components/ntp_snippets/content_suggestions_service.cc

// 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.

#include "components/ntp_snippets/content_suggestions_service.h"

#include <algorithm>
#include <iterator>
#include <set>
#include <utility>

#include "base/bind.h"
#include "base/containers/contains.h"
#include "base/containers/cxx20_erase.h"
#include "base/location.h"
#include "base/metrics/histogram_macros.h"
#include "base/strings/string_number_conversions.h"
#include "base/threading/thread_task_runner_handle.h"
#include "base/time/default_clock.h"
#include "base/values.h"
#include "components/favicon/core/large_icon_service.h"
#include "components/favicon_base/fallback_icon_style.h"
#include "components/favicon_base/favicon_types.h"
#include "components/ntp_snippets/content_suggestions_metrics.h"
#include "components/ntp_snippets/pref_names.h"
#include "components/ntp_snippets/remote/remote_suggestions_provider.h"
#include "components/prefs/pref_registry_simple.h"
#include "components/prefs/pref_service.h"
#include "net/traffic_annotation/network_traffic_annotation.h"
#include "ui/gfx/image/image.h"

namespace ntp_snippets {

namespace {

// Enumeration listing all possible outcomes for fetch attempts of favicons for
// content suggestions. Used for UMA histograms, so do not change existing
// values. Insert new values at the end, and update the histogram definition.
// GENERATED_JAVA_ENUM_PACKAGE: org.chromium.chrome.browser.ntp.snippets
enum class FaviconFetchResult {
  SUCCESS_CACHED = 0,
  SUCCESS_FETCHED = 1,
  FAILURE = 2,
  COUNT = 3
};

}  // namespace

ContentSuggestionsService::ContentSuggestionsService(
    State state,
    signin::IdentityManager* identity_manager,
    history::HistoryService* history_service,
    favicon::LargeIconService* large_icon_service,
    PrefService* pref_service,
    std::unique_ptr<CategoryRanker> category_ranker,
    std::unique_ptr<UserClassifier> user_classifier,
    std::unique_ptr<RemoteSuggestionsScheduler> remote_suggestions_scheduler)
    : state_(state),
      remote_suggestions_provider_(nullptr),
      large_icon_service_(large_icon_service),
      pref_service_(pref_service),
      remote_suggestions_scheduler_(std::move(remote_suggestions_scheduler)),
      user_classifier_(std::move(user_classifier)),
      category_ranker_(std::move(category_ranker)) {
  // Can be null in tests.
  if (identity_manager) {
    identity_manager_observation_.Observe(identity_manager);
  }

  if (history_service) {
    history_service_observation_.Observe(history_service);
  }

  RestoreDismissedCategoriesFromPrefs();
}

ContentSuggestionsService::~ContentSuggestionsService() = default;

void ContentSuggestionsService::Shutdown() {
  remote_suggestions_provider_ = nullptr;
  remote_suggestions_scheduler_ = nullptr;
  suggestions_by_category_.clear();
  providers_by_category_.clear();
  categories_.clear();
  providers_.clear();
  state_ = State::DISABLED;
  for (Observer& observer : observers_) {
    observer.ContentSuggestionsServiceShutdown();
  }
}

// static
void ContentSuggestionsService::RegisterProfilePrefs(
    PrefRegistrySimple* registry) {
  registry->RegisterListPref(prefs::kDismissedCategories);
}

std::vector<Category> ContentSuggestionsService::GetCategories() const {
  std::vector<Category> sorted_categories = categories_;
  std::sort(sorted_categories.begin(), sorted_categories.end(),
            [this](const Category& left, const Category& right) {
              return category_ranker_->Compare(left, right);
            });
  return sorted_categories;
}

CategoryStatus ContentSuggestionsService::GetCategoryStatus(
    Category category) const {
  if (state_ == State::DISABLED) {
    return CategoryStatus::ALL_SUGGESTIONS_EXPLICITLY_DISABLED;
  }

  auto iterator = providers_by_category_.find(category);
  if (iterator == providers_by_category_.end()) {
    return CategoryStatus::NOT_PROVIDED;
  }

  return iterator->second->GetCategoryStatus(category);
}

absl::optional<CategoryInfo> ContentSuggestionsService::GetCategoryInfo(
    Category category) const {
  auto iterator = providers_by_category_.find(category);
  if (iterator == providers_by_category_.end()) {
    return absl::optional<CategoryInfo>();
  }
  return iterator->second->GetCategoryInfo(category);
}

