// Copyright 2012 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_VARIATIONS_SERVICE_VARIATIONS_SERVICE_H_
#define COMPONENTS_VARIATIONS_SERVICE_VARIATIONS_SERVICE_H_

#include <memory>
#include <optional>
#include <string>
#include <vector>

#include "base/compiler_specific.h"
#include "base/feature.h"
#include "base/gtest_prod_util.h"
#include "base/memory/raw_ptr.h"
#include "base/memory/weak_ptr.h"
#include "base/metrics/field_trial.h"
#include "base/observer_list.h"
#include "base/sequence_checker.h"
#include "base/time/time.h"
#include "base/types/pass_key.h"
#include "components/variations/client_filterable_state.h"
#include "components/variations/entropy_provider.h"
#include "components/variations/metrics.h"
#include "components/variations/processed_study.h"
#include "components/variations/service/safe_seed_manager.h"
#include "components/variations/service/variations_field_trial_creator.h"
#include "components/variations/service/variations_service_client.h"
#include "components/variations/variations_request_scheduler.h"
#include "components/variations/variations_seed_simulator.h"
#include "components/variations/variations_seed_store.h"
#include "components/web_resource/resource_request_allowed_notifier.h"
#include "url/gurl.h"

class PrefService;
class PrefRegistrySimple;

namespace base {
class FeatureList;
class Version;
}  // namespace base

namespace metrics {
class MetricsStateManager;
}

namespace network {
class SimpleURLLoader;
}

namespace user_prefs {
class PrefRegistrySyncable;
}

namespace variations {
struct StudyGroupNames;
class VariationsSeed;
}  // namespace variations

namespace metrics {
class RuntimeMutableFeaturesHandlerBase;
}

namespace variations {

#if BUILDFLAG(IS_CHROMEOS)
class DeviceVariationsRestrictionByPolicyApplicator;
#endif

// When enabled, runtime mutable field trials from the periodically fetched
// seeds will be applied to the current session.
BASE_DECLARE_FEATURE(kVariationsRuntimeMutability);

// Used to (a) set up field trials based on stored variations seed data and (b)
// fetch new seed data from the variations server.
class VariationsService
    : public web_resource::ResourceRequestAllowedNotifier::Observer {
 public:
  class Observer {
   public:
    // How critical a detected experiment change is. Whether it should be
    // handled on a "best-effort" basis or, for a more critical change, if it
    // should be given higher priority.
    enum Severity {
      BEST_EFFORT,
      CRITICAL,
    };

    // Called when the VariationsService detects that there will be significant
    // experiment changes on a restart. This notification can then be used to
    // update UI (i.e. badging an icon).
    virtual void OnExperimentChangesDetected(Severity severity) {}

    // Called when a new seed has been successfully fetched from the
    // variations server.
    virtual void OnSeedFetched() {}

    // Called when the VariationsService is being destroyed.
    virtual void OnVariationsServiceDestroyed() {}

   protected:
    virtual ~Observer() = default;
  };

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

  ~VariationsService() override;

  // Enum used to choose whether GetVariationsServerURL will return an HTTPS
  // URL or an HTTP one. The HTTP URL is used as a fallback for seed retrieval
  // in cases where an HTTPS connection fails.
  enum HttpOptions { USE_HTTP, USE_HTTPS };

  // Should be called before startup of the main message loop.
  void PerformPreMainMessageLoopStartup();

  // Adds an observer to listen for detected experiment changes.
  void AddObserver(Observer* observer);

  // Removes a previously-added observer.
  void RemoveObserver(Observer* observer);

  // Called when the application enters foreground. This may trigger a
  // FetchVariationsSeed call.
  // TODO(rkaplow): Handle this and the similar event in metrics_service by
  // observing an 'OnAppEnterForeground' event instead of requiring the frontend
  // code to notify each service individually.
  void OnAppEnterForeground();

  // Sets the value of the "restrict" URL param to the variations service that
  // should be used for variation seed requests. This takes precedence over any
  // value coming from policy prefs. This should be called prior to any calls
  // to |StartRepeatedVariationsSeedFetch|.
  void SetRestrictMode(const std::string& restrict_mode);

