text: /*
   * Copyright (c) 2020-2022, Andreas Kling <kling@serenityos.org>
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #include <LibWeb/Dump.h>
  #include <LibWeb/Layout/BlockFormattingContext.h>
  #include <LibWeb/Layout/Box.h>
  #include <LibWeb/Layout/FlexFormattingContext.h>
  #include <LibWeb/Layout/FormattingContext.h>
  #include <LibWeb/Layout/InlineFormattingContext.h>
  #include <LibWeb/Layout/ReplacedBox.h>
  #include <LibWeb/Layout/SVGFormattingContext.h>
  #include <LibWeb/Layout/SVGSVGBox.h>
  #include <LibWeb/Layout/TableBox.h>
  #include <LibWeb/Layout/TableCellBox.h>
  #include <LibWeb/Layout/TableFormattingContext.h>
  
  namespace Web::Layout {
  
  FormattingContext::FormattingContext(Type type, FormattingState& state, Box const& context_box, FormattingContext* parent)
      : m_type(type)
      , m_parent(parent)
      , m_context_box(context_box)
      , m_state(state)
  {
  }
  
  FormattingContext::~FormattingContext() = default;
  
  bool FormattingContext::creates_block_formatting_context(const Box& box)
  {
      if (box.is_root_element())
          return true;
      if (box.is_floating())
          return true;
      if (box.is_absolutely_positioned())
          return true;
      if (box.is_inline_block())
          return true;
      if (is<TableCellBox>(box))
          return true;
  
      CSS::Overflow overflow_x = box.computed_values().overflow_x();
      if ((overflow_x != CSS::Overflow::Visible) && (overflow_x != CSS::Overflow::Clip))
          return true;
  
      CSS::Overflow overflow_y = box.computed_values().overflow_y();
      if ((overflow_y != CSS::Overflow::Visible) && (overflow_y != CSS::Overflow::Clip))
          return true;
  
      auto display = box.computed_values().display();
  
      if (display.is_flow_root_inside())
          return true;
  
      if (box.parent()) {
          auto parent_display = box.parent()->computed_values().display();
          if (parent_display.is_flex_inside()) {
              // FIXME: Flex items (direct children of the element with display: flex or inline-flex) if they are neither flex nor grid nor table containers themselves.
              if (!display.is_flex_inside())
                  return true;
          }
      }
  
      // FIXME: table-caption
      // FIXME: anonymous table cells
      // FIXME: Elements with contain: layout, content, or paint.
      // FIXME: grid
      // FIXME: multicol
      // FIXME: column-span: all
      return false;
  }
  
  OwnPtr<FormattingContext> FormattingContext::create_independent_formatting_context_if_needed(FormattingState& state, Box const& child_box)
  {
      if (!child_box.can_have_children())
          return {};
  
      auto child_display = child_box.computed_values().display();
  
      if (is<SVGSVGBox>(child_box))
          return make<SVGFormattingContext>(state, child_box, this);
  
      if (child_display.is_flex_inside())
          return make<FlexFormattingContext>(state, child_box, this);
  
      if (creates_block_formatting_context(child_box))
          return make<BlockFormattingContext>(state, verify_cast<BlockContainer>(child_box), this);
  
      if (child_display.is_table_inside())
          return make<TableFormattingContext>(state, verify_cast<TableBox>(child_box), this);
  
      VERIFY(is_block_formatting_context());
      if (child_box.children_are_inline())
          return make<InlineFormattingContext>(state, verify_cast<BlockContainer>(child_box), static_cast<BlockFormattingContext&>(*this));
  
      // The child box is a block container that doesn't create its own BFC.
      // It will be formatted by this BFC.
      if (!child_display.is_flow_inside()) {
          dbgln("FIXME: Child box doesn't create BFC, but inside is also not flow! display={}", child_display.to_string());
          // HACK: Instead of crashing, create a dummy formatting context that does nothing.
          // FIXME: Remove this once it's no longer needed. It currently swallows problem with standalone
          //        table-related boxes that don't get fixed up by CSS anonymous table box generation.
          struct DummyFormattingContext : public FormattingContext {
              DummyFormattingContext(FormattingState& state, Box const& box)
                  : FormattingContext(Type::Block, state, box)
              {
              }
              virtual void run(Box const&, LayoutMode) override { }
          };
          return make<DummyFormattingContext>(state, child_box);
      }
      VERIFY(child_box.is_block_container());
      VERIFY(child_display.is_flow_inside());
      return {};
  }
  
  OwnPtr<FormattingContext> FormattingContext::layout_inside(Box const& child_box, LayoutMode layout_mode)
  {
      if (!child_box.can_have_children())
          return {};
  
      auto independent_formatting_context = create_independent_formatting_context_if_needed(m_state, child_box);
      if (independent_formatting_context)
          independent_formatting_context->run(child_box, layout_mode);
      else
          run(child_box, layout_mode);
  
      return independent_formatting_context;
  }
  
  static float greatest_child_width(FormattingState const& state, Box const& box)
  {
      float max_width = 0;
      if (box.children_are_inline()) {
          for (auto& child : state.get(verify_cast<BlockContainer>(box)).line_boxes) {
              max_width = max(max_width, child.width());
          }
      } else {
          box.for_each_child_of_type<Box>([&](auto& child) {
              max_width = max(max_width, state.get(child).border_box_width());
          });
      }
      return max_width;
  }
  
  FormattingContext::ShrinkToFitResult FormattingContext::calculate_shrink_to_fit_widths(Box const& box)
  {
      // Calculate the preferred width by formatting the content without breaking lines
      // other than where explicit line breaks occur.
      (void)layout_inside(box, LayoutMode::OnlyRequiredLineBreaks);
      float preferred_width = greatest_child_width(m_state, box);
  
      // Also calculate the preferred minimum width, e.g., by trying all possible line breaks.
      // CSS 2.2 does not define the exact algorithm.
  
