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

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

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

namespace Web::Layout {

GridFormattingContext::GridFormattingContext(LayoutState& state, BlockContainer const& block_container, FormattingContext* parent)
    : BlockFormattingContext(state, block_container, parent)
{
}

GridFormattingContext::~GridFormattingContext() = default;

void GridFormattingContext::run(Box const& box, LayoutMode, [[maybe_unused]] AvailableSpace const& available_width, [[maybe_unused]] AvailableSpace const& available_height)
{
    auto should_skip_is_anonymous_text_run = [&](Box& child_box) -> bool {
        if (child_box.is_anonymous() && !child_box.first_child_of_type<BlockContainer>()) {
            bool contains_only_white_space = true;
            child_box.for_each_in_subtree([&](auto const& node) {
                if (!is<TextNode>(node) || !static_cast<TextNode const&>(node).dom_node().data().is_whitespace()) {
                    contains_only_white_space = false;
                    return IterationDecision::Break;
                }
                return IterationDecision::Continue;
            });
            if (contains_only_white_space)
                return true;
        }
        return false;
    };

    auto maybe_add_column_to_occupation_grid = [](int needed_number_of_columns, Vector<Vector<bool>>& occupation_grid) -> void {
        int current_column_count = (int)occupation_grid[0].size();
        if (needed_number_of_columns <= current_column_count)
            return;
        for (auto& occupation_grid_row : occupation_grid)
            for (int idx = 0; idx < (needed_number_of_columns + 1) - current_column_count; idx++)
                occupation_grid_row.append(false);
    };

    auto maybe_add_row_to_occupation_grid = [](int needed_number_of_rows, Vector<Vector<bool>>& occupation_grid) -> void {
        if (needed_number_of_rows <= (int)occupation_grid.size())
            return;

        Vector<bool> new_occupation_grid_row;
        for (int idx = 0; idx < (int)occupation_grid[0].size(); idx++)
            new_occupation_grid_row.append(false);

        for (int idx = 0; idx < needed_number_of_rows - (int)occupation_grid.size(); idx++)
            occupation_grid.append(new_occupation_grid_row);
    };

    auto set_occupied_cells = [](int row_start, int row_end, int column_start, int column_end, Vector<Vector<bool>>& occupation_grid) -> void {
        for (int row_index = 0; row_index < (int)occupation_grid.size(); row_index++) {
            if (row_index >= row_start && row_index < row_end) {
                for (int column_index = 0; column_index < (int)occupation_grid[0].size(); column_index++) {
                    if (column_index >= column_start && column_index < column_end) {
                        occupation_grid[row_index][column_index] = true;
                    }
                }
            }
        }
    };

    // 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.
    struct PositionedBox {
        Box const& box;
        int row { 0 };
        int row_span { 1 };
        int column { 0 };
        int column_span { 1 };
        float computed_height { 0 };
    };
    Vector<PositionedBox> positioned_boxes;

    Vector<Vector<bool>> occupation_grid;
    Vector<bool> occupation_grid_row;
    for (int column_index = 0; column_index < max((int)box.computed_values().grid_template_columns().size(), 1); column_index++)
        occupation_grid_row.append(false);
    for (int row_index = 0; row_index < max((int)box.computed_values().grid_template_rows().size(), 1); row_index++)
        occupation_grid.append(occupation_grid_row);

    Vector<Box const&> boxes_to_place;
    box.for_each_child_of_type<Box>([&](Box& child_box) {
        if (should_skip_is_anonymous_text_run(child_box))
            return IterationDecision::Continue;
        boxes_to_place.append(child_box);
        return IterationDecision::Continue;
    });

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

    // FIXME: 0. Generate anonymous grid items

    // 1. Position anything that's not auto-positioned.
    for (size_t i = 0; i < boxes_to_place.size(); i++) {
        auto const& child_box = boxes_to_place[i];
        if (child_box.computed_values().grid_row_start().is_auto()
            || child_box.computed_values().grid_row_end().is_auto()
            || child_box.computed_values().grid_column_start().is_auto()
            || child_box.computed_values().grid_column_end().is_auto())
            continue;

        int row_start = child_box.computed_values().grid_row_start().position();
        int row_end = child_box.computed_values().grid_row_end().position();
        int column_start = child_box.computed_values().grid_column_start().position();
        int column_end = child_box.computed_values().grid_column_end().position();
        int row_span = 1;
        int column_span = 1;

        // https://drafts.csswg.org/css-grid/#grid-placement-int
        // [ <integer [−∞,−1]> | <integer [1,∞]> ] && <custom-ident>?
        // Contributes the Nth grid line to the grid item’s placement. If a negative integer is given, it
        // instead counts in reverse, starting from the end edge of the explicit grid.
        if (row_end < 0)
            row_end = static_cast<int>(occupation_grid.size()) + row_end + 2;
        if (column_end < 0)
            column_end = static_cast<int>(occupation_grid[0].size()) + column_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 are assumed to have that name for the purpose
        // of finding this position.

