ladybird/Userland/Libraries/LibWeb/Layout/GridFormattingContext.cpp

/*
 * Copyright (c) 2022-2023, Martin Falisse <mfalisse@outlook.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibWeb/DOM/Node.h>
#include <LibWeb/Layout/Box.h>
#include <LibWeb/Layout/GridFormattingContext.h>

namespace Web::Layout {

GridFormattingContext::GridFormattingContext(LayoutState& state, Box const& grid_container, FormattingContext* parent)
    : FormattingContext(Type::Grid, state, grid_container, parent)
{
}

GridFormattingContext::~GridFormattingContext() = default;

CSSPixels GridFormattingContext::resolve_definite_track_size(CSS::GridSize const& grid_size, AvailableSpace const& available_space)
{
    VERIFY(grid_size.is_definite());
    switch (grid_size.type()) {
    case CSS::GridSize::Type::Length:
        if (grid_size.length().is_auto())
            break;
        return grid_size.length().to_px(grid_container());
    case CSS::GridSize::Type::Percentage:
        if (available_space.width.is_definite())
            return grid_size.percentage().as_fraction() * available_space.width.to_px().value();
        break;
    default:
        VERIFY_NOT_REACHED();
    }
    return 0;
}

size_t GridFormattingContext::count_of_gap_tracks(Vector<TemporaryTrack> const& tracks) const
{
    size_t count = 0;
    for (auto& track : tracks) {
        if (track.is_gap)
            count++;
    }
    return count;
}

int GridFormattingContext::get_count_of_tracks(Vector<CSS::ExplicitGridTrack> const& track_list, AvailableSpace const& available_space)
{
    auto track_count = 0;
    for (auto const& explicit_grid_track : track_list) {
        if (explicit_grid_track.is_repeat() && explicit_grid_track.repeat().is_default())
            track_count += explicit_grid_track.repeat().repeat_count() * explicit_grid_track.repeat().grid_track_size_list().track_list().size();
        else
            track_count += 1;
    }

    if (track_list.size() == 1
        && track_list.first().is_repeat()
        && (track_list.first().repeat().is_auto_fill() || track_list.first().repeat().is_auto_fit())) {
        track_count = count_of_repeated_auto_fill_or_fit_tracks(track_list, available_space);
    }

    return track_count;
}

int GridFormattingContext::count_of_repeated_auto_fill_or_fit_tracks(Vector<CSS::ExplicitGridTrack> const& track_list, AvailableSpace const& available_space)
{
    // https://www.w3.org/TR/css-grid-2/#auto-repeat
    // 7.2.3.2. Repeat-to-fill: auto-fill and auto-fit repetitions
    // On a subgridded axis, the auto-fill keyword is only valid once per <line-name-list>, and repeats
    // enough times for the name list to match the subgrid’s specified grid span (falling back to 0 if
    // the span is already fulfilled).

    // Otherwise on a standalone axis, when auto-fill is given as the repetition number
    // If the grid container has a definite size or max size in the relevant axis, then the number of
    // repetitions is the largest possible positive integer that does not cause the grid to overflow the
    // content box of its grid container

    CSSPixels sum_of_grid_track_sizes = 0;
    // (treating each track as its max track sizing function if that is definite or its minimum track sizing
    // function otherwise, flooring the max track sizing function by the min track sizing function if both
    // are definite, and taking gap into account)
    // FIXME: take gap into account
    for (auto& explicit_grid_track : track_list.first().repeat().grid_track_size_list().track_list()) {
        auto track_sizing_function = explicit_grid_track;
        if (track_sizing_function.is_minmax()) {
            if (track_sizing_function.minmax().max_grid_size().is_definite() && !track_sizing_function.minmax().min_grid_size().is_definite())
                sum_of_grid_track_sizes += resolve_definite_track_size(track_sizing_function.minmax().max_grid_size(), available_space);
            else if (track_sizing_function.minmax().min_grid_size().is_definite() && !track_sizing_function.minmax().max_grid_size().is_definite())
                sum_of_grid_track_sizes += resolve_definite_track_size(track_sizing_function.minmax().min_grid_size(), available_space);
            else if (track_sizing_function.minmax().min_grid_size().is_definite() && track_sizing_function.minmax().max_grid_size().is_definite())
                sum_of_grid_track_sizes += min(resolve_definite_track_size(track_sizing_function.minmax().min_grid_size(), available_space), resolve_definite_track_size(track_sizing_function.minmax().max_grid_size(), available_space));
        } else {
            sum_of_grid_track_sizes += min(resolve_definite_track_size(track_sizing_function.grid_size(), available_space), resolve_definite_track_size(track_sizing_function.grid_size(), available_space));
        }
    }
    return max(1, static_cast<int>((get_free_space(available_space.width, m_grid_columns).to_px() / sum_of_grid_track_sizes).value()));

    // For the purpose of finding the number of auto-repeated tracks in a standalone axis, the UA must
    // floor the track size to a UA-specified value to avoid division by zero. It is suggested that this
    // floor be 1px.
}

void GridFormattingContext::place_item_with_row_and_column_position(Box const& child_box)
{
    int row_start = child_box.computed_values().grid_row_start().raw_value() - 1;
    int row_end = child_box.computed_values().grid_row_end().raw_value() - 1;
    int column_start = child_box.computed_values().grid_column_start().raw_value() - 1;
    int column_end = child_box.computed_values().grid_column_end().raw_value() - 1;

    // https://www.w3.org/TR/css-grid-2/#line-placement
    // 8.3. Line-based Placement: the grid-row-start, grid-column-start, grid-row-end, and grid-column-end properties

    // https://www.w3.org/TR/css-grid-2/#grid-placement-slot
    // First attempt to match the grid area’s edge to a named grid area: if there is a grid line whose
    // line name is <custom-ident>-start (for grid-*-start) / <custom-ident>-end (for grid-*-end),
    // contributes the first such line to the grid item’s placement.

    // Otherwise, treat this as if the integer 1 had been specified along with the <custom-ident>.

    // https://www.w3.org/TR/css-grid-2/#grid-placement-int
    // Contributes the Nth grid line to the grid item’s placement. If a negative integer is given, it
    // instead counts in reverse, starting from the end edge of the explicit grid.
    if (row_end < 0)
        row_end = m_occupation_grid.row_count() + row_end + 2;
    if (column_end < 0)
        column_end = m_occupation_grid.column_count() + column_end + 2;

    // If a name is given as a <custom-ident>, only lines with that name are counted. If not enough
    // lines with that name exist, all implicit grid lines are assumed to have that name for the purpose
    // of finding this position.

    // https://www.w3.org/TR/css-grid-2/#grid-placement-span-int
    // Contributes a grid span to the grid item’s placement such that the corresponding edge of the grid
    // item’s grid area is N lines from its opposite edge in the corresponding direction. For example,
    // grid-column-end: span 2 indicates the second grid line in the endward direction from the
    // grid-column-start line.
    int row_span = 1;
    int column_span = 1;
    if (child_box.computed_values().grid_row_start().is_position() && child_box.computed_values().grid_row_end().is_span())
        row_span = child_box.computed_values().grid_row_end().raw_value();
    if (child_box.computed_values().grid_column_start().is_position() && child_box.computed_values().grid_column_end().is_span())
        column_span = child_box.computed_values().grid_column_end().raw_value();
    if (child_box.computed_values().grid_row_end().is_position() && child_box.computed_values().grid_row_start().is_span()) {
        row_span = child_box.computed_values().grid_row_start().raw_value();
        row_start = row_end - row_span;
    }
    if (child_box.computed_values().grid_column_end().is_position() && child_box.computed_values().grid_column_start().is_span()) {
        column_span = child_box.computed_values().grid_column_start().raw_value();
        column_start = column_end - column_span;
    }

    // If a name is given as a <custom-ident>, only lines with that name are counted. If not enough
    // lines with that name exist, all implicit grid lines on the side of the explicit grid
    // corresponding to the search direction are assumed to have that name for the purpose of counting
    // this span.

    // https://drafts.csswg.org/css-grid/#grid-placement-auto
    // auto
    // The property contributes nothing to the grid item’s placement, indicating auto-placement or a
    // default span of one. (See § 8 Placing Grid Items, above.)

