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 // Copyright (c) 2008 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 BASE_SYSTEM_MONITOR_H_

 #define BASE_SYSTEM_MONITOR_H_

 #include "base/observer_list_threadsafe.h"

 #include "base/singleton.h"

 // Windows HiRes timers drain the battery faster so we need to know the battery

 // status.  This isn't true for other platforms.

 #if defined(OS_WIN)

 #define ENABLE_BATTERY_MONITORING 1

 #else

 #undef ENABLE_BATTERY_MONITORING

 #endif  // !OS_WIN

 namespace base {

 // Class for monitoring various system-related subsystems

 // such as power management, network status, etc.

 // TODO(mbelshe):  Add support beyond just power management.

 class SystemMonitor {

  public:

   // Access to the Singleton

   static SystemMonitor* Get() {

     // Uses the LeakySingletonTrait because cleanup is optional.

     return

         Singleton<SystemMonitor, LeakySingletonTraits<SystemMonitor> >::get();

   }

   // Start the System Monitor within a process.  This method

   // is provided so that the battery check can be deferred.

   // The MessageLoop must be started before calling this

   // method.

   // This is a no-op on platforms for which ENABLE_BATTERY_MONITORING is

   // disabled.

   static void Start();

   //

   // Power-related APIs

   //

   // Is the computer currently on battery power.

   // Can be called on any thread.

   bool BatteryPower() {

     // Using a lock here is not necessary for just a bool.

     return battery_in_use_;

   }

   // Normalized list of power events.

   enum PowerEvent {

     POWER_STATE_EVENT,  // The Power status of the system has changed.

     SUSPEND_EVENT,      // The system is being suspended.

     RESUME_EVENT        // The system is being resumed.

   };

   // Callbacks will be called on the thread which creates the SystemMonitor.

   // During the callback, Add/RemoveObserver will block until the callbacks

   // are finished. Observers should implement quick callback functions; if

   // lengthy operations are needed, the observer should take care to invoke

   // the operation on an appropriate thread.

   class PowerObserver {

   public:

     // Notification of a change in power status of the computer, such

     // as from switching between battery and A/C power.

     virtual void OnPowerStateChange(SystemMonitor*) = 0;

     // Notification that the system is suspending.

     virtual void OnSuspend(SystemMonitor*) = 0;

     // Notification that the system is resuming.

     virtual void OnResume(SystemMonitor*) = 0;

   };

   // Add a new observer.

   // Can be called from any thread.

   // Must not be called from within a notification callback.

   void AddObserver(PowerObserver* obs);

   // Remove an existing observer.

   // Can be called from any thread.

   // Must not be called from within a notification callback.

   void RemoveObserver(PowerObserver* obs);

 #if defined(OS_WIN)

   // Windows-specific handling of a WM_POWERBROADCAST message.

   // Embedders of this API should hook their top-level window

   // message loop and forward WM_POWERBROADCAST through this call.

   void ProcessWmPowerBroadcastMessage(int event_id);

 #endif

   // Cross-platform handling of a power event.

   void ProcessPowerMessage(PowerEvent event_id);

   // Constructor.

   // Don't use this; access SystemMonitor via the Singleton.

   SystemMonitor();

  private:

   // Platform-specific method to check whether the system is currently

   // running on battery power.  Returns true if running on batteries,

   // false otherwise.

   bool IsBatteryPower();

   // Checks the battery status and notifies observers if the battery

   // status has changed.

   void BatteryCheck();

   // Functions to trigger notifications.

   void NotifyPowerStateChange();

   void NotifySuspend();

   void NotifyResume();

   scoped_refptr<ObserverListThreadSafe<PowerObserver> > observer_list_;

   bool battery_in_use_;

   bool suspended_;

 #if defined(ENABLE_BATTERY_MONITORING)

   base::OneShotTimer<SystemMonitor> delayed_battery_check_;

 #endif

   DISALLOW_COPY_AND_ASSIGN(SystemMonitor);

 };

 }

 #endif  // BASE_SYSTEM_MONITOR_H_