// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_METRICS_METRICS_STATE_MANAGER_H_
#define COMPONENTS_METRICS_METRICS_STATE_MANAGER_H_

#include <memory>
#include <string>
#include <string_view>

#include "base/callback_list.h"
#include "base/files/file_path.h"
#include "base/functional/callback.h"
#include "base/gtest_prod_util.h"
#include "base/memory/raw_ptr.h"
#include "base/metrics/field_trial.h"
#include "components/metrics/clean_exit_beacon.h"
#include "components/metrics/client_info.h"
#include "components/metrics/cloned_install_detector.h"
#include "components/metrics/entropy_state.h"
#include "components/variations/entropy_provider.h"

class PrefService;
class PrefRegistrySimple;

namespace metrics_services_manager {
class MetricsServicesManager;
}

namespace metrics {

class EnabledStateProvider;
class MetricsProvider;

// Denotes whether this session is a background or foreground session at
// startup. May be unknown. A background session refers to the situation in
// which the browser process starts; does some work, e.g. servicing a sync; and
// ends without ever becoming visible. Note that the point in startup at which
// this value is determined is likely before the UI is visible.
//
// These values are persisted to logs. Entries should not be renumbered and
// numeric values should never be reused.
enum class StartupVisibility {
  kUnknown = 0,
  kBackground = 1,
  kForeground = 2,
  kMaxValue = kForeground,
};

// Denotes the type of EntropyProvider to use for default one-time
// randomization.
enum class EntropyProviderType {
  kDefault = 0,  // Enable high entropy randomization if possible.
  kLow = 1,      // Always use low entropy randomization.
};

// Options to apply to trial randomization.
struct EntropyParams {
  // The type of entropy to use for default one-time randomization.
  EntropyProviderType default_entropy_provider_type =
      EntropyProviderType::kDefault;
  // Force trial randomization into benchmarking mode, which disables
  // randomization. Users may also be put in this mode if the
  // --enable_benchmarking command line flag is passed.
  bool force_benchmarking_mode = false;
};

// Responsible for managing MetricsService state prefs, specifically the UMA
// client id and low entropy source. Code outside the metrics directory should
// not be instantiating or using this class directly.
class MetricsStateManager final {
 public:
  // A callback that can be invoked to store client info to persistent storage.
  // Storing an empty client_id will resulted in the backup being voided.
  typedef base::RepeatingCallback<void(const ClientInfo& client_info)>
      StoreClientInfoCallback;

  // A callback that can be invoked to load client info stored through the
  // StoreClientInfoCallback.
  typedef base::RepeatingCallback<std::unique_ptr<ClientInfo>(void)>
      LoadClientInfoCallback;

  MetricsStateManager(const MetricsStateManager&) = delete;
  MetricsStateManager& operator=(const MetricsStateManager&) = delete;

  ~MetricsStateManager();

  std::unique_ptr<MetricsProvider> GetProvider();

  // Returns true if the user has consented to sending metric reports, and there
  // is no other reason to disable reporting. One such reason is client
  // sampling, and this client isn't in the sample.
  bool IsMetricsReportingEnabled();

  // Returns true if Extended Variations Safe Mode is supported on this
  // platform. Variations Safe Mode is a mechanism that allows Chrome to fall
  // back to a "safe" seed so that clients can recover from a problematic
  // experiment, for example, one that causes browser crashes. See the design
  // doc for more details:
  // https://docs.google.com/document/d/17UN2pLSa5JZqk8f3LeYZIftXewxqcITotgalTrJvGSY.
  //
  // Extended Variations Safe Mode builds on this by allowing clients to recover
  // from problematic experiments that cause browser crashes earlier on in
  // startup.
  bool IsExtendedSafeModeSupported() const;

  // Returns the client ID for this client, or the empty string if the user is
  // not opted in to metrics reporting.
  const std::string& client_id() const { return client_id_; }

  // Returns the low entropy sources for this client.
  int GetLowEntropySource();
  int GetOldLowEntropySource();
  int GetPseudoLowEntropySource();

