// Copyright 2019 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 MEDIA_LEARNING_IMPL_LEARNING_TASK_CONTROLLER_HELPER_H_
#define MEDIA_LEARNING_IMPL_LEARNING_TASK_CONTROLLER_HELPER_H_

#include <map>
#include <memory>

#include "base/callback.h"
#include "base/component_export.h"
#include "base/memory/scoped_refptr.h"
#include "base/memory/weak_ptr.h"
#include "base/sequenced_task_runner.h"
#include "base/threading/sequence_bound.h"
#include "media/learning/common/learning_task_controller.h"
#include "media/learning/impl/feature_provider.h"
#include "services/metrics/public/cpp/ukm_source_id.h"

namespace media {
namespace learning {

class LearningTaskControllerHelperTest;

// Helper class for managing LabelledExamples that are constructed
// incrementally.  Keeps track of in-flight examples as they're added via
// BeginObservation, updated with features from a FeatureProvider, or given a
// TargetValue.  When examples are complete, it provides them to a callback for
// further processing.
//
// Since both the mojo LearningTaskController and LearningTaskControllerImpl
// will need to do almost exactly the same thing, this class handles the common
// logic for them.
class COMPONENT_EXPORT(LEARNING_IMPL) LearningTaskControllerHelper
    : public base::SupportsWeakPtr<LearningTaskControllerHelper> {
 public:
  // Callback to add labelled examples as training data.
  using AddExampleCB =
      base::RepeatingCallback<void(LabelledExample, ukm::SourceId)>;

  // TODO(liberato): Consider making the FP not optional.
  LearningTaskControllerHelper(const LearningTask& task,
                               AddExampleCB add_example_cb,
                               SequenceBoundFeatureProvider feature_provider =
                                   SequenceBoundFeatureProvider());
  virtual ~LearningTaskControllerHelper();

  // See LearningTaskController::BeginObservation.
  void BeginObservation(base::UnguessableToken id, FeatureVector features);
  void CompleteObservation(base::UnguessableToken id,
                           const ObservationCompletion& completion);
  void CancelObservation(base::UnguessableToken id);

 private:
  // Record of an example that has been started by RecordObservedFeatures, but
  // not finished yet.
  struct PendingExample {
    // The example we're constructing.
    LabelledExample example;
    // Has the FeatureProvider added features?
    bool features_done = false;
    // Has the client added a TargetValue?
    // TODO(liberato): Should it provide a weight with the target value?
    bool target_done = false;

    ukm::SourceId source_id = ukm::kInvalidSourceId;
  };

  // [non-repeating int] = example
  using PendingExampleMap = std::map<base::UnguessableToken, PendingExample>;

  // Called on any sequence when features are ready.  Will call OnFeatureReady
  // if called on |task_runner|, or will post to |task_runner|.
  static void OnFeaturesReadyTrampoline(
      scoped_refptr<base::SequencedTaskRunner> task_runner,
      base::WeakPtr<LearningTaskControllerHelper> weak_this,
      base::UnguessableToken id,
      FeatureVector features);

  // Called when a new feature vector has been finished by |feature_provider_|,
  // if needed, to actually add the example.
  void OnFeaturesReady(base::UnguessableToken example_id,
                       FeatureVector features);

  // If |example| is finished, then send it to the LearningSession and remove it
  // from the map.  Otherwise, do nothing.
  void ProcessExampleIfFinished(PendingExampleMap::iterator example);

  // The task we'll add examples to.
  LearningTask task_;

  // Optional feature provider.
  SequenceBoundFeatureProvider feature_provider_;

  // All outstanding PendingExamples.
  PendingExampleMap pending_examples_;

  // While the handling of |pending_examples_| is an implementation detail, we
  // still let tests verify the map size, to help catch cases where we forget to
  // remove things from the map and slowly leak memory.
  size_t pending_example_count_for_testing() const {
    return pending_examples_.size();
  }

  scoped_refptr<base::SequencedTaskRunner> task_runner_;

  // Callback to which we'll send finished examples.
  AddExampleCB add_example_cb_;

  friend class LearningTaskControllerHelperTest;
};

}  // namespace learning
}  // namespace media

#endif  // MEDIA_LEARNING_IMPL_LEARNING_TASK_CONTROLLER_HELPER_H_