    // https://www.w3.org/TR/css-grid-2/#common-uses-named-lines
    // 8.1.3. Named Lines and Spans
    // Instead of counting lines by number, lines can be referenced by their line name:
    if (child_box.computed_values().grid_column_end().has_line_name()) {
        if (auto grid_area_index = find_valid_grid_area(child_box.computed_values().grid_column_end().line_name()); grid_area_index > -1)
            column_end = m_valid_grid_areas[grid_area_index].column_end;
        else if (auto line_name_index = get_line_index_by_line_name(child_box.computed_values().grid_column_end().line_name(), grid_container().computed_values().grid_template_columns()); line_name_index > -1)
            column_end = line_name_index;
        else
            column_end = 1;
        column_start = column_end - 1;
    }
    if (child_box.computed_values().grid_column_start().has_line_name()) {
        if (auto grid_area_index = find_valid_grid_area(child_box.computed_values().grid_column_end().line_name()); grid_area_index > -1)
            column_start = m_valid_grid_areas[grid_area_index].column_start;
        else if (auto line_name_index = get_line_index_by_line_name(child_box.computed_values().grid_column_start().line_name(), grid_container().computed_values().grid_template_columns()); line_name_index > -1)
            column_start = line_name_index;
        else
            column_start = 0;
    }
    if (child_box.computed_values().grid_row_end().has_line_name()) {
        if (auto grid_area_index = find_valid_grid_area(child_box.computed_values().grid_row_end().line_name()); grid_area_index > -1)
            row_end = m_valid_grid_areas[grid_area_index].row_end;
        else if (auto line_name_index = get_line_index_by_line_name(child_box.computed_values().grid_row_end().line_name(), grid_container().computed_values().grid_template_rows()); line_name_index > -1)
            row_end = line_name_index;
        else
            row_end = 1;
        row_start = row_end - 1;
    }
    if (child_box.computed_values().grid_row_start().has_line_name()) {
        if (auto grid_area_index = find_valid_grid_area(child_box.computed_values().grid_row_end().line_name()); grid_area_index > -1)
            row_start = m_valid_grid_areas[grid_area_index].row_start;
        else if (auto line_name_index = get_line_index_by_line_name(child_box.computed_values().grid_row_start().line_name(), grid_container().computed_values().grid_template_rows()); line_name_index > -1)
            row_start = line_name_index;
        else
            row_start = 0;
    }

    // If there are multiple lines of the same name, they effectively establish a named set of grid
    // lines, which can be exclusively indexed by filtering the placement by name:

    // https://drafts.csswg.org/css-grid/#grid-placement-errors
    // 8.3.1. Grid Placement Conflict Handling
    // If the placement for a grid item contains two lines, and the start line is further end-ward than
    // the end line, swap the two lines. If the start line is equal to the end line, remove the end
    // line.
    if (child_box.computed_values().grid_row_start().is_position() && child_box.computed_values().grid_row_end().is_position()) {
        if (row_start > row_end)
            swap(row_start, row_end);
        if (row_start != row_end)
            row_span = row_end - row_start;
    }
    if (child_box.computed_values().grid_column_start().is_position() && child_box.computed_values().grid_column_end().is_position()) {
        if (column_start > column_end)
            swap(column_start, column_end);
        if (column_start != column_end)
            column_span = column_end - column_start;
    }

    // If the placement contains two spans, remove the one contributed by the end grid-placement
    // property.
    if (child_box.computed_values().grid_row_start().is_span() && child_box.computed_values().grid_row_end().is_span())
        row_span = child_box.computed_values().grid_row_start().raw_value();
    if (child_box.computed_values().grid_column_start().is_span() && child_box.computed_values().grid_column_end().is_span())
        column_span = child_box.computed_values().grid_column_start().raw_value();

    // FIXME: If the placement contains only a span for a named line, replace it with a span of 1.

    m_grid_items.append(GridItem(child_box, row_start, row_span, column_start, column_span));

    m_occupation_grid.maybe_add_row(row_start + 1);
    m_occupation_grid.maybe_add_column(column_start + 1);
    m_occupation_grid.set_occupied(column_start, column_start + column_span, row_start, row_start + row_span);
}

void GridFormattingContext::place_item_with_row_position(Box const& child_box)
{
    int row_start = child_box.computed_values().grid_row_start().raw_value() - 1;
    int row_end = child_box.computed_values().grid_row_end().raw_value() - 1;

    // https://www.w3.org/TR/css-grid-2/#line-placement
    // 8.3. Line-based Placement: the grid-row-start, grid-column-start, grid-row-end, and grid-column-end properties

    // https://www.w3.org/TR/css-grid-2/#grid-placement-slot
    // First attempt to match the grid area’s edge to a named grid area: if there is a grid line whose
    // line name is <custom-ident>-start (for grid-*-start) / <custom-ident>-end (for grid-*-end),
    // contributes the first such line to the grid item’s placement.

    // Otherwise, treat this as if the integer 1 had been specified along with the <custom-ident>.

    // https://www.w3.org/TR/css-grid-2/#grid-placement-int
    // Contributes the Nth grid line to the grid item’s placement. If a negative integer is given, it
    // instead counts in reverse, starting from the end edge of the explicit grid.
    if (row_end < 0)
        row_end = m_occupation_grid.row_count() + row_end + 2;

    // If a name is given as a <custom-ident>, only lines with that name are counted. If not enough
    // lines with that name exist, all implicit grid lines are assumed to have that name for the purpose
    // of finding this position.

    // https://www.w3.org/TR/css-grid-2/#grid-placement-span-int
    // Contributes a grid span to the grid item’s placement such that the corresponding edge of the grid
    // item’s grid area is N lines from its opposite edge in the corresponding direction. For example,
    // grid-column-end: span 2 indicates the second grid line in the endward direction from the
    // grid-column-start line.
    int row_span = 1;
    if (child_box.computed_values().grid_row_start().is_position() && child_box.computed_values().grid_row_end().is_span())
        row_span = child_box.computed_values().grid_row_end().raw_value();
    if (child_box.computed_values().grid_row_end().is_position() && child_box.computed_values().grid_row_start().is_span()) {
        row_span = child_box.computed_values().grid_row_start().raw_value();
        row_start = row_end - row_span;
        // FIXME: Remove me once have implemented spans overflowing into negative indexes, e.g., grid-row: span 2 / 1
        if (row_start < 0)
            row_start = 0;
    }

    // If a name is given as a <custom-ident>, only lines with that name are counted. If not enough
    // lines with that name exist, all implicit grid lines on the side of the explicit grid
    // corresponding to the search direction are assumed to have that name for the purpose of counting
    // this span.

    // https://drafts.csswg.org/css-grid/#grid-placement-auto
    // auto
    // The property contributes nothing to the grid item’s placement, indicating auto-placement or a
    // default span of one. (See § 8 Placing Grid Items, above.)

    // https://www.w3.org/TR/css-grid-2/#common-uses-named-lines
    // 8.1.3. Named Lines and Spans
    // Instead of counting lines by number, lines can be referenced by their line name:
    if (child_box.computed_values().grid_row_end().has_line_name()) {
        if (auto grid_area_index = find_valid_grid_area(child_box.computed_values().grid_row_end().line_name()); grid_area_index > -1)
            row_end = m_valid_grid_areas[grid_area_index].row_end;
        else if (auto line_name_index = get_line_index_by_line_name(child_box.computed_values().grid_row_end().line_name(), grid_container().computed_values().grid_template_rows()); line_name_index > -1)
            row_end = line_name_index;
        else
            row_end = 1;
        row_start = row_end - 1;
    }
    if (child_box.computed_values().grid_row_start().has_line_name()) {
        if (auto grid_area_index = find_valid_grid_area(child_box.computed_values().grid_row_end().line_name()); grid_area_index > -1)
            row_start = m_valid_grid_areas[grid_area_index].row_start;
        else if (auto line_name_index = get_line_index_by_line_name(child_box.computed_values().grid_row_start().line_name(), grid_container().computed_values().grid_template_rows()); line_name_index > -1)
            row_start = line_name_index;
        else
            row_start = 0;
    }

    // If there are multiple lines of the same name, they effectively establish a named set of grid
    // lines, which can be exclusively indexed by filtering the placement by name:

    // https://drafts.csswg.org/css-grid/#grid-placement-errors
    // 8.3.1. Grid Placement Conflict Handling
    // If the placement for a grid item contains two lines, and the start line is further end-ward than
    // the end line, swap the two lines. If the start line is equal to the end line, remove the end
    // line.
    if (child_box.computed_values().grid_row_start().is_position() && child_box.computed_values().grid_row_end().is_position()) {
        if (row_start > row_end)
            swap(row_start, row_end);
        if (row_start != row_end)
            row_span = row_end - row_start;
    }
    // FIXME: Have yet to find the spec for this.
    if (!child_box.computed_values().grid_row_start().is_position() && child_box.computed_values().grid_row_end().is_position() && row_end == 0)
        row_start = 0;

    // If the placement contains two spans, remove the one contributed by the end grid-placement
    // property.
    if (child_box.computed_values().grid_row_start().is_span() && child_box.computed_values().grid_row_end().is_span())
        row_span = child_box.computed_values().grid_row_start().raw_value();

    // FIXME: If the placement contains only a span for a named line, replace it with a span of 1.

    m_occupation_grid.maybe_add_row(row_start + row_span);

    int column_start = 0;
    auto column_span = child_box.computed_values().grid_column_start().is_span() ? child_box.computed_values().grid_column_start().raw_value() : 1;
    // https://drafts.csswg.org/css-grid/#auto-placement-algo
    // 8.5. Grid Item Placement Algorithm
    // 3.3. If the largest column span among all the items without a definite column position is larger
    // than the width of the implicit grid, add columns to the end of the implicit grid to accommodate
    // that column span.
    m_occupation_grid.maybe_add_column(column_span);
    bool found_available_column = false;
    for (size_t column_index = column_start; column_index < m_occupation_grid.column_count(); column_index++) {
        if (!m_occupation_grid.is_occupied(column_index, row_start)) {
            found_available_column = true;
            column_start = column_index;
            break;
        }
    }
    if (!found_available_column) {
        column_start = m_occupation_grid.column_count();
        m_occupation_grid.maybe_add_column(column_start + column_span);
    }
    m_occupation_grid.set_occupied(column_start, column_start + column_span, row_start, row_start + row_span);

    m_grid_items.append(GridItem(child_box, row_start, row_span, column_start, column_span));
}

void GridFormattingContext::place_item_with_column_position(Box const& child_box, int& auto_placement_cursor_x, int& auto_placement_cursor_y)
{
    int column_start = child_box.computed_values().grid_column_start().raw_value() - 1;
    int column_end = child_box.computed_values().grid_column_end().raw_value() - 1;

    // https://www.w3.org/TR/css-grid-2/#line-placement
    // 8.3. Line-based Placement: the grid-row-start, grid-column-start, grid-row-end, and grid-column-end properties

    // https://www.w3.org/TR/css-grid-2/#grid-placement-slot
    // First attempt to match the grid area’s edge to a named grid area: if there is a grid line whose
    // line name is <custom-ident>-start (for grid-*-start) / <custom-ident>-end (for grid-*-end),
    // contributes the first such line to the grid item’s placement.

