components/sessions/core/session_id_generator.h

// Copyright 2018 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 COMPONENTS_SESSIONS_CORE_SESSION_ID_GENERATOR_H_
#define COMPONENTS_SESSIONS_CORE_SESSION_ID_GENERATOR_H_

#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/singleton.h"
#include "base/sequence_checker.h"
#include "components/sessions/core/session_id.h"
#include "components/sessions/core/sessions_export.h"

class PrefRegistrySimple;
class PrefService;

namespace sessions {

class SESSIONS_EXPORT SessionIdGenerator {
 public:
  // Returns the singleton instance of this class.
  static SessionIdGenerator* GetInstance();

  // Register preferences used by this class.
  static void RegisterPrefs(PrefRegistrySimple* prefs);

  // Initialization of the singleton. Must be called exactly once. |local_state|
  // must not be null and must exist until Shutdown() is called.
  void Init(PrefService* local_state);
  void Shutdown();

  // Creates a new instance representing an ID that has never been used before
  // locally (even across browser restarts). Must be preceded by Init().
  SessionID NewUnique();

  // Preference name used to persist the last ID.
  static std::string GetLastValuePrefNameForTest();

  // Internal random function injection for tests.
  using RandomGenerator = base::RepeatingCallback<SessionID::id_type()>;
  void SetRandomGeneratorForTest(const RandomGenerator& rand_generator);

 private:
  friend struct base::DefaultSingletonTraits<SessionIdGenerator>;

  SessionIdGenerator();
  ~SessionIdGenerator();

  void IncrementValueBy(int increment);

  SEQUENCE_CHECKER(sequence_checker_);
  PrefService* local_state_;
  SessionID::id_type last_value_;

  // Used to override the random number generator for tests.
  RandomGenerator rand_generator_;

  DISALLOW_COPY_AND_ASSIGN(SessionIdGenerator);
};

}  // namespace sessions

#endif  // COMPONENTS_SESSIONS_CORE_SESSION_ID_GENERATOR_H_