ladybird/Libraries/LibWeb/Layout/GridFormattingContext.cpp

/*
 * Copyright (c) 2023-2025, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
 * Copyright (c) 2022-2023, Martin Falisse <mfalisse@outlook.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

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

namespace Web::Layout {

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

static Alignment to_alignment(CSS::JustifyContent value)
{
    switch (value) {
    case CSS::JustifyContent::Left:
        return Alignment::Start;
    case CSS::JustifyContent::Right:
        return Alignment::End;
    case CSS::JustifyContent::FlexStart:
    case CSS::JustifyContent::Start:
        return Alignment::Start;
    case CSS::JustifyContent::FlexEnd:
    case CSS::JustifyContent::End:
        return Alignment::End;
    case CSS::JustifyContent::Center:
        return Alignment::Center;
    case CSS::JustifyContent::SpaceBetween:
        return Alignment::SpaceBetween;
    case CSS::JustifyContent::SpaceAround:
        return Alignment::SpaceAround;
    case CSS::JustifyContent::SpaceEvenly:
        return Alignment::SpaceEvenly;
    case CSS::JustifyContent::Stretch:
        return Alignment::Stretch;
    case CSS::JustifyContent::Normal:
        return Alignment::Normal;
    default:
        VERIFY_NOT_REACHED();
    }
}

static Alignment to_alignment(CSS::JustifyItems value)
{
    switch (value) {
    case CSS::JustifyItems::Baseline:
        return Alignment::Baseline;
    case CSS::JustifyItems::Center:
        return Alignment::Center;
    case CSS::JustifyItems::End:
        return Alignment::End;
    case CSS::JustifyItems::FlexEnd:
        return Alignment::End;
    case CSS::JustifyItems::FlexStart:
        return Alignment::Start;
    case CSS::JustifyItems::Legacy:
        return Alignment::Normal;
    case CSS::JustifyItems::Normal:
        return Alignment::Normal;
    case CSS::JustifyItems::Safe:
        return Alignment::Safe;
    case CSS::JustifyItems::SelfEnd:
        return Alignment::SelfEnd;
    case CSS::JustifyItems::SelfStart:
        return Alignment::SelfStart;
    case CSS::JustifyItems::Start:
        return Alignment::Start;
    case CSS::JustifyItems::Stretch:
        return Alignment::Stretch;
    case CSS::JustifyItems::Unsafe:
        return Alignment::Unsafe;
    case CSS::JustifyItems::Left:
        return Alignment::Start;
    case CSS::JustifyItems::Right:
        return Alignment::End;
    default:
        VERIFY_NOT_REACHED();
    }
}

static Alignment to_alignment(CSS::AlignContent value)
{
    switch (value) {
    case CSS::AlignContent::Start:
        return Alignment::Start;
    case CSS::AlignContent::End:
        return Alignment::End;
    case CSS::AlignContent::Center:
        return Alignment::Center;
    case CSS::AlignContent::SpaceBetween:
        return Alignment::SpaceBetween;
    case CSS::AlignContent::SpaceAround:
        return Alignment::SpaceAround;
    case CSS::AlignContent::SpaceEvenly:
        return Alignment::SpaceEvenly;
    case CSS::AlignContent::Stretch:
        return Alignment::Stretch;
    case CSS::AlignContent::Normal:
        return Alignment::Normal;
    case CSS::AlignContent::FlexStart:
        return Alignment::Start;
    case CSS::AlignContent::FlexEnd:
        return Alignment::End;
    default:
        VERIFY_NOT_REACHED();
    }
}

static Alignment to_alignment(CSS::AlignItems value)
{
    switch (value) {
    case CSS::AlignItems::Baseline:
        return Alignment::Baseline;
    case CSS::AlignItems::Center:
        return Alignment::Center;
    case CSS::AlignItems::End:
        return Alignment::End;
    case CSS::AlignItems::FlexEnd:
        return Alignment::End;
    case CSS::AlignItems::FlexStart:
        return Alignment::Start;
    case CSS::AlignItems::Normal:
        return Alignment::Normal;
    case CSS::AlignItems::Safe:
        return Alignment::Safe;
    case CSS::AlignItems::SelfEnd:
        return Alignment::SelfEnd;
    case CSS::AlignItems::SelfStart:
        return Alignment::SelfStart;
    case CSS::AlignItems::Start:
        return Alignment::Start;
    case CSS::AlignItems::Stretch:
        return Alignment::Stretch;
    case CSS::AlignItems::Unsafe:
        return Alignment::Unsafe;
    default:
        VERIFY_NOT_REACHED();
    }
}

GridFormattingContext::GridTrack GridFormattingContext::GridTrack::create_from_definition(CSS::ExplicitGridTrack const& definition, bool is_auto_fit = false)
{
    // NOTE: repeat() is expected to be expanded beforehand.
    VERIFY(!definition.is_repeat());

    if (definition.is_minmax()) {
        return GridTrack {
            .min_track_sizing_function = definition.minmax().min_grid_size(),
            .max_track_sizing_function = definition.minmax().max_grid_size(),
            .is_auto_fit = is_auto_fit,
        };
    }

    // https://drafts.csswg.org/css-grid-2/#algo-terms
    // min track sizing function:
    // If the track was sized with a minmax() function, this is the first argument to that function.
    // If the track was sized with a <flex> value or fit-content() function, auto. Otherwise, the track’s sizing function.
    auto min_track_sizing_function = definition.grid_size();
    if (min_track_sizing_function.is_flexible_length()) {
        min_track_sizing_function = CSS::GridSize::make_auto();
    }
    auto max_track_sizing_function = definition.grid_size();

    return GridTrack {
        .min_track_sizing_function = min_track_sizing_function,
        .max_track_sizing_function = max_track_sizing_function,
        .is_auto_fit = is_auto_fit,
    };
}

GridFormattingContext::GridTrack GridFormattingContext::GridTrack::create_auto()
{
    return GridTrack {
        .min_track_sizing_function = CSS::GridSize::make_auto(),
        .max_track_sizing_function = CSS::GridSize::make_auto(),
    };
}

GridFormattingContext::GridTrack GridFormattingContext::GridTrack::create_gap(CSSPixels size)
{
    return GridTrack {
        .min_track_sizing_function = CSS::GridSize(CSS::Length::make_px(size)),
        .max_track_sizing_function = CSS::GridSize(CSS::Length::make_px(size)),
        .base_size = size,
        .is_gap = true,
    };
}

GridFormattingContext::GridFormattingContext(LayoutState& state, LayoutMode layout_mode, Box const& grid_container, FormattingContext* parent)
    : FormattingContext(Type::Grid, layout_mode, state, grid_container, parent)
    , m_grid_container_used_values(state.get_mutable(grid_container))
{
}

GridFormattingContext::~GridFormattingContext() = default;

CSSPixels GridFormattingContext::resolve_definite_track_size(CSS::GridSize const& grid_size, AvailableSpace const& available_space) const
{
    VERIFY(grid_size.is_definite());
    if (grid_size.type() == CSS::GridSize::Type::LengthPercentage)
        return grid_size.css_size().to_px(grid_container(), available_space.width.to_px_or_zero());
    VERIFY_NOT_REACHED();
}

int GridFormattingContext::count_of_repeated_auto_fill_or_fit_tracks(GridDimension dimension, CSS::ExplicitGridTrack const& repeated_track)
{
    // 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

    auto const& grid_computed_values = grid_container().computed_values();
    CSSPixels size_of_repeated_tracks = 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)
    auto const& repeat_track_list = repeated_track.repeat().grid_track_size_list().track_list();
    for (auto const& explicit_grid_track : repeat_track_list) {
        auto const& track_sizing_function = explicit_grid_track;
        CSSPixels track_size = 0;
        if (track_sizing_function.is_minmax()) {
            auto const& min_size = track_sizing_function.minmax().min_grid_size();
            auto const& max_size = track_sizing_function.minmax().max_grid_size();
            if (max_size.is_definite()) {
                track_size = resolve_definite_track_size(max_size, *m_available_space);
                if (min_size.is_definite())
                    track_size = min(track_size, resolve_definite_track_size(min_size, *m_available_space));
            } else if (min_size.is_definite()) {
                track_size = resolve_definite_track_size(min_size, *m_available_space);
            } else {
                VERIFY_NOT_REACHED();
            }
        } else {
            track_size = resolve_definite_track_size(track_sizing_function.grid_size(), *m_available_space);
        }
        size_of_repeated_tracks += track_size;
    }

    if (size_of_repeated_tracks == 0)
        return 0;

    auto const& available_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;
    auto const& gap = dimension == GridDimension::Column ? grid_computed_values.column_gap() : grid_computed_values.row_gap();
    auto gap_px = gap_to_px(gap, grid_container(), available_size.to_px_or_zero());
    auto size_of_repeated_tracks_with_gap = size_of_repeated_tracks + repeat_track_list.size() * gap_px;
    // Otherwise, if the grid container has a definite min size in the relevant axis, the number of repetitions is the
    // smallest possible positive integer that fulfills that minimum requirement
    if (available_size.is_definite()) {
        // NOTE: Gap size is added to free space to compensate for the fact that the last track does not have a gap
        auto free_space = available_size.to_px_or_zero();
        auto number_of_repetitions = ((free_space + gap_px) / size_of_repeated_tracks_with_gap).to_int();
        // If any number of repetitions would overflow, then 1 repetition.
        return max(1, number_of_repetitions);
    }
    // Otherwise, the specified track list repeats only once.
    return 1;

    // 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.
}

GridFormattingContext::PlacementPosition GridFormattingContext::resolve_grid_position(Box const& child_box, GridDimension dimension)
{
    auto const& computed_values = child_box.computed_values();
    auto const& placement_start = dimension == GridDimension::Row ? computed_values.grid_row_start() : computed_values.grid_column_start();
    auto const& placement_end = dimension == GridDimension::Row ? computed_values.grid_row_end() : computed_values.grid_column_end();

    CSS::CalculationResolutionContext resolution_context { .length_resolution_context = CSS::Length::ResolutionContext::for_layout_node(child_box) };

    Optional<i64> placement_start_line_number = placement_start.has_line_number() ? placement_start.line_number().resolved(resolution_context) : Optional<i64> {};
    Optional<i64> placement_end_line_number = placement_end.has_line_number() ? placement_end.line_number().resolved(resolution_context) : Optional<i64> {};

    PlacementPosition result;

    if (placement_start_line_number.has_value() && placement_start_line_number.value() > 0)
        result.start = placement_start_line_number.value() - 1;
    else if (placement_start_line_number.has_value()) {
        auto explicit_line_count = dimension == GridDimension::Row ? m_explicit_rows_line_count : m_explicit_columns_line_count;
        result.start = explicit_line_count + placement_start_line_number.value();
    }
    if (placement_end_line_number.has_value())
        result.end = *placement_end_line_number - 1;

    if (result.end < 0) {
        if (dimension == GridDimension::Row)
            result.end = m_occupation_grid.row_count() + result.end + 2;
        else
            result.end = m_occupation_grid.column_count() + result.end + 2;
    }

    // FIXME: 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.
    if (placement_end.is_span())
        result.span = placement_end.span().resolved(resolution_context).value();
    if (placement_start.is_span()) {
        result.span = placement_start.span().resolved(resolution_context).value();
        result.start = result.end - result.span;
        // FIXME: Remove me once have implemented spans overflowing into negative indexes, e.g., grid-row: span 2 / 1
        if (result.start < 0)
            result.start = 0;
    }

    if (placement_end.has_identifier()) {
        auto area_end_line_name = MUST(String::formatted("{}-end", placement_end.identifier()));
        auto line_number = placement_end_line_number.value_or(1);
        if (auto area_end_line_index = get_nth_line_index_by_line_name(dimension, area_end_line_name, line_number); area_end_line_index.has_value()) {
            result.end = area_end_line_index.value();
        } else if (auto line_name_index = get_nth_line_index_by_line_name(dimension, placement_end.identifier(), line_number); line_name_index.has_value()) {
            result.end = line_name_index.value();
        } else {
            result.end = 1;
        }
        result.start = result.end - 1;
    }

    if (placement_start.has_identifier()) {
        auto area_start_line_name = MUST(String::formatted("{}-start", placement_start.identifier()));
        auto line_number = placement_start_line_number.value_or(1);
        if (auto area_start_line_index = get_nth_line_index_by_line_name(dimension, area_start_line_name, line_number); area_start_line_index.has_value()) {
            result.start = area_start_line_index.value();
        } else if (auto line_name_index = get_nth_line_index_by_line_name(dimension, placement_start.identifier(), line_number); line_name_index.has_value()) {
            result.start = line_name_index.value();
        } else {
            result.start = 0;
        }
    }

    if (!placement_start.is_positioned() && placement_end.is_positioned() && !placement_end.is_span()) {
        if (result.span == 0)
            result.span = 1;
        result.start = result.end - result.span;
        if (result.start < 0)
            result.start = 0;
    }

    if (placement_start.is_positioned() && placement_end.is_positioned()) {
        if (result.start > result.end)
            swap(result.start, result.end);
        if (result.start != result.end)
            result.span = result.end - result.start;
    }

