrapper_containing_block_width.value_or(available_space.width.to_px_or_zero());

    // If 'margin-left', or 'margin-right' are computed as 'auto', their used value is '0'.
    auto margin_left = computed_values.margin().left().to_px_or_zero(box, width_of_containing_block);
    auto margin_right = computed_values.margin().right().to_px_or_zero(box, width_of_containing_block);

    // table-wrapper can't have borders or paddings but it might have margin taken from table-root.
    auto available_width = width_of_containing_block - margin_left - margin_right;

    Optional<Box const&> table_box;
    box.for_each_in_subtree_of_type<Box>([&](Box const& child_box) {
        if (child_box.display().is_table_inside()) {
            table_box = child_box;
            return TraversalDecision::Break;
        }
        return TraversalDecision::Continue;
    });
    VERIFY(table_box.has_value());

    LayoutState throwaway_state(box);
    auto& containing_block_state = throwaway_state.populate_node_from(m_state, *box.containing_block());
    // CSS Grid lays out grid items into their grid-area containing blocks, which need not match the layout-tree
    // containing block. Use the explicit grid-area width when measuring a table wrapper for grid alignment.
    if (table_wrapper_containing_block_width.has_value())
        containing_block_state.set_content_width(*table_wrapper_containing_block_width);

    auto& table_box_state = throwaway_state.get_mutable(*table_box);
    auto const& table_box_computed_values = table_box->computed_values();
    table_box_state.border_left = table_box_computed_values.border_left().width;
    table_box_state.border_right = table_box_computed_values.border_right().width;
    table_box_state.padding_left = table_box_computed_values.padding().left().to_px_or_zero(*table_box, width_of_containing_block);
    table_box_state.padding_right = table_box_computed_values.padding().right().to_px_or_zero(*table_box, width_of_containing_block);

    auto context = make<TableFormattingContext>(throwaway_state, LayoutMode::IntrinsicSizing, *table_box, this);
    context->run_until_width_calculation(m_state.get(*table_box).available_inner_space_or_constraints_from(available_space));

    auto table_used_width = throwaway_state.get(*table_box).border_box_width();
    if (table_wrapper_width_mode == TableWrapperWidthMode::UseTableUsedWidthIfNotAuto
        && !table_box->computed_values().width().is_auto()) {
        return table_used_width;
    }
    return available_space.width.is_definite() ? min(table_used_width, available_width) : table_used_width;
}

// 17.5.3 Table height algorithms
// https://www.w3.org/TR/CSS22/tables.html#height-layout
CSSPixels FormattingContext::compute_table_box_height_inside_table_wrapper(Box const& box, AvailableSpace const& available_space)
{
    // Table wrapper height should be equal to height of table box it contains

    auto const& computed_values = box.computed_values();

    auto width_of_containing_block = available_space.width.to_px_or_zero();
    auto height_of_containing_block = available_space.height.to_px_or_zero();

    // If 'margin-top', or 'margin-bottom' are computed as 'auto', their used value is '0'.
    auto margin_top = computed_values.margin().top().resolved_or_auto(box, width_of_containing_block).to_px_or_zero(box);
    auto margin_bottom = computed_values.margin().bottom().resolved_or_auto(box, width_of_containing_block).to_px_or_zero(box);

    // table-wrapper can't have borders or paddings but it might have margin taken from table-root.
    auto available_height = height_of_containing_block - margin_top - margin_bottom;

    LayoutState throwaway_state(box);
    throwaway_state.populate_node_from(m_state, *box.containing_block());

    auto context = create_independent_formatting_context_if_needed(throwaway_state, LayoutMode::IntrinsicSizing, box);
    VERIFY(context);
    context->run(m_state.get(box).available_inner_space_or_constraints_from(available_space));

    Optional<Box const&> table_box;
    box.for_each_in_subtree_of_type<Box>([&](Box const& child_box) {
        if (child_box.display().is_table_inside()) {
            table_box = child_box;
            return TraversalDecision::Break;
        }
        return TraversalDecision::Continue;
    });
    VERIFY(table_box.has_value());

    auto table_used_height = throwaway_state.get(*table_box).border_box_height();
    return available_space.height.is_definite() ? min(table_used_height, available_height) : table_used_height;
}

// 10.3.2 Inline, replaced elements, https://www.w3.org/TR/CSS22/visudet.html#inline-replaced-width
CSSPixels FormattingContext::tentative_width_for_replaced_element(Box const& box, CSS::Size const& computed_width, AvailableSpace const& available_space) const
{
    // Treat percentages of indefinite containing block widths as 0 (the initial width).
    if (computed_width.is_percentage() && !m_state.get(*box.containing_block()).has_definite_width())
        return 0;

    auto computed_height = should_treat_height_as_auto(box, available_space) ? CSS::Size::make_auto() : box.computed_values().height();

    CSSPixels used_width = 0;
    if (computed_width.is_auto()) {
        used_width = computed_width.to_px(box, available_space.width.to_px_or_zero());
    } else {
        used_width = calculate_inner_width(box, available_space.width, computed_width);
    }

    // If 'height' and 'width' both have computed values of 'auto' and the element also has an intrinsic width,
    // then that intrinsic width is the used value of 'width'.
    auto intrinsic = box.auto_content_box_size();
    if (computed_height.is_auto() && computed_width.is_auto() && intrinsic.has_width())
        return intrinsic.width.value();

    // If 'height' and 'width' both have computed values of 'auto' and the element has no intrinsic width,
    // but does have an intrinsic height and intrinsic ratio;
    // or if 'width' has a computed value of 'auto',
    // 'height' has some other computed value, and the element does have an intrinsic ratio; then the used value of 'width' is:
    //
    //     (used height) * (intrinsic ratio)
    if ((computed_height.is_auto() && computed_width.is_auto() && !intrinsic.has_width() && intrinsic.has_height() && box.has_preferred_aspect_ratio())
        || (computed_width.is_auto() && !computed_height.is_auto() && box.has_preferred_aspect_ratio())) {
        return compute_height_for_replaced_element(box, available_space) * box.preferred_aspect_ratio().value();
    }

    // If 'height' and 'width' both have computed values of 'auto' and the element has an intrinsic ratio but no intrinsic height or width,
    // then the used value of 'width' is undefined in CSS 2.2. However, it is suggested that, if the containing block's width does not itself
    // depend on the replaced element's width, then the used value of 'width' is calculated from the constraint equation used for block-level,
    // non-replaced elements in normal flow.
    if (computed_height.is_auto() && computed_width.is_auto() && !intrinsic.has_width() && !intrinsic.has_height() && box.has_preferred_aspect_ratio()) {
        return calculate_stretch_fit_width(box, available_space.width);
    }

    // Otherwise, if 'width' has a computed value of 'auto', and the element has an intrinsic width, then that intrinsic width is the used value of 'width'.
    if (computed_width.is_auto() && intrinsic.has_width())
        return intrinsic.width.value();

    // Otherwise, if 'width' has a computed value of 'auto', but none of the conditions above are met, then the used value of 'width' becomes 300px.
    // If 300px is too wide to fit the device, UAs should use the width of the largest rectangle that has a 2:1 ratio and fits the device instead.
    if (computed_width.is_auto())
        return 300;

    return used_width;
}

void FormattingContext::compute_width_for_absolutely_positioned_element(Box const& box, AvailableSpace const& available_space)
{
    if (box_is_sized_as_replaced_element(box, available_space))
        compute_width_for_absolutely_positioned_replaced_element(box, available_space);
    else
        compute_width_for_absolutely_positioned_non_replaced_element(box, available_space);
}

void FormattingContext::compute_height_for_absolutely_positioned_element(Box const& box, AvailableSpace const& available_space, BeforeOrAfterInsideLayout before_or_after_inside_layout)
{
    if (box_is_sized_as_replaced_element(box, available_space))
        compute_height_for_absolutely_positioned_replaced_element(box, available_space, before_or_after_inside_layout);
    else
        compute_height_for_absolutely_positioned_non_replaced_element(box, available_space, before_or_after_inside_layout);
}

CSSPixels FormattingContext::compute_width_for_replaced_element(Box const& box, AvailableSpace const& available_space) const
{
    // 10.3.4 Block-level, replaced elements in normal flow...
    // 10.3.2 Inline, replaced elements

    auto computed_width = should_treat_width_as_auto(box, available_space) ? CSS::Size::make_auto() : box.computed_values().width();
    auto computed_height = should_treat_height_as_auto(box, available_space) ? CSS::Size::make_auto() : box.computed_values().height();

    // 1. The tentative used width is calculated (without 'min-width' and 'max-width')
    auto used_width = tentative_width_for_replaced_element(box, computed_width, available_space);

    if (computed_width.is_auto() && computed_height.is_auto() && box.has_preferred_aspect_ratio()) {
        CSSPixels w = used_width;
        CSSPixels h = tentative_height_for_replaced_element(box, computed_height, available_space);
        used_width = solve_replaced_size_constraint(w, h, box, available_space).width();
    }

    // 2. If the tentative used width is greater than 'max-width', the rules above are applied again,
    //    but this time using the computed value of 'max-width' as the computed value for 'width'.
    if (!should_treat_max_width_as_none(box, available_space.width)) {
        auto const& computed_max_width = box.computed_values().max_width();
        auto max_width = calculate_inner_width(box, available_space.width, computed_max_width);
        if (used_width > max_width)
            used_width = tentative_width_for_replaced_element(box, computed_max_width, available_space);
    }

    // 3. If the resulting width is smaller than 'min-width', the rules above are applied again,
    //    but this time using the value of 'min-width' as the computed value for 'width'.
    auto computed_min_width = box.computed_values().min_width();
    if (!computed_min_width.is_auto()) {
        auto min_width = calculate_inner_width(box, available_space.width, computed_min_width);
        if (used_width < min_width)
            used_width = tentative_width_for_replaced_element(box, computed_min_width, available_space);
    }

    return used_width;
}

// 10.6.2 Inline replaced elements, block-level replaced elements in normal flow, 'inline-block' replaced elements in normal flow and floating replaced elements
// https://www.w3.org/TR/CSS22/visudet.html#inline-replaced-height
CSSPixels FormattingContext::tentative_height_for_replaced_element(Box const& box, CSS::Size const& computed_height, AvailableSpace const& available_space) const
{
    auto intrinsic = box.auto_content_box_size();
    // If 'height' and 'width' both have computed values of 'auto' and the element also has
    // an intrinsic height, then that intrinsic height is the used value of 'height'.
    if (should_treat_width_as_auto(box, available_space) && should_treat_height_as_auto(box, available_space) && intrinsic.has_height())
        return intrinsic.height.value();

    // Otherwise, if 'height' has a computed value of 'auto', and the element has an intrinsic ratio then the used value of 'height' is:
    //
    //     (used width) / (intrinsic ratio)
    if (computed_height.is_auto() && box.has_preferred_aspect_ratio())
        return m_state.get(box).content_width() / box.preferred_aspect_ratio().value();

    // Otherwise, if 'height' has a computed value of 'auto', and the element has an intrinsic height, then that intrinsic height is the used value of 'height'.
    if (computed_height.is_auto() && intrinsic.has_height())
        return intrinsic.height.value();

    // Otherwise, if 'height' has a computed value of 'auto', but none of the conditions above are met,
    // then the used value of 'height' must be set to the height of the largest rectangle that has a 2:1 ratio, has a height not greater than 150px,
    // and has a width not greater than the device width.
    if (computed_height.is_auto())
        return 150;

    // FIXME: Handle cases when available_space is not definite.
    return calculate_inner_height(box, available_space, computed_height);
}

CSSPixels FormattingContext::compute_height_for_replaced_element(Box const& box, AvailableSpace const& available_space) const
{
    // 10.6.2 Inline replaced elements
    // 10.6.4 Block-level replaced elements in normal flow
    // 10.6.6 Floating replaced elements
    // 10.6.10 'inline-block' replaced elements in normal flow

    auto computed_width = should_treat_width_as_auto(box, available_space) ? CSS::Size::make_auto() : box.computed_values().width();
    auto computed_height = should_treat_height_as_auto(box, available_space) ? CSS::Size::make_auto() : box.computed_values().height();

    // 1. The tentative used height is calculated (without 'min-height' and 'max-height')
    CSSPixels used_height = tentative_height_for_replaced_element(box, computed_height, available_space);

