/*

* Copyright (C) 2023 Apple Inc.

*

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*

* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY

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*/

#pragma once

#include "LayoutUnit.h"

#include "RenderStyleConstants.h"

#include "WritingMode.h"

#include <wtf/WeakHashSet.h>

namespace WebCore {

class RenderBox;

// These classes are used to implement the Baseline Alignment logic, as described in the CSS Box Alignment

// specification.

// https://drafts.csswg.org/css-align/#baseline-terms

//

// A baseline-sharing group is composed of boxes that participate in baseline alignment together. This is

// possible only if they:

//

// * Share an alignment context along an axis perpendicular to their baseline alignment axis.

// * Have compatible baseline alignment preferences (i.e., the baselines that want to align are on the same

// side of the alignment context).

//

// Once the BaselineGroup is instantiated, defined by a 'block flow direction' and a 'baseline-preference'

// (first/last baseline), it's ready to collect the items that will participate in the Baseline Alignment logic.

//

class BaselineGroup {

public:

// It stores an item (if not already present) and update the max_ascent associated to this

// baseline-sharing group.

void update(const RenderBox&, LayoutUnit ascent);

LayoutUnit maxAscent() const { return m_maxAscent; }

int computeSize() const { return m_items.computeSize(); }

auto begin() { return m_items.begin(); }

auto end() { return m_items.end(); }

private:

friend class BaselineAlignmentState;

BaselineGroup(BlockFlowDirection, ItemPosition childPreference);

// Determines whether a baseline-sharing group is compatible with an item, based on its 'block-flow' and

// 'baseline-preference'

bool isCompatible(BlockFlowDirection, ItemPosition) const;

// Determines whether the baseline-sharing group's associated block-flow is opposite (LR vs RL) to particular

// item's writing-mode.

bool isOppositeBlockFlow(BlockFlowDirection) const;

// Determines whether the baseline-sharing group's associated block-flow is orthogonal (vertical vs horizontal)

// to particular item's writing-mode.

bool isOrthogonalBlockFlow(BlockFlowDirection) const;

BlockFlowDirection m_blockFlow;

ItemPosition m_preference;

LayoutUnit m_maxAscent;

WeakHashSet<RenderBox> m_items;

};

//

// BaselineAlignmentState provides an API to interact with baseline sharing groups in various

// ways such as adding items to appropriate ones and querying the baseline sharing group for

// an item. A BaselineAlignmentState should be created by a formatting context to use for each

// of its baseline alignment contexts.

//

// https://drafts.csswg.org/css-align-3/#baseline-sharing-group

// A Baseline alignment-context may handle several baseline-sharing groups. In order to create an instance, we

// need to pass the required data to define the first baseline-sharing group; a BaselineAlignmentState must have at

// least one baseline-sharing group.

//

// By adding new items to a BaselineAlignmentState, the baseline-sharing groups it handles are automatically updated,

// if there is one that is compatible with such item. Otherwise, a new baseline-sharing group is created,

// compatible with the new item.

class BaselineAlignmentState {

WTF_MAKE_FAST_ALLOCATED;

public:

BaselineAlignmentState(const RenderBox& child, ItemPosition preference, LayoutUnit ascent);

const BaselineGroup& sharedGroup(const RenderBox& child, ItemPosition preference) const;

// Updates the baseline-sharing group compatible with the item.

// We pass the item's baseline-preference to avoid dependencies with the LayoutGrid class, which is the one

// managing the alignment behavior of the Grid Items.

void updateSharedGroup(const RenderBox& child, ItemPosition preference, LayoutUnit ascent);

Vector<BaselineGroup>& sharedGroups();

private:

// Returns the baseline-sharing group compatible with an item.

// We pass the item's baseline-preference to avoid dependencies with the LayoutGrid class, which is the one

// managing the alignment behavior of the Grid Items.

// FIXME: Properly implement baseline-group compatibility.

// See https://github.com/w3c/csswg-drafts/issues/721

BaselineGroup& findCompatibleSharedGroup(const RenderBox& child, ItemPosition preference);

Vector<BaselineGroup> m_sharedGroups;

};

} // namespace WebCore