    // Otherwise, treat this as if the integer 1 had been specified along with the <custom-ident>.

    // https://www.w3.org/TR/css-grid-2/#grid-placement-int
    // Contributes the Nth grid line to the grid item’s placement. If a negative integer is given, it
    // instead counts in reverse, starting from the end edge of the explicit grid.
    if (column_end < 0)
        column_end = m_occupation_grid.column_count() + column_end + 2;

    // If a name is given as a <custom-ident>, only lines with that name are counted. If not enough
    // lines with that name exist, all implicit grid lines are assumed to have that name for the purpose
    // of finding this position.

    // https://www.w3.org/TR/css-grid-2/#grid-placement-span-int
    // Contributes a grid span to the grid item’s placement such that the corresponding edge of the grid
    // item’s grid area is N lines from its opposite edge in the corresponding direction. For example,
    // grid-column-end: span 2 indicates the second grid line in the endward direction from the
    // grid-column-start line.
    int column_span = 1;
    auto row_span = child_box.computed_values().grid_row_start().is_span() ? child_box.computed_values().grid_row_start().raw_value() : 1;
    if (child_box.computed_values().grid_column_start().is_position() && child_box.computed_values().grid_column_end().is_span())
        column_span = child_box.computed_values().grid_column_end().raw_value();
    if (child_box.computed_values().grid_column_end().is_position() && child_box.computed_values().grid_column_start().is_span()) {
        column_span = child_box.computed_values().grid_column_start().raw_value();
        column_start = column_end - column_span;
        // FIXME: Remove me once have implemented spans overflowing into negative indexes, e.g., grid-column: span 2 / 1
        if (column_start < 0)
            column_start = 0;
    }
    // FIXME: Have yet to find the spec for this.
    if (!child_box.computed_values().grid_column_start().is_position() && child_box.computed_values().grid_column_end().is_position() && column_end == 0)
        column_start = 0;

    // If a name is given as a <custom-ident>, only lines with that name are counted. If not enough
    // lines with that name exist, all implicit grid lines on the side of the explicit grid
    // corresponding to the search direction are assumed to have that name for the purpose of counting
    // this span.

    // https://drafts.csswg.org/css-grid/#grid-placement-auto
    // auto
    // The property contributes nothing to the grid item’s placement, indicating auto-placement or a
    // default span of one. (See § 8 Placing Grid Items, above.)

    // https://www.w3.org/TR/css-grid-2/#common-uses-named-lines
    // 8.1.3. Named Lines and Spans
    // Instead of counting lines by number, lines can be referenced by their line name:
    if (child_box.computed_values().grid_column_end().has_line_name()) {
        if (auto grid_area_index = find_valid_grid_area(child_box.computed_values().grid_column_end().line_name()); grid_area_index > -1)
            column_end = m_valid_grid_areas[grid_area_index].column_end;
        else if (auto line_name_index = get_line_index_by_line_name(child_box.computed_values().grid_column_end().line_name(), grid_container().computed_values().grid_template_columns()); line_name_index > -1)
            column_end = line_name_index;
        else
            column_end = 1;
        column_start = column_end - 1;
    }
    if (child_box.computed_values().grid_column_start().has_line_name()) {
        if (auto grid_area_index = find_valid_grid_area(child_box.computed_values().grid_column_end().line_name()); grid_area_index > -1)
            column_start = m_valid_grid_areas[grid_area_index].column_start;
        else if (auto line_name_index = get_line_index_by_line_name(child_box.computed_values().grid_column_start().line_name(), grid_container().computed_values().grid_template_columns()); line_name_index > -1)
            column_start = line_name_index;
        else
            column_start = 0;
    }

    // If there are multiple lines of the same name, they effectively establish a named set of grid
    // lines, which can be exclusively indexed by filtering the placement by name:

    // https://drafts.csswg.org/css-grid/#grid-placement-errors
    // 8.3.1. Grid Placement Conflict Handling
    // If the placement for a grid item contains two lines, and the start line is further end-ward than
    // the end line, swap the two lines. If the start line is equal to the end line, remove the end
    // line.
    if (child_box.computed_values().grid_column_start().is_position() && child_box.computed_values().grid_column_end().is_position()) {
        if (column_start > column_end)
            swap(column_start, column_end);
        if (column_start != column_end)
            column_span = column_end - column_start;
    }

    // If the placement contains two spans, remove the one contributed by the end grid-placement
    // property.
    if (child_box.computed_values().grid_column_start().is_span() && child_box.computed_values().grid_column_end().is_span())
        column_span = child_box.computed_values().grid_column_start().raw_value();

    // FIXME: If the placement contains only a span for a named line, replace it with a span of 1.

    // 4.1.1.1. Set the column position of the cursor to the grid item's column-start line. If this is
    // less than the previous column position of the cursor, increment the row position by 1.
    if (column_start < auto_placement_cursor_x)
        auto_placement_cursor_y++;
    auto_placement_cursor_x = column_start;

    m_occupation_grid.maybe_add_column(auto_placement_cursor_x + 1);
    m_occupation_grid.maybe_add_row(auto_placement_cursor_y + 1);

    // 4.1.1.2. Increment the cursor's row position until a value is found where the grid item does not
    // overlap any occupied grid cells (creating new rows in the implicit grid as necessary).
    while (true) {
        if (!m_occupation_grid.is_occupied(column_start, auto_placement_cursor_y)) {
            break;
        }
        auto_placement_cursor_y++;
        m_occupation_grid.maybe_add_row(auto_placement_cursor_y + row_span);
    }
    // 4.1.1.3. Set the item's row-start line to the cursor's row position, and set the item's row-end
    // line according to its span from that position.
    m_occupation_grid.set_occupied(column_start, column_start + column_span, auto_placement_cursor_y, auto_placement_cursor_y + row_span);

    m_grid_items.append(GridItem(child_box, auto_placement_cursor_y, row_span, column_start, column_span));
}

void GridFormattingContext::place_item_with_no_declared_position(Box const& child_box, int& auto_placement_cursor_x, int& auto_placement_cursor_y)
{
    // 4.1.2.1. Increment the column position of the auto-placement cursor until either this item's grid
    // area does not overlap any occupied grid cells, or the cursor's column position, plus the item's
    // column span, overflow the number of columns in the implicit grid, as determined earlier in this
    // algorithm.
    auto column_start = 0;
    auto column_span = 1;
    if (child_box.computed_values().grid_column_start().is_span())
        column_span = child_box.computed_values().grid_column_start().raw_value();
    else if (child_box.computed_values().grid_column_end().is_span())
        column_span = child_box.computed_values().grid_column_end().raw_value();
    // https://drafts.csswg.org/css-grid/#auto-placement-algo
    // 8.5. Grid Item Placement Algorithm
    // 3.3. If the largest column span among all the items without a definite column position is larger
    // than the width of the implicit grid, add columns to the end of the implicit grid to accommodate
    // that column span.
    m_occupation_grid.maybe_add_column(column_span);
    auto row_start = 0;
    auto row_span = 1;
    if (child_box.computed_values().grid_row_start().is_span())
        row_span = child_box.computed_values().grid_row_start().raw_value();
    else if (child_box.computed_values().grid_row_end().is_span())
        row_span = child_box.computed_values().grid_row_end().raw_value();
    auto found_unoccupied_area = false;
    for (size_t row_index = auto_placement_cursor_y; row_index < m_occupation_grid.row_count(); row_index++) {
        for (size_t column_index = auto_placement_cursor_x; column_index < m_occupation_grid.column_count(); column_index++) {
            if (column_span + column_index <= m_occupation_grid.column_count()) {
                auto found_all_available = true;
                for (int span_index = 0; span_index < column_span; span_index++) {
                    if (m_occupation_grid.is_occupied(column_index + span_index, row_index))
                        found_all_available = false;
                }
                if (found_all_available) {
                    found_unoccupied_area = true;
                    column_start = column_index;
                    row_start = row_index;
                    goto finish;
                }
            }
        }
        auto_placement_cursor_x = 0;
        auto_placement_cursor_y++;
    }
finish:

    // 4.1.2.2. If a non-overlapping position was found in the previous step, set the item's row-start
    // and column-start lines to the cursor's position. Otherwise, increment the auto-placement cursor's
    // row position (creating new rows in the implicit grid as necessary), set its column position to the
    // start-most column line in the implicit grid, and return to the previous step.
    if (!found_unoccupied_area) {
        row_start = m_occupation_grid.row_count();
        m_occupation_grid.maybe_add_row(m_occupation_grid.row_count() + 1);
    }

    m_occupation_grid.set_occupied(column_start, column_start + column_span, row_start, row_start + row_span);
    m_grid_items.append(GridItem(child_box, row_start, row_span, column_start, column_span));
}

void GridFormattingContext::initialize_grid_tracks_from_definition(AvailableSpace const& available_space, Vector<CSS::ExplicitGridTrack> const& tracks_definition, Vector<TemporaryTrack>& tracks)
{
    auto track_count = get_count_of_tracks(tracks_definition, available_space);
    for (auto const& track_definition : tracks_definition) {
        auto repeat_count = (track_definition.is_repeat() && track_definition.repeat().is_default()) ? track_definition.repeat().repeat_count() : 1;
        if (track_definition.is_repeat()) {
            if (track_definition.repeat().is_auto_fill() || track_definition.repeat().is_auto_fit())
                repeat_count = track_count;
        }
        for (auto _ = 0; _ < repeat_count; _++) {
            switch (track_definition.type()) {
            case CSS::ExplicitGridTrack::Type::MinMax:
                tracks.append(TemporaryTrack(track_definition.minmax().min_grid_size(), track_definition.minmax().max_grid_size()));
                break;
            case CSS::ExplicitGridTrack::Type::Repeat:
                for (auto& explicit_grid_track : track_definition.repeat().grid_track_size_list().track_list()) {
                    auto track_sizing_function = explicit_grid_track;
                    if (track_sizing_function.is_minmax())
                        tracks.append(TemporaryTrack(track_sizing_function.minmax().min_grid_size(), track_sizing_function.minmax().max_grid_size()));
                    else
                        tracks.append(TemporaryTrack(track_sizing_function.grid_size()));
                }
                break;
            case CSS::ExplicitGridTrack::Type::Default:
                tracks.append(TemporaryTrack(track_definition.grid_size()));
                break;
            default:
                VERIFY_NOT_REACHED();
            }
        }
    }
}

void GridFormattingContext::initialize_grid_tracks_for_columns_and_rows(AvailableSpace const& available_space)
{
    initialize_grid_tracks_from_definition(available_space, grid_container().computed_values().grid_template_columns().track_list(), m_grid_columns);
    initialize_grid_tracks_from_definition(available_space, grid_container().computed_values().grid_template_rows().track_list(), m_grid_rows);

    for (size_t column_index = m_grid_columns.size(); column_index < m_occupation_grid.column_count(); column_index++)
        m_grid_columns.append(TemporaryTrack());
    for (size_t row_index = m_grid_rows.size(); row_index < m_occupation_grid.row_count(); row_index++)
        m_grid_rows.append(TemporaryTrack());
}

void GridFormattingContext::initialize_gap_tracks(AvailableSpace const& available_space)
{
    // https://www.w3.org/TR/css-grid-2/#gutters
    // 11.1. Gutters: the row-gap, column-gap, and gap properties
    // For the purpose of track sizing, each gutter is treated as an extra, empty, fixed-size track of
    // the specified size, which is spanned by any grid items that span across its corresponding grid
    // line.
    if (!grid_container().computed_values().column_gap().is_auto()) {
        for (size_t column_index = 1; column_index < (m_occupation_grid.column_count() * 2) - 1; column_index += 2) {
            auto column_gap_width = grid_container().computed_values().column_gap().to_px(grid_container(), available_space.width.to_px());
            m_grid_columns.insert(column_index, TemporaryTrack(column_gap_width, true));
        }
    }
    if (!grid_container().computed_values().row_gap().is_auto()) {
        for (size_t row_index = 1; row_index < (m_occupation_grid.row_count() * 2) - 1; row_index += 2) {
            auto column_gap_height = grid_container().computed_values().row_gap().to_px(grid_container(), available_space.height.to_px());
            m_grid_rows.insert(row_index, TemporaryTrack(column_gap_height, true));
        }
    }
}

void GridFormattingContext::initialize_track_sizes(AvailableSize const& available_size, Vector<TemporaryTrack>& tracks)
{
    // https://www.w3.org/TR/css-grid-2/#algo-init
    // 12.4. Initialize Track Sizes
    // Initialize each track’s base size and growth limit.

    // For each track, if the track’s min track sizing function is:
    for (auto& track : tracks) {
        if (track.is_gap)
            continue;

        switch (track.min_track_sizing_function.type()) {
        // - A fixed sizing function
        // Resolve to an absolute length and use that size as the track’s initial base size.
        case CSS::GridSize::Type::Length: {
            if (!track.min_track_sizing_function.length().is_auto())
                track.base_size = track.min_track_sizing_function.length().to_px(grid_container());
            break;
        }
        case CSS::GridSize::Type::Percentage: {
            if (available_size.is_definite())
                track.base_size = track.min_track_sizing_function.percentage().as_fraction() * available_size.to_px().value();
            break;
        }
        // - An intrinsic sizing function
        // Use an initial base size of zero.
        case CSS::GridSize::Type::FlexibleLength:
        case CSS::GridSize::Type::MaxContent:
        case CSS::GridSize::Type::MinContent: {
            track.base_size = 0;
            break;
        }
        default:
            VERIFY_NOT_REACHED();
        }

        // For each track, if the track’s max track sizing function is:
        switch (track.max_track_sizing_function.type()) {
        // - A fixed sizing function
        // Resolve to an absolute length and use that size as the track’s initial growth limit.
        case CSS::GridSize::Type::Length: {
            if (!track.max_track_sizing_function.length().is_auto())
                track.growth_limit = track.max_track_sizing_function.length().to_px(grid_container());
            else
                // - An intrinsic sizing function
                // Use an initial growth limit of infinity.
                track.growth_limit = INFINITY;
            break;
        }
        case CSS::GridSize::Type::Percentage: {
            if (available_size.is_definite())
                track.growth_limit = track.max_track_sizing_function.percentage().as_fraction() * available_size.to_px().value();
            break;
        }
        // - A flexible sizing function
        // Use an initial growth limit of infinity.
        case CSS::GridSize::Type::FlexibleLength: {
            track.growth_limit = INFINITY;
            break;
        }
        // - An intrinsic sizing function
        // Use an initial growth limit of infinity.
        case CSS::GridSize::Type::MaxContent:
        case CSS::GridSize::Type::MinContent: {
            track.growth_limit = INFINITY;
            break;
        }
        default:
            VERIFY_NOT_REACHED();
        }

        // In all cases, if the growth limit is less than the base size, increase the growth limit to match
        // the base size.
        if (track.growth_limit < track.base_size)
            track.growth_limit = track.base_size;
    }
}

void GridFormattingContext::resolve_intrinsic_track_sizes(GridDimension const dimension, AvailableSize const& available_size, Vector<TemporaryTrack>& tracks)
{
    // https://www.w3.org/TR/css-grid-2/#algo-content
    // 12.5. Resolve Intrinsic Track Sizes
    // This step resolves intrinsic track sizing functions to absolute lengths. First it resolves those
    // sizes based on items that are contained wholly within a single track. Then it gradually adds in
    // the space requirements of items that span multiple tracks, evenly distributing the extra space
    // across those tracks insofar as possible.

    // FIXME: 1. Shim baseline-aligned items so their intrinsic size contributions reflect their baseline alignment.

    auto calculate_item_min_content_contribution = [&](GridItem const& item) {
        if (dimension == GridDimension::Column) {
            return calculate_min_content_width(item.box());
        } else {
            return content_based_minimum_height(item);
        }
    };

    size_t index = 0;
    for (auto& track : tracks) {
        if (track.is_gap) {
            ++index;
            continue;
        }

        Vector<GridItem&> grid_items_of_track;
        for (auto& grid_item : m_grid_items) {
            if (dimension == GridDimension::Column) {
                if (grid_item.gap_adjusted_column(grid_container()) == index && grid_item.raw_column_span() == 1) {
                    grid_items_of_track.append(grid_item);

                    track.border_left = max(track.border_left, grid_item.box().computed_values().border_left().width);
                    track.border_right = max(track.border_right, grid_item.box().computed_values().border_right().width);
                }
            } else {
                if (grid_item.gap_adjusted_row(grid_container()) == index && grid_item.raw_row_span() == 1) {
                    grid_items_of_track.append(grid_item);

                    track.border_top = max(track.border_top, grid_item.box().computed_values().border_top().width);
                    track.border_bottom = max(track.border_bottom, grid_item.box().computed_values().border_bottom().width);
                }
            }
        }

        if (!track.min_track_sizing_function.is_intrinsic_track_sizing() && !track.max_track_sizing_function.is_intrinsic_track_sizing()) {
            ++index;
            continue;
        }

        switch (track.min_track_sizing_function.type()) {
        // - For min-content minimums:
        // If the track has a min-content min track sizing function, set its base size to the maximum of the
        // items’ min-content contributions, floored at zero.
        case CSS::GridSize::Type::MinContent: {
            CSSPixels base_size = 0;
            for (auto& item : grid_items_of_track) {
                base_size = max(base_size, calculate_item_min_content_contribution(item));
            }
            track.base_size = base_size;
        } break;
        // - For max-content minimums:
        // If the track has a max-content min track sizing function, set its base size to the maximum of the
        // items’ max-content contributions, floored at zero.
        case CSS::GridSize::Type::MaxContent: {
            CSSPixels base_size = 0;
            for (auto& item : grid_items_of_track) {
                base_size = max(base_size, calculate_item_min_content_contribution(item));
            }
            track.base_size = base_size;
        } break;
        // - For auto minimums:
        // If the track has an auto min track sizing function and the grid container is being sized under a
        // min-/max-content constraint, set the track’s base size to the maximum of its items’ limited
        // min-/max-content contributions (respectively), floored at zero. The limited min-/max-content
        // contribution of an item is (for this purpose) its min-/max-content contribution (accordingly),
        // limited by the max track sizing function (which could be the argument to a fit-content() track
        // sizing function) if that is fixed and ultimately floored by its minimum contribution (defined
        // below).
        // FIXME: Container min/max-content
        case CSS::GridSize::Type::Length:
        // Otherwise, set the track’s base size to the maximum of its items’ minimum contributions, floored
        // at zero. The minimum contribution of an item is the smallest outer size it can have.
        // Specifically, if the item’s computed preferred size behaves as auto or depends on the size of its
        // containing block in the relevant axis, its minimum contribution is the outer size that would
        // result from assuming the item’s used minimum size as its preferred size; else the item’s minimum
        // contribution is its min-content contribution. Because the minimum contribution often depends on
        // the size of the item’s content, it is considered a type of intrinsic size contribution.
        case CSS::GridSize::Type::Percentage:
        case CSS::GridSize::Type::FlexibleLength: {
            CSSPixels base_size = 0;
            for (auto& item : grid_items_of_track) {
                base_size = max(base_size, calculate_item_min_content_contribution(item));
            }
            track.base_size = base_size;
        } break;
        default:
            VERIFY_NOT_REACHED();
        }