        // FIXME: An <integer> value of zero makes the declaration invalid.

        // https://drafts.csswg.org/css-grid/#grid-placement-errors
        // 8.3.1. Grid Placement Conflict Handling
        // If the placement for a grid item contains two lines, and the start line is further end-ward than
        // the end line, swap the two lines. If the start line is equal to the end line, remove the end
        // line.
        if (row_start > row_end) {
            auto temp = row_end;
            row_end = row_start;
            row_start = temp;
        }
        if (column_start > column_end) {
            auto temp = column_end;
            column_end = column_start;
            column_start = temp;
        }
        if (row_start != row_end)
            row_span = row_end - row_start;
        if (column_start != column_end)
            column_span = column_end - column_start;
        // FIXME: If the placement contains two spans, remove the one contributed by the end grid-placement
        // property.

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

        row_start -= 1;
        column_start -= 1;
        positioned_boxes.append({ child_box, row_start, row_span, column_start, column_span });

        maybe_add_row_to_occupation_grid(row_start + row_span, occupation_grid);
        maybe_add_column_to_occupation_grid(column_start + column_span, occupation_grid);
        set_occupied_cells(row_start, row_start + row_span, column_start, column_start + column_span, occupation_grid);
        boxes_to_place.remove(i);
        i--;
    }

    // 2. Process the items locked to a given row.
    // FIXME: Do "dense" packing
    for (size_t i = 0; i < boxes_to_place.size(); i++) {
        auto const& child_box = boxes_to_place[i];
        if (child_box.computed_values().grid_row_start().is_auto()
            || child_box.computed_values().grid_row_end().is_auto())
            continue;

        int row_start = child_box.computed_values().grid_row_start().position();
        int row_end = child_box.computed_values().grid_row_end().position();
        int row_span = 1;

        // https://drafts.csswg.org/css-grid/#grid-placement-int
        // [ <integer [−∞,−1]> | <integer [1,∞]> ] && <custom-ident>?
        // Contributes the Nth grid line to the grid item’s placement. If a negative integer is given, it
        // instead counts in reverse, starting from the end edge of the explicit grid.
        if (row_end < 0)
            row_end = static_cast<int>(occupation_grid.size()) + row_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 are assumed to have that name for the purpose
        // of finding this position.

        // FIXME: An <integer> value of zero makes the declaration invalid.

        // https://drafts.csswg.org/css-grid/#grid-placement-errors
        // 8.3.1. Grid Placement Conflict Handling
        // If the placement for a grid item contains two lines, and the start line is further end-ward than
        // the end line, swap the two lines. If the start line is equal to the end line, remove the end
        // line.
        if (row_start > row_end) {
            auto temp = row_end;
            row_end = row_start;
            row_start = temp;
        }
        if (row_start != row_end)
            row_span = row_end - row_start;
        // FIXME: If the placement contains two spans, remove the one contributed by the end grid-placement
        // property.

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

        row_start -= 1;
        maybe_add_row_to_occupation_grid(row_start + row_span, occupation_grid);

        int column_start = 0;
        int column_span = 1;
        bool found_available_column = false;
        for (int column_index = column_start; column_index < (int)occupation_grid[0].size(); column_index++) {
            if (!occupation_grid[0][column_index]) {
                found_available_column = true;
                column_start = column_index;
                break;
            }
        }
        if (!found_available_column) {
            column_start = occupation_grid[0].size();
            maybe_add_column_to_occupation_grid(column_start + column_span, occupation_grid);
        }
        set_occupied_cells(row_start, row_start + row_span, column_start, column_start + column_span, occupation_grid);

        positioned_boxes.append({ child_box, row_start, row_span, column_start, column_span });
        boxes_to_place.remove(i);
        i--;
    }

    // 3. Determine the columns in the implicit grid.
    // NOTE: "implicit grid" here is the same as the 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.
    // NOTE: Done in step 1, 2, and will be done in step 4.

