path: root/Userland/Libraries/LibWeb/CSS/ResolvedCSSStyleDeclaration.cpp

/*
 * Copyright (c) 2021-2022, Andreas Kling <kling@serenityos.org>
 * Copyright (c) 2021, Tobias Christiansen <tobyase@serenityos.org>
 * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Debug.h>
#include <AK/NonnullRefPtr.h>
#include <LibWeb/CSS/Enums.h>
#include <LibWeb/CSS/ResolvedCSSStyleDeclaration.h>
#include <LibWeb/CSS/StyleComputer.h>
#include <LibWeb/DOM/Document.h>
#include <LibWeb/DOM/Element.h>
#include <LibWeb/Layout/InitialContainingBlock.h>
#include <LibWeb/Painting/PaintableBox.h>
#include <LibWeb/Painting/StackingContext.h>

namespace Web::CSS {

ResolvedCSSStyleDeclaration* ResolvedCSSStyleDeclaration::create(DOM::Element& element)
{
    auto& window_object = element.document().window();
    return window_object.heap().allocate<ResolvedCSSStyleDeclaration>(window_object.realm(), element);
}

ResolvedCSSStyleDeclaration::ResolvedCSSStyleDeclaration(DOM::Element& element)
    : CSSStyleDeclaration(element.document().window())
    , m_element(element)
{
}

void ResolvedCSSStyleDeclaration::visit_edges(Cell::Visitor& visitor)
{
    Base::visit_edges(visitor);
    visitor.visit(m_element.ptr());
}

size_t ResolvedCSSStyleDeclaration::length() const
{
    return 0;
}

String ResolvedCSSStyleDeclaration::item(size_t index) const
{
    (void)index;
    return {};
}

static RefPtr<StyleValue> style_value_for_display(CSS::Display display)
{
    if (display.is_none())
        return IdentifierStyleValue::create(CSS::ValueID::None);

    if (display.is_outside_and_inside()) {
        NonnullRefPtrVector<StyleValue> values;
        switch (display.outside()) {
        case CSS::Display::Outside::Inline:
            values.append(IdentifierStyleValue::create(CSS::ValueID::Inline));
            break;
        case CSS::Display::Outside::Block:
            values.append(IdentifierStyleValue::create(CSS::ValueID::Block));
            break;
        case CSS::Display::Outside::RunIn:
            values.append(IdentifierStyleValue::create(CSS::ValueID::RunIn));
            break;
        }
        switch (display.inside()) {
        case CSS::Display::Inside::Flow:
            values.append(IdentifierStyleValue::create(CSS::ValueID::Flow));
            break;
        case CSS::Display::Inside::FlowRoot:
            values.append(IdentifierStyleValue::create(CSS::ValueID::FlowRoot));
            break;
        case CSS::Display::Inside::Table:
            values.append(IdentifierStyleValue::create(CSS::ValueID::Table));
            break;
        case CSS::Display::Inside::Flex:
            values.append(IdentifierStyleValue::create(CSS::ValueID::Flex));
            break;
        case CSS::Display::Inside::Grid:
            values.append(IdentifierStyleValue::create(CSS::ValueID::Grid));
            break;
        case CSS::Display::Inside::Ruby:
            values.append(IdentifierStyleValue::create(CSS::ValueID::Ruby));
            break;
        }

        return StyleValueList::create(move(values), StyleValueList::Separator::Space);
    }

