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 * modification, are permitted provided that the following conditions
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#include "config.h"
#include "PositionedLayoutConstraints.h"

#include "AnchorPositionEvaluator.h"
#include "ContainerNodeInlines.h"
#include "InlineIteratorBoxInlines.h"
#include "InlineIteratorInlineBox.h"
#include "RenderElementInlines.h"
#include "RenderGrid.h"
#include "RenderInline.h"
#include "RenderLayer.h"
#include "RenderView.h"
#include "StyleComputedStyle.h"
#include "StylePositionArea.h"

namespace WebCore {

using namespace CSS::Literals;

PositionedLayoutConstraints::PositionedLayoutConstraints(const RenderBox& renderer, LogicalBoxAxis selfAxis)
    : PositionedLayoutConstraints(renderer, renderer.style(), selfAxis)
{
}

PositionedLayoutConstraints::PositionedLayoutConstraints(const RenderBox& renderer, const Style::ComputedStyle& style, LogicalBoxAxis selfAxis)
    : m_renderer(renderer)
    , m_container(downcast<RenderBoxModelObject>(*renderer.container())) // Using containingBlock() would be wrong for relpositioned inlines.
    , m_containingWritingMode(m_container->writingMode())
    , m_parentWritingMode(renderer.parent() ? renderer.parent()->writingMode() : WritingMode())
    , m_writingMode(style.writingMode())
    , m_selfAxis(selfAxis)
    , m_containingAxis(!isOrthogonal() ? selfAxis : oppositeAxis(selfAxis))
    , m_physicalAxis(selfAxis == LogicalBoxAxis::Inline ? m_writingMode.inlineAxis() : m_writingMode.blockAxis())
    , m_style(style)
    , m_alignment(m_containingAxis == LogicalBoxAxis::Inline ? style.justifySelf().resolve() : style.alignSelf().resolve())
    , m_defaultAnchorBox(needsAnchor() ? Style::AnchorPositionEvaluator::defaultAnchorForBox(renderer) : nullptr)
    , m_marginBefore { 0_css_px }
    , m_marginAfter { 0_css_px }
    , m_insetBefore { 0_css_px }
    , m_insetAfter { 0_css_px }
{
    ASSERT(m_container);
    ASSERT(renderer.parent());

    // Compute basic containing block info.
    m_originalContainingRange = renderer.containingBlockRangeForPositioned(*m_container, m_physicalAxis);
    m_containingRange = m_originalContainingRange;
    m_containingInlineSize = (LogicalBoxAxis::Inline == m_containingAxis) ? m_containingRange.size()
        : renderer.containingBlockRangeForPositioned(*m_container, oppositeAxis(m_physicalAxis)).size();

    // Adjust for grid-area.
    captureGridArea();

    // Capture the anchor geometry and adjust for position-area.
    captureAnchorGeometry();
}

void PositionedLayoutConstraints::computeInsets()
{
    // Cache insets and margins, etc.
    captureInsets();

    if (m_useStaticPosition)
        computeStaticPosition();

    if (containingCoordsAreFlipped()) {
        // Ideally this check is incorporated into captureInsets() but currently it needs to happen after computeStaticPosition() because containingCoordsAreFlipped() depends on m_useStaticPosition.
        std::swap(m_marginBefore, m_marginAfter);
        std::swap(m_insetBefore, m_insetAfter);
    }

    // Compute the inset-modified containing block.
    m_insetModifiedContainingRange = m_containingRange;
    m_insetModifiedContainingRange.shiftMinEdgeBy(insetBeforeValue());
    m_insetModifiedContainingRange.shiftMaxEdgeBy(-insetAfterValue());
}

bool PositionedLayoutConstraints::needsAnchor() const
{
    return !m_style.positionArea().isNone() || m_alignment.position() == ItemPosition::AnchorCenter;
}

bool PositionedLayoutConstraints::containingCoordsAreFlipped() const
{
    bool orthogonalOpposing = (m_containingAxis == LogicalBoxAxis::Inline && m_writingMode.isBlockFlipped()) || (m_containingAxis == LogicalBoxAxis::Block && m_containingWritingMode.isBlockFlipped());
    // FIXME: Static position has a confusing implementation. Leaving it alone for now.
    return !m_useStaticPosition && ((isBlockOpposing() && m_containingAxis == LogicalBoxAxis::Block) || (isOrthogonal() && orthogonalOpposing));
}

static bool isFlippedOnAxis(WritingMode writingMode, BoxAxis physicalAxis)
{
    bool axisIsBlock = writingMode.isHorizontal() != (physicalAxis == BoxAxis::Horizontal);
    return axisIsBlock ? writingMode.isBlockFlipped() : writingMode.isInlineFlipped();
}

bool PositionedLayoutConstraints::isOrthogonalToContainingBlockWithFlippedParent() const
{
    // Grid items use alignment-based static positioning.
    if (is<RenderGrid>(m_container) && m_container.get() == m_renderer->parent())
        return false;
    if (!isOrthogonal())
        return false;
    return isFlippedOnAxis(m_parentWritingMode, m_physicalAxis);
}