const std::vector<ContentSuggestion>&
ContentSuggestionsService::GetSuggestionsForCategory(Category category) const {
  auto iterator = suggestions_by_category_.find(category);
  if (iterator == suggestions_by_category_.end()) {
    return no_suggestions_;
  }
  return iterator->second;
}

void ContentSuggestionsService::FetchSuggestionImage(
    const ContentSuggestion::ID& suggestion_id,
    ImageFetchedCallback callback) {
  if (!providers_by_category_.count(suggestion_id.category())) {
    LOG(WARNING) << "Requested image for suggestion " << suggestion_id
                 << " for unavailable category " << suggestion_id.category();
    base::ThreadTaskRunnerHandle::Get()->PostTask(
        FROM_HERE, base::BindOnce(std::move(callback), gfx::Image()));
    return;
  }
  providers_by_category_[suggestion_id.category()]->FetchSuggestionImage(
      suggestion_id, std::move(callback));
}

void ContentSuggestionsService::FetchSuggestionImageData(
    const ContentSuggestion::ID& suggestion_id,
    ImageDataFetchedCallback callback) {
  if (!providers_by_category_.count(suggestion_id.category())) {
    LOG(WARNING) << "Requested image for suggestion " << suggestion_id
                 << " for unavailable category " << suggestion_id.category();
    base::ThreadTaskRunnerHandle::Get()->PostTask(
        FROM_HERE, base::BindOnce(std::move(callback), std::string()));
    return;
  }
  providers_by_category_[suggestion_id.category()]->FetchSuggestionImageData(
      suggestion_id, std::move(callback));
}

// TODO(jkrcal): Split the favicon fetching into a separate class.
void ContentSuggestionsService::FetchSuggestionFavicon(
    const ContentSuggestion::ID& suggestion_id,
    int minimum_size_in_pixel,
    int desired_size_in_pixel,
    ImageFetchedCallback callback) {
  const GURL& domain_with_favicon = GetFaviconDomain(suggestion_id);
  if (!domain_with_favicon.is_valid() || !large_icon_service_) {
    base::ThreadTaskRunnerHandle::Get()->PostTask(
        FROM_HERE, base::BindOnce(std::move(callback), gfx::Image()));
    return;
  }

  GetFaviconFromCache(domain_with_favicon, minimum_size_in_pixel,
                      desired_size_in_pixel, std::move(callback),
                      /*continue_to_google_server=*/true);
}

GURL ContentSuggestionsService::GetFaviconDomain(
    const ContentSuggestion::ID& suggestion_id) {
  const std::vector<ContentSuggestion>& suggestions =
      suggestions_by_category_[suggestion_id.category()];
  auto position =
      std::find_if(suggestions.begin(), suggestions.end(),
                   [&suggestion_id](const ContentSuggestion& suggestion) {
                     return suggestion_id == suggestion.id();
                   });
  if (position != suggestions.end()) {
    return position->url_with_favicon();
  }

  // Look up the URL in the archive of |remote_suggestions_provider_|.
  // TODO(jkrcal): Fix how Fetch more works or find other ways to remove this
  // hack. crbug.com/714031
  if (providers_by_category_[suggestion_id.category()] ==
      remote_suggestions_provider_) {
    return remote_suggestions_provider_->GetUrlWithFavicon(suggestion_id);
  }
  return GURL();
}

void ContentSuggestionsService::GetFaviconFromCache(
    const GURL& publisher_url,
    int minimum_size_in_pixel,
    int desired_size_in_pixel,
    ImageFetchedCallback callback,
    bool continue_to_google_server) {
  // TODO(jkrcal): Create a general wrapper function in LargeIconService that
  // does handle the get-from-cache-and-fallback-to-google-server functionality
  // in one shot (for all clients that do not need to react in between).

