[NTP Snippets] Refactor background scheduling for remote suggestions

components/ntp_snippets/remote/remote_suggestions_provider.h

Index: components/ntp_snippets/remote/remote_suggestions_provider.h
diff --git a/components/ntp_snippets/remote/remote_suggestions_provider.h b/components/ntp_snippets/remote/remote_suggestions_provider.h
index 1c76a5862a7b95d1aab0cfb49257e2b5d742cd94..0b7e43a95fddf18c1795556a0317215478405f73 100644
--- a/components/ntp_snippets/remote/remote_suggestions_provider.h
+++ b/components/ntp_snippets/remote/remote_suggestions_provider.h
@@ -25,7 +25,7 @@
 #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"
 
@@ -44,6 +44,7 @@ class ImageFetcher;
 namespace ntp_snippets {
 
 class RemoteSuggestionsDatabase;
+class RemoteSuggestionsHardScheduler;
 class UserClassifier;
 
 // Retrieves fresh content data (articles) from the server, stores them and
@@ -59,7 +60,8 @@ class UserClassifier;
 // 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
@@ -71,7 +73,7 @@ class RemoteSuggestionsProvider final
       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,
@@ -91,11 +93,7 @@ class RemoteSuggestionsProvider final
   // 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.
@@ -111,10 +109,9 @@ class RemoteSuggestionsProvider final
     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;
@@ -259,6 +256,9 @@ class RemoteSuggestionsProvider final
   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();
@@ -387,8 +387,8 @@ class RemoteSuggestionsProvider final
   // 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_;