    if (display.is_internal()) {
        switch (display.internal()) {
        case CSS::Display::Internal::TableRowGroup:
            return IdentifierStyleValue::create(CSS::ValueID::TableRowGroup);
        case CSS::Display::Internal::TableHeaderGroup:
            return IdentifierStyleValue::create(CSS::ValueID::TableHeaderGroup);
        case CSS::Display::Internal::TableFooterGroup:
            return IdentifierStyleValue::create(CSS::ValueID::TableFooterGroup);
        case CSS::Display::Internal::TableRow:
            return IdentifierStyleValue::create(CSS::ValueID::TableRow);
        case CSS::Display::Internal::TableCell:
            return IdentifierStyleValue::create(CSS::ValueID::TableCell);
        case CSS::Display::Internal::TableColumnGroup:
            return IdentifierStyleValue::create(CSS::ValueID::TableColumnGroup);
        case CSS::Display::Internal::TableColumn:
            return IdentifierStyleValue::create(CSS::ValueID::TableColumn);
        case CSS::Display::Internal::TableCaption:
            return IdentifierStyleValue::create(CSS::ValueID::TableCaption);
        case CSS::Display::Internal::RubyBase:
            return IdentifierStyleValue::create(CSS::ValueID::RubyBase);
        case CSS::Display::Internal::RubyText:
            return IdentifierStyleValue::create(CSS::ValueID::RubyText);
        case CSS::Display::Internal::RubyBaseContainer:
            return IdentifierStyleValue::create(CSS::ValueID::RubyBaseContainer);
        case CSS::Display::Internal::RubyTextContainer:
            return IdentifierStyleValue::create(CSS::ValueID::RubyTextContainer);
        }
    }

    TODO();
}

static NonnullRefPtr<StyleValue> value_or_default(Optional<StyleProperty> property, NonnullRefPtr<StyleValue> default_style)
{
    if (property.has_value())
        return property.value().value;
    return default_style;
}

static NonnullRefPtr<StyleValue> style_value_for_length_percentage(LengthPercentage const& length_percentage)
{
    if (length_percentage.is_percentage())
        return PercentageStyleValue::create(length_percentage.percentage());
    if (length_percentage.is_length())
        return LengthStyleValue::create(length_percentage.length());
    return length_percentage.calculated();
}

RefPtr<StyleValue> ResolvedCSSStyleDeclaration::style_value_for_property(Layout::NodeWithStyle const& layout_node, PropertyID property_id) const
{
    switch (property_id) {
    case CSS::PropertyID::Background: {
        auto maybe_background_color = property(CSS::PropertyID::BackgroundColor);
        auto maybe_background_image = property(CSS::PropertyID::BackgroundImage);
        auto maybe_background_position = property(CSS::PropertyID::BackgroundPosition);
        auto maybe_background_size = property(CSS::PropertyID::BackgroundSize);
        auto maybe_background_repeat = property(CSS::PropertyID::BackgroundRepeat);
        auto maybe_background_attachment = property(CSS::PropertyID::BackgroundAttachment);
        auto maybe_background_origin = property(CSS::PropertyID::BackgroundOrigin);
        auto maybe_background_clip = property(CSS::PropertyID::BackgroundClip);

