text: /*
   * Copyright (c) 2020-2022, Andreas Kling <kling@serenityos.org>
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #include <AK/QuickSort.h>
  #include <AK/StringBuilder.h>
  #include <LibGfx/Painter.h>
  #include <LibWeb/Layout/Box.h>
  #include <LibWeb/Layout/InitialContainingBlock.h>
  #include <LibWeb/Layout/ReplacedBox.h>
  #include <LibWeb/Painting/PaintableBox.h>
  #include <LibWeb/Painting/StackingContext.h>
  
  namespace Web::Painting {
  
  static void paint_node(Layout::Node const& layout_node, PaintContext& context, PaintPhase phase)
  {
      if (auto const* paintable = layout_node.paintable())
          paintable->paint(context, phase);
  }
  
  StackingContext::StackingContext(Layout::Box& box, StackingContext* parent)
      : m_box(box)
      , m_parent(parent)
  {
      VERIFY(m_parent != this);
      if (m_parent)
          m_parent->m_children.append(this);
  }
  
  void StackingContext::sort()
  {
      quick_sort(m_children, [](auto& a, auto& b) {
          auto a_z_index = a->m_box.computed_values().z_index().value_or(0);
          auto b_z_index = b->m_box.computed_values().z_index().value_or(0);
          if (a_z_index == b_z_index)
              return a->m_box.is_before(b->m_box);
          return a_z_index < b_z_index;
      });
  
      for (auto* child : m_children)
          child->sort();
  }
  
  void StackingContext::paint_descendants(PaintContext& context, Layout::Node& box, StackingContextPaintPhase phase) const
  {
      if (phase == StackingContextPaintPhase::Foreground) {
          if (auto* paintable = box.paintable())
              paintable->before_children_paint(context, PaintPhase::Foreground);
      }
  
      box.for_each_child([&](auto& child) {
          if (child.establishes_stacking_context())
              return;
          bool child_is_inline_or_replaced = child.is_inline() || is<Layout::ReplacedBox>(child);
          switch (phase) {
          case StackingContextPaintPhase::BackgroundAndBorders:
              if (!child_is_inline_or_replaced && !child.is_floating() && !child.is_positioned()) {
                  paint_node(child, context, PaintPhase::Background);
                  paint_node(child, context, PaintPhase::Border);
                  paint_descendants(context, child, phase);
              }
              break;
          case StackingContextPaintPhase::Floats:
              if (!child.is_positioned()) {
                  if (child.is_floating()) {
                      paint_node(child, context, PaintPhase::Background);
                      paint_node(child, context, PaintPhase::Border);
                      paint_descendants(context, child, StackingContextPaintPhase::BackgroundAndBorders);
                  }
                  paint_descendants(context, child, phase);
              }
              break;
          case StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced:
              if (!child.is_positioned()) {
                  if (child_is_inline_or_replaced) {
                      paint_node(child, context, PaintPhase::Background);
                      paint_node(child, context, PaintPhase::Border);
                      paint_descendants(context, child, StackingContextPaintPhase::BackgroundAndBorders);
                  }
                  paint_descendants(context, child, phase);
              }
              break;
          case StackingContextPaintPhase::Foreground:
              if (!child.is_positioned()) {
                  paint_node(child, context, PaintPhase::Foreground);
                  paint_descendants(context, child, phase);
              }
              break;
          case StackingContextPaintPhase::FocusAndOverlay:
              if (context.has_focus()) {
                  paint_node(child, context, PaintPhase::FocusOutline);
              }
              paint_node(child, context, PaintPhase::Overlay);
              paint_descendants(context, child, phase);
              break;
          }
      });
  
      if (phase == StackingContextPaintPhase::Foreground) {
          if (auto* paintable = box.paintable())
              paintable->after_children_paint(context, PaintPhase::Foreground);
      }
  }
  
  void StackingContext::paint_internal(PaintContext& context) const
  {
      // For a more elaborate description of the algorithm, see CSS 2.1 Appendix E
      // Draw the background and borders for the context root (steps 1, 2)
      paint_node(m_box, context, PaintPhase::Background);
      paint_node(m_box, context, PaintPhase::Border);
      // Draw positioned descendants with negative z-indices (step 3)
      for (auto* child : m_children) {
          if (child->m_box.computed_values().z_index().has_value() && child->m_box.computed_values().z_index().value() < 0)
              child->paint(context);
      }
      // Draw the background and borders for block-level children (step 4)
      paint_descendants(context, m_box, StackingContextPaintPhase::BackgroundAndBorders);
      // Draw the non-positioned floats (step 5)
      paint_descendants(context, m_box, StackingContextPaintPhase::Floats);
      // Draw inline content, replaced content, etc. (steps 6, 7)
      paint_descendants(context, m_box, StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced);
      paint_node(m_box, context, PaintPhase::Foreground);
      paint_descendants(context, m_box, StackingContextPaintPhase::Foreground);
      // Draw other positioned descendants (steps 8, 9)
      for (auto* child : m_children) {
          if (child->m_box.computed_values().z_index().has_value() && child->m_box.computed_values().z_index().value() < 0)
              continue;
          child->paint(context);
      }
  