    // However, for replaced elements with both 'width' and 'height' computed as 'auto',
    // use the algorithm under 'Minimum and maximum widths'
    // https://www.w3.org/TR/CSS22/visudet.html#min-max-widths
    // to find the used width and height.
    if ((computed_width.is_auto() && computed_height.is_auto() && box.has_preferred_aspect_ratio())) {
        // NOTE: This is a special case where calling tentative_width_for_replaced_element() would call us right back,
        //       and we'd end up in an infinite loop. So we need to handle this case separately.
        if (auto intrinsic = box.auto_content_box_size(); intrinsic.has_width() || !intrinsic.has_height()) {
            CSSPixels w = tentative_width_for_replaced_element(box, computed_width, available_space);
            CSSPixels h = used_height;
            used_height = solve_replaced_size_constraint(w, h, box, available_space).height();
        }
    }
    // 2. If this tentative height is greater than 'max-height', the rules above are applied again,
    //    but this time using the value of 'max-height' as the computed value for 'height'.
    if (!should_treat_max_height_as_none(box, available_space.height)) {
        auto const& computed_max_height = box.computed_values().max_height();
        auto max_height = calculate_inner_height(box, available_space, computed_max_height);
        if (used_height > max_height)
            used_height = tentative_height_for_replaced_element(box, computed_max_height, available_space);
    }

    // 3. If the resulting height is smaller than 'min-height', the rules above are applied again,
    //    but this time using the value of 'min-height' as the computed value for 'height'.
    auto computed_min_height = box.computed_values().min_height();
    if (!computed_min_height.is_auto()) {
        auto min_height = calculate_inner_height(box, available_space, computed_min_height);
        if (used_height < min_height)
            used_height = tentative_height_for_replaced_element(box, computed_min_height, available_space);
    }

    return used_height;
}

void FormattingContext::compute_width_for_absolutely_positioned_non_replaced_element(Box const& box, AvailableSpace const& available_space)
{
    auto width_of_containing_block = available_space.width.to_px_or_zero();
    auto const& computed_values = box.computed_values();
    auto& box_state = m_state.get_mutable(box);

    auto margin_left = CSS::LengthOrAuto::make_auto();
    auto margin_right = CSS::LengthOrAuto::make_auto();
    auto const border_left = computed_values.border_left().width;
    auto const border_right = computed_values.border_right().width;
    auto const padding_left = box_state.padding_left;
    auto const padding_right = box_state.padding_right;

    auto computed_left = computed_values.inset().left();
    auto computed_right = computed_values.inset().right();
    auto left = computed_values.inset().left().to_px_or_zero(box, width_of_containing_block);
    auto right = computed_values.inset().right().to_px_or_zero(box, width_of_containing_block);

    auto try_compute_width = [&](CSS::LengthOrAuto const& a_width) {
        margin_left = computed_values.margin().left().resolved_or_auto(box, width_of_containing_block);
        margin_right = computed_values.margin().right().resolved_or_auto(box, width_of_containing_block);

        auto width = a_width;

        auto solve_for_left = [&] {
            return width_of_containing_block - margin_left.to_px_or_zero(box) - border_left - padding_left - width.to_px_or_zero(box) - padding_right - border_right - margin_right.to_px_or_zero(box) - right;
        };

        auto solve_for_width = [&] {
            return CSS::Length::make_px(max(CSSPixels(0), width_of_containing_block - left - margin_left.to_px_or_zero(box) - border_left - padding_left - padding_right - border_right - margin_right.to_px_or_zero(box) - right));
        };

        auto solve_for_right = [&] {
            return width_of_containing_block - left - margin_left.to_px_or_zero(box) - border_left - padding_left - width.to_px_or_zero(box) - padding_right - border_right - margin_right.to_px_or_zero(box);
        };

        // If all three of 'left', 'width', and 'right' are 'auto':
        if (computed_left.is_auto() && width.is_auto() && computed_right.is_auto()) {
            // First set any 'auto' values for 'margin-left' and 'margin-right' to 0.
            if (margin_left.is_auto())
                margin_left = CSS::Length::make_px(0);
            if (margin_right.is_auto())
                margin_right = CSS::Length::make_px(0);
            // Then, if the 'direction' property of the element establishing the static-position containing block
            // is 'ltr' set 'left' to the static position and apply rule number three below;
            // otherwise, set 'right' to the static position and apply rule number one below.

            // NOTE: As with compute_height_for_absolutely_positioned_non_replaced_element, we actually apply these
            //       steps in the opposite order since the static position may depend on the width of the box.

            auto result = calculate_shrink_to_fit_widths(box);
            auto available_width = solve_for_width();
            CSSPixels content_width = min(max(result.preferred_minimum_width, available_width.to_px(box)), result.preferred_width);
            width = CSS::Length::make_px(content_width);
            m_state.get_mutable(box).set_content_width(content_width);

            auto static_position = m_state.get(box).static_position();

            left = static_position.x();
            right = solve_for_right();
        }

        // If none of the three is auto:
        if (!computed_left.is_auto() && !width.is_auto() && !computed_right.is_auto()) {
            // If both margin-left and margin-right are auto,
            // solve the equation under the extra constraint that the two margins get equal values
            // FIXME: unless this would make them negative, in which case when direction of the containing block is ltr (rtl), set margin-left (margin-right) to 0 and solve for margin-right (margin-left).
            auto size_available_for_margins = width_of_containing_block - border_left - padding_left - width.to_px_or_zero(box) - padding_right - border_right - left - right;
            if (margin_left.is_auto() && margin_right.is_auto()) {
                margin_left = CSS::Length::make_px(size_available_for_margins / 2);
                margin_right = CSS::Length::make_px(size_available_for_margins / 2);
                return width;
            }

            // If one of margin-left or margin-right is auto, solve the equation for that value.
            if (margin_left.is_auto()) {
                margin_left = CSS::Length::make_px(size_available_for_margins);
                return width;
            }
            if (margin_right.is_auto()) {
                margin_right = CSS::Length::make_px(size_available_for_margins);
                return width;
            }
            // If the values are over-constrained, ignore the value for left
            // (in case the direction property of the containing block is rtl)
            // or right (in case direction is ltr) and solve for that value.

            // NOTE: At this point we *are* over-constrained since none of margin-left, left, width, right, or margin-right are auto.
            // FIXME: Check direction.
            right = solve_for_right();
            return width;
        }

        if (margin_left.is_auto())
            margin_left = CSS::Length::make_px(0);
        if (margin_right.is_auto())
            margin_right = CSS::Length::make_px(0);

        // 1. 'left' and 'width' are 'auto' and 'right' is not 'auto',
        //    then the width is shrink-to-fit. Then solve for 'left'
        if (computed_left.is_auto() && width.is_auto() && !computed_right.is_auto()) {
            auto result = calculate_shrink_to_fit_widths(box);
            auto available_width = solve_for_width();
            width = CSS::Length::make_px(min(max(result.preferred_minimum_width, available_width.to_px(box)), result.preferred_width));
            left = solve_for_left();
        }

        // 2. 'left' and 'right' are 'auto' and 'width' is not 'auto',
        //    then if the 'direction' property of the element establishing
        //    the static-position containing block is 'ltr' set 'left'
        //    to the static position, otherwise set 'right' to the static position.
        //    Then solve for 'left' (if 'direction is 'rtl') or 'right' (if 'direction' is 'ltr').
        else if (computed_left.is_auto() && computed_right.is_auto() && !width.is_auto()) {
            // FIXME: Check direction
            auto static_position = m_state.get(box).static_position();
            left = static_position.x();
            right = solve_for_right();
        }

        // 3. 'width' and 'right' are 'auto' and 'left' is not 'auto',
        //    then the width is shrink-to-fit. Then solve for 'right'
        else if (width.is_auto() && computed_right.is_auto() && !computed_left.is_auto()) {
            auto result = calculate_shrink_to_fit_widths(box);
            auto available_width = solve_for_width();
            width = CSS::Length::make_px(min(max(result.preferred_minimum_width, available_width.to_px(box)), result.preferred_width));
            right = solve_for_right();
        }

        // 4. 'left' is 'auto', 'width' and 'right' are not 'auto', then solve for 'left'
        else if (computed_left.is_auto() && !width.is_auto() && !computed_right.is_auto()) {
            left = solve_for_left();
        }

        // 5. 'width' is 'auto', 'left' and 'right' are not 'auto', then solve for 'width'
        else if (width.is_auto() && !computed_left.is_auto() && !computed_right.is_auto()) {
            width = solve_for_width();
        }

        // 6. 'right' is 'auto', 'left' and 'width' are not 'auto', then solve for 'right'
        else if (computed_right.is_auto() && !computed_left.is_auto() && !width.is_auto()) {
            right = solve_for_right();
        }

        return width;
    };

    // 1. The tentative used width is calculated (without 'min-width' and 'max-width')
    auto used_width = try_compute_width([&] -> CSS::LengthOrAuto {
        if (is<TableWrapper>(box))
            return CSS::Length::make_px(compute_table_box_width_inside_table_wrapper(box, available_space));
        if (computed_values.width().is_auto())
            return CSS::LengthOrAuto::make_auto();
        return CSS::Length::make_px(calculate_inner_width(box, available_space.width, computed_values.width()));
    }());

    // 2. The tentative used width is greater than 'max-width', the rules above are applied again,
    //    but this time using the computed value of 'max-width' as the computed value for 'width'.
    if (!should_treat_max_width_as_none(box, available_space.width)) {
        auto max_width = calculate_inner_width(box, available_space.width, computed_values.max_width());
        if (used_width.to_px_or_zero(box) > max_width) {
            used_width = try_compute_width(CSS::Length::make_px(max_width));
        }
    }

    // 3. If the resulting width is smaller than 'min-width', the rules above are applied again,
    //    but this time using the value of 'min-width' as the computed value for 'width'.
    if (!computed_values.min_width().is_auto()) {
        auto min_width = calculate_inner_width(box, available_space.width, computed_values.min_width());
        if (used_width.to_px_or_zero(box) < min_width) {
            used_width = try_compute_width(CSS::Length::make_px(min_width));
        }
    }

    box_state.set_content_width(used_width.to_px_or_zero(box));
    box_state.inset_left = left;
    box_state.inset_right = right;
    box_state.margin_left = margin_left.to_px_or_zero(box);
    box_state.margin_right = margin_right.to_px_or_zero(box);
}

// https://drafts.csswg.org/css2/#abs-replaced-width
void FormattingContext::compute_width_for_absolutely_positioned_replaced_element(Box const& box, AvailableSpace const& available_space)
{
    // 10.3.8 Absolutely positioned, replaced elements
    // In this case, section 10.3.7 applies up through and including the constraint equation,
    // but the rest of section 10.3.7 is replaced by the following rules:

    // 1. The used value of 'width' is determined as for inline replaced elements.

    auto width = compute_width_for_replaced_element(box, available_space);
    auto width_of_containing_block = available_space.width.to_px_or_zero();
    auto const& computed_values = box.computed_values();
    auto& box_state = m_state.get_mutable(box);
    auto const border_left = computed_values.border_left().width;
    auto const border_right = computed_values.border_right().width;
    auto const padding_left = box_state.padding_left;
    auto const padding_right = box_state.padding_right;
    auto available = width_of_containing_block - width - border_left - padding_left - padding_right - border_right;
    auto left = computed_values.inset().left();
    auto margin_left = computed_values.margin().left();
    auto right = computed_values.inset().right();
    auto margin_right = computed_values.margin().right();
    auto static_position = m_state.get(box).static_position();

    auto to_px = [&](CSS::LengthPercentageOrAuto const& l) {
        return l.to_px_or_zero(box, width_of_containing_block);
    };

    // If 'margin-left' or 'margin-right' is specified as 'auto' its used value is determined by the rules below.
    // 2. If both 'left' and 'right' have the value 'auto', then if the 'direction' property of the
    // element establishing the static-position containing block is 'ltr', set 'left' to the static
    // position; else if 'direction' is 'rtl', set 'right' to the static position.
    if (left.is_auto() && right.is_auto()) {
        left = CSS::Length::make_px(static_position.x());
    }

    // 3. If 'left' or 'right' are 'auto', replace any 'auto' on 'margin-left' or 'margin-right' with '0'.
    if (left.is_auto() || right.is_auto()) {
        if (margin_left.is_auto())
            margin_left = CSS::Length::make_px(0);
        if (margin_right.is_auto())
            margin_right = CSS::Length::make_px(0);
    }