        return BackgroundStyleValue::create(
            value_or_default(maybe_background_color, InitialStyleValue::the()),
            value_or_default(maybe_background_image, IdentifierStyleValue::create(CSS::ValueID::None)),
            value_or_default(maybe_background_position, PositionStyleValue::create(PositionEdge::Left, Length::make_px(0), PositionEdge::Top, Length::make_px(0))),
            value_or_default(maybe_background_size, IdentifierStyleValue::create(CSS::ValueID::Auto)),
            value_or_default(maybe_background_repeat, BackgroundRepeatStyleValue::create(CSS::Repeat::Repeat, CSS::Repeat::Repeat)),
            value_or_default(maybe_background_attachment, IdentifierStyleValue::create(CSS::ValueID::Scroll)),
            value_or_default(maybe_background_origin, IdentifierStyleValue::create(CSS::ValueID::PaddingBox)),
            value_or_default(maybe_background_clip, IdentifierStyleValue::create(CSS::ValueID::BorderBox)));
    }
    case PropertyID::BackgroundColor:
        return ColorStyleValue::create(layout_node.computed_values().background_color());
    case CSS::PropertyID::BorderBottom: {
        auto border = layout_node.computed_values().border_bottom();
        auto width = LengthStyleValue::create(Length::make_px(border.width));
        auto style = IdentifierStyleValue::create(to_value_id(border.line_style));
        auto color = ColorStyleValue::create(border.color);
        return BorderStyleValue::create(width, style, color);
    }
    case CSS::PropertyID::BorderBottomColor:
        return ColorStyleValue::create(layout_node.computed_values().border_bottom().color);
    case CSS::PropertyID::BorderBottomLeftRadius: {
        auto const& border_radius = layout_node.computed_values().border_bottom_left_radius();
        return BorderRadiusStyleValue::create(border_radius.horizontal_radius, border_radius.vertical_radius);
    }
    case CSS::PropertyID::BorderBottomRightRadius: {
        auto const& border_radius = layout_node.computed_values().border_bottom_right_radius();
        return BorderRadiusStyleValue::create(border_radius.horizontal_radius, border_radius.vertical_radius);
    }
    case CSS::PropertyID::BorderBottomStyle:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().border_bottom().line_style));
    case CSS::PropertyID::BorderBottomWidth:
        return LengthStyleValue::create(Length::make_px(layout_node.computed_values().border_bottom().width));
    case CSS::PropertyID::BorderLeft: {
        auto border = layout_node.computed_values().border_left();
        auto width = LengthStyleValue::create(Length::make_px(border.width));
        auto style = IdentifierStyleValue::create(to_value_id(border.line_style));
        auto color = ColorStyleValue::create(border.color);
        return BorderStyleValue::create(width, style, color);
    }
    case CSS::PropertyID::BorderLeftColor:
        return ColorStyleValue::create(layout_node.computed_values().border_left().color);
    case CSS::PropertyID::BorderLeftStyle:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().border_left().line_style));
    case CSS::PropertyID::BorderLeftWidth:
        return LengthStyleValue::create(Length::make_px(layout_node.computed_values().border_left().width));
    case CSS::PropertyID::BorderRadius: {
        auto maybe_top_left_radius = property(CSS::PropertyID::BorderTopLeftRadius);
        auto maybe_top_right_radius = property(CSS::PropertyID::BorderTopRightRadius);
        auto maybe_bottom_left_radius = property(CSS::PropertyID::BorderBottomLeftRadius);
        auto maybe_bottom_right_radius = property(CSS::PropertyID::BorderBottomRightRadius);
        RefPtr<BorderRadiusStyleValue> top_left_radius, top_right_radius, bottom_left_radius, bottom_right_radius;
        if (maybe_top_left_radius.has_value()) {
            VERIFY(maybe_top_left_radius.value().value->is_border_radius());
            top_left_radius = maybe_top_left_radius.value().value->as_border_radius();
        }
        if (maybe_top_right_radius.has_value()) {
            VERIFY(maybe_top_right_radius.value().value->is_border_radius());
            top_right_radius = maybe_top_right_radius.value().value->as_border_radius();
        }
        if (maybe_bottom_left_radius.has_value()) {
            VERIFY(maybe_bottom_left_radius.value().value->is_border_radius());
            bottom_left_radius = maybe_bottom_left_radius.value().value->as_border_radius();
        }
        if (maybe_bottom_right_radius.has_value()) {
            VERIFY(maybe_bottom_right_radius.value().value->is_border_radius());
            bottom_right_radius = maybe_bottom_right_radius.value().value->as_border_radius();
        }

