[ASDataController] Simplify data controller (#2923)

* Start removing ASChangeSetDataController

* Continue removing ASChangeSetDataController

* Remove unnecessary change

* ASDataController is no longer an abstract class, remove its assertion

* Get back beginUpdates and endUpdatesAnimated:completion in ASCollectionNode

AsyncDisplayKit/ASCollectionView.mm

@@ -26,6 +26,7 @@
 #import "ASCollectionViewLayoutFacilitatorProtocol.h"
 #import "ASSectionContext.h"
 #import "ASCollectionView+Undeprecated.h"
+#import "_ASHierarchyChangeSet.h"
 
 /**
  * A macro to get self.collectionNode and assign it to a local variable, or return
@@ -196,7 +197,17 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
    * (0 sections) we always check at least once after each update (initial reload is the first update.)
    */
   BOOL _hasEverCheckedForBatchFetchingDueToUpdate;
-    
+
+  /**
+   * The change set that we're currently building, if any.
+   */
+  _ASHierarchyChangeSet *_changeSet;
+  
+  /**
+   * Counter used to keep track of nested batch updates.
+   */
+  NSInteger _batchUpdateCount;
+  
   struct {
     unsigned int scrollViewDidScroll:1;
     unsigned int scrollViewWillBeginDragging:1;
@@ -352,6 +363,8 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
 - (void)dealloc
 {
   ASDisplayNodeAssertMainThread();
+  ASDisplayNodeCAssert(_batchUpdateCount == 0, @"ASCollectionView deallocated in the middle of a batch update.");
+  
   // Sometimes the UIKit classes can call back to their delegate even during deallocation, due to animation completion blocks etc.
   _isDeallocating = YES;
   [self setAsyncDelegate:nil];
@@ -402,6 +415,12 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
 - (void)waitUntilAllUpdatesAreCommitted
 {
   ASDisplayNodeAssertMainThread();
+  if (_batchUpdateCount > 0) {
+    // This assertion will be enabled soon.
+    //    ASDisplayNodeFailAssert(@"Should not call %@ during batch update", NSStringFromSelector(_cmd));
+    return;
+  }
+  
   [_dataController waitUntilAllUpdatesAreCommitted];
 }
 
@@ -761,15 +780,43 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
   return _dataController;
 }
 
+- (void)beginUpdates
+{
+  ASDisplayNodeAssertMainThread();
+  // _changeSet must be available during batch update
+  ASDisplayNodeAssertTrue((_batchUpdateCount > 0) == (_changeSet != nil));
+  
+  if (_batchUpdateCount == 0) {
+    _changeSet = [[_ASHierarchyChangeSet alloc] initWithOldData:[_dataController itemCountsFromDataSource]];
+  }
+  _batchUpdateCount++;  
+}
+
+- (void)endUpdatesAnimated:(BOOL)animated completion:(nullable void (^)(BOOL))completion
+{
+  ASDisplayNodeAssertMainThread();
+  ASDisplayNodeAssertNotNil(_changeSet, @"_changeSet must be available when batch update ends");
+
+  _batchUpdateCount--;
+  // Prevent calling endUpdatesAnimated:completion: in an unbalanced way
+  NSAssert(_batchUpdateCount >= 0, @"endUpdatesAnimated:completion: called without having a balanced beginUpdates call");
+  
+  [_changeSet addCompletionHandler:completion];
+  
+  if (_batchUpdateCount == 0) {
+    [_dataController updateWithChangeSet:_changeSet animated:animated];
+    _changeSet = nil;
+  }
+}
+
 - (void)performBatchAnimated:(BOOL)animated updates:(void (^)())updates completion:(void (^)(BOOL))completion
 {
   ASDisplayNodeAssertMainThread();
-  
-  [_dataController beginUpdates];
+  [self beginUpdates];
   if (updates) {
     updates();
   }
-  [_dataController endUpdatesAnimated:animated completion:completion];
+  [self endUpdatesAnimated:animated completion:completion];
 }
 