      (void)layout_inside(box, LayoutMode::AllPossibleLineBreaks);
      float preferred_minimum_width = greatest_child_width(m_state, box);
  
      return { preferred_width, preferred_minimum_width };
  }
  
  static Gfx::FloatSize solve_replaced_size_constraint(FormattingState const& state, float w, float h, ReplacedBox const& box)
  {
      // 10.4 Minimum and maximum widths: 'min-width' and 'max-width'
  
      auto const& containing_block = *box.containing_block();
      auto const& containing_block_state = state.get(containing_block);
      auto width_of_containing_block = CSS::Length::make_px(containing_block_state.content_width);
      auto height_of_containing_block = CSS::Length::make_px(containing_block_state.content_height);
  
      auto specified_min_width = box.computed_values().min_width().has_value() ? box.computed_values().min_width()->resolved(box, width_of_containing_block).to_px(box) : 0;
      auto specified_max_width = box.computed_values().max_width().has_value() ? box.computed_values().max_width()->resolved(box, width_of_containing_block).to_px(box) : w;
      auto specified_min_height = box.computed_values().min_height().has_value() ? box.computed_values().min_height()->resolved(box, height_of_containing_block).to_px(box) : 0;
      auto specified_max_height = box.computed_values().max_height().has_value() ? box.computed_values().max_height()->resolved(box, height_of_containing_block).to_px(box) : h;
  
      auto min_width = min(specified_min_width, specified_max_width);
      auto max_width = max(specified_min_width, specified_max_width);
      auto min_height = min(specified_min_height, specified_max_height);
      auto max_height = max(specified_min_height, specified_max_height);
  
      if (w > max_width)
          return { w, max(max_width * h / w, min_height) };
      if (w < min_width)
          return { max_width, min(min_width * h / w, max_height) };
      if (h > max_height)
          return { max(max_height * w / h, min_width), max_height };
      if (h < min_height)
          return { min(min_height * w / h, max_width), min_height };
      if ((w > max_width && h > max_height) && (max_width / w < max_height / h))
          return { max_width, max(min_height, max_width * h / w) };
      if ((w > max_width && h > max_height) && (max_width / w > max_height / h))
          return { max(min_width, max_height * w / h), max_height };
      if ((w < min_width && h < min_height) && (min_width / w < min_height / h))
          return { min(max_width, min_height * w / h), min_height };
      if ((w < min_width && h < min_height) && (min_width / w > min_height / h))
          return { min_width, min(max_height, min_width * h / w) };
      if (w < min_width && h > max_height)
          return { min_width, max_height };
      if (w > max_width && h < min_height)
          return { max_width, min_height };
      return { w, h };
  }
  
  float FormattingContext::compute_auto_height_for_block_level_element(FormattingState const& state, Box const& box)
  {
      if (creates_block_formatting_context(box))
          return compute_auto_height_for_block_formatting_context_root(state, verify_cast<BlockContainer>(box));
  
      auto const& box_state = state.get(box);
  
      // https://www.w3.org/TR/CSS22/visudet.html#normal-block
      // 10.6.3 Block-level non-replaced elements in normal flow when 'overflow' computes to 'visible'
  
      // The element's height is the distance from its top content edge to the first applicable of the following:
  
      // 1. the bottom edge of the last line box, if the box establishes a inline formatting context with one or more lines
      if (box.children_are_inline() && !box_state.line_boxes.is_empty()) {
          // Find the top content edge (if negative).
          float top_content_edge = 0;
          for (auto const& fragment : box_state.line_boxes.first().fragments()) {
              float fragment_top_content_edge = fragment.offset().y() - fragment.border_box_top();
              if (fragment_top_content_edge < top_content_edge)
                  top_content_edge = fragment_top_content_edge;
          }
          return box_state.line_boxes.last().bottom() - top_content_edge;
      }
  
      // 2. the bottom edge of the bottom (possibly collapsed) margin of its last in-flow child, if the child's bottom margin does not collapse with the element's bottom margin
      // FIXME: 3. the bottom border edge of the last in-flow child whose top margin doesn't collapse with the element's bottom margin
      if (!box.children_are_inline()) {
          Optional<float> top;
          Optional<float> bottom;
          box.for_each_child_of_type<Box>([&](Layout::Box& child_box) {
              if (child_box.is_absolutely_positioned() || child_box.is_floating())
                  return;
  
              // FIXME: Handle margin collapsing.
              auto const& child_box_state = state.get(child_box);
              float child_box_top = child_box_state.offset.y() - child_box_state.border_box_top();
              float child_box_bottom = child_box_state.offset.y() + child_box_state.content_height + child_box_state.margin_box_bottom();
  
              if (!top.has_value() || child_box_top < top.value())
                  top = child_box_top;
              if (!bottom.has_value() || child_box_bottom > bottom.value())
                  bottom = child_box_bottom;
          });
          return bottom.value_or(0) - top.value_or(0);
      }
  