        return BorderRadiusShorthandStyleValue::create(top_left_radius.release_nonnull(), top_right_radius.release_nonnull(), bottom_right_radius.release_nonnull(), bottom_left_radius.release_nonnull());
    }
    case CSS::PropertyID::BorderRight: {
        auto border = layout_node.computed_values().border_right();
        auto width = LengthStyleValue::create(Length::make_px(border.width));
        auto style = IdentifierStyleValue::create(to_value_id(border.line_style));
        auto color = ColorStyleValue::create(border.color);
        return BorderStyleValue::create(width, style, color);
    }
    case CSS::PropertyID::BorderRightColor:
        return ColorStyleValue::create(layout_node.computed_values().border_right().color);
    case CSS::PropertyID::BorderRightStyle:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().border_right().line_style));
    case CSS::PropertyID::BorderRightWidth:
        return LengthStyleValue::create(Length::make_px(layout_node.computed_values().border_right().width));
    case CSS::PropertyID::BorderTop: {
        auto border = layout_node.computed_values().border_top();
        auto width = LengthStyleValue::create(Length::make_px(border.width));
        auto style = IdentifierStyleValue::create(to_value_id(border.line_style));
        auto color = ColorStyleValue::create(border.color);
        return BorderStyleValue::create(width, style, color);
    }
    case CSS::PropertyID::BorderTopColor:
        return ColorStyleValue::create(layout_node.computed_values().border_top().color);
    case CSS::PropertyID::BorderTopLeftRadius: {
        auto const& border_radius = layout_node.computed_values().border_top_left_radius();
        return BorderRadiusStyleValue::create(border_radius.horizontal_radius, border_radius.vertical_radius);
    }
    case CSS::PropertyID::BorderTopRightRadius: {
        auto const& border_radius = layout_node.computed_values().border_top_right_radius();
        return BorderRadiusStyleValue::create(border_radius.horizontal_radius, border_radius.vertical_radius);
    }
    case CSS::PropertyID::BorderTopStyle:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().border_top().line_style));
    case CSS::PropertyID::BorderTopWidth:
        return LengthStyleValue::create(Length::make_px(layout_node.computed_values().border_top().width));
    case CSS::PropertyID::BoxShadow: {
        auto box_shadow_layers = layout_node.computed_values().box_shadow();
        if (box_shadow_layers.is_empty())
            return {};

        auto make_box_shadow_style_value = [](ShadowData const& data) {
            return ShadowStyleValue::create(data.color, data.offset_x, data.offset_y, data.blur_radius, data.spread_distance, data.placement);
        };

        if (box_shadow_layers.size() == 1)
            return make_box_shadow_style_value(box_shadow_layers.first());