bool PositionedLayoutConstraints::isParentOpposingContainingBlock() const
{
    if (is<RenderGrid>(m_container) && m_container.get() == m_renderer->parent())
        return false;
    bool parentFlipped = isFlippedOnAxis(m_parentWritingMode, m_physicalAxis);
    // Only block-flip matters for the containing block -- direction (rtl) does not flip the physical containing range.
    bool physicalAxisIsCBBlock = m_containingWritingMode.isHorizontal() != (m_physicalAxis == BoxAxis::Horizontal);
    bool containingBlockFlipped = physicalAxisIsCBBlock && m_containingWritingMode.isBlockFlipped();
    return parentFlipped != containingBlockFlipped;
}

void PositionedLayoutConstraints::captureInsets()
{
    bool isHorizontal = BoxAxis::Horizontal == m_physicalAxis;

    if (isHorizontal) {
        m_bordersPlusPadding = m_renderer->borderLeft() + m_renderer->paddingLeft() + m_renderer->paddingRight() + m_renderer->borderRight();
        m_useStaticPosition = m_style.left().isAuto() && m_style.right().isAuto() && !m_defaultAnchorBox;
    } else {
        m_bordersPlusPadding = m_renderer->borderTop() + m_renderer->paddingTop() + m_renderer->paddingBottom() + m_renderer->borderBottom();
        m_useStaticPosition = m_style.top().isAuto() && m_style.bottom().isAuto() && !m_defaultAnchorBox;
    }

    if (LogicalBoxAxis::Inline == m_selfAxis) {
        m_marginBefore = isHorizontal ? m_style.marginLeft() : m_style.marginTop();
        m_marginAfter = isHorizontal ? m_style.marginRight() : m_style.marginBottom();
        m_insetBefore = m_style.logicalLeft();
        m_insetAfter = m_style.logicalRight();
    } else {
        auto staticPositionIsFromFlippedParent = m_useStaticPosition && isOrthogonalToContainingBlockWithFlippedParent();
        m_marginBefore = staticPositionIsFromFlippedParent ? m_style.marginAfter() : m_style.marginBefore();
        m_marginAfter = staticPositionIsFromFlippedParent ? m_style.marginBefore() : m_style.marginAfter();
        m_insetBefore = m_style.logicalTop();
        m_insetAfter = m_style.logicalBottom();
    }

    if (m_defaultAnchorBox) {
        // If the box uses anchor-center or position-area and does have a default anchor box,
        // then it doesn't use static positioning.
        m_useStaticPosition = false;
    }
}

// MARK: - Adjustments to the containing block.

void PositionedLayoutConstraints::expandToScrollableArea(LayoutRange& containingRange, const std::optional<ScrollPosition> fromScrollPosition) const
{
    auto containingBlock = dynamicDowncast<RenderBox>(m_container.get());
    if (!containingBlock || !containingBlock->hasRenderOverflow()
        || (!containingBlock->isRenderView() && !containingBlock->hasPotentiallyScrollableOverflow()))
        return;

    auto scrollableArea = containingBlock->scrollablePaddingAreaOverflowRect();
    auto scrollableRange = BoxAxis::Horizontal == m_physicalAxis ? scrollableArea.xRange() : scrollableArea.yRange();
    containingRange.capMinEdgeTo(scrollableRange.min());
    containingRange.floorMaxEdgeTo(scrollableRange.max());

    if (fromScrollPosition) {
        auto scrollOffset = BoxAxis::Horizontal == m_physicalAxis ? fromScrollPosition->x() : fromScrollPosition->y();
        containingRange.moveBy(-scrollOffset);
    }
}

void PositionedLayoutConstraints::captureGridArea()
{
    const CheckedPtr gridContainer = dynamicDowncast<RenderGrid>(m_container.get());
    if (!gridContainer)
        return;

    if (LogicalBoxAxis::Inline == m_containingAxis) {
        m_containingRange = gridContainer->gridAreaRangeForOutOfFlow(m_renderer, Style::GridTrackSizingDirection::Columns);
        m_containingInlineSize = m_containingRange.size();
    } else {
        m_containingRange = gridContainer->gridAreaRangeForOutOfFlow(m_renderer, Style::GridTrackSizingDirection::Rows);
        m_containingInlineSize = gridContainer->gridAreaRangeForOutOfFlow(m_renderer, Style::GridTrackSizingDirection::Columns).size();
    }

    if (!startIsBefore()) {
        auto containerSize = BoxAxis::Horizontal == m_physicalAxis
            ? gridContainer->borderBoxWidth() : gridContainer->borderBoxHeight();
        m_containingRange.moveTo(containerSize - m_containingRange.max());
    }

    // FIXME: Get PositionedLayoutConstraints to work in pre-corrected coordinates instead of assuming it's wrong and doing "fixup" afterwards, so we don't have to "unfixup" here.
    if (LogicalBoxAxis::Inline == m_containingAxis) {
        if (BoxAxis::Horizontal == m_physicalAxis) {
            if (gridContainer->shouldPlaceVerticalScrollbarOnLeft())
                m_containingRange.moveBy(-gridContainer->verticalScrollbarWidth());
        } else {
            if (!m_containingWritingMode.isInlineTopToBottom())
                m_containingRange.moveBy(-gridContainer->horizontalScrollbarHeight());
        }
    }
}

LayoutRange PositionedLayoutConstraints::extractRange(LayoutRect anchorRect)
{
    LayoutRange anchorRange;
    if (BoxAxis::Horizontal == m_physicalAxis)
        anchorRange.set(anchorRect.x(), anchorRect.width());
    else
        anchorRange.set(anchorRect.y(), anchorRect.height());

    if (m_containingWritingMode.isBlockFlipped() && LogicalBoxAxis::Block == m_containingAxis) {
        // Coordinate fixup for flipped blocks.
        anchorRange.moveTo(m_containingRange.max() - anchorRange.max() + m_container->borderAfter());
    }
    return anchorRange;
}

void PositionedLayoutConstraints::captureAnchorGeometry()
{
    if (!m_defaultAnchorBox)
        return;

