[iOS] Trigger infinite feed for Discover feed

When a user scrolls near the bottom of the NTP (with a variable offset),
the Discover provider function for loading the next feed's page is
called.

Bug: 1085419
Change-Id: I26c493bc588905e0018902261eb3d050291a83ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2237717
Commit-Queue: Adam Trudeau-Arcaro <adamta@google.com>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795335}

ios/chrome/browser/ui/content_suggestions/BUILD.gn

@@ -4,10 +4,12 @@
 
 source_set("content_suggestions") {
   sources = [
+    "content_suggestions_action_handler.h",
     "content_suggestions_alert_factory.h",
     "content_suggestions_alert_factory.mm",
     "content_suggestions_category_wrapper.h",
     "content_suggestions_category_wrapper.mm",
+    "content_suggestions_consumer.h",
     "content_suggestions_coordinator.h",
     "content_suggestions_coordinator.mm",
     "content_suggestions_favicon_mediator.h",
@@ -105,11 +107,13 @@ source_set("constants") {
 
 source_set("content_suggestions_ui") {
   sources = [
+    "content_suggestions_action_handler.h",
     "content_suggestions_collection_controlling.h",
     "content_suggestions_collection_synchronizing.h",
     "content_suggestions_collection_updater.h",
     "content_suggestions_collection_updater.mm",
     "content_suggestions_commands.h",
+    "content_suggestions_consumer.h",
     "content_suggestions_data_sink.h",
     "content_suggestions_data_source.h",
     "content_suggestions_header_controlling.h",
@@ -143,6 +147,7 @@ source_set("content_suggestions_ui") {
     "resources:ntp_search_icon",
     "//base",
     "//components/strings",
+    "//ios/chrome/browser",
     "//ios/chrome/browser/ui:feature_flags",
     "//ios/chrome/browser/ui/collection_view",
     "//ios/chrome/browser/ui/commands",
@@ -162,6 +167,8 @@ source_set("content_suggestions_ui") {
     "//ios/chrome/common/ui/colors",
     "//ios/chrome/common/ui/favicon",
     "//ios/chrome/common/ui/util",
+    "//ios/public/provider/chrome/browser",
+    "//ios/public/provider/chrome/browser/discover_feed",
     "//ios/web/common",
     "//ui/base",
   ]

ios/chrome/browser/ui/content_suggestions/cells/content_suggestions_discover_item.mm

@@ -53,6 +53,10 @@
 @implementation ContentSuggestionsDiscoverCell
 
 - (void)setDiscoverFeedView:(UIViewController*)discoverFeed {
+  if (_discoverFeed == discoverFeed) {
+    return;
+  }
+  [_discoverFeed.view removeFromSuperview];
   _discoverFeed = discoverFeed;
   if (discoverFeed) {
     UIView* discoverView = discoverFeed.view;
@@ -76,7 +80,8 @@
   if (!self.discoverFeed) {
     return 0;
   }
-
+  // TODO(crbug.com/1092900): Make this more robust. Will require
+  // the provider to expose the feed as a UICollectionViewController.
   for (UIView* view in self.discoverFeed.view.subviews) {
     if ([view isKindOfClass:[UICollectionView class]]) {
       feedView = static_cast<UICollectionView*>(view);

ios/chrome/browser/ui/content_suggestions/content_suggestions_action_handler.h

+// Copyright 2020 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 IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTIONS_ACTION_HANDLER_H_
+#define IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTIONS_ACTION_HANDLER_H_
+
+// Action handler protocol for the content suggestions view controller.
+@protocol ContentSuggestionsActionHandler
+// Paginates the Discover feed by appending a set of articles to
+// the bottom of it.
+- (void)loadMoreFeedArticles;
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTIONS_ACTION_HANDLER_H_

ios/chrome/browser/ui/content_suggestions/content_suggestions_consumer.h

+// Copyright 2020 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 IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTIONS_CONSUMER_H_
+#define IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTIONS_CONSUMER_H_
+
+// Consumer protocol for the content suggestions view controller.
+@protocol ContentSuggestionsConsumer
+// Notifies the consumer to set the content suggestions enabled
+// based on the user setting.
+- (void)setContentSuggestionsEnabled:(BOOL)enabled;
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTIONS_CONSUMER_H_

ios/chrome/browser/ui/content_suggestions/content_suggestions_coordinator.mm

@@ -34,6 +34,7 @@
 #import "ios/chrome/browser/ui/commands/command_dispatcher.h"
 #import "ios/chrome/browser/ui/commands/open_new_tab_command.h"
 #import "ios/chrome/browser/ui/content_suggestions/cells/content_suggestions_most_visited_item.h"
+#import "ios/chrome/browser/ui/content_suggestions/content_suggestions_action_handler.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_data_sink.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_feature.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_header_synchronizer.h"
@@ -70,6 +71,7 @@
 #endif
 
