text: // Copyright 2013 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 CHROME_BROWSER_PREFS_SYNCED_PREF_CHANGE_REGISTRAR_H_
  #define CHROME_BROWSER_PREFS_SYNCED_PREF_CHANGE_REGISTRAR_H_
  
  #include <map>
  #include <string>
  
  #include "base/callback.h"
  #include "chrome/browser/prefs/pref_service_syncable.h"
  #include "chrome/browser/prefs/synced_pref_observer.h"
  
  // Manages the registration of one or more SyncedPrefObservers on a
  // PrefServiceSyncable. This is modeled after base::PrefChangeRegistrar, and
  // it should be used whenever it's necessary to determine whether a pref change
  // has come from sync or from some other mechanism (managed, UI, external, etc.)
  class SyncedPrefChangeRegistrar : public SyncedPrefObserver {
   public:
    // Registered callbacks may optionally take a path argument.
    // The boolean argument indicates whether (true) or not (false)
    // the change was a result of syncing.
    typedef base::Callback<void(bool)> ChangeCallback;
    typedef base::Callback<void(const std::string&, bool)> NamedChangeCallback;
  
    explicit SyncedPrefChangeRegistrar(PrefServiceSyncable* pref_service);
    virtual ~SyncedPrefChangeRegistrar();
  
    // Register an observer callback for sync change events on the pref at
    // |path|. Only one callback may be registered per pref.
    void Add(const char* path, const ChangeCallback& callback);
    void Add(const char* path, const NamedChangeCallback& callback);
  
    // Remove the registered observer for |path|.
    void Remove(const char* path);
  
    // Remove all registered observers.
    void RemoveAll();
  
    // Indicates whether or not an observer is already registered for |path|.
    bool IsObserved(const char* path) const;
  
   private:
    // SyncedPrefObserver implementation
    void OnSyncedPrefChanged(const std::string& path, bool from_sync) override;
  
    typedef std::map<std::string, NamedChangeCallback> ObserverMap;
  
    PrefServiceSyncable* pref_service_;
    ObserverMap observers_;
  
    DISALLOW_COPY_AND_ASSIGN(SyncedPrefChangeRegistrar);
  };
  
  #endif  // CHROME_BROWSER_PREFS_SYNCED_PREF_CHANGE_REGISTRAR_H_
  