    // Store the anchor geometry.
    LayoutRect anchorRect = Style::AnchorPositionEvaluator::computeAnchorRectRelativeToContainingBlock(*m_defaultAnchorBox, *m_container, m_renderer.get());
    m_anchorArea = extractRange(anchorRect);

    // Adjust containing block for position-area.
    if (m_style.positionArea().isNone())
        return;
    m_containingRange = adjustForPositionArea(m_containingRange, m_anchorArea, m_physicalAxis);

    // Margin basis is always against the inline axis.
    if (LogicalBoxAxis::Inline == m_containingAxis) {
        m_containingInlineSize = m_containingRange.size();
        return;
    }
    // Else we're representing the block axis, but need the inline dimensions.
    auto inlineAxis = oppositeAxis(m_physicalAxis);
    LayoutRange inlineContainingBlock(m_container->borderLogicalLeft(), m_containingInlineSize);
    auto inlineAnchorArea = BoxAxis::Horizontal == inlineAxis
        ? LayoutRange { anchorRect.x(), anchorRect.width() }
        : LayoutRange { anchorRect.y(), anchorRect.height() };
    m_containingInlineSize = adjustForPositionArea(inlineContainingBlock, inlineAnchorArea, inlineAxis).size();
}

LayoutRange PositionedLayoutConstraints::adjustForPositionArea(const LayoutRange rangeToAdjust, const LayoutRange anchorArea, const BoxAxis containerAxis)
{
    ASSERT(!m_style.positionArea().isNone());
    ASSERT(m_defaultAnchorBox);
    ASSERT(needsAnchor());
    ASSERT(anchorArea.size() >= 0);

    auto adjustedRange = rangeToAdjust;
    switch (m_style.positionArea().tryValue()->coordMatchedTrackForAxis(containerAxis, m_containingWritingMode, m_writingMode)) {
    case Style::PositionAreaTrack::Start:
        adjustedRange.shiftMaxEdgeTo(anchorArea.min());
        adjustedRange.floorSizeFromMaxEdge();
        return adjustedRange;
    case Style::PositionAreaTrack::SpanStart:
        adjustedRange.shiftMaxEdgeTo(anchorArea.max());
        adjustedRange.capMinEdgeTo(anchorArea.min());
        return adjustedRange;
    case Style::PositionAreaTrack::End:
        adjustedRange.shiftMinEdgeTo(anchorArea.max());
        adjustedRange.floorSizeFromMinEdge();
        return adjustedRange;
    case Style::PositionAreaTrack::SpanEnd:
        adjustedRange.shiftMinEdgeTo(anchorArea.min());
        adjustedRange.floorMaxEdgeTo(anchorArea.max());
        return adjustedRange;
    case Style::PositionAreaTrack::Center:
        adjustedRange = anchorArea;
        return adjustedRange;
    case Style::PositionAreaTrack::SpanAll:
        adjustedRange.capMinEdgeTo(anchorArea.min());
        adjustedRange.floorMaxEdgeTo(anchorArea.max());
        return adjustedRange;
    default:
        ASSERT_NOT_REACHED();
        return adjustedRange;
    };
}

// MARK: - Resolving margins and alignment (after sizing).

std::optional<LayoutUnit> PositionedLayoutConstraints::remainingSpaceForStaticAlignment(LayoutUnit itemSize) const
{
    if (!m_useStaticPosition || m_containingAxis == LogicalBoxAxis::Inline)
        return { };

    if (auto* parent = dynamicDowncast<RenderGrid>(m_renderer->parent())) {
        auto& itemStyle = m_renderer->style();
        auto itemResolvedAlignSelf = itemStyle.alignSelf().resolve(&parent->style());

        switch (itemResolvedAlignSelf.position()) {
        case ItemPosition::Center:
        case ItemPosition::FlexEnd:
        case ItemPosition::SelfEnd:
        case ItemPosition::End: {
            if (m_container.get() == parent)
                return { };

            // FIXME: This is probably not the correct set of writing mode checks.

            auto& containingBlockStyle = m_container->style();
            if (!containingBlockStyle.writingMode().isHorizontal())
                return { };

            if (!containingBlockStyle.writingMode().isBidiLTR())
                return { };

            auto& parentStyle = parent->style();
            if (!parentStyle.writingMode().isHorizontal())
                return { };

            if (!parentStyle.writingMode().isBidiLTR())
                return { };

            if (!itemStyle.writingMode().isHorizontal())
                return { };

            if (!itemStyle.writingMode().isBidiLTR())
                return { };

            if (itemResolvedAlignSelf.positionType() != ItemPositionType::NonLegacy)
                return { };

            if (itemResolvedAlignSelf.overflow() != OverflowAlignment::Default)
                return { };

            auto remainingSpace = parent->contentBoxLogicalHeight() - itemSize;
#if ASSERT_ENABLED
            m_isEligibleForStaticRangeAlignment = remainingSpace >= 0_lu;
#endif
            if (remainingSpace >= 0_lu)
                return remainingSpace;
            return { };
        }
        default:
            return { };
        }
    }
    return { };
}

bool PositionedLayoutConstraints::shouldAlignStaticPositionInInlineAxis() const
{
    // justify-self can align an out-of-flow box within its static-position rectangle when both
    // inline-axis insets are auto. See https://drafts.csswg.org/css-align-3/#justify-abspos
    if (!m_useStaticPosition)
        return false;

