[ios] Saves Feed scrolling offset for refactored NTP.

- Sets the NTPViewController to the ntp_home_mediator so it can
save/load the Feed scrolling offset for the refactored feed.
- Adds setContentOffset to ntp_view_controller to set the offset to the
saved value.

Bug: 1114792
Change-Id: Ib4256a3cb4d65a8e7e6e6f00ec017a13a1447250
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2628316
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Adam Trudeau-Arcaro <adamta@google.com>
Cr-Commit-Position: refs/heads/master@{#843392}

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

@@ -26,8 +26,8 @@ class WebState;
 
 @property(nonatomic, weak) id<NewTabPageControllerDelegate> toolbarDelegate;
 
-// Whether the Suggestions UI is displayed. If this is true, start is a no-op.
-@property(nonatomic, readonly) BOOL visible;
+// YES if the coordinator has started. If YES, start is a no-op.
+@property(nonatomic, readonly) BOOL started;
 
 @property(nonatomic, strong, readonly)
     ContentSuggestionsHeaderViewController* headerController;

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

@@ -137,12 +137,12 @@
 - (void)start {
   DCHECK(self.browser);
   DCHECK(self.ntpMediator);
-  if (self.visible) {
+  if (self.started) {
     // Prevent this coordinator from being started twice in a row
     return;
   }
 
-  _visible = YES;
+  _started = YES;
 
   // Make sure that the omnibox is unfocused to prevent having it visually
   // focused while the NTP is just created (with the fakebox visible).
@@ -349,7 +349,7 @@
         ->RemoveFeedViewController(self.discoverFeedViewController);
   }
   self.contentSuggestionsExpanded = nil;
-  _visible = NO;
+  _started = NO;
 }
 
 - (UIViewController*)viewController {

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

@@ -33,6 +33,7 @@ class Browser;
 @class ContentSuggestionsMetricsRecorder;
 @class ContentSuggestionsViewController;
 @protocol LogoVendor;
+@class NewTabPageViewController;
 @protocol NTPHomeConsumer;
 @class NTPHomeMetrics;
 @class DiscoverFeedMetricsRecorder;
@@ -74,9 +75,6 @@ class VoiceSearchAvailability;
 @property(nonatomic, strong) NTPHomeMetrics* NTPMetrics;
 // Recorder for the metrics related to the Discover feed.
 @property(nonatomic, strong) DiscoverFeedMetricsRecorder* discoverFeedMetrics;
-// View Controller displaying the suggestions.
-@property(nonatomic, weak)
-    ContentSuggestionsViewController* suggestionsViewController;
 // Primary collection view controller that receives scroll events.
 // In the refactored NTP, the Discover feed collection view behaves as the
 // primary NTP scroll view. Otherwise, the content suggestions collection view
@@ -85,6 +83,21 @@ class VoiceSearchAvailability;
 // refactored NTP.
 @property(nonatomic, weak) id<ContentSuggestionsCollectionControlling>
     primaryViewController;
+// View Controller for the NTP if using the non refactored NTP or the Feed is
+// not visible.
+// TODO(crbug.com/1114792): Create a protocol to avoid duplication and update
+// comment.
+@property(nonatomic, weak)
+    ContentSuggestionsViewController* suggestionsViewController;
+// View Controller forthe NTP if using the refactored NTP and the Feed is
+// visible.
+// TODO(crbug.com/1114792): Create a protocol to avoid duplication and update
+// comment.
+@property(nonatomic, weak) NewTabPageViewController* ntpViewController;
+// TODO(crbug.com/1114792): Update this comment to remove "refactored" when the
+// NTP refactors launches.
+@property(nonatomic, assign, getter=isRefactoredFeedVisible)
+    BOOL refactoredFeedVisible;
 @property(nonatomic, weak)
     ContentSuggestionsHeaderSynchronizer* headerCollectionInteractionHandler;
 // Mediator for the ContentSuggestions.