      // 4. zero, otherwise
      return 0;
  }
  
  // https://www.w3.org/TR/CSS22/visudet.html#root-height
  float FormattingContext::compute_auto_height_for_block_formatting_context_root(FormattingState const& state, BlockContainer const& root)
  {
      // 10.6.7 'Auto' heights for block formatting context roots
      Optional<float> top;
      Optional<float> bottom;
  
      if (root.children_are_inline()) {
          // If it only has inline-level children, the height is the distance between
          // the top content edge and the bottom of the bottommost line box.
          auto const& line_boxes = state.get(root).line_boxes;
          top = 0;
          if (!line_boxes.is_empty()) {
              // Find the top edge (if negative).
              for (auto const& fragment : line_boxes.first().fragments()) {
                  float fragment_top_content_edge = fragment.offset().y();
                  if (!top.has_value() || fragment_top_content_edge < *top)
                      top = fragment_top_content_edge;
              }
              // Find the bottom edge.
              bottom = line_boxes.last().bottom();
          }
      } else {
          // If it has block-level children, the height is the distance between
          // the top margin-edge of the topmost block-level child box
          // and the bottom margin-edge of the bottommost block-level child box.
          root.for_each_child_of_type<Box>([&](Layout::Box& child_box) {
              // Absolutely positioned children are ignored,
              // and relatively positioned boxes are considered without their offset.
              // Note that the child box may be an anonymous block box.
              if (child_box.is_absolutely_positioned())
                  return IterationDecision::Continue;
  
              // FIXME: This doesn't look right.
              if ((root.computed_values().overflow_y() == CSS::Overflow::Visible) && child_box.is_floating())
                  return IterationDecision::Continue;
  
              auto const& child_box_state = state.get(child_box);
  
              float child_box_top = child_box_state.offset.y() - child_box_state.margin_box_top();
              float child_box_bottom = child_box_state.offset.y() + child_box_state.content_height + child_box_state.margin_box_bottom();
  
              if (!top.has_value() || child_box_top < top.value())
                  top = child_box_top;
  
              if (!bottom.has_value() || child_box_bottom > bottom.value())
                  bottom = child_box_bottom;
  
              return IterationDecision::Continue;
          });
          // In addition, if the element has any floating descendants
          // whose bottom margin edge is below the element's bottom content edge,
          // then the height is increased to include those edges.
          root.for_each_child_of_type<Box>([&](Layout::Box& child_box) {
              if (!child_box.is_floating())
                  return IterationDecision::Continue;
  
              auto const& child_box_state = state.get(child_box);
              float child_box_bottom = child_box_state.offset.y() + child_box_state.content_height + child_box_state.margin_box_bottom();
  
              if (!bottom.has_value() || child_box_bottom > bottom.value())
                  bottom = child_box_bottom;
  
              return IterationDecision::Continue;
          });
      }
      return bottom.value_or(0) - top.value_or(0);
  }
  
  // 10.3.2 Inline, replaced elements, https://www.w3.org/TR/CSS22/visudet.html#inline-replaced-width
  float FormattingContext::tentative_width_for_replaced_element(FormattingState const& state, ReplacedBox const& box, CSS::Length const& computed_width)
  {
      auto const& containing_block = *box.containing_block();
      auto height_of_containing_block = CSS::Length::make_px(state.get(containing_block).content_height);
      auto computed_height = box.computed_values().height().has_value() ? box.computed_values().height()->resolved(box, height_of_containing_block).resolved(box) : CSS::Length::make_auto();
  
      float used_width = computed_width.to_px(box);
  
      // If 'height' and 'width' both have computed values of 'auto' and the element also has an intrinsic width,
      // then that intrinsic width is the used value of 'width'.
      if (computed_height.is_auto() && computed_width.is_auto() && box.has_intrinsic_width())
          return box.intrinsic_width().value();
  
      // If 'height' and 'width' both have computed values of 'auto' and the element has no intrinsic width,
      // but does have an intrinsic height and intrinsic ratio;
      // or if 'width' has a computed value of 'auto',
      // 'height' has some other computed value, and the element does have an intrinsic ratio; then the used value of 'width' is:
      //
      //     (used height) * (intrinsic ratio)
      if ((computed_height.is_auto() && computed_width.is_auto() && !box.has_intrinsic_width() && box.has_intrinsic_height() && box.has_intrinsic_aspect_ratio())
          || (computed_width.is_auto() && box.has_intrinsic_aspect_ratio())) {
          return compute_height_for_replaced_element(state, box) * box.intrinsic_aspect_ratio().value();
      }
  
      // If 'height' and 'width' both have computed values of 'auto' and the element has an intrinsic ratio but no intrinsic height or width,
      // then the used value of 'width' is undefined in CSS 2.2. However, it is suggested that, if the containing block's width does not itself
      // depend on the replaced element's width, then the used value of 'width' is calculated from the constraint equation used for block-level,
      // non-replaced elements in normal flow.
  
      // Otherwise, if 'width' has a computed value of 'auto', and the element has an intrinsic width, then that intrinsic width is the used value of 'width'.
      if (computed_width.is_auto() && box.has_intrinsic_width())
          return box.intrinsic_width().value();
  