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

        // 4.1.1. If the item has a definite column position:
        if (!child_box.computed_values().grid_column_start().is_auto()) {
            int column_start = child_box.computed_values().grid_column_start().position();
            int column_end = child_box.computed_values().grid_column_end().position();
            int column_span = 1;

            // https://drafts.csswg.org/css-grid/#grid-placement-int
            // [ <integer [−∞,−1]> | <integer [1,∞]> ] && <custom-ident>?
            // Contributes the Nth grid line to the grid item’s placement. If a negative integer is given, it
            // instead counts in reverse, starting from the end edge of the explicit grid.
            if (column_end < 0)
                column_end = static_cast<int>(occupation_grid[0].size()) + column_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 are assumed to have that name for the purpose
            // of finding this position.

            // FIXME: An <integer> value of zero makes the declaration invalid.

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

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

            column_start -= 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.
            auto_placement_cursor_x = column_start;
            if (column_start < auto_placement_cursor_x)
                auto_placement_cursor_y++;

            maybe_add_column_to_occupation_grid(auto_placement_cursor_x + 1, occupation_grid);
            maybe_add_row_to_occupation_grid(auto_placement_cursor_y + 1, occupation_grid);

            // 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 (!occupation_grid[auto_placement_cursor_y][column_start]) {
                    break;
                }
                auto_placement_cursor_y++;
                maybe_add_row_to_occupation_grid(auto_placement_cursor_y + 1, occupation_grid);
            }
            // 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.
            set_occupied_cells(auto_placement_cursor_y, auto_placement_cursor_y + 1, column_start, column_start + column_span, occupation_grid);

            positioned_boxes.append({ child_box, auto_placement_cursor_y, 1, column_start, column_span });
        }
        // 4.1.2. If the item has an automatic grid position in both axes:
        else {
            // 4.1.2.1. Increment the column position of the auto-placement cursor until either this item's grid
            // area does not overlap any occupied grid cells, or the cursor's column position, plus the item's
            // column span, overflow the number of columns in the implicit grid, as determined earlier in this
            // algorithm.
            auto column_start = 0;
            auto column_span = 1;
            auto row_start = 0;
            auto row_span = 1;
            auto found_unoccupied_cell = false;
            for (int row_index = auto_placement_cursor_y; row_index < (int)occupation_grid.size(); row_index++) {
                for (int column_index = auto_placement_cursor_x; column_index < (int)occupation_grid[0].size(); column_index++) {
                    if (!occupation_grid[row_index][column_index]) {
                        found_unoccupied_cell = true;
                        column_start = column_index;
                        row_start = row_index;
                        goto finish;
                    }
                    auto_placement_cursor_x = 0;
                }
                auto_placement_cursor_x = 0;
                auto_placement_cursor_y++;
            }
        finish:

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

            set_occupied_cells(row_start, row_start + row_span, column_start, column_start + column_span, occupation_grid);
            positioned_boxes.append({ child_box, row_start, row_span, column_start, column_span });
        }
        boxes_to_place.remove(i);
        i--;

        // FIXME: 4.2. For dense packing:
    }

    auto& box_state = m_state.get_mutable(box);
    for (auto& positioned_box : positioned_boxes) {
        auto& child_box_state = m_state.get_mutable(positioned_box.box);
        if (child_box_state.content_height() > positioned_box.computed_height)
            positioned_box.computed_height = child_box_state.content_height();
        (void)layout_inside(positioned_box.box, LayoutMode::Normal);
        if (child_box_state.content_height() > positioned_box.computed_height)
            positioned_box.computed_height = child_box_state.content_height();
    }

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

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

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

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

    // The grid sizing algorithm defines how to resolve these sizing constraints into used track sizes.

    struct GridTrack {
        CSS::GridTrackSize min_track_sizing_function;
        CSS::GridTrackSize max_track_sizing_function;
        float base_size { 0 };
        float growth_limit { 0 };
    };
    Vector<GridTrack> grid_rows;
    Vector<GridTrack> grid_columns;

    for (auto& column_size : box.computed_values().grid_template_columns())
        grid_columns.append({ column_size, column_size });
    for (auto& row_size : box.computed_values().grid_template_rows())
        grid_rows.append({ row_size, row_size });

    for (int column_index = grid_columns.size(); column_index < static_cast<int>(occupation_grid[0].size()); column_index++)
        grid_columns.append({ CSS::GridTrackSize::make_auto(), CSS::GridTrackSize::make_auto() });
    for (int row_index = grid_rows.size(); row_index < static_cast<int>(occupation_grid.size()); row_index++)
        grid_rows.append({ CSS::GridTrackSize::make_auto(), CSS::GridTrackSize::make_auto() });