      paint_node(m_box, context, PaintPhase::FocusOutline);
      paint_node(m_box, context, PaintPhase::Overlay);
      paint_descendants(context, m_box, StackingContextPaintPhase::FocusAndOverlay);
  }
  
  void StackingContext::paint(PaintContext& context) const
  {
      Gfx::PainterStateSaver saver(context.painter());
      if (m_box.is_fixed_position()) {
          context.painter().translate(context.scroll_offset());
      }
  
      auto opacity = m_box.computed_values().opacity();
      if (opacity == 0.0f)
          return;
  
      if (opacity < 1.0f) {
          auto bitmap_or_error = Gfx::Bitmap::try_create(Gfx::BitmapFormat::BGRA8888, context.painter().target()->size());
          if (bitmap_or_error.is_error())
              return;
          auto bitmap = bitmap_or_error.release_value_but_fixme_should_propagate_errors();
          Gfx::Painter painter(bitmap);
          PaintContext paint_context(painter, context.palette(), context.scroll_offset());
          paint_internal(paint_context);
          context.painter().blit(Gfx::IntPoint(m_box.paint_box()->absolute_position()), bitmap, Gfx::IntRect(m_box.paint_box()->absolute_rect()), opacity);
      } else {
          paint_internal(context);
      }
  }
  
  HitTestResult StackingContext::hit_test(Gfx::IntPoint const& position, HitTestType type) const
  {
      // NOTE: Hit testing basically happens in reverse painting order.
      // https://www.w3.org/TR/CSS22/visuren.html#z-index
  
      // 7. the child stacking contexts with positive stack levels (least positive first).
      for (ssize_t i = m_children.size() - 1; i >= 0; --i) {
          auto const& child = *m_children[i];
          if (child.m_box.computed_values().z_index().value_or(0) < 0)
              break;
          auto result = child.hit_test(position, type);
          if (result.paintable)
              return result;
      }
  
      HitTestResult result;
      // 6. the child stacking contexts with stack level 0 and the positioned descendants with stack level 0.
      m_box.for_each_in_subtree_of_type<Layout::Box>([&](Layout::Box const& box) {
          if (box.is_positioned() && !box.paint_box()->stacking_context()) {
              result = box.paint_box()->hit_test(position, type);
              if (result.paintable)
                  return IterationDecision::Break;
          }
          return IterationDecision::Continue;
      });
      if (result.paintable)
          return result;
  
      // 5. the in-flow, inline-level, non-positioned descendants, including inline tables and inline blocks.
      if (m_box.children_are_inline() && is<Layout::BlockContainer>(m_box)) {
          auto result = m_box.paint_box()->hit_test(position, type);
          if (result.paintable)
              return result;
      }
  
      // 4. the non-positioned floats.
      m_box.for_each_in_subtree_of_type<Layout::Box>([&](Layout::Box const& box) {
          if (box.is_floating()) {
              result = box.paint_box()->hit_test(position, type);
              if (result.paintable)
                  return IterationDecision::Break;
          }
          return IterationDecision::Continue;
      });
  
      // 3. the in-flow, non-inline-level, non-positioned descendants.
      if (!m_box.children_are_inline()) {
          m_box.for_each_in_subtree_of_type<Layout::Box>([&](Layout::Box const& box) {
              if (!box.is_absolutely_positioned() && !box.is_floating()) {
                  result = box.paint_box()->hit_test(position, type);
                  if (result.paintable)
                      return IterationDecision::Break;
              }
              return IterationDecision::Continue;
          });
          if (result.paintable)
              return result;
      }
  
      // 2. the child stacking contexts with negative stack levels (most negative first).
      for (ssize_t i = m_children.size() - 1; i >= 0; --i) {
          auto const& child = *m_children[i];
          if (child.m_box.computed_values().z_index().value_or(0) < 0)
              break;
          auto result = child.hit_test(position, type);
          if (result.paintable)
              return result;
      }
  
      // 1. the background and borders of the element forming the stacking context.
      if (m_box.paint_box()->absolute_border_box_rect().contains(position.to_type<float>())) {
          return HitTestResult {
              .paintable = m_box.paintable(),
          };
      }
  
      return {};
  }
  
  void StackingContext::dump(int indent) const
  {
      StringBuilder builder;
      for (int i = 0; i < indent; ++i)
          builder.append(' ');
      builder.appendff("SC for {} {} [children: {}] (z-index: ", m_box.debug_description(), m_box.paint_box()->absolute_rect(), m_children.size());
      if (m_box.computed_values().z_index().has_value())
          builder.appendff("{}", m_box.computed_values().z_index().value());
      else
          builder.append("auto");
      builder.append(')');
      dbgln("{}", builder.string_view());
      for (auto& child : m_children)
          child->dump(indent + 1);
  }
  
  }
  