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

@@ -42,8 +42,10 @@
 #import "ios/chrome/browser/ui/content_suggestions/ntp_home_consumer.h"
 #import "ios/chrome/browser/ui/content_suggestions/ntp_home_metrics.h"
 #import "ios/chrome/browser/ui/content_suggestions/user_account_image_update_delegate.h"
+#import "ios/chrome/browser/ui/ntp/discover_feed_wrapper_view_controller.h"
 #include "ios/chrome/browser/ui/ntp/metrics.h"
 #import "ios/chrome/browser/ui/ntp/new_tab_page_header_constants.h"
+#import "ios/chrome/browser/ui/ntp/new_tab_page_view_controller.h"
 #import "ios/chrome/browser/ui/ntp/notification_promo_whats_new.h"
 #import "ios/chrome/browser/ui/util/uikit_ui_util.h"
 #import "ios/chrome/browser/url_loading/url_loading_browser_agent.h"
@@ -642,10 +644,17 @@ const char kNTPHelpURL[] =
   web::NavigationManager* manager = webState->GetNavigationManager();
   web::NavigationItem* item = manager->GetLastCommittedItem();
   web::PageDisplayState displayState;
-  UIEdgeInsets contentInset =
-      self.suggestionsViewController.collectionView.contentInset;
-  CGPoint contentOffset =
-      self.suggestionsViewController.collectionView.contentOffset;
+
+  // TODO(crbug.com/1114792): Create a protocol to stop having references to
+  // both of these ViewControllers directly.
+  UICollectionView* collectionView =
+      self.refactoredFeedVisible
+          ? self.ntpViewController.discoverFeedWrapperViewController
+                .feedCollectionView
+          : self.suggestionsViewController.collectionView;
+  UIEdgeInsets contentInset = collectionView.contentInset;
+  CGPoint contentOffset = collectionView.contentOffset;
+
   contentOffset.y -=
       self.headerCollectionInteractionHandler.collectionShiftingOffset;
   displayState.scroll_state() =
@@ -662,8 +671,15 @@ const char kNTPHelpURL[] =
   web::NavigationItem* item = navigationManager->GetVisibleItem();
   CGFloat offset =
       item ? item->GetPageDisplayState().scroll_state().content_offset().y : 0;
-  if (offset > 0)
-    [self.suggestionsViewController setContentOffset:offset];
+  if (offset > 0) {
+    // TODO(crbug.com/1114792): Create a protocol to stop having references to
+    // both of these ViewControllers directly.
+    if ([self isRefactoredFeedVisible]) {
+      [self.ntpViewController setContentOffset:offset];
+    } else {
+      [self.suggestionsViewController setContentOffset:offset];
+    }
+  }
 }
 
 // Fetches and update user's avatar on NTP, or use default avatar if user is

ios/chrome/browser/ui/ntp/discover_feed_wrapper_view_controller.mm

@@ -20,6 +20,16 @@
     // TODO(crbug.com/1114792): Handle case where feed is disabled, replacing it
     // with a regular scroll view.
     _discoverFeed = discoverFeed;
+
+    // Iterates through subviews to find collection view containing feed
+    // articles.
+    // TODO(crbug.com/1085419): Once the CollectionView is cleanly exposed,
+    // remove this loop.
+    for (UIView* view in _discoverFeed.view.subviews) {
+      if ([view isKindOfClass:[UICollectionView class]]) {
+        _feedCollectionView = static_cast<UICollectionView*>(view);
+      }
+    }
   }
   return self;
 }
@@ -28,16 +38,6 @@
   [super viewDidLoad];
 
   UIView* discoverView = self.discoverFeed.view;
-
-  // Iterates through subviews to find collection view containing feed articles.
-  // TODO(crbug.com/1085419): Once the CollectionView is cleanly exposed, remove
-  // this loop.
-  for (UIView* view in discoverView.subviews) {
-    if ([view isKindOfClass:[UICollectionView class]]) {
-      _feedCollectionView = static_cast<UICollectionView*>(view);
-    }
-  }
-
   [self.discoverFeed willMoveToParentViewController:self];
   [self addChildViewController:self.discoverFeed];
   [self.view addSubview:discoverView];

ios/chrome/browser/ui/ntp/new_tab_page_coordinator.mm

@@ -168,10 +168,12 @@
 
   [self.contentSuggestionsCoordinator start];
 
+  self.ntpMediator.refactoredFeedVisible = [self isNTPRefactoredAndFeedVisible];
   if ([self isNTPRefactoredAndFeedVisible]) {
     self.ntpViewController = [[NewTabPageViewController alloc]
         initWithContentSuggestionsViewController:
             self.contentSuggestionsCoordinator.viewController];
+    self.ntpMediator.ntpViewController = self.ntpViewController;
 
     UIViewController* discoverFeedViewController =
         ios::GetChromeBrowserProvider()
@@ -297,7 +299,8 @@
 }
 
 - (void)willUpdateSnapshot {
-  if ([self isNTPRefactoredAndFeedVisible]) {
+  if (self.contentSuggestionsCoordinator.started &&
+      [self isNTPRefactoredAndFeedVisible]) {
     [self.ntpViewController willUpdateSnapshot];
   } else {
     [self.contentSuggestionsCoordinator willUpdateSnapshot];
@@ -436,6 +439,9 @@
 