      // Otherwise, if 'width' has a computed value of 'auto', but none of the conditions above are met, then the used value of 'width' becomes 300px.
      // If 300px is too wide to fit the device, UAs should use the width of the largest rectangle that has a 2:1 ratio and fits the device instead.
      if (computed_width.is_auto())
          return 300;
  
      return used_width;
  }
  
  void FormattingContext::compute_width_for_absolutely_positioned_element(Box const& box)
  {
      if (is<ReplacedBox>(box))
          compute_width_for_absolutely_positioned_replaced_element(verify_cast<ReplacedBox>(box));
      else
          compute_width_for_absolutely_positioned_non_replaced_element(box);
  }
  
  void FormattingContext::compute_height_for_absolutely_positioned_element(Box const& box)
  {
      if (is<ReplacedBox>(box))
          compute_height_for_absolutely_positioned_replaced_element(verify_cast<ReplacedBox>(box));
      else
          compute_height_for_absolutely_positioned_non_replaced_element(box);
  }
  
  float FormattingContext::compute_width_for_replaced_element(FormattingState const& state, ReplacedBox const& box)
  {
      // 10.3.4 Block-level, replaced elements in normal flow...
      // 10.3.2 Inline, replaced elements
  
      auto zero_value = CSS::Length::make_px(0);
      auto const& containing_block = *box.containing_block();
      auto width_of_containing_block = CSS::Length::make_px(state.get(containing_block).content_width);
  
      auto margin_left = box.computed_values().margin().left.resolved(box, width_of_containing_block).resolved(box);
      auto margin_right = box.computed_values().margin().right.resolved(box, width_of_containing_block).resolved(box);
  
      // A computed value of 'auto' for 'margin-left' or 'margin-right' becomes a used value of '0'.
      if (margin_left.is_auto())
          margin_left = zero_value;
      if (margin_right.is_auto())
          margin_right = zero_value;
  
      auto specified_width = box.computed_values().width().has_value() ? box.computed_values().width()->resolved(box, width_of_containing_block).resolved(box) : CSS::Length::make_auto();
  
      // 1. The tentative used width is calculated (without 'min-width' and 'max-width')
      auto used_width = tentative_width_for_replaced_element(state, box, specified_width);
  
      // 2. The tentative used width is greater than 'max-width', the rules above are applied again,
      //    but this time using the computed value of 'max-width' as the computed value for 'width'.
      auto specified_max_width = box.computed_values().max_width().has_value() ? box.computed_values().max_width()->resolved(box, width_of_containing_block).resolved(box) : CSS::Length::make_auto();
      if (!specified_max_width.is_auto()) {
          if (used_width > specified_max_width.to_px(box)) {
              used_width = tentative_width_for_replaced_element(state, box, specified_max_width);
          }
      }
  
      // 3. If the resulting width is smaller than 'min-width', the rules above are applied again,
      //    but this time using the value of 'min-width' as the computed value for 'width'.
      auto specified_min_width = box.computed_values().min_width().has_value() ? box.computed_values().min_width()->resolved(box, width_of_containing_block).resolved(box) : CSS::Length::make_auto();
      if (!specified_min_width.is_auto()) {
          if (used_width < specified_min_width.to_px(box)) {
              used_width = tentative_width_for_replaced_element(state, box, specified_min_width);
          }
      }
  
      return used_width;
  }
  
  // 10.6.2 Inline replaced elements, block-level replaced elements in normal flow, 'inline-block' replaced elements in normal flow and floating replaced elements
  // https://www.w3.org/TR/CSS22/visudet.html#inline-replaced-height
  float FormattingContext::tentative_height_for_replaced_element(FormattingState const& state, ReplacedBox const& box, CSS::Length const& computed_height)
  {
      auto const& containing_block = *box.containing_block();
      auto width_of_containing_block = CSS::Length::make_px(state.get(containing_block).content_width);
      auto computed_width = box.computed_values().width().has_value() ? box.computed_values().width()->resolved(box, width_of_containing_block).resolved(box) : CSS::Length::make_auto();
  
      // If 'height' and 'width' both have computed values of 'auto' and the element also has
      // an intrinsic height, then that intrinsic height is the used value of 'height'.
      if (computed_width.is_auto() && computed_height.is_auto() && box.has_intrinsic_height())
          return box.intrinsic_height().value();
  
      // Otherwise, if 'height' has a computed value of 'auto', and the element has an intrinsic ratio then the used value of 'height' is:
      //
      //     (used width) / (intrinsic ratio)
      if (computed_height.is_auto() && box.has_intrinsic_aspect_ratio())
          return compute_width_for_replaced_element(state, box) / box.intrinsic_aspect_ratio().value();
  
      // Otherwise, if 'height' has a computed value of 'auto', and the element has an intrinsic height, then that intrinsic height is the used value of 'height'.
      if (computed_height.is_auto() && box.has_intrinsic_height())
          return box.intrinsic_height().value();
  
      // Otherwise, if 'height' has a computed value of 'auto', but none of the conditions above are met,
      // then the used value of 'height' must be set to the height of the largest rectangle that has a 2:1 ratio, has a height not greater than 150px,
      // and has a width not greater than the device width.
      if (computed_height.is_auto())
          return 150;
  
      return computed_height.to_px(box);
  }
  
  float FormattingContext::compute_height_for_replaced_element(FormattingState const& state, ReplacedBox const& box)
  {
      // 10.6.2 Inline replaced elements, block-level replaced elements in normal flow,
      // 'inline-block' replaced elements in normal flow and floating replaced elements
  
      auto const& containing_block = *box.containing_block();
      auto const& containing_block_state = state.get(containing_block);
      auto width_of_containing_block = CSS::Length::make_px(containing_block_state.content_width);
      auto height_of_containing_block = CSS::Length::make_px(containing_block_state.content_height);
      auto specified_width = box.computed_values().width().has_value() ? box.computed_values().width()->resolved(box, width_of_containing_block).resolved(box) : CSS::Length::make_auto();
      auto specified_height = box.computed_values().height().has_value() ? box.computed_values().height()->resolved(box, height_of_containing_block).resolved(box) : CSS::Length::make_auto();
  
      float used_height = tentative_height_for_replaced_element(state, box, specified_height);
  
