ContentSuggestions collection adds items with animation

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

Index: ios/chrome/browser/ui/content_suggestions/content_suggestions_collection_updater.mm
diff --git a/ios/chrome/browser/ui/content_suggestions/content_suggestions_collection_updater.mm b/ios/chrome/browser/ui/content_suggestions/content_suggestions_collection_updater.mm
index 9bce87675c3a920f5ac961ccab2f41921f845a03..83866cc2b435f2d28cee5b235171caf7f5b8dad3 100644
--- a/ios/chrome/browser/ui/content_suggestions/content_suggestions_collection_updater.mm
+++ b/ios/chrome/browser/ui/content_suggestions/content_suggestions_collection_updater.mm
@@ -87,13 +87,6 @@ SectionIdentifier SectionIdentifierForInfo(
     NSMutableDictionary<NSNumber*, ContentSuggestionsSectionInformation*>*
         sectionInfoBySectionIdentifier;
 
-// Adds a new section if needed and returns the section identifier.
-- (NSInteger)addSectionIfNeeded:
-    (ContentSuggestionsSectionInformation*)sectionInformation;
-// Resets the models, removing the current CollectionViewItem and the
-// SectionInfo.
-- (void)resetModels;
-
 @end
 
 @implementation ContentSuggestionsCollectionUpdater
@@ -135,7 +128,8 @@ SectionIdentifier SectionIdentifierForInfo(
     return;
   }
 
-  [self addSuggestions:[self.dataSource suggestionsForSection:sectionInfo]];
+  [self.collectionViewController
+      addSuggestions:[self.dataSource suggestionsForSection:sectionInfo]];
 }
 
 - (void)clearSuggestion:(ContentSuggestionIdentifier*)suggestionIdentifier {
@@ -170,7 +164,8 @@ SectionIdentifier SectionIdentifierForInfo(
 
 - (void)reloadAllData {
   [self resetModels];
-  [self addSuggestions:[self.dataSource allSuggestions]];
+  [self.collectionViewController
+      addSuggestions:[self.dataSource allSuggestions]];
 }
 
 - (void)clearSection:(ContentSuggestionsSectionInformation*)sectionInfo {
@@ -196,50 +191,20 @@ SectionIdentifier SectionIdentifierForInfo(
   return ContentSuggestionTypeForItemType(item.type);
 }
 
-#pragma mark - ContentSuggestionsArticleItemDelegate
-
-- (void)loadImageForArticleItem:(ContentSuggestionsArticleItem*)articleItem {
-  NSInteger sectionIdentifier =
-      SectionIdentifierForInfo(articleItem.suggestionIdentifier.sectionInfo);
-
-  __weak ContentSuggestionsCollectionUpdater* weakSelf = self;
-  __weak ContentSuggestionsArticleItem* weakArticle = articleItem;
-  void (^imageFetchedCallback)(const gfx::Image&) = ^(const gfx::Image& image) {
-    if (image.IsEmpty()) {
-      return;
-    }
-
-    ContentSuggestionsCollectionUpdater* strongSelf = weakSelf;
-    ContentSuggestionsArticleItem* strongArticle = weakArticle;
-    if (!strongSelf || !strongArticle) {
-      return;
-    }
-
-    strongArticle.image = image.CopyUIImage();
-    [strongSelf.collectionViewController
-        reconfigureCellsForItems:@[ strongArticle ]
-         inSectionWithIdentifier:sectionIdentifier];
-  };
-
-  [self.dataSource.imageFetcher
-      fetchImageForSuggestion:articleItem.suggestionIdentifier
-                     callback:imageFetchedCallback];
-}
-
-#pragma mark - Private methods
-
-// Add the |suggestions| to the model and reload the data.
-- (void)addSuggestions:(NSArray<ContentSuggestion*>*)suggestions {
+- (NSArray<NSIndexPath*>*)addSuggestionsToModel:
+    (NSArray<ContentSuggestion*>*)suggestions {
   if (suggestions.count == 0) {
-    return;
+    return [NSArray array];
   }
 
   CollectionViewModel* model =
       self.collectionViewController.collectionViewModel;
 
