Move ranker_model_loader to a new component.

components/translate/core/browser/ranker_model_loader.h

-// Copyright 2017 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_TRANSLATE_CORE_BROWSER_RANKER_MODEL_LOADER_H_
-#define COMPONENTS_TRANSLATE_CORE_BROWSER_RANKER_MODEL_LOADER_H_
-
-#include <memory>
-#include <string>
-
-#include "base/callback.h"
-#include "base/files/file_path.h"
-#include "base/memory/ref_counted.h"
-#include "base/memory/weak_ptr.h"
-#include "base/sequence_checker.h"
-#include "base/time/time.h"
-#include "url/gurl.h"
-
-namespace base {
-class SequencedTaskRunner;
-}  // namespace base
-
-namespace chrome_intelligence {
-class RankerModel;
-}  // namespace chrome_intelligence
-
-namespace translate {
-
-class TranslateURLFetcher;
-
-// Enumeration denoting the outcome of an attempt to download the model. This
-// must be kept in sync with the RankerModelStatus enum in histograms.xml
-enum class RankerModelStatus {
-  OK = 0,
-  DOWNLOAD_THROTTLED = 1,
-  DOWNLOAD_FAILED = 2,
-  PARSE_FAILED = 3,
-  VALIDATION_FAILED = 4,
-  INCOMPATIBLE = 5,
-  LOAD_FROM_CACHE_FAILED = 6,
-  MODEL_LOADING_ABANDONED = 7,
-
-  // Insert new values above this line.
-  MAX
-};
-
-// If enabled, downloads a translate ranker model and uses it to determine
-// whether the user should be given a translation prompt or not.
-class RankerModelLoader {
- public:
-  // Callback to validate a ranker model on behalf of the model loader client.
-  // For example, the callback might validate that the model is compatible with
-  // the features generated when ranking translation offerings.  This will be
-  // called on the sequence on which the model loader was constructed.
-  using ValidateModelCallback = base::RepeatingCallback<RankerModelStatus(
-      const chrome_intelligence::RankerModel&)>;
-
-  // Called to transfer ownership of a loaded model back to the model loader
-  // client. This will be called on the sequence on which the model loader was
-  // constructed.
-  using OnModelAvailableCallback = base::RepeatingCallback<void(
-      std::unique_ptr<chrome_intelligence::RankerModel>)>;
-
-  // |validate_model_callback| may be called on any sequence; it must be thread
-  // safe.
-  //
-  // |on_model_available_callback| will be called on the sequence on which the
-  // ranker model loader is constructed.
-  //
-  // |model_path| denotes the file path at which the model is cached. The loader
-  // will attempt to load the model from this path first, falling back to the
-  // |model_url| if the model cannot be loaded or has expired. Upon downloading
-  // a fresh model from |model_url| the model will be persisted to |model_path|
-  // for subsequent caching.
-  //
-  // |model_url| denotes the URL from which the model should be loaded, if it
-  // has not already been cached at |model_path|.
-  //
-  // |uma_prefix| will be used as a prefix for the names of all UMA metrics
-  // generated by this loader.
-  RankerModelLoader(ValidateModelCallback validate_model_callback,
-                    OnModelAvailableCallback on_model_available_callback,
-                    base::FilePath model_path,
-                    GURL model_url,
-                    std::string uma_prefix);
-
-  ~RankerModelLoader();
-
-  // Call this method periodically to notify the model loader the ranker is
-  // actively in use. The user's engagement with the ranked feature is used
-  // as a proxy for network availability and activity. If a model download
-  // is pending, this will trigger (subject to retry and frequency limits) a
-  // model download attempt.
-  void NotifyOfRankerActivity();
-
- private:
-  // A enum to track the current loader state.
-  enum class LoaderState {
-    // The loader is newly created and has not started trying to load the model.