    // 4. If at this point both 'margin-left' and 'margin-right' are still 'auto', solve the equation
    // under the extra constraint that the two margins must get equal values, unless this would make
    // them negative, in which case when the direction of the containing block is 'ltr' ('rtl'),
    // set 'margin-left' ('margin-right') to zero and solve for 'margin-right' ('margin-left').
    if (margin_left.is_auto() && margin_right.is_auto()) {
        auto remainder = available - to_px(left) - to_px(right);
        if (remainder < 0) {
            margin_left = CSS::Length::make_px(0);
            margin_right = CSS::Length::make_px(0);
        } else {
            margin_left = CSS::Length::make_px(remainder / 2);
            margin_right = CSS::Length::make_px(remainder / 2);
        }
    }

    // 5. If at this point there is an 'auto' left, solve the equation for that value.
    if (left.is_auto()) {
        left = CSS::Length::make_px(available - to_px(right) - to_px(margin_left) - to_px(margin_right));
    } else if (right.is_auto()) {
        right = CSS::Length::make_px(available - to_px(left) - to_px(margin_left) - to_px(margin_right));
    } else if (margin_left.is_auto()) {
        margin_left = CSS::Length::make_px(available - to_px(left) - to_px(right) - to_px(margin_right));
    } else if (margin_right.is_auto()) {
        margin_right = CSS::Length::make_px(available - to_px(left) - to_px(margin_left) - to_px(right));
    }

    // 6. If at this point the values are over-constrained, ignore the value for either 'left'
    // (in case the 'direction' property of the containing block is 'rtl') or 'right'
    // (in case 'direction' is 'ltr') and solve for that value.
    if (0 != available - to_px(left) - to_px(right) - to_px(margin_left) - to_px(margin_right)) {
        right = CSS::Length::make_px(available - to_px(left) - to_px(margin_left) - to_px(margin_right));
    }

    box_state.inset_left = to_px(left);
    box_state.inset_right = to_px(right);
    box_state.margin_left = to_px(margin_left);
    box_state.margin_right = to_px(margin_right);
    box_state.set_content_width(width);
}

// https://drafts.csswg.org/css-position-3/#abs-non-replaced-height
void FormattingContext::compute_height_for_absolutely_positioned_non_replaced_element(Box const& box, AvailableSpace const& available_space, BeforeOrAfterInsideLayout before_or_after_inside_layout)
{
    // 5.3. The Height Of Absolutely Positioned, Non-Replaced Elements

    // For absolutely positioned elements, the used values of the vertical dimensions must satisfy this constraint:
    // top + margin-top + border-top-width + padding-top + height + padding-bottom + border-bottom-width + margin-bottom + bottom = height of containing block

    // NOTE: This function is called twice: both before and after inside layout.
    //       In the before pass, if it turns out we need the automatic height of the box, we abort these steps.
    //       This allows the box to retain an indefinite height from the perspective of inside layout.

    auto apply_min_max_height_constraints = [this, &box, &available_space](CSS::LengthOrAuto const& unconstrained_height) -> CSS::LengthOrAuto {
        auto const& computed_min_height = box.computed_values().min_height();
        auto const& computed_max_height = box.computed_values().max_height();
        auto constrained_height = unconstrained_height;
        if (!computed_max_height.is_none()) {
            auto inner_max_height = calculate_inner_height(box, available_space, computed_max_height);
            if (inner_max_height < constrained_height.to_px_or_zero(box))
                constrained_height = CSS::Length::make_px(inner_max_height);
        }
        if (!computed_min_height.is_auto()) {
            auto inner_min_height = calculate_inner_height(box, available_space, computed_min_height);
            if (inner_min_height > constrained_height.to_px_or_zero(box))
                constrained_height = CSS::Length::make_px(inner_min_height);
        }
        return constrained_height;
    };

    auto margin_top = box.computed_values().margin().top();
    auto margin_bottom = box.computed_values().margin().bottom();
    auto top = box.computed_values().inset().top();
    auto bottom = box.computed_values().inset().bottom();

    auto width_of_containing_block = available_space.width.to_px_or_zero();
    auto height_of_containing_block = available_space.height.to_px_or_zero();

    enum class ClampToZero {
        No,
        Yes,
    };

    auto& state = m_state.get(box);
    auto try_compute_height = [&](CSS::LengthOrAuto height) -> CSS::LengthOrAuto {
        // Reset values that may have been modified by a previous call (when re-solving for min/max-height).
        margin_top = box.computed_values().margin().top();
        margin_bottom = box.computed_values().margin().bottom();
        top = box.computed_values().inset().top();
        bottom = box.computed_values().inset().bottom();

        auto solve_for = [&](CSS::LengthOrAuto const& length_or_auto, ClampToZero clamp_to_zero = ClampToZero::No) {
            auto unclamped_value = height_of_containing_block
                - top.to_px_or_zero(box, height_of_containing_block)
                - margin_top.to_px_or_zero(box, width_of_containing_block)
                - box.computed_values().border_top().width
                - state.padding_top
                - height.to_px_or_zero(box)
                - state.padding_bottom
                - box.computed_values().border_bottom().width
                - margin_bottom.to_px_or_zero(box, width_of_containing_block)
                - bottom.to_px_or_zero(box, height_of_containing_block)
                + length_or_auto.to_px_or_zero(box);
            if (clamp_to_zero == ClampToZero::Yes)
                return CSS::Length::make_px(max(CSSPixels(0), unclamped_value));
            return CSS::Length::make_px(unclamped_value);
        };

        auto solve_for_top = [&] {
            top = solve_for(top.resolved_or_auto(box, height_of_containing_block));
        };

        auto solve_for_bottom = [&] {
            bottom = solve_for(bottom.resolved_or_auto(box, height_of_containing_block));
        };

        auto solve_for_height = [&] {
            height = solve_for(height, ClampToZero::Yes);
        };

        auto solve_for_margin_top = [&] {
            margin_top = solve_for(margin_top.resolved_or_auto(box, width_of_containing_block));
        };

        auto solve_for_margin_bottom = [&] {
            margin_bottom = solve_for(margin_bottom.resolved_or_auto(box, width_of_containing_block));
        };

        auto solve_for_margin_top_and_margin_bottom = [&] {
            auto remainder = solve_for(CSS::Length::make_px(margin_top.to_px_or_zero(box, width_of_containing_block) + margin_bottom.to_px_or_zero(box, width_of_containing_block))).to_px(box);
            margin_top = CSS::Length::make_px(remainder / 2);
            margin_bottom = CSS::Length::make_px(remainder / 2);
        };

        // If all three of top, height, and bottom are auto:
        if (top.is_auto() && height.is_auto() && bottom.is_auto()) {
            // First set any auto values for margin-top and margin-bottom to 0,
            if (margin_top.is_auto())
                margin_top = CSS::Length::make_px(0);
            if (margin_bottom.is_auto())
                margin_bottom = CSS::Length::make_px(0);

            // then set top to the static position,
            // and finally apply rule number three below.

            // NOTE: We actually perform these two steps in the opposite order,
            //       because the static position may depend on the height of the box (due to alignment properties).

            auto maybe_height = compute_auto_height_for_absolutely_positioned_element(box, available_space, before_or_after_inside_layout);
            if (!maybe_height.has_value())
                return height;
            height = CSS::Length::make_px(maybe_height.value());

            auto constrained_height = apply_min_max_height_constraints(height);
            m_state.get_mutable(box).set_content_height(constrained_height.to_px_or_zero(box));

            auto static_position = m_state.get(box).static_position();
            top = CSS::Length::make_px(static_position.y());

            solve_for_bottom();
        }

        // If none of the three are auto:
        else if (!top.is_auto() && !height.is_auto() && !bottom.is_auto()) {
            // If both margin-top and margin-bottom are auto,
            if (margin_top.is_auto() && margin_bottom.is_auto()) {
                // solve the equation under the extra constraint that the two margins get equal values.
                solve_for_margin_top_and_margin_bottom();
            }

            // If one of margin-top or margin-bottom is auto,
            else if (margin_top.is_auto() || margin_bottom.is_auto()) {
                // solve the equation for that value.
                if (margin_top.is_auto())
                    solve_for_margin_top();
                else
                    solve_for_margin_bottom();
            }

            // If the values are over-constrained,
            else {
                // ignore the value for bottom and solve for that value.
                solve_for_bottom();
            }
        }

        // Otherwise,
        else {
            // set auto values for margin-top and margin-bottom to 0,
            if (margin_top.is_auto())
                margin_top = CSS::Length::make_px(0);
            if (margin_bottom.is_auto())
                margin_bottom = CSS::Length::make_px(0);

            // and pick one of the following six rules that apply.

            // 1. If top and height are auto and bottom is not auto,
            if (top.is_auto() && height.is_auto() && !bottom.is_auto()) {
                // then the height is based on the Auto heights for block formatting context roots,
                auto maybe_height = compute_auto_height_for_absolutely_positioned_element(box, available_space, before_or_after_inside_layout);
                if (!maybe_height.has_value())
                    return height;
                height = CSS::Length::make_px(maybe_height.value());

                // and solve for top.
                solve_for_top();
            }

            // 2. If top and bottom are auto and height is not auto,
            else if (top.is_auto() && bottom.is_auto() && !height.is_auto()) {
                // then set top to the static position,
                top = CSS::Length::make_px(m_state.get(box).static_position().y());

                // then solve for bottom.
                solve_for_bottom();
            }

            // 3. If height and bottom are auto and top is not auto,
            else if (height.is_auto() && bottom.is_auto() && !top.is_auto()) {
                // then the height is based on the Auto heights for block formatting context roots,
                auto maybe_height = compute_auto_height_for_absolutely_positioned_element(box, available_space, before_or_after_inside_layout);
                if (!maybe_height.has_value())
                    return height;
                height = CSS::Length::make_px(maybe_height.value());

                // and solve for bottom.
                solve_for_bottom();
            }

            // 4. If top is auto, height and bottom are not auto,
            else if (top.is_auto() && !height.is_auto() && !bottom.is_auto()) {
                // then solve for top.
                solve_for_top();
            }

            // 5. If height is auto, top and bottom are not auto,
            else if (height.is_auto() && !top.is_auto() && !bottom.is_auto()) {
                // then solve for height.
                solve_for_height();
            }

            // 6. If bottom is auto, top and height are not auto,
            else if (bottom.is_auto() && !top.is_auto() && !height.is_auto()) {
                // then solve for bottom.
                solve_for_bottom();
            }
        }

        return height;
    };

    // Compute the height based on box type and CSS properties:
    // https://www.w3.org/TR/css-sizing-3/#box-sizing
    auto used_height = try_compute_height([&] -> CSS::LengthOrAuto {
        if (is<TableWrapper>(box))
            return CSS::Length::make_px(compute_table_box_height_inside_table_wrapper(box, available_space));
        if (should_treat_height_as_auto(box, available_space))
            return CSS::LengthOrAuto::make_auto();
        return CSS::Length::make_px(calculate_inner_height(box, available_space, box.computed_values().height()));
    }());

    // If the tentative used height is greater than 'max-height', the rules above are applied again,
    // but this time using the computed value of 'max-height' as the computed value for 'height'.
    auto const& computed_max_height = box.computed_values().max_height();
    if (!used_height.is_auto() && !computed_max_height.is_none()) {
        auto max_height = calculate_inner_height(box, available_space, computed_max_height);
        if (used_height.to_px_or_zero(box) > max_height)
            used_height = try_compute_height(CSS::Length::make_px(max_height));
    }

    // If the resulting height is smaller than 'min-height', the rules above are applied again,
    // but this time using the value of 'min-height' as the computed value for 'height'.
    auto const& computed_min_height = box.computed_values().min_height();
    if (!used_height.is_auto() && !computed_min_height.is_auto()) {
        auto min_height = calculate_inner_height(box, available_space, computed_min_height);
        if (used_height.to_px_or_zero(box) < min_height)
            used_height = try_compute_height(CSS::Length::make_px(min_height));
    }

    // For the before-inside-layout pass where height is still auto, apply min-max as a simple clamp.
    if (used_height.is_auto())
        used_height = apply_min_max_height_constraints(used_height);

    // NOTE: The following is not directly part of any spec, but this is where we resolve
    //       the final used values for vertical margin/border/padding.

    auto& box_state = m_state.get_mutable(box);
    box_state.set_content_height(used_height.to_px_or_zero(box));

    // do not set calculated insets or margins on the first pass, there will be a second pass
    if (box.computed_values().height().is_auto() && before_or_after_inside_layout == BeforeOrAfterInsideLayout::Before)
        return;
    if (computed_height_establishes_definite_containing_block_height(box.computed_values().height()))
        box_state.set_has_definite_height(true);
    box_state.inset_top = top.to_px_or_zero(box, height_of_containing_block);
    box_state.inset_bottom = bottom.to_px_or_zero(box, height_of_containing_block);
    box_state.margin_top = margin_top.to_px_or_zero(box, width_of_containing_block);
    box_state.margin_bottom = margin_bottom.to_px_or_zero(box, width_of_containing_block);
}

// FIXME: Containing block handling for absolutely positioned elements needs architectural improvements.
//
//        The CSS specification defines the containing block as a *rectangle*, not a box. For most cases,
//        this rectangle is derived from the padding box of the nearest positioned ancestor Box. However,
//        when the positioned ancestor is an *inline* element (e.g., a <span> with position: relative),
//        the containing block rectangle should be the bounding box of that inline's fragments.
//
//        Currently, Layout::Node::m_containing_block is typed as Layout::Box*, which cannot represent
//        inline elements. The proper fix would be to:
//        1. Separate the concept of "the node that establishes the containing block" from "the containing
//           block rectangle".
//        2. Store a reference to the establishing node (which could be InlineNode or Box).
//        3. Compute the containing block rectangle on demand based on the establishing node's type.
//
//        For now, we use a surgical workaround: when laying out an absolutely positioned element, we check
//        if there's an inline element with position:relative (or other containing-block-establishing
//        properties) between the abspos element and its current containing_block(). If found, we compute
//        the inline's fragment bounding box and use that for sizing and positioning, then adjust the final
//        offset to be relative to the containing_block() Box that the rest of the system expects.