    // Only the box's own inline axis (justify-self); orthogonal / block-axis static positioning
    // keeps the existing static-position path.
    if (m_selfAxis != LogicalBoxAxis::Inline || m_containingAxis != LogicalBoxAxis::Inline)
        return false;

    // The static position must be established by a non-replaced block container, matching where
    // justify-self applies to in-flow block-level boxes. Flex and grid containers position their
    // abspos children with their own rules, and inline boxes don't align their out-of-flow
    // children -- none of those are block containers.
    CheckedPtr parent = m_renderer->parent();
    if (!parent || !parent->isBlockContainer())
        return false;

    // normal / stretch / legacy keeps the box at its static position, which the existing path
    // already computes correctly for every writing-mode / direction combination. Note that auto
    // resolves against the parent's justify-items, so it may still resolve to a real alignment here.
    return !m_style.justifySelf().resolve(m_renderer->parentStyle()).isNormalStretchOrLegacy();
}

// See CSS2 § 10.3.7-8 and 10.6.4-5.
void PositionedLayoutConstraints::resolvePosition(RenderBox::LogicalExtentComputedValues& computedValues) const
{
    // Static position should have resolved one of our insets by now.
    ASSERT(!m_useStaticPosition || !(m_insetBefore.isAuto() && m_insetAfter.isAuto()));

    auto usedMarginBefore = marginBeforeValue();
    auto usedMarginAfter = marginAfterValue();
    auto alignmentShift = 0_lu;

    auto outerSize = usedMarginBefore + computedValues.extent + usedMarginAfter;
    auto remainingSpace = insetModifiedContainingSize() - outerSize;

    bool honorAutoInsets = !m_defaultAnchorBox || m_alignment.isNormal();
    bool hasAutoBeforeInset = m_insetBefore.isAuto() && honorAutoInsets;
    bool hasAutoAfterInset = m_insetAfter.isAuto() && honorAutoInsets;
    bool hasAutoBeforeMargin = m_marginBefore.isAuto() && !m_defaultAnchorBox;
    bool hasAutoAfterMargin = m_marginAfter.isAuto() && !m_defaultAnchorBox;

    if ((hasAutoBeforeMargin || hasAutoAfterMargin) && !hasAutoBeforeInset && !hasAutoAfterInset) {
        // Distribute remainingSpace to auto margins.
        if (hasAutoBeforeMargin && hasAutoAfterMargin) {
            // Distribute usable space to both margins equally.
            auto usableRemainingSpace = (LogicalBoxAxis::Inline == m_containingAxis)
                ? std::max(0_lu, remainingSpace) : remainingSpace;
            usedMarginBefore = usedMarginAfter = usableRemainingSpace / 2;

            // Distribute unused space to the end side.
            auto unusedSpace = remainingSpace - (usedMarginBefore + usedMarginAfter);
            if (startIsBefore())
                usedMarginAfter += unusedSpace;
            else
                usedMarginBefore += unusedSpace;
        } else if (hasAutoBeforeMargin)
            usedMarginBefore = remainingSpace;
        else if (hasAutoAfterMargin)
            usedMarginAfter = remainingSpace;
    } else {
        if (auto staticRemainingSpace = remainingSpaceForStaticAlignment(outerSize))
            alignmentShift = resolveAlignmentShift(*staticRemainingSpace, outerSize);
        else if (shouldAlignStaticPositionInInlineAxis()) {
            // Both insets were auto (static position) and an explicit justify-self was specified:
            // align the box's margin box within its static-position rectangle.
            // https://drafts.csswg.org/css-align-3/#justify-abspos
            alignmentShift = resolveAlignmentShift(remainingSpace, outerSize);
        } else if (hasAutoBeforeInset != hasAutoAfterInset)
            alignmentShift = hasAutoAfterInset ? 0_lu : remainingSpace;
        else // Align into remaining space.
            alignmentShift = resolveAlignmentShift(remainingSpace, outerSize);
    };

    auto position = m_insetModifiedContainingRange.min() + usedMarginBefore + alignmentShift;

    computedValues.position = position;
    if (LogicalBoxAxis::Inline == m_selfAxis) {
        if (m_writingMode.isLogicalLeftInlineStart() == !containingCoordsAreFlipped()) {
            computedValues.margins.start = usedMarginBefore;
            computedValues.margins.end = usedMarginAfter;
        } else {
            computedValues.margins.start = usedMarginAfter;
            computedValues.margins.end = usedMarginBefore;
        }
    } else if (containingCoordsAreFlipped()) {
        computedValues.margins.before = usedMarginAfter;
        computedValues.margins.after = usedMarginBefore;
    } else {
        computedValues.margins.before = usedMarginBefore;
        computedValues.margins.after = usedMarginAfter;
    }
}

LayoutUnit PositionedLayoutConstraints::resolveAlignmentShift(LayoutUnit unusedSpace, LayoutUnit itemSize) const
{
    bool startIsBefore = this->startIsBefore();
    bool isOverflowing = unusedSpace < 0_lu;
    if (isOverflowing && OverflowAlignment::Safe == m_alignment.overflow())
        return startIsBefore ? 0_lu : unusedSpace;

