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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 COMPONENTS_METRICS_DAILY_EVENT_H_
      6 #define COMPONENTS_METRICS_DAILY_EVENT_H_
      7 
      8 #include "base/macros.h"
      9 #include "base/memory/scoped_ptr.h"
     10 #include "base/memory/scoped_vector.h"
     11 #include "base/time/time.h"
     12 
     13 class PrefRegistrySimple;
     14 class PrefService;
     15 
     16 namespace metrics {
     17 
     18 // DailyEvent is used for throttling an event to about once per day, even if
     19 // the program is restarted more frequently.  It is based on local machine
     20 // time, so it could be fired more often if the clock is changed.
     21 //
     22 // The service using the DailyEvent should first provide all of the Observers
     23 // for the interval, and then arrange for CheckInterval() to be called
     24 // periodically to test if the event should be fired.
     25 class DailyEvent {
     26  public:
     27   // Observer receives notifications from a DailyEvent.
     28   // Observers must be added before the DailyEvent begins checking time,
     29   // and will be owned by the DailyEvent.
     30   class Observer {
     31    public:
     32     Observer();
     33     virtual ~Observer();
     34 
     35     // Called when the daily event is fired.
     36     virtual void OnDailyEvent() = 0;
     37 
     38    private:
     39     DISALLOW_COPY_AND_ASSIGN(Observer);
     40   };
     41 
     42   // Constructs DailyEvent monitor which stores the time it last fired in the
     43   // preference |pref_name|. |pref_name| should be registered by calling
     44   // RegisterPref before using this object.
     45   // Caller is responsible for ensuring that |pref_service| and |pref_name|
     46   // outlive the DailyEvent.
     47   // |histogram_name| is the name of the UMA metric which record when this
     48   // interval fires, and should be registered in histograms.xml
     49   DailyEvent(PrefService* pref_service,
     50              const char* pref_name,
     51              const std::string& histogram_name);
     52   ~DailyEvent();
     53 
     54   // Adds a observer to be notified when a day elapses. All observers should
     55   // be registered before the the DailyEvent starts checking time.
     56   void AddObserver(scoped_ptr<Observer> observer);
     57 
     58   // Checks if a day has elapsed. If it has, OnDailyEvent will be called on
     59   // all observers.
     60   void CheckInterval();
     61 
     62   // Registers the preference used by this interval.
     63   static void RegisterPref(PrefRegistrySimple* registry, const char* pref_name);
     64 
     65  private:
     66   // Handles an interval elapsing.
     67   void OnInterval(base::Time now);
     68 
     69   // A weak pointer to the PrefService object to read and write preferences
     70   // from. Calling code should ensure this object continues to exist for the
     71   // lifetime of the DailyEvent object.
     72   PrefService* pref_service_;
     73 
     74   // The name of the preference to store the last fired time in.
     75   // Calling code should ensure this outlives the DailyEvent.
     76   const char* pref_name_;
     77 
     78   // The name of the histogram to record intervals.
     79   std::string histogram_name_;
     80 
     81   // A list of observers.
     82   ScopedVector<Observer> observers_;
     83 
     84   // The time that the daily event was last fired.
     85   base::Time last_fired_;
     86 
     87   DISALLOW_COPY_AND_ASSIGN(DailyEvent);
     88 };
     89 
     90 }  // namespace metrics
     91 
     92 #endif  // COMPONENTS_METRICS_DAILY_EVENT_H_
     93