    // FIXME: Have yet to find the spec for this.
    if (!placement_start.is_positioned() && placement_end.is_positioned() && result.end == 0)
        result.start = 0;

    // If the placement contains two spans, remove the one contributed by the end grid-placement
    // property.
    if (placement_start.is_span() && placement_end.is_span())
        result.span = placement_start.span().resolved(resolution_context).value();

    return result;
}

void GridFormattingContext::place_item_with_row_and_column_position(Box const& child_box)
{
    auto row_placement_position = resolve_grid_position(child_box, GridDimension::Row);
    auto column_placement_position = resolve_grid_position(child_box, GridDimension::Column);

    auto row_start = row_placement_position.start;
    auto row_span = row_placement_position.span;
    auto column_start = column_placement_position.start;
    auto column_span = column_placement_position.span;

    record_grid_placement(GridItem {
        .box = child_box,
        .used_values = m_state.get_mutable(child_box),
        .row = row_start,
        .row_span = row_span,
        .column = column_start,
        .column_span = column_span });
}

void GridFormattingContext::place_item_with_row_position(Box const& child_box)
{
    auto placement_position = resolve_grid_position(child_box, GridDimension::Row);
    auto row_start = placement_position.start;
    size_t row_span = placement_position.span;

    auto const& grid_column_start = child_box.computed_values().grid_column_start();
    int column_start = 0;
    size_t column_span = grid_column_start.is_span() ? grid_column_start.span().resolved({ .length_resolution_context = CSS::Length::ResolutionContext::for_layout_node(child_box) }).value() : 1;

    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();
    }

    record_grid_placement(GridItem {
        .box = child_box,
        .used_values = m_state.get_mutable(child_box),
        .row = row_start,
        .row_span = row_span,
        .column = column_start,
        .column_span = column_span });
}

void GridFormattingContext::place_item_with_column_position(Box const& child_box, int& auto_placement_cursor_x, int& auto_placement_cursor_y)
{
    auto placement_position = resolve_grid_position(child_box, GridDimension::Column);
    auto column_start = placement_position.start;
    size_t column_span = placement_position.span;

    auto const& grid_row_start = child_box.computed_values().grid_row_start();
    size_t row_span = grid_row_start.is_span() ? grid_row_start.span().resolved({ .length_resolution_context = CSS::Length::ResolutionContext::for_layout_node(child_box) }).value() : 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;

    // 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++;
    }
    // 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.

    record_grid_placement(GridItem {
        .box = child_box,
        .used_values = m_state.get_mutable(child_box),
        .row = auto_placement_cursor_y,
        .row_span = row_span,
        .column = column_start,
        .column_span = column_span });
}

FoundUnoccupiedPlace OccupationGrid::find_unoccupied_place(GridDimension dimension, int& column_index, int& row_index, int column_span, int row_span) const
{
    if (dimension == GridDimension::Column) {
        while (row_index <= max_row_index()) {
            while (column_index <= max_column_index()) {
                auto enough_span_for_span = column_index + column_span - 1 <= max_column_index();
                if (enough_span_for_span && !is_occupied(column_index, row_index))
                    return FoundUnoccupiedPlace::Yes;
                column_index++;
            }
            row_index++;
            column_index = min_column_index();
        }
    } else {
        while (column_index <= max_column_index()) {
            while (row_index <= max_row_index()) {
                auto enough_span_for_span = row_index + row_span - 1 <= max_row_index();
                if (enough_span_for_span && !is_occupied(column_index, row_index))
                    return FoundUnoccupiedPlace::Yes;
                row_index++;
            }
            column_index++;
            row_index = min_row_index();
        }
    }

    return FoundUnoccupiedPlace::No;
}

void GridFormattingContext::place_item_with_no_declared_position(Box const& child_box, int& auto_placement_cursor_x, int& auto_placement_cursor_y)
{
    auto const& computed_values = child_box.computed_values();
    auto const& grid_row_start = computed_values.grid_row_start();
    auto const& grid_row_end = computed_values.grid_row_end();
    auto const& grid_column_start = computed_values.grid_column_start();
    auto const& grid_column_end = computed_values.grid_column_end();

    CSS::CalculationResolutionContext resolution_context { .length_resolution_context = CSS::Length::ResolutionContext::for_layout_node(child_box) };

    auto column_start = 0;
    size_t column_span = 1;
    if (grid_column_start.is_span())
        column_span = grid_column_start.span().resolved(resolution_context).value();
    else if (grid_column_end.is_span())
        column_span = grid_column_end.span().resolved(resolution_context).value();
    auto row_start = 0;
    size_t row_span = 1;
    if (grid_row_start.is_span())
        row_span = grid_row_start.span().resolved(resolution_context).value();
    else if (grid_row_end.is_span())
        row_span = grid_row_end.span().resolved(resolution_context).value();

    auto const& auto_flow = grid_container().computed_values().grid_auto_flow();
    auto dimension = auto_flow.row ? GridDimension::Column : GridDimension::Row;

    // 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 found_unoccupied_area = m_occupation_grid.find_unoccupied_place(dimension, auto_placement_cursor_x, auto_placement_cursor_y, column_span, row_span);

    // 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 == FoundUnoccupiedPlace::Yes) {
        column_start = auto_placement_cursor_x;
        row_start = auto_placement_cursor_y;

        auto_placement_cursor_x += column_span - 1;
        auto_placement_cursor_y += row_span - 1;

        if (dimension == GridDimension::Column) {
            auto_placement_cursor_x++;
            auto_placement_cursor_y = m_occupation_grid.min_row_index();
        } else {
            auto_placement_cursor_y++;
            auto_placement_cursor_x = m_occupation_grid.min_column_index();
        }
    } else {
        column_start = auto_placement_cursor_x;
        row_start = auto_placement_cursor_y;

        auto_placement_cursor_x += column_span - 1;
        auto_placement_cursor_y += row_span - 1;
    }

    record_grid_placement(GridItem {
        .box = child_box,
        .used_values = m_state.get_mutable(child_box),
        .row = row_start,
        .row_span = row_span,
        .column = column_start,
        .column_span = column_span });
}

void GridFormattingContext::record_grid_placement(GridItem grid_item)
{
    m_occupation_grid.set_occupied(grid_item.column.value(), grid_item.column.value() + grid_item.column_span.value(), grid_item.row.value(), grid_item.row.value() + grid_item.row_span.value());
    m_grid_items.append(grid_item);
}

void GridFormattingContext::initialize_grid_tracks_from_definition(GridDimension dimension)
{
    auto const& grid_computed_values = grid_container().computed_values();
    auto const& tracks_definition = dimension == GridDimension::Column ? grid_computed_values.grid_template_columns().track_list() : grid_computed_values.grid_template_rows().track_list();
    auto& tracks = dimension == GridDimension::Column ? m_grid_columns : m_grid_rows;
    for (auto const& track_definition : tracks_definition) {
        int repeat_count = 1;
        bool is_auto_fit = false;
        if (track_definition.is_repeat()) {
            is_auto_fit = track_definition.repeat().is_auto_fit();
            if (track_definition.repeat().is_auto_fill() || is_auto_fit)
                repeat_count = count_of_repeated_auto_fill_or_fit_tracks(dimension, track_definition);
            else
                repeat_count = track_definition.repeat().repeat_count();
        }
        for (auto _ = 0; _ < repeat_count; _++) {
            if (track_definition.is_default() || track_definition.is_minmax()) {
                tracks.append(GridTrack::create_from_definition(track_definition, is_auto_fit));
            } else if (track_definition.is_repeat()) {
                for (auto& explicit_grid_track : track_definition.repeat().grid_track_size_list().track_list()) {
                    tracks.append(GridTrack::create_from_definition(explicit_grid_track, is_auto_fit));
                }
            } else {
                VERIFY_NOT_REACHED();
            }
        }
    }
}

void GridFormattingContext::initialize_grid_tracks_for_columns_and_rows()
{
    auto const& grid_computed_values = grid_container().computed_values();

    auto const& grid_auto_columns = grid_computed_values.grid_auto_columns().track_list();
    size_t implicit_column_index = 0;
    // NOTE: If there are implicit tracks created by items with negative indexes they should prepend explicitly defined tracks
    auto negative_index_implied_column_tracks_count = abs(m_occupation_grid.min_column_index());
    for (int column_index = 0; column_index < negative_index_implied_column_tracks_count; column_index++) {
        if (grid_auto_columns.size() > 0) {
            auto definition = grid_auto_columns[implicit_column_index % grid_auto_columns.size()];
            m_grid_columns.append(GridTrack::create_from_definition(definition));
        } else {
            m_grid_columns.append(GridTrack::create_auto());
        }
        implicit_column_index++;
    }
    initialize_grid_tracks_from_definition(GridDimension::Column);
    for (size_t column_index = m_grid_columns.size(); column_index < m_occupation_grid.column_count(); column_index++) {
        if (grid_auto_columns.size() > 0) {
            auto definition = grid_auto_columns[implicit_column_index % grid_auto_columns.size()];
            m_grid_columns.append(GridTrack::create_from_definition(definition));
        } else {
            m_grid_columns.append(GridTrack::create_auto());
        }
        implicit_column_index++;
    }

    auto const& grid_auto_rows = grid_computed_values.grid_auto_rows().track_list();
    size_t implicit_row_index = 0;
    // NOTE: If there are implicit tracks created by items with negative indexes they should prepend explicitly defined tracks
    auto negative_index_implied_row_tracks_count = abs(m_occupation_grid.min_row_index());
    for (int row_index = 0; row_index < negative_index_implied_row_tracks_count; row_index++) {
        if (grid_auto_rows.size() > 0) {
            auto definition = grid_auto_rows[implicit_row_index % grid_auto_rows.size()];
            m_grid_rows.append(GridTrack::create_from_definition(definition));
        } else {
            m_grid_rows.append(GridTrack::create_auto());
        }
        implicit_row_index++;
    }
    initialize_grid_tracks_from_definition(GridDimension::Row);
    for (size_t row_index = m_grid_rows.size(); row_index < m_occupation_grid.row_count(); row_index++) {
        if (grid_auto_rows.size() > 0) {
            auto definition = grid_auto_rows[implicit_row_index % grid_auto_rows.size()];
            m_grid_rows.append(GridTrack::create_from_definition(definition));
        } else {
            m_grid_rows.append(GridTrack::create_auto());
        }
        implicit_row_index++;
    }

    m_column_lines.resize(m_grid_columns.size() + 1);
    m_row_lines.resize(m_grid_rows.size() + 1);
}

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 (m_grid_columns.size() > 0) {
        CSSPixels column_gap_width = 0;
        if (!grid_container().computed_values().column_gap().has<CSS::NormalGap>()) {
            column_gap_width = gap_to_px(grid_container().computed_values().column_gap(), grid_container(), available_space.width.to_px_or_zero());
        }

        m_column_gap_tracks.ensure_capacity(m_grid_columns.size() - 1);

        for (size_t column_index = 0; column_index < m_grid_columns.size(); column_index++) {
            m_grid_columns_and_gaps.append(m_grid_columns[column_index]);

            if (column_index != m_grid_columns.size() - 1) {
                m_column_gap_tracks.unchecked_append(GridTrack::create_gap(column_gap_width));
                m_grid_columns_and_gaps.append(m_column_gap_tracks.last());
            }
        }
    }

    if (!m_grid_rows.is_empty()) {
        CSSPixels row_gap_height = 0;
        if (!grid_container().computed_values().row_gap().has<CSS::NormalGap>()) {
            row_gap_height = gap_to_px(grid_container().computed_values().row_gap(), grid_container(), available_space.height.to_px_or_zero());
        }

        m_row_gap_tracks.ensure_capacity(m_grid_rows.size() - 1);

        for (size_t row_index = 0; row_index < m_grid_rows.size(); row_index++) {
            m_grid_rows_and_gaps.append(m_grid_rows[row_index]);

            if (row_index != m_grid_rows.size() - 1) {
                m_row_gap_tracks.unchecked_append(GridTrack::create_gap(row_gap_height));
                m_grid_rows_and_gaps.append(m_row_gap_tracks.last());
            }
        }
    }
}

void GridFormattingContext::initialize_track_sizes(GridDimension dimension)
{
    // https://www.w3.org/TR/css-grid-2/#algo-init
    // 12.4. Initialize Track Sizes
    // Initialize each track’s base size and growth limit.