      if (specified_width.is_auto() && specified_height.is_auto() && box.has_intrinsic_aspect_ratio()) {
          float w = tentative_width_for_replaced_element(state, box, specified_width);
          float h = used_height;
          used_height = solve_replaced_size_constraint(state, w, h, box).height();
      }
  
      return used_height;
  }
  
  void FormattingContext::compute_width_for_absolutely_positioned_non_replaced_element(Box const& box)
  {
      auto& containing_block_state = m_state.get(*box.containing_block());
      auto& box_state = m_state.get_mutable(box);
  
      auto width_of_containing_block = CSS::Length::make_px(containing_block_state.content_width);
      auto& computed_values = box.computed_values();
      auto zero_value = CSS::Length::make_px(0);
  
      auto margin_left = CSS::Length::make_auto();
      auto margin_right = CSS::Length::make_auto();
      const auto border_left = computed_values.border_left().width;
      const auto border_right = computed_values.border_right().width;
      const auto padding_left = computed_values.padding().left.resolved(box, width_of_containing_block).to_px(box);
      const auto padding_right = computed_values.padding().right.resolved(box, width_of_containing_block).to_px(box);
  
      auto try_compute_width = [&](const auto& a_width) {
          margin_left = computed_values.margin().left.resolved(box, width_of_containing_block).resolved(box);
          margin_right = computed_values.margin().right.resolved(box, width_of_containing_block).resolved(box);
  
          auto left = computed_values.offset().left.resolved(box, width_of_containing_block).resolved(box);
          auto right = computed_values.offset().right.resolved(box, width_of_containing_block).resolved(box);
          auto width = a_width;
  
          auto solve_for_left = [&] {
              return CSS::Length(containing_block_state.content_width - margin_left.to_px(box) - border_left - padding_left - width.to_px(box) - padding_right - border_right - margin_right.to_px(box) - right.to_px(box), CSS::Length::Type::Px);
          };
  
          auto solve_for_width = [&] {
              return CSS::Length(containing_block_state.content_width - left.to_px(box) - margin_left.to_px(box) - border_left - padding_left - padding_right - border_right - margin_right.to_px(box) - right.to_px(box), CSS::Length::Type::Px);
          };
  
          auto solve_for_right = [&] {
              return CSS::Length(containing_block_state.content_width - left.to_px(box) - margin_left.to_px(box) - border_left - padding_left - width.to_px(box) - padding_right - border_right - margin_right.to_px(box), CSS::Length::Type::Px);
          };
  
          // If all three of 'left', 'width', and 'right' are 'auto':
          if (left.is_auto() && width.is_auto() && right.is_auto()) {
              // First set any 'auto' values for 'margin-left' and 'margin-right' to 0.
              if (margin_left.is_auto())
                  margin_left = CSS::Length::make_px(0);
              if (margin_right.is_auto())
                  margin_right = CSS::Length::make_px(0);
              // Then, if the 'direction' property of the element establishing the static-position containing block
              // is 'ltr' set 'left' to the static position and apply rule number three below;
              // otherwise, set 'right' to the static position and apply rule number one below.
              // FIXME: This is very hackish.
              left = CSS::Length::make_px(0);
              goto Rule3;
          }
  
          if (!left.is_auto() && !width.is_auto() && !right.is_auto()) {
              // FIXME: This should be solved in a more complicated way.
              return width;
          }
  
          if (margin_left.is_auto())
              margin_left = CSS::Length::make_px(0);
          if (margin_right.is_auto())
              margin_right = CSS::Length::make_px(0);
  
          // 1. 'left' and 'width' are 'auto' and 'right' is not 'auto',
          //    then the width is shrink-to-fit. Then solve for 'left'
          if (left.is_auto() && width.is_auto() && !right.is_auto()) {
              auto result = calculate_shrink_to_fit_widths(box);
              solve_for_left();
              auto available_width = solve_for_width();
              width = CSS::Length(min(max(result.preferred_minimum_width, available_width.to_px(box)), result.preferred_width), CSS::Length::Type::Px);
          }
  
          // 2. 'left' and 'right' are 'auto' and 'width' is not 'auto',
          //    then if the 'direction' property of the element establishing
          //    the static-position containing block is 'ltr' set 'left'
          //    to the static position, otherwise set 'right' to the static position.
          //    Then solve for 'left' (if 'direction is 'rtl') or 'right' (if 'direction' is 'ltr').
          else if (left.is_auto() && right.is_auto() && !width.is_auto()) {
              // FIXME: Check direction
              // FIXME: Use the static-position containing block
              left = zero_value;
              right = solve_for_right();
          }
  
          // 3. 'width' and 'right' are 'auto' and 'left' is not 'auto',
          //    then the width is shrink-to-fit. Then solve for 'right'
          else if (width.is_auto() && right.is_auto() && !left.is_auto()) {
          Rule3:
              auto result = calculate_shrink_to_fit_widths(box);
              auto available_width = solve_for_width();
              width = CSS::Length(min(max(result.preferred_minimum_width, available_width.to_px(box)), result.preferred_width), CSS::Length::Type::Px);
              right = solve_for_right();
          }
  
          // 4. 'left' is 'auto', 'width' and 'right' are not 'auto', then solve for 'left'
          else if (left.is_auto() && !width.is_auto() && !right.is_auto()) {
              left = solve_for_left();
          }
  
          // 5. 'width' is 'auto', 'left' and 'right' are not 'auto', then solve for 'width'
          else if (width.is_auto() && !left.is_auto() && !right.is_auto()) {
              width = solve_for_width();
          }
  