// Computes the bounding box rectangle of an inline node's fragments, in the coordinate
// space of the abspos containing block. Returns the padding-box rect because that's the
// edge containing blocks are formed by.
//
// When an inline element has block-level descendants, the layout tree splits the inline
// into "before"/"middle"/"after" anonymous wrappers; we walk all of them so the rect
// covers the inline's full extent (matching getClientRects() for split inlines).
static Optional<CSSPixelRect> compute_inline_containing_block_rect(InlineNode const& inline_node, Box const& abspos_containing_block, LayoutState const& state)
{
    auto const* inline_dom_node = inline_node.dom_node();
    if (!inline_dom_node)
        return {};

    auto const* outer_block = inline_node.non_anonymous_containing_block();
    if (!outer_block)
        return {};

    Optional<CSSPixelRect> bounding_rect;
    auto union_rect = [&](CSSPixelRect const& rect) {
        bounding_rect = bounding_rect.has_value() ? bounding_rect->united(rect) : rect;
    };

    // Walk outer_block's subtree in pre-order, threading the running offset from
    // abspos_containing_block down so we don't have to re-walk to the root for every
    // matching node. We prune subtrees rooted at non-anonymous boxes that don't belong
    // to the inline (sibling content can't contribute to its rect), and skip out-of-flow
    // descendants (they aren't part of the inline's fragments).
    auto walk = [&](this auto& self, Node const& node, CSSPixelPoint offset) -> void {
        auto const* used_values = state.try_get(node);
        if (used_values && !used_values->line_boxes.is_empty()) {
            for (auto const& line_box : used_values->line_boxes) {
                for (auto const& fragment : line_box.fragments()) {
                    if (auto const* dom = fragment.layout_node().dom_node(); dom && inline_dom_node->is_inclusive_ancestor_of(*dom))
                        union_rect({ fragment.offset() + offset, fragment.size() });
                }
            }
        }

        for (auto const* child = node.first_child(); child; child = child->next_sibling()) {
            if (child->is_absolutely_positioned() || child->is_floating())
                continue;
            auto const* child_used_values = state.try_get(*child);
            auto child_offset = child_used_values ? offset + child_used_values->offset : offset;
            auto const* box_child = as_if<Box>(child);
            if (box_child && !box_child->is_anonymous()) {
                auto const* dom = box_child->dom_node();
                if (!dom || !inline_dom_node->is_inclusive_ancestor_of(*dom))
                    continue;
                // child_offset addresses the box's content area; the border-box origin sits
                // (border-left + padding-left, border-top + padding-top) before that.
                if (child_used_values) {
                    auto const border_box_origin = child_offset - CSSPixelPoint {
                        child_used_values->border_left + child_used_values->padding_left,
                        child_used_values->border_top + child_used_values->padding_top,
                    };
                    union_rect({ border_box_origin, { child_used_values->border_box_width(), child_used_values->border_box_height() } });
                }
            }
            self(*child, child_offset);
        }
    };

    CSSPixelPoint outer_offset;
    for (Node const* ancestor = outer_block; ancestor && ancestor != &abspos_containing_block; ancestor = ancestor->parent()) {
        if (auto const* used_values = state.try_get(*ancestor))
            outer_offset.translate_by(used_values->offset);
    }
    walk(*outer_block, outer_offset);

    if (!bounding_rect.has_value())
        return {};

    // Expand the bounding rect by the inline's padding to get the padding box.
    if (auto const* inline_used_values = state.try_get(inline_node)) {
        bounding_rect->inflate(
            inline_used_values->padding_top,
            inline_used_values->padding_right,
            inline_used_values->padding_bottom,
            inline_used_values->padding_left);
    }

    return bounding_rect;
}

AbsposContainingBlockInfo FormattingContext::resolve_abspos_containing_block_info(Box const& box)
{
    auto const& computed_values = box.computed_values();

    // Per-axis mode: auto+auto insets -> static position, otherwise -> inset from rect
    auto horizontal_axis_mode = (computed_values.inset().left().is_auto() && computed_values.inset().right().is_auto())
        ? AbsposAxisMode::StaticPosition
        : AbsposAxisMode::InsetFromRect;
    auto vertical_axis_mode = (computed_values.inset().top().is_auto() && computed_values.inset().bottom().is_auto())
        ? AbsposAxisMode::StaticPosition
        : AbsposAxisMode::InsetFromRect;

    // Check if there's an inline element that should be the real containing block.
    auto inline_containing_block = box.inline_containing_block_if_applicable();
    if (inline_containing_block && box.containing_block()) {
        auto rect = compute_inline_containing_block_rect(*inline_containing_block, *box.containing_block(), m_state);
        if (rect.has_value())
            return { *rect, horizontal_axis_mode, vertical_axis_mode, {}, {} };
    }

    // Normal case: padding box of the actual containing block.
    VERIFY(box.containing_block());
    auto& containing_block_state = m_state.get(*box.containing_block());
    CSSPixelRect rect {
        -containing_block_state.padding_left,
        -containing_block_state.padding_top,
        containing_block_state.content_width() + containing_block_state.padding_left + containing_block_state.padding_right,
        containing_block_state.content_height() + containing_block_state.padding_top + containing_block_state.padding_bottom
    };
    return { rect, horizontal_axis_mode, vertical_axis_mode, {}, {} };
}

// https://drafts.csswg.org/css-anchor-position-1/#anchor-pos
void FormattingContext::resolve_anchor_insets(Box& box) const
{
    // https://drafts.csswg.org/css-anchor-position-1/#resolving-anchor
    // An anchor() function is a resolvable anchor function only if all the following conditions are true:
    //   - It's applied to an absolutely positioned box.
    //   - If its <anchor-side> specifies a physical keyword, it's specified in an inset property applicable to that
    //     axis.
    //   - There is a target anchor element for the box it's used on, and the <anchor-name> value specified in the
    //     function.
    // NB: The first two conditions are guaranteed: this function is called from layout_absolutely_positioned_element(),
    //     and we only resolve anchor() values in inset properties.
    // FIXME: Support anchor-scope, position-try-fallbacks, anchor-size(), and other anchor positioning features.

    auto const* element = as_if<DOM::Element>(box.dom_node());
    if (!element)
        return;

    auto computed = element->computed_properties();
    if (!computed)
        return;
    auto const& top = computed->property(CSS::PropertyID::Top);
    auto const& right = computed->property(CSS::PropertyID::Right);
    auto const& bottom = computed->property(CSS::PropertyID::Bottom);
    auto const& left = computed->property(CSS::PropertyID::Left);
    if (!top.is_anchor() && !right.is_anchor() && !bottom.is_anchor() && !left.is_anchor())
        return;

    auto containing_block = box.containing_block();
    if (!containing_block)
        return;

    auto const& default_anchor_name = box.computed_values().position_anchor();
    auto const& containing_block_state = m_state.get(*containing_block);

    // https://drafts.csswg.org/css-anchor-position-1/#determining
    // Several features of this specification refer to the position and size of an anchor box. Unless otherwise
    // specified, this refers to the border box edge of the principal box of relevant anchor element.
    // https://drafts.csswg.org/css-anchor-position-1/#acceptable-anchor-element
    // FIXME: An element possible anchor is an acceptable anchor element for an absolutely positioned element positioned
    //        el if all of the following are true:
    //        - possible anchor is laid out strictly before positioned el [...]
    auto resolve_anchor_rect = [&](CSS::AnchorStyleValue const& anchor) -> Optional<CSSPixelRect> {
        auto const& name = anchor.anchor_name().has_value() ? anchor.anchor_name() : default_anchor_name;
        if (!name.has_value())
            return {};

        auto anchor_element = element->document().element_by_anchor_name(name.value(), *element);
        if (!anchor_element)
            return {};

        // NB: We use unsafe_layout_node() because we are in the middle of layout.
        auto anchor_layout_node = anchor_element->unsafe_layout_node();
        if (!anchor_layout_node || !is<Box>(*anchor_layout_node))
            return {};

        auto const& anchor_box = as<Box>(*anchor_layout_node);
        auto const& anchor_state = m_state.get(anchor_box);
        auto anchor_border_box_origin = anchor_state.cumulative_offset()
            - CSSPixelPoint { anchor_state.border_box_left(), anchor_state.border_box_top() };
        auto containing_block_padding_box_origin = containing_block_state.cumulative_offset()
            - CSSPixelPoint { containing_block_state.padding_left, containing_block_state.padding_top };
        return CSSPixelRect {
            anchor_border_box_origin - containing_block_padding_box_origin,
            { anchor_state.border_box_width(), anchor_state.border_box_height() },
        };
    };

    // https://drafts.csswg.org/css-anchor-position-1/#anchor-pos
    // An anchor() function representing a resolvable anchor function resolves at computed value time (using style &
    // layout interleaving) to the <length> that would align the edge of the positioned boxes' inset-modified containing
    // block corresponding to the property the function appears in with the specified edge of the target anchor
    // element's anchor box.
    auto containing_block_direction = containing_block->computed_values().direction();
    auto box_direction = box.computed_values().direction();
    auto resolve_anchor_side = [&](CSS::AnchorStyleValue const& anchor, bool is_from_end, bool is_horizontal_axis)
        -> Optional<CSSPixels> {
        auto maybe_rect = resolve_anchor_rect(anchor);
        if (!maybe_rect.has_value())
            return {};
        auto const& rect = maybe_rect.value();
        auto const& side = *anchor.anchor_side();
        if (side.is_keyword()) {
            switch (side.to_keyword()) {
            // https://drafts.csswg.org/css-anchor-position-1/#typedef-anchor-side
            // top | right | bottom | left
            //     Refers to the specified side of the anchor box.
            // If its <anchor-side> specifies a physical keyword, it's specified in an inset property applicable to that
            // axis.
            case CSS::Keyword::Top:
                return is_horizontal_axis ? Optional<CSSPixels> {} : rect.top();
            case CSS::Keyword::Bottom:
                return is_horizontal_axis ? Optional<CSSPixels> {} : rect.bottom();
            case CSS::Keyword::Left:
                return is_horizontal_axis ? rect.left() : Optional<CSSPixels> {};
            case CSS::Keyword::Right:
                return is_horizontal_axis ? rect.right() : Optional<CSSPixels> {};

            // center
            //     Equivalent to 50%.
            case CSS::Keyword::Center:
                if (is_horizontal_axis)
                    return rect.left() + rect.width() / 2;
                return rect.top() + rect.height() / 2;

            // start | end
            //     Refers to one of the sides of the anchor box in the same axis as the inset property it's used in,
            //     by resolving the keyword against the writing mode of the positioned box's containing block.
            case CSS::Keyword::Start:
            case CSS::Keyword::End: {
                bool is_start = side.to_keyword() == CSS::Keyword::Start;
                if (is_horizontal_axis) {
                    bool use_left = (containing_block_direction == CSS::Direction::Ltr) == is_start;
                    return use_left ? rect.left() : rect.right();
                }
                return is_start ? rect.top() : rect.bottom();
            }