    auto& tracks_and_gaps = dimension == GridDimension::Column ? m_grid_columns_and_gaps : m_grid_rows_and_gaps;
    auto& available_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;

    for (auto& track : tracks_and_gaps) {
        if (track.is_gap)
            continue;

        if (track.min_track_sizing_function.is_fixed(available_size)) {
            track.base_size = track.min_track_sizing_function.css_size().to_px(grid_container(), available_size.to_px_or_zero());
        } else if (track.min_track_sizing_function.is_intrinsic(available_size)) {
            track.base_size = 0;
        }

        if (track.max_track_sizing_function.is_fixed(available_size)) {
            track.growth_limit = track.max_track_sizing_function.css_size().to_px(grid_container(), available_size.to_px_or_zero());
        } else if (track.max_track_sizing_function.is_flexible_length()) {
            track.growth_limit = {};
        } else if (track.max_track_sizing_function.is_intrinsic(available_size)) {
            track.growth_limit = {};
        } else {
            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.has_value() && track.growth_limit.value() < track.base_size)
            track.growth_limit = track.base_size;
    }
}

void GridFormattingContext::resolve_intrinsic_track_sizes(GridDimension dimension)
{
    // 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.

    auto& tracks_and_gaps = dimension == GridDimension::Column ? m_grid_columns_and_gaps : m_grid_rows_and_gaps;

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

    // 2. Size tracks to fit non-spanning items:
    increase_sizes_to_accommodate_spanning_items_crossing_content_sized_tracks(dimension, 1);

    // 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.
    // Repeat incrementally for items with greater spans until all items have been considered.
    size_t max_item_span = 1;
    for (auto& item : m_grid_items)
        max_item_span = max(item.span(dimension), max_item_span);
    for (size_t span = 2; span <= max_item_span; span++)
        increase_sizes_to_accommodate_spanning_items_crossing_content_sized_tracks(dimension, span);

    // 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
    increase_sizes_to_accommodate_spanning_items_crossing_flexible_tracks(dimension);

    // 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_and_gaps) {
        if (!track.growth_limit.has_value())
            track.growth_limit = track.base_size;
    }
}

template<typename Match>
void GridFormattingContext::distribute_extra_space_across_spanned_tracks_base_size(GridDimension dimension, CSSPixels item_size_contribution, SpaceDistributionPhase phase, Vector<GridTrack&>& spanned_tracks, Match matcher)
{
    auto& available_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;

    Vector<GridTrack&> affected_tracks;
    for (auto& track : spanned_tracks) {
        if (matcher(track))
            affected_tracks.append(track);
    }

    if (affected_tracks.size() == 0)
        return;

    for (auto& track : affected_tracks)
        track.item_incurred_increase = 0;

    // 1. Find the space to distribute:
    CSSPixels spanned_tracks_sizes_sum = 0;
    for (auto& track : spanned_tracks)
        spanned_tracks_sizes_sum += track.base_size;

    // Subtract the corresponding size of every spanned track from the item’s size contribution to find the item’s
    // remaining size contribution.
    auto extra_space = max(CSSPixels(0), item_size_contribution - spanned_tracks_sizes_sum);

    // 2. Distribute space up to limits:
    while (extra_space > 0) {
        auto all_frozen = all_of(affected_tracks, [](auto const& track) { return track.base_size_frozen; });
        if (all_frozen)
            break;

        // 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
        CSSPixels increase_per_track = max(CSSPixels::smallest_positive_value(), extra_space / affected_tracks.size());
        for (auto& track : affected_tracks) {
            if (track.base_size_frozen)
                continue;

            auto increase = min(increase_per_track, extra_space);

            if (track.growth_limit.has_value()) {
                auto maximum_increase = track.growth_limit.value() - track.base_size;
                if (track.item_incurred_increase + increase >= maximum_increase) {
                    track.base_size_frozen = true;
                    increase = maximum_increase - track.item_incurred_increase;
                }
            }
            track.item_incurred_increase += increase;
            extra_space -= increase;
        }
    }

    // 3. Distribute space beyond limits
    if (extra_space > 0) {
        Vector<GridTrack&> tracks_to_grow_beyond_limits;

        // If space remains after all tracks are frozen, unfreeze and continue to
        // distribute space to the item-incurred increase of...
        if (phase == SpaceDistributionPhase::AccommodateMinimumContribution || phase == SpaceDistributionPhase::AccommodateMinContentContribution) {
            // when accommodating minimum contributions or accommodating min-content contributions: any affected track
            // that happens to also have an intrinsic max track sizing function
            for (auto& track : affected_tracks) {
                if (track.max_track_sizing_function.is_intrinsic(available_size))
                    tracks_to_grow_beyond_limits.append(track);
            }

            // if there are no such tracks, then all affected tracks.
            if (tracks_to_grow_beyond_limits.size() == 0)
                tracks_to_grow_beyond_limits = affected_tracks;
        }
        // FIXME: 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.

        CSSPixels increase_per_track = extra_space / affected_tracks.size();
        for (auto& track : affected_tracks) {
            auto increase = min(increase_per_track, extra_space);
            track.item_incurred_increase += increase;
            extra_space -= increase;
        }
    }

    // 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.
    for (auto& track : affected_tracks) {
        if (track.item_incurred_increase > track.planned_increase)
            track.planned_increase = track.item_incurred_increase;
    }
}

template<typename Match>
void GridFormattingContext::distribute_extra_space_across_spanned_tracks_growth_limit(CSSPixels item_size_contribution, Vector<GridTrack&>& spanned_tracks, Match matcher)
{
    Vector<GridTrack&> affected_tracks;
    for (auto& track : spanned_tracks) {
        if (matcher(track))
            affected_tracks.append(track);
    }

    for (auto& track : affected_tracks)
        track.item_incurred_increase = 0;

    if (affected_tracks.size() == 0)
        return;

    // 1. Find the space to distribute:
    CSSPixels spanned_tracks_sizes_sum = 0;
    for (auto& track : spanned_tracks) {
        if (track.growth_limit.has_value()) {
            spanned_tracks_sizes_sum += track.growth_limit.value();
        } else {
            spanned_tracks_sizes_sum += track.base_size;
        }
    }

    // Subtract the corresponding size of every spanned track from the item’s size contribution to find the item’s
    // remaining size contribution.
    auto extra_space = max(CSSPixels(0), item_size_contribution - spanned_tracks_sizes_sum);

    // 2. Distribute space up to limits:
    while (extra_space > 0) {
        auto all_frozen = all_of(affected_tracks, [](auto const& track) { return track.growth_limit_frozen; });
        if (all_frozen)
            break;

        // 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
        CSSPixels increase_per_track = max(CSSPixels::smallest_positive_value(), extra_space / affected_tracks.size());
        for (auto& track : affected_tracks) {
            if (track.growth_limit_frozen)
                continue;

            auto increase = min(increase_per_track, extra_space);

            // For growth limits, the limit is infinity if it is marked as infinitely growable, and equal to the
            // growth limit otherwise.
            if (!track.infinitely_growable && track.growth_limit.has_value()) {
                auto maximum_increase = track.growth_limit.value() - track.base_size;
                if (track.item_incurred_increase + increase >= maximum_increase) {
                    track.growth_limit_frozen = true;
                    increase = maximum_increase - track.item_incurred_increase;
                }
            }
            track.item_incurred_increase += increase;
            extra_space -= increase;
        }
    }

    // FIXME: 3. Distribute space beyond limits

    // 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.
    for (auto& track : spanned_tracks) {
        if (track.item_incurred_increase > track.planned_increase)
            track.planned_increase = track.item_incurred_increase;
    }
}

void GridFormattingContext::increase_sizes_to_accommodate_spanning_items_crossing_content_sized_tracks(GridDimension dimension, size_t span)
{
    auto& available_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;
    auto& tracks = dimension == GridDimension::Column ? m_grid_columns : m_grid_rows;
    for (auto& item : m_grid_items) {
        auto const item_span = item.span(dimension);
        if (item_span != span)
            continue;

        Vector<GridTrack&> spanned_tracks;
        for_each_spanned_track_by_item(item, dimension, [&](GridTrack& track) {
            spanned_tracks.append(track);
        });

        auto item_spans_tracks_with_flexible_sizing_function = any_of(spanned_tracks, [](auto& track) {
            return track.max_track_sizing_function.is_flexible_length();
        });
        if (item_spans_tracks_with_flexible_sizing_function)
            continue;

        // 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.
        auto item_size_contribution = [&] {
            // 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.
            if (available_size.is_intrinsic_sizing_constraint())
                return calculate_limited_min_content_contribution(item, dimension);
            return calculate_minimum_contribution(item, dimension);
        }();
        distribute_extra_space_across_spanned_tracks_base_size(dimension, item_size_contribution, SpaceDistributionPhase::AccommodateMinimumContribution, spanned_tracks, [&](GridTrack const& track) {
            return track.min_track_sizing_function.is_intrinsic(available_size);
        });
        for (auto& track : spanned_tracks) {
            track.base_size += track.planned_increase;
            track.planned_increase = 0;
        }

        // 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.
        auto item_min_content_contribution = calculate_min_content_contribution(item, dimension);
        distribute_extra_space_across_spanned_tracks_base_size(dimension, item_min_content_contribution, SpaceDistributionPhase::AccommodateMinContentContribution, spanned_tracks, [&](GridTrack const& track) {
            return track.min_track_sizing_function.is_min_content() || track.min_track_sizing_function.is_max_content();
        });
        for (auto& track : spanned_tracks) {
            track.base_size += track.planned_increase;
            track.planned_increase = 0;
        }

        // 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.
        if (available_size.is_max_content()) {
            auto item_limited_max_content_contribution = calculate_limited_max_content_contribution(item, dimension);
            distribute_extra_space_across_spanned_tracks_base_size(dimension, item_limited_max_content_contribution, SpaceDistributionPhase::AccommodateMaxContentContribution, spanned_tracks, [&](GridTrack const& track) {
                return track.min_track_sizing_function.is_auto(available_size) || track.min_track_sizing_function.is_max_content();
            });
            for (auto& track : spanned_tracks) {
                track.base_size += track.planned_increase;
                track.planned_increase = 0;
            }
        }

        // 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.
        for (auto& track : tracks) {
            if (track.growth_limit.has_value() && track.growth_limit.value() < track.base_size)
                track.growth_limit = track.base_size;
        }

        // 5. For intrinsic maximums: Next increase the growth limit of tracks with an intrinsic max track sizing
        distribute_extra_space_across_spanned_tracks_growth_limit(item_min_content_contribution, spanned_tracks, [&](GridTrack const& track) {
            return track.max_track_sizing_function.is_intrinsic(available_size);
        });
        for (auto& track : spanned_tracks) {
            if (!track.growth_limit.has_value()) {
                // If the affected size is an infinite growth limit, set it to the track’s base size plus the planned increase.
                track.growth_limit = track.base_size + track.planned_increase;
                // Mark any tracks whose growth limit changed from infinite to finite in this step as infinitely growable
                // for the next step.
                track.infinitely_growable = true;
            } else {
                track.growth_limit.value() += track.planned_increase;
            }
            track.planned_increase = 0;
        }

        // 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.
        auto item_max_content_contribution = calculate_max_content_contribution(item, dimension);
        distribute_extra_space_across_spanned_tracks_growth_limit(item_max_content_contribution, spanned_tracks, [&](GridTrack const& track) {
            return track.max_track_sizing_function.is_max_content() || track.max_track_sizing_function.is_auto(available_size) || track.max_track_sizing_function.is_fit_content();
        });
        for (auto& track : spanned_tracks) {
            if (track.max_track_sizing_function.is_fit_content()) {
                track.growth_limit.value() += track.planned_increase;
                if (track.growth_limit.value() < track.base_size)
                    track.growth_limit = track.base_size;
                if (available_size.is_definite()) {
                    auto fit_content_limit = track.max_track_sizing_function.css_size().to_px(grid_container(), available_size.to_px_or_zero());
                    if (track.growth_limit.value() > fit_content_limit)
                        track.growth_limit = fit_content_limit;
                }
            } else if (!track.growth_limit.has_value()) {
                // If the affected size is an infinite growth limit, set it to the track’s base size plus the planned increase.
                track.growth_limit = track.base_size + track.planned_increase;
            } else {
                track.growth_limit.value() += track.planned_increase;
            }
            track.planned_increase = 0;
        }
    }
}

void GridFormattingContext::increase_sizes_to_accommodate_spanning_items_crossing_flexible_tracks(GridDimension dimension)
{
    auto& tracks = dimension == GridDimension::Column ? m_grid_columns : m_grid_rows;
    auto const& available_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;
    for (auto& item : m_grid_items) {
        Vector<GridTrack&> spanned_tracks;
        for_each_spanned_track_by_item(item, dimension, [&](GridTrack& track) {
            spanned_tracks.append(track);
        });

        auto item_spans_tracks_with_flexible_sizing_function = any_of(spanned_tracks, [](auto& track) {
            return track.max_track_sizing_function.is_flexible_length();
        });
        if (!item_spans_tracks_with_flexible_sizing_function)
            continue;