          // 6. 'right' is 'auto', 'left' and 'width' are not 'auto', then solve for 'right'
          else if (right.is_auto() && !left.is_auto() && !width.is_auto()) {
              right = solve_for_right();
          }
  
          return width;
      };
  
      auto specified_width = computed_values.width().has_value() ? computed_values.width()->resolved(box, width_of_containing_block).resolved(box) : CSS::Length::make_auto();
  
      // 1. The tentative used width is calculated (without 'min-width' and 'max-width')
      auto used_width = try_compute_width(specified_width);
  
      // 2. The tentative used width is greater than 'max-width', the rules above are applied again,
      //    but this time using the computed value of 'max-width' as the computed value for 'width'.
      auto specified_max_width = computed_values.max_width().has_value() ? computed_values.max_width()->resolved(box, width_of_containing_block).resolved(box) : CSS::Length::make_auto();
      if (!specified_max_width.is_auto()) {
          if (used_width.to_px(box) > specified_max_width.to_px(box)) {
              used_width = try_compute_width(specified_max_width);
          }
      }
  
      // 3. If the resulting width is smaller than 'min-width', the rules above are applied again,
      //    but this time using the value of 'min-width' as the computed value for 'width'.
      auto specified_min_width = computed_values.min_width().has_value() ? computed_values.min_width()->resolved(box, width_of_containing_block).resolved(box) : CSS::Length::make_auto();
      if (!specified_min_width.is_auto()) {
          if (used_width.to_px(box) < specified_min_width.to_px(box)) {
              used_width = try_compute_width(specified_min_width);
          }
      }
  
      box_state.content_width = used_width.to_px(box);
  
      box_state.margin_left = margin_left.to_px(box);
      box_state.margin_right = margin_right.to_px(box);
      box_state.border_left = border_left;
      box_state.border_right = border_right;
      box_state.padding_left = padding_left;
      box_state.padding_right = padding_right;
  }
  
  void FormattingContext::compute_width_for_absolutely_positioned_replaced_element(ReplacedBox const& box)
  {
      // 10.3.8 Absolutely positioned, replaced elements
      // The used value of 'width' is determined as for inline replaced elements.
      // FIXME: This const_cast is gross.
      const_cast<ReplacedBox&>(box).prepare_for_replaced_layout();
      m_state.get_mutable(box).content_width = compute_width_for_replaced_element(m_state, box);
  }
  
  // https://www.w3.org/TR/CSS22/visudet.html#abs-non-replaced-height
  void FormattingContext::compute_height_for_absolutely_positioned_non_replaced_element(Box const& box)
  {
      // 10.6.4 Absolutely positioned, non-replaced elements
  
      // FIXME: The section below is partly on-spec, partly ad-hoc.
      auto& computed_values = box.computed_values();
      auto const& containing_block = *box.containing_block();
      auto const& containing_block_state = m_state.get(containing_block);
      auto& box_state = m_state.get_mutable(box);
      auto width_of_containing_block = CSS::Length::make_px(containing_block_state.content_width);
      auto height_of_containing_block = CSS::Length::make_px(containing_block_state.content_height);
  
      CSS::Length specified_top = computed_values.offset().top.resolved(box, height_of_containing_block).resolved(box);
      CSS::Length specified_bottom = computed_values.offset().bottom.resolved(box, height_of_containing_block).resolved(box);
      CSS::Length specified_height = CSS::Length::make_auto();
  
      if (computed_values.height().has_value() && computed_values.height()->is_percentage()
          && !(containing_block.computed_values().height().has_value() && containing_block.computed_values().height()->is_length() && containing_block.computed_values().height()->length().is_absolute())) {
          // specified_height is already auto
      } else {
          specified_height = computed_values.height().has_value() ? computed_values.height()->resolved(box, height_of_containing_block).resolved(box) : CSS::Length::make_auto();
      }
  
      auto specified_max_height = computed_values.max_height().has_value() ? computed_values.max_height()->resolved(box, height_of_containing_block).resolved(box) : CSS::Length::make_auto();
      auto specified_min_height = computed_values.min_height().has_value() ? computed_values.min_height()->resolved(box, height_of_containing_block).resolved(box) : CSS::Length::make_auto();
  
      box_state.margin_top = computed_values.margin().top.resolved(box, width_of_containing_block).to_px(box);
      box_state.margin_bottom = computed_values.margin().bottom.resolved(box, width_of_containing_block).to_px(box);
      box_state.border_top = computed_values.border_top().width;
      box_state.border_bottom = computed_values.border_bottom().width;
      box_state.padding_top = computed_values.padding().top.resolved(box, width_of_containing_block).to_px(box);
      box_state.padding_bottom = computed_values.padding().bottom.resolved(box, width_of_containing_block).to_px(box);
  
      if (specified_height.is_auto() && specified_top.is_auto() && specified_bottom.is_auto()) {
          specified_height = CSS::Length(compute_auto_height_for_block_level_element(m_state, box), CSS::Length::Type::Px);
      }
  
      else if (specified_height.is_auto() && !specified_top.is_auto() && specified_bottom.is_auto()) {
          specified_height = CSS::Length(compute_auto_height_for_block_level_element(m_state, box), CSS::Length::Type::Px);
          box_state.offset_bottom = containing_block_state.content_height - specified_height.to_px(box) - specified_top.to_px(box) - box_state.margin_top - box_state.padding_top - box_state.border_top - box_state.margin_bottom - box_state.padding_bottom - box_state.border_bottom;
      }
  