    // https://drafts.csswg.org/css-grid/#algo-overview
    // 12.1. Grid Sizing Algorithm
    // FIXME: Deals with subgrids, min-content, and justify-content.. not implemented yet

    // https://drafts.csswg.org/css-grid/#algo-track-sizing
    // 12.3. Track Sizing Algorithm

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

    // 1. Initialize Track Sizes
    // 2. Resolve Intrinsic Track Sizes
    // 3. Maximize Tracks
    // 4. Expand Flexible Tracks
    // 5. [[#algo-stretch|Expand Stretched auto Tracks]]

    // https://drafts.csswg.org/css-grid/#algo-init
    // 12.4. Initialize Track Sizes

    // Initialize each track’s base size and growth limit.
    for (auto& grid_column : grid_columns) {
        // For each track, if the track’s min track sizing function is:
        switch (grid_column.min_track_sizing_function.type()) {
        // - A fixed sizing function
        // Resolve to an absolute length and use that size as the track’s initial base size.
        // Indefinite lengths cannot occur, as they’re treated as auto.
        case CSS::GridTrackSize::Type::Length:
            if (!grid_column.min_track_sizing_function.length().is_auto())
                grid_column.base_size = grid_column.min_track_sizing_function.length().to_px(box);
            break;
        case CSS::GridTrackSize::Type::Percentage:
            grid_column.base_size = grid_column.min_track_sizing_function.percentage().as_fraction() * box_state.content_width();
            break;
        // - An intrinsic sizing function
        // Use an initial base size of zero.
        case CSS::GridTrackSize::Type::FlexibleLength:
            break;
        default:
            VERIFY_NOT_REACHED();
        }

        // For each track, if the track’s max track sizing function is:
        switch (grid_column.max_track_sizing_function.type()) {
        // - A fixed sizing function
        // Resolve to an absolute length and use that size as the track’s initial growth limit.
        case CSS::GridTrackSize::Type::Length:
            if (!grid_column.max_track_sizing_function.length().is_auto())
                grid_column.growth_limit = grid_column.max_track_sizing_function.length().to_px(box);
            else
                // - An intrinsic sizing function
                // Use an initial growth limit of infinity.
                grid_column.growth_limit = -1;
            break;
        case CSS::GridTrackSize::Type::Percentage:
            grid_column.growth_limit = grid_column.max_track_sizing_function.percentage().as_fraction() * box_state.content_width();
            break;
        // - A flexible sizing function
        // Use an initial growth limit of infinity.
        case CSS::GridTrackSize::Type::FlexibleLength:
            grid_column.growth_limit = -1;
            break;
        default:
            VERIFY_NOT_REACHED();
        }
    }

    // Initialize each track’s base size and growth limit.
    for (auto& grid_row : grid_rows) {
        // For each track, if the track’s min track sizing function is:
        switch (grid_row.min_track_sizing_function.type()) {
        // - A fixed sizing function
        // Resolve to an absolute length and use that size as the track’s initial base size.
        // Indefinite lengths cannot occur, as they’re treated as auto.
        case CSS::GridTrackSize::Type::Length:
            if (!grid_row.min_track_sizing_function.length().is_auto())
                grid_row.base_size = grid_row.min_track_sizing_function.length().to_px(box);
            break;
        case CSS::GridTrackSize::Type::Percentage:
            grid_row.base_size = grid_row.min_track_sizing_function.percentage().as_fraction() * box_state.content_height();
            break;
        // - An intrinsic sizing function
        // Use an initial base size of zero.
        case CSS::GridTrackSize::Type::FlexibleLength:
            break;
        default:
            VERIFY_NOT_REACHED();
        }

        // For each track, if the track’s max track sizing function is:
        switch (grid_row.max_track_sizing_function.type()) {
        // - A fixed sizing function
        // Resolve to an absolute length and use that size as the track’s initial growth limit.
        case CSS::GridTrackSize::Type::Length:
            if (!grid_row.max_track_sizing_function.length().is_auto())
                grid_row.growth_limit = grid_row.max_track_sizing_function.length().to_px(box);
            else
                // - An intrinsic sizing function
                // Use an initial growth limit of infinity.
                grid_row.growth_limit = -1;
            break;
        case CSS::GridTrackSize::Type::Percentage:
            grid_row.growth_limit = grid_row.max_track_sizing_function.percentage().as_fraction() * box_state.content_height();
            break;
        // - A flexible sizing function
        // Use an initial growth limit of infinity.
        case CSS::GridTrackSize::Type::FlexibleLength:
            grid_row.growth_limit = -1;
            break;
        default:
            VERIFY_NOT_REACHED();
        }
    }

    // FIXME: In all cases, if the growth limit is less than the base size, increase the growth limit to match
    // the base size.

