[NTP Snippets] Refactor background scheduling for remote suggestions

components/ntp_snippets/remote/scheduling_remote_suggestions_provider.h

+// Copyright 2016 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_NTP_SNIPPETS_REMOTE_SCHEDULING_REMOTE_SUGGESTIONS_PROVIDER_H_
+#define COMPONENTS_NTP_SNIPPETS_REMOTE_SCHEDULING_REMOTE_SUGGESTIONS_PROVIDER_H_
+
+#include <memory>
+#include <set>
+#include <string>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/time/time.h"
+#include "components/ntp_snippets/content_suggestions_provider.h"
+#include "components/ntp_snippets/remote/persistent_scheduler.h"
+#include "components/ntp_snippets/remote/remote_suggestions_provider.h"
+#include "components/ntp_snippets/remote/remote_suggestions_scheduler.h"
+
+class PrefRegistrySimple;
+class PrefService;
+
+namespace ntp_snippets {
+
+struct Status;
+class UserClassifier;
+
+// A wrapper around RemoteSuggestionsProvider that introduces periodic fetching.
+//
+// The class initiates fetches on its own in these situations:
+//  - initial fetch when the provider is constructed and we have no suggestions;
+//  - regular fetches according to its schedule.
+// TODO(jkrcal): After soft fetch on Chrome startup is introduced, remove
+// the initial fetch completely.
+//
+// The class also needs to understand when last fetch trials and successful
+// fetches happen and thus it intercepts following interactive fetch requests:
+//  - Fetch() - after "More" button of a remote section is pressed in the UI;
+// TODO(jkrcal): Clarify what Fetch() should do for this provider and maybe stop
+// intercepting it.
+// TODO(jkrcal): Intercept also ReloadSuggestions() call (after the user swipes
+// away everything incl. all empty sections and presses "More"); Not done in the
+// first shot because  it implements a public interface function without any
+// callback.
+// This class is final because it does things in its constructor which make it
+// unsafe to derive from it.
+// TODO(jkrcal): Introduce two-phase initialization and make the class not
+// final? (see the same comment for RemoteSuggestionsProvider)
+class SchedulingRemoteSuggestionsProvider final
+    : public ContentSuggestionsProvider,
+      public RemoteSuggestionsScheduler {
+ public:
+  SchedulingRemoteSuggestionsProvider(
+      Observer* observer,
+      std::unique_ptr<RemoteSuggestionsProvider> provider,
+      PersistentScheduler* persistent_scheduler,
+      const UserClassifier* user_classifier,
+      PrefService* pref_service);
+
+  ~SchedulingRemoteSuggestionsProvider() override;
+
+  static void RegisterProfilePrefs(PrefRegistrySimple* registry);
+
+  // RemoteSuggestionsScheduler implementation.
+  void RescheduleFetching() override;
+  void OnPersistentSchedulerWakeUp() override;
+
+  // ContentSuggestionsProvider implementation.
+  CategoryStatus GetCategoryStatus(Category category) override;
+  CategoryInfo GetCategoryInfo(Category category) override;
+  void DismissSuggestion(const ContentSuggestion::ID& suggestion_id) override;
+  void FetchSuggestionImage(const ContentSuggestion::ID& suggestion_id,
+                            const ImageFetchedCallback& callback) override;
+  void Fetch(const Category& category,
+             const std::set<std::string>& known_suggestion_ids,
+             const FetchDoneCallback& callback) override;
+  void ReloadSuggestions() override;
+  void ClearHistory(
+      base::Time begin,
+      base::Time end,
+      const base::Callback<bool(const GURL& url)>& filter) override;
+  void ClearCachedSuggestions(Category category) override;
+  void OnSignInStateChanged() override;
+  void GetDismissedSuggestionsForDebugging(
+      Category category,
+      const DismissedSuggestionsCallback& callback) override;
+  void ClearDismissedSuggestionsForDebugging(Category category) override;
+
+ private:
+  // Abstract description of the fetching schedule.
+  struct FetchingSchedule;
+
+  // Callback that is notified whenever the status of |provider_| changes.
+  void OnProviderStatusChanged(
+      RemoteSuggestionsProvider::ProviderStatus status);
+
+  // After the call, updates will be scheduled in the future. Idempotent, can be
+  // run any time later without impacting the current schedule.
+  // If you want to enforce rescheduling, call Unschedule() and then Schedule().
+  void StartScheduling();
+
+  // After the call, no updates will happen before another call to Schedule().
+  // Idempotent, can be run any time later without impacting the current
+  // schedule.
+  void StopScheduling();
+
+  // Callback after Fetch is completed.
+  void FetchFinished(const FetchDoneCallback& callback,
+                     Status status_code,
+                     std::vector<ContentSuggestion> suggestions);
+
+  FetchingSchedule GetDesiredFetchingSchedule() const;
+  FetchingSchedule GetLastFetchingSchedule() const;
+  void StoreLastFetchingSchedule(const FetchingSchedule& schedule);
+
+  // Common function to call after each fetch.
+  void OnFetchCompleted(Status status);
+
+  // Applies the provided |schedule|.
+  void ApplyFetchingSchedule(const FetchingSchedule& schedule);
+
+  // Interface for doing all the actual work (apart from scheduling).
+  std::unique_ptr<RemoteSuggestionsProvider> provider_;
+
+  // Interface for scheduling hard fetches, OS dependent. Not owned, may be
+  // null.
+  PersistentScheduler* persistent_scheduler_;
+
+  // Used to adapt the schedule based on usage activity of the user. Not owned.
+  const UserClassifier* user_classifier_;
+
+  PrefService* pref_service_;
+
+  DISALLOW_COPY_AND_ASSIGN(SchedulingRemoteSuggestionsProvider);
+};
+
+}  // namespace ntp_snippets
+
+#endif  // COMPONENTS_NTP_SNIPPETS_REMOTE_SCHEDULING_REMOTE_SUGGESTIONS_PROVIDER_H_