      else if (specified_height.is_auto() && !specified_top.is_auto() && !specified_bottom.is_auto()) {
          specified_height = CSS::Length(containing_block_state.content_height - specified_top.to_px(box) - box_state.margin_top - box_state.padding_top - box_state.border_top - specified_bottom.to_px(box) - box_state.margin_bottom - box_state.padding_bottom - box_state.border_bottom, CSS::Length::Type::Px);
      }
  
      if (!specified_height.is_auto()) {
          float used_height = specified_height.to_px(box);
          if (!specified_max_height.is_auto())
              used_height = min(used_height, specified_max_height.to_px(box));
          if (!specified_min_height.is_auto())
              used_height = max(used_height, specified_min_height.to_px(box));
          box_state.content_height = used_height;
      }
  }
  
  void FormattingContext::layout_absolutely_positioned_element(Box const& box)
  {
      auto const& containing_block_state = m_state.get(*box.containing_block());
      auto width_of_containing_block = CSS::Length::make_px(containing_block_state.content_width);
      auto height_of_containing_block = CSS::Length::make_px(containing_block_state.content_height);
      auto& box_state = m_state.get_mutable(box);
  
      auto specified_width = box.computed_values().width().has_value() ? box.computed_values().width()->resolved(box, width_of_containing_block).resolved(box) : CSS::Length::make_auto();
  
      compute_width_for_absolutely_positioned_element(box);
      auto independent_formatting_context = layout_inside(box, LayoutMode::Default);
      compute_height_for_absolutely_positioned_element(box);
  
      box_state.margin_left = box.computed_values().margin().left.resolved(box, width_of_containing_block).to_px(box);
      box_state.margin_top = box.computed_values().margin().top.resolved(box, height_of_containing_block).to_px(box);
      box_state.margin_right = box.computed_values().margin().right.resolved(box, width_of_containing_block).to_px(box);
      box_state.margin_bottom = box.computed_values().margin().bottom.resolved(box, height_of_containing_block).to_px(box);
  
      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.offset_left = box.computed_values().offset().left.resolved(box, width_of_containing_block).to_px(box);
      box_state.offset_top = box.computed_values().offset().top.resolved(box, height_of_containing_block).to_px(box);
      box_state.offset_right = box.computed_values().offset().right.resolved(box, width_of_containing_block).to_px(box);
      box_state.offset_bottom = box.computed_values().offset().bottom.resolved(box, height_of_containing_block).to_px(box);
  
      auto is_auto = [](auto const& length_percentage) {
          return length_percentage.is_length() && length_percentage.length().is_auto();
      };
  
      if (is_auto(box.computed_values().offset().left) && specified_width.is_auto() && is_auto(box.computed_values().offset().right)) {
          if (is_auto(box.computed_values().margin().left))
              box_state.margin_left = 0;
          if (is_auto(box.computed_values().margin().right))
              box_state.margin_right = 0;
      }
  
      Gfx::FloatPoint used_offset;
  
      if (!is_auto(box.computed_values().offset().left)) {
          float x_offset = box_state.offset_left
              + box_state.border_box_left();
          used_offset.set_x(x_offset + box_state.margin_left);
      } else if (!is_auto(box.computed_values().offset().right)) {
          float x_offset = 0
              - box_state.offset_right
              - box_state.border_box_right();
          used_offset.set_x(containing_block_state.content_width + x_offset - box_state.content_width - box_state.margin_right);
      } else {
          float x_offset = box_state.margin_box_left();
          used_offset.set_x(x_offset);
      }
  
      if (!is_auto(box.computed_values().offset().top)) {
          float y_offset = box_state.offset_top
              + box_state.border_box_top();
          used_offset.set_y(y_offset + box_state.margin_top);
      } else if (!is_auto(box.computed_values().offset().bottom)) {
          float y_offset = 0
              - box_state.offset_bottom
              - box_state.border_box_bottom();
          used_offset.set_y(containing_block_state.content_height + y_offset - box_state.content_height - box_state.margin_bottom);
      } else {
          float y_offset = box_state.margin_box_top();
          used_offset.set_y(y_offset);
      }
  
      box_state.offset = used_offset;
  
      if (independent_formatting_context)
          independent_formatting_context->parent_context_did_dimension_child_root_box();
  }
  
  void FormattingContext::compute_height_for_absolutely_positioned_replaced_element(ReplacedBox const& box)
  {
      // 10.6.5 Absolutely positioned, replaced elements
      // The used value of 'height' is determined as for inline replaced elements.
      m_state.get_mutable(box).content_height = compute_height_for_replaced_element(m_state, box);
  }
  
  void FormattingContext::compute_position(Box const& box)
  {
      // 9.4.3 Relative positioning
      // Once a box has been laid out according to the normal flow or floated, it may be shifted relative to this position.
  
      if (box.computed_values().position() != CSS::Position::Relative)
          return;
  
      auto& box_state = m_state.get_mutable(box);
      auto const& computed_values = box.computed_values();
      float width_of_containing_block = m_state.get(*box.containing_block()).content_width;
      auto width_of_containing_block_as_length = CSS::Length::make_px(width_of_containing_block);
  
      auto specified_left = computed_values.offset().left.resolved(box, width_of_containing_block_as_length).resolved(box);
      auto specified_right = computed_values.offset().right.resolved(box, width_of_containing_block_as_length).resolved(box);
  