  // Use desired_size = 0 for getting the icon from the cache (so that the icon
  // is not poorly rescaled by LargeIconService).
  large_icon_service_->GetLargeIconImageOrFallbackStyleForPageUrl(
      publisher_url, minimum_size_in_pixel, /*desired_size_in_pixel=*/0,
      base::BindOnce(&ContentSuggestionsService::OnGetFaviconFromCacheFinished,
                     base::Unretained(this), publisher_url,
                     minimum_size_in_pixel, desired_size_in_pixel,
                     std::move(callback), continue_to_google_server),
      &favicons_task_tracker_);
}

void ContentSuggestionsService::OnGetFaviconFromCacheFinished(
    const GURL& publisher_url,
    int minimum_size_in_pixel,
    int desired_size_in_pixel,
    ImageFetchedCallback callback,
    bool continue_to_google_server,
    const favicon_base::LargeIconImageResult& result) {
  if (!result.image.IsEmpty()) {
    std::move(callback).Run(result.image);
    // Update the time when the icon was last requested - postpone thus the
    // automatic eviction of the favicon from the favicon database.
    large_icon_service_->TouchIconFromGoogleServer(result.icon_url);
    return;
  }

  if (!continue_to_google_server ||
      (result.fallback_icon_style &&
       !result.fallback_icon_style->is_default_background_color)) {
    // We cannot download from the server if there is some small icon in the
    // cache (resulting in non-default background color) or if we already did
    // so.
    std::move(callback).Run(gfx::Image());
    return;
  }

  // Try to fetch the favicon from a Google favicon server.
  // TODO(jkrcal): Currently used only for Articles for you which have public
  // URLs. Let the provider decide whether |publisher_url| may be private or
  // not.
  net::NetworkTrafficAnnotationTag traffic_annotation =
      net::DefineNetworkTrafficAnnotation("content_suggestion_get_favicon", R"(
        semantics {
          sender: "Content Suggestion"
          description:
            "Sends a request to a Google server to retrieve the favicon bitmap "
            "for an article suggestion on the new tab page (URLs are public "
            "and provided by Google)."
          trigger:
            "A request can be sent if Chrome does not have a favicon for a "
            "particular page."
          data: "Page URL and desired icon size."
          destination: GOOGLE_OWNED_SERVICE
        }
        policy {
          cookies_allowed: NO
          setting: "This feature cannot be disabled by settings."
          policy_exception_justification: "Not implemented."
        })");
  large_icon_service_
      ->GetLargeIconOrFallbackStyleFromGoogleServerSkippingLocalCache(
          publisher_url,
          /*may_page_url_be_private=*/false,
          /*should_trim_page_url_path=*/false, traffic_annotation,
          base::BindOnce(
              &ContentSuggestionsService::OnGetFaviconFromGoogleServerFinished,
              base::Unretained(this), publisher_url, minimum_size_in_pixel,
              desired_size_in_pixel, std::move(callback)));
}

void ContentSuggestionsService::OnGetFaviconFromGoogleServerFinished(
    const GURL& publisher_url,
    int minimum_size_in_pixel,
    int desired_size_in_pixel,
    ImageFetchedCallback callback,
    favicon_base::GoogleFaviconServerRequestStatus status) {
  if (status != favicon_base::GoogleFaviconServerRequestStatus::SUCCESS) {
    std::move(callback).Run(gfx::Image());
    return;
  }

  GetFaviconFromCache(publisher_url, minimum_size_in_pixel,
                      desired_size_in_pixel, std::move(callback),
                      /*continue_to_google_server=*/false);
}

void ContentSuggestionsService::ClearHistory(
    base::Time begin,
    base::Time end,
    const base::RepeatingCallback<bool(const GURL& url)>& filter) {
  for (const auto& provider : providers_) {
    provider->ClearHistory(begin, end, filter);
  }
  category_ranker_->ClearHistory(begin, end);
  // This potentially removed personalized data which we shouldn't display
  // anymore.
  for (Observer& observer : observers_) {
    observer.OnFullRefreshRequired();
  }
}

void ContentSuggestionsService::ClearAllCachedSuggestions() {
  suggestions_by_category_.clear();
  for (const auto& provider : providers_) {
    provider->ClearCachedSuggestions();
  }
  for (Observer& observer : observers_) {
    observer.OnFullRefreshRequired();
  }
}

void ContentSuggestionsService::GetDismissedSuggestionsForDebugging(
    Category category,
    DismissedSuggestionsCallback callback) {
  auto iterator = providers_by_category_.find(category);
  if (iterator != providers_by_category_.end()) {
    iterator->second->GetDismissedSuggestionsForDebugging(category,
                                                          std::move(callback));
  } else {
    std::move(callback).Run(std::vector<ContentSuggestion>());
  }
}

void ContentSuggestionsService::ClearDismissedSuggestionsForDebugging(
    Category category) {
  auto iterator = providers_by_category_.find(category);
  if (iterator != providers_by_category_.end()) {
    iterator->second->ClearDismissedSuggestionsForDebugging(category);
  }
}

void ContentSuggestionsService::DismissSuggestion(
    const ContentSuggestion::ID& suggestion_id) {
  if (!providers_by_category_.count(suggestion_id.category())) {
    LOG(WARNING) << "Dismissed suggestion " << suggestion_id
                 << " for unavailable category " << suggestion_id.category();
    return;
  }

  metrics::RecordContentSuggestionDismissed();

  providers_by_category_[suggestion_id.category()]->DismissSuggestion(
      suggestion_id);