  // Returns true if the restrict mode is likely that of a dogfood client, false
  // otherwise. Note that that this might be a bit over-broad, returning true
  // for clients that are not actually dogfooders.
  bool IsLikelyDogfoodClient() const;

  // Sets the return value for subsequent calls to `IsLikelyDogfoodClient()`.
  // This is a convenience function only for testing, because the two approaches
  // that follow production code paths are cumbersome to get right:
  // * `SetRestrictMode` also configures this behavior, but must be called early
  //   during the `VariationsService` initialization flow.
  // * Enterprise policies also configure this behavior, but the logic is
  //   different per-platform. In particular, Ash ChromeOS and Lacros each have
  //   distinct flows vs. other platforms.
  //
  // Warning: Depending on exactly when this is called, this might also change
  // the constructed variations server URL's params. In other cases, it will
  // cause the server URL to be out of sync with the `restrict_mode_`. In tests
  // that require these to be in sync, prefer to call `SetRestrictMode()` at the
  // appropriate time.
  void SetIsLikelyDogfoodClientForTesting(bool is_dogfood_client);

  // Returns the variations server URL. |http_options| determines whether to
  // use the http or https URL. This function will return an empty GURL when
  // the restrict param exists for USE_HTTP, to indicate that no HTTP fallback
  // should happen in that case.
  GURL GetVariationsServerURL(HttpOptions http_options);

  // Returns the permanent overridden country code stored for this client. This
  // value will not be updated on Chrome updates.
  // Country code is in the format of lowercase ISO 3166-1 alpha-2. Example: us,
  // br, in.
  std::string GetOverriddenPermanentCountry() const;

  // Returns the permanent country code stored for this client.
  // Country code is in the format of lowercase ISO 3166-1 alpha-2. Example: us,
  // br, in. This can only be called after field trials have been initialized or
  // if OverrideStoredPermanentCountry() has been called.
  std::string GetStoredPermanentCountry() const;

  // Forces an override of the stored permanent country. Returns true
  // if the variable has been updated. Return false if the override country is
  // the same as the stored variable, or if the update failed for any other
  // reason.
  bool OverrideStoredPermanentCountry(const std::string& override_country);

  // Returns what variations will consider to be the latest country. Returns
  // empty if it is not available.
  // Country code is in the format of lowercase ISO 3166-1 alpha-2. Example: us,
  // br, in.
  std::string GetLatestCountry() const;

  // Returns what variations will consider to be the latest administrative area
  // code. Returns empty if it is not available. Example: us-ca, us-ny.
  std::string GetLatestGeoLevel1() const;

  // Ensures the locale that was used for evaluating variations matches the
  // passed |locale|. This is used to ensure that the locale determined after
  // loading the resource bundle (which is passed here) corresponds to what
  // was used for variations during an earlier stage of start up.
  void EnsureLocaleEquals(const std::string& locale);

  // Exposed for testing.
  static std::string GetDefaultVariationsServerURLForTesting();

  static base::PassKey<VariationsService> CreatePassKeyForTesting() {
    return base::PassKey<VariationsService>();
  }

  // Register Variations related prefs in Local State.
  static void RegisterPrefs(PrefRegistrySimple* registry);

  // Register Variations related prefs in the Profile prefs.
  static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);

  // Creates a VariationsService instance. Does not take ownership of
  // |state_manager|, so callers should ensure that |state_manager| is valid for
  // the lifetime of this class.
  //
  // |client| provides some platform-specific operations for variations. Must
  // not be null.
  // |local_state| provides access to Local State prefs. Must not be null.
  // |state_manager| provides access to metrics state info. Must not be null.
  // |disable_network_switch| is a command-line switch that can be used to
  // disable network communication.
  // |network_connection_tracker_getter| allows the VariationsService to
  // observe network state changes.
  static std::unique_ptr<VariationsService> Create(
      std::unique_ptr<VariationsServiceClient> client,
      PrefService* local_state,
      metrics::MetricsStateManager* state_manager,
      const char* disable_network_switch,
      web_resource::ResourceRequestAllowedNotifier::
          NetworkConnectionTrackerGetter network_connection_tracker_getter);