  // The CleanExitBeacon, used to determine whether the previous Chrome browser
  // session terminated gracefully.
  CleanExitBeacon* clean_exit_beacon() { return &clean_exit_beacon_; }
  const CleanExitBeacon* clean_exit_beacon() const {
    return &clean_exit_beacon_;
  }

  // Returns true if the session was deemed a background session during startup.
  // Note that this is not equivalent to !is_foreground_session() because the
  // type of session may be unknown.
  bool is_background_session() const {
    return startup_visibility_ == StartupVisibility::kBackground;
  }

  // Returns true if the session was deemed a foreground session during startup.
  // Note that this is not equivalent to !is_background_session() because the
  // type of session may be unknown.
  bool is_foreground_session() const {
    return startup_visibility_ == StartupVisibility::kForeground;
  }

  // Instantiates the FieldTrialList.
  //
  // Side effect: Initializes |clean_exit_beacon_|.
  void InstantiateFieldTrialList();

  // Signals whether the session has shutdown cleanly. Passing `false` for
  // |has_session_shutdown_cleanly| means that Chrome has launched and has not
  // yet shut down safely. Passing `true` signals that Chrome has shut down
  // safely.
  //
  // Seeing a call with `false` without a matching call with `true` suggests
  // that Chrome crashed or otherwise did not shut down cleanly, e.g. maybe the
  // OS crashed.
  //
  // If |is_extended_safe_mode| is true, then |has_session_shutdown_cleanly| is
  // written to disk synchronously. If false, a write is scheduled, and for
  // clients in the Extended Variations Safe Mode experiment, a synchronous
  // write is done, too.
  //
  // Note: |is_extended_safe_mode| should be true only for the Extended
  // Variations Safe Mode experiment.
  void LogHasSessionShutdownCleanly(bool has_session_shutdown_cleanly,
                                    bool is_extended_safe_mode = false);

  // Forces the client ID to be generated. This is useful in case it's needed
  // before recording.
  void ForceClientIdCreation();

  // Checks if this install was cloned or imaged from another machine. If a
  // clone is detected, resets the client id and low entropy source. This
  // should not be called more than once.
  void CheckForClonedInstall();

  // Checks if the cloned install detector says that client ids should be reset.
  bool ShouldResetClientIdsOnClonedInstall();

  // Wrapper around ClonedInstallDetector::AddOnClonedInstallDetectedCallback().
  base::CallbackListSubscription AddOnClonedInstallDetectedCallback(
      base::OnceClosure callback);

  // Creates entropy providers for trial randomization.
  //
  // If this StateManager supports high entropy randomization, and there is
  // either consent to report metrics or this is the first run of Chrome,
  // this method returns an entropy provider that has a high source of entropy,
  // partially based on the client ID or provisional client ID. Otherwise, it
  // only returns an entropy provider that is based on a low entropy source.
  //
  // When |enable_limited_entropy_mode| is true, a limited entropy
  // randomization source value will be generated for this client.
  std::unique_ptr<const variations::EntropyProviders> CreateEntropyProviders(
      bool enable_limited_entropy_mode);

  ClonedInstallDetector* cloned_install_detector_for_testing() {
    return &cloned_install_detector_;
  }

  // Creates the MetricsStateManager, enforcing that only a single instance
  // of the class exists at a time. Returns nullptr if an instance exists
  // already.
  //
  // On Windows, |backup_registry_key| is used to store a backup of the clean
  // exit beacon. It is ignored on other platforms.
  //
  // |user_data_dir| is the path to the client's user data directory. If empty,
  // a separate file will not be used for Variations Safe Mode prefs.
  //
  // |startup_visibility| denotes whether this session is expected to come to
  // the foreground.
  static std::unique_ptr<MetricsStateManager> Create(
      PrefService* local_state,
      EnabledStateProvider* enabled_state_provider,
      const std::wstring& backup_registry_key,
      const base::FilePath& user_data_dir,
      StartupVisibility startup_visibility = StartupVisibility::kUnknown,
      EntropyParams entropy_params = {},
      StoreClientInfoCallback store_client_info = StoreClientInfoCallback(),
      LoadClientInfoCallback load_client_info = LoadClientInfoCallback());