        switch (track.max_track_sizing_function.type()) {
        // - For min-content maximums:
        // If the track has a min-content max track sizing function, set its growth limit to the maximum of
        // the items’ min-content contributions.
        case CSS::GridSize::Type::MinContent: {
            CSSPixels growth_limit = 0;
            for (auto& item : grid_items_of_track) {
                growth_limit = max(growth_limit, calculate_item_min_content_contribution(item));
            }
            track.growth_limit = growth_limit;
        } break;
        // - For max-content maximums:
        // If the track has a max-content max track sizing function, set its growth limit to the maximum of
        // the items’ max-content contributions. For fit-content() maximums, furthermore clamp this growth
        // limit by the fit-content() argument.
        case CSS::GridSize::Type::MaxContent: {
            CSSPixels growth_limit = 0;
            for (auto& item : grid_items_of_track) {
                growth_limit = max(growth_limit, calculate_item_min_content_contribution(item));
            }
            track.growth_limit = growth_limit;
        } break;
        case CSS::GridSize::Type::Length:
        case CSS::GridSize::Type::Percentage:
        case CSS::GridSize::Type::FlexibleLength:
            break;
        default:
            VERIFY_NOT_REACHED();
        }

        // In all cases, if a track’s growth limit is now less than its base size, increase the growth limit
        // to match the base size.
        if (track.growth_limit < track.base_size)
            track.growth_limit = track.base_size;

        ++index;
    }

    // https://www.w3.org/TR/css-grid-2/#auto-repeat
    // The auto-fit keyword behaves the same as auto-fill, except that after grid item placement any
    // empty repeated tracks are collapsed. An empty track is one with no in-flow grid items placed into
    // or spanning across it. (This can result in all tracks being collapsed, if they’re all empty.)
    if (dimension == GridDimension::Column // FIXME: Handle for columns
        && grid_container().computed_values().grid_template_columns().track_list().size() == 1
        && grid_container().computed_values().grid_template_columns().track_list().first().is_repeat()
        && grid_container().computed_values().grid_template_columns().track_list().first().repeat().is_auto_fit()) {
        for (size_t idx = 0; idx < m_grid_columns.size(); idx++) {
            auto column_to_check = grid_container().computed_values().column_gap().is_auto() ? idx : idx / 2;
            if (m_occupation_grid.is_occupied(column_to_check, 0))
                continue;
            if (!grid_container().computed_values().column_gap().is_auto() && idx % 2 != 0)
                continue;

            // A collapsed track is treated as having a fixed track sizing function of 0px
            m_grid_columns[idx].base_size = 0;
            m_grid_columns[idx].growth_limit = 0;

            // FIXME: And the gutters on either side of it—including any space allotted through distributed
            // alignment—collapse.
        }
    }

    // 3. Increase sizes to accommodate spanning items crossing content-sized tracks: Next, consider the
    // items with a span of 2 that do not span a track with a flexible sizing function.
    // FIXME: Content-sized tracks not implemented (min-content, etc.)

    // 3.1. For intrinsic minimums: First increase the base size of tracks with an intrinsic min track sizing
    // function by distributing extra space as needed to accommodate these items’ minimum contributions.

    // If the grid container is being sized under a min- or max-content constraint, use the items’
    // limited min-content contributions in place of their minimum contributions here. (For an item
    // spanning multiple tracks, the upper limit used to calculate its limited min-/max-content
    // contribution is the sum of the fixed max track sizing functions of any tracks it spans, and is
    // applied if it only spans such tracks.)

    // 3.2. For content-based minimums: Next continue to increase the base size of tracks with a min track
    // sizing function of min-content or max-content by distributing extra space as needed to account
    // for these items' min-content contributions.

    // 3.3. For max-content minimums: Next, if the grid container is being sized under a max-content
    // constraint, continue to increase the base size of tracks with a min track sizing function of auto
    // or max-content by distributing extra space as needed to account for these items' limited
    // max-content contributions.

    // In all cases, continue to increase the base size of tracks with a min track sizing function of
    // max-content by distributing extra space as needed to account for these items' max-content
    // contributions.

    // 3.4. If at this point any track’s growth limit is now less than its base size, increase its growth
    // limit to match its base size.

    // 3.5. For intrinsic maximums: Next increase the growth limit of tracks with an intrinsic max track
    // sizing function by distributing extra space as needed to account for these items' min-content
    // contributions. Mark any tracks whose growth limit changed from infinite to finite in this step as
    // infinitely growable for the next step.

    // 3.6. For max-content maximums: Lastly continue to increase the growth limit of tracks with a max track
    // sizing function of max-content by distributing extra space as needed to account for these items'
    // max-content contributions. However, limit the growth of any fit-content() tracks by their
    // fit-content() argument.

    // Repeat incrementally for items with greater spans until all items have been considered.

    // FIXME: 4. Increase sizes to accommodate spanning items crossing flexible tracks: Next, repeat the previous
    // step instead considering (together, rather than grouped by span size) all items that do span a
    // track with a flexible sizing function while

    // - distributing space only to flexible tracks (i.e. treating all other tracks as having a fixed
    // sizing function)

    // - if the sum of the flexible sizing functions of all flexible tracks spanned by the item is greater
    // than zero, distributing space to such tracks according to the ratios of their flexible sizing
    // functions rather than distributing space equally

    // FIXME: 5. If any track still has an infinite growth limit (because, for example, it had no items placed in
    // it or it is a flexible track), set its growth limit to its base size.
    for (auto& track : tracks) {
        if (track.growth_limit == INFINITY) {
            track.growth_limit = track.base_size;
        }
    }

    // https://www.w3.org/TR/css-grid-2/#extra-space
    // 12.5.1. Distributing Extra Space Across Spanned Tracks
    // To distribute extra space by increasing the affected sizes of a set of tracks as required by a
    // set of intrinsic size contributions,
    CSSPixels sum_of_track_sizes = 0;
    for (auto& it : tracks)
        sum_of_track_sizes += it.base_size;

    // 1. Maintain separately for each affected base size or growth limit a planned increase, initially
    // set to 0. (This prevents the size increases from becoming order-dependent.)

    // 2. For each considered item,

    // 2.1. Find the space to distribute: Subtract the corresponding size (base size or growth limit) of
    // every spanned track from the item’s size contribution to find the item’s remaining size
    // contribution. (For infinite growth limits, substitute the track’s base size.) This is the space
    // to distribute. Floor it at zero.

    // For base sizes, the limit is its growth limit. For growth limits, the limit is infinity if it is
    // marked as infinitely growable, and equal to the growth limit otherwise. If the affected size was
    // a growth limit and the track is not marked infinitely growable, then each item-incurred increase
    // will be zero.
    // extra-space = max(0, size-contribution - ∑track-sizes)
    for (auto& track : tracks) {
        if (track.is_gap)
            continue;
        track.space_to_distribute = max(CSSPixels(0), track.growth_limit - track.base_size);
    }

    auto remaining_free_space = available_size.is_definite() ? available_size.to_px() - sum_of_track_sizes : 0;

    // 2.2. Distribute space up to limits: Find the item-incurred increase for each spanned track with an
    // affected size by: distributing the space equally among such tracks, freezing a track’s
    // item-incurred increase as its affected size + item-incurred increase reaches its limit (and
    // continuing to grow the unfrozen tracks as needed).
    auto count_of_unfrozen_tracks = 0;
    for (auto& track : tracks) {
        if (track.space_to_distribute > 0)
            count_of_unfrozen_tracks++;
    }
    while (remaining_free_space > 0) {
        if (count_of_unfrozen_tracks == 0)
            break;
        auto free_space_to_distribute_per_track = remaining_free_space / count_of_unfrozen_tracks;

        for (auto& track : tracks) {
            if (track.space_to_distribute == 0)
                continue;
            // 2.4. For each affected track, if the track’s item-incurred increase is larger than the track’s planned
            // increase set the track’s planned increase to that value.
            if (track.space_to_distribute <= free_space_to_distribute_per_track) {
                track.planned_increase += track.space_to_distribute;
                remaining_free_space -= track.space_to_distribute;
                track.space_to_distribute = 0;
            } else {
                track.space_to_distribute -= free_space_to_distribute_per_track;
                track.planned_increase += free_space_to_distribute_per_track;
                remaining_free_space -= free_space_to_distribute_per_track;
            }
        }

        count_of_unfrozen_tracks = 0;
        for (auto& track : tracks) {
            if (track.space_to_distribute > 0)
                count_of_unfrozen_tracks++;
        }
        if (remaining_free_space == 0)
            break;
    }

    // 2.3. Distribute space beyond limits: If space remains after all tracks are frozen, unfreeze and
    // continue to distribute space to the item-incurred increase of…

    // - when accommodating minimum contributions or accommodating min-content contributions: any affected
    // track that happens to also have an intrinsic max track sizing function; if there are no such
    // tracks, then all affected tracks.