    ItemPosition resolvedAlignment = resolveAlignmentValue();
    ASSERT(ItemPosition::Auto != resolvedAlignment);

    LayoutUnit shift;
    if (ItemPosition::AnchorCenter == resolvedAlignment) {
        auto anchorCenterPosition = m_anchorArea.min() + (m_anchorArea.size() - itemSize) / 2;
        shift = anchorCenterPosition - m_insetModifiedContainingRange.min();
        if (m_alignment.overflow() == OverflowAlignment::Safe) {
            if (startIsBefore) {
                if (shift < 0)
                    shift = 0;
            } else {
                if (shift > unusedSpace)
                    shift = unusedSpace;
            }
        }
        if (!isOverflowing && OverflowAlignment::Default == m_alignment.overflow()) {
            // Avoid introducing overflow of the IMCB.
            if (shift < 0)
                shift = 0;
            else if (shift > unusedSpace)
                shift = unusedSpace;
        }
    } else {
        auto alignmentSpace = StyleSelfAlignmentData::adjustmentFromStartEdge(unusedSpace, resolvedAlignment, m_containingAxis, m_containingWritingMode, m_writingMode);
        shift = startIsBefore ? alignmentSpace : unusedSpace - alignmentSpace;
    }

    if (isOverflowing && ItemPosition::Normal != resolvedAlignment
        && OverflowAlignment::Default == m_alignment.overflow()) {
        // Allow overflow, but try to stay within the containing block.
        // See https://www.w3.org/TR/css-align-3/#auto-safety-position

        auto containingRange = m_originalContainingRange;
        if (m_defaultAnchorBox && PositionType::Fixed == m_style.position()) {
            // We didn't modify the m_containingRange to include scrollable area for positioning,
            // but we should allow it for overflow management if we can scroll to reach that overflow.
            if (auto renderView = dynamicDowncast<RenderView>(m_container.get())) {
                CheckedRef view = renderView->frameView();
                auto scrollPosition = view->constrainedScrollPosition(ScrollPosition(view->scrollPositionRespectingCustomFixedPosition()));
                expandToScrollableArea(containingRange, scrollPosition);
            }
        }

        auto spaceAfter = std::max(0_lu, containingRange.max() - m_insetModifiedContainingRange.max());
        auto spaceBefore = std::max(0_lu, m_insetModifiedContainingRange.min() - containingRange.min());

        auto [allowsInfiniteOverflowBefore, allowsInfiniteOverflowAfter] = containerAllowsInfiniteOverflow();

        if (startIsBefore) {
            // Avoid overflow on the end side
            spaceAfter += (unusedSpace - shift);
            if (spaceAfter < 0 && !allowsInfiniteOverflowAfter)
                shift += spaceAfter;
            // Disallow overflow on the start side.
            spaceBefore += shift;
            if (spaceBefore < 0 && !allowsInfiniteOverflowBefore)
                shift -= spaceBefore;
        } else {
            // Avoid overflow on the end side
            spaceBefore += shift;
            if (spaceBefore < 0 && !allowsInfiniteOverflowBefore)
                shift -= spaceBefore;
            // Disallow overflow on the start side.
            spaceAfter += (unusedSpace - shift);
            if (spaceAfter < 0 && !allowsInfiniteOverflowAfter)
                shift += spaceAfter;
        }

    }
    return shift;
}

ItemPosition PositionedLayoutConstraints::resolveAlignmentValue() const
{
    if (m_useStaticPosition) {
        // At the static position an explicit justify-self aligns the box within its
        // static-position rectangle, resolving against the parent (the static-position
        // containing block); auto resolves to the parent's justify-items.
        if (shouldAlignStaticPositionInInlineAxis())
            return m_style.justifySelf().resolve(m_renderer->parentStyle()).position();
#if ASSERT_ENABLED
        ASSERT(m_isEligibleForStaticRangeAlignment);
#endif
        return m_style.alignSelf().resolve(m_renderer->parentStyle()).position();
    }

    auto alignmentPosition = [&] {
        auto itemPosition = m_alignment.position();
        return (ItemPosition::Auto == itemPosition) ? ItemPosition::Normal : itemPosition;
    }();

    if (auto positionAreaValue = m_style.positionArea().tryValue(); positionAreaValue && ItemPosition::Normal == alignmentPosition)
        alignmentPosition = positionAreaValue->defaultAlignmentForAxis(m_physicalAxis, m_containingWritingMode, m_writingMode);

    if (!m_defaultAnchorBox && alignmentPosition == ItemPosition::AnchorCenter)
        return ItemPosition::Center;
    return alignmentPosition;
}

std::pair<bool, bool> PositionedLayoutConstraints::containerAllowsInfiniteOverflow() const
{
    if (!(m_container->hasPotentiallyScrollableOverflow() || (is<RenderView>(m_container) && PositionType::Fixed != m_style.position())))
        return { false, false };
    auto* containerBox = dynamicDowncast<RenderBox>(m_container.get());
    ASSERT(containerBox);
    if (!containerBox)
        return { false, false };

    auto overflowLimits = containerBox->allowedLayoutOverflow(); // Already in flipped coordinates.
    return m_physicalAxis == BoxAxis::Vertical
        ? std::pair<bool, bool> { !overflowLimits.top(), !overflowLimits.bottom() }
        : std::pair<bool, bool> { !overflowLimits.left(), !overflowLimits.right() };
}