  // Registers local state prefs used by this class.
  static void RegisterPrefs(PrefRegistrySimple* registry);

 private:
  FRIEND_TEST_ALL_PREFIXES(MetricsStateManagerTest, CheckProviderResetIds);
  FRIEND_TEST_ALL_PREFIXES(MetricsStateManagerTest, CheckProviderLogNormal);
  FRIEND_TEST_ALL_PREFIXES(MetricsStateManagerTest,
                           CheckProviderLogNormalWithParams);
  FRIEND_TEST_ALL_PREFIXES(
      MetricsStateManagerTest,
      CheckProviderResetIds_PreviousIdOnlyReportInResetSession);
  FRIEND_TEST_ALL_PREFIXES(MetricsStateManagerTest, EntropySourceUsed_Low);
  FRIEND_TEST_ALL_PREFIXES(MetricsStateManagerTest, EntropySourceUsed_High);
  FRIEND_TEST_ALL_PREFIXES(MetricsStateManagerTest,
                           ProvisionalClientId_PromotedToClientId);
  FRIEND_TEST_ALL_PREFIXES(MetricsStateManagerTest,
                           ProvisionalClientId_PersistedAcrossFirstRuns);
  FRIEND_TEST_ALL_PREFIXES(MetricsStateManagerTest, ResetBackup);
  FRIEND_TEST_ALL_PREFIXES(MetricsStateManagerTest, ResetMetricsIDs);
  friend class ::metrics_services_manager::MetricsServicesManager;

  // Designates which entropy source was returned from this class.
  // This is used for testing to validate that we return the correct source
  // depending on the state of the service.
  enum EntropySourceType {
    ENTROPY_SOURCE_NONE,
    ENTROPY_SOURCE_LOW,
    ENTROPY_SOURCE_HIGH,
    ENTROPY_SOURCE_ENUM_SIZE,
  };

  // These values are persisted to logs. Entries should not be renumbered and
  // numerical values should never be reused.
  enum class ClientIdSource {
    // Recorded when the client ID in Local State matches the cached copy.
    kClientIdMatches = 0,
    // Recorded when we are somehow missing the cached client ID and we are
    // able to recover it from the Local State.
    kClientIdFromLocalState = 1,
    // Recorded when we are somehow missing the client ID stored in Local State
    // yet are able to recover it from a backup location.
    kClientIdBackupRecovered = 2,
    // Recorded when we are somehow missing the client ID in Local State, cache
    // and backup and there is no provisional client ID, so a new client ID is
    // generated.
    kClientIdNew = 3,
    // Recorded when we are somehow missing the client ID in Local State, cache
    // and backup, so we promote the provisional client ID.
    kClientIdFromProvisionalId = 4,
    // Not recorded anymore.
    kClientIdFromExternalDeprecated = 5,
    kMaxValue = kClientIdFromExternalDeprecated,
  };

  // Creates the MetricsStateManager with the given |local_state|. Uses
  // |enabled_state_provider| to query whether there is consent for metrics
  // reporting, and if it is enabled. Clients should instead use Create(), which
  // enforces that a single instance of this class be alive at any given time.
  // |store_client_info| should back up client info to persistent storage such
  // that it is later retrievable by |load_client_info|.
  MetricsStateManager(PrefService* local_state,
                      EnabledStateProvider* enabled_state_provider,
                      const std::wstring& backup_registry_key,
                      const base::FilePath& user_data_dir,
                      EntropyParams entropy_params,
                      StartupVisibility startup_visibility,
                      StoreClientInfoCallback store_client_info,
                      LoadClientInfoCallback load_client_info);

  // Returns the ClonedInstallDetector. This is useful in case we're checking
  // whether an install was detected in this session.
  // Marked as private (exposed selectively via friend classes) for the metrics
  // team to be able to control and monitor if/how this function gets called.
  const ClonedInstallDetector& GetClonedInstallDetector() const;

