// 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 COMPONENTS_VARIATIONS_SERVICE_VARIATIONS_SERVICE_H_
#define COMPONENTS_VARIATIONS_SERVICE_VARIATIONS_SERVICE_H_

#include <memory>
#include <string>

#include "base/compiler_specific.h"
#include "base/gtest_prod_util.h"
#include "base/macros.h"
#include "base/memory/weak_ptr.h"
#include "base/metrics/field_trial.h"
#include "base/observer_list.h"
#include "base/threading/thread_checker.h"
#include "base/time/time.h"
#include "components/variations/service/ui_string_overrider.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/version_info/version_info.h"
#include "components/web_resource/resource_request_allowed_notifier.h"
#include "net/url_request/url_fetcher_delegate.h"
#include "url/gurl.h"

class PrefService;
class PrefRegistrySimple;

namespace base {
class FeatureList;
class Version;
}

namespace metrics {
class MetricsStateManager;
}

namespace user_prefs {
class PrefRegistrySyncable;
}

namespace variations {
class VariationsSeed;
}

namespace variations {

// Used to setup field trials based on stored variations seed data, and fetch
// new seed data from the variations server.
class VariationsService
    : public net::URLFetcherDelegate,
      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) = 0;

   protected:
    virtual ~Observer() {}
  };

  ~VariationsService() override;

  // Creates field trials based on the variations seed loaded from local state.
  // If there is a problem loading the seed data, all trials specified by the
  // seed may not be created. Some field trials are configured to override or
  // associate with (for reporting) specific features. These associations are
  // registered with |feature_list|.
  bool CreateTrialsFromSeed(base::FeatureList* feature_list);

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

  // Calls FetchVariationsSeed once and repeats this periodically. See
  // implementation for details on the period. Must be called after
  // |CreateTrialsFromSeed|.
  void StartRepeatedVariationsSeedFetch();

  // 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);

  // Exposed for testing.
  void SetCreateTrialsFromSeedCalledForTesting(bool called);

  // Returns the variations server URL, which can vary if a command-line flag is
  // set and/or the variations restrict pref is set in |local_prefs|. Declared
  // static for test purposes.
  GURL GetVariationsServerURL(PrefService* local_prefs,
                              const std::string& restrict_mode_override);

  // 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
  std::string GetStoredPermanentCountry();

  // 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);

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

  // 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);

  // Factory method for creating a VariationsService. Does not take ownership of
  // |state_manager|. Caller should ensure that |state_manager| is valid for the
  // lifetime of this class.
  static std::unique_ptr<VariationsService> Create(
      std::unique_ptr<VariationsServiceClient> client,
      PrefService* local_state,
      metrics::MetricsStateManager* state_manager,
      const char* disable_network_switch,
      const UIStringOverrider& ui_string_overrider);

  // Factory method for creating a VariationsService in a testing context.
  static std::unique_ptr<VariationsService> CreateForTesting(
      std::unique_ptr<VariationsServiceClient> client,
      PrefService* local_state);

  // 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 invalid variations seed signature in base64 format, or an empty
  // string if the signature was valid, missing, or if signature verification is
  // disabled.
  std::string GetInvalidVariationsSeedSignature() const;

 protected:
  // Starts the fetching process once, where |OnURLFetchComplete| is called with
  // the response.
  virtual void DoActualFetch();

  // Stores the seed to prefs. Set as virtual and protected so that it can be
  // overridden by tests.
  virtual bool StoreSeed(const std::string& seed_data,
                         const std::string& seed_signature,
                         const std::string& country_code,
                         const base::Time& date_fetched,
                         bool is_delta_compressed,
                         bool is_gzip_compressed);

  // Create an entropy provider based on low entropy. This is used to create
  // trials for studies that should only depend on low entropy, such as studies
  // that send experiment IDs to Google web properties. Virtual for testing.
  virtual std::unique_ptr<const base::FieldTrial::EntropyProvider>
  CreateLowEntropyProvider();