        // 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.
        auto item_size_contribution = [&] {
            // 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.
            if (available_size.is_intrinsic_sizing_constraint())
                return calculate_limited_min_content_contribution(item, dimension);
            return calculate_minimum_contribution(item, dimension);
        }();
        distribute_extra_space_across_spanned_tracks_base_size(dimension,
            item_size_contribution, SpaceDistributionPhase::AccommodateMinimumContribution, spanned_tracks, [&](GridTrack const& track) {
                return track.max_track_sizing_function.is_flexible_length();
            });

        for (auto& track : spanned_tracks) {
            track.base_size += track.planned_increase;
            track.planned_increase = 0;
        }

        // 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.
        for (auto& track : tracks) {
            if (track.growth_limit.has_value() && track.growth_limit.value() < track.base_size)
                track.growth_limit = track.base_size;
        }
    }
}

void GridFormattingContext::maximize_tracks_using_available_size(AvailableSpace const& available_space, GridDimension dimension)
{
    // https://www.w3.org/TR/css-grid-2/#algo-grow-tracks
    // 12.6. Maximize Tracks

    auto& tracks = dimension == GridDimension::Column ? m_grid_columns : m_grid_rows;

    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_space, dimension);
        if (free_space.is_max_content() || free_space.is_indefinite())
            return CSSPixels::max();
        if (free_space.is_min_content())
            return 0;
        return free_space.to_px_or_zero();
    };

    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();
        for (auto& track : tracks) {
            if (track.base_size_frozen)
                continue;
            VERIFY(track.growth_limit.has_value());
            track.base_size = min(track.growth_limit.value(), 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();
    }
}

void GridFormattingContext::maximize_tracks(GridDimension dimension)
{
    // https://www.w3.org/TR/css-grid-2/#algo-grow-tracks
    // 12.6. Maximize Tracks

    auto& tracks = dimension == GridDimension::Column ? m_grid_columns : m_grid_rows;

    Vector<CSSPixels> saved_base_sizes;
    for (auto& track : tracks)
        saved_base_sizes.append(track.base_size);

    maximize_tracks_using_available_size(*m_available_space, dimension);

    // 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.
    CSSPixels grid_container_inner_size = 0;
    for (auto& track : tracks)
        grid_container_inner_size += track.base_size;
    auto const& available_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;
    auto const& computed_values = grid_container().computed_values();
    auto should_treat_grid_container_maximum_size_as_none = [&] {
        if (dimension == GridDimension::Column)
            return should_treat_max_width_as_none(grid_container(), available_size);
        return !computed_values.max_height().is_auto();
    }();

    if (!should_treat_grid_container_maximum_size_as_none) {
        auto maximum_size = calculate_grid_container_maximum_size(dimension);
        if (grid_container_inner_size > maximum_size) {
            for (size_t i = 0; i < tracks.size(); i++)
                tracks[i].base_size = saved_base_sizes[i];
            auto available_space_with_max_width = *m_available_space;
            if (dimension == GridDimension::Column)
                available_space_with_max_width.width = AvailableSize::make_definite(maximum_size);
            else
                available_space_with_max_width.height = AvailableSize::make_definite(maximum_size);
            maximize_tracks_using_available_size(available_space_with_max_width, dimension);
        }
    }
}

void GridFormattingContext::expand_flexible_tracks(GridDimension dimension)
{
    // 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& tracks_and_gaps = dimension == GridDimension::Column ? m_grid_columns_and_gaps : m_grid_rows_and_gaps;
    auto& tracks = dimension == GridDimension::Column ? m_grid_columns : m_grid_rows;
    auto& available_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;
    // FIXME: This should ideally take a Span, as that is more idomatic, but Span does not yet support holding references
    auto find_the_size_of_an_fr = [&](Vector<GridTrack&> const& tracks, CSSPixels space_to_fill) -> CSSPixelFraction {
        // https://www.w3.org/TR/css-grid-2/#algo-find-fr-size
        auto treat_track_as_inflexiable = MUST(AK::Bitmap::create(tracks.size(), false));
        do {
            // 1. Let leftover space be the space to fill minus the base sizes of the non-flexible grid tracks.
            auto leftover_space = space_to_fill;
            for (auto track_index = 0u; track_index < tracks.size(); track_index++) {
                if (treat_track_as_inflexiable.view().get(track_index) || !tracks[track_index].max_track_sizing_function.is_flexible_length()) {
                    leftover_space -= tracks[track_index].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.
            CSSPixels flex_factor_sum = 0;
            for (auto track_index = 0u; track_index < tracks.size(); track_index++) {
                if (treat_track_as_inflexiable.view().get(track_index) || !tracks[track_index].max_track_sizing_function.is_flexible_length())
                    continue;
                flex_factor_sum += CSSPixels::nearest_value_for(tracks[track_index].max_track_sizing_function.flex_factor());
            }
            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;

            // 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.
            bool need_to_restart = false;
            for (auto track_index = 0u; track_index < tracks.size(); track_index++) {
                if (treat_track_as_inflexiable.view().get(track_index) || !tracks[track_index].max_track_sizing_function.is_flexible_length())
                    continue;
                auto scaled_fraction = CSSPixels::nearest_value_for(tracks[track_index].max_track_sizing_function.flex_factor()) * hypothetical_fr_size;
                if (scaled_fraction < tracks[track_index].base_size) {
                    treat_track_as_inflexiable.set(track_index, true);
                    need_to_restart = true;
                }
            }
            if (need_to_restart)
                continue;

            // 5. Return the hypothetical fr size.
            return hypothetical_fr_size;
        } while (true);

        VERIFY_NOT_REACHED();
    };

    // First, find the grid’s used flex fraction:
    auto flex_fraction = [&]() -> CSSPixelFraction {
        auto free_space = get_free_space(*m_available_space, dimension);
        // If the free space is zero or if sizing the grid container under a min-content constraint:
        if ((free_space.is_definite() && free_space.to_px_or_zero() == 0) || available_size.is_min_content()) {
            // The used flex fraction is zero.
            return 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(tracks_and_gaps, available_size.to_px_or_zero());
        } else {
            // Otherwise, if the free space is an indefinite length:
            // The used flex fraction is the maximum of:
            CSSPixelFraction result = 0;
            // For each flexible track, if the flexible track’s flex factor is greater than one, the result of dividing
            // the track’s base size by its flex factor; otherwise, the track’s base size.
            for (auto& track : tracks) {
                if (track.max_track_sizing_function.is_flexible_length()) {
                    if (track.max_track_sizing_function.flex_factor() > 1) {
                        result = max(result, track.base_size / CSSPixels::nearest_value_for(track.max_track_sizing_function.flex_factor()));
                    } else {
                        result = max(result, track.base_size / 1);
                    }
                }
            }
            // For each grid item that crosses a flexible track, the result of finding the size of an fr using all the
            // grid tracks that the item crosses and a space to fill of the item’s max-content contribution.
            for (auto& item : m_grid_items) {
                Vector<GridTrack&> spanned_tracks;
                bool crosses_flexible_track = false;
                for_each_spanned_track_by_item(item, dimension, [&](GridTrack& track) {
                    spanned_tracks.append(track);
                    if (track.max_track_sizing_function.is_flexible_length())
                        crosses_flexible_track = true;
                });

                if (crosses_flexible_track)
                    result = max(result, find_the_size_of_an_fr(spanned_tracks, calculate_max_content_contribution(item, dimension)));
            }

            return result;
        }
    }();

    // 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_and_gaps) {
        if (track.max_track_sizing_function.is_flexible_length()) {
            auto scaled_fraction = CSSPixels::nearest_value_for(track.max_track_sizing_function.flex_factor()) * flex_fraction;
            if (scaled_fraction > track.base_size) {
                track.base_size = scaled_fraction;
            }
        }
    }
}

void GridFormattingContext::stretch_auto_tracks(GridDimension dimension)
{
    // https://www.w3.org/TR/css-grid-2/#algo-stretch
    // 12.8. Stretch auto Tracks
    // 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.

    auto content_distribution_property_is_normal_or_stretch = false;
    if (dimension == GridDimension::Column) {
        auto const& justify_content = grid_container().computed_values().justify_content();
        content_distribution_property_is_normal_or_stretch = justify_content == CSS::JustifyContent::Normal || justify_content == CSS::JustifyContent::Stretch;
    } else {
        auto const& align_content = grid_container().computed_values().align_content();
        content_distribution_property_is_normal_or_stretch = align_content == CSS::AlignContent::Normal || align_content == CSS::AlignContent::Stretch;
    }

    if (!content_distribution_property_is_normal_or_stretch)
        return;

    auto& tracks_and_gaps = dimension == GridDimension::Column ? m_grid_columns_and_gaps : m_grid_rows_and_gaps;
    auto& available_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;

    auto count_of_auto_max_sizing_tracks = 0;
    for (auto& track : tracks_and_gaps) {
        if (track.max_track_sizing_function.is_auto(available_size))
            count_of_auto_max_sizing_tracks++;
    }

    if (count_of_auto_max_sizing_tracks == 0)
        return;

    CSSPixels remaining_space = get_free_space(*m_available_space, dimension).to_px_or_zero();
    auto remaining_space_to_distribute_per_track = remaining_space / count_of_auto_max_sizing_tracks;
    for (auto& track : tracks_and_gaps) {
        if (!track.max_track_sizing_function.is_auto(available_size))
            continue;
        track.base_size += remaining_space_to_distribute_per_track;
    }
}

void GridFormattingContext::run_track_sizing(GridDimension dimension)
{
    // https://www.w3.org/TR/css-grid-2/#algo-track-sizing
    // 12.3. Track Sizing Algorithm

    // 1. Initialize Track Sizes
    initialize_track_sizes(dimension);

    // 2. Resolve Intrinsic Track Sizes
    resolve_intrinsic_track_sizes(dimension);

    // 3. Maximize Tracks
    maximize_tracks(dimension);

    // 4. Expand Flexible Tracks
    expand_flexible_tracks(dimension);

    // 5. Expand Stretched auto Tracks
    stretch_auto_tracks(dimension);

    // 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_grid_areas()
{
    // 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.
    auto const& rows = grid_container().computed_values().grid_template_areas();

    HashMap<String, GridArea> grid_areas;

    auto find_area_rectangle = [&](size_t x_start, size_t y_start, String const& name) {
        bool invalid = false;
        size_t x_end = x_start;
        size_t y_end = y_start;
        while (x_end < rows[y_start].size() && rows[y_start][x_end] == name)
            x_end++;
        while (y_end < rows.size() && rows[y_end][x_start] == name)
            y_end++;
        for (size_t y = y_start; y < y_end; y++) {
            for (size_t x = x_start; x < x_end; x++) {
                if (rows[y][x] != name) {
                    // If a named grid area spans multiple grid cells, but those cells do not form a single filled-in rectangle, the declaration is invalid.
                    invalid = true;
                    break;
                }
            }
        }
        grid_areas.set(name, { name, y_start, y_end, x_start, x_end, invalid });
    };

    for (size_t y = 0; y < rows.size(); y++) {
        for (size_t x = 0; x < rows[y].size(); x++) {
            auto name = rows[y][x];
            if (auto grid_area = grid_areas.get(name); grid_area.has_value())
                continue;
            find_area_rectangle(x, y, name);
        }
    }

    size_t max_column_line_index_of_area = 0;
    size_t max_row_line_index_of_area = 0;
    for (auto const& grid_area : grid_areas) {
        max_column_line_index_of_area = max(max_column_line_index_of_area, grid_area.value.column_end);
        max_row_line_index_of_area = max(max_row_line_index_of_area, grid_area.value.row_end);
    }

    if (max_column_line_index_of_area >= m_column_lines.size())
        m_column_lines.resize(max_column_line_index_of_area + 1);
    if (max_row_line_index_of_area >= m_row_lines.size())
        m_row_lines.resize(max_row_line_index_of_area + 1);