    // - when accommodating max-content contributions: any affected track that happens to also have a
    // max-content max track sizing function; if there are no such tracks, then all affected tracks.

    // - when handling any intrinsic growth limit: all affected tracks.

    // For this purpose, the max track sizing function of a fit-content() track is treated as
    // max-content until it reaches the limit specified as the fit-content() argument, after which it is
    // treated as having a fixed sizing function of that argument.

    // This step prioritizes the distribution of space for accommodating space required by the
    // tracks’ min track sizing functions beyond their current growth limits based on the types of their
    // max track sizing functions.

    // 3. Update the tracks' affected sizes by adding in the planned increase so that the next round of
    // space distribution will account for the increase. (If the affected size is an infinite growth
    // limit, set it to the track’s base size plus the planned increase.)
    for (auto& track : tracks)
        track.base_size += track.planned_increase;
}

void GridFormattingContext::maximize_tracks(AvailableSize const& available_size, Vector<TemporaryTrack>& tracks)
{
    // https://www.w3.org/TR/css-grid-2/#algo-grow-tracks
    // 12.6. Maximize Tracks

    auto get_free_space_px = [&]() -> CSSPixels {
        // For the purpose of this step: if sizing the grid container under a max-content constraint, the
        // free space is infinite; if sizing under a min-content constraint, the free space is zero.
        auto free_space = get_free_space(available_size, tracks);
        if (free_space.is_max_content()) {
            return INFINITY;
        } else if (free_space.is_min_content()) {
            return 0;
        } else {
            return free_space.to_px();
        }
    };

    auto free_space_px = get_free_space_px();

    // If the free space is positive, distribute it equally to the base sizes of all tracks, freezing
    // tracks as they reach their growth limits (and continuing to grow the unfrozen tracks as needed).
    while (free_space_px > 0) {
        auto free_space_to_distribute_per_track = free_space_px / (tracks.size() - count_of_gap_tracks(tracks));
        for (auto& track : tracks) {
            if (track.is_gap)
                continue;
            VERIFY(track.growth_limit != INFINITY);
            track.base_size = min(track.growth_limit, track.base_size + free_space_to_distribute_per_track);
        }
        if (get_free_space_px() == free_space_px)
            break;
        free_space_px = get_free_space_px();
    }

    // FIXME: If this would cause the grid to be larger than the grid container’s inner size as limited by its
    // max-width/height, then redo this step, treating the available grid space as equal to the grid
    // container’s inner size when it’s sized to its max-width/height.
}

void GridFormattingContext::expand_flexible_tracks(AvailableSize const& available_size, Vector<TemporaryTrack>& tracks)
{
    // https://drafts.csswg.org/css-grid/#algo-flex-tracks
    // 12.7. Expand Flexible Tracks
    // This step sizes flexible tracks using the largest value it can assign to an fr without exceeding
    // the available space.

    auto find_the_size_of_an_fr = [&]() -> CSSPixels {
        // https://www.w3.org/TR/css-grid-2/#algo-find-fr-size

        VERIFY(available_size.is_definite());

        // 1. Let leftover space be the space to fill minus the base sizes of the non-flexible grid tracks.
        auto leftover_space = available_size.to_px();
        for (auto& track : tracks) {
            if (!track.max_track_sizing_function.is_flexible_length()) {
                leftover_space -= track.base_size;
            }
        }

        // 2. Let flex factor sum be the sum of the flex factors of the flexible tracks.
        //    If this value is less than 1, set it to 1 instead.
        auto flex_factor_sum = 0;
        for (auto& track : tracks) {
            if (track.max_track_sizing_function.is_flexible_length())
                flex_factor_sum++;
        }
        if (flex_factor_sum < 1)
            flex_factor_sum = 1;

        // 3. Let the hypothetical fr size be the leftover space divided by the flex factor sum.
        auto hypothetical_fr_size = leftover_space / flex_factor_sum;

        // FIXME: 4. If the product of the hypothetical fr size and a flexible track’s flex factor is less than the track’s
        //    base size, restart this algorithm treating all such tracks as inflexible.

        // 5. Return the hypothetical fr size.
        return hypothetical_fr_size;
    };

    // First, find the grid’s used flex fraction:
    auto flex_fraction = [&]() {
        auto free_space = get_free_space(available_size, tracks);
        // If the free space is zero or if sizing the grid container under a min-content constraint:
        if (free_space.to_px() == 0 || available_size.is_min_content()) {
            // The used flex fraction is zero.
            return CSSPixels(0);
            // Otherwise, if the free space is a definite length:
        } else if (free_space.is_definite()) {
            // The used flex fraction is the result of finding the size of an fr using all of the grid tracks and a space
            // to fill of the available grid space.
            return find_the_size_of_an_fr();
        } else {
            // FIXME
            return CSSPixels(0);
        }
    }();

    // For each flexible track, if the product of the used flex fraction and the track’s flex factor is greater than
    // the track’s base size, set its base size to that product.
    for (auto& track : tracks) {
        if (track.max_track_sizing_function.flexible_length() * flex_fraction > track.base_size) {
            track.base_size = track.max_track_sizing_function.flexible_length() * flex_fraction;
        }
    }
}

void GridFormattingContext::stretch_auto_tracks(AvailableSize const& available_size, Vector<TemporaryTrack>& tracks)
{
    // https://drafts.csswg.org/css-grid/#algo-stretch
    // 12.8. Stretch auto Tracks

    // When the content-distribution property of the grid container is normal or stretch in this axis,
    // this step expands tracks that have an auto max track sizing function by dividing any remaining
    // positive, definite free space equally amongst them. If the free space is indefinite, but the grid
    // container has a definite min-width/height, use that size to calculate the free space for this
    // step instead.
    CSSPixels used_space = 0;
    for (auto& track : tracks) {
        if (!(track.max_track_sizing_function.is_length() && track.max_track_sizing_function.length().is_auto()))
            used_space += track.base_size;
    }

    CSSPixels remaining_space = available_size.is_definite() ? available_size.to_px() - used_space : 0;
    auto count_of_auto_max_sizing_tracks = 0;
    for (auto& track : tracks) {
        if (track.max_track_sizing_function.is_length() && track.max_track_sizing_function.length().is_auto())
            count_of_auto_max_sizing_tracks++;
    }

    for (auto& track : tracks) {
        if (track.max_track_sizing_function.is_length() && track.max_track_sizing_function.length().is_auto())
            track.base_size = max(track.base_size, remaining_space / count_of_auto_max_sizing_tracks);
    }
}

void GridFormattingContext::run_track_sizing(GridDimension const dimension, AvailableSpace const& available_space, Vector<TemporaryTrack>& tracks)
{
    auto track_available_size = dimension == GridDimension::Column ? available_space.width : available_space.height;

    initialize_track_sizes(track_available_size, tracks);

    resolve_intrinsic_track_sizes(dimension, track_available_size, tracks);

    maximize_tracks(track_available_size, tracks);

    expand_flexible_tracks(track_available_size, tracks);

    stretch_auto_tracks(track_available_size, tracks);

    // If calculating the layout of a grid item in this step depends on the available space in the block
    // axis, assume the available space that it would have if any row with a definite max track sizing
    // function had that size and all other rows were infinite. If both the grid container and all
    // tracks have definite sizes, also apply align-content to find the final effective size of any gaps
    // spanned by such items; otherwise ignore the effects of track alignment in this estimation.
}

void GridFormattingContext::build_valid_grid_areas()
{
    Vector<GridArea> found_grid_areas;

    auto get_index_of_found_grid_area = [&](String needle) -> int {
        for (size_t x = 0; x < found_grid_areas.size(); x++) {
            if (found_grid_areas[x].name == needle)
                return static_cast<int>(x);
        }
        return -1;
    };

    // https://www.w3.org/TR/css-grid-2/#grid-template-areas-property
    // If a named grid area spans multiple grid cells, but those cells do not form a single
    // filled-in rectangle, the declaration is invalid.
    for (size_t y = 0; y < grid_container().computed_values().grid_template_areas().size(); y++) {
        for (size_t x = 0; x < grid_container().computed_values().grid_template_areas()[y].size(); x++) {
            auto grid_area_idx = get_index_of_found_grid_area(grid_container().computed_values().grid_template_areas()[y][x]);
            if (grid_area_idx == -1) {
                found_grid_areas.append({ grid_container().computed_values().grid_template_areas()[y][x], y, y + 1, x, x + 1 });
            } else {
                auto& grid_area = found_grid_areas[grid_area_idx];
                if (grid_area.row_start == y) {
                    if (grid_area.column_end == x)
                        grid_area.column_end = grid_area.column_end + 1;
                    else
                        return;
                } else {
                    if (grid_area.row_end == y) {
                        if (grid_area.column_start != x)
                            return;
                        grid_area.row_end = grid_area.row_end + 1;
                    } else if (grid_area.row_end == y + 1) {
                        if (grid_area.column_end < x || grid_area.column_end > x + 1)
                            return;
                    } else {
                        return;
                    }
                }
            }
        }
    }

    for (auto const& checked_grid_area : found_grid_areas)
        m_valid_grid_areas.append(checked_grid_area);
}

int GridFormattingContext::find_valid_grid_area(String const& needle)
{
    for (size_t x = 0; x < m_valid_grid_areas.size(); x++) {
        if (m_valid_grid_areas[x].name == needle)
            return static_cast<int>(x);
    }
    return -1;
}

void GridFormattingContext::place_grid_items(AvailableSpace const& available_space)
{
    auto grid_template_columns = grid_container().computed_values().grid_template_columns();
    auto grid_template_rows = grid_container().computed_values().grid_template_rows();
    auto column_count = get_count_of_tracks(grid_template_columns.track_list(), available_space);
    auto row_count = get_count_of_tracks(grid_template_rows.track_list(), available_space);