bool PositionedLayoutConstraints::alignmentAppliesStretch(ItemPosition normalAlignment) const
{
    auto alignmentPosition = m_alignment.position();
    if (m_style.positionArea().isNone() && (ItemPosition::Auto == alignmentPosition || ItemPosition::Normal == alignmentPosition))
        alignmentPosition = normalAlignment;
    return ItemPosition::Stretch == alignmentPosition;
}

bool NODELETE PositionedLayoutConstraints::insetFitsContent() const
{
    return (m_insetBefore.isAuto() || m_insetAfter.isAuto())
        && !m_defaultAnchorBox; // position-area and align-center zero out auto insets.
}

bool PositionedLayoutConstraints::needsGridAreaAdjustmentBeforeStaticPositioning() const
{
    if (m_containingAxis == LogicalBoxAxis::Block)
        return true;

    auto* parent = m_renderer->parent();
    // When the grid container is a parent we do not take the normal static positioning path.
    if (!m_container->isRenderGrid() || parent == m_container)
        return false;

    auto parentWritingMode = parent->writingMode();
    if (parentWritingMode.isLogicalLeftInlineStart() && !parentWritingMode.isOrthogonal(m_writingMode))
        return false;

    return true;
}

// MARK: - Static Position Computation

void PositionedLayoutConstraints::computeStaticPosition()
{
    ASSERT(m_useStaticPosition);

    if (is<RenderGrid>(m_container)) {
        // Grid Containers have special behavior, see https://www.w3.org/TR/css-grid/#abspos
        if (m_container.get() == m_renderer->parent()) {
            // Fake the static layout right here so it integrates with grid-area properly.
            m_useStaticPosition = false; // Avoid the static position code path.
            m_insetBefore = 0_css_px;
            m_insetAfter = 0_css_px;

            if (m_alignment.isNormal()) {
                // This very likely was 'auto' before resolution, so re-resolve it against the static position containing block.
                if (LogicalBoxAxis::Inline == m_containingAxis) {
                    m_alignment = m_style.justifySelf().resolve(&m_container->style());
                } else
                    m_alignment = m_style.alignSelf().resolve(&m_container->style());
            }
            if (m_alignment.isNormal())
                m_alignment.setPosition(ItemPosition::Start);
            if (OverflowAlignment::Default == m_alignment.overflow())
                m_alignment.setOverflow(OverflowAlignment::Unsafe);

            // Unclear if this is spec-compliant, but it is the current interop behavior.
            if (m_marginBefore.isAuto())
                m_marginBefore = 0_css_px;
            if (m_marginAfter.isAuto())
                m_marginAfter = 0_css_px;
            return;
        }
        // Rewind grid-area adjustments and fall through to the existing static position code.
        if (needsGridAreaAdjustmentBeforeStaticPositioning())
            m_containingRange.moveTo(m_originalContainingRange.min());
    }

    auto staticDistance = m_selfAxis == LogicalBoxAxis::Inline ? computedInlineStaticDistance() : computedBlockStaticDistance();
    auto shouldUseInsetBefore = [&] {
        if (m_selfAxis == LogicalBoxAxis::Block)
            return !isParentOpposingContainingBlock();
        auto shouldUseInsetBefore = m_parentWritingMode.isOrthogonal(selfWritingMode()) || !m_parentWritingMode.isInlineFlipped(); // This is what trunk has.
        if (!shouldUseInsetBefore) {
            // FIXME: Figure out why.
            shouldUseInsetBefore = m_containingWritingMode.isOrthogonal(m_parentWritingMode) && m_containingWritingMode.isBlockFlipped();
        }
        if (shouldUseInsetBefore && isParentOpposingContainingBlock())
            shouldUseInsetBefore = false;
        return shouldUseInsetBefore;
    };
    // Since the static position is computed during in flow layout, the computed
    // position should already have zoom computed in. We need to divide out the zoom
    // so that we get the same position when evaluating the inset.
    if (shouldUseInsetBefore())
        m_insetBefore = Style::InsetEdge::Fixed { staticDistance / m_style.usedZoomForLength().value };
    else
        m_insetAfter = Style::InsetEdge::Fixed { (containingSize() - staticDistance) / m_style.usedZoomForLength().value };
}

static LayoutPoint positionInContainer(const RenderBox& container, const RenderBox& child, LayoutPoint positionInChild)
{
    auto containerWritingMode = container.writingMode();
    auto childWritingMode = child.writingMode();
    auto childInFlowOffset = childWritingMode.isHorizontal() ? child.offsetForInFlowPosition() : child.offsetForInFlowPosition().transposedSize();
    auto childLogicalLeft = childInFlowOffset.width() + child.logicalLeft();
    auto childLogicalTop = childInFlowOffset.height() + child.logicalTop();

    if (containerWritingMode.isOrthogonal(childWritingMode)) {
        auto topLeft = LayoutPoint { childLogicalLeft + positionInChild.x(), childLogicalTop + positionInChild.y() };
        if (childWritingMode.isBlockFlipped())
            topLeft.setY(childLogicalTop + child.logicalHeight() - positionInChild.y());
        if (containerWritingMode.isBlockFlipped())
            topLeft.setX(childLogicalLeft + child.logicalWidth() - positionInChild.x());
        return topLeft.transposedPoint();
    }

    if (containerWritingMode.isBlockOpposing(childWritingMode))
        return { childLogicalLeft + positionInChild.x(), childLogicalTop + child.logicalHeight() - positionInChild.y() };

    return { childLogicalLeft + positionInChild.x(), childLogicalTop + positionInChild.y() };
}

static LayoutPoint staticDistance(const RenderBoxModelObject& container, const RenderBox& outOfFlowBox)
{
    // Static position is relative to the candidate box's parent (it is computed during normal in-flow layout as if the candidate box was in-flow)
    // 1. traverse the ancestor chain and convert static position relative to each container all the way up to the containing block
    // 2. adjust the final static position with the containing block's border
    // 3. pick x or y depending on what direction we are actually interested in (note that it's always the block directon from the
    //    candidate box's point of view but it could very well be the inline distance from the containing block's point of view.)