    // https://www.w3.org/TR/css-grid-2/#implicitly-assigned-line-name
    // 7.3.2. Implicitly-Assigned Line Names
    // The grid-template-areas property generates implicitly-assigned line names from the named grid areas in the
    // template. For each named grid area foo, four implicitly-assigned line names are created: two named foo-start,
    // naming the row-start and column-start lines of the named grid area, and two named foo-end, naming the row-end
    // and column-end lines of the named grid area.
    for (auto const& it : grid_areas) {
        auto const& grid_area = it.value;
        m_column_lines[grid_area.column_start].append({ .name = MUST(String::formatted("{}-start", grid_area.name)), .implicit = true });
        m_column_lines[grid_area.column_end].append({ .name = MUST(String::formatted("{}-end", grid_area.name)), .implicit = true });
        m_row_lines[grid_area.row_start].append({ .name = MUST(String::formatted("{}-start", grid_area.name)), .implicit = true });
        m_row_lines[grid_area.row_end].append({ .name = MUST(String::formatted("{}-end", grid_area.name)), .implicit = true });
    }
}

void GridFormattingContext::place_grid_items()
{
    auto grid_template_columns = grid_container().computed_values().grid_template_columns();
    auto grid_template_rows = grid_container().computed_values().grid_template_rows();
    auto column_tracks_count = m_column_lines.size() - 1;
    auto row_tracks_count = m_row_lines.size() - 1;

    // 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.
    HashMap<int, Vector<GC::Ref<Box const>>> order_item_bucket;
    grid_container().for_each_child_of_type<Box>([&](Box& child_box) {
        if (can_skip_is_anonymous_text_run(child_box))
            return IterationDecision::Continue;

        if (child_box.is_out_of_flow(*this))
            return IterationDecision::Continue;

        child_box.set_grid_item(true);

        auto& order_bucket = order_item_bucket.ensure(child_box.computed_values().order());
        order_bucket.append(child_box);

        return IterationDecision::Continue;
    });

    m_occupation_grid = OccupationGrid(column_tracks_count, row_tracks_count);

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

    auto keys = order_item_bucket.keys();
    quick_sort(keys, [](auto& a, auto& b) { return a < b; });

    // FIXME: 0. Generate anonymous grid items

    // 1. Position anything that's not auto-positioned.
    for (auto key : keys) {
        auto& boxes_to_place = order_item_bucket.get(key).value();
        for (size_t i = 0; i < boxes_to_place.size(); i++) {
            auto const& child_box = boxes_to_place[i];
            auto const& computed_values = child_box->computed_values();
            if (is_auto_positioned_track(computed_values.grid_row_start(), computed_values.grid_row_end())
                || is_auto_positioned_track(computed_values.grid_column_start(), computed_values.grid_column_end()))
                continue;
            place_item_with_row_and_column_position(child_box);
            boxes_to_place.remove(i);
            i--;
        }
    }

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

    // 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.
    for (auto key : keys) {
        auto& boxes_to_place = order_item_bucket.get(key).value();
        for (auto const& child_box : boxes_to_place) {
            auto const& grid_column_start = child_box->computed_values().grid_column_start();
            auto const& grid_column_end = child_box->computed_values().grid_column_end();

            CSS::CalculationResolutionContext resolution_context { .length_resolution_context = CSS::Length::ResolutionContext::for_layout_node(child_box) };

            int column_span = 1;
            if (grid_column_start.is_span())
                column_span = grid_column_start.span().resolved(resolution_context).value();
            else if (grid_column_end.is_span())
                column_span = grid_column_end.span().resolved(resolution_context).value();

            if (column_span - 1 > m_occupation_grid.max_column_index())
                m_occupation_grid.set_max_column_index(column_span - 1);
        }
    }

    // 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 (auto key : keys) {
        auto& boxes_to_place = order_item_bucket.get(key).value();
        for (size_t i = 0; i < boxes_to_place.size(); i++) {
            auto const& child_box = boxes_to_place[i];
            auto const& computed_values = child_box->computed_values();
            // 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_track(computed_values.grid_column_start(), 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);

            boxes_to_place.remove(i);
            i--;

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

    // NOTE: When final implicit grid sizes are known, we can offset their positions so leftmost grid track has 0 index.
    for (auto& item : m_grid_items) {
        item.row = item.row.value() - m_occupation_grid.min_row_index();
        item.column = item.column.value() - m_occupation_grid.min_column_index();
    }
}

void GridFormattingContext::determine_grid_container_height()
{
    CSSPixels total_y = 0;
    for (auto& grid_row : m_grid_rows_and_gaps)
        total_y += grid_row.base_size;
    m_automatic_content_height = total_y;
}

Alignment GridFormattingContext::alignment_for_item(Box const& box, GridDimension dimension) const
{
    if (dimension == GridDimension::Column) {
        switch (box.computed_values().justify_self()) {
        case CSS::JustifySelf::Auto:
            return to_alignment(grid_container().computed_values().justify_items());
        case CSS::JustifySelf::End:
            return Alignment::End;
        case CSS::JustifySelf::Normal:
            return Alignment::Normal;
        case CSS::JustifySelf::SelfStart:
            return Alignment::SelfStart;
        case CSS::JustifySelf::SelfEnd:
            return Alignment::SelfEnd;
        case CSS::JustifySelf::FlexStart:
            return Alignment::Start;
        case CSS::JustifySelf::FlexEnd:
            return Alignment::End;
        case CSS::JustifySelf::Center:
            return Alignment::Center;
        case CSS::JustifySelf::Baseline:
            return Alignment::Baseline;
        case CSS::JustifySelf::Start:
            return Alignment::Start;
        case CSS::JustifySelf::Stretch:
            return Alignment::Stretch;
        case CSS::JustifySelf::Safe:
            return Alignment::Safe;
        case CSS::JustifySelf::Unsafe:
            return Alignment::Unsafe;
        case CSS::JustifySelf::Left:
            return Alignment::Start;
        case CSS::JustifySelf::Right:
            return Alignment::End;
        default:
            VERIFY_NOT_REACHED();
        }
    }
    switch (box.computed_values().align_self()) {
    case CSS::AlignSelf::Auto:
        return to_alignment(grid_container().computed_values().align_items());
    case CSS::AlignSelf::End:
        return Alignment::End;
    case CSS::AlignSelf::Normal:
        return Alignment::Normal;
    case CSS::AlignSelf::SelfStart:
        return Alignment::SelfStart;
    case CSS::AlignSelf::SelfEnd:
        return Alignment::SelfEnd;
    case CSS::AlignSelf::FlexStart:
        return Alignment::Start;
    case CSS::AlignSelf::FlexEnd:
        return Alignment::End;
    case CSS::AlignSelf::Center:
        return Alignment::Center;
    case CSS::AlignSelf::Baseline:
        return Alignment::Baseline;
    case CSS::AlignSelf::Start:
        return Alignment::Start;
    case CSS::AlignSelf::Stretch:
        return Alignment::Stretch;
    case CSS::AlignSelf::Safe:
        return Alignment::Safe;
    case CSS::AlignSelf::Unsafe:
        return Alignment::Unsafe;
    default:
        VERIFY_NOT_REACHED();
    }
}

void GridFormattingContext::resolve_grid_item_sizes(GridDimension dimension)
{
    for (auto& item : m_grid_items) {
        CSSPixels containing_block_size = containing_block_size_for_item(item, dimension);
        Alignment alignment = alignment_for_item(item.box, dimension);

        auto const& preferred_size = item.preferred_size(dimension);

        struct ItemAlignment {
            CSSPixels margin_start;
            CSSPixels margin_end;
            CSSPixels size;
        };

        auto try_compute_size = [&item, containing_block_size, alignment, dimension](CSSPixels a_size, CSS::Size const& css_size) -> ItemAlignment {
            ItemAlignment result = {
                .margin_start = item.used_margin_start(dimension),
                .margin_end = item.used_margin_end(dimension),
                .size = a_size
            };

            // Auto margins absorb positive free space prior to alignment via the box alignment properties.
            auto free_space_left_for_margins = containing_block_size - result.size - item.used_margin_box_start(dimension) - item.used_margin_box_end(dimension);
            if (item.margin_start(dimension).is_auto() && item.margin_end(dimension).is_auto()) {
                result.margin_start = free_space_left_for_margins / 2;
                result.margin_end = free_space_left_for_margins / 2;
            } else if (item.margin_start(dimension).is_auto()) {
                result.margin_start = free_space_left_for_margins;
            } else if (item.margin_end(dimension).is_auto()) {
                result.margin_end = free_space_left_for_margins;
            } else if (css_size.is_auto() && !item.box->is_replaced_box()) {
                result.size += free_space_left_for_margins;
            }

            auto free_space_left_for_alignment = containing_block_size - a_size - item.used_margin_box_start(dimension) - item.used_margin_box_end(dimension);
            switch (alignment) {
            case Alignment::Normal:
            case Alignment::Stretch:
                break;
            case Alignment::Center:
                result.margin_start += free_space_left_for_alignment / 2;
                result.margin_end += free_space_left_for_alignment / 2;
                result.size = a_size;
                break;
            case Alignment::Baseline:
            case Alignment::Start:
                result.margin_end += free_space_left_for_alignment;
                result.size = a_size;
                break;
            case Alignment::End:
                result.margin_start += free_space_left_for_alignment;
                result.size = a_size;
                break;
            default:
                break;
            }

            return result;
        };

        AvailableSpace available_space {
            AvailableSize::make_definite(containing_block_size_for_item(item, GridDimension::Column)),
            AvailableSize::make_definite(containing_block_size_for_item(item, GridDimension::Row))
        };

        auto calculate_inner_size = [this, &item, dimension, available_space](CSS::Size const& size) {
            if (dimension == GridDimension::Column)
                return calculate_inner_width(item.box, available_space.width, size);
            return calculate_inner_height(item.box, available_space, size);
        };

        auto tentative_size_for_replaced_element = [this, &item, dimension, available_space](CSS::Size const& size) {
            if (dimension == GridDimension::Column)
                return tentative_width_for_replaced_element(item.box, size, available_space);
            return tentative_height_for_replaced_element(item.box, size, available_space);
        };

        ItemAlignment used_alignment;
        if (item.box->is_replaced_box() && item.box->has_natural_width()) {
            auto width = tentative_size_for_replaced_element(preferred_size);
            used_alignment = try_compute_size(width, item.preferred_size(dimension));
        } else {
            if (preferred_size.is_auto() || preferred_size.is_fit_content()) {
                auto fit_content_size = dimension == GridDimension::Column ? calculate_fit_content_width(item.box, available_space) : calculate_fit_content_height(item.box, available_space);
                used_alignment = try_compute_size(fit_content_size, preferred_size);
            } else {
                auto size_px = calculate_inner_size(preferred_size);
                used_alignment = try_compute_size(size_px, preferred_size);
            }
        }

        bool should_treat_maximum_size_as_none = dimension == GridDimension::Column ? should_treat_max_width_as_none(item.box, available_space.width) : should_treat_max_height_as_none(item.box, available_space.height);
        if (!should_treat_maximum_size_as_none) {
            auto const& maximum_size = item.maximum_size(dimension);
            auto max_size_px = calculate_inner_size(maximum_size);
            auto max_width_alignment = try_compute_size(max_size_px, maximum_size);
            if (used_alignment.size > max_width_alignment.size) {
                used_alignment = max_width_alignment;
            }
        }

        auto const& minimum_size = item.minimum_size(dimension);
        if (!minimum_size.is_auto()) {
            auto min_size_alignment = try_compute_size(calculate_inner_size(minimum_size), minimum_size);
            if (used_alignment.size < min_size_alignment.size) {
                used_alignment = min_size_alignment;
            }
        }

        if (dimension == GridDimension::Column) {
            item.used_values.margin_left = used_alignment.margin_start;
            item.used_values.margin_right = used_alignment.margin_end;
            item.used_values.set_content_width(used_alignment.size);
        } else {
            item.used_values.margin_top = used_alignment.margin_start;
            item.used_values.margin_bottom = used_alignment.margin_end;
            item.used_values.set_content_height(used_alignment.size);
        }
    }
}

void GridFormattingContext::resolve_track_spacing(GridDimension dimension)
{
    auto is_column_dimension = dimension == GridDimension::Column;

    auto total_gap_space = is_column_dimension ? m_available_space->width.to_px_or_zero() : m_available_space->height.to_px_or_zero();

    auto& grid_tracks = is_column_dimension ? m_grid_columns : m_grid_rows;
    for (auto& track : grid_tracks) {
        total_gap_space -= track.base_size;
    }
    total_gap_space = max(total_gap_space, 0);

    auto gap_track_count = is_column_dimension ? m_column_gap_tracks.size() : m_row_gap_tracks.size();
    if (gap_track_count == 0)
        return;