            // self-start | self-end
            //     Refers to one of the sides of the anchor box in the same axis as the inset property it's used in,
            //     by resolving the keyword against the writing mode of the positioned box.
            case CSS::Keyword::SelfStart:
            case CSS::Keyword::SelfEnd: {
                bool is_start = side.to_keyword() == CSS::Keyword::SelfStart;
                if (is_horizontal_axis) {
                    bool use_left = (box_direction == CSS::Direction::Ltr) == is_start;
                    return use_left ? rect.left() : rect.right();
                }
                return is_start ? rect.top() : rect.bottom();
            }

            // inside | outside
            //     Resolves to one of the anchor box's sides, depending on which inset property it's used in. inside
            //     refers to the same side as the inset property, while outside refers to the opposite.
            case CSS::Keyword::Inside:
            case CSS::Keyword::Outside: {
                bool same_side = side.to_keyword() == CSS::Keyword::Inside;
                if (is_horizontal_axis) {
                    return (is_from_end == same_side) ? rect.right() : rect.left();
                }
                return (is_from_end == same_side) ? rect.bottom() : rect.top();
            }

            default:
                VERIFY_NOT_REACHED();
            }
        }
        if (side.is_percentage()) {
            // <percentage>
            //     Refers to a position a corresponding percentage between the start and end sides, with 0% being
            //     equivalent to start and 100% being equivalent to end.
            auto percentage = side.as_percentage().percentage().as_fraction();
            if (is_horizontal_axis) {
                auto start = containing_block_direction == CSS::Direction::Ltr ? rect.left() : rect.right();
                auto end = containing_block_direction == CSS::Direction::Ltr ? rect.right() : rect.left();
                return start + CSSPixels::nearest_value_for((end - start).to_double() * percentage);
            }
            return rect.top() + CSSPixels::nearest_value_for(rect.height().to_double() * percentage);
        }
        return {};
    };

    auto resolve_anchor_for_inset = [&](CSS::AnchorStyleValue const& anchor, bool is_from_end, bool is_horizontal_axis)
        -> CSS::LengthPercentageOrAuto {
        auto maybe_side_px = resolve_anchor_side(anchor, is_from_end, is_horizontal_axis);

        // If any of these conditions are false, the anchor() function computes to its specified fallback value. If no
        // fallback value is specified, it makes the declaration referencing it invalid at computed-value time.
        // NB: The fallback value can itself be an anchor(), so we walk the chain.
        auto const* current = &anchor;
        while (!maybe_side_px.has_value()) {
            auto const& fallback = current->fallback_value();
            if (!fallback)
                return CSS::LengthPercentageOrAuto::make_auto();
            if (!fallback->is_anchor())
                return CSS::LengthPercentageOrAuto::from_style_value(*fallback);
            current = &fallback->as_anchor();
            maybe_side_px = resolve_anchor_side(*current, is_from_end, is_horizontal_axis);
        }

        // For inset properties measuring from the end edge (right, bottom), the resolved length is the distance from
        // the anchor side to the corresponding edge of the containing block's padding box.
        auto side_px = maybe_side_px.release_value();
        if (is_from_end) {
            auto containing_block_extent = is_horizontal_axis
                ? containing_block_state.padding_box_width()
                : containing_block_state.padding_box_height();
            return { CSS::LengthPercentage { CSS::Length::make_px(containing_block_extent - side_px) } };
        }
        return { CSS::LengthPercentage { CSS::Length::make_px(side_px) } };
    };

    auto const& existing_inset = box.computed_values().inset();
    box.mutable_computed_values().set_inset({
        top.is_anchor() ? resolve_anchor_for_inset(top.as_anchor(), false, false) : existing_inset.top(),
        right.is_anchor() ? resolve_anchor_for_inset(right.as_anchor(), true, true) : existing_inset.right(),
        bottom.is_anchor() ? resolve_anchor_for_inset(bottom.as_anchor(), true, false) : existing_inset.bottom(),
        left.is_anchor() ? resolve_anchor_for_inset(left.as_anchor(), false, true) : existing_inset.left(),
    });
}

void FormattingContext::layout_absolutely_positioned_children()
{
    if (m_layout_mode != LayoutMode::Normal)
        return;
    for (auto& child : context_box().contained_abspos_children()) {
        auto& box = as<Box>(*child);
        layout_absolutely_positioned_element(box);
    }
}

void FormattingContext::layout_absolutely_positioned_element(Box& box)
{
    // SVG elements cannot be absolutely positioned.
    VERIFY(!box.is_svg_box());

    resolve_anchor_insets(box);

    auto containing_block_info = resolve_abspos_containing_block_info(box);

    auto const available_space = AvailableSpace(AvailableSize::make_definite(clamp_to_max_dimension_value(containing_block_info.rect.width())), AvailableSize::make_definite(clamp_to_max_dimension_value(containing_block_info.rect.height())));

    auto& containing_block_state = m_state.get_mutable(*box.containing_block());

    // The size of the containing block of an abspos box is always definite from the perspective of the abspos box.
    // Since abspos boxes are laid out last, we can mark the containing block as having definite sizes at this point.
    containing_block_state.set_has_definite_width(true);
    containing_block_state.set_has_definite_height(true);

    auto& box_state = m_state.get_mutable(box);
    auto const& computed_values = box.computed_values();

    // The border computed values are not changed by the compute_height & width calculations below.
    // The spec only adjusts and computes sizes, insets and margins.
    box_state.border_left = computed_values.border_left().width;
    box_state.border_right = computed_values.border_right().width;
    box_state.border_top = computed_values.border_top().width;
    box_state.border_bottom = computed_values.border_bottom().width;

    auto const containing_block_width = available_space.width.to_px_or_zero();
    box_state.padding_left = computed_values.padding().left().to_px_or_zero(box, containing_block_width);
    box_state.padding_right = computed_values.padding().right().to_px_or_zero(box, containing_block_width);
    box_state.padding_top = computed_values.padding().top().to_px_or_zero(box, containing_block_width);
    box_state.padding_bottom = computed_values.padding().bottom().to_px_or_zero(box, containing_block_width);

    compute_width_for_absolutely_positioned_element(box, available_space);

    // NOTE: We compute height before *and* after doing inside layout.
    //       This is done so that inside layout can resolve percentage heights.
    //       In some situations, e.g with non-auto top & bottom values, the height can be determined early.
    compute_height_for_absolutely_positioned_element(box, available_space, BeforeOrAfterInsideLayout::Before);

    // If the box width and/or height is fixed and/or or resolved from inset properties,
    // mark the size as being definite (since layout was not required to resolve it, per CSS-SIZING-3).
    auto is_non_auto = [](auto const& length_percentage) {
        return !length_percentage.is_auto();
    };
    if (is_non_auto(computed_values.inset().left()) && is_non_auto(computed_values.inset().right())) {
        box_state.set_has_definite_width(true);
    }
    if (is_non_auto(computed_values.inset().top()) && is_non_auto(computed_values.inset().bottom())
        && (computed_values.height().is_auto() || computed_height_establishes_definite_containing_block_height(computed_values.height()))) {
        box_state.set_has_definite_height(true);
    }

    // NOTE: BFC is special, as their abspos auto height depends on performing inside layout.
    //       For other formatting contexts, the height we've resolved early is good.
    //       See FormattingContext::compute_auto_height_for_absolutely_positioned_element()
    //       for the special-casing of BFC roots.
    if (!creates_block_formatting_context(box)) {
        auto height_resolved_from_aspect_ratio = computed_values.height().is_auto()
            && box.has_preferred_aspect_ratio()
            && box_state.has_definite_width();
        box_state.set_has_definite_width(true);
        if ((!computed_values.height().is_auto() && computed_height_establishes_definite_containing_block_height(computed_values.height())) || height_resolved_from_aspect_ratio)
            box_state.set_has_definite_height(true);
    }

    auto independent_formatting_context = layout_inside(box, LayoutMode::Normal, box_state.available_inner_space_or_constraints_from(available_space));

    if (computed_values.height().is_auto()) {
        compute_height_for_absolutely_positioned_element(box, available_space, BeforeOrAfterInsideLayout::After);
    }

    // Apply grid alignment for auto inset axes
    if (containing_block_info.horizontal_alignment.has_value() && computed_values.inset().left().is_auto() && computed_values.inset().right().is_auto()) {
        auto available_space_for_alignment = containing_block_info.rect.width() - box_state.margin_box_width();
        switch (*containing_block_info.horizontal_alignment) {
        case Alignment::Center:
            box_state.inset_left = available_space_for_alignment / 2;
            box_state.inset_right = available_space_for_alignment / 2;
            break;
        case Alignment::Start:
            box_state.inset_right = available_space_for_alignment;
            break;
        case Alignment::End:
            box_state.inset_left = available_space_for_alignment;
            break;
        case Alignment::Normal:
        case Alignment::Stretch:
        default:
            break;
        }
    }

    if (containing_block_info.vertical_alignment.has_value() && computed_values.inset().top().is_auto() && computed_values.inset().bottom().is_auto()) {
        auto available_space_for_alignment = containing_block_info.rect.height() - box_state.margin_box_height();
        switch (*containing_block_info.vertical_alignment) {
        case Alignment::Center:
            box_state.inset_top = available_space_for_alignment / 2;
            box_state.inset_bottom = available_space_for_alignment / 2;
            break;
        case Alignment::Start:
        case Alignment::SelfStart:
            box_state.inset_bottom = available_space_for_alignment;
            break;
        case Alignment::End:
        case Alignment::SelfEnd:
            box_state.inset_top = available_space_for_alignment;
            break;
        case Alignment::Normal:
        case Alignment::Stretch:
        case Alignment::Baseline:
        default:
            break;
        }
    }

    CSSPixelPoint used_offset;

    auto static_position = m_state.get(box).static_position();
    auto const* static_position_cb = box.static_position_containing_block();
    auto actual_containing_block = box.containing_block();
    if (static_position_cb && static_position_cb != actual_containing_block.ptr()) {
        auto offset = m_state.get(*static_position_cb).cumulative_offset() - m_state.get(*actual_containing_block).cumulative_offset();
        static_position += offset;
    }

    // Horizontal axis
    if (containing_block_info.horizontal_axis_mode == AbsposAxisMode::StaticPosition)
        used_offset.set_x(static_position.x());
    else
        used_offset.set_x(containing_block_info.rect.x() + box_state.inset_left);

    // Vertical axis
    if (containing_block_info.vertical_axis_mode == AbsposAxisMode::StaticPosition)
        used_offset.set_y(static_position.y());
    else
        used_offset.set_y(containing_block_info.rect.y() + box_state.inset_top);

    used_offset.translate_by(box_state.margin_box_left(), box_state.margin_box_top());

    box_state.set_content_offset(used_offset);

    if (independent_formatting_context)
        independent_formatting_context->parent_context_did_dimension_child_root_box();
}

void FormattingContext::compute_height_for_absolutely_positioned_replaced_element(Box const& box, AvailableSpace const& available_space, BeforeOrAfterInsideLayout before_or_after_inside_layout)
{
    // 10.6.5 Absolutely positioned, replaced elements
    // This situation is similar to 10.6.4, except that the element has an intrinsic height.