 @interface ContentSuggestionsCoordinator () <
+    ContentSuggestionsActionHandler,
     ContentSuggestionsMenuProvider,
     ContentSuggestionsViewControllerAudience,
     DiscoverFeedDelegate,
@@ -99,6 +101,7 @@
 // Delegate for handling Discover feed header UI changes.
 @property(nonatomic, weak) id<DiscoverFeedHeaderChanging>
     discoverFeedHeaderDelegate;
+@property(nonatomic) CGFloat discoverFeedHeight;
 
 @end
 
@@ -215,12 +218,16 @@
       self.browser->GetCommandDispatcher(), SnackbarCommands);
   self.suggestionsViewController.dispatcher = dispatcher;
   self.suggestionsViewController.discoverFeedMenuHandler = self;
+
   self.discoverFeedHeaderDelegate =
       self.suggestionsViewController.discoverFeedHeaderDelegate;
-
   [self.discoverFeedHeaderDelegate
       changeDiscoverFeedHeaderVisibility:[self.contentSuggestionsVisible
                                                  value]];
+  self.suggestionsViewController.contentSuggestionsEnabled =
+      prefs->FindPreference(prefs::kArticlesForYouEnabled);
+  self.suggestionsViewController.handler = self;
+  self.contentSuggestionsMediator.consumer = self.suggestionsViewController;
 
   if (@available(iOS 13.0, *)) {
     self.suggestionsViewController.menuProvider = self;
@@ -431,6 +438,26 @@
       self.discoverFeedViewController;
 }
 
+#pragma mark - ContentSuggestionsActionHandler
+
+- (void)loadMoreFeedArticles {
+  CGFloat currentHeight = 0;
+  for (UIView* view in self.discoverFeedViewController.view.subviews) {
+    if ([view isKindOfClass:[UICollectionView class]]) {
+      UICollectionView* feedView = static_cast<UICollectionView*>(view);
+      currentHeight = feedView.contentSize.height;
+    }
+  }
+  // TODO(crbug.com/1085419): Track number of cards from protocol instead of
+  // height to determine whether or not we should fetch more cards.
+  if (currentHeight > self.discoverFeedHeight) {
+    ios::GetChromeBrowserProvider()
+        ->GetDiscoverFeedProvider()
+        ->LoadMoreFeedArticles();
+    self.discoverFeedHeight = currentHeight;
+  }
+}
+
 #pragma mark - Public methods
 
 - (UIView*)view {

ios/chrome/browser/ui/content_suggestions/content_suggestions_mediator.h

@@ -28,6 +28,7 @@ class MostVisitedSites;
 }
 
 @protocol ContentSuggestionsCommands;
+@protocol ContentSuggestionsConsumer;
 @protocol ContentSuggestionsGestureCommands;
 @protocol ContentSuggestionsHeaderProvider;
 @class ContentSuggestionIdentifier;
@@ -79,6 +80,9 @@ class ReadingListModel;
 // Delegate used to communicate to communicate events to the DiscoverFeed.
 @property(nonatomic, weak) id<DiscoverFeedDelegate> discoverFeedDelegate;
 
+// The consumer for this mediator.
+@property(nonatomic, weak) id<ContentSuggestionsConsumer> consumer;
+
 // Disconnects the mediator.
 - (void)disconnect;
 

ios/chrome/browser/ui/content_suggestions/content_suggestions_mediator.mm

@@ -30,6 +30,7 @@
 #import "ios/chrome/browser/ui/content_suggestions/cells/suggested_content.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_category_wrapper.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_commands.h"
+#import "ios/chrome/browser/ui/content_suggestions/content_suggestions_consumer.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_data_sink.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_favicon_mediator.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_feature.h"
@@ -85,8 +86,8 @@ const NSInteger kMaxNumMostVisitedTiles = 4;
 // Whether the contents section should be hidden completely.
 // Don't use PrefBackedBoolean or PrefMember as this value needs to be checked
 // when the Preference is updated.
-@property(nullable, nonatomic, assign)
-    const PrefService::Preference* contentArticlesEnabled;
+@property(nonatomic, assign)
+    const PrefService::Preference* contentSuggestionsEnabled;
 // Most visited items from the MostVisitedSites service currently displayed.
 @property(nonatomic, strong)
     NSMutableArray<ContentSuggestionsMostVisitedItem*>* mostVisitedItems;
@@ -155,7 +156,7 @@ const NSInteger kMaxNumMostVisitedTiles = 4;
               discoverFeed:(UIViewController*)discoverFeed {
   self = [super init];
   if (self) {
-    _contentArticlesEnabled =
+    _contentSuggestionsEnabled =
         prefService->FindPreference(prefs::kArticlesForYouEnabled);
     _suggestionBridge =
         std::make_unique<ContentSuggestionsServiceBridge>(self, contentService);
@@ -216,6 +217,13 @@ const NSInteger kMaxNumMostVisitedTiles = 4;
   [self.dataSink reloadAllData];
 }
 