    CSSPixels space_between_tracks = 0;
    Alignment alignment;
    if (is_column_dimension) {
        alignment = to_alignment(grid_container().computed_values().justify_content());
    } else {
        alignment = to_alignment(grid_container().computed_values().align_content());
    }

    switch (alignment) {
    case Alignment::SpaceBetween:
        space_between_tracks = CSSPixels(total_gap_space / gap_track_count);
        break;
    case Alignment::SpaceAround:
        space_between_tracks = CSSPixels(total_gap_space / (gap_track_count + 1));
        break;
    case Alignment::SpaceEvenly:
        space_between_tracks = CSSPixels(total_gap_space / (gap_track_count + 2));
        break;
    case Alignment::Normal:
    case Alignment::Stretch:
    case Alignment::Start:
    case Alignment::End:
    case Alignment::Center:
    default:
        break;
    }

    auto const& computed_gap = is_column_dimension ? grid_container().computed_values().column_gap() : grid_container().computed_values().row_gap();
    auto const& available_size = is_column_dimension ? m_available_space->width.to_px_or_zero() : m_available_space->height.to_px_or_zero();
    space_between_tracks = max(space_between_tracks, gap_to_px(computed_gap, grid_container(), available_size));

    auto& gap_tracks = is_column_dimension ? m_column_gap_tracks : m_row_gap_tracks;
    for (auto& track : gap_tracks) {
        track.base_size = space_between_tracks;
    }
}

void GridFormattingContext::resolve_items_box_metrics(GridDimension dimension)
{
    for (auto& item : m_grid_items) {
        auto& computed_values = item.box->computed_values();

        CSSPixels containing_block_width = containing_block_size_for_item(item, GridDimension::Column);
        if (dimension == GridDimension::Column) {
            item.used_values.padding_right = computed_values.padding().right().to_px(grid_container(), containing_block_width);
            item.used_values.padding_left = computed_values.padding().left().to_px(grid_container(), containing_block_width);

            item.used_values.margin_right = computed_values.margin().right().to_px(grid_container(), containing_block_width);
            item.used_values.margin_left = computed_values.margin().left().to_px(grid_container(), containing_block_width);

            item.used_values.border_right = computed_values.border_right().width;
            item.used_values.border_left = computed_values.border_left().width;
        } else {
            item.used_values.padding_top = computed_values.padding().top().to_px(grid_container(), containing_block_width);
            item.used_values.padding_bottom = computed_values.padding().bottom().to_px(grid_container(), containing_block_width);

            item.used_values.margin_top = computed_values.margin().top().to_px(grid_container(), containing_block_width);
            item.used_values.margin_bottom = computed_values.margin().bottom().to_px(grid_container(), containing_block_width);

            item.used_values.border_top = computed_values.border_top().width;
            item.used_values.border_bottom = computed_values.border_bottom().width;
        }
    }
}

void GridFormattingContext::collapse_auto_fit_tracks_if_needed(GridDimension dimension)
{
    // 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.)
    auto& tracks = dimension == GridDimension::Column ? m_grid_columns : m_grid_rows;
    for (size_t track_index = 0; track_index < tracks.size(); track_index++) {
        if (!tracks[track_index].is_auto_fit)
            continue;
        if (m_occupation_grid.is_occupied(dimension == GridDimension::Column ? track_index : 0, dimension == GridDimension::Row ? track_index : 0))
            continue;

        // NOTE: A collapsed track is treated as having a fixed track sizing function of 0px
        tracks[track_index].min_track_sizing_function = CSS::GridSize(CSS::Length::make_px(0));
        tracks[track_index].max_track_sizing_function = CSS::GridSize(CSS::Length::make_px(0));
    }
}

CSSPixelRect GridFormattingContext::get_grid_area_rect(GridItem const& grid_item) const
{
    CSSPixelRect area_rect;

    auto place_into_track = [&](GridDimension dimension) {
        auto const& tracks_and_gaps = dimension == GridDimension::Column ? m_grid_columns_and_gaps : m_grid_rows_and_gaps;

        auto resolved_span = grid_item.span(dimension) * 2;
        auto gap_adjusted_position = grid_item.gap_adjusted_position(dimension);

        int start = gap_adjusted_position;
        int end = start + resolved_span;
        VERIFY(start <= end);

        auto grid_container_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;

        CSSPixels sum_of_base_sizes_including_gaps = 0;
        for (auto const& track : tracks_and_gaps) {
            sum_of_base_sizes_including_gaps += track.base_size;
        }

        Alignment alignment;
        if (dimension == GridDimension::Column) {
            alignment = to_alignment(grid_container().computed_values().justify_content());
        } else {
            alignment = to_alignment(grid_container().computed_values().align_content());
        }
        CSSPixels start_offset = 0;
        CSSPixels end_offset = 0;
        if (alignment == Alignment::Center || alignment == Alignment::SpaceAround || alignment == Alignment::SpaceEvenly) {
            auto free_space = grid_container_size.to_px_or_zero() - sum_of_base_sizes_including_gaps;
            free_space = max(free_space, 0);
            start_offset = free_space / 2;
            end_offset = free_space / 2;
        } else if (alignment == Alignment::End) {
            auto free_space = grid_container_size.to_px_or_zero() - sum_of_base_sizes_including_gaps;
            start_offset = free_space;
            end_offset = free_space;
        }

        for (int i = 0; i < min(start, tracks_and_gaps.size()); i++)
            start_offset += tracks_and_gaps[i].base_size;
        for (int i = 0; i < min(end, tracks_and_gaps.size()); i++) {
            end_offset += tracks_and_gaps[i].base_size;
        }

        if (dimension == GridDimension::Column) {
            area_rect.set_x(start_offset);
            area_rect.set_width(end_offset - start_offset);
        } else {
            area_rect.set_y(start_offset);
            area_rect.set_height(end_offset - start_offset);
        }
    };

    auto place_into_track_formed_by_last_line_and_grid_container_padding_edge = [&](GridDimension dimension) {
        VERIFY(grid_item.box->is_absolutely_positioned());
        auto const& tracks_and_gaps = dimension == GridDimension::Column ? m_grid_columns_and_gaps : m_grid_rows_and_gaps;
        CSSPixels offset = 0;
        for (auto const& row_track : tracks_and_gaps) {
            offset += row_track.base_size;
        }
        CSSPixels size = dimension == GridDimension::Column ? m_grid_container_used_values.padding_right : m_grid_container_used_values.padding_bottom;
        if (dimension == GridDimension::Column) {
            area_rect.set_x(offset);
            area_rect.set_width(size);
        } else {
            area_rect.set_y(offset);
            area_rect.set_height(size);
        }
    };

    if (grid_item.row.has_value()) {
        if (grid_item.row == (int)m_grid_rows.size()) {
            place_into_track_formed_by_last_line_and_grid_container_padding_edge(GridDimension::Row);
        } else {
            place_into_track(GridDimension::Row);
        }
    } else {
        // https://www.w3.org/TR/css-grid-2/#abspos-items
        // Instead of auto-placement, an auto value for a grid-placement property contributes a special line to the placement whose position
        // is that of the corresponding padding edge of the grid container (the padding edge of the scrollable area, if the grid container
        // overflows). These lines become the first and last lines (0th and -0th) of the augmented grid used for positioning absolutely-positioned items.
        CSSPixels height = 0;
        for (auto const& row_track : m_grid_rows_and_gaps) {
            height += row_track.base_size;
        }
        height += m_grid_container_used_values.padding_top;
        height += m_grid_container_used_values.padding_bottom;
        area_rect.set_height(height);
        area_rect.set_y(-m_grid_container_used_values.padding_top);
    }

    if (grid_item.column.has_value()) {
        if (grid_item.column == (int)m_grid_columns.size()) {
            place_into_track_formed_by_last_line_and_grid_container_padding_edge(GridDimension::Column);
        } else {
            place_into_track(GridDimension::Column);
        }
    } else {
        CSSPixels width = 0;
        for (auto const& col_track : m_grid_columns_and_gaps) {
            width += col_track.base_size;
        }
        width += m_grid_container_used_values.padding_left;
        width += m_grid_container_used_values.padding_right;
        area_rect.set_width(width);
        area_rect.set_x(-m_grid_container_used_values.padding_left);
    }

    return area_rect;
}

void GridFormattingContext::run(AvailableSpace const& available_space)
{
    // OPTIMIZATION: If we're in intrinsic sizing layout, but the grid container is not the
    //               box being measured, we can skip everything here.
    //               The parent formatting context has already figured out our size anyway.
    if (m_layout_mode == LayoutMode::IntrinsicSizing
        && !available_space.width.is_intrinsic_sizing_constraint()
        && !available_space.height.is_intrinsic_sizing_constraint()) {
        return;
    }

    m_available_space = available_space;

    init_grid_lines(GridDimension::Column);
    init_grid_lines(GridDimension::Row);

    build_grid_areas();

    auto const& grid_computed_values = grid_container().computed_values();

    // NOTE: We store explicit grid sizes to later use in determining the position of items with negative index.
    m_explicit_columns_line_count = m_column_lines.size();
    m_explicit_rows_line_count = m_row_lines.size();

    place_grid_items();

    initialize_grid_tracks_for_columns_and_rows();

    initialize_gap_tracks(available_space);

    collapse_auto_fit_tracks_if_needed(GridDimension::Column);
    collapse_auto_fit_tracks_if_needed(GridDimension::Row);

    for (auto& item : m_grid_items) {
        auto& computed_values = item.box->computed_values();

        // NOTE: As the containing blocks of grid items are created by implicit grid areas that are not present in the
        // layout tree, the initial value of has_definite_width/height computed by LayoutState::UsedValues::set_node
        // will be incorrect for anything other (auto, percentage, calculated) than fixed lengths.
        // Therefor, it becomes necessary to reset this value to indefinite.
        // TODO: Handle this in LayoutState::UsedValues::set_node
        if (!computed_values.width().is_length())
            item.used_values.set_indefinite_content_width();
        if (!computed_values.height().is_length())
            item.used_values.set_indefinite_content_height();

        if (item.box->is_replaced_box()) {
            auto& replaced_box = static_cast<Layout::ReplacedBox const&>(*item.box);
            // FIXME: This const_cast is gross.
            const_cast<Layout::ReplacedBox&>(replaced_box).prepare_for_replaced_layout();
        }
    }

    // Do the first pass of resolving grid items box metrics to compute values that are independent of a track width
    resolve_items_box_metrics(GridDimension::Column);

    run_track_sizing(GridDimension::Column);

    // Do the second pass of resolving box metrics to compute values that depend on a track width
    resolve_items_box_metrics(GridDimension::Column);

    // Once the sizes of column tracks, which determine the widths of the grid areas forming the containing blocks
    // for grid items, ara calculated, it becomes possible to determine the final widths of the grid items.
    resolve_grid_item_sizes(GridDimension::Column);

    // Do the first pass of resolving grid items box metrics to compute values that are independent of a track height
    resolve_items_box_metrics(GridDimension::Row);

    run_track_sizing(GridDimension::Row);

    // Do the second pass of resolving box metrics to compute values that depend on a track height
    resolve_items_box_metrics(GridDimension::Row);

    resolve_grid_item_sizes(GridDimension::Row);

    determine_grid_container_height();

    resolve_track_spacing(GridDimension::Column);

    resolve_track_spacing(GridDimension::Row);

    CSSPixels min_height = 0;
    if (!grid_computed_values.min_height().is_auto())
        min_height = calculate_inner_height(grid_container(), available_space, grid_computed_values.min_height());

    // If automatic grid container height is less than min-height, we need to re-run the track sizing algorithm
    if (m_automatic_content_height < min_height) {
        resolve_items_box_metrics(GridDimension::Row);

        AvailableSize width(available_space.width);
        AvailableSize height(AvailableSize::make_definite(min_height));
        m_available_space = AvailableSpace(width, height);
        run_track_sizing(GridDimension::Row);

        resolve_items_box_metrics(GridDimension::Row);

        resolve_grid_item_sizes(GridDimension::Row);

        determine_grid_container_height();
    }

    if (m_layout_mode == LayoutMode::IntrinsicSizing) {
        determine_intrinsic_size_of_grid_container(available_space);
        return;
    }

    for (auto& grid_item : m_grid_items) {
        CSSPixelPoint margin_offset = { grid_item.used_values.margin_box_left(), grid_item.used_values.margin_box_top() };
        auto const grid_area_rect = get_grid_area_rect(grid_item);
        grid_item.used_values.offset = grid_area_rect.top_left() + margin_offset;
        compute_inset(grid_item.box, grid_area_rect.size());

        auto available_space_for_children = AvailableSpace(AvailableSize::make_definite(grid_item.used_values.content_width()), AvailableSize::make_definite(grid_item.used_values.content_height()));
        grid_item.used_values.set_has_definite_width(true);
        grid_item.used_values.set_has_definite_height(true);
        if (auto independent_formatting_context = layout_inside(grid_item.box, LayoutMode::Normal, available_space_for_children))
            independent_formatting_context->parent_context_did_dimension_child_root_box();
    }

    auto serialize = [](auto const& tracks, auto const& lines) {
        CSS::GridTrackSizeList result;
        for (size_t i = 0; i < lines.size(); ++i) {
            auto const& names = lines[i];
            if (!names.is_empty()) {
                CSS::GridLineNames grid_line_names;
                for (auto const& [name, implicit] : names) {
                    if (!implicit)
                        grid_line_names.append(name);
                }
                result.append(CSS::GridLineNames { move(grid_line_names) });
            }

            if (i < tracks.size()) {
                auto const& track = tracks[i];
                result.append(CSS::ExplicitGridTrack { CSS::GridSize { CSS::LengthPercentage(CSS::Length::make_px(track.base_size)) } });
            }
        }
        return result;
    };

    auto grid_track_columns = serialize(m_grid_columns, m_column_lines);
    auto grid_track_rows = serialize(m_grid_rows, m_row_lines);

    // getComputedStyle() needs to return the resolved values of grid-template-columns and grid-template-rows
    // so they need to be saved in the state, and then assigned to paintables in LayoutState::commit()
    m_grid_container_used_values.set_grid_template_columns(CSS::GridTrackSizeListStyleValue::create(move(grid_track_columns)));
    m_grid_container_used_values.set_grid_template_rows(CSS::GridTrackSizeListStyleValue::create(move(grid_track_rows)));
}

// https://www.w3.org/TR/css-grid-2/#abspos-items
void GridFormattingContext::layout_absolutely_positioned_element(Box const& box)
{
    auto& box_state = m_state.get_mutable(box);
    auto const& computed_values = box.computed_values();

    auto grid_area_rect = [&] -> CSSPixelRect {
        // NOTE: Grid areas form containing blocks for abspos elements, but
        //       `Node::containing_block()` is not aware of that. Therefore, we need to
        //       find the closest grid item ancestor in order to identify grid area it belongs to.
        NodeWithStyle const* containing_grid_item = &box;
        while (containing_grid_item->parent() && containing_grid_item->parent() != &grid_container())
            containing_grid_item = containing_grid_item->parent();

        auto const& computed_values = containing_grid_item->computed_values();
        VERIFY(containing_grid_item);

        // NOTE: If abspos box is contained by in-flow grid item its grid position is already determined.
        if (containing_grid_item->is_grid_item()) {
            auto item = *m_grid_items.find_if([containing_grid_item](GridItem const& grid_item) {
                return grid_item.box == containing_grid_item;
            });
            return get_grid_area_rect(item);
        }

        GridItem item { as<Box>(*containing_grid_item), box_state, {}, {}, {}, {} };
        auto is_auto_row = is_auto_positioned_track(computed_values.grid_row_start(), computed_values.grid_row_end());
        auto is_auto_column = is_auto_positioned_track(computed_values.grid_column_start(), computed_values.grid_column_end());

        auto row_placement_position = resolve_grid_position(box, GridDimension::Row);
        auto column_placement_position = resolve_grid_position(box, GridDimension::Column);
        if (!is_auto_row) {
            item.row = row_placement_position.start;
            item.row_span = row_placement_position.span;
        }
        if (!is_auto_column) {
            item.column = column_placement_position.start;
            item.column_span = column_placement_position.span;
        }
        return get_grid_area_rect(item);
    }();

    auto available_width = AvailableSize::make_definite(grid_area_rect.width());
    auto available_height = AvailableSize::make_definite(grid_area_rect.height());
    AvailableSpace available_space { available_width, available_height };

    // The border computed values are not changed by the compute_height & width calculations below.
    // The spec only adjusts and computes sizes, insets and margins.
    box_state.border_left = box.computed_values().border_left().width;
    box_state.border_right = box.computed_values().border_right().width;
    box_state.border_top = box.computed_values().border_top().width;
    box_state.border_bottom = box.computed_values().border_bottom().width;
    box_state.padding_left = box.computed_values().padding().left().to_px(grid_container(), grid_area_rect.width());
    box_state.padding_right = box.computed_values().padding().right().to_px(grid_container(), grid_area_rect.width());
    box_state.padding_top = box.computed_values().padding().top().to_px(grid_container(), grid_area_rect.width());
    box_state.padding_bottom = box.computed_values().padding().bottom().to_px(grid_container(), grid_area_rect.width());

    compute_width_for_absolutely_positioned_element(box, available_space);

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

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

    compute_height_for_absolutely_positioned_element(box, available_space, BeforeOrAfterInsideLayout::After);

    if (computed_values.inset().left().is_auto() && computed_values.inset().right().is_auto()) {
        auto width_left_for_alignment = grid_area_rect.width() - box_state.margin_box_width();
        switch (alignment_for_item(box, GridDimension::Column)) {
        case Alignment::Normal:
        case Alignment::Stretch:
            break;
        case Alignment::Center:
            box_state.inset_left = width_left_for_alignment / 2;
            box_state.inset_right = width_left_for_alignment / 2;
            break;
        case Alignment::Start:
            box_state.inset_right = width_left_for_alignment;
            break;
        case Alignment::End:
            box_state.inset_left = width_left_for_alignment;
            break;
        default:
            break;
        }
    }

    if (computed_values.inset().top().is_auto() && computed_values.inset().bottom().is_auto()) {
        auto height_left_for_alignment = grid_area_rect.height() - box_state.margin_box_height();
        switch (alignment_for_item(box, GridDimension::Row)) {
        case Alignment::Baseline:
            // FIXME: Not implemented
        case Alignment::Stretch:
        case Alignment::Normal:
            break;
        case Alignment::Start:
        case Alignment::SelfStart:
            box_state.inset_bottom = height_left_for_alignment;
            break;
        case Alignment::End:
        case Alignment::SelfEnd: {
            box_state.inset_top = height_left_for_alignment;
            break;
        }
        case Alignment::Center:
            box_state.inset_top = height_left_for_alignment / 2;
            box_state.inset_bottom = height_left_for_alignment / 2;
            break;
        default:
            break;
        }
    }

    // If an absolutely positioned element’s containing block is generated by a grid container,
    // the containing block corresponds to the grid area determined by its grid-placement properties.
    // The offset properties (top/right/bottom/left) then indicate offsets inwards from the corresponding
    // edges of this containing block, as normal.
    CSSPixelPoint used_offset;
    used_offset.set_x(grid_area_rect.x() + box_state.inset_left + box_state.margin_box_left());
    used_offset.set_y(grid_area_rect.y() + box_state.inset_top + box_state.margin_box_top());

    box_state.set_content_offset(used_offset);

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

void GridFormattingContext::parent_context_did_dimension_child_root_box()
{
    if (m_layout_mode != LayoutMode::Normal)
        return;

    grid_container().for_each_child_of_type<Box>([&](Layout::Box& box) {
        if (box.is_absolutely_positioned()) {
            m_state.get_mutable(box).set_static_position_rect(calculate_static_position_rect(box));
        }
        return IterationDecision::Continue;
    });

    for (auto const& child : grid_container().contained_abspos_children()) {
        auto const& box = as<Box>(*child);
        layout_absolutely_positioned_element(box);
    }
}

void GridFormattingContext::determine_intrinsic_size_of_grid_container(AvailableSpace const& available_space)
{
    // https://www.w3.org/TR/css-grid-1/#intrinsic-sizes
    // The max-content size (min-content size) of a grid container is the sum of the grid container’s track sizes
    // (including gutters) in the appropriate axis, when the grid is sized under a max-content constraint (min-content constraint).

    if (available_space.height.is_intrinsic_sizing_constraint()) {
        CSSPixels grid_container_height = 0;
        for (auto& track : m_grid_rows_and_gaps) {
            grid_container_height += track.base_size;
        }
        m_grid_container_used_values.set_content_height(grid_container_height);
    }

    if (available_space.width.is_intrinsic_sizing_constraint()) {
        CSSPixels grid_container_width = 0;
        for (auto& track : m_grid_columns_and_gaps) {
            grid_container_width += track.base_size;
        }
        m_grid_container_used_values.set_content_width(grid_container_width);
    }
}

CSSPixels GridFormattingContext::automatic_content_width() const
{
    return m_grid_container_used_values.content_width();
}

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

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(AvailableSpace const& available_space, GridDimension dimension) 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.
    auto& available_size = dimension == GridDimension::Column ? available_space.width : available_space.height;
    auto& tracks = dimension == GridDimension::Column ? m_grid_columns_and_gaps : m_grid_rows_and_gaps;
    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_or_zero() - sum_base_sizes));
    }

    return available_size;
}

Optional<int> GridFormattingContext::get_nth_line_index_by_line_name(GridDimension dimension, String const& line_name, int nth_line)
{
    auto const& lines = dimension == GridDimension::Column ? m_column_lines : m_row_lines;
    size_t line_index = nth_line < 0 ? lines.size() + nth_line : nth_line - 1;
    // FIXME: If not enough lines with the 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.
    // Source: https://drafts.csswg.org/css-grid/#line-placement
    for (size_t actual_line_index = 0; actual_line_index < lines.size(); actual_line_index++) {
        for (auto const& line : lines[actual_line_index]) {
            if (line.name == line_name) {
                // https://drafts.csswg.org/css-grid/#line-placement
                // Contributes the nth grid line to the grid item’s placement.
                if (line_index == 0)
                    return static_cast<int>(actual_line_index);
                else
                    line_index--;
            }
        }
    }
    return {};
}

void GridFormattingContext::init_grid_lines(GridDimension dimension)
{
    auto const& grid_computed_values = grid_container().computed_values();
    auto const& lines_definition = dimension == GridDimension::Column ? grid_computed_values.grid_template_columns() : grid_computed_values.grid_template_rows();
    auto& lines = dimension == GridDimension::Column ? m_column_lines : m_row_lines;

    Vector<CSS::GridLineName> line_names;
    Function<void(CSS::GridTrackSizeList const&)> expand_lines_definition = [&](CSS::GridTrackSizeList const& lines_definition) {
        for (auto const& item : lines_definition.list()) {
            if (item.has<CSS::GridLineNames>()) {
                line_names.extend(item.get<CSS::GridLineNames>().names());
            } else if (item.has<CSS::ExplicitGridTrack>()) {
                auto const& explicit_track = item.get<CSS::ExplicitGridTrack>();
                if (explicit_track.is_default() || explicit_track.is_minmax()) {
                    lines.append(line_names);
                    line_names.clear();
                } else if (explicit_track.is_repeat()) {
                    int repeat_count = 0;
                    if (explicit_track.repeat().is_auto_fill() || explicit_track.repeat().is_auto_fit())
                        repeat_count = count_of_repeated_auto_fill_or_fit_tracks(dimension, explicit_track);
                    else
                        repeat_count = explicit_track.repeat().repeat_count();
                    auto const& repeat_track = explicit_track.repeat();
                    for (int i = 0; i < repeat_count; i++)
                        expand_lines_definition(repeat_track.grid_track_size_list());
                } else {
                    VERIFY_NOT_REACHED();
                }
            }
        }
    };

    expand_lines_definition(lines_definition);
    lines.append(line_names);
}

void OccupationGrid::set_occupied(int column_start, int column_end, int row_start, int row_end)
{
    for (int row_index = row_start; row_index < row_end; row_index++) {
        for (int column_index = column_start; column_index < column_end; column_index++) {
            m_min_column_index = min(m_min_column_index, column_index);
            m_max_column_index = max(m_max_column_index, column_index);
            m_min_row_index = min(m_min_row_index, row_index);
            m_max_row_index = max(m_max_row_index, row_index);

            m_occupation_grid.set(GridPosition { .row = row_index, .column = column_index });
        }
    }
}

bool OccupationGrid::is_occupied(int column_index, int row_index) const
{
    return m_occupation_grid.contains(GridPosition { row_index, column_index });
}

int GridItem::gap_adjusted_row() const
{
    return row.value() * 2;
}

int GridItem::gap_adjusted_column() const
{
    return column.value() * 2;
}

CSSPixels GridFormattingContext::calculate_grid_container_maximum_size(GridDimension dimension) const
{
    auto const& computed_values = grid_container().computed_values();
    if (dimension == GridDimension::Column)
        return calculate_inner_width(grid_container(), m_available_space->width, computed_values.max_width());
    return calculate_inner_height(grid_container(), m_available_space.value(), computed_values.max_height());
}

CSSPixels GridFormattingContext::calculate_min_content_size(GridItem const& item, GridDimension dimension) const
{
    if (dimension == GridDimension::Column) {
        return calculate_min_content_width(item.box);
    }
    return calculate_min_content_height(item.box, item.available_space().width.to_px_or_zero());
}

CSSPixels GridFormattingContext::calculate_max_content_size(GridItem const& item, GridDimension dimension) const
{
    if (dimension == GridDimension::Column) {
        return calculate_max_content_width(item.box);
    }
    return calculate_max_content_height(item.box, item.available_space().width.to_px_or_zero());
}

CSSPixels GridFormattingContext::containing_block_size_for_item(GridItem const& item, GridDimension dimension) const
{
    CSSPixels containing_block_size = 0;
    for_each_spanned_track_by_item(item, dimension, [&](GridTrack const& track) {
        containing_block_size += track.base_size;
    });
    return containing_block_size;
}

CSSPixels GridFormattingContext::calculate_min_content_contribution(GridItem const& item, GridDimension dimension) const
{
    auto available_space_for_item = item.available_space();

    auto should_treat_preferred_size_as_auto = [&] {
        if (dimension == GridDimension::Column)
            return should_treat_width_as_auto(item.box, available_space_for_item);
        return should_treat_height_as_auto(item.box, available_space_for_item);
    }();

    auto maximum_size = CSSPixels::max();
    if (auto const& css_maximum_size = item.maximum_size(dimension); css_maximum_size.is_length()) {
        maximum_size = css_maximum_size.length().to_px(item.box);
    }

    if (should_treat_preferred_size_as_auto) {
        auto result = item.add_margin_box_sizes(calculate_min_content_size(item, dimension), dimension);
        return min(result, maximum_size);
    }

    auto preferred_size = item.preferred_size(dimension);
    if (dimension == GridDimension::Column) {
        auto width = calculate_inner_width(item.box, m_available_space->width, preferred_size);
        return min(item.add_margin_box_sizes(width, dimension), maximum_size);
    }
    auto height = calculate_inner_height(item.box, *m_available_space, preferred_size);
    return min(item.add_margin_box_sizes(height, dimension), maximum_size);
}

CSSPixels GridFormattingContext::calculate_max_content_contribution(GridItem const& item, GridDimension dimension) const
{
    auto available_space_for_item = item.available_space();

    auto should_treat_preferred_size_as_auto = [&] {
        if (dimension == GridDimension::Column)
            return should_treat_width_as_auto(item.box, available_space_for_item);
        return should_treat_height_as_auto(item.box, available_space_for_item);
    }();

    auto maximum_size = CSSPixels::max();
    if (auto const& css_maximum_size = item.maximum_size(dimension); css_maximum_size.is_length()) {
        maximum_size = css_maximum_size.length().to_px(item.box);
    }

    auto preferred_size = item.preferred_size(dimension);
    if (should_treat_preferred_size_as_auto || preferred_size.is_fit_content()) {
        auto fit_content_size = dimension == GridDimension::Column ? calculate_fit_content_width(item.box, available_space_for_item) : calculate_fit_content_height(item.box, available_space_for_item);
        auto result = item.add_margin_box_sizes(fit_content_size, dimension);
        return min(result, maximum_size);
    }

    auto containing_block_size = containing_block_size_for_item(item, dimension);
    auto result = item.add_margin_box_sizes(preferred_size.to_px(grid_container(), containing_block_size), dimension);
    return min(result, maximum_size);
}

CSSPixels GridFormattingContext::calculate_limited_min_content_contribution(GridItem const& item, GridDimension dimension) const
{
    // The limited min-content contribution of an item is its min-content contribution,
    // 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.
    auto min_content_contribution = calculate_min_content_contribution(item, dimension);
    auto minimum_contribution = calculate_minimum_contribution(item, dimension);
    if (min_content_contribution < minimum_contribution)
        return minimum_contribution;

    auto should_treat_max_size_as_none = [&]() {
        switch (dimension) {
        case GridDimension::Row:
            return should_treat_max_height_as_none(grid_container(), m_available_space->height);
        case GridDimension::Column:
            return should_treat_max_width_as_none(grid_container(), m_available_space->width);
        default:
            VERIFY_NOT_REACHED();
        }
    }();

    // FIXME: limit by max track sizing function instead of grid container maximum size
    if (!should_treat_max_size_as_none) {
        auto max_size = calculate_grid_container_maximum_size(dimension);
        if (min_content_contribution > max_size)
            return max_size;
    }

    return min_content_contribution;
}

CSSPixels GridFormattingContext::calculate_limited_max_content_contribution(GridItem const& item, GridDimension dimension) const
{
    // The limited max-content contribution of an item is its max-content contribution,
    // 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.
    auto max_content_contribution = calculate_max_content_contribution(item, dimension);
    auto minimum_contribution = calculate_minimum_contribution(item, dimension);
    if (max_content_contribution < minimum_contribution)
        return minimum_contribution;

    // FIXME: limit by max track sizing function instead of grid container maximum size
    auto const& available_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;
    if (!should_treat_max_width_as_none(grid_container(), available_size)) {
        auto max_width = calculate_grid_container_maximum_size(dimension);
        if (max_content_contribution > max_width)
            return max_width;
    }

    return max_content_contribution;
}

CSSPixels GridFormattingContext::content_size_suggestion(GridItem const& item, GridDimension dimension) const
{
    // The content size suggestion is the min-content size in the relevant axis
    // FIXME: clamped, if it has a preferred aspect ratio, by any definite opposite-axis minimum and maximum sizes
    // converted through the aspect ratio.
    return calculate_min_content_size(item, dimension);
}

Optional<CSSPixels> GridFormattingContext::specified_size_suggestion(GridItem const& item, GridDimension dimension) const
{
    // https://www.w3.org/TR/css-grid-1/#specified-size-suggestion
    // If the item’s preferred size in the relevant axis is definite, then the specified size suggestion is that size.
    // It is otherwise undefined.
    auto has_definite_preferred_size = dimension == GridDimension::Column ? item.used_values.has_definite_width() : item.used_values.has_definite_height();
    if (has_definite_preferred_size) {
        // FIXME: consider margins, padding and borders because it is outer size.
        auto containing_block_size = containing_block_size_for_item(item, dimension);
        return item.preferred_size(dimension).to_px(item.box, containing_block_size);
    }

    return {};
}

Optional<CSSPixels> GridFormattingContext::transferred_size_suggestion(GridItem const& item, GridDimension dimension) const
{
    // https://www.w3.org/TR/css-grid-2/#transferred-size-suggestion
    // If the item has a preferred aspect ratio and its preferred size in the opposite axis is definite, then the transferred
    // size suggestion is that size (clamped by the opposite-axis minimum and maximum sizes if they are definite), converted
    // through the aspect ratio. It is otherwise undefined.
    if (!item.box->preferred_aspect_ratio().has_value()) {
        return {};
    }

    CSS::Size const& preferred_size_in_opposite_axis = item.preferred_size(dimension == GridDimension::Column ? GridDimension::Row : GridDimension::Column);
    if (preferred_size_in_opposite_axis.is_length()) {
        auto opposite_axis_size = preferred_size_in_opposite_axis.length().to_px(item.box);
        // FIXME: Clamp by opposite-axis minimum and maximum sizes if they are definite
        return opposite_axis_size * item.box->preferred_aspect_ratio().value();
    }

    return {};
}

CSSPixels GridFormattingContext::content_based_minimum_size(GridItem const& item, GridDimension dimension) const
{
    // https://www.w3.org/TR/css-grid-1/#content-based-minimum-size

    CSSPixels result = 0;
    // The content-based minimum size for a grid item in a given dimension is its specified size suggestion if it exists,
    if (auto specified_size_suggestion = this->specified_size_suggestion(item, dimension); specified_size_suggestion.has_value()) {
        result = specified_size_suggestion.value();
    }
    // otherwise its transferred size suggestion if that exists,
    else if (auto transferred_size_suggestion = this->transferred_size_suggestion(item, dimension); transferred_size_suggestion.has_value()) {
        result = transferred_size_suggestion.value();
    }
    // else its content size suggestion.
    else {
        result = content_size_suggestion(item, dimension);
    }

    // However, if in a given dimension the grid item spans only grid tracks that have a fixed max track sizing function, then
    // its specified size suggestion and content size suggestion in that dimension (and its input from this dimension to the
    // transferred size suggestion in the opposite dimension) are further clamped to less than or equal to the stretch fit into
    // the grid area’s maximum size in that dimension, as represented by the sum of those grid tracks’ max track sizing functions
    // plus any intervening fixed gutters.
    // FIXME: Account for intervening fixed gutters.
    auto const& tracks = dimension == GridDimension::Column ? m_grid_columns : m_grid_rows;
    auto const& available_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;
    auto item_track_index = item.raw_position(dimension);
    auto item_track_span = item.span(dimension);
    bool spans_only_tracks_with_limited_max_track_sizing_function = true;
    CSSPixels sum_of_max_sizing_functions = 0;
    for (size_t index = 0; index < item_track_span; index++) {
        auto const& track = tracks[item_track_index + index];
        if (!track.max_track_sizing_function.is_fixed(available_size)) {
            spans_only_tracks_with_limited_max_track_sizing_function = false;
            break;
        }
        sum_of_max_sizing_functions += track.max_track_sizing_function.length_percentage().to_px(item.box, m_available_space->width.to_px_or_zero());
    }
    if (spans_only_tracks_with_limited_max_track_sizing_function) {
        result = min(result, sum_of_max_sizing_functions);
    }

    // In all cases, the size suggestion is additionally clamped by the maximum size in the affected axis, if it’s definite.
    auto const& maximum_size = item.maximum_size(dimension);
    if (maximum_size.is_length()) {
        auto maximum_size_px = maximum_size.length().to_px(item.box);
        result = min(result, maximum_size_px);
    }

    // If the item is a compressible replaced element, and has a definite preferred size or maximum size in the relevant axis,
    // the size suggestion is capped by those sizes; for this purpose, any indefinite percentages in these sizes are resolved
    // against zero (and considered definite).
    // FIXME: "compressible replaced element" includes more elements than is_replaced_box().
    auto const& preferred_size = item.preferred_size(dimension);
    if (item.box->is_replaced_box() && (preferred_size.is_percentage() || maximum_size.is_percentage())) {
        // NOTE: Implements "for this purpose, any indefinite percentages in these sizes are resolved
        //       against zero (and considered definite)." part.
        result = 0;
    }

    return result;
}

CSSPixels GridFormattingContext::automatic_minimum_size(GridItem const& item, GridDimension dimension) const
{
    // To provide a more reasonable default minimum size for grid items, the used value of its automatic minimum size
    // in a given axis is the content-based minimum size if all of the following are true:
    // - it is not a scroll container
    // - it spans at least one track in that axis whose min track sizing function is auto
    // - if it spans more than one track in that axis, none of those tracks are flexible
    auto const& tracks = dimension == GridDimension::Column ? m_grid_columns : m_grid_rows;
    auto item_track_index = item.raw_position(dimension);
    auto item_track_span = item.span(dimension);

    AvailableSize const& available_size = dimension == GridDimension::Column ? m_available_space->width : m_available_space->height;

    bool spans_auto_tracks = false;
    bool spans_flexible_tracks = false;
    for (size_t index = 0; index < item_track_span; index++) {
        auto const& track = tracks[item_track_index + index];
        if (track.max_track_sizing_function.is_flexible_length())
            spans_flexible_tracks = true;
        if (track.min_track_sizing_function.is_auto(available_size))
            spans_auto_tracks = true;
    }
    if (spans_auto_tracks && !item.box->is_scroll_container() && (item_track_span == 1 || !spans_flexible_tracks)) {
        return content_based_minimum_size(item, dimension);
    }

    // Otherwise, the automatic minimum size is zero, as usual.
    return 0;
}

CSSPixels GridFormattingContext::calculate_minimum_contribution(GridItem const& item, GridDimension dimension) const
{
    // 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.

    auto preferred_size = item.preferred_size(dimension);
    auto should_treat_preferred_size_as_auto = [&] {
        if (dimension == GridDimension::Column)
            return should_treat_width_as_auto(item.box, item.available_space());
        return should_treat_height_as_auto(item.box, item.available_space());
    }();

    if (should_treat_preferred_size_as_auto) {
        auto minimum_size = item.minimum_size(dimension);
        if (minimum_size.is_auto())
            return item.add_margin_box_sizes(automatic_minimum_size(item, dimension), dimension);
        auto containing_block_size = containing_block_size_for_item(item, dimension);
        return item.add_margin_box_sizes(minimum_size.to_px(grid_container(), containing_block_size), dimension);
    }

    return calculate_min_content_contribution(item, dimension);
}

StaticPositionRect GridFormattingContext::calculate_static_position_rect(Box const& box) const
{
    // Result of this function is only used when containing block is not a grid container.
    // If the containing block is a grid container then static position is a grid area rect and
    // layout_absolutely_positioned_element() defined for GFC knows how to handle this case.
    StaticPositionRect static_position;
    auto const& box_state = m_state.get(box);
    static_position.rect = { { 0, 0 }, { box_state.content_width(), box_state.content_height() } };
    return static_position;
}

}

namespace AK {

template<>
struct Traits<Web::Layout::GridPosition> : public DefaultTraits<Web::Layout::GridPosition> {
    static unsigned hash(Web::Layout::GridPosition const& key) { return pair_int_hash(key.row, key.column); }
};

}