    // The used value of 'height' is determined as for inline replaced elements.
    auto height = compute_height_for_replaced_element(box, available_space);

    auto height_of_containing_block = available_space.height.to_px_or_zero();
    auto const& computed_values = box.computed_values();
    auto& box_state = m_state.get_mutable(box);
    auto const border_top = computed_values.border_top().width;
    auto const border_bottom = computed_values.border_bottom().width;
    auto const padding_top = box_state.padding_top;
    auto const padding_bottom = box_state.padding_bottom;
    auto available = height_of_containing_block - height - border_top - padding_top - padding_bottom - border_bottom;
    auto top = computed_values.inset().top();
    auto margin_top = computed_values.margin().top();
    auto bottom = computed_values.inset().bottom();
    auto margin_bottom = computed_values.margin().bottom();
    auto static_position = m_state.get(box).static_position();

    auto to_px = [&](CSS::LengthPercentageOrAuto const& l) {
        return l.to_px_or_zero(box, height_of_containing_block);
    };

    // If 'margin-top' or 'margin-bottom' is specified as 'auto' its used value is determined by the rules below.
    // 2. If both 'top' and 'bottom' have the value 'auto', replace 'top' with the element's static position.
    if (top.is_auto() && bottom.is_auto()) {
        top = CSS::Length::make_px(static_position.x());
    }

    // 3. If 'bottom' is 'auto', replace any 'auto' on 'margin-top' or 'margin-bottom' with '0'.
    if (bottom.is_auto()) {
        if (margin_top.is_auto())
            margin_top = CSS::Length::make_px(0);
        if (margin_bottom.is_auto())
            margin_bottom = CSS::Length::make_px(0);
    }

    // 4. If at this point both 'margin-top' and 'margin-bottom' are still 'auto',
    // solve the equation under the extra constraint that the two margins must get equal values.
    if (margin_top.is_auto() && margin_bottom.is_auto()) {
        auto remainder = available - to_px(top) - to_px(bottom);
        margin_top = CSS::Length::make_px(remainder / 2);
        margin_bottom = CSS::Length::make_px(remainder / 2);
    }

    // 5. If at this point there is an 'auto' left, solve the equation for that value.
    if (top.is_auto()) {
        top = CSS::Length::make_px(available - to_px(bottom) - to_px(margin_top) - to_px(margin_bottom));
    } else if (bottom.is_auto()) {
        bottom = CSS::Length::make_px(available - to_px(top) - to_px(margin_top) - to_px(margin_bottom));
    } else if (margin_top.is_auto()) {
        margin_top = CSS::Length::make_px(available - to_px(top) - to_px(bottom) - to_px(margin_bottom));
    } else if (margin_bottom.is_auto()) {
        margin_bottom = CSS::Length::make_px(available - to_px(top) - to_px(margin_top) - to_px(bottom));
    }

    // 6. If at this point the values are over-constrained, ignore the value for 'bottom' and solve for that value.
    if (0 != available - to_px(top) - to_px(bottom) - to_px(margin_top) - to_px(margin_bottom)) {
        bottom = CSS::Length::make_px(available - to_px(top) - to_px(margin_top) - to_px(margin_bottom));
    }

    box_state.set_content_height(height);

    // do not set calculated insets or margins on the first pass, there will be a second pass
    if (box.computed_values().height().is_auto() && before_or_after_inside_layout == BeforeOrAfterInsideLayout::Before)
        return;
    if (computed_height_establishes_definite_containing_block_height(box.computed_values().height()))
        box_state.set_has_definite_height(true);
    box_state.inset_top = to_px(top);
    box_state.inset_bottom = to_px(bottom);
    box_state.margin_top = to_px(margin_top);
    box_state.margin_bottom = to_px(margin_bottom);
}

// https://www.w3.org/TR/css-position-3/#relpos-insets
void FormattingContext::compute_inset(NodeWithStyleAndBoxModelMetrics const& box, CSSPixelSize containing_block_size)
{
    if (box.computed_values().position() != CSS::Positioning::Relative)
        return;

    auto resolve_two_opposing_insets = [&](CSS::LengthPercentageOrAuto const& computed_first, CSS::LengthPercentageOrAuto const& computed_second, CSSPixels& used_start, CSSPixels& used_end, CSSPixels reference_for_percentage) {
        auto resolved_first = computed_first.to_px_or_zero(box, reference_for_percentage);
        auto resolved_second = computed_second.to_px_or_zero(box, reference_for_percentage);

        if (computed_first.is_auto() && computed_second.is_auto()) {
            // If opposing inset properties in an axis both compute to auto (their initial values),
            // their used values are zero (i.e., the boxes stay in their original position in that axis).
            used_start = 0;
            used_end = 0;
        } else if (computed_first.is_auto() || computed_second.is_auto()) {
            // If only one is auto, its used value becomes the negation of the other, and the box is shifted by the specified amount.
            if (computed_first.is_auto()) {
                used_end = resolved_second;
                used_start = -used_end;
            } else {
                used_start = resolved_first;
                used_end = -used_start;
            }
        } else {
            // If neither is auto, the position is over-constrained; (with respect to the writing mode of its containing block)
            // the computed end side value is ignored, and its used value becomes the negation of the start side.
            used_start = resolved_first;
            used_end = -used_start;
        }
    };

    auto& box_state = m_state.get_mutable(box);
    auto const& computed_values = box.computed_values();

    // NOTE: Percentage heights resolve against the containing block's used height. If the containing block's height is
    //       indefinite, percentage insets behave as auto.
    auto treat_percentage_as_auto = [&](CSS::LengthPercentageOrAuto const& value) -> CSS::LengthPercentageOrAuto {
        if (value.contains_percentage()) {
            auto containing_block = box.containing_block();
            while (containing_block && containing_block->is_anonymous() && !containing_block->display().is_table_cell())
                containing_block = containing_block->containing_block();
            if (containing_block && !m_state.get(*containing_block).has_definite_height())
                return CSS::LengthPercentageOrAuto::make_auto();
        }
        return value;
    };

    // FIXME: Respect the containing block's writing-mode.
    resolve_two_opposing_insets(computed_values.inset().left(), computed_values.inset().right(), box_state.inset_left, box_state.inset_right, containing_block_size.width());
    resolve_two_opposing_insets(treat_percentage_as_auto(computed_values.inset().top()), treat_percentage_as_auto(computed_values.inset().bottom()), box_state.inset_top, box_state.inset_bottom, containing_block_size.height());
}

// https://drafts.csswg.org/css-sizing-3/#fit-content-size
CSSPixels FormattingContext::calculate_fit_content_width(Layout::Box const& box, AvailableSpace const& available_space) const
{
    // If the available space in a given axis is definite, equal to clamp(min-content size, stretch-fit size,
    // max-content size) (i.e. max(min-content size, min(max-content size, stretch-fit size))).
    if (available_space.width.is_definite()) {
        return max(calculate_min_content_width(box),
            min(calculate_stretch_fit_width(box, available_space.width),
                calculate_max_content_width(box)));
    }

    // When sizing under a min-content constraint, equal to the min-content size.
    if (available_space.width.is_min_content())
        return calculate_min_content_width(box);

    // Otherwise, equal to the max-content size in that axis.
    return calculate_max_content_width(box);
}

// https://drafts.csswg.org/css-sizing-3/#fit-content-size
CSSPixels FormattingContext::calculate_fit_content_height(Layout::Box const& box, AvailableSpace const& available_space) const
{
    // If the available space in a given axis is definite,
    // equal to clamp(min-content size, stretch-fit size, max-content size)
    // (i.e. max(min-content size, min(max-content size, stretch-fit size))).
    if (available_space.height.is_definite()) {
        return max(calculate_min_content_height(box, available_space.width.to_px_or_zero()),
            min(calculate_stretch_fit_height(box, available_space.height),
                calculate_max_content_height(box, available_space.width.to_px_or_zero())));
    }

    // When sizing under a min-content constraint, equal to the min-content size.
    if (available_space.height.is_min_content())
        return calculate_min_content_height(box, available_space.width.to_px_or_zero());

    // Otherwise, equal to the max-content size in that axis.
    return calculate_max_content_height(box, available_space.width.to_px_or_zero());
}

CSSPixels FormattingContext::calculate_min_content_width(Layout::Box const& box) const
{
    if (box.is_replaced_box()) {
        // https://www.w3.org/TR/css-sizing-3/#replaced-percentage-min-contribution
        // NOTE: If the box is replaced, a cyclic percentage in the value of any max size property or
        //       preferred size property (width/max-width/height/max-height), is resolved against zero
        //       when calculating the min-content contribution in the corresponding axis.
        // FIXME: If the box also has a preferred aspect ratio, then this min-content contribution is
        //        floored by any <length-percentage> minimum size from the opposite axis—resolving any
        //        such percentage against zero—transferred through the preferred aspect ratio.
        if (auto const& width = box.computed_values().width(); width.is_percentage())
            return width.to_px(box, 0);
        if (auto const& max_width = box.computed_values().max_width(); max_width.is_percentage())
            return max_width.to_px(box, 0);
    }
    if (auto auto_size = box.auto_content_box_size(); auto_size.has_width())
        return auto_size.width.value();

    // Boxes with no children have zero intrinsic width.
    if (!box.has_children())
        return 0;

    auto& cache = box.cached_intrinsic_sizes().min_content_width;
    if (cache.has_value())
        return cache.value();

    LayoutState throwaway_state(box);
    throwaway_state.populate_node_from(m_state, *box.containing_block());

    auto& box_state = throwaway_state.get_mutable(box);
    box_state.width_constraint = SizeConstraint::MinContent;
    box_state.set_indefinite_content_width();

    auto context = const_cast<FormattingContext*>(this)->create_independent_formatting_context(throwaway_state, LayoutMode::IntrinsicSizing, box);

    auto available_width = AvailableSize::make_min_content();
    auto available_height = box_state.has_definite_height()
        ? AvailableSize::make_definite(box_state.content_height())
        : AvailableSize::make_indefinite();

    context->run(AvailableSpace(available_width, available_height));

    auto min_content_width = clamp_to_max_dimension_value(context->automatic_content_width());
    cache.emplace(min_content_width);
    return min_content_width;
}

CSSPixels FormattingContext::calculate_max_content_width(Layout::Box const& box) const
{
    auto auto_size = box.auto_content_box_size();
    if (!auto_size.has_width()) {
        // https://drafts.csswg.org/css-sizing-3/#cyclic-percentage-contribution
        // "If the box is non-replaced, then the entire value of any max size property or preferred size property
        // ('width'/'max-width'/'height'/'max-height') specified as an expression containing a percentage [...] that is
        // cyclic is treated for the purpose of calculating the box's intrinsic size contributions only as that
        // property's initial value."
        //
        // This means an `appearance: none` text input with a cyclic `width: 100%` still contributes its `width: auto`
        // size to max-content sizing. Do not use this for min-content sizing: CSS Sizing's "Compressible Replaced
        // Elements" section considers non-button-like <input> controls replaced for the percentage-sized replaced
        // element rule, so their cyclic-percentage min-content contribution can still compress toward zero.
        if (auto appearance_none_text_input_auto_size = appearance_none_text_input_auto_content_box_size(box);
            appearance_none_text_input_auto_size.has_value()) {
            auto_size = appearance_none_text_input_auto_size.value();
        }
    }
    if (auto_size.has_width())
        return auto_size.width.value();

    Optional<CSSPixels> definite_height;
    if (box.is_replaced_box() && !auto_size.has_height()) {
        if (auto const& box_state = m_state.get(box); box_state.has_definite_height())
            definite_height = box_state.content_height();
    }

    if (auto max_content_width = max_content_size_for_replaced_element_without_natural_size(box, auto_size, SizeDimension::Width, definite_height); max_content_width.has_value())
        return max_content_width.value();

    // Boxes with no children have zero intrinsic width.
    if (!box.has_children())
        return 0;

    auto& cache = box.cached_intrinsic_sizes().max_content_width;
    if (cache.has_value())
        return cache.value();

    LayoutState throwaway_state(box);
    throwaway_state.populate_node_from(m_state, *box.containing_block());

    auto const& actual_box_state = m_state.get(box);

    auto& box_state = throwaway_state.get_mutable(box);
    box_state.width_constraint = SizeConstraint::MaxContent;
    box_state.set_indefinite_content_width();

    box_state.border_left = actual_box_state.border_left;
    box_state.padding_left = actual_box_state.padding_left;

    box_state.border_right = actual_box_state.border_right;
    box_state.padding_right = actual_box_state.padding_right;

    auto context = const_cast<FormattingContext*>(this)->create_independent_formatting_context(throwaway_state, LayoutMode::IntrinsicSizing, box);

    auto available_width = AvailableSize::make_max_content();
    auto available_height = box_state.has_definite_height()
        ? AvailableSize::make_definite(box_state.content_height())
        : AvailableSize::make_indefinite();

    context->run(AvailableSpace(available_width, available_height));

    auto max_content_width = clamp_to_max_dimension_value(context->automatic_content_width());
    cache.emplace(max_content_width);
    return max_content_width;
}

// https://www.w3.org/TR/css-sizing-3/#min-content-block-size
CSSPixels FormattingContext::calculate_min_content_height(Layout::Box const& box, CSSPixels width) const
{
    // For block containers, tables, and inline boxes, this is equivalent to the max-content block size.
    if (box.is_block_container() || box.display().is_table_inside())
        return calculate_max_content_height(box, width);

    if (auto auto_size = box.auto_content_box_size(); auto_size.has_height()) {
        if (auto_size.has_aspect_ratio())
            return width / auto_size.aspect_ratio.value();
        return auto_size.height.value();
    }