  // Remove the suggestion locally if it is present. A suggestion may be missing
  // localy e.g. if it was sent to UI through |Fetch| or it has been dismissed
  // from a different NTP.
  RemoveSuggestionByID(suggestion_id);
}

void ContentSuggestionsService::DismissCategory(Category category) {
  auto providers_it = providers_by_category_.find(category);
  if (providers_it == providers_by_category_.end()) {
    return;
  }

  metrics::RecordCategoryDismissed();

  ContentSuggestionsProvider* provider = providers_it->second;
  UnregisterCategory(category, provider);

  dismissed_providers_by_category_[category] = provider;
  StoreDismissedCategoriesToPrefs();

  category_ranker_->OnCategoryDismissed(category);
}

void ContentSuggestionsService::RestoreDismissedCategories() {
  // Make a copy as the original will be modified during iteration.
  auto dismissed_providers_by_category_copy = dismissed_providers_by_category_;
  for (const auto& category_provider_pair :
       dismissed_providers_by_category_copy) {
    RestoreDismissedCategory(category_provider_pair.first);
  }
  StoreDismissedCategoriesToPrefs();
  DCHECK(dismissed_providers_by_category_.empty());
}

void ContentSuggestionsService::AddObserver(Observer* observer) {
  observers_.AddObserver(observer);
}

void ContentSuggestionsService::RemoveObserver(Observer* observer) {
  observers_.RemoveObserver(observer);
}

void ContentSuggestionsService::RegisterProvider(
    std::unique_ptr<ContentSuggestionsProvider> provider) {
  DCHECK(state_ == State::ENABLED);
  providers_.push_back(std::move(provider));
}

void ContentSuggestionsService::Fetch(
    const Category& category,
    const std::set<std::string>& known_suggestion_ids,
    FetchDoneCallback callback) {
  auto providers_it = providers_by_category_.find(category);
  if (providers_it == providers_by_category_.end()) {
    return;
  }

  metrics::RecordFetchAction();

  providers_it->second->Fetch(category, known_suggestion_ids,
                              std::move(callback));
}

void ContentSuggestionsService::ReloadSuggestions() {
  for (const auto& provider : providers_) {
    provider->ReloadSuggestions();
  }
}

bool ContentSuggestionsService::AreRemoteSuggestionsEnabled() const {
  return remote_suggestions_provider_ &&
         !remote_suggestions_provider_->IsDisabled();
}

////////////////////////////////////////////////////////////////////////////////
// Private methods

void ContentSuggestionsService::OnNewSuggestions(
    ContentSuggestionsProvider* provider,
    Category category,
    std::vector<ContentSuggestion> suggestions) {
  // Providers shouldn't call this when they're in a non-available state.
  DCHECK(
      IsCategoryStatusInitOrAvailable(provider->GetCategoryStatus(category)));

  if (TryRegisterProviderForCategory(provider, category)) {
    NotifyCategoryStatusChanged(category);
  } else if (IsCategoryDismissed(category)) {
    // The category has been registered as a dismissed one. We need to
    // check if the dismissal can be cleared now that we received new data.
    if (suggestions.empty()) {
      return;
    }

    RestoreDismissedCategory(category);
    StoreDismissedCategoriesToPrefs();

    NotifyCategoryStatusChanged(category);
  }

  if (!IsCategoryStatusAvailable(provider->GetCategoryStatus(category))) {
    // A provider shouldn't send us suggestions while it's not available.
    DCHECK(suggestions.empty());
    return;
  }

  suggestions_by_category_[category] = std::move(suggestions);

  for (Observer& observer : observers_) {
    observer.OnNewSuggestions(category);
  }
}

void ContentSuggestionsService::OnCategoryStatusChanged(
    ContentSuggestionsProvider* provider,
    Category category,
    CategoryStatus new_status) {
  if (new_status == CategoryStatus::NOT_PROVIDED) {
    UnregisterCategory(category, provider);
  } else {
    if (!IsCategoryStatusAvailable(new_status)) {
      suggestions_by_category_.erase(category);
    }
    TryRegisterProviderForCategory(provider, category);
    DCHECK_EQ(new_status, provider->GetCategoryStatus(category));
  }

