ladybird/Userland/Libraries/LibWeb/Layout/FlexFormattingContext.h

/*
 * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <LibWeb/Layout/Box.h>
#include <LibWeb/Layout/FormattingContext.h>

namespace Web::Layout {

class FlexFormattingContext final : public FormattingContext {
public:
    FlexFormattingContext(LayoutState&, Box const& flex_container, FormattingContext* parent);
    ~FlexFormattingContext();

    virtual bool inhibits_floating() const override { return true; }

    virtual void run(Box const&, LayoutMode, AvailableSpace const&) override;
    virtual CSSPixels automatic_content_width() const override;
    virtual CSSPixels automatic_content_height() const override;

    Box const& flex_container() const { return context_box(); }

    virtual bool can_determine_size_of_child() const override;
    virtual void determine_width_of_child(Box const&, AvailableSpace const&) override;
    virtual void determine_height_of_child(Box const&, AvailableSpace const&) override;

    virtual CSSPixelPoint calculate_static_position(Box const&) const override;

private:
    [[nodiscard]] bool should_treat_main_size_as_auto(Box const&) const;
    [[nodiscard]] bool should_treat_cross_size_as_auto(Box const&) const;

    [[nodiscard]] CSSPixels adjust_main_size_through_aspect_ratio_for_cross_size_min_max_constraints(Box const&, CSSPixels main_size, CSS::Size const& min_cross_size, CSS::Size const& max_cross_size) const;
    [[nodiscard]] CSSPixels calculate_main_size_from_cross_size_and_aspect_ratio(CSSPixels cross_size, double aspect_ratio) const;
    [[nodiscard]] CSSPixels calculate_cross_size_from_main_size_and_aspect_ratio(CSSPixels main_size, double aspect_ratio) const;

    void dump_items() const;

    struct DirectionAgnosticMargins {
        CSSPixels main_before { 0 };
        CSSPixels main_after { 0 };
        CSSPixels cross_before { 0 };
        CSSPixels cross_after { 0 };

        bool main_before_is_auto { false };
        bool main_after_is_auto { false };
        bool cross_before_is_auto { false };
        bool cross_after_is_auto { false };
    };

    struct FlexItem {
        JS::NonnullGCPtr<Box> box;
        Optional<CSS::FlexBasis> used_flex_basis {};
        bool used_flex_basis_is_definite { false };
        CSSPixels flex_base_size { 0 };
        CSSPixels hypothetical_main_size { 0 };
        CSSPixels hypothetical_cross_size { 0 };
        CSSPixels hypothetical_cross_size_with_margins() { return hypothetical_cross_size + margins.cross_before + margins.cross_after + borders.cross_after + borders.cross_before + padding.cross_after + padding.cross_before; }
        CSSPixels target_main_size { 0 };
        bool frozen { false };
        Optional<double> flex_factor {};
        double scaled_flex_shrink_factor { 0 };
        double desired_flex_fraction { 0 };

        CSSPixels outer_hypothetical_main_size() const
        {
            return hypothetical_main_size + margins.main_before + margins.main_after + borders.main_before + borders.main_after + padding.main_before + padding.main_after;
        }

        CSSPixels outer_target_main_size() const
        {
            return target_main_size + margins.main_before + margins.main_after + borders.main_before + borders.main_after + padding.main_before + padding.main_after;
        }

        CSSPixels outer_flex_base_size() const
        {
            return flex_base_size + margins.main_before + margins.main_after + borders.main_before + borders.main_after + padding.main_before + padding.main_after;
        }

        // The used main size of this flex item. Empty until determined.
        Optional<CSSPixels> main_size {};

        // The used cross size of this flex item. Empty until determined.
        Optional<CSSPixels> cross_size {};

        CSSPixels main_offset { 0 };
        CSSPixels cross_offset { 0 };
        DirectionAgnosticMargins margins {};
        DirectionAgnosticMargins borders {};
        DirectionAgnosticMargins padding {};
        bool is_min_violation { false };
        bool is_max_violation { false };

        CSSPixels add_main_margin_box_sizes(CSSPixels content_size) const
        {
            return content_size + margins.main_before + margins.main_after + borders.main_before + borders.main_after + padding.main_before + padding.main_after;
        }

        CSSPixels add_cross_margin_box_sizes(CSSPixels content_size) const
        {
            return content_size + margins.cross_before + margins.cross_after + borders.cross_before + borders.cross_after + padding.cross_before + padding.cross_after;
        }
    };

    struct FlexLine {
        Vector<FlexItem&> items;
        CSSPixels cross_size { 0 };
        CSSPixels remaining_free_space { 0 };
        double chosen_flex_fraction { 0 };

        double sum_of_flex_factor_of_unfrozen_items() const;
        double sum_of_scaled_flex_shrink_factor_of_unfrozen_items() const;
    };