    // https://drafts.csswg.org/css-grid/#overview-placement
    // 2.2. Placing Items
    // The contents of the grid container are organized into individual grid items (analogous to
    // flex items), which are then assigned to predefined areas in the grid. They can be explicitly
    // placed using coordinates through the grid-placement properties or implicitly placed into
    // empty areas using auto-placement.
    grid_container().for_each_child_of_type<Box>([&](Box& child_box) {
        if (can_skip_is_anonymous_text_run(child_box))
            return IterationDecision::Continue;
        m_boxes_to_place.append(child_box);
        return IterationDecision::Continue;
    });

    m_occupation_grid = OccupationGrid(column_count, row_count);

    build_valid_grid_areas();

    // https://drafts.csswg.org/css-grid/#auto-placement-algo
    // 8.5. Grid Item Placement Algorithm

    // FIXME: 0. Generate anonymous grid items

    // 1. Position anything that's not auto-positioned.
    for (size_t i = 0; i < m_boxes_to_place.size(); i++) {
        auto const& child_box = m_boxes_to_place[i];
        if (is_auto_positioned_row(child_box->computed_values().grid_row_start(), child_box->computed_values().grid_row_end())
            || is_auto_positioned_column(child_box->computed_values().grid_column_start(), child_box->computed_values().grid_column_end()))
            continue;
        place_item_with_row_and_column_position(child_box);
        m_boxes_to_place.remove(i);
        i--;
    }

    // 2. Process the items locked to a given row.
    // FIXME: Do "dense" packing
    for (size_t i = 0; i < m_boxes_to_place.size(); i++) {
        auto const& child_box = m_boxes_to_place[i];
        if (is_auto_positioned_row(child_box->computed_values().grid_row_start(), child_box->computed_values().grid_row_end()))
            continue;
        place_item_with_row_position(child_box);
        m_boxes_to_place.remove(i);
        i--;
    }

    // 3. Determine the columns in the implicit grid.
    // NOTE: "implicit grid" here is the same as the m_occupation_grid

    // 3.1. Start with the columns from the explicit grid.
    // NOTE: Done in step 1.

    // 3.2. Among all the items with a definite column position (explicitly positioned items, items
    // positioned in the previous step, and items not yet positioned but with a definite column) add
    // columns to the beginning and end of the implicit grid as necessary to accommodate those items.
    // NOTE: "Explicitly positioned items" and "items positioned in the previous step" done in step 1
    // and 2, respectively. Adding columns for "items not yet positioned but with a definite column"
    // will be done in step 4.

    // 4. Position the remaining grid items.
    // For each grid item that hasn't been positioned by the previous steps, in order-modified document
    // order:
    auto auto_placement_cursor_x = 0;
    auto auto_placement_cursor_y = 0;
    for (size_t i = 0; i < m_boxes_to_place.size(); i++) {
        auto const& child_box = m_boxes_to_place[i];
        // 4.1. For sparse packing:
        // FIXME: no distinction made. See #4.2

        // 4.1.1. If the item has a definite column position:
        if (!is_auto_positioned_column(child_box->computed_values().grid_column_start(), child_box->computed_values().grid_column_end()))
            place_item_with_column_position(child_box, auto_placement_cursor_x, auto_placement_cursor_y);

        // 4.1.2. If the item has an automatic grid position in both axes:
        else
            place_item_with_no_declared_position(child_box, auto_placement_cursor_x, auto_placement_cursor_y);

        m_boxes_to_place.remove(i);
        i--;

        // FIXME: 4.2. For dense packing:
    }
}

void GridFormattingContext::run(Box const& box, LayoutMode, AvailableSpace const& available_space)
{
    place_grid_items(available_space);

    // https://drafts.csswg.org/css-grid/#overview-sizing
    // 2.3. Sizing the Grid
    // Once the grid items have been placed, the sizes of the grid tracks (rows and columns) are
    // calculated, accounting for the sizes of their contents and/or available space as specified in
    // the grid definition.

    // https://www.w3.org/TR/css-grid-2/#layout-algorithm
    // 12. Grid Sizing
    // This section defines the grid sizing algorithm, which determines the size of all grid tracks and,
    // by extension, the entire grid.

    // Each track has specified minimum and maximum sizing functions (which may be the same). Each
    // sizing function is either:

    // - A fixed sizing function (<length> or resolvable <percentage>).
    // - An intrinsic sizing function (min-content, max-content, auto, fit-content()).
    // - A flexible sizing function (<flex>).

    // The grid sizing algorithm defines how to resolve these sizing constraints into used track sizes.
    initialize_grid_tracks_for_columns_and_rows(available_space);

    initialize_gap_tracks(available_space);

    // https://www.w3.org/TR/css-grid-2/#algo-overview
    // 12.1. Grid Sizing Algorithm

    // 1. First, the track sizing algorithm is used to resolve the sizes of the grid columns.
    // In this process, any grid item which is subgridded in the grid container’s inline axis is treated
    // as empty and its grid items (the grandchildren) are treated as direct children of the grid
    // container (their grandparent). This introspection is recursive.

    // Items which are subgridded only in the block axis, and whose grid container size in the inline
    // axis depends on the size of its contents are also introspected: since the size of the item in
    // this dimension can be dependent on the sizing of its subgridded tracks in the other, the size
    // contribution of any such item to this grid’s column sizing (see Resolve Intrinsic Track Sizes) is
    // taken under the provision of having determined its track sizing only up to the same point in the
    // Grid Sizing Algorithm as this itself. E.g. for the first pass through this step, the item will
    // have its tracks sized only through this first step; if a second pass of this step is triggered
    // then the item will have completed a first pass through steps 1-3 as well as the second pass of
    // this step prior to returning its size for consideration in this grid’s column sizing. Again, this
    // introspection is recursive.

    // https://www.w3.org/TR/css-grid-2/#algo-track-sizing
    // 12.3. Track Sizing Algorithm

    // The remainder of this section is the track sizing algorithm, which calculates from the min and
    // max track sizing functions the used track size. Each track has a base size, a <length> which
    // grows throughout the algorithm and which will eventually be the track’s final size, and a growth
    // limit, a <length> which provides a desired maximum size for the base size. There are 5 steps:

    // 1. Initialize Track Sizes
    // 2. Resolve Intrinsic Track Sizes
    // 3. Maximize Tracks
    // 4. Expand Flexible Tracks
    // 5. Expand Stretched auto Tracks

    run_track_sizing(GridDimension::Column, available_space, m_grid_columns);

    // https://www.w3.org/TR/css-grid-2/#algo-overview
    // 12.1. Grid Sizing Algorithm
    // 2. Next, the track sizing algorithm resolves the sizes of the grid rows.
    // In this process, any grid item which is subgridded in the grid container’s block axis is treated
    // as empty and its grid items (the grandchildren) are treated as direct children of the grid
    // container (their grandparent). This introspection is recursive.

    // As with sizing columns, items which are subgridded only in the inline axis, and whose grid
    // container size in the block axis depends on the size of its contents are also introspected. (As
    // with sizing columns, the size contribution to this grid’s row sizing is taken under the provision
    // of having determined its track sizing only up to this corresponding point in the algorithm; and
    // again, this introspection is recursive.)

    // To find the inline-axis available space for any items whose block-axis size contributions require
    // it, use the grid column sizes calculated in the previous step. If the grid container’s inline
    // size is definite, also apply justify-content to account for the effective column gap sizes.

    // https://www.w3.org/TR/css-grid-2/#algo-track-sizing
    // 12.3. Track Sizing Algorithm

    // The remainder of this section is the track sizing algorithm, which calculates from the min and
    // max track sizing functions the used track size. Each track has a base size, a <length> which
    // grows throughout the algorithm and which will eventually be the track’s final size, and a growth
    // limit, a <length> which provides a desired maximum size for the base size. There are 5 steps:

    // 1. Initialize Track Sizes
    // 2. Resolve Intrinsic Track Sizes
    // 3. Maximize Tracks
    // 4. Expand Flexible Tracks
    // 5. Expand Stretched auto Tracks

    run_track_sizing(GridDimension::Row, available_space, m_grid_rows);

    // https://www.w3.org/TR/css-grid-2/#algo-overview
    // 12.1. Grid Sizing Algorithm
    // 3. Then, if the min-content contribution of any grid item has changed based on the row sizes and
    // alignment calculated in step 2, re-resolve the sizes of the grid columns with the new min-content
    // and max-content contributions (once only).

    // To find the block-axis available space for any items whose inline-axis size contributions require
    // it, use the grid row sizes calculated in the previous step. If the grid container’s block size is
    // definite, also apply align-content to account for the effective row gap sizes

    // 4. Next, if the min-content contribution of any grid item has changed based on the column sizes and
    // alignment calculated in step 3, re-resolve the sizes of the grid rows with the new min-content
    // and max-content contributions (once only).

    // To find the inline-axis available space for any items whose block-axis size contributions require
    // it, use the grid column sizes calculated in the previous step. If the grid container’s inline
    // size is definite, also apply justify-content to account for the effective column gap sizes.

    // 5. Finally, the grid container is sized using the resulting size of the grid as its content size,
    // and the tracks are aligned within the grid container according to the align-content and
    // justify-content properties.