+- (void)setConsumer:(id<ContentSuggestionsConsumer>)consumer {
+  _consumer = consumer;
+  [self.consumer
+      setContentSuggestionsEnabled:self.contentSuggestionsEnabled->GetValue()
+                                       ->GetBool()];
+}
+
 - (void)blockMostVisitedURL:(GURL)URL {
   _mostVisitedSites->AddOrRemoveBlacklistedUrl(URL, true);
   [self useFreshMostVisited];
@@ -275,7 +283,7 @@ const NSInteger kMaxNumMostVisitedTiles = 4;
   // TODO(crbug.com/1105624): Observe the kArticlesForYouEnabled Pref in order
   // to hide the DiscoverFeed section if the finch flag is enabled.
   if (IsDiscoverFeedEnabled() &&
-      self.contentArticlesEnabled->GetValue()->GetBool()) {
+      self.contentSuggestionsEnabled->GetValue()->GetBool()) {
     [sectionsInfo addObject:self.discoverSectionInfo];
   }
 
@@ -473,6 +481,9 @@ const NSInteger kMaxNumMostVisitedTiles = 4;
       [self.dataSink section:sectionInfo isLoading:NO];
     }
   }
+  [self.consumer
+      setContentSuggestionsEnabled:self.contentSuggestionsEnabled->GetValue()
+                                       ->GetBool()];
 }
 
 - (void)contentSuggestionsService:
@@ -687,13 +698,13 @@ const NSInteger kMaxNumMostVisitedTiles = 4;
 
 // ntp_snippets doesn't differentiate between disabled vs collapsed, so if
 // the status is |CATEGORY_EXPLICITLY_DISABLED|, check the value of
-// |contentArticlesEnabled|.
+// |contentSuggestionsEnabled|.
 - (BOOL)isCategoryInitOrAvailable:(ntp_snippets::Category)category {
   ntp_snippets::CategoryStatus status =
       self.contentService->GetCategoryStatus(category);
   if (category.IsKnownCategory(ntp_snippets::KnownCategories::ARTICLES) &&
       status == ntp_snippets::CategoryStatus::CATEGORY_EXPLICITLY_DISABLED)
-    return self.contentArticlesEnabled->GetValue()->GetBool();
+    return self.contentSuggestionsEnabled->GetValue()->GetBool();
   else
     return IsCategoryStatusInitOrAvailable(
         self.contentService->GetCategoryStatus(category));
@@ -701,13 +712,13 @@ const NSInteger kMaxNumMostVisitedTiles = 4;
 
 // ntp_snippets doesn't differentiate between disabled vs collapsed, so if
 // the status is |CATEGORY_EXPLICITLY_DISABLED|, check the value of
-// |contentArticlesEnabled|.
+// |contentSuggestionsEnabled|.
 - (BOOL)isCategoryAvailable:(ntp_snippets::Category)category {
   ntp_snippets::CategoryStatus status =
       self.contentService->GetCategoryStatus(category);
   if (category.IsKnownCategory(ntp_snippets::KnownCategories::ARTICLES) &&
       status == ntp_snippets::CategoryStatus::CATEGORY_EXPLICITLY_DISABLED) {
-    return self.contentArticlesEnabled->GetValue()->GetBool();
+    return self.contentSuggestionsEnabled->GetValue()->GetBool();
   } else {
     return IsCategoryStatusAvailable(
         self.contentService->GetCategoryStatus(category));

ios/chrome/browser/ui/content_suggestions/content_suggestions_view_controller.h

@@ -9,8 +9,10 @@
 
 #import "ios/chrome/browser/ui/collection_view/collection_view_controller.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_collection_controlling.h"
+#import "ios/chrome/browser/ui/content_suggestions/content_suggestions_consumer.h"
 
 @class ContentSuggestionsSectionInformation;
+@protocol ContentSuggestionsActionHandler;
 @protocol ContentSuggestionsCommands;
 @protocol ContentSuggestionsDataSource;
 @protocol ContentSuggestionsHeaderSynchronizing;
@@ -29,7 +31,8 @@ extern NSString* const
 