    // https://drafts.csswg.org/css-grid/#algo-content
    // 12.5. Resolve Intrinsic Track Sizes
    // This step resolves intrinsic track sizing functions to absolute lengths. First it resolves those
    // sizes based on items that are contained wholly within a single track. Then it gradually adds in
    // the space requirements of items that span multiple tracks, evenly distributing the extra space
    // across those tracks insofar as possible.

    // FIXME: 1. Shim baseline-aligned items so their intrinsic size contributions reflect their baseline
    // alignment. For the items in each baseline-sharing group, add a “shim” (effectively, additional
    // margin) on the start/end side (for first/last-baseline alignment) of each item so that, when
    // start/end-aligned together their baselines align as specified.

    // Consider these “shims” as part of the items’ intrinsic size contribution for the purpose of track
    // sizing, below. If an item uses multiple intrinsic size contributions, it can have different shims
    // for each one.

    // 2. Size tracks to fit non-spanning items: For each track with an intrinsic track sizing function and
    // not a flexible sizing function, consider the items in it with a span of 1:
    int index = 0;
    for (auto& grid_column : grid_columns) {
        if (!grid_column.min_track_sizing_function.is_intrinsic_track_sizing()) {
            ++index;
            continue;
        }

        Vector<Box const&> boxes_of_column;
        for (auto& positioned_box : positioned_boxes) {
            if (positioned_box.column == index && positioned_box.column_span == 1)
                boxes_of_column.append(positioned_box.box);
        }

        // - For min-content minimums:
        // If the track has a min-content min track sizing function, set its base size to the maximum of the
        // items’ min-content contributions, floored at zero.
        // FIXME: Not implemented yet min-content.

        // - For max-content minimums:
        // If the track has a max-content min track sizing function, set its base size to the maximum of the
        // items’ max-content contributions, floored at zero.
        // FIXME: Not implemented yet max-content.

        // - For auto minimums:
        // If the track has an auto min track sizing function and the grid container is being sized under a
        // min-/max-content constraint, set the track’s base size to the maximum of its items’ limited
        // min-/max-content contributions (respectively), floored at zero. The limited min-/max-content
        // contribution of an item is (for this purpose) its min-/max-content contribution (accordingly),
        // limited by the max track sizing function (which could be the argument to a fit-content() track
        // sizing function) if that is fixed and ultimately floored by its minimum contribution (defined
        // below).
        // FIXME: Not implemented yet min-/max-content.

        // Otherwise, set the track’s base size to the maximum of its items’ minimum contributions, floored
        // at zero. The minimum contribution of an item is the smallest outer size it can have.
        // Specifically, if the item’s computed preferred size behaves as auto or depends on the size of its
        // containing block in the relevant axis, its minimum contribution is the outer size that would
        // result from assuming the item’s used minimum size as its preferred size; else the item’s minimum
        // contribution is its min-content contribution. Because the minimum contribution often depends on
        // the size of the item’s content, it is considered a type of intrinsic size contribution.
        // For items with a specified minimum size of auto (the initial value), the minimum contribution is
        // usually equivalent to the min-content contribution—but can differ in some cases, see § 6.6
        // Automatic Minimum Size of Grid Items. Also, minimum contribution ≤ min-content contribution ≤
        // max-content contribution.
        float grid_column_width = 0;
        for (auto& box_of_column : boxes_of_column)
            grid_column_width = max(grid_column_width, calculate_min_content_width(box_of_column));
        grid_column.base_size = grid_column_width;

        // - For min-content maximums:
        // If the track has a min-content max track sizing function, set its growth limit to the maximum of
        // the items’ min-content contributions.
        // FIXME: Not implemented yet min-content maximums.

        // - For max-content maximums:
        // If the track has a max-content max track sizing function, set its growth limit to the maximum of
        // the items’ max-content contributions. For fit-content() maximums, furthermore clamp this growth
        // limit by the fit-content() argument.
        // FIXME: Not implemented yet max-content maximums.