    auto initialStaticPosition = [&] {
        // Static position is already in the coordinate system of the container (minus the flip in inline direction).
        auto staticPosition = LayoutPoint { outOfFlowBox.layer()->staticInlinePosition(), outOfFlowBox.layer()->staticBlockPosition() };
        // We are relative to a RenderBox ancestor unless the containing block itself is an inline box.
        auto* staticPositionContainingBlock = outOfFlowBox.parent();
        for (; staticPositionContainingBlock && !is<RenderBox>(staticPositionContainingBlock) && staticPositionContainingBlock != &container; staticPositionContainingBlock = staticPositionContainingBlock->container()) { }
        if (auto* renderBox = dynamicDowncast<RenderBox>(staticPositionContainingBlock); renderBox && renderBox->writingMode().isInlineFlipped())
            staticPosition.setX(renderBox->logicalWidth() - staticPosition.x());
        return staticPosition;
    };

    auto staticPosition = LayoutPoint { };
    auto* child = &outOfFlowBox;
    auto hasSeenNonInlineBoxContainer = false;
    for (auto* ancestorContainer = child->parent(); ancestorContainer && ancestorContainer != &container; ancestorContainer = ancestorContainer->container()) {
        CheckedPtr containerBox = dynamicDowncast<RenderBox>(*ancestorContainer);
        if (!containerBox)
            continue;

        staticPosition = child == &outOfFlowBox ? initialStaticPosition() : positionInContainer(*containerBox, *child, staticPosition);
        child = containerBox.get();
        hasSeenNonInlineBoxContainer = true;
    }

    if (!hasSeenNonInlineBoxContainer && is<RenderInline>(container)) {
        // This is a simple case of when the containing block is formed by a positioned inline box with no block boxes in-between (e.g <span style="position: relative">)
        return initialStaticPosition();
    }

    auto* containingBlock = dynamicDowncast<RenderBox>(container);
    // m_insetBefore is expected to be relative to the padding box (while staticPosition is relative to the border box).
    auto containingBlockBorderSize = LayoutSize { };
    if (containingBlock)
        containingBlockBorderSize = containingBlock->writingMode().isInlineFlipped() ? LayoutSize(containingBlock->borderEnd(), containingBlock->borderBefore()) : LayoutSize(containingBlock->borderStart(), containingBlock->borderBefore());
    else {
        containingBlock = child->containingBlock();
        ASSERT(containingBlock);
        // Note that we don't take the border here as we passed the real containing block.
    }

    staticPosition = child == &outOfFlowBox ? initialStaticPosition() : positionInContainer(*containingBlock, *child, staticPosition);
    staticPosition -= containingBlockBorderSize;
    return staticPosition;
}

LayoutUnit PositionedLayoutConstraints::computedInlineStaticDistance() const
{
    // Note that at this point staticPosition is relative to the containing block (x is inline direction, y is block direction) which may not match with the box's slef writing mode.
    auto staticPosition = staticDistance(*m_container, m_renderer.get());
    auto staticDistance = !isOrthogonal() ? staticPosition.x() : staticPosition.y();
    if (CheckedPtr gridContainer = dynamicDowncast<RenderGrid>(m_container.get())) {
        // Special grid handling: move static distance back to relative to border box and adjust with our offset.
        auto containingBlockBorderSize = !isOrthogonal() ? (gridContainer->writingMode().isInlineFlipped() ? gridContainer->borderEnd() : gridContainer->borderStart()) : gridContainer->borderBefore();
        staticDistance += containingBlockBorderSize;
        staticDistance -= m_containingRange.min();
    }
    return staticDistance;
}

LayoutUnit PositionedLayoutConstraints::computedBlockStaticDistance() const
{
    // Note that at this point staticPosition is relative to the containing block (x is inline direction, y is block direction) which may not match with the box's slef writing mode.
    auto staticPosition = staticDistance(*m_container, m_renderer.get());
    return !isOrthogonal() ? staticPosition.y() : staticPosition.x();
}

static bool NODELETE shouldInlineStaticDistanceAdjustedWithBoxHeight(WritingMode containinigBlockWritingMode, WritingMode parentWritingMode, WritingMode outOfFlowBoxWritingMode)
{
    if (!containinigBlockWritingMode.isOrthogonal(parentWritingMode))
        return false;

    if (parentWritingMode.isOrthogonal(outOfFlowBoxWritingMode))
        return parentWritingMode.isBlockFlipped();

    return containinigBlockWritingMode.isBlockFlipped() && !parentWritingMode.isInlineFlipped();
}

void PositionedLayoutConstraints::fixupLogicalLeftPosition(RenderBox::LogicalExtentComputedValues& computedValues) const
{
    if (m_useStaticPosition) {
        auto shouldAdjustWithBoxExtent = [&] {
            if (isParentOpposingContainingBlock())
                return false;
            if (m_container.get() == m_renderer->parent())
                return false;
            return shouldInlineStaticDistanceAdjustedWithBoxHeight(m_containingWritingMode, m_parentWritingMode, selfWritingMode());
        };
        if (shouldAdjustWithBoxExtent())
            computedValues.position -= computedValues.extent;
        return;
    }

    if (m_writingMode.isHorizontal()) {
        CheckedPtr containingBox = dynamicDowncast<RenderBox>(container());
        if (containingBox && containingBox->shouldPlaceVerticalScrollbarOnLeft())
            computedValues.position += containingBox->verticalScrollbarWidth();
    }

