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// 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.
#include <memory>
#include <vector>
#include "base/macros.h"
#include "base/time/time.h"
class PrefRegistrySimple;
class PrefService;
namespace metrics {
// DailyEvent is used for throttling an event to about once per day, even if
// the program is restarted more frequently. It is based on local machine
// time, so it could be fired more often if the clock is changed.
// The service using the DailyEvent should first provide all of the Observers
// for the interval, and then arrange for CheckInterval() to be called
// periodically to test if the event should be fired.
class DailyEvent {
// Different reasons that Observer::OnDailyEvent() is called.
// This enum is used for histograms and must not be renumbered.
enum class IntervalType {
// Observer receives notifications from a DailyEvent.
// Observers must be added before the DailyEvent begins checking time,
// and will be owned by the DailyEvent.
class Observer {
virtual ~Observer();
// Called when the daily event is fired.
virtual void OnDailyEvent(IntervalType type) = 0;
// Constructs DailyEvent monitor which stores the time it last fired in the
// preference |pref_name|. |pref_name| should be registered by calling
// RegisterPref before using this object.
// Caller is responsible for ensuring that |pref_service| and |pref_name|
// outlive the DailyEvent.
// |histogram_name| is the name of the UMA metric which record when this
// interval fires, and should be registered in histograms.xml
DailyEvent(PrefService* pref_service,
const char* pref_name,
const std::string& histogram_name);
// Adds a observer to be notified when a day elapses. All observers should
// be registered before the the DailyEvent starts checking time.
void AddObserver(std::unique_ptr<Observer> observer);
// Checks if a day has elapsed. If it has, OnDailyEvent will be called on
// all observers.
void CheckInterval();
// Registers the preference used by this interval.
static void RegisterPref(PrefRegistrySimple* registry, const char* pref_name);
// Handles an interval elapsing because of |type|.
void OnInterval(base::Time now, IntervalType type);
// A weak pointer to the PrefService object to read and write preferences
// from. Calling code should ensure this object continues to exist for the
// lifetime of the DailyEvent object.
PrefService* pref_service_;
// The name of the preference to store the last fired time in.
// Calling code should ensure this outlives the DailyEvent.
const char* pref_name_;
// The name of the histogram to record intervals.
std::string histogram_name_;
// A list of observers.
std::vector<std::unique_ptr<Observer>> observers_;
// The time that the daily event was last fired.
base::Time last_fired_;
} // namespace metrics