        // In all cases, if a track’s growth limit is now less than its base size, increase the growth limit
        // to match the base size.
        if (grid_column.growth_limit != -1 && grid_column.growth_limit < grid_column.base_size)
            grid_column.growth_limit = grid_column.base_size;
        ++index;
    }

    index = 0;
    for (auto& grid_row : grid_rows) {
        if (!grid_row.min_track_sizing_function.is_intrinsic_track_sizing()) {
            ++index;
            continue;
        }

        Vector<PositionedBox&> positioned_boxes_of_row;
        for (auto& positioned_box : positioned_boxes) {
            if (positioned_box.row == index && positioned_box.row_span == 1)
                positioned_boxes_of_row.append(positioned_box);
        }

        // - For min-content minimums:
        // If the track has a min-content min track sizing function, set its base size to the maximum of the
        // items’ min-content contributions, floored at zero.
        // FIXME: Not implemented yet min-content.

        // - For max-content minimums:
        // If the track has a max-content min track sizing function, set its base size to the maximum of the
        // items’ max-content contributions, floored at zero.
        // FIXME: Not implemented yet max-content.

        // - For auto minimums:
        // If the track has an auto min track sizing function and the grid container is being sized under a
        // min-/max-content constraint, set the track’s base size to the maximum of its items’ limited
        // min-/max-content contributions (respectively), floored at zero. The limited min-/max-content
        // contribution of an item is (for this purpose) its min-/max-content contribution (accordingly),
        // limited by the max track sizing function (which could be the argument to a fit-content() track
        // sizing function) if that is fixed and ultimately floored by its minimum contribution (defined
        // below).
        // FIXME: Not implemented yet min-/max-content.

        // Otherwise, set the track’s base size to the maximum of its items’ minimum contributions, floored
        // at zero. The minimum contribution of an item is the smallest outer size it can have.
        // Specifically, if the item’s computed preferred size behaves as auto or depends on the size of its
        // containing block in the relevant axis, its minimum contribution is the outer size that would
        // result from assuming the item’s used minimum size as its preferred size; else the item’s minimum
        // contribution is its min-content contribution. Because the minimum contribution often depends on
        // the size of the item’s content, it is considered a type of intrinsic size contribution.
        // For items with a specified minimum size of auto (the initial value), the minimum contribution is
        // usually equivalent to the min-content contribution—but can differ in some cases, see § 6.6
        // Automatic Minimum Size of Grid Items. Also, minimum contribution ≤ min-content contribution ≤
        // max-content contribution.
        float grid_row_height = 0;
        for (auto& positioned_box : positioned_boxes_of_row)
            grid_row_height = max(grid_row_height, positioned_box.computed_height);
        grid_row.base_size = grid_row_height;

        // - For min-content maximums:
        // If the track has a min-content max track sizing function, set its growth limit to the maximum of
        // the items’ min-content contributions.
        // FIXME: Not implemented yet min-content maximums.

        // - For max-content maximums:
        // If the track has a max-content max track sizing function, set its growth limit to the maximum of
        // the items’ max-content contributions. For fit-content() maximums, furthermore clamp this growth
        // limit by the fit-content() argument.
        // FIXME: Not implemented yet max-content maximums.

        // In all cases, if a track’s growth limit is now less than its base size, increase the growth limit
        // to match the base size.
        if (grid_row.growth_limit != -1 && grid_row.growth_limit < grid_row.base_size)
            grid_row.growth_limit = grid_row.base_size;
        ++index;
    }

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

    // 3.1. For intrinsic minimums: First distribute extra space to base sizes of tracks with an intrinsic
    // min track sizing function, to accommodate these items’ minimum contributions.

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

    // 3.2. For content-based minimums: Next continue to distribute extra space to the base sizes of tracks
    // with a min track sizing function of min-content or max-content, to accommodate these items'
    // min-content contributions.

    // 3.3. For max-content minimums: Next, if the grid container is being sized under a max-content
    // constraint, continue to distribute extra space to the base sizes of tracks with a min track
    // sizing function of auto or max-content, to accommodate these items' limited max-content
    // contributions.

    // In all cases, continue to distribute extra space to the base sizes of tracks with a min track
    // sizing function of max-content, to accommodate these items' max-content contributions.

