[NTP Snippets] Refactor background scheduling for remote suggestions

components/ntp_snippets/remote/remote_suggestions_provider.h

 // Copyright 2015 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_REMOTE_SUGGESTIONS_PROVIDER_H_
 #define COMPONENTS_NTP_SNIPPETS_REMOTE_REMOTE_SUGGESTIONS_PROVIDER_H_
 
 #include <cstddef>
 #include <deque>
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "components/image_fetcher/image_fetcher_delegate.h"
 #include "components/ntp_snippets/category.h"
 #include "components/ntp_snippets/category_factory.h"
 #include "components/ntp_snippets/category_status.h"
 #include "components/ntp_snippets/content_suggestion.h"
 #include "components/ntp_snippets/content_suggestions_provider.h"
 #include "components/ntp_snippets/remote/ntp_snippet.h"
 #include "components/ntp_snippets/remote/ntp_snippets_fetcher.h"
-#include "components/ntp_snippets/remote/ntp_snippets_scheduler.h"
+#include "components/ntp_snippets/remote/remote_suggestions_scheduler.h"
 #include "components/ntp_snippets/remote/remote_suggestions_status_service.h"
 #include "components/ntp_snippets/remote/request_throttler.h"
 
 class PrefRegistrySimple;
 class PrefService;
 
 namespace gfx {
 class Image;
 }  // namespace gfx
 
 namespace image_fetcher {
 class ImageDecoder;
 class ImageFetcher;
 }  // namespace image_fetcher
 
 namespace ntp_snippets {
 
 class RemoteSuggestionsDatabase;
+class RemoteSuggestionsHardScheduler;
 class UserClassifier;
 
 // Retrieves fresh content data (articles) from the server, stores them and
 // provides them as content suggestions.
 // This class is final because it does things in its constructor which make it
 // unsafe to derive from it.
 // TODO(treib): Introduce two-phase initialization and make the class not final?
 // TODO(jkrcal): this class grows really, really large. The fact that
 // NTPSnippetService also implements ImageFetcherDelegate adds unnecessary
 // complexity (and after all the Service is conceptually not an
 // ImagerFetcherDeletage ;-)). Instead, the cleaner solution would  be to define
 // a CachedImageFetcher class that handles the caching aspects and looks like an
 // image fetcher to the NTPSnippetService.
 class RemoteSuggestionsProvider final
     : public ContentSuggestionsProvider,
-      public image_fetcher::ImageFetcherDelegate {
+      public image_fetcher::ImageFetcherDelegate,
+      public RemoteSuggestionsScheduler::Updater {

[tschumann, 2016/12/09 17:27:28]

can we try to not inherit / implement yet another interface ;-) ?
Inheritance is a very tight coupling and makes it super hard to understand the
relationships and interfaces (it also often muddies the 1 class - 1 purpose
rule).

This interface has only a single method, can't we register a callback instead?
So simply change scheduler_.SetUpdater(this); to take a callback (and rename to
something like OnUpdate() or SetUpdateCallback().

IMO, the ideal world would be that RemoteSuggestionsProvider only implements a
single interface, namely ContentSuggestionsProvider (that's the only is-a
relationship that seems justified).

[markusheintz_, 2016/12/12 14:36:16]

+1

[markusheintz_, 2016/12/12 15:32:28]

+1

I would even call the method that is then passed as callback to the scheduler
"OnScheduledUpdate" because this is the "event" that the
RemoteSuggestionsScheduler should "emit". 

[jkrcal, 2016/12/14 09:42:09]

Done.

  public:
   // |application_language_code| should be a ISO 639-1 compliant string, e.g.
   // 'en' or 'en-US'. Note that this code should only specify the language, not
   // the locale, so 'en_US' (English language with US locale) and 'en-GB_US'
   // (British English person in the US) are not language codes.
   RemoteSuggestionsProvider(
       Observer* observer,
       CategoryFactory* category_factory,
       PrefService* pref_service,
       const std::string& application_language_code,
       const UserClassifier* user_classifier,
-      NTPSnippetsScheduler* scheduler,
+      RemoteSuggestionsHardScheduler* hard_scheduler,
       std::unique_ptr<NTPSnippetsFetcher> snippets_fetcher,
       std::unique_ptr<image_fetcher::ImageFetcher> image_fetcher,
       std::unique_ptr<image_fetcher::ImageDecoder> image_decoder,
       std::unique_ptr<RemoteSuggestionsDatabase> database,
       std::unique_ptr<RemoteSuggestionsStatusService> status_service);
 