  if (!IsCategoryDismissed(category)) {
    NotifyCategoryStatusChanged(category);
  }
}

void ContentSuggestionsService::OnSuggestionInvalidated(
    ContentSuggestionsProvider* provider,
    const ContentSuggestion::ID& suggestion_id) {
  RemoveSuggestionByID(suggestion_id);
  for (Observer& observer : observers_) {
    observer.OnSuggestionInvalidated(suggestion_id);
  }
}
// signin::IdentityManager::Observer implementation
void ContentSuggestionsService::OnPrimaryAccountChanged(
    const signin::PrimaryAccountChangeEvent& event_details) {
  switch (event_details.GetEventTypeFor(signin::ConsentLevel::kSync)) {
    case signin::PrimaryAccountChangeEvent::Type::kSet:
      OnSignInStateChanged(/*has_signed_in=*/true);
      break;
    case signin::PrimaryAccountChangeEvent::Type::kCleared:
      OnSignInStateChanged(/*has_signed_in=*/false);
      break;
    case signin::PrimaryAccountChangeEvent::Type::kNone:
      break;
  }
}

// history::HistoryServiceObserver implementation.
void ContentSuggestionsService::OnURLsDeleted(
    history::HistoryService* history_service,
    const history::DeletionInfo& deletion_info) {
  // We don't care about expired entries.
  if (deletion_info.is_from_expiration()) {
    return;
  }

  if (deletion_info.IsAllHistory()) {
    base::RepeatingCallback<bool(const GURL& url)> filter =
        base::BindRepeating([](const GURL& url) { return true; });
    ClearHistory(base::Time(), base::Time::Max(), filter);
  } else {
    // If a user deletes a single URL, we don't consider this a clear user
    // intend to clear our data.
    // TODO(tschumann): Single URL deletions should be handled on a case-by-case
    // basis. However this depends on the provider's details and thus cannot be
    // done here. Introduce a OnURLsDeleted() method on the providers to move
    // this decision further down.
    if (deletion_info.deleted_rows().size() < 2) {
      return;
    }
    std::set<GURL> deleted_urls;
    for (const history::URLRow& row : deletion_info.deleted_rows()) {
      deleted_urls.insert(row.url());
    }
    base::RepeatingCallback<bool(const GURL& url)> filter =
        base::BindRepeating([](const std::set<GURL>& set,
                               const GURL& url) { return set.count(url) != 0; },
                            deleted_urls);
    // We usually don't have any time-related information (the URLRow objects
    // usually don't provide a |last_visit()| timestamp. Hence we simply clear
    // the whole history for the selected URLs.
    ClearHistory(base::Time(), base::Time::Max(), filter);
  }
}

void ContentSuggestionsService::HistoryServiceBeingDeleted(
    history::HistoryService* history_service) {
  DCHECK(history_service_observation_.IsObservingSource(history_service));
  history_service_observation_.Reset();
}

bool ContentSuggestionsService::TryRegisterProviderForCategory(
    ContentSuggestionsProvider* provider,
    Category category) {
  auto it = providers_by_category_.find(category);
  if (it != providers_by_category_.end()) {
    DCHECK_EQ(it->second, provider);
    return false;
  }

  auto dismissed_it = dismissed_providers_by_category_.find(category);
  if (dismissed_it != dismissed_providers_by_category_.end()) {
    // The initialisation of dismissed categories registers them with |nullptr|
    // for providers, we need to check for that to see if the provider is
    // already registered or not.
    if (!dismissed_it->second) {
      dismissed_it->second = provider;
    } else {
      DCHECK_EQ(dismissed_it->second, provider);
    }
    return false;
  }

  RegisterCategory(category, provider);
  return true;
}

void ContentSuggestionsService::RegisterCategory(
    Category category,
    ContentSuggestionsProvider* provider) {
  DCHECK(!base::Contains(providers_by_category_, category));
  DCHECK(!IsCategoryDismissed(category));

  providers_by_category_[category] = provider;
  categories_.push_back(category);
  if (IsCategoryStatusAvailable(provider->GetCategoryStatus(category))) {
    suggestions_by_category_.insert(
        std::make_pair(category, std::vector<ContentSuggestion>()));
  }
}

void ContentSuggestionsService::UnregisterCategory(
    Category category,
    ContentSuggestionsProvider* provider) {
  auto providers_it = providers_by_category_.find(category);
  if (providers_it == providers_by_category_.end()) {
    DCHECK(IsCategoryDismissed(category));
    return;
  }