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

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

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

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

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

    // if the sum of the flexible sizing functions of all flexible tracks spanned by the item is greater
    // than or equal to one, distributing space to such tracks according to the ratios of their flexible
    // sizing functions rather than distributing space equally; and if the sum is less than one,
    // distributing that proportion of space according to the ratios of their flexible sizing functions
    // and the rest equally

    // FIXME: 5. If any track still has an infinite growth limit (because, for example, it had no items placed in
    // it or it is a flexible track), set its growth limit to its base size.

    // https://drafts.csswg.org/css-grid/#extra-space
    // 12.5.1. Distributing Extra Space Across Spanned Tracks

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

    // 2. For each accommodated item, considering only tracks the item spans:

    // 2.1. Find the space to distribute: Subtract the affected size of every spanned track (not just the
    // affected tracks) from the item’s size contribution, flooring it at zero. (For infinite growth
    // limits, substitute the track’s base size.) This remaining size contribution is the space to
    // distribute.
    // space = max(0, size contribution - ∑track-sizes)

    // 2.2. Distribute space up to limits:

    // Find the item-incurred increase for each affected track by: distributing the space equally among
    // these tracks, freezing a track’s item-incurred increase as its affected size + item-incurred
    // increase reaches its limit (and continuing to grow the unfrozen tracks as needed).

    // For base sizes, the limit is its growth limit. For growth limits, the limit is infinity if it is
    // marked as infinitely growable, and equal to the growth limit otherwise.

    // If the affected size was a growth limit and the track is not marked infinitely growable, then each
    // item-incurred increase will be zero.

    // 2.3. Distribute space beyond limits:

    // If extra space remains at this point, unfreeze and continue to distribute space to the
    // item-incurred increase of…

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

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

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

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

    // This step prioritizes the distribution of space for accommodating size contributions beyond the
    // tracks' current growth limits based on the types of their max track sizing functions.

    // 2.4. For each affected track, if the track’s item-incurred increase is larger than the track’s planned
    // increase set the track’s planned increase to that value.

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

    // https://drafts.csswg.org/css-grid/#algo-grow-tracks
    // 12.6. Maximize Tracks

    // 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).

    // 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.

    // 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.
    // FIXME: Do later as at the moment all growth limits are equal to base sizes.

    // 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.

    // First, find the grid’s used flex fraction:
    auto column_flex_factor_sum = 0;
    for (auto& grid_column : grid_columns) {
        if (grid_column.min_track_sizing_function.is_flexible_length())
            column_flex_factor_sum++;
    }
    // See 12.7.1.
    // 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.
    if (column_flex_factor_sum < 1)
        column_flex_factor_sum = 1;

    // See 12.7.1.
    float sized_column_widths = 0;
    for (auto& grid_column : grid_columns) {
        if (!grid_column.min_track_sizing_function.is_flexible_length())
            sized_column_widths += grid_column.base_size;
    }
    // Let leftover space be the space to fill minus the base sizes of the non-flexible grid tracks.
    double free_horizontal_space = box_state.content_width() - sized_column_widths;

    // If the free space is zero or if sizing the grid container under a min-content constraint:
    // The used flex fraction is zero.
    // FIXME: Add min-content constraint check.

    // Otherwise, if the free space is a definite length:
    // 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.
    if (free_horizontal_space > 0) {
        for (auto& grid_column : grid_columns) {
            if (grid_column.min_track_sizing_function.is_flexible_length()) {
                // See 12.7.1.
                // Let the hypothetical fr size be the leftover space divided by the flex factor sum.
                auto hypothetical_fr_size = static_cast<double>(1.0 / column_flex_factor_sum) * free_horizontal_space;
                // 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.
                grid_column.base_size = max(grid_column.base_size, hypothetical_fr_size);
            }
        }
    }

    // First, find the grid’s used flex fraction:
    auto row_flex_factor_sum = 0;
    for (auto& grid_row : grid_rows) {
        if (grid_row.min_track_sizing_function.is_flexible_length())
            row_flex_factor_sum++;
    }
    // See 12.7.1.
    // 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.
    if (row_flex_factor_sum < 1)
        row_flex_factor_sum = 1;

    // See 12.7.1.
    float sized_row_heights = 0;
    for (auto& grid_row : grid_rows) {
        if (!grid_row.min_track_sizing_function.is_flexible_length())
            sized_row_heights += grid_row.base_size;
    }
    // Let leftover space be the space to fill minus the base sizes of the non-flexible grid tracks.
    double free_vertical_space = box_state.content_height() - sized_row_heights;

    // If the free space is zero or if sizing the grid container under a min-content constraint:
    // The used flex fraction is zero.
    // FIXME: Add min-content constraint check.