   ~RemoteSuggestionsProvider() override;
 
   static void RegisterProfilePrefs(PrefRegistrySimple* registry);
 
   // Returns whether the service is ready. While this is false, the list of
   // snippets will be empty, and all modifications to it (fetch, dismiss, etc)
   // will be ignored.
   bool ready() const { return state_ == State::READY; }
 
   // Returns whether the service is initialized. While this is false, some
   // calls may trigger DCHECKs.
   bool initialized() const { return ready() || state_ == State::DISABLED; }
 
-  // Fetchs content suggestions from the Content Suggestions server for all
-  // remote categories in the background.
-  void FetchSnippetsInTheBackground();
-
-  // Fetchs content suggestions from the Content Suggestions server for all
+  // Fetches content suggestions from the Content Suggestions server for all
   // remote categories. The request to the server is performed as an interactive
   // request. Interactive requests are used for actions triggered by the user
   // and request lower latency processing.
   void FetchSnippetsForAllCategories();
 
   // Fetches snippets from the server for specified hosts and adds them to the
   // current ones. Only called from chrome://snippets-internals, DO NOT USE
   // otherwise! Ignored while ready() is false.
   void FetchSnippetsFromHosts(const std::set<std::string>& hosts,
                               bool interactive_request);
 
   const NTPSnippetsFetcher* snippets_fetcher() const {
     return snippets_fetcher_.get();
   }
 
-  // (Re)schedules the periodic fetching of snippets. If |force| is true, the
-  // tasks will be re-scheduled even if they already exist and have the correct
-  // periods.
-  void RescheduleFetching(bool force);
+  RemoteSuggestionsScheduler* scheduler() {

[tschumann, 2016/12/09 17:27:28]

nit: who actually needs access to this scheduler? Seems like you're exposing
implementation details which would be better hidden behind (possibly adapted)
facade methods.

[jkrcal, 2016/12/14 09:42:09]

Done.

+    return &scheduler_;
+  }
 
   // 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;
@@ skipping 124 matching lines @@
 
   // Returns the URL of the image of a snippet if it is among the current or
   // among the archived snippets in the matching category. Returns an empty URL
   // otherwise.
   GURL FindSnippetImageUrl(const ContentSuggestion::ID& suggestion_id) const;
 
   // image_fetcher::ImageFetcherDelegate implementation.
   void OnImageDataFetched(const std::string& id_within_category,
                           const std::string& image_data) override;
 
+  // RemoteSuggestionsScheduler::Updater implementation
+  void UpdateRemoteSuggestionsBySchedule() override;
+
   // Callbacks for the RemoteSuggestionsDatabase.
   void OnDatabaseLoaded(NTPSnippet::PtrVector snippets);
   void OnDatabaseError();
 
   // Callback for fetch-more requests with the NTPSnippetsFetcher.
   void OnFetchMoreFinished(
       const FetchDoneCallback& fetching_callback,
       NTPSnippetsFetcher::FetchResult fetch_result,
       NTPSnippetsFetcher::OptionalFetchedCategories fetched_categories);
 
@@ skipping 108 matching lines @@
   const Category articles_category_;
 
   std::map<Category, CategoryContent, Category::CompareByID> category_contents_;
 
   // The ISO 639-1 code of the language used by the application.
   const std::string application_language_code_;
 
   // Classifier that tells us how active the user is. Not owned.
   const UserClassifier* user_classifier_;
 
-  // Scheduler for fetching snippets. Not owned.
-  NTPSnippetsScheduler* scheduler_;
+  // Scheduler for fetching snippets.
+  RemoteSuggestionsScheduler scheduler_;
 
   // The snippets fetcher.
   std::unique_ptr<NTPSnippetsFetcher> snippets_fetcher_;
 
   std::unique_ptr<image_fetcher::ImageFetcher> image_fetcher_;
   std::unique_ptr<image_fetcher::ImageDecoder> image_decoder_;
 
   // The database for persisting snippets.
   std::unique_ptr<RemoteSuggestionsDatabase> database_;
   base::TimeTicks database_load_start_;
@@ skipping 15 matching lines @@
 
   // A clock for getting the time. This allows to inject a tick clock in tests.
   std::unique_ptr<base::TickClock> tick_clock_;
 
   DISALLOW_COPY_AND_ASSIGN(RemoteSuggestionsProvider);
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_REMOTE_REMOTE_SUGGESTIONS_PROVIDER_H_