[Offline Pages] Set up the initial prefetching service.

chrome/browser/android/offline_pages/offline_page_suggestions_observer.cc

+// 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 "chrome/browser/android/offline_pages/offline_page_suggestions_observer.h"
+
+#include <unordered_set>
+
+#include "base/memory/ptr_util.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "chrome/browser/android/offline_pages/prefetch_service_factory.h"
+#include "components/ntp_snippets/category.h"
+#include "components/ntp_snippets/category_status.h"
+#include "components/offline_pages/core/offline_page_feature.h"
+#include "components/offline_pages/core/prefetch/prefetch_service_impl.h"
+
+namespace offline_pages {
+
+int kOfflinePageSuggestionsObserverUserDataKey;
+
+namespace {
+
+// The default delegate that contains external dependencies for the Offline Page
+// Suggestions Observer.  This is unused in tests, which implement their own
+// Delegate.
+class DefaultDelegate : public SuggestionsObserver::Delegate {
+ public:
+  explicit DefaultDelegate(ntp_snippets::ContentSuggestionsService* service);
+  ~DefaultDelegate() override = default;
+
+  std::vector<GURL> GetSuggestionURLs(
+      const ntp_snippets::Category& category) override;
+  PrefetchService* GetPrefetchService(
+      content::BrowserContext* context) override;
+
+ private:
+  ntp_snippets::ContentSuggestionsService* service_;
+};
+
+DefaultDelegate::DefaultDelegate(
+    ntp_snippets::ContentSuggestionsService* service)
+    : service_(service) {}
+
+std::vector<GURL> DefaultDelegate::GetSuggestionURLs(
+    const ntp_snippets::Category& category) {
+  std::vector<GURL> suggestion_urls;
+  auto& categories = service_->GetSuggestionsForCategory(category);
+  for (const ntp_snippets::ContentSuggestion& suggestion : categories) {
+    suggestion_urls.emplace_back(suggestion.url());
+  }
+  return suggestion_urls;
+}
+
+PrefetchService* DefaultDelegate::GetPrefetchService(
+    content::BrowserContext* context) {
+  return PrefetchServiceFactory::GetForBrowserContext(context);
+}
+
+}  // namespace
+
+// static
+void SuggestionsObserver::ObserveContentSuggestionsService(
+    content::BrowserContext* browser_context,
+    ntp_snippets::ContentSuggestionsService* service) {
+  if (!offline_pages::IsPrefetchingOfflinePagesEnabled())
+    return;
+
+  auto category = ntp_snippets::Category::FromKnownCategory(
+      ntp_snippets::KnownCategories::ARTICLES);
+  auto suggestions_observer = base::MakeUnique<SuggestionsObserver>(
+      browser_context, base::MakeUnique<DefaultDelegate>(service), category);
+  service->AddObserver(suggestions_observer.get());
+  service->SetUserData(&kOfflinePageSuggestionsObserverUserDataKey,
+                       suggestions_observer.release());

[jianli, 2017/04/11 22:39:55]

Who is responsible to clean this up?

[dewittj, 2017/04/12 00:22:48]

UserData::Data is owned by the class that inherits from base::SupportsUserData.

+}
+
+SuggestionsObserver::SuggestionsObserver(
+    content::BrowserContext* browser_context,
+    std::unique_ptr<Delegate> delegate,

[jianli, 2017/04/11 22:39:55]

nit: normally we pass delegate as the last argument

[dewittj, 2017/04/12 00:22:48]

Done.

+    const ntp_snippets::Category& category)
+    : delegate_(std::move(delegate)),

[jianli, 2017/04/11 22:39:55]

nit: it would be better to declare these member variables in same order as
parameters, if possible.

[dewittj, 2017/04/12 00:22:48]

Done.

+      browser_context_(browser_context),
+      category_(category) {}
+
+SuggestionsObserver::~SuggestionsObserver() = default;
+
+void SuggestionsObserver::OnNewSuggestions(ntp_snippets::Category category) {
+  if (category != category_ ||
+      category_status_ != ntp_snippets::CategoryStatus::AVAILABLE) {
+    return;
+  }
+
+  std::vector<GURL> suggestion_urls = delegate_->GetSuggestionURLs(category_);
+  if (suggestion_urls.empty())
+    return;
+
+  PrefetchService* service = delegate_->GetPrefetchService(browser_context_);
+  service->OnNewURLsToPrefetch(suggestion_urls);
+}
+
+void SuggestionsObserver::OnCategoryStatusChanged(
+    ntp_snippets::Category category,
+    ntp_snippets::CategoryStatus new_status) {
+  if (category != category_)
+    return;
+
+  category_status_ = new_status;

[jianli, 2017/04/11 22:39:55]

Do we want a DCHECK to ensure new_status is different?

[dewittj, 2017/04/12 00:22:48]

It seems aggressive to do that.  Perhaps an early return is better.

+
+  if (category_status_ ==
+          ntp_snippets::CategoryStatus::CATEGORY_EXPLICITLY_DISABLED ||
+      category_status_ ==
+          ntp_snippets::CategoryStatus::ALL_SUGGESTIONS_EXPLICITLY_DISABLED) {
+    PrefetchService* service = delegate_->GetPrefetchService(browser_context_);
+    service->RemoveAllUnprocessedURLsToPrefetch();

[Dmitry Titov, 2017/04/11 21:50:46]

Do you mean to have a TODO here to actually remove only the ones from a
category?

[dewittj, 2017/04/12 00:22:48]

Done.

+  }
+}
+
+void SuggestionsObserver::OnSuggestionInvalidated(
+    const ntp_snippets::ContentSuggestion::ID& suggestion_id) {
+  // TODO(dewittj): Keep track of ContentSuggestion::IDs so we can invalidate
+  // suggestions as well.
+  NOTIMPLEMENTED();
+}
+
+void SuggestionsObserver::OnFullRefreshRequired() {
+  PrefetchService* service = delegate_->GetPrefetchService(browser_context_);
+  service->RemoveAllUnprocessedURLsToPrefetch();
+  OnNewSuggestions(category_);
+}
+
+void SuggestionsObserver::ContentSuggestionsServiceShutdown() {
+  // No need to do anything here, we will just stop getting events.
+}
+
+}  // namespace offline_pages