    // Once the size of each grid area is thus established, the grid items are laid out into their
    // respective containing blocks. The grid area’s width and height are considered definite for this
    // purpose.

    auto layout_box = [&](int row_start, int row_end, int column_start, int column_end, Box const& child_box) -> void {
        if (column_start < 0 || row_start < 0)
            return;
        auto& child_box_state = m_state.get_mutable(child_box);
        CSSPixels x_start = 0;
        CSSPixels x_end = 0;
        CSSPixels y_start = 0;
        CSSPixels y_end = 0;
        for (int i = 0; i < column_start; i++)
            x_start += m_grid_columns[i].base_size;
        for (int i = 0; i < column_end; i++)
            x_end += m_grid_columns[i].base_size;
        for (int i = 0; i < row_start; i++)
            y_start += m_grid_rows[i].full_vertical_size();
        for (int i = 0; i < row_end; i++) {
            if (i >= row_start)
                y_end += m_grid_rows[i].base_size;
            else
                y_end += m_grid_rows[i].full_vertical_size();
        }
        child_box_state.set_content_width(max(CSSPixels(0), x_end - x_start - m_grid_columns[column_start].border_left - m_grid_columns[column_start].border_right));
        child_box_state.set_content_height(y_end - y_start);
        child_box_state.offset = { x_start + m_grid_columns[column_start].border_left, y_start + m_grid_rows[row_start].border_top };

        child_box_state.border_left = child_box.computed_values().border_left().width;
        child_box_state.border_right = child_box.computed_values().border_right().width;
        child_box_state.border_top = child_box.computed_values().border_top().width;
        child_box_state.border_bottom = child_box.computed_values().border_bottom().width;

        auto available_space_for_children = AvailableSpace(AvailableSize::make_definite(child_box_state.content_width()), AvailableSize::make_definite(child_box_state.content_height()));
        if (auto independent_formatting_context = layout_inside(child_box, LayoutMode::Normal, available_space_for_children))
            independent_formatting_context->parent_context_did_dimension_child_root_box();
    };

    for (auto& grid_item : m_grid_items) {
        auto resolved_row_span = box.computed_values().row_gap().is_auto() ? grid_item.raw_row_span() : grid_item.raw_row_span() * 2;
        if (!box.computed_values().row_gap().is_auto() && grid_item.gap_adjusted_row(box) == 0)
            resolved_row_span -= 1;
        if (grid_item.gap_adjusted_row(box) + resolved_row_span > m_grid_rows.size())
            resolved_row_span = m_grid_rows.size() - grid_item.gap_adjusted_row(box);

        auto resolved_column_span = box.computed_values().column_gap().is_auto() ? grid_item.raw_column_span() : grid_item.raw_column_span() * 2;
        if (!box.computed_values().column_gap().is_auto() && grid_item.gap_adjusted_column(box) == 0)
            resolved_column_span -= 1;
        if (grid_item.gap_adjusted_column(box) + resolved_column_span > m_grid_columns.size())
            resolved_column_span = m_grid_columns.size() - grid_item.gap_adjusted_column(box);

        layout_box(
            grid_item.gap_adjusted_row(box),
            grid_item.gap_adjusted_row(box) + resolved_row_span,
            grid_item.gap_adjusted_column(box),
            grid_item.gap_adjusted_column(box) + resolved_column_span,
            grid_item.box());
    }

    CSSPixels total_y = 0;
    for (auto& grid_row : m_grid_rows)
        total_y += grid_row.full_vertical_size();
    m_automatic_content_height = total_y;
}

CSSPixels GridFormattingContext::automatic_content_width() const
{
    return greatest_child_width(context_box());
}

CSSPixels GridFormattingContext::automatic_content_height() const
{
    return m_automatic_content_height;
}

bool GridFormattingContext::is_auto_positioned_row(CSS::GridTrackPlacement const& grid_row_start, CSS::GridTrackPlacement const& grid_row_end) const
{
    return is_auto_positioned_track(grid_row_start, grid_row_end);
}

bool GridFormattingContext::is_auto_positioned_column(CSS::GridTrackPlacement const& grid_column_start, CSS::GridTrackPlacement const& grid_column_end) const
{
    return is_auto_positioned_track(grid_column_start, grid_column_end);
}

bool GridFormattingContext::is_auto_positioned_track(CSS::GridTrackPlacement const& grid_track_start, CSS::GridTrackPlacement const& grid_track_end) const
{
    return grid_track_start.is_auto_positioned() && grid_track_end.is_auto_positioned();
}

AvailableSize GridFormattingContext::get_free_space(AvailableSize const& available_size, Vector<TemporaryTrack> const& tracks) const
{
    // https://www.w3.org/TR/css-grid-2/#algo-terms
    // free space: Equal to the available grid space minus the sum of the base sizes of all the grid
    // tracks (including gutters), floored at zero. If available grid space is indefinite, the free
    // space is indefinite as well.
    if (available_size.is_definite()) {
        CSSPixels sum_base_sizes = 0;
        for (auto& track : tracks)
            sum_base_sizes += track.base_size;
        return AvailableSize::make_definite(max(CSSPixels(0), available_size.to_px() - sum_base_sizes));
    }

    return available_size;
}

int GridFormattingContext::get_line_index_by_line_name(String const& needle, CSS::GridTrackSizeList grid_track_size_list)
{
    if (grid_track_size_list.track_list().size() == 0)
        return -1;

    auto repeated_tracks_count = 0;
    for (size_t x = 0; x < grid_track_size_list.track_list().size(); x++) {
        if (grid_track_size_list.track_list()[x].is_repeat()) {
            // FIXME: Calculate amount of columns/rows if auto-fill/fit
            if (!grid_track_size_list.track_list()[x].repeat().is_default())
                return -1;
            auto repeat = grid_track_size_list.track_list()[x].repeat().grid_track_size_list();
            for (size_t y = 0; y < repeat.track_list().size(); y++) {
                for (size_t z = 0; z < repeat.line_names()[y].size(); z++) {
                    if (repeat.line_names()[y][z] == needle)
                        return x + repeated_tracks_count;
                    repeated_tracks_count++;
                }
            }
        } else {
            for (size_t y = 0; y < grid_track_size_list.line_names()[x].size(); y++) {
                if (grid_track_size_list.line_names()[x][y] == needle)
                    return x + repeated_tracks_count;
            }
        }
    }
    for (size_t y = 0; y < grid_track_size_list.line_names()[grid_track_size_list.track_list().size()].size(); y++) {
        if (grid_track_size_list.line_names()[grid_track_size_list.track_list().size()][y] == needle)
            return grid_track_size_list.track_list().size() + repeated_tracks_count;
    }
    return -1;
}

OccupationGrid::OccupationGrid(size_t column_count, size_t row_count)
{
    Vector<bool> occupation_grid_row;
    for (size_t column_index = 0; column_index < max(column_count, 1); column_index++)
        occupation_grid_row.append(false);
    for (size_t row_index = 0; row_index < max(row_count, 1); row_index++)
        m_occupation_grid.append(occupation_grid_row);
}

OccupationGrid::OccupationGrid()
{
}

void OccupationGrid::maybe_add_column(size_t needed_number_of_columns)
{
    if (needed_number_of_columns <= column_count())
        return;
    auto column_count_before_modification = column_count();
    for (auto& occupation_grid_row : m_occupation_grid)
        for (size_t idx = 0; idx < needed_number_of_columns - column_count_before_modification; idx++)
            occupation_grid_row.append(false);
}

void OccupationGrid::maybe_add_row(size_t needed_number_of_rows)
{
    if (needed_number_of_rows <= row_count())
        return;

    Vector<bool> new_occupation_grid_row;
    for (size_t idx = 0; idx < column_count(); idx++)
        new_occupation_grid_row.append(false);

    for (size_t idx = 0; idx < needed_number_of_rows - row_count(); idx++)
        m_occupation_grid.append(new_occupation_grid_row);
}

void OccupationGrid::set_occupied(size_t column_start, size_t column_end, size_t row_start, size_t row_end)
{
    for (size_t row_index = 0; row_index < row_count(); row_index++) {
        if (row_index >= row_start && row_index < row_end) {
            for (size_t column_index = 0; column_index < column_count(); column_index++) {
                if (column_index >= column_start && column_index < column_end)
                    set_occupied(column_index, row_index);
            }
        }
    }
}

void OccupationGrid::set_occupied(size_t column_index, size_t row_index)
{
    m_occupation_grid[row_index][column_index] = true;
}

bool OccupationGrid::is_occupied(size_t column_index, size_t row_index)
{
    return m_occupation_grid[row_index][column_index];
}

size_t GridItem::gap_adjusted_row(Box const& grid_box) const
{
    return grid_box.computed_values().row_gap().is_auto() ? m_row : m_row * 2;
}

size_t GridItem::gap_adjusted_column(Box const& grid_box) const
{
    return grid_box.computed_values().column_gap().is_auto() ? m_column : m_column * 2;
}

// https://www.w3.org/TR/css-grid-2/#min-size-auto
CSSPixels GridFormattingContext::content_based_minimum_height(GridItem const& item)
{
    // The content-based minimum size for a grid item in a given dimension is its specified size suggestion if it exists
    if (!item.box().computed_values().height().is_auto()) {
        if (item.box().computed_values().height().is_length())
            return item.box().computed_values().height().length().to_px(item.box());
    }
    // FIXME: otherwise its transferred size suggestion if that exists
    // else its content size suggestion
    return calculate_min_content_height(item.box(), AvailableSize::make_definite(m_grid_columns[item.gap_adjusted_column(grid_container())].base_size));
}

}