        NonnullRefPtrVector<StyleValue> box_shadow;
        box_shadow.ensure_capacity(box_shadow_layers.size());
        for (auto const& layer : box_shadow_layers)
            box_shadow.append(make_box_shadow_style_value(layer));
        return StyleValueList::create(move(box_shadow), StyleValueList::Separator::Comma);
    }
    case CSS::PropertyID::BoxSizing:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().box_sizing()));
    case CSS::PropertyID::Clear:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().clear()));
    case CSS::PropertyID::Clip:
        return RectStyleValue::create(layout_node.computed_values().clip().to_rect());
    case CSS::PropertyID::Color:
        return ColorStyleValue::create(layout_node.computed_values().color());
    case CSS::PropertyID::Cursor:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().cursor()));
    case CSS::PropertyID::Display:
        return style_value_for_display(layout_node.computed_values().display());
    case CSS::PropertyID::FlexBasis: {
        switch (layout_node.computed_values().flex_basis().type) {
        case FlexBasis::Content:
            return IdentifierStyleValue::create(CSS::ValueID::Content);
        case FlexBasis::LengthPercentage:
            return style_value_for_length_percentage(*layout_node.computed_values().flex_basis().length_percentage);
        case FlexBasis::Auto:
            return IdentifierStyleValue::create(CSS::ValueID::Auto);
        default:
            VERIFY_NOT_REACHED();
        }
        break;
    case CSS::PropertyID::FlexDirection:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().flex_direction()));
    case CSS::PropertyID::FlexGrow:
        return NumericStyleValue::create_float(layout_node.computed_values().flex_grow());
    case CSS::PropertyID::FlexShrink:
        return NumericStyleValue::create_float(layout_node.computed_values().flex_shrink());
    case CSS::PropertyID::FlexWrap:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().flex_wrap()));
    case CSS::PropertyID::Float:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().float_()));
    case CSS::PropertyID::GridColumn: {
        auto maybe_grid_column_end = property(CSS::PropertyID::GridColumnEnd);
        auto maybe_grid_column_start = property(CSS::PropertyID::GridColumnStart);
        RefPtr<GridTrackPlacementStyleValue> grid_column_start, grid_column_end;
        if (maybe_grid_column_end.has_value()) {
            VERIFY(maybe_grid_column_end.value().value->is_grid_track_placement());
            grid_column_end = maybe_grid_column_end.value().value->as_grid_track_placement();
        }
        if (maybe_grid_column_start.has_value()) {
            VERIFY(maybe_grid_column_start.value().value->is_grid_track_placement());
            grid_column_start = maybe_grid_column_start.value().value->as_grid_track_placement();
        }
        return GridTrackPlacementShorthandStyleValue::create(grid_column_end.release_nonnull(), grid_column_start.release_nonnull());
    }
    case CSS::PropertyID::GridColumnEnd:
        return GridTrackPlacementStyleValue::create(layout_node.computed_values().grid_column_end());
    case CSS::PropertyID::GridColumnStart:
        return GridTrackPlacementStyleValue::create(layout_node.computed_values().grid_column_start());
    case CSS::PropertyID::GridRow: {
        auto maybe_grid_row_end = property(CSS::PropertyID::GridRowEnd);
        auto maybe_grid_row_start = property(CSS::PropertyID::GridRowStart);
        RefPtr<GridTrackPlacementStyleValue> grid_row_start, grid_row_end;
        if (maybe_grid_row_end.has_value()) {
            VERIFY(maybe_grid_row_end.value().value->is_grid_track_placement());
            grid_row_end = maybe_grid_row_end.value().value->as_grid_track_placement();
        }
        if (maybe_grid_row_start.has_value()) {
            VERIFY(maybe_grid_row_start.value().value->is_grid_track_placement());
            grid_row_start = maybe_grid_row_start.value().value->as_grid_track_placement();
        }
        return GridTrackPlacementShorthandStyleValue::create(grid_row_end.release_nonnull(), grid_row_start.release_nonnull());
    }
    case CSS::PropertyID::GridRowEnd:
        return GridTrackPlacementStyleValue::create(layout_node.computed_values().grid_row_end());
    case CSS::PropertyID::GridRowStart:
        return GridTrackPlacementStyleValue::create(layout_node.computed_values().grid_row_start());
    case CSS::PropertyID::GridTemplateColumns:
        return GridTrackSizeStyleValue::create(layout_node.computed_values().grid_template_columns());
    case CSS::PropertyID::GridTemplateRows:
        return GridTrackSizeStyleValue::create(layout_node.computed_values().grid_template_rows());
    case CSS::PropertyID::Height:
        return style_value_for_length_percentage(layout_node.computed_values().height());
    case CSS::PropertyID::ImageRendering:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().image_rendering()));
