// Copyright (c) 2010 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 NET_BASE_NETWORK_CHANGE_NOTIFIER_H_
#define NET_BASE_NETWORK_CHANGE_NOTIFIER_H_
#pragma once

#include "base/basictypes.h"
#include "base/observer_list_threadsafe.h"
#include "net/base/net_export.h"

namespace net {

// NetworkChangeNotifier monitors the system for network changes, and notifies
// registered observers of those events.  Observers may register on any thread,
// and will be called back on the thread from which they registered.
class NET_EXPORT NetworkChangeNotifier {
 public:
  class NET_EXPORT IPAddressObserver {
   public:
    virtual ~IPAddressObserver() {}

    // Will be called when the IP address of the primary interface changes.
    // This includes when the primary interface itself changes.
    virtual void OnIPAddressChanged() = 0;

   protected:
    IPAddressObserver() {}

   private:
    DISALLOW_COPY_AND_ASSIGN(IPAddressObserver);
  };

  class NET_EXPORT OnlineStateObserver {
   public:
    virtual ~OnlineStateObserver() {}

    // Will be called when the online state of the system may have changed.
    // See NetworkChangeNotifier::IsOffline() for important caveats about
    // the unreliability of this signal.
    virtual void OnOnlineStateChanged(bool online) = 0;

   protected:
    OnlineStateObserver() {}

   private:
    DISALLOW_COPY_AND_ASSIGN(OnlineStateObserver);
  };

  virtual ~NetworkChangeNotifier();

  // See the description of NetworkChangeNotifier::IsOffline().
  // Implementations must be thread-safe. Implementations must also be
  // cheap as this could be called (repeatedly) from the IO thread.
  virtual bool IsCurrentlyOffline() const = 0;

  // Creates the process-wide, platform-specific NetworkChangeNotifier.  The
  // caller owns the returned pointer.  You may call this on any thread.  You
  // may also avoid creating this entirely (in which case nothing will be
  // monitored), but if you do create it, you must do so before any other
  // threads try to access the API below, and it must outlive all other threads
  // which might try to use it.
  static NetworkChangeNotifier* Create();

  // Returns true if there is currently no internet connection.
  //
  // A return value of |true| is a pretty strong indicator that the user
  // won't be able to connect to remote sites. However, a return value of
  // |false| is inconclusive; even if some link is up, it is uncertain
  // whether a particular connection attempt to a particular remote site
  // will be successfully.
  static bool IsOffline();

  // Like Create(), but for use in tests.  The mock object doesn't monitor any
  // events, it merely rebroadcasts notifications when requested.
  static NetworkChangeNotifier* CreateMock();

  // Registers |observer| to receive notifications of network changes.  The
  // thread on which this is called is the thread on which |observer| will be
  // called back with notifications.  This is safe to call if Create() has not
  // been called (as long as it doesn't race the Create() call on another
  // thread), in which case it will simply do nothing.
  static void AddIPAddressObserver(IPAddressObserver* observer);
  static void AddOnlineStateObserver(OnlineStateObserver* observer);

  // Unregisters |observer| from receiving notifications.  This must be called
  // on the same thread on which AddObserver() was called.  Like AddObserver(),
  // this is safe to call if Create() has not been called (as long as it doesn't
  // race the Create() call on another thread), in which case it will simply do
  // nothing.  Technically, it's also safe to call after the notifier object has
  // been destroyed, if the call doesn't race the notifier's destruction, but
  // there's no reason to use the API in this risky way, so don't do it.
  static void RemoveIPAddressObserver(IPAddressObserver* observer);
  static void RemoveOnlineStateObserver(OnlineStateObserver* observer);

#ifdef UNIT_TEST
  // Allow unit tests to trigger notifications.
  static void NotifyObserversOfIPAddressChangeForTests() {
    NotifyObserversOfIPAddressChange();
  }
#endif

 protected:
  NetworkChangeNotifier();

  // Broadcasts a notification to all registered observers.  Note that this
  // happens asynchronously, even for observers on the current thread, even in
  // tests.
  static void NotifyObserversOfIPAddressChange();
  void NotifyObserversOfOnlineStateChange();

 private:
  const scoped_refptr<ObserverListThreadSafe<IPAddressObserver> >
      ip_address_observer_list_;
  const scoped_refptr<ObserverListThreadSafe<OnlineStateObserver> >
      online_state_observer_list_;

  DISALLOW_COPY_AND_ASSIGN(NetworkChangeNotifier);
};

}  // namespace net

#endif  // NET_BASE_NETWORK_CHANGE_NOTIFIER_H_