+  NSMutableArray<NSIndexPath*>* indexPaths = [NSMutableArray array];
   for (ContentSuggestion* suggestion in suggestions) {
     NSInteger sectionIdentifier =
-        [self addSectionIfNeeded:suggestion.suggestionIdentifier.sectionInfo];
+        SectionIdentifierForInfo(suggestion.suggestionIdentifier.sectionInfo);
+
     ContentSuggestionsArticleItem* articleItem =
         [[ContentSuggestionsArticleItem alloc]
             initWithType:ItemTypeForContentSuggestionType(suggestion.type)
@@ -253,30 +218,71 @@ SectionIdentifier SectionIdentifierForInfo(
 
     articleItem.suggestionIdentifier = suggestion.suggestionIdentifier;
 
+    NSInteger section = [model sectionForSectionIdentifier:sectionIdentifier];
+    NSInteger itemNumber = [model numberOfItemsInSection:section];
     [model addItem:articleItem toSectionWithIdentifier:sectionIdentifier];
-  }
 
-  if ([self.collectionViewController isViewLoaded]) {
-    [self.collectionViewController.collectionView reloadData];
+    [indexPaths
+        addObject:[NSIndexPath indexPathForItem:itemNumber inSection:section]];
   }
+
+  return indexPaths;
 }
 
-- (NSInteger)addSectionIfNeeded:
-    (ContentSuggestionsSectionInformation*)sectionInformation {
-  NSInteger sectionIdentifier = SectionIdentifierForInfo(sectionInformation);
+- (NSIndexSet*)addSectionsForSuggestionsToModel:
+    (NSArray<ContentSuggestion*>*)suggestions {
+  NSMutableIndexSet* indexSet = [NSMutableIndexSet indexSet];
 
   CollectionViewModel* model =
       self.collectionViewController.collectionViewModel;
-  if (![model hasSectionForSectionIdentifier:sectionIdentifier]) {
-    [model addSectionWithIdentifier:sectionIdentifier];
-    self.sectionInfoBySectionIdentifier[@(sectionIdentifier)] =
-        sectionInformation;
-    [self.sectionInfoBySectionIdentifier setObject:sectionInformation
-                                            forKey:@(sectionIdentifier)];
+  for (ContentSuggestion* suggestion in suggestions) {
+    ContentSuggestionsSectionInformation* sectionInfo =
+        suggestion.suggestionIdentifier.sectionInfo;
+    NSInteger sectionIdentifier = SectionIdentifierForInfo(sectionInfo);
+
+    if (![model hasSectionForSectionIdentifier:sectionIdentifier]) {
+      [model addSectionWithIdentifier:sectionIdentifier];
+      self.sectionInfoBySectionIdentifier[@(sectionIdentifier)] = sectionInfo;
+      [indexSet addIndex:[model sectionForSectionIdentifier:sectionIdentifier]];
+    }
   }
-  return sectionIdentifier;
+  return indexSet;
 }
 
+#pragma mark - ContentSuggestionsArticleItemDelegate
+
+- (void)loadImageForArticleItem:(ContentSuggestionsArticleItem*)articleItem {
+  NSInteger sectionIdentifier =
+      SectionIdentifierForInfo(articleItem.suggestionIdentifier.sectionInfo);
+
+  __weak ContentSuggestionsCollectionUpdater* weakSelf = self;
+  __weak ContentSuggestionsArticleItem* weakArticle = articleItem;
+  void (^imageFetchedCallback)(const gfx::Image&) = ^(const gfx::Image& image) {
+    if (image.IsEmpty()) {
+      return;
+    }
+
+    ContentSuggestionsCollectionUpdater* strongSelf = weakSelf;
+    ContentSuggestionsArticleItem* strongArticle = weakArticle;
+    if (!strongSelf || !strongArticle) {
+      return;
+    }
+
+    strongArticle.image = image.CopyUIImage();
+    [strongSelf.collectionViewController
+        reconfigureCellsForItems:@[ strongArticle ]
+         inSectionWithIdentifier:sectionIdentifier];
+  };
+
+  [self.dataSource.imageFetcher
+      fetchImageForSuggestion:articleItem.suggestionIdentifier
+                     callback:imageFetchedCallback];
+}
+
+#pragma mark - Private methods
+
+// Resets the models, removing the current CollectionViewItem and the
+// SectionInfo.
 - (void)resetModels {
   [self.collectionViewController loadModel];
   self.sectionInfoBySectionIdentifier = [[NSMutableDictionary alloc] init];