From 68e58bf60e41dc56ec2e92881a82bc838b322a82 Mon Sep 17 00:00:00 2001
From: Andy Wang <ownzandy@fb.com>
Date: Mon, 9 Mar 2020 17:46:34 -0700
Subject: [PATCH] Add fullyVisibleCellsForSectionController to
 IGListCollectionContext [IGListKit]

Reviewed By: chritto

Differential Revision: D20261859

fbshipit-source-id: 919132f935462c2a57270f0afaba511adc936995
---
 Source/IGListKit/IGListAdapter.m           | 16 ++++++++++++++++
 Source/IGListKit/IGListCollectionContext.h |  9 +++++++++
 2 files changed, 25 insertions(+)

diff --git a/Source/IGListKit/IGListAdapter.m b/Source/IGListKit/IGListAdapter.m
index 033aaa87..4c2741df 100644
--- a/Source/IGListKit/IGListAdapter.m
+++ b/Source/IGListKit/IGListAdapter.m
@@ -927,6 +927,22 @@
     return nil;
 }
 
+- (NSArray<UICollectionViewCell *> *)fullyVisibleCellsForSectionController:(IGListSectionController *)sectionController {
+    NSMutableArray *cells = [NSMutableArray new];
+    UICollectionView *collectionView = self.collectionView;
+    NSArray *visibleCells = [collectionView visibleCells];
+    const NSInteger section = [self sectionForSectionController:sectionController];
+    for (UICollectionViewCell *cell in visibleCells) {
+        if ([collectionView indexPathForCell:cell].section == section) {
+            const CGRect cellRect = [cell convertRect:cell.bounds toView:collectionView];
+            if (CGRectContainsRect(UIEdgeInsetsInsetRect(collectionView.bounds, collectionView.contentInset), cellRect)) {
+                [cells addObject:cell];
+            }
+        }
+    }
+    return cells;
+}
+
 - (NSArray<UICollectionViewCell *> *)visibleCellsForSectionController:(IGListSectionController *)sectionController {
     NSMutableArray *cells = [NSMutableArray new];
     UICollectionView *collectionView = self.collectionView;
diff --git a/Source/IGListKit/IGListCollectionContext.h b/Source/IGListKit/IGListCollectionContext.h
index 29bd3f32..be16b3ea 100644
--- a/Source/IGListKit/IGListCollectionContext.h
+++ b/Source/IGListKit/IGListCollectionContext.h
@@ -85,6 +85,15 @@ NS_SWIFT_NAME(ListCollectionContext)
 - (nullable __kindof UICollectionViewCell *)cellForItemAtIndex:(NSInteger)index
                                              sectionController:(IGListSectionController *)sectionController;
 
+/**
+ Returns the fully visible cells for the given section controller.
+
+ @param sectionController The section controller requesting this information.
+
+ @return An array of fully visible cells, or an empty array if none are found.
+ */
+- (NSArray<UICollectionViewCell *> *)fullyVisibleCellsForSectionController:(IGListSectionController *)sectionController;
+
 /**
  Returns the visible cells for the given section controller.