extensions/common/value_counter.h

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef EXTENSIONS_COMMON_VALUE_COUNTER_H_
#define EXTENSIONS_COMMON_VALUE_COUNTER_H_

#include <memory>
#include <vector>

#include "base/macros.h"

namespace base {
class Value;
}

namespace extensions {

// Keeps a running count of Values, like map<Value, int>. Adding/removing
// values increments/decrements the count associated with a given Value.
//
// Add() and Remove() are linear in the number of Values in the ValueCounter,
// because there is no operator<() defined on Value, so we must iterate to find
// whether a Value is equal to an existing one.
class ValueCounter {
 public:
  ValueCounter();
  ~ValueCounter();

  // Adds |value| to the set. In the case where a Value equal to |value|
  // doesn't already exist in this map, this function makes a copy of |value|
  // and returns true. Otherwise, it returns false.
  bool Add(const base::Value& value);

  // Removes |value| from the set, and returns true if it removed the last
  // value equal to |value|. If there are more equal values, or if there
  // weren't any in the first place, returns false.
  bool Remove(const base::Value& value);

  // Returns true if there are no values of any type being counted.
  bool is_empty() const { return entries_.empty(); }

 private:
  struct Entry;
  std::vector<std::unique_ptr<Entry>> entries_;

  DISALLOW_COPY_AND_ASSIGN(ValueCounter);
};

}  // namespace extensions

#endif  // EXTENSIONS_COMMON_VALUE_COUNTER_H_