  DCHECK_EQ(provider, providers_it->second);
  providers_by_category_.erase(providers_it);
  categories_.erase(
      std::find(categories_.begin(), categories_.end(), category));
  suggestions_by_category_.erase(category);
}

bool ContentSuggestionsService::RemoveSuggestionByID(
    const ContentSuggestion::ID& suggestion_id) {
  std::vector<ContentSuggestion>* suggestions =
      &suggestions_by_category_[suggestion_id.category()];
  auto position =
      std::find_if(suggestions->begin(), suggestions->end(),
                   [&suggestion_id](const ContentSuggestion& suggestion) {
                     return suggestion_id == suggestion.id();
                   });
  if (position == suggestions->end()) {
    return false;
  }
  suggestions->erase(position);

  return true;
}

void ContentSuggestionsService::NotifyCategoryStatusChanged(Category category) {
  for (Observer& observer : observers_) {
    observer.OnCategoryStatusChanged(category, GetCategoryStatus(category));
  }
}

void ContentSuggestionsService::OnSignInStateChanged(bool has_signed_in) {
  // First notify the providers, so they can make the required changes.
  for (const auto& provider : providers_) {
    provider->OnSignInStateChanged(has_signed_in);
  }

  // Finally notify the observers so they refresh only after the backend is
  // ready.
  for (Observer& observer : observers_) {
    observer.OnFullRefreshRequired();
  }
}

bool ContentSuggestionsService::IsCategoryDismissed(Category category) const {
  return base::Contains(dismissed_providers_by_category_, category);
}

void ContentSuggestionsService::RestoreDismissedCategory(Category category) {
  auto dismissed_it = dismissed_providers_by_category_.find(category);
  DCHECK(base::Contains(dismissed_providers_by_category_, category));

  // Keep the reference to the provider and remove it from the dismissed ones,
  // because the category registration enforces that it's not dismissed.
  ContentSuggestionsProvider* provider = dismissed_it->second;
  dismissed_providers_by_category_.erase(dismissed_it);

  if (provider) {
    RegisterCategory(category, provider);
  }
}

void ContentSuggestionsService::RestoreDismissedCategoriesFromPrefs() {
  // This must only be called at startup.
  DCHECK(dismissed_providers_by_category_.empty());
  DCHECK(providers_by_category_.empty());

  const base::Value* list = pref_service_->GetList(prefs::kDismissedCategories);
  for (const base::Value& entry : list->GetList()) {
    if (!entry.is_int()) {
      DLOG(WARNING) << "Invalid category pref value: " << entry;
      continue;
    }

    // When the provider is registered, it will be stored in this map.
    dismissed_providers_by_category_[Category::FromIDValue(entry.GetInt())] =
        nullptr;
  }
}

void ContentSuggestionsService::StoreDismissedCategoriesToPrefs() {
  base::ListValue list;
  for (const auto& category_provider_pair : dismissed_providers_by_category_) {
    list.Append(category_provider_pair.first.id());
  }

  pref_service_->Set(prefs::kDismissedCategories, list);
}

void ContentSuggestionsService::DestroyCategoryAndItsProvider(
    Category category) {
  // Destroying articles category is more complex and not implemented.
  DCHECK_NE(category, Category::FromKnownCategory(KnownCategories::ARTICLES));

  if (providers_by_category_.count(category) != 1) {
    return;
  }

  {  // Destroy the provider and delete its mentions.
    ContentSuggestionsProvider* raw_provider = providers_by_category_[category];
    base::EraseIf(
        providers_,
        [&raw_provider](
            const std::unique_ptr<ContentSuggestionsProvider>& provider) {
          return provider.get() == raw_provider;
        });
    providers_by_category_.erase(category);

    if (dismissed_providers_by_category_.count(category) == 1) {
      dismissed_providers_by_category_[category] = nullptr;
    }
  }

  suggestions_by_category_.erase(category);

  auto it = std::find(categories_.begin(), categories_.end(), category);
  categories_.erase(it);

  // Notify observers that the category is gone.
  NotifyCategoryStatusChanged(category);
}

}  // namespace ntp_snippets