  // Enables fetching the seed for testing, even for unofficial builds. This
  // should be used along with overriding |DoActualFetch| or using
  // |net::TestURLLoaderFactory|.
  static void EnableFetchForTesting();

  // Set the PrefService responsible for getting policy-related preferences,
  // such as the restrict parameter.
  void set_policy_pref_service(PrefService* service) {
    DCHECK(service);
    policy_pref_service_ = service;
  }

  // Returns the ClientFilterableState, i.e., the state used to do trial
  // filtering. Should only be used for testing and debugging purposes.
  std::unique_ptr<ClientFilterableState> GetClientFilterableStateForVersion();

  web_resource::ResourceRequestAllowedNotifier*
  GetResourceRequestAllowedNotifierForTesting() {
    return resource_request_allowed_notifier_.get();
  }

  // Wrapper around VariationsFieldTrialCreator::SetUpFieldTrials().
  bool SetUpFieldTrials(
      const std::vector<std::string>& variation_ids,
      const std::vector<base::FeatureList::FeatureOverrideInfo>&
          extra_overrides,
      std::unique_ptr<base::FeatureList> feature_list,
      PlatformFieldTrials* platform_field_trials);

  // Calls to the callback with the studies and their groups which could
  // possibly be forced.
  void GetStudiesAvailableToForce(
      base::OnceCallback<void(std::vector<StudyGroupNames>)> done_callback);

  // The seed type used.
  SeedType GetSeedType() const;

  VariationsSource GetVariationsSource() const;

  int request_count() const { return request_count_; }

  // Pauses or resumes variations seed fetching.
  void SetSeedFetchingPaused(
      base::PassKey<metrics::RuntimeMutableFeaturesHandlerBase> pass_key,
      bool paused);

  // Returns true if variations seed fetching is paused.
  bool IsSeedFetchingPaused() const;

  // Wrapper for SimulateAndApplyRuntimeMutableChanges.
  void SimulateAndApplyUploadedSeed(
      base::PassKey<metrics::RuntimeMutableFeaturesHandlerBase> pass_key,
      const VariationsSeed& seed) {
    SimulateAndApplyRuntimeMutableChanges(seed);
  }

  // Cancels the currently pending fetch request.
  void CancelCurrentRequestForTesting();

  // Exposes StartRepeatedVariationsSeedFetch for testing.
  void StartRepeatedVariationsSeedFetchForTesting();

  // Allows the embedder to override the platform and override the OS name in
  // the variations server url. This is useful for android webview and weblayer
  // which are distinct from regular android chrome.
  void OverridePlatform(Study::Platform platform,
                        const std::string& osname_server_param_override);

  // Returns the seed store. Exposed for testing.
  VariationsSeedStore* GetSeedStoreForTesting();

  // Returns the fetch time of the latest seed. Returns base::Time() if there is
  // no seed.
  base::Time GetLatestSeedFetchTime();

  // Calls `done_callback` with the stored seed info for debugging. Reads either
  // the latest or the safe seed, according to the specified `seed_type`.
  void GetStoredSeedInfoForDebugging(
      base::OnceCallback<void(StoredSeedInfo)> done_callback,
      VariationsSeedStore::SeedType seed_type);

 protected:
  // Gets the serial number of the most recent Finch seed. Virtual for testing.
  virtual const std::string& GetLatestSerialNumber();

  // Starts the fetching process once, where |OnURLFetchComplete| is called with
  // the response. This calls DoFetchToURL with the set url.
  virtual void DoActualFetch();

  // Attempts a seed fetch from the set |url|. |header_serial_number| is the
  // value to be sent in the "If-None-Match" header (plaintext for HTTPS
  // requests, and encrypted for HTTP retries).
  virtual void DoFetchFromURL(const GURL& url,
                              std::string header_serial_number);

  // Stores the seed to prefs. Set as virtual and protected so that it can be
  // overridden by tests.
  // Note: Strings are passed by value to support std::move() semantics.
  virtual void StoreSeed(std::string seed_data,
                         std::string seed_signature,
                         std::string country_code,
                         std::string geo_level1,
                         base::Time date_fetched,
                         bool is_delta_compressed,
                         bool is_gzip_compressed);

  // Processes the result of StoreSeed().
  void OnSeedStoreResult(bool is_delta_compressed,
                         bool store_success,
                         VariationsSeed seed);