  // Creates the VariationsService with the given |local_state| prefs service
  // and |state_manager|. Does not take ownership of |state_manager|. Caller
  // should ensure that |state_manager| is valid for the lifetime of this class.
  // Use the |Create| factory method to create a VariationsService.
  VariationsService(
      std::unique_ptr<VariationsServiceClient> client,
      std::unique_ptr<web_resource::ResourceRequestAllowedNotifier> notifier,
      PrefService* local_state,
      metrics::MetricsStateManager* state_manager,
      const UIStringOverrider& ui_string_overrider);

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

 private:
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, Observer);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, SeedStoredWhenOKStatus);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, SeedNotStoredWhenNonOKStatus);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, InstanceManipulations);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest,
                           LoadPermanentConsistencyCountry);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, CountryHeader);
  FRIEND_TEST_ALL_PREFIXES(VariationsServiceTest, GetVariationsServerURL);

  // Set of different possible values to report for the
  // Variations.LoadPermanentConsistencyCountryResult histogram. This enum must
  // be kept consistent with its counterpart in histograms.xml.
  enum LoadPermanentConsistencyCountryResult {
    LOAD_COUNTRY_NO_PREF_NO_SEED = 0,
    LOAD_COUNTRY_NO_PREF_HAS_SEED,
    LOAD_COUNTRY_INVALID_PREF_NO_SEED,
    LOAD_COUNTRY_INVALID_PREF_HAS_SEED,
    LOAD_COUNTRY_HAS_PREF_NO_SEED_VERSION_EQ,
    LOAD_COUNTRY_HAS_PREF_NO_SEED_VERSION_NEQ,
    LOAD_COUNTRY_HAS_BOTH_VERSION_EQ_COUNTRY_EQ,
    LOAD_COUNTRY_HAS_BOTH_VERSION_EQ_COUNTRY_NEQ,
    LOAD_COUNTRY_HAS_BOTH_VERSION_NEQ_COUNTRY_EQ,
    LOAD_COUNTRY_HAS_BOTH_VERSION_NEQ_COUNTRY_NEQ,
    LOAD_COUNTRY_MAX,
  };

  // Loads the seed from the variations store into |seed|. If successfull,
  // |seed| will contain the loaded data and true is returned. Set as virtual
  // so that it can be overridden by tests.
  virtual bool LoadSeed(VariationsSeed* seed);

  // Sets the stored permanent country pref for this client.
  void StorePermanentCountry(const base::Version& version,
                             const std::string& country);

  // 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 NotifyObservers(
      const variations::VariationsSeedSimulator::Result& result);

  // net::URLFetcherDelegate implementation:
  void OnURLFetchComplete(const net::URLFetcher* source) override;

  // 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(
      std::unique_ptr<variations::VariationsSeed> seed,
      const base::Version& version);

  // Record the time of the most recent successful fetch.
  void RecordLastFetchTime();

  // Loads the country code to use for filtering permanent consistency studies,
  // updating the stored country code if the stored value was for a different
  // Chrome version. The country used for permanent consistency studies is kept
  // consistent between Chrome upgrades in order to avoid annoying the user due
  // to experiment churn while traveling.
  std::string LoadPermanentConsistencyCountry(
      const base::Version& version,
      const std::string& latest_country);

  std::unique_ptr<VariationsServiceClient> client_;
  UIStringOverrider ui_string_overrider_;

  // The pref service used to store persist the variations seed.
  PrefService* local_state_;

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

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

  VariationsSeedStore seed_store_;

  // 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<net::URLFetcher> pending_seed_request_;

  // 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_;

  // Tracks whether |CreateTrialsFromSeed| has been called, to ensure that
  // it gets called prior to |StartRepeatedVariationsSeedFetch|.
  bool create_trials_from_seed_called_;

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

  // Indicates that the next request to the variations service shouldn't specify
  // that it supports delta compression. Set to true when a delta compressed
  // response encountered an error.
  bool disable_deltas_for_next_request_;

  // 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_;

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

  base::ThreadChecker thread_checker_;

  base::WeakPtrFactory<VariationsService> weak_ptr_factory_;

  DISALLOW_COPY_AND_ASSIGN(VariationsService);
};

}  // namespace variations

#endif  // COMPONENTS_VARIATIONS_SERVICE_VARIATIONS_SERVICE_H_