    CSSPixels main_gap() const;
    CSSPixels cross_gap() const;
    bool has_definite_main_size(Box const&) const;
    bool has_definite_cross_size(Box const&) const;
    CSSPixels inner_main_size(Box const&) const;
    CSSPixels inner_cross_size(Box const&) const;
    bool has_main_min_size(Box const&) const;
    bool has_cross_min_size(Box const&) const;
    CSSPixels specified_main_max_size(Box const&) const;
    CSSPixels specified_cross_max_size(Box const&) const;
    bool is_cross_auto(Box const&) const;
    CSSPixels specified_main_min_size(Box const&) const;
    CSSPixels specified_cross_min_size(Box const&) const;
    bool has_main_max_size(Box const&) const;
    bool has_cross_max_size(Box const&) const;
    CSSPixels automatic_minimum_size(FlexItem const&) const;
    CSSPixels content_based_minimum_size(FlexItem const&) const;
    Optional<CSSPixels> specified_size_suggestion(FlexItem const&) const;
    Optional<CSSPixels> transferred_size_suggestion(FlexItem const&) const;
    CSSPixels content_size_suggestion(FlexItem const&) const;
    CSS::Size const& computed_main_size(Box const&) const;
    CSS::Size const& computed_main_min_size(Box const&) const;
    CSS::Size const& computed_main_max_size(Box const&) const;
    CSS::Size const& computed_cross_size(Box const&) const;
    CSS::Size const& computed_cross_min_size(Box const&) const;
    CSS::Size const& computed_cross_max_size(Box const&) const;

    CSSPixels get_pixel_width(Box const&, CSS::Size const&) const;
    CSSPixels get_pixel_height(Box const&, CSS::Size const&) const;

    bool flex_item_is_stretched(FlexItem const&) const;

    void set_main_size(Box const&, CSSPixels size);
    void set_cross_size(Box const&, CSSPixels size);
    void set_offset(Box const&, CSSPixels main_offset, CSSPixels cross_offset);
    void set_main_axis_first_margin(FlexItem&, CSSPixels margin);
    void set_main_axis_second_margin(FlexItem&, CSSPixels margin);

    void copy_dimensions_from_flex_items_to_boxes();

    void generate_anonymous_flex_items();

    void determine_available_space_for_items(AvailableSpace const&);

    void determine_flex_base_size_and_hypothetical_main_size(FlexItem&);

    void determine_main_size_of_flex_container();

    void collect_flex_items_into_flex_lines();

    void resolve_flexible_lengths();
    void resolve_flexible_lengths_for_line(FlexLine&);

    void resolve_cross_axis_auto_margins();

    void determine_hypothetical_cross_size_of_item(FlexItem&, bool resolve_percentage_min_max_sizes);

    void calculate_cross_size_of_each_flex_line();

    void handle_align_content_stretch();

    CSS::AlignItems alignment_for_item(Box const&) const;

    void determine_used_cross_size_of_each_flex_item();

    void distribute_any_remaining_free_space();

    void align_all_flex_items_along_the_cross_axis();

    void determine_flex_container_used_cross_size();

    void align_all_flex_lines();

    bool is_row_layout() const { return m_flex_direction == CSS::FlexDirection::Row || m_flex_direction == CSS::FlexDirection::RowReverse; }
    bool is_single_line() const { return flex_container().computed_values().flex_wrap() == CSS::FlexWrap::Nowrap; }
    bool is_direction_reverse() const { return m_flex_direction == CSS::FlexDirection::ColumnReverse || m_flex_direction == CSS::FlexDirection::RowReverse; }
    void populate_specified_margins(FlexItem&, CSS::FlexDirection) const;

    void determine_intrinsic_size_of_flex_container();
    [[nodiscard]] CSSPixels calculate_intrinsic_main_size_of_flex_container();
    [[nodiscard]] CSSPixels calculate_intrinsic_cross_size_of_flex_container();

    [[nodiscard]] CSSPixels calculate_cross_min_content_contribution(FlexItem const&, bool resolve_percentage_min_max_sizes) const;
    [[nodiscard]] CSSPixels calculate_cross_max_content_contribution(FlexItem const&, bool resolve_percentage_min_max_sizes) const;
    [[nodiscard]] CSSPixels calculate_main_min_content_contribution(FlexItem const&) const;
    [[nodiscard]] CSSPixels calculate_main_max_content_contribution(FlexItem const&) const;

    [[nodiscard]] CSSPixels calculate_min_content_main_size(FlexItem const&) const;
    [[nodiscard]] CSSPixels calculate_max_content_main_size(FlexItem const&) const;
    [[nodiscard]] CSSPixels calculate_min_content_cross_size(FlexItem const&) const;
    [[nodiscard]] CSSPixels calculate_max_content_cross_size(FlexItem const&) const;

    [[nodiscard]] CSSPixels calculate_fit_content_main_size(FlexItem const&) const;
    [[nodiscard]] CSSPixels calculate_fit_content_cross_size(FlexItem const&) const;

    CSSPixels calculate_clamped_fit_content_width(Box const&, AvailableSpace const&) const;

    virtual void parent_context_did_dimension_child_root_box() override;

    CSS::FlexBasis used_flex_basis_for_item(FlexItem const&) const;

    LayoutState::UsedValues& m_flex_container_state;

    Vector<FlexLine> m_flex_lines;
    Vector<FlexItem> m_flex_items;
    CSS::FlexDirection m_flex_direction {};

    struct AxisAgnosticAvailableSpace {
        AvailableSize main;
        AvailableSize cross;
        AvailableSpace space;
    };
    Optional<AxisAgnosticAvailableSpace> m_available_space_for_items;
    Optional<AxisAgnosticAvailableSpace> m_available_space_for_flex_container;
};

}