[ios] Separately handle sync vs async drops in tab grid

Handles synchronous localObject drops differently from
asynchronous drops from another app.

Bug: 1128531, 1128656
Change-Id: I45b124f1f8bb887a465a753e40a9fa5cc74c5e78
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2438011
Commit-Queue: Mark Cogan <marq@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811653}

ios/chrome/browser/ui/tab_grid/grid/grid_cell.h

@@ -32,7 +32,7 @@
 @property(nonatomic, weak) UIImage* snapshot;
 @property(nonatomic, copy) NSString* title;
 @property(nonatomic, assign) BOOL titleHidden;
-@property(nonatomic, readonly) UIBezierPath* visiblePath;
+@property(nonatomic, readonly) UIDragPreviewParameters* dragPreviewParameters;
 @end
 
 // A GridCell for use in animated transitions that only shows selection state

ios/chrome/browser/ui/tab_grid/grid/grid_cell.mm

@@ -255,10 +255,13 @@ void PositionView(UIView* view, CGPoint point) {
   _titleHidden = titleHidden;
 }
 
-- (UIBezierPath*)visiblePath {
-  return [UIBezierPath
+- (UIDragPreviewParameters*)dragPreviewParameters {
+  UIBezierPath* visiblePath = [UIBezierPath
       bezierPathWithRoundedRect:self.bounds
                    cornerRadius:self.contentView.layer.cornerRadius];
+  UIDragPreviewParameters* params = [[UIDragPreviewParameters alloc] init];
+  params.visiblePath = visiblePath;
+  return params;
 }
 
 #pragma mark - Private

ios/chrome/browser/ui/tab_grid/grid/grid_drag_drop_handler.h

@@ -25,10 +25,21 @@
 
 // Tells the receiver to incorporate the |dragItem| into the model layer at the
 // |destinationIndex|. |fromSameCollection| is an indication that the operation
-// is a reorder within the same collection.
+// is a reorder within the same collection. |dragItem| must have a localObject,
+// which means the item is dragged from within the same app.
 - (void)dropItem:(UIDragItem*)dragItem
                toIndex:(NSUInteger)destinationIndex
     fromSameCollection:(BOOL)fromSameCollection;
+
+// Tells the receiver to asynchronously extract data from |itemProvider| into
+// the model layer at the |destinationIndex|. |placeholderContext| is used to
+// delete the placeholder once the item is ready to be inserted into the model
+// layer.
+- (void)dropItemFromProvider:(NSItemProvider*)itemProvider
+                     toIndex:(NSUInteger)destinationIndex
+          placeholderContext:
+              (id<UICollectionViewDropPlaceholderContext>)placeholderContext;
+
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_TAB_GRID_GRID_GRID_DRAG_DROP_HANDLER_H_

ios/chrome/browser/ui/tab_grid/grid/grid_view_controller.mm

@@ -438,11 +438,9 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
 
 - (UIDragPreviewParameters*)collectionView:(UICollectionView*)collectionView
     dragPreviewParametersForItemAtIndexPath:(NSIndexPath*)indexPath {
-  UIDragPreviewParameters* params = [[UIDragPreviewParameters alloc] init];
-  GridCell* cell = base::mac::ObjCCastStrict<GridCell>(
+  GridCell* gridCell = base::mac::ObjCCastStrict<GridCell>(
       [self.collectionView cellForItemAtIndexPath:indexPath]);
-  params.visiblePath = cell.visiblePath;
-  return params;
+  return gridCell.dragPreviewParameters;
 }
 
 #pragma mark - UICollectionViewDropDelegate
@@ -471,21 +469,52 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
         (id<UICollectionViewDropCoordinator>)coordinator {
   id<UICollectionViewDropItem> item = coordinator.items.firstObject;
 
-  NSIndexPath* dropIndexPath = coordinator.destinationIndexPath;
-  if (!dropIndexPath) {
-    dropIndexPath = [NSIndexPath indexPathForItem:(self.items.count - 1)
-                                        inSection:0];
+  // Append to the end of the collection, unless drop index is specified.
+  NSUInteger destinationIndex = self.items.count;
+  if (item.sourceIndexPath) {
+    // The sourceIndexPath is non-nil if the drop item is from this same
+    // collection view. Move to last position rather than appending if this is a
+    // reorder operation.
+    destinationIndex = self.items.count - 1;
+  }
+  if (coordinator.destinationIndexPath) {
+    destinationIndex =
+        base::checked_cast<NSUInteger>(coordinator.destinationIndexPath.item);
   }
+  NSIndexPath* dropIndexPath = [NSIndexPath indexPathForItem:destinationIndex
+                                                   inSection:0];
 
-  NSUInteger destinationIndex =
-      base::checked_cast<NSUInteger>(dropIndexPath.item);
+  // Drop synchronously if local object is available.
+  if (item.dragItem.localObject) {
     [coordinator dropItem:item.dragItem toItemAtIndexPath:dropIndexPath];
-
-  // TODO(crbug.com/1095200): Handle the edge case that two windows are
-  // simultaneously dragging and dropping.
+    // The sourceIndexPath is non-nil if the drop item is from this same
+    // collection view.
     [self.dragDropHandler dropItem:item.dragItem
                            toIndex:destinationIndex
-              fromSameCollection:collectionView.hasActiveDrag];
+                fromSameCollection:(item.sourceIndexPath != nil)];
+    return;
+  }
+
+  // Drop asynchronously if local object is not available.
+  UICollectionViewDropPlaceholder* placeholder =
+      [[UICollectionViewDropPlaceholder alloc]
+          initWithInsertionIndexPath:dropIndexPath
+                     reuseIdentifier:kCellIdentifier];
+  placeholder.cellUpdateHandler = ^(UICollectionViewCell* placeholderCell) {
+    GridCell* gridCell = base