  // Use the |Create| factory method to create a VariationsService. See |Create|
  // for more details.
  VariationsService(
      std::unique_ptr<VariationsServiceClient> client,
      std::unique_ptr<web_resource::ResourceRequestAllowedNotifier> notifier,
      PrefService* local_state,
      metrics::MetricsStateManager* state_manager);

  // Sets the URL for querying the variations server. Used for testing.
  void set_variations_server_url(const GURL& url) {
    variations_server_url_ = url;
  }

  // Sets the URL for querying the variations server when doing HTTP retries.
  // Used for testing.
  void set_insecure_variations_server_url(const GURL& url) {
    insecure_variations_server_url_ = url;
  }

  // Sets the |last_request_was_http_retry_| flag. Used for testing.
  void set_last_request_was_http_retry(bool was_http_retry) {
    last_request_was_http_retry_ = was_http_retry;
  }

  // The client that provides access to the embedder's environment.
  // Protected so testing subclasses can access it.
  VariationsServiceClient* client() { return client_.get(); }

  // Exposes MaybeRetryOverHTTP for testing.
  bool CallMaybeRetryOverHTTPForTesting();

  // Records that a new seed has been stored. Writes the currently active seed
  // to the |seed_store| as a safe seed, if appropriate. Also, clears failure
  // streaks.
  void RecordSuccessfulFetchNewSeed();

  // Like VariationsService::RecordSuccessfulFetchNewSeed(), but intended to be
  // called for 304 responses from the variations server. Also, updates the seed
  // date and client fetch time.
  void RecordSuccessfulFetchSeedNotModified(base::Time response_date);

  // Performs a simulation of the given `seed` to find any runtime mutable
  // changes that need to be applied to the current session, and apply them.
  // Virtual and protected for testing.
  virtual void SimulateAndApplyRuntimeMutableChanges(
      const VariationsSeed& seed);

 private:
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest,
                           Observer_OnExperimentChangesDetected);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, Observer_OnSeedFetched);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, SeedStoredWhenOKStatus);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, SeedNotStoredWhenNonOKStatus);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, InstanceManipulations);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, CountryHeader);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, GetVariationsServerURL);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, VariationsURLHasParams);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, RequestsInitiallyAllowed);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, RequestsInitiallyNotAllowed);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest,
                           SafeMode_SuccessfulFetchClearsFailureStreaks);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest,
                           SafeMode_NotModifiedFetchClearsFailureStreaks);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, InsecurelyFetchedSetWhenHTTP);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest,
                           InsecurelyFetchedNotSetWhenHTTPS);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, DoNotRetryAfterARetry);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest,
                           DoNotRetryIfInsecureURLIsHTTPS);

  void InitResourceRequestedAllowedNotifier();

  // Calls FetchVariationsSeed once and repeats this periodically. See
  // implementation for details on the period.
  void StartRepeatedVariationsSeedFetch();

  // Checks if prerequisites for fetching the Variations seed are met, and if
  // so, performs the actual fetch using |DoActualFetch|.
  void FetchVariationsSeed();

  // Notify any observers of this service based on the simulation |result|.
  void NotifyExperimentChangesDetected(const SeedSimulationResult& result);

  // Notify observers that a variations seed has been successfully fetched.
  void NotifySeedFetched();

  // Called by SimpleURLLoader when |pending_seed_request_| load completes.
  void OnSimpleLoaderComplete(std::optional<std::string> response_body);

  // Retry the fetch over HTTP, called by OnSimpleLoaderComplete when a request
  // fails. Returns true is the fetch was successfully started, this does not
  // imply the actual fetch was successful.
  bool MaybeRetryOverHTTP();

  // Fetches the seed over HTTPS.
  void FetchSeedOverHTTPS();

  // Fetches the seed over HTTP, encrypting the serial number in the background.
  void FetchSeedOverHTTP();

  // Continuation of FetchSeedOverHTTP() after the serial number has been
  // encrypted in the background.
  void ContinueRetryOverHTTP(
      const GURL& url,
      std::optional<std::string> encrypted_serial_number);