-    // This state can transition to LOADING_FROM_FILE or, if |model_path_| is
-    // empty, to LOADING_FROM_URL. If both |model_path_| and |model_url_| are
-    // empty/invalid then it can transition to FINISHED.
-    NOT_STARTED,
-    // The loader is busy loading the model from |model_path_| in the
-    // background. This state can transition to FINISHED if the loaded model is
-    // compatible and up to date; otherwise, this state can transition to IDLE.
-    LOADING_FROM_FILE,
-    // The loader is not currently busy. The loader can transition to the
-    // LOADING_FROM_URL_ state if |model_url_| is valid; the loader can also
-    // transition to FINISHED if it the maximum number of download attempts
-    // has been reached.
-    IDLE,
-    // The loader is busy loading the model from |model_url_| in the background.
-    // This state can transition to FINISHED if the loaded model is valid;
-    // otherwise, this state can re-transition to IDLE.
-    LOADING_FROM_URL,
-    // The loader has finished. This is the terminal state.
-    FINISHED
-  };
-
-  // Asynchronously initiates loading the model from model_path_;
-  void StartLoadFromFile();
-
-  // Called when the background worker has finished loading |data| from
-  // |model_path_|. If |data| is empty, the load from |model_path_| failed.
-  void OnFileLoaded(const std::string& data);
-
-  // Asynchronously initiates loading the model from |model_url_|.
-  void StartLoadFromURL();
-
-  // Called when |url_fetcher_| has finished loading |data| from |model_url_|.
-  //
-  // This call signature is mandated by TranslateURLFetcher.
-  //
-  // id - the id given to the TranslateURLFetcher on creation
-  // success - true of the download was successful
-  // data - the body of the downloads response
-  void OnURLFetched(int id, bool success, const std::string& data);
-
-  // Parse |data| and return a validated model. Returns nullptr on failure.
-  std::unique_ptr<chrome_intelligence::RankerModel> CreateAndValidateModel(
-      const std::string& data);
-
-  // Helper function to log |model_status| to UMA and return it.
-  RankerModelStatus ReportModelStatus(RankerModelStatus model_status);
-
-  // Validates that ranker model loader tasks are all performed on the same
-  // sequence.
-  base::SequenceChecker sequence_checker_;
-
-  // The task runner on which background tasks are performed.
-  const scoped_refptr<base::SequencedTaskRunner> background_task_runner_;
-
-  // Validates a ranker model on behalf of the model loader client. This will be
-  // called on the sequence on which the model leader was constructed.
-  const ValidateModelCallback validate_model_cb_;
-
-  // Transfers ownership of a loaded model back to the model loader client.
-  // This will be called on the sequence on which the model loader was
-  // constructed.
-  const OnModelAvailableCallback on_model_available_cb_;
-
-  // The path at which the model is (or should be) cached.
-  const base::FilePath model_path_;
-
-  // The URL from which to download the model if the model is not in the cache
-  // or the cached model is invalid/expired.
-  const GURL model_url_;
-
-  // This will prefix all UMA metrics generated by the model loader.
-  const std::string uma_prefix_;
-
-  // Used to download model data from |model_url_|.
-  std::unique_ptr<TranslateURLFetcher> url_fetcher_;
-
-  // The next time before which no new attempts to download the model should be
-  // attempted.
-  base::TimeTicks next_earliest_download_time_;
-
-  // Tracks the last time of the last attempt to load a model, either from file
-  // of from URL. Used for UMA reporting of load durations.
-  base::TimeTicks load_start_time_;
-
-  // The current state of the loader.
-  LoaderState state_ = LoaderState::NOT_STARTED;
-
-  // Creates weak pointer references to the loader.
-  base::WeakPtrFactory<RankerModelLoader> weak_ptr_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(RankerModelLoader);
-};
-
-}  // namespace translate
-
-#endif  // COMPONENTS_TRANSLATE_CORE_BROWSER_RANKER_MODEL_LOADER_H_