  // Backs up the current client info via |store_client_info_|.
  void BackUpCurrentClientInfo();

  // Loads the client info via |load_client_info_|.
  std::unique_ptr<ClientInfo> LoadClientInfo();

  // Gets the limited entropy randomization source. For clients that only use
  // the low entropy source (e.g. Android Webview), this will return the empty
  // string.
  std::string_view GetLimitedEntropyRandomizationSource();

  // Returns the high entropy source for this client, which is composed of a
  // client ID and the low entropy source. This is intended to be unique for
  // each install. UMA must be enabled (and |client_id_| must be set) or
  // |kMetricsProvisionalClientID| must be set before calling this.
  std::string GetHighEntropySource();

  // Updates |entropy_source_returned_| with |type| iff the current value is
  // ENTROPY_SOURCE_NONE and logs the new value in a histogram.
  void UpdateEntropySourceReturnedValue(EntropySourceType type);

  // Returns the first entropy source that was returned by this service since
  // start up, or NONE if neither was returned yet. This is exposed for testing
  // only.
  EntropySourceType entropy_source_returned() const {
    return entropy_source_returned_;
  }

  std::string initial_client_id_for_testing() const {
    return initial_client_id_;
  }

  // Reset the client id and low entropy source if the kMetricsResetMetricIDs
  // pref is true.
  void ResetMetricsIDsIfNecessary();

  bool ShouldGenerateProvisionalClientId(bool is_first_run);

  // Whether an instance of this class exists. Used to enforce that there aren't
  // multiple instances of this class at a given time.
  static bool instance_exists_;

  // Weak pointer to the local state prefs store.
  const raw_ptr<PrefService> local_state_;

  // Weak pointer to an enabled state provider. Used to know whether the user
  // has consented to reporting, and if reporting should be done.
  raw_ptr<EnabledStateProvider> enabled_state_provider_;

  // Specified options for controlling trial randomization.
  const EntropyParams entropy_params_;

  // A callback run during client id creation so this MetricsStateManager can
  // store a backup of the newly generated ID.
  const StoreClientInfoCallback store_client_info_;

  // A callback run if this MetricsStateManager can't get the client id from
  // its typical location and wants to attempt loading it from this backup.
  const LoadClientInfoCallback load_client_info_;

  // A beacon used to determine whether the previous Chrome browser session
  // terminated gracefully.
  CleanExitBeacon clean_exit_beacon_;

  // The identifier that's sent to the server with the log reports.
  std::string client_id_;

  // The client id that was used do field trial randomization. This field should
  // only be changed when we need to do group assignment. |initial_client_id|
  // should left blank iff a client id was not used to do field trial
  // randomization.
  std::string initial_client_id_;

  // An instance of EntropyState for getting the entropy source values.
  EntropyState entropy_state_;

  // The last entropy source returned by this service, used for testing.
  EntropySourceType entropy_source_returned_;

  // The value of prefs::kMetricsResetIds seen upon startup, i.e., the value
  // that was appropriate in the previous session. Used when reporting previous
  // session (stability) data.
  bool metrics_ids_were_reset_;

  // The value of the metrics id before reseting. Only possibly valid if the
  // metrics id was reset. May be blank if the metrics id was reset but Chrome
  // has no record of what the previous metrics id was.
  std::string previous_client_id_;

  // The detector for understanding the cloned nature of the install so that we
  // can reset client ids.
  ClonedInstallDetector cloned_install_detector_;

  // The type of session, e.g. a foreground session, at startup. This value is
  // used only during startup. On Android WebLayer, Android WebView, and iOS,
  // the visibility is unknown at this point in startup.
  const StartupVisibility startup_visibility_;

  // Force enables the creation of a provisional client ID on first run even if
  // this is not a Chrome-branded build. Used for testing.
  static bool enable_provisional_client_id_for_testing_;
};

}  // namespace metrics

#endif  // COMPONENTS_METRICS_METRICS_STATE_MANAGER_H_