third_party/WebKit/Source/core/dom/ChildListMutationScope.h

/*
 * Copyright (C) 2011 Google Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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#ifndef ChildListMutationScope_h
#define ChildListMutationScope_h

#include "core/dom/Document.h"
#include "core/dom/MutationObserver.h"
#include "core/dom/Node.h"
#include "platform/heap/Handle.h"
#include "wtf/Noncopyable.h"

namespace blink {

class MutationObserverInterestGroup;

// ChildListMutationAccumulator is not meant to be used directly;
// ChildListMutationScope is the public interface.
//
// One ChildListMutationAccumulator for a given Node is shared between all the
// active ChildListMutationScopes for that Node. Once the last
// ChildListMutationScope is destructed the accumulator enqueues a mutation
// record for the recorded mutations and the accumulator can be garbage
// collected.
class ChildListMutationAccumulator final
    : public GarbageCollected<ChildListMutationAccumulator> {
 public:
  static ChildListMutationAccumulator* getOrCreate(Node&);

  void childAdded(Node*);
  void willRemoveChild(Node*);

  bool hasObservers() const { return m_observers; }

  // Register and unregister mutation scopes that are using this mutation
  // accumulator.
  void enterMutationScope() { m_mutationScopes++; }
  void leaveMutationScope();

  DECLARE_TRACE();

 private:
  ChildListMutationAccumulator(Node*, MutationObserverInterestGroup*);

  void enqueueMutationRecord();
  bool isEmpty();
  bool isAddedNodeInOrder(Node*);
  bool isRemovedNodeInOrder(Node*);

  Member<Node> m_target;

  HeapVector<Member<Node>> m_removedNodes;
  HeapVector<Member<Node>> m_addedNodes;
  Member<Node> m_previousSibling;
  Member<Node> m_nextSibling;
  Member<Node> m_lastAdded;

  Member<MutationObserverInterestGroup> m_observers;

  unsigned m_mutationScopes;
};

class ChildListMutationScope final {
  WTF_MAKE_NONCOPYABLE(ChildListMutationScope);
  STACK_ALLOCATED();

 public:
  explicit ChildListMutationScope(Node& target) {
    if (target.document().hasMutationObserversOfType(
            MutationObserver::ChildList)) {
      m_accumulator = ChildListMutationAccumulator::getOrCreate(target);
      // Register another user of the accumulator.
      m_accumulator->enterMutationScope();
    }
  }

  ~ChildListMutationScope() {
    if (m_accumulator) {
      // Unregister a user of the accumulator. If this is the last user
      // the accumulator will enqueue a mutation record for the mutations.
      m_accumulator->leaveMutationScope();
    }
  }

  void childAdded(Node& child) {
    if (m_accumulator && m_accumulator->hasObservers())
      m_accumulator->childAdded(&child);
  }

  void willRemoveChild(Node& child) {
    if (m_accumulator && m_accumulator->hasObservers())
      m_accumulator->willRemoveChild(&child);
  }

 private:
  Member<ChildListMutationAccumulator> m_accumulator;
};

}  // namespace blink

#endif  // ChildListMutationScope_h