  // ResourceRequestAllowedNotifier::Observer implementation:
  void OnResourceRequestsAllowed() override;

  // Performs a variations seed simulation with the given |seed| and |version|
  // and logs the simulation results as histograms.
  void PerformSimulationWithVersion(const VariationsSeed& seed,
                                    const base::Version& version);

  // Applies the runtime mutable changes of the `trial`'s selected group to the
  // current session.
  ApplyRuntimeMutableChangesResult ApplyRuntimeMutableChanges(
      base::FieldTrial* simulated_trial,
      const ProcessedStudy& processed_study);

  // Calls `done_callback` with the studies and their groups which could
  // possibly be forced from the given `seed`.
  void GetStudiesAvailableToForceFromSeed(
      base::OnceCallback<void(std::vector<StudyGroupNames>)> done_callback,
      bool success,
      VariationsSeed seed);

  std::unique_ptr<VariationsServiceClient> client_;

  // The pref service used to store persist the variations seed.
  raw_ptr<PrefService> local_state_;

  // Used for instantiating entropy providers for variations seed simulation.
  // Weak pointer.
  raw_ptr<metrics::MetricsStateManager> state_manager_;

  // Used to obtain policy-related preferences. Depending on the platform, will
  // either be Local State or Profile prefs.
  raw_ptr<PrefService> policy_pref_service_;

  // Contains the scheduler instance that handles timing for requests to the
  // server. Initially NULL and instantiated when the initial fetch is
  // requested.
  std::unique_ptr<VariationsRequestScheduler> request_scheduler_;

  // Contains the current seed request. Will only have a value while a request
  // is pending, and will be reset by |OnURLFetchComplete|.
  std::unique_ptr<network::SimpleURLLoader> pending_seed_request_;

  // Tracks whether a seed fetch is in progress. This covers the entire
  // duration of the process, including the initial HTTPS request, the
  // asynchronous encryption phase, and the HTTP retry if applicable.
  bool is_fetching_seed_ = false;

  // The value of the "restrict" URL param to the variations server that has
  // been specified via |SetRestrictMode|. If empty, the URL param will be set
  // based on policy prefs.
  std::string restrict_mode_;

  // The URL to use for querying the variations server.
  GURL variations_server_url_;

  // HTTP URL used as a fallback if HTTPS fetches fail. If not set, retries
  // over HTTP will not be attempted.
  GURL insecure_variations_server_url_;

  // Tracks whether the initial request to the variations server had completed.
  bool initial_request_completed_ = false;

  // Tracks whether any errors resolving delta compression were encountered
  // since the last time a seed was fetched successfully.
  bool delta_error_since_last_success_ = false;

  // Helper class used to tell this service if it's allowed to make network
  // resource requests.
  std::unique_ptr<web_resource::ResourceRequestAllowedNotifier>
      resource_request_allowed_notifier_;

  // The start time of the last seed request. This is used to measure the
  // latency of seed requests. Initially zero.
  base::TimeTicks last_request_started_time_;

  // The number of requests to the variations server that have been performed.
  int request_count_ = 0;

  // List of observers of the VariationsService.
  base::ObserverList<Observer>::Unchecked observer_list_;

  // The main entry point for managing safe mode state.
  SafeSeedManager safe_seed_manager_;

  // Used to provide entropy to field trials.
  std::unique_ptr<const EntropyProviders> entropy_providers_;

  // Member responsible for creating trials from a variations seed.
  VariationsFieldTrialCreator field_trial_creator_;

  // True if the last request was a retry over http.
  bool last_request_was_http_retry_ = false;

  // When not empty, contains an override for the os name in the variations
  // server url.
  std::string osname_server_param_override_;

  // True if variations seed fetching is paused.
  bool seed_fetching_paused_ = false;

#if BUILDFLAG(IS_CHROMEOS)
  std::unique_ptr<DeviceVariationsRestrictionByPolicyApplicator>
      device_variations_restrictions_by_policy_applicator_;
#endif

  SEQUENCE_CHECKER(sequence_checker_);

  base::WeakPtrFactory<VariationsService> weak_ptr_factory_{this};
};

}  // namespace variations

#endif  // COMPONENTS_VARIATIONS_SERVICE_VARIATIONS_SERVICE_H_