 - (void)performBatchUpdates:(void (^)())updates completion:(void (^)(BOOL))completion
@@ -789,27 +836,35 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
 {
   ASDisplayNodeAssertMainThread();
   if (sections.count == 0) { return; }
-  [_dataController insertSections:sections withAnimationOptions:kASCollectionViewAnimationNone];
+  [self performBatchUpdates:^{
+    [_changeSet insertSections:sections animationOptions:kASCollectionViewAnimationNone];
+  } completion:nil];
 }
 
 - (void)deleteSections:(NSIndexSet *)sections
 {
   ASDisplayNodeAssertMainThread();
   if (sections.count == 0) { return; }
-  [_dataController deleteSections:sections withAnimationOptions:kASCollectionViewAnimationNone];
+  [self performBatchUpdates:^{
+    [_changeSet deleteSections:sections animationOptions:kASCollectionViewAnimationNone];
+  } completion:nil];
 }
 
 - (void)reloadSections:(NSIndexSet *)sections
 {
   ASDisplayNodeAssertMainThread();
   if (sections.count == 0) { return; }
-  [_dataController reloadSections:sections withAnimationOptions:kASCollectionViewAnimationNone];
+  [self performBatchUpdates:^{
+    [_changeSet reloadSections:sections animationOptions:kASCollectionViewAnimationNone];
+  } completion:nil];
 }
 
 - (void)moveSection:(NSInteger)section toSection:(NSInteger)newSection
 {
   ASDisplayNodeAssertMainThread();
-  [_dataController moveSection:section toSection:newSection withAnimationOptions:kASCollectionViewAnimationNone];
+  [self performBatchUpdates:^{
+    [_changeSet moveSection:section toSection:newSection animationOptions:kASCollectionViewAnimationNone];
+  } completion:nil];
 }
 
 - (id<ASSectionContext>)contextForSection:(NSInteger)section
@@ -822,27 +877,35 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
 {
   ASDisplayNodeAssertMainThread();
   if (indexPaths.count == 0) { return; }
-  [_dataController insertRowsAtIndexPaths:indexPaths withAnimationOptions:kASCollectionViewAnimationNone];
+  [self performBatchUpdates:^{
+    [_changeSet insertItems:indexPaths animationOptions:kASCollectionViewAnimationNone];
+  } completion:nil];
 }
 
 - (void)deleteItemsAtIndexPaths:(NSArray *)indexPaths
 {
   ASDisplayNodeAssertMainThread();
   if (indexPaths.count == 0) { return; }
-  [_dataController deleteRowsAtIndexPaths:indexPaths withAnimationOptions:kASCollectionViewAnimationNone];
+  [self performBatchUpdates:^{
+    [_changeSet deleteItems:indexPaths animationOptions:kASCollectionViewAnimationNone];
+  } completion:nil];
 }
 
 - (void)reloadItemsAtIndexPaths:(NSArray *)indexPaths
 {
   ASDisplayNodeAssertMainThread();
   if (indexPaths.count == 0) { return; }
-  [_dataController reloadRowsAtIndexPaths:indexPaths withAnimationOptions:kASCollectionViewAnimationNone];
+  [self performBatchUpdates:^{
+    [_changeSet reloadItems:indexPaths animationOptions:kASCollectionViewAnimationNone];
+  } completion:nil];
 }
 
 - (void)moveItemAtIndexPath:(NSIndexPath *)indexPath toIndexPath:(NSIndexPath *)newIndexPath
 {
   ASDisplayNodeAssertMainThread();
-  [_dataController moveRowAtIndexPath:indexPath toIndexPath:newIndexPath withAnimationOptions:kASCollectionViewAnimationNone];
+  [self performBatchUpdates:^{
+    [_changeSet moveItemAtIndexPath:indexPath toIndexPath:newIndexPath animationOptions:kASCollectionViewAnimationNone];
+  } completion:nil];
 }
 
 #pragma mark -