    case CSS::PropertyID::JustifyContent:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().justify_content()));
    case CSS::PropertyID::ListStyleType:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().list_style_type()));
    case CSS::PropertyID::Margin: {
        auto margin = layout_node.computed_values().margin();
        auto values = NonnullRefPtrVector<StyleValue> {};
        values.append(style_value_for_length_percentage(margin.top));
        values.append(style_value_for_length_percentage(margin.right));
        values.append(style_value_for_length_percentage(margin.bottom));
        values.append(style_value_for_length_percentage(margin.left));
        return StyleValueList::create(move(values), StyleValueList::Separator::Space);
    }
    case CSS::PropertyID::MarginBottom:
        return style_value_for_length_percentage(layout_node.computed_values().margin().bottom);
    case CSS::PropertyID::MarginLeft:
        return style_value_for_length_percentage(layout_node.computed_values().margin().left);
    case CSS::PropertyID::MarginRight:
        return style_value_for_length_percentage(layout_node.computed_values().margin().right);
    case CSS::PropertyID::MarginTop:
        return style_value_for_length_percentage(layout_node.computed_values().margin().top);
    case CSS::PropertyID::MaxHeight:
        return style_value_for_length_percentage(layout_node.computed_values().max_height());
    case CSS::PropertyID::MaxWidth:
        return style_value_for_length_percentage(layout_node.computed_values().max_width());
    case CSS::PropertyID::MinHeight:
        return style_value_for_length_percentage(layout_node.computed_values().min_height());
    case CSS::PropertyID::MinWidth:
        return style_value_for_length_percentage(layout_node.computed_values().min_width());
    case CSS::PropertyID::Opacity:
        return NumericStyleValue::create_float(layout_node.computed_values().opacity());
    case CSS::PropertyID::Order:
        return NumericStyleValue::create_integer(layout_node.computed_values().order());
    case CSS::PropertyID::OverflowX:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().overflow_x()));
    case CSS::PropertyID::OverflowY:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().overflow_y()));
    case CSS::PropertyID::Padding: {
        auto padding = layout_node.computed_values().padding();
        auto values = NonnullRefPtrVector<StyleValue> {};
        values.append(style_value_for_length_percentage(padding.top));
        values.append(style_value_for_length_percentage(padding.right));
        values.append(style_value_for_length_percentage(padding.bottom));
        values.append(style_value_for_length_percentage(padding.left));
        return StyleValueList::create(move(values), StyleValueList::Separator::Space);
    }
    case CSS::PropertyID::PaddingBottom:
    case CSS::PropertyID::PaddingLeft:
        return style_value_for_length_percentage(layout_node.computed_values().padding().left);
        return style_value_for_length_percentage(layout_node.computed_values().padding().bottom);
    case CSS::PropertyID::PaddingRight:
        return style_value_for_length_percentage(layout_node.computed_values().padding().right);
    case CSS::PropertyID::PaddingTop:
        return style_value_for_length_percentage(layout_node.computed_values().padding().top);
    case CSS::PropertyID::Position:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().position()));
    case CSS::PropertyID::TextAlign:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().text_align()));
    case CSS::PropertyID::TextDecorationLine: {
        auto text_decoration_lines = layout_node.computed_values().text_decoration_line();
        if (text_decoration_lines.is_empty())
            return IdentifierStyleValue::create(ValueID::None);
        NonnullRefPtrVector<StyleValue> style_values;
        for (auto const& line : text_decoration_lines) {
            style_values.append(IdentifierStyleValue::create(to_value_id(line)));
        }
        return StyleValueList::create(move(style_values), StyleValueList::Separator::Space);
    }
    case CSS::PropertyID::TextDecorationStyle:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().text_decoration_style()));
    case CSS::PropertyID::TextTransform:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().text_transform()));
    case CSS::PropertyID::Transform: {
        // NOTE: The computed value for `transform` serializes as a single `matrix(...)` value, instead of
        //       the original list of transform functions. So, we produce a StyleValue for that.
        //       https://www.w3.org/TR/css-transforms-1/#serialization-of-the-computed-value
        auto transformations = layout_node.computed_values().transformations();
        if (transformations.is_empty())
            return IdentifierStyleValue::create(ValueID::None);