    // Boxes with no children have zero intrinsic height.
    if (!box.has_children())
        return 0;

    auto& cache = box.cached_intrinsic_sizes().min_content_height.ensure(width);
    if (cache.has_value())
        return cache.value();

    LayoutState throwaway_state(box);
    throwaway_state.populate_node_from(m_state, *box.containing_block());

    auto& box_state = throwaway_state.get_mutable(box);
    box_state.height_constraint = SizeConstraint::MinContent;
    box_state.set_indefinite_content_height();
    box_state.set_content_width(width);

    auto context = const_cast<FormattingContext*>(this)->create_independent_formatting_context(throwaway_state, LayoutMode::IntrinsicSizing, box);

    context->run(AvailableSpace(AvailableSize::make_definite(width), AvailableSize::make_min_content()));

    auto min_content_height = clamp_to_max_dimension_value(context->automatic_content_height());
    cache.emplace(min_content_height);
    return min_content_height;
}

CSSPixels FormattingContext::calculate_max_content_height(Layout::Box const& box, CSSPixels width) const
{
    if (box.has_preferred_aspect_ratio())
        return width / *box.preferred_aspect_ratio();

    if (auto auto_size = box.auto_content_box_size(); auto_size.has_height())
        return auto_size.height.value();
    if (auto max_content_height = max_content_size_for_replaced_element_without_natural_size(box, box.auto_content_box_size(), SizeDimension::Height); max_content_height.has_value())
        return max_content_height.value();

    // Boxes with no children have zero intrinsic height.
    if (!box.has_children())
        return 0;

    auto& cache_slot = box.cached_intrinsic_sizes().max_content_height.ensure(width);
    if (cache_slot.has_value())
        return cache_slot.value();

    LayoutState throwaway_state(box);
    throwaway_state.populate_node_from(m_state, *box.containing_block());

    auto& box_state = throwaway_state.get_mutable(box);
    box_state.height_constraint = SizeConstraint::MaxContent;
    box_state.set_indefinite_content_height();
    box_state.set_content_width(width);

    auto context = const_cast<FormattingContext*>(this)->create_independent_formatting_context(throwaway_state, LayoutMode::IntrinsicSizing, box);

    context->run(AvailableSpace(AvailableSize::make_definite(width), AvailableSize::make_max_content()));

    auto max_content_height = clamp_to_max_dimension_value(context->automatic_content_height());
    cache_slot.emplace(max_content_height);
    return max_content_height;
}

CSSPixels FormattingContext::calculate_inner_width(Layout::Box const& box, AvailableSize const& available_width, CSS::Size const& width) const
{
    VERIFY(!width.is_auto());

    auto width_of_containing_block = available_width.to_px_or_zero();
    if (width.is_fit_content()) {
        return calculate_fit_content_width(box, AvailableSpace { available_width, AvailableSize::make_indefinite() });
    }
    if (width.is_max_content()) {
        return calculate_max_content_width(box);
    }
    if (width.is_min_content()) {
        return calculate_min_content_width(box);
    }

    auto& computed_values = box.computed_values();
    if (computed_values.box_sizing() == CSS::BoxSizing::BorderBox) {
        auto const& state = m_state.get(box);
        auto inner_width = width.to_px(box, width_of_containing_block)
            - computed_values.border_left().width
            - state.padding_left
            - computed_values.border_right().width
            - state.padding_right;
        return max(inner_width, 0);
    }

    return width.to_px(box, width_of_containing_block);
}

CSSPixels FormattingContext::calculate_inner_height(Box const& box, AvailableSpace const& available_space, CSS::Size const& height) const
{
    if (height.is_auto() && box.has_preferred_aspect_ratio()) {
        if (*box.preferred_aspect_ratio() == 0)
            return CSSPixels(0);
        return m_state.get(box).content_width() / *box.preferred_aspect_ratio();
    }

    VERIFY(!height.is_auto());

    if (height.is_fit_content()) {
        return calculate_fit_content_height(box, available_space);
    }
    if (height.is_max_content()) {
        return calculate_max_content_height(box, available_space.width.to_px_or_zero());
    }
    if (height.is_min_content()) {
        return calculate_min_content_height(box, available_space.width.to_px_or_zero());
    }

    CSSPixels height_of_containing_block = available_space.height.to_px_or_zero();
    // NOTE: Percentage heights are resolved against the containing block's used height,
    //       not the available space height. The containing block's height must be definite
    //       for percentage resolution to work (otherwise should_treat_height_as_auto
    //       should have returned true and we wouldn't be here).
    // NOTE: We only do this when available space height is indefinite. If it's definite,
    //       we trust that the caller has set it up correctly (e.g., grid/flex items get
    //       their cell/area size as available space).
    if (height.contains_percentage() && available_space.height.is_indefinite()) {
        auto containing_block = box.containing_block();
        while (containing_block && containing_block->is_anonymous() && !containing_block->display().is_table_cell())
            containing_block = containing_block->containing_block();

        // https://quirks.spec.whatwg.org/#the-percentage-height-calculation-quirk
        // In quirks mode, walk up to find an ancestor with explicit height or the viewport.
        // NOTE: Flex/grid items resolve percentage heights against their container, not via quirk.
        bool is_flex_or_grid_item = box.parent() && (box.parent()->display().is_flex_inside() || box.parent()->display().is_grid_inside());
        auto shadow_root = box.dom_node() ? box.dom_node()->containing_shadow_root() : nullptr;
        bool is_in_ua_shadow_tree = shadow_root && shadow_root->is_user_agent_internal();
        if (box.document().in_quirks_mode() && !box.is_anonymous() && !is_flex_or_grid_item && !is_in_ua_shadow_tree) {
            while (containing_block && !containing_block->is_viewport()
                && containing_block->computed_values().height().is_auto())
                containing_block = containing_block->containing_block();
        }

        if (auto const* containing_block_used_values = containing_block ? m_state.try_get(*containing_block) : nullptr) {
            if (containing_block_used_values->has_definite_height())
                height_of_containing_block = containing_block_used_values->content_height();
        }
    }
    auto& computed_values = box.computed_values();

    if (computed_values.box_sizing() == CSS::BoxSizing::BorderBox) {
        auto const& state = m_state.get(box);
        auto inner_height = height.to_px(box, height_of_containing_block)
            - computed_values.border_top().width
            - state.padding_top
            - computed_values.border_bottom().width
            - state.padding_bottom;
        return max(inner_height, 0);
    }

    return height.to_px(box, height_of_containing_block);
}

CSSPixels FormattingContext::containing_block_width_for(NodeWithStyleAndBoxModelMetrics const& node) const
{
    auto const& used_values = m_state.get(node);
    switch (used_values.width_constraint) {
    case SizeConstraint::MinContent:
        return 0;
    case SizeConstraint::MaxContent:
        return CSSPixels::max();
    case SizeConstraint::None:
        return used_values.containing_block_used_values()->content_width();
    }
    VERIFY_NOT_REACHED();
}

// https://drafts.csswg.org/css-sizing-3/#stretch-fit-size
CSSPixels FormattingContext::calculate_stretch_fit_width(Box const& box, AvailableSize const& available_width) const
{
    // The size a box would take if its outer size filled the available space in the given axis;
    // in other words, the stretch fit into the available space, if that is definite.

    // Undefined if the available space is indefinite.
    if (!available_width.is_definite())
        return 0;

    auto const& box_state = m_state.get(box);
    return available_width.to_px_or_zero()
        - box_state.margin_left
        - box_state.margin_right
        - box_state.padding_left
        - box_state.padding_right
        - box_state.border_left
        - box_state.border_right;
}

// https://drafts.csswg.org/css-sizing-3/#stretch-fit-size
CSSPixels FormattingContext::calculate_stretch_fit_height(Box const& box, AvailableSize const& available_height) const
{
    // The size a box would take if its outer size filled the available space in the given axis;
    // in other words, the stretch fit into the available space, if that is definite.
    // Undefined if the available space is indefinite.
    auto const& box_state = m_state.get(box);
    return available_height.to_px_or_zero()
        - box_state.margin_top
        - box_state.margin_bottom
        - box_state.padding_top
        - box_state.padding_bottom
        - box_state.border_top
        - box_state.border_bottom;
}

bool FormattingContext::should_treat_width_as_auto(Box const& box, AvailableSpace const& available_space) const
{
    auto const& computed_width = box.computed_values().width();
    if (computed_width.is_auto())
        return true;

    // https://drafts.csswg.org/css-sizing-3/#cyclic-percentage-contribution
    if (computed_width.contains_percentage()) {
        if (!box.is_replaced_box() && available_space.width.is_min_content())
            return true;
        if (available_space.width.is_max_content())
            return true;
        if (available_space.width.is_indefinite())
            return true;
    }
    // AD-HOC: If the box has a preferred aspect ratio and an intrinsic keyword for width...
    if (box.has_preferred_aspect_ratio() && computed_width.is_intrinsic_sizing_constraint()) {
        // If the box has no natural height to resolve the aspect ratio, we treat the width as auto.
        if (!box.auto_content_box_size().has_height())
            return true;
        // If the box has definite height, we can resolve the width through the aspect ratio.
        if (m_state.get(box).has_definite_height())
            return true;
    }
    return false;
}

bool FormattingContext::should_treat_height_as_auto(Box const& box, AvailableSpace const& available_space) const
{
    auto computed_height = box.computed_values().height();
    if (computed_height.is_auto()) {
        auto const& box_state = m_state.get(box);
        if (box_state.has_definite_width() && box.has_preferred_aspect_ratio())
            return false;
        return true;
    }

    // https://drafts.csswg.org/css-sizing-3/#cyclic-percentage-contribution
    if (computed_height.contains_percentage()) {
        if (!box.is_replaced_box() && available_space.height.is_min_content())
            return true;
        if (available_space.height.is_max_content())
            return true;
        // https://www.w3.org/TR/CSS22/visudet.html#the-height-property
        // If the height of the containing block is not specified explicitly (i.e., it depends on
        // content height), and this element is not absolutely positioned, the percentage value
        // is treated as 'auto'.
        // https://quirks.spec.whatwg.org/#the-percentage-height-calculation-quirk
        // In quirks mode, percentage heights can resolve even without explicit containing block
        // height. The quirk applies to DOM elements only (not anonymous boxes), and excludes
        // table-related display types.
        if (!box.is_absolutely_positioned()) {
            auto percentage_height_quirk_applies = [&] {
                if (!box.document().in_quirks_mode() || box.is_anonymous())
                    return false;
                if (box.display().is_table_inside())
                    return false;
                // Flex/grid items resolve percentage heights against their container, not via quirk.
                if (auto* parent = box.parent(); parent && parent->display().is_flex_inside())
                    return false;
                if (auto* parent = box.parent(); parent && parent->display().is_grid_inside())
                    return false;
                // The quirk should not apply inside user agent shadow trees.
                if (auto const* dom_node = box.dom_node()) {
                    if (auto shadow_root = dom_node->containing_shadow_root(); shadow_root && shadow_root->is_user_agent_internal())
                        return false;
                }
                return true;
            }();
            if (!percentage_height_quirk_applies) {
                // NOTE: Anonymous blocks inherit height definiteness from their containing block.
                //       However, anonymous table cells are proper containing blocks with their own
                //       height semantics, so we must not walk past them.
                auto containing_block = box.containing_block();
                while (containing_block && containing_block->is_anonymous() && !containing_block->display().is_table_cell())
                    containing_block = containing_block->containing_block();
                if (!containing_block)
                    return true;
                auto const* containing_block_used_values = m_state.try_get(*containing_block);
                if (!containing_block_used_values)
                    return true;
                if (!containing_block_used_values->has_definite_height())
                    return true;
            }
        }
    }

    // AD-HOC: If the box has a preferred aspect ratio and an intrinsic keyword for height...
    if (box.has_preferred_aspect_ratio() && computed_height.is_intrinsic_sizing_constraint()) {
        // If the box has no natural width to resolve the aspect ratio, we treat the height as auto.
        if (!box.auto_content_box_size().has_width())
            return true;
        // If the box has definite width, we can resolve the height through the aspect ratio.
        if (m_state.get(box).has_definite_width())
            return true;
    }
    return false;
}

bool FormattingContext::can_skip_is_anonymous_text_run(Box& box)
{
    if (box.is_anonymous() && !box.is_generated_for_pseudo_element() && !box.first_child_of_type<BlockContainer>()) {
        bool contains_only_white_space = true;
        box.for_each_in_subtree([&](auto const& node) {
            if (!is<TextNode>(node) || !static_cast<TextNode const&>(node).dom_node().data().is_ascii_whitespace()) {
                contains_only_white_space = false;
                return TraversalDecision::Break;
            }
            return TraversalDecision::Continue;
        });
        if (contains_only_white_space)
            return true;
    }
    return false;
}