    // FIXME: This hack is needed to calculate the logical left position for a 'rtl' relatively
    // positioned, inline because right now, it is using the logical left position
    // of the first line box when really it should use the last line box. When
    // this is fixed elsewhere, this adjustment should be removed.

    CheckedPtr renderInline = dynamicDowncast<RenderInline>(container());
    if (!renderInline || m_containingWritingMode.isLogicalLeftInlineStart())
        return;

    auto firstInlineBox = InlineIterator::lineLeftmostInlineBoxFor(*renderInline);
    if (!firstInlineBox)
        return;

    auto lastInlineBox = [&] {
        auto inlineBox = firstInlineBox;
        for (; inlineBox->nextInlineBoxLineRightward(); inlineBox.traverseInlineBoxLineRightward()) { }
        return inlineBox;
    }();
    if (firstInlineBox == lastInlineBox)
        return;

    auto lastInlineBoxPaddingBoxVisualRight = lastInlineBox->logicalLeftIgnoringInlineDirection() + renderInline->borderLogicalLeft();
    // FIXME: This does not work with decoration break clone.
    auto firstInlineBoxPaddingBoxVisualRight = firstInlineBox->logicalLeftIgnoringInlineDirection();
    auto adjustment = lastInlineBoxPaddingBoxVisualRight - firstInlineBoxPaddingBoxVisualRight;
    computedValues.position += adjustment - m_containingRange.min();
}

// FIXME: Let's move this over to RenderBoxModelObject and collapse some of the logic here.
static bool NODELETE shouldBlockStaticDistanceAdjustedWithBoxHeight(const RenderBoxModelObject& containingBlock, const RenderElement& parent, WritingMode outOfFlowBoxWritingMode)
{
    // This is where we check if the final static position needs to be adjusted with the height of the out-of-flow box.
    // In ::computeBlockStaticDistance we convert the static position relative to the containing block but in some cases
    // this final static position still points to the wrong side of the box (i.e. at computeBlockStaticDistance we don't know yet the height
    // which may contribute to the logical top position. see details below.)

    auto parentWritingMode = parent.writingMode();
    auto containinigBlockWritingMode = containingBlock.writingMode();

    if (containinigBlockWritingMode.blockDirection() == parentWritingMode.blockDirection() && parentWritingMode.blockDirection() == outOfFlowBoxWritingMode.blockDirection())
        return false;

    auto isParentInlineFlipped = parentWritingMode.isInlineFlipped();
    if (containinigBlockWritingMode.isOrthogonal(outOfFlowBoxWritingMode)) {
        if (&containingBlock == &parent) {
            // <div id=containinigBlock class=rtl>
            //   <div id=outOfFlowBox class=ltr>
            return isParentInlineFlipped;
        }

        if (!containinigBlockWritingMode.isOrthogonal(parentWritingMode))
            return isParentInlineFlipped;

        return parentWritingMode.isBlockFlipped();
    }

    ASSERT(containinigBlockWritingMode.blockDirection() == outOfFlowBoxWritingMode.blockDirection() || containinigBlockWritingMode.isBlockOpposing(outOfFlowBoxWritingMode));
    if (!parentWritingMode.isOrthogonal(containinigBlockWritingMode)) {
        // inline direction does not matter as all participants are on the same axis.
        if (containinigBlockWritingMode.blockDirection() == outOfFlowBoxWritingMode.blockDirection()) {
            // <div id=containinigBlock class=vrl>
            //   <div id=parent class=vlr>
            //     <div id=outOfFlowBox class=vrl>
            return true;
        }

        // <div id=containinigBlock class=vlr>
        //   <div id=parent class=vrl>
        //     <div id=outOfFlowBox class=vrl>
        return parentWritingMode.isBlockOpposing(containinigBlockWritingMode);
    }

    // Orhogonal parent.
    // <div id=containinigBlock class=vrl>
    //   <div id=parent class=htb>
    //     <div id=outOfFlowBox class=vlr>
    return containinigBlockWritingMode.isBlockFlipped() != isParentInlineFlipped;
}

void PositionedLayoutConstraints::adjustLogicalTopWithLogicalHeightIfNeeded(RenderBox::LogicalExtentComputedValues& computedValues) const
{
    if (!m_useStaticPosition || m_selfAxis != LogicalBoxAxis::Block)
        return;
    if (isParentOpposingContainingBlock()) {
        // When the static position was corrected to insetAfter, the position is already at the correct edge.
        return;
    }
    if (shouldBlockStaticDistanceAdjustedWithBoxHeight(*m_container, *m_renderer->parent(), m_writingMode))
        computedValues.position -= computedValues.extent;
}

}