      if (specified_left.is_auto() && specified_right.is_auto()) {
          // If both 'left' and 'right' are 'auto' (their initial values), the used values are '0' (i.e., the boxes stay in their original position).
          box_state.offset_left = 0;
          box_state.offset_right = 0;
      } else if (specified_left.is_auto()) {
          // If 'left' is 'auto', its used value is minus the value of 'right' (i.e., the boxes move to the left by the value of 'right').
          box_state.offset_right = specified_right.to_px(box);
          box_state.offset_left = 0 - box_state.offset_right;
      } else if (specified_right.is_auto()) {
          // If 'right' is specified as 'auto', its used value is minus the value of 'left'.
          box_state.offset_left = specified_left.to_px(box);
          box_state.offset_right = 0 - box_state.offset_left;
      } else {
          // If neither 'left' nor 'right' is 'auto', the position is over-constrained, and one of them has to be ignored.
          // If the 'direction' property of the containing block is 'ltr', the value of 'left' wins and 'right' becomes -'left'.
          // If 'direction' of the containing block is 'rtl', 'right' wins and 'left' is ignored.
          // FIXME: Check direction (assuming 'ltr' for now).
          box_state.offset_left = specified_left.to_px(box);
          box_state.offset_right = 0 - box_state.offset_left;
      }
  }
  
  FormattingState::IntrinsicSizes FormattingContext::calculate_intrinsic_sizes(Layout::Box const& box) const
  {
      // If we have cached intrinsic sizes for this box, use them.
      auto it = m_state.intrinsic_sizes.find(&box);
      if (it != m_state.intrinsic_sizes.end())
          return it->value;
  
      // Nothing cached, perform two throwaway layouts to determine the intrinsic sizes.
      // FIXME: This should handle replaced elements with "native" intrinsic size properly!
  
      auto& cached_box_sizes = m_state.intrinsic_sizes.ensure(&box);
      auto const& containing_block = *box.containing_block();
      {
          FormattingState throwaway_state(&m_state);
          throwaway_state.get_mutable(containing_block).content_width = INFINITY;
          throwaway_state.get_mutable(containing_block).content_height = INFINITY;
          auto independent_formatting_context = const_cast<FormattingContext*>(this)->create_independent_formatting_context_if_needed(throwaway_state, box);
          VERIFY(independent_formatting_context);
  
          independent_formatting_context->run(box, LayoutMode::OnlyRequiredLineBreaks);
          cached_box_sizes.max_content_size.set_width(greatest_child_width(throwaway_state, box));
          cached_box_sizes.max_content_size.set_height(BlockFormattingContext::compute_theoretical_height(throwaway_state, box));
      }
  
      {
          FormattingState throwaway_state(&m_state);
          throwaway_state.get_mutable(containing_block).content_width = 0;
          throwaway_state.get_mutable(containing_block).content_height = 0;
          auto independent_formatting_context = const_cast<FormattingContext*>(this)->create_independent_formatting_context_if_needed(throwaway_state, box);
          VERIFY(independent_formatting_context);
          independent_formatting_context->run(box, LayoutMode::AllPossibleLineBreaks);
          cached_box_sizes.min_content_size.set_width(greatest_child_width(throwaway_state, box));
          cached_box_sizes.min_content_size.set_height(BlockFormattingContext::compute_theoretical_height(throwaway_state, box));
      }
  
      if (cached_box_sizes.min_content_size.width() > cached_box_sizes.max_content_size.width()) {
          float tmp = cached_box_sizes.min_content_size.width();
          cached_box_sizes.min_content_size.set_width(cached_box_sizes.max_content_size.width());
          cached_box_sizes.max_content_size.set_width(tmp);
      }
  
      if (cached_box_sizes.min_content_size.height() > cached_box_sizes.max_content_size.height()) {
          float tmp = cached_box_sizes.min_content_size.height();
          cached_box_sizes.min_content_size.set_height(cached_box_sizes.max_content_size.height());
          cached_box_sizes.max_content_size.set_height(tmp);
      }
  
      return cached_box_sizes;
  }
  
  FormattingContext::MinAndMaxContentSize FormattingContext::calculate_min_and_max_content_width(Layout::Box const& box) const
  {
      auto const& sizes = calculate_intrinsic_sizes(box);
      return { sizes.min_content_size.width(), sizes.max_content_size.width() };
  }
  
  FormattingContext::MinAndMaxContentSize FormattingContext::calculate_min_and_max_content_height(Layout::Box const& box) const
  {
      auto const& sizes = calculate_intrinsic_sizes(box);
      return { sizes.min_content_size.height(), sizes.max_content_size.height() };
  }
  
  float FormattingContext::calculate_fit_content_size(float min_content_size, float max_content_size, Optional<float> available_space) const
  {
      // If the available space in a given axis is definite, equal to clamp(min-content size, stretch-fit size, max-content size)
      // (i.e. max(min-content size, min(max-content size, stretch-fit size))).
      if (available_space.has_value()) {
          // FIXME: Compute the real stretch-fit size.
          auto stretch_fit_size = *available_space;
          auto s = max(min_content_size, min(max_content_size, stretch_fit_size));
          return s;
      }
  
      // FIXME: When sizing under a min-content constraint, equal to the min-content size.
  
      // Otherwise, equal to the max-content size in that axis.
      return max_content_size;
  }
  
  float FormattingContext::calculate_fit_content_width(Layout::Box const& box, Optional<float> available_space) const
  {
      auto [min_content_size, max_content_size] = calculate_min_and_max_content_width(box);
      return calculate_fit_content_size(min_content_size, max_content_size, available_space);
  }
  
  float FormattingContext::calculate_fit_content_height(Layout::Box const& box, Optional<float> available_space) const
  {
      auto [min_content_size, max_content_size] = calculate_min_and_max_content_height(box);
      return calculate_fit_content_size(min_content_size, max_content_size, available_space);
  }
  }
  