[Offline Pages] Add a GCMAppHandler for offline page prefetch.

components/offline_pages/core/prefetch/suggested_articles_observer.cc

Index: components/offline_pages/core/prefetch/suggested_articles_observer.cc
diff --git a/components/offline_pages/core/prefetch/suggested_articles_observer.cc b/components/offline_pages/core/prefetch/suggested_articles_observer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..dd568b6792d1a1e18caa0d6bd5be003c12e5fb94
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+++ b/components/offline_pages/core/prefetch/suggested_articles_observer.cc
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+// 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.
+
+#include "components/offline_pages/core/prefetch/suggested_articles_observer.h"
+
+#include <unordered_set>
+
+#include "base/memory/ptr_util.h"
+#include "components/ntp_snippets/category.h"
+#include "components/ntp_snippets/category_status.h"
+#include "components/offline_pages/core/client_namespace_constants.h"
+#include "components/offline_pages/core/offline_page_feature.h"
+#include "components/offline_pages/core/prefetch/prefetch_service_impl.h"
+
+using ntp_snippets::Category;
+using ntp_snippets::ContentSuggestion;
+
+namespace offline_pages {
+
+namespace {
+
+const ntp_snippets::Category& ArticlesCategory() {
+  static ntp_snippets::Category articles =
+      Category::FromKnownCategory(ntp_snippets::KnownCategories::ARTICLES);
+  return articles;
+}
+
+ClientId CreateClientIDFromSuggestionId(const ContentSuggestion::ID& id) {
+  return ClientId(kSuggestedArticlesNamespace, id.id_within_category());
+}
+
+}  // namespace
+
+SuggestedArticlesObserver::SuggestedArticlesObserver(
+    ntp_snippets::ContentSuggestionsService* content_suggestions_service,
+    PrefetchService* prefetch_service)
+    : content_suggestions_service_(content_suggestions_service),
+      prefetch_service_(prefetch_service) {
+  // The content suggestions service can be |nullptr| in tests.
+  if (content_suggestions_service_)
+    content_suggestions_service_->AddObserver(this);
+}
+
+SuggestedArticlesObserver::~SuggestedArticlesObserver() = default;
+
+void SuggestedArticlesObserver::OnNewSuggestions(Category category) {
+  // TODO(dewittj): Change this to check whether a given category is not
+  // a _remote_ category.
+  if (category != ArticlesCategory() ||
+      category_status_ != ntp_snippets::CategoryStatus::AVAILABLE) {
+    return;
+  }
+
+  const std::vector<ContentSuggestion>& suggestions =
+      test_articles_ ? *test_articles_
+                     : content_suggestions_service_->GetSuggestionsForCategory(
+                           ArticlesCategory());
+  if (suggestions.empty())
+    return;
+
+  std::vector<PrefetchService::PrefetchURL> prefetch_urls;
+  for (const ContentSuggestion& suggestion : suggestions) {
+    prefetch_urls.push_back(
+        {CreateClientIDFromSuggestionId(suggestion.id()), suggestion.url()});
+  }
+
+  prefetch_service_->AddCandidatePrefetchURLs(prefetch_urls);
+}
+
+void SuggestedArticlesObserver::OnCategoryStatusChanged(
+    Category category,
+    ntp_snippets::CategoryStatus new_status) {
+  if (category != ArticlesCategory() || category_status_ == new_status)
+    return;
+
+  category_status_ = new_status;
+
+  if (category_status_ ==
+          ntp_snippets::CategoryStatus::CATEGORY_EXPLICITLY_DISABLED ||
+      category_status_ ==
+          ntp_snippets::CategoryStatus::ALL_SUGGESTIONS_EXPLICITLY_DISABLED) {
+    prefetch_service_->RemoveAllUnprocessedPrefetchURLs(
+        kSuggestedArticlesNamespace);
+  }
+}
+
+void SuggestedArticlesObserver::OnSuggestionInvalidated(
+    const ContentSuggestion::ID& suggestion_id) {
+  prefetch_service_->RemovePrefetchURLsByClientId(
+      CreateClientIDFromSuggestionId(suggestion_id));
+}
+
+void SuggestedArticlesObserver::OnFullRefreshRequired() {
+  prefetch_service_->RemoveAllUnprocessedPrefetchURLs(
+      kSuggestedArticlesNamespace);
+  OnNewSuggestions(ArticlesCategory());
+}
+
+void SuggestedArticlesObserver::ContentSuggestionsServiceShutdown() {
+  // No need to do anything here, we will just stop getting events.
+}
+
+std::vector<ntp_snippets::ContentSuggestion>*
+SuggestedArticlesObserver::GetTestingArticles() {
+  if (!test_articles_) {
+    test_articles_ =
+        base::MakeUnique<std::vector<ntp_snippets::ContentSuggestion>>();
+  }
+  return test_articles_.get();
+}
+
+}  // namespace offline_pages