text: // Copyright (c) 2012 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_PREFS_OVERLAY_USER_PREF_STORE_H_
  #define BASE_PREFS_OVERLAY_USER_PREF_STORE_H_
  
  #include <stdint.h>
  
  #include <map>
  #include <string>
  
  #include "base/macros.h"
  #include "base/memory/ref_counted.h"
  #include "base/observer_list.h"
  #include "base/prefs/base_prefs_export.h"
  #include "base/prefs/persistent_pref_store.h"
  #include "base/prefs/pref_value_map.h"
  
  // PersistentPrefStore that directs all write operations into an in-memory
  // PrefValueMap. Read operations are first answered by the PrefValueMap.
  // If the PrefValueMap does not contain a value for the requested key,
  // the look-up is passed on to an underlying PersistentPrefStore |underlay_|.
  class BASE_PREFS_EXPORT OverlayUserPrefStore : public PersistentPrefStore,
                                                 public PrefStore::Observer {
   public:
    explicit OverlayUserPrefStore(PersistentPrefStore* underlay);
  
    // Returns true if a value has been set for the |key| in this
    // OverlayUserPrefStore, i.e. if it potentially overrides a value
    // from the |underlay_|.
    virtual bool IsSetInOverlay(const std::string& key) const;
  
    // Methods of PrefStore.
    void AddObserver(PrefStore::Observer* observer) override;
    void RemoveObserver(PrefStore::Observer* observer) override;
    bool HasObservers() const override;
    bool IsInitializationComplete() const override;
    bool GetValue(const std::string& key,
                  const base::Value** result) const override;
  
    // Methods of PersistentPrefStore.
    bool GetMutableValue(const std::string& key, base::Value** result) override;
    void SetValue(const std::string& key,
                  scoped_ptr<base::Value> value,
                  uint32_t flags) override;
    void SetValueSilently(const std::string& key,
                          scoped_ptr<base::Value> value,
                          uint32_t flags) override;
    void RemoveValue(const std::string& key, uint32_t flags) override;
    bool ReadOnly() const override;
    PrefReadError GetReadError() const override;
    PrefReadError ReadPrefs() override;
    void ReadPrefsAsync(ReadErrorDelegate* delegate) override;
    void CommitPendingWrite() override;
    void SchedulePendingLossyWrites() override;
    void ReportValueChanged(const std::string& key, uint32_t flags) override;
  
    // Methods of PrefStore::Observer.
    void OnPrefValueChanged(const std::string& key) override;
    void OnInitializationCompleted(bool succeeded) override;
  
    void RegisterOverlayPref(const std::string& key);
    void RegisterOverlayPref(const std::string& overlay_key,
                             const std::string& underlay_key);
  
   protected:
    ~OverlayUserPrefStore() override;
  
   private:
    typedef std::map<std::string, std::string> NamesMap;
  
    const std::string& GetOverlayKey(const std::string& underlay_key) const;
    const std::string& GetUnderlayKey(const std::string& overlay_key) const;
  
    // Returns true if |key| corresponds to a preference that shall be stored in
    // an in-memory PrefStore that is not persisted to disk.
    bool ShallBeStoredInOverlay(const std::string& key) const;
  
    base::ObserverList<PrefStore::Observer, true> observers_;
    PrefValueMap overlay_;
    scoped_refptr<PersistentPrefStore> underlay_;
    NamesMap overlay_to_underlay_names_map_;
    NamesMap underlay_to_overlay_names_map_;
  
    DISALLOW_COPY_AND_ASSIGN(OverlayUserPrefStore);
  };
  
  #endif  // BASE_PREFS_OVERLAY_USER_PREF_STORE_H_
  