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      1 // Copyright 2014 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef EXTENSIONS_COMMON_VALUE_COUNTER_H_
      6 #define EXTENSIONS_COMMON_VALUE_COUNTER_H_
      7 
      8 #include <vector>
      9 
     10 #include "base/memory/linked_ptr.h"
     11 
     12 namespace base {
     13 class Value;
     14 }
     15 
     16 namespace extensions {
     17 
     18 // Keeps a running count of Values, like map<Value, int>. Adding / removing
     19 // values increments / decrements the count associated with a given Value.
     20 //
     21 // Add() and Remove() are linear in the number of Values in the ValueCounter,
     22 // because there is no operator<() defined on Value, so we must iterate to find
     23 // whether a Value is equal to an existing one.
     24 class ValueCounter {
     25  public:
     26   ValueCounter();
     27   ~ValueCounter();
     28 
     29   // Adds |value| to the set and returns how many equal values are in the set
     30   // after. Does not take ownership of |value|. In the case where a Value equal
     31   // to |value| doesn't already exist in this map, this function makes a
     32   // DeepCopy() of |value|.
     33   int Add(const base::Value& value);
     34 
     35   // Removes |value| from the set and returns how many equal values are in
     36   // the set after.
     37   int Remove(const base::Value& value);
     38 
     39   // Same as Add() but only performs the add if the value isn't present.
     40   int AddIfMissing(const base::Value& value);
     41 
     42  private:
     43   class Entry {
     44    public:
     45     explicit Entry(const base::Value& value);
     46     ~Entry();
     47 
     48     int Increment();
     49     int Decrement();
     50 
     51     const base::Value* value() const { return value_.get(); }
     52     int count() const { return count_; }
     53 
     54    private:
     55     linked_ptr<base::Value> value_;
     56     int count_;
     57 
     58     DISALLOW_COPY_AND_ASSIGN(Entry);
     59   };
     60   typedef std::vector<linked_ptr<Entry> > EntryList;
     61 
     62   int AddImpl(const base::Value& value, bool increment);
     63 
     64   EntryList entries_;
     65 
     66   DISALLOW_COPY_AND_ASSIGN(ValueCounter);
     67 };
     68 
     69 }  // namespace extensions
     70 
     71 #endif  // EXTENSIONS_COMMON_VALUE_COUNTER_H_
     72