 // YES if we're using the refactored NTP and the Discover Feed is visible.
 - (BOOL)isNTPRefactoredAndFeedVisible {
+  // Make sure we call this only if self.contentSuggestionsCoordinator has been
+  // started.
+  DCHECK(self.contentSuggestionsCoordinator.started);
   return IsRefactoredNTP() &&
          [self.contentSuggestionsCoordinator isDiscoverFeedVisible];
 }

ios/chrome/browser/ui/ntp/new_tab_page_view_controller.h

@@ -50,6 +50,10 @@
 // Called when a snapshot of the content will be taken.
 - (void)willUpdateSnapshot;
 
+// Sets the collection contentOffset to |offset|, or caches the value and
+// applies it after the first layout.
+- (void)setContentOffset:(CGFloat)offset;
+
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_NTP_NEW_TAB_PAGE_VIEW_CONTROLLER_H_

ios/chrome/browser/ui/ntp/new_tab_page_view_controller.mm

@@ -13,6 +13,7 @@
 #import "ios/chrome/browser/ui/ntp/discover_feed_wrapper_view_controller.h"
 #import "ios/chrome/browser/ui/ntp/new_tab_page_content_delegate.h"
 #import "ios/chrome/browser/ui/overscroll_actions/overscroll_actions_controller.h"
+#import "ios/chrome/browser/ui/toolbar/public/toolbar_utils.h"
 #import "ios/chrome/browser/ui/util/named_guide.h"
 #import "ios/chrome/browser/ui/util/uikit_ui_util.h"
 #import "ios/chrome/common/ui/util/constraints_ui_util.h"
@@ -50,6 +51,9 @@ const CGFloat kOffsetToPinOmnibox = 100;
 // view.
 @property(nonatomic, weak) ContentSuggestionsLayout* contentSuggestionsLayout;
 
+// Initial scrolling offset, used to restore the previous scrolling position.
+@property(nonatomic, assign) CGFloat initialContentOffset;
+
 @end
 
 @implementation NewTabPageViewController
@@ -66,6 +70,7 @@ const CGFloat kOffsetToPinOmnibox = 100;
     // TODO(crbug.com/1114792): Instantiate this depending on the initial scroll
     // position.
     _scrolledIntoFeed = NO;
+    _initialContentOffset = NAN;
   }
 
   return self;
@@ -142,6 +147,8 @@ const CGFloat kOffsetToPinOmnibox = 100;
   self.discoverFeedWrapperViewController.feedCollectionView.contentInset =
       UIEdgeInsetsMake(collectionView.contentSize.height, 0, 0, 0);
   self.headerSynchronizer.additionalOffset = collectionView.contentSize.height;
+
+  [self applyContentOffset];
 }
 
 - (void)viewWillAppear:(BOOL)animated {
@@ -202,10 +209,20 @@ const CGFloat kOffsetToPinOmnibox = 100;
   [self updateOverscrollActionsState];
 }
 
+#pragma mark - Public
+
 - (void)willUpdateSnapshot {
   [self.overscrollActionsController clear];
 }
 
+- (void)setContentOffset:(CGFloat)offset {
+  self.initialContentOffset = offset;
+  if (self.isViewLoaded && self.collectionView.window &&
+      self.collectionView.contentSize.height != 0) {
+    [self applyContentOffset];
+  }
+}
+
 #pragma mark - UIScrollViewDelegate
 
 - (void)scrollViewDidScroll:(UIScrollView*)scrollView {
@@ -326,6 +343,28 @@ const CGFloat kOffsetToPinOmnibox = 100;
   [self.ntpContentDelegate reloadContentSuggestions];
 }
 
+// Sets the collectionView's contentOffset if |_initialContentOffset| is set.
+- (void)applyContentOffset {
+  if (!isnan(self.initialContentOffset)) {
+    UICollectionView* collection =
+        self.discoverFeedWrapperViewController.feedCollectionView;
+    // Don't set the offset such as the content of the collection is smaller
+    // than the part of the collection which should be displayed with that
+    // offset, taking into account the size of the toolbar.
+    CGFloat offset = MAX(
+        0, MIN(self.initialContentOffset,
+               collection.contentSize.height - collection.bounds.size.height -
+                   ToolbarExpandedHeight(
+                       self.traitCollection.preferredContentSizeCategory) +
+                   collection.contentInset.bottom));
+    if (collection.contentOffset.y != offset) {
+      collection.contentOffset = CGPointMake(0, offset);
+      // TODO(crbug.com/1114792): Add the FakeOmnibox if necessary.
+    }
+  }
+  self.initialContentOffset = NAN;
+}
+
 #pragma mark - Setters
 
 // Sets whether or not the NTP is scrolled into the feed and notifies the