        // The transform matrix is held by the StackingContext, so we need to make sure we have one first.
        auto* initial_containing_block = layout_node.document().layout_node();
        VERIFY(initial_containing_block);
        const_cast<Layout::InitialContainingBlock&>(*initial_containing_block).build_stacking_context_tree_if_needed();

        VERIFY(layout_node.paintable());
        auto const& paintable_box = verify_cast<Painting::PaintableBox const>(layout_node.paintable());
        VERIFY(paintable_box->stacking_context());
        auto affine_matrix = paintable_box->stacking_context()->affine_transform_matrix();

        NonnullRefPtrVector<StyleValue> parameters;
        parameters.ensure_capacity(6);
        parameters.append(NumericStyleValue::create_float(affine_matrix.a()));
        parameters.append(NumericStyleValue::create_float(affine_matrix.b()));
        parameters.append(NumericStyleValue::create_float(affine_matrix.c()));
        parameters.append(NumericStyleValue::create_float(affine_matrix.d()));
        parameters.append(NumericStyleValue::create_float(affine_matrix.e()));
        parameters.append(NumericStyleValue::create_float(affine_matrix.f()));

        NonnullRefPtr<StyleValue> matrix_function = TransformationStyleValue::create(TransformFunction::Matrix, move(parameters));
        // Elsewhere we always store the transform property's value as a StyleValueList of TransformationStyleValues,
        // so this is just for consistency.
        NonnullRefPtrVector<StyleValue> matrix_functions;
        matrix_functions.append(matrix_function);
        return StyleValueList::create(move(matrix_functions), StyleValueList::Separator::Space);
    }
    case CSS::PropertyID::VerticalAlign:
        if (auto const* length_percentage = layout_node.computed_values().vertical_align().get_pointer<CSS::LengthPercentage>()) {
            if (length_percentage->is_length())
                return LengthStyleValue::create(length_percentage->length());
            if (length_percentage->is_percentage())
                return PercentageStyleValue::create(length_percentage->percentage());
            VERIFY_NOT_REACHED();
        }
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().vertical_align().get<CSS::VerticalAlign>()));
    case CSS::PropertyID::WhiteSpace:
        return IdentifierStyleValue::create(to_value_id(layout_node.computed_values().white_space()));
    case CSS::PropertyID::Width:
        return style_value_for_length_percentage(layout_node.computed_values().width());
    case CSS::PropertyID::ZIndex: {
        auto maybe_z_index = layout_node.computed_values().z_index();
        if (!maybe_z_index.has_value())
            return {};
        return NumericStyleValue::create_integer(maybe_z_index.release_value());
    }
    case CSS::PropertyID::Invalid:
        return IdentifierStyleValue::create(CSS::ValueID::Invalid);
    case CSS::PropertyID::Custom:
        dbgln_if(LIBWEB_CSS_DEBUG, "Computed style for custom properties was requested (?)");
        return {};
    default:
        dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Computed style for the '{}' property was requested", string_from_property_id(property_id));
        return {};
    }
    }
}

Optional<StyleProperty> ResolvedCSSStyleDeclaration::property(PropertyID property_id) const
{
    if (CSS::property_affects_layout(property_id)) {
        const_cast<DOM::Document&>(m_element->document()).update_layout();
    } else {
        // FIXME: If we had a way to update style for a single element, this would be a good place to use it.
        const_cast<DOM::Document&>(m_element->document()).update_style();
    }

    if (!m_element->layout_node()) {
        auto style = m_element->document().style_computer().compute_style(const_cast<DOM::Element&>(*m_element));
        return StyleProperty {
            .property_id = property_id,
            .value = style->property(property_id),
        };
    }

    auto& layout_node = *m_element->layout_node();
    auto value = style_value_for_property(layout_node, property_id);
    if (!value)
        return {};
    return StyleProperty {
        .property_id = property_id,
        .value = value.release_nonnull(),
    };
}

// https://drafts.csswg.org/cssom/#dom-cssstyledeclaration-setproperty
DOM::ExceptionOr<void> ResolvedCSSStyleDeclaration::set_property(PropertyID, StringView, StringView)
{
    // 1. If the computed flag is set, then throw a NoModificationAllowedError exception.
    return DOM::NoModificationAllowedError::create("Cannot modify properties in result of getComputedStyle()");
}

// https://drafts.csswg.org/cssom/#dom-cssstyledeclaration-removeproperty
DOM::ExceptionOr<String> ResolvedCSSStyleDeclaration::remove_property(PropertyID)
{
    // 1. If the computed flag is set, then throw a NoModificationAllowedError exception.
    return DOM::NoModificationAllowedError::create("Cannot remove properties from result of getComputedStyle()");
}

String ResolvedCSSStyleDeclaration::serialized() const
{
    // https://www.w3.org/TR/cssom/#dom-cssstyledeclaration-csstext
    // If the computed flag is set, then return the empty string.

    // NOTE: ResolvedCSSStyleDeclaration is something you would only get from window.getComputedStyle(),
    //       which returns what the spec calls "resolved style". The "computed flag" is always set here.
    return String::empty();
}

}