CSSPixelRect FormattingContext::absolute_content_rect(Box const& box) const
{
    auto const& box_state = m_state.get(box);
    CSSPixelRect rect { box_state.offset, box_state.content_size() };
    for (auto* block = box_state.containing_block_used_values(); block; block = block->containing_block_used_values())
        rect.translate_by(block->offset);
    return rect;
}

Box const* FormattingContext::box_child_to_derive_baseline_from(Box const& box) const
{
    if (!box.has_children() || box.children_are_inline())
        return nullptr;
    // Find the last in-flow child that has a baseline (either directly via line boxes, or via its descendants).
    for (auto const* child = box.last_child(); child; child = child->previous_sibling()) {
        auto const* child_box = as_if<Box>(*child);
        if (!child_box)
            continue;
        if (child_box->is_out_of_flow(*this))
            continue;
        if (!m_state.get(*child_box).line_boxes.is_empty())
            return child_box;
        if (box_child_to_derive_baseline_from(*child_box))
            return child_box;
    }
    return nullptr;
}

CSSPixels FormattingContext::box_baseline(Box const& box) const
{
    auto const& box_state = m_state.get(box);

    // https://drafts.csswg.org/css2/#propdef-vertical-align
    auto const& vertical_align = box.computed_values().vertical_align();
    if (vertical_align.has<CSS::VerticalAlign>()) {
        switch (vertical_align.get<CSS::VerticalAlign>()) {
        case CSS::VerticalAlign::Top:
            // Top: Align the top of the aligned subtree with the top of the line box.
            return box_state.border_box_top();
        case CSS::VerticalAlign::Middle:
            // Middle: Align the vertical midpoint of the box with the baseline of the parent box plus half the x-height of the parent.
            return box_state.margin_box_height() / 2 + CSSPixels::nearest_value_for(box.containing_block()->first_available_font().pixel_metrics().x_height / 2);
        case CSS::VerticalAlign::Bottom:
            // Bottom: Align the bottom of the aligned subtree with the bottom of the line box.
            return box_state.content_height() + box_state.margin_box_top();
        case CSS::VerticalAlign::TextTop:
            // TextTop: Align the top of the box with the top of the parent's content area (see 10.6.1).
            return box.computed_values().font_size();
        case CSS::VerticalAlign::TextBottom:
            // TextBottom: Align the bottom of the box with the bottom of the parent's content area (see 10.6.1).
            return box_state.margin_box_height() - CSSPixels::nearest_value_for(box.containing_block()->first_available_font().pixel_metrics().descent * 2);
        default:
            break;
        }
    }

    // https://drafts.csswg.org/css2/#propdef-vertical-align
    // The baseline of an 'inline-block' is the baseline of its last line box in the normal flow, unless it has either
    // no in-flow line boxes or if its 'overflow' property has a computed value other than 'visible', in which case the
    // baseline is the bottom margin edge.
    // NB: This overflow exception only applies to inline-block, not to inline-flex or inline-grid containers, which
    //     always derive their baselines from their content per CSS Align and the respective Flexbox/Grid specs.
    auto const& display = box.display();
    auto const& overflow_x = box.computed_values().overflow_x();
    auto const& overflow_y = box.computed_values().overflow_y();
    bool has_visible_overflow = overflow_x == CSS::Overflow::Visible && overflow_y == CSS::Overflow::Visible;
    bool is_flex_or_grid_container = display.is_flex_inside() || display.is_grid_inside();
    bool is_inline_flex_or_grid_container = display.is_inline_outside() && is_flex_or_grid_container;
    bool always_derive_from_content = is_flex_or_grid_container || has_visible_overflow;

    if (always_derive_from_content && !box_state.line_boxes.is_empty()) {
        auto const& last_line_box = box_state.line_boxes.last();
        auto last_line_box_top = last_line_box.bottom() - last_line_box.block_length();
        return box_state.margin_box_top() + last_line_box_top + last_line_box.baseline();
    }

    // Derive baseline from block children if the box is flex/grid inside or has visible overflow.
    // AD-HOC: We also derive baseline from children for <input> elements. Per the HTML spec, inputs have
    //         `overflow: clip !important`, so CSS2 says to use bottom margin edge. However, the internal shadow tree
    //         baseline should determine the control's baseline for proper alignment with adjacent text.
    //         https://html.spec.whatwg.org/multipage/rendering.html#form-controls
    if (auto const* child_box = box_child_to_derive_baseline_from(box)) {
        if (always_derive_from_content || is<HTML::HTMLInputElement>(box.dom_node())) {
            auto const& child_box_state = m_state.get(*child_box);
            auto child_offset_from_margin_edge = child_box_state.offset.y() - child_box_state.margin_box_top();

            // https://drafts.csswg.org/css-flexbox-1/#flex-baselines
            // Otherwise, if the flex container has at least one flex item, the flex container's first/last main-axis
            // baseline set is generated from the alignment baseline of the startmost/endmost flex item.
            // https://drafts.csswg.org/css-grid-1/#grid-baselines
            // Otherwise, the grid container's first (last) baseline set is generated from the alignment baseline of the
            // first (last) grid item in row-major grid order.
            // FIXME: This does not yet select the spec-defined startmost/endmost flex item, or the first/last grid item
            //        in row-major grid order.
            if (is_inline_flex_or_grid_container && !child_box_state.line_boxes.is_empty() && !child_box_state.line_boxes.first().is_empty()) {
                auto const& first_line_box = child_box_state.line_boxes.first();
                auto first_line_box_top = first_line_box.bottom() - first_line_box.block_length();
                auto child_first_line_baseline = child_box_state.margin_box_top() + first_line_box_top + first_line_box.baseline();
                return box_state.margin_box_top() + child_offset_from_margin_edge + child_first_line_baseline;
            }

            return box_state.margin_box_top() + child_offset_from_margin_edge + box_baseline(*child_box);
        }
    }

    // If none of the children have a baseline set, the bottom margin edge of the box is used.
    return box_state.margin_box_height();
}

[[nodiscard]] static CSSPixelRect margin_box_rect(LayoutState::UsedValues const& used_values)
{
    return {
        {
            -max(used_values.margin_box_left(), 0),
            -max(used_values.margin_box_top(), 0),
        },
        {
            max(used_values.margin_box_left(), 0) + used_values.content_width() + max(used_values.margin_box_right(), 0),
            max(used_values.margin_box_top(), 0) + used_values.content_height() + max(used_values.margin_box_bottom(), 0),
        },
    };
}

CSSPixelRect FormattingContext::content_box_rect(Box const& box) const
{
    return content_box_rect(m_state.get(box));
}

CSSPixelRect FormattingContext::content_box_rect(LayoutState::UsedValues const& used_values) const
{
    return CSSPixelRect { used_values.offset, used_values.content_size() };
}

CSSPixelRect FormattingContext::content_box_rect_in_ancestor_coordinate_space(LayoutState::UsedValues const& used_values, Box const& ancestor_box) const
{
    CSSPixelRect rect = { { 0, 0 }, used_values.content_size() };
    for (auto const* current = &used_values; current; current = current->containing_block_used_values()) {
        if (&current->node() == &ancestor_box)
            return rect;
        rect.translate_by(current->offset);
    }
    // If we get here, ancestor_box was not a containing block ancestor of `box`!
    VERIFY_NOT_REACHED();
}

CSSPixelRect FormattingContext::margin_box_rect_in_ancestor_coordinate_space(LayoutState::UsedValues const& used_values, Box const& ancestor_box) const
{
    auto rect = margin_box_rect(used_values);
    for (auto const* current = &used_values; current; current = current->containing_block_used_values()) {
        if (&current->node() == &ancestor_box)
            return rect;
        rect.translate_by(current->offset);
    }
    // If we get here, ancestor_box was not a containing block ancestor of `box`!
    VERIFY_NOT_REACHED();
}

CSSPixelRect FormattingContext::margin_box_rect_in_ancestor_coordinate_space(Box const& box, Box const& ancestor_box) const
{
    return margin_box_rect_in_ancestor_coordinate_space(m_state.get(box), ancestor_box);
}

bool FormattingContext::box_is_sized_as_replaced_element(Box const& box, AvailableSpace const& available_space) const
{
    // When a box has a preferred aspect ratio, its automatic sizes are calculated the same as for a
    // replaced element with a natural aspect ratio and no natural size in that axis, see e.g. CSS2 §10
    // and CSS Flexible Box Model Level 1 §9.2.
    // https://www.w3.org/TR/css-sizing-4/#aspect-ratio-automatic
    if (box.is_replaced_box() && box.has_auto_content_box_size())
        return true;

    if (box.has_preferred_aspect_ratio() || box.has_auto_content_box_size()) {
        // From CSS2:
        // If height and width both have computed values of auto and the element has an intrinsic ratio but no intrinsic height or width,
        // then the used value of width is undefined in CSS 2.
        // However, it is suggested that, if the containing block’s width does not itself depend on the replaced element’s width,
        // then the used value of width is calculated from the constraint equation used for block-level, non-replaced elements in normal flow.

        // AD-HOC: If box has preferred aspect ratio but width and height are not specified, then we should
        //         size it as a normal box to match other browsers.

        auto auto_size = box.auto_content_box_size();
        if (should_treat_width_as_auto(box, available_space)
            && should_treat_height_as_auto(box, available_space)
            && !auto_size.has_width()
            && !auto_size.has_height()) {
            return false;
        }
        return true;
    }

    return false;
}

bool FormattingContext::should_treat_max_width_as_none(Box const& box, AvailableSize const& available_width) const
{
    auto const& max_width = box.computed_values().max_width();
    if (max_width.is_none())
        return true;
    if (available_width.is_max_content() && max_width.is_max_content())
        return true;
    // https://drafts.csswg.org/css-sizing-3/#cyclic-percentage-contribution
    if (max_width.contains_percentage()) {
        if (available_width.is_max_content())
            return true;
        if (available_width.is_min_content()) {
            if (!box.is_replaced_box())
                return true;
            return false;
        }
        auto containing_block = box.containing_block();
        while (containing_block && containing_block->is_anonymous() && !containing_block->display().is_table_cell())
            containing_block = containing_block->containing_block();
        auto const* containing_block_used_values = containing_block ? m_state.try_get(*containing_block) : nullptr;
        if (!containing_block_used_values)
            return true;
        if (!containing_block_used_values->has_definite_width())
            return true;
    }
    if (max_width.is_fit_content() && available_width.is_intrinsic_sizing_constraint())
        return true;
    if (max_width.is_max_content() && available_width.is_max_content())
        return true;
    if (max_width.is_min_content() && available_width.is_min_content())
        return true;
    return false;
}

bool FormattingContext::should_treat_max_height_as_none(Box const& box, AvailableSize const& available_height) const
{
    // https://www.w3.org/TR/CSS22/visudet.html#min-max-heights
    // If the height of the containing block is not specified explicitly (i.e., it depends on content height),
    // and this element is not absolutely positioned, the percentage value is treated as '0' (for 'min-height')
    // or 'none' (for 'max-height').
    auto const& max_height = box.computed_values().max_height();
    if (max_height.is_none())
        return true;
    if (max_height.contains_percentage()) {
        if (available_height.is_min_content())
            return false;
        auto containing_block = box.containing_block();
        while (containing_block && containing_block->is_anonymous() && !containing_block->display().is_table_cell())
            containing_block = containing_block->containing_block();
        auto const* containing_block_used_values = containing_block ? m_state.try_get(*containing_block) : nullptr;
        if (!containing_block_used_values)
            return true;
        if (!containing_block_used_values->has_definite_height())
            return true;
    }
    if (max_height.is_fit_content() && available_height.is_intrinsic_sizing_constraint())
        return true;
    if (max_height.is_max_content() && available_height.is_max_content())
        return true;
    if (max_height.is_min_content() && available_height.is_min_content())
        return true;
    return false;
}

CSSPixels FormattingContext::gap_to_px(Variant<CSS::LengthPercentage, CSS::NormalGap> const& gap, CSSPixels reference_value) const
{
    return gap.visit(
        [](CSS::NormalGap) { return CSSPixels(0); },
        [&](auto const& gap) { return gap.to_px(context_box(), reference_value); });
}

}