 // CollectionViewController to display the suggestions items.
 @interface ContentSuggestionsViewController
-    : CollectionViewController <ContentSuggestionsCollectionControlling>
+    : CollectionViewController <ContentSuggestionsCollectionControlling,
+                                ContentSuggestionsConsumer>
 
 - (instancetype)initWithStyle:(CollectionViewControllerStyle)style
     NS_DESIGNATED_INITIALIZER;
@@ -57,7 +60,10 @@ extern NSString* const
     discoverFeedHeaderDelegate;
 @property(nonatomic, weak) id<ContentSuggestionsMetricsRecording>
     metricsRecorder;
-
+// Whether or not the contents section should be hidden completely.
+@property(nonatomic, assign) BOOL contentSuggestionsEnabled;
+// Delegate for handling actions relating to content suggestions.
+@property(nonatomic, weak) id<ContentSuggestionsActionHandler> handler;
 // Provider of menu configurations for the contentSuggestions component.
 @property(nonatomic, weak) id<ContentSuggestionsMenuProvider> menuProvider
     API_AVAILABLE(ios(13.0));

ios/chrome/browser/ui/content_suggestions/content_suggestions_view_controller.mm

@@ -16,10 +16,12 @@
 #import "ios/chrome/browser/ui/content_suggestions/cells/content_suggestions_most_visited_cell.h"
 #import "ios/chrome/browser/ui/content_suggestions/cells/content_suggestions_most_visited_item.h"
 #import "ios/chrome/browser/ui/content_suggestions/cells/suggested_content.h"
+#import "ios/chrome/browser/ui/content_suggestions/content_suggestions_action_handler.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_collection_updater.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_collection_utils.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_commands.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_constants.h"
+#import "ios/chrome/browser/ui/content_suggestions/content_suggestions_feature.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_header_synchronizing.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_layout.h"
 #import "ios/chrome/browser/ui/content_suggestions/content_suggestions_menu_provider.h"
@@ -49,6 +51,8 @@ using CSCollectionViewItem = CollectionViewItem<SuggestedContent>;
 const CGFloat kMostVisitedBottomMargin = 13;
 const CGFloat kCardBorderRadius = 11;
 const CGFloat kDiscoverFeedContentWith = 430;
+// Value representing offset from bottom of the page to trigger pagination.
+const CGFloat kPaginationOffset = 100;
 }
 
 NSString* const kContentSuggestionsMostVisitedAccessibilityIdentifierPrefix =
@@ -643,6 +647,14 @@ NSString* const kContentSuggestionsMostVisitedAccessibilityIdentifierPrefix =
   [self.headerSynchronizer updateFakeOmniboxOnCollectionScroll];
   self.scrolledToTop =
       scrollView.contentOffset.y >= [self.headerSynchronizer pinnedOffsetY];
+
+  if (IsDiscoverFeedEnabled() && self.contentSuggestionsEnabled) {
+    float scrollPosition =
+        scrollView.contentOffset.y + scrollView.frame.size.height;
+    if (scrollPosition >= scrollView.contentSize.height - kPaginationOffset) {
+      [self.handler loadMoreFeedArticles];
+    }
+  }
 }
 
 - (BOOL)scrollViewShouldScrollToTop:(UIScrollView*)scrollView {
@@ -807,4 +819,10 @@ NSString* const kContentSuggestionsMostVisitedAccessibilityIdentifierPrefix =
   [self.discoverFeedMenuHandler openDiscoverFeedMenu:menuButton];
 }
 
+#pragma mark - ContentSuggestionsConsumer
+
+- (void)setContentSuggestionsEnabled:(BOOL)enabled {
+  _contentSuggestionsEnabled = enabled;
+}
+
 @end

ios/public/provider/chrome/browser/discover_feed/discover_feed_provider.h

@@ -47,6 +47,8 @@ class DiscoverFeedProvider {
   // Methods to register or remove observers.
   virtual void AddObserver(Observer* observer);
   virtual void RemoveObserver(Observer* observer);
+  // Loads and appends the next set of articles in the feed.
+  virtual void LoadMoreFeedArticles();
 };
 
 #endif  // IOS_PUBLIC_PROVIDER_CHROME_BROWSER_DISCOVER_FEED_DISCOVER_FEED_PROVIDER_H_

ios/public/provider/chrome/browser/discover_feed/discover_feed_provider.mm

@@ -24,3 +24,4 @@ void DiscoverFeedProvider::RefreshFeedWithCompletion(
 
 void DiscoverFeedProvider::AddObserver(Observer* observer) {}
 void DiscoverFeedProvider::RemoveObserver(Observer* observer) {}
+void DiscoverFeedProvider::LoadMoreFeedArticles() {}