    // Otherwise, if the free space is a definite length:
    // 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.
    if (free_vertical_space > 0) {
        for (auto& grid_row : grid_rows) {
            if (grid_row.min_track_sizing_function.is_flexible_length()) {
                // See 12.7.1.
                // Let the hypothetical fr size be the leftover space divided by the flex factor sum.
                auto hypothetical_fr_size = static_cast<double>(1.0 / row_flex_factor_sum) * free_vertical_space;
                // 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.
                grid_row.base_size = max(grid_row.base_size, hypothetical_fr_size);
            }
        }
    }

    // Otherwise, if the free space is an indefinite length:
    // FIXME: No tracks will have indefinite length as per current implementation.

    // The used flex fraction is the maximum of:
    // 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 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.

    // If using this flex fraction would cause the grid to be smaller than the grid container’s
    // min-width/height (or larger than the grid container’s max-width/height), then redo this step,
    // treating the free space as definite and the available grid space as equal to the grid container’s
    // inner size when it’s sized to its min-width/height (max-width/height).

    // 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.

    // https://drafts.csswg.org/css-grid/#algo-find-fr-size
    // 12.7.1. Find the Size of an fr

    // This algorithm finds the largest size that an fr unit can be without exceeding the target size.
    // It must be called with a set of grid tracks and some quantity of space to fill.

    // 1. Let leftover space be the space to fill minus the base sizes of the non-flexible grid tracks.

    // 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.

    // 3. Let the hypothetical fr size be the leftover space divided by the flex factor sum.

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

    // 5. Return the hypothetical fr size.

    // https://drafts.csswg.org/css-grid/#algo-stretch
    // 12.8. Stretch auto Tracks

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

    float remaining_horizontal_space = box_state.content_width() - used_horizontal_space;
    auto count_of_auto_max_column_tracks = 0;
    for (auto& grid_column : grid_columns) {
        if (grid_column.max_track_sizing_function.is_length() && grid_column.max_track_sizing_function.length().is_auto())
            count_of_auto_max_column_tracks++;
    }
    for (auto& grid_column : grid_columns) {
        if (grid_column.max_track_sizing_function.is_length() && grid_column.max_track_sizing_function.length().is_auto())
            grid_column.base_size = max(grid_column.base_size, remaining_horizontal_space / count_of_auto_max_column_tracks);
    }

    float used_vertical_space = 0;
    for (auto& grid_row : grid_rows) {
        if (!(grid_row.max_track_sizing_function.is_length() && grid_row.max_track_sizing_function.length().is_auto()))
            used_vertical_space += grid_row.base_size;
    }

    float remaining_vertical_space = box_state.content_height() - used_vertical_space;
    auto count_of_auto_max_row_tracks = 0;
    for (auto& grid_row : grid_rows) {
        if (grid_row.max_track_sizing_function.is_length() && grid_row.max_track_sizing_function.length().is_auto())
            count_of_auto_max_row_tracks++;
    }
    for (auto& grid_row : grid_rows) {
        if (grid_row.max_track_sizing_function.is_length() && grid_row.max_track_sizing_function.length().is_auto())
            grid_row.base_size = max(grid_row.base_size, remaining_vertical_space / count_of_auto_max_row_tracks);
    }

    // Do layout
    auto layout_box = [&](int row_start, int row_end, int column_start, int column_end, Box const& child_box) -> void {
        auto& child_box_state = m_state.get_mutable(child_box);
        float x_start = 0;
        float x_end = 0;
        float y_start = 0;
        float y_end = 0;
        for (int i = 0; i < column_start; i++)
            x_start += grid_columns[i].base_size;
        for (int i = 0; i < column_end; i++)
            x_end += grid_columns[i].base_size;
        for (int i = 0; i < row_start; i++)
            y_start += grid_rows[i].base_size;
        for (int i = 0; i < row_end; i++)
            y_end += grid_rows[i].base_size;
        child_box_state.set_content_width(x_end - x_start);
        child_box_state.set_content_height(y_end - y_start);
        child_box_state.offset = { x_start, y_start };
    };

    for (auto& positioned_box : positioned_boxes)
        layout_box(positioned_box.row, positioned_box.row + positioned_box.row_span, positioned_box.column, positioned_box.column + positioned_box.column_span, positioned_box.box);

    float total_y = 0;
    for (auto& grid_row : grid_rows)
        total_y += grid_row.base_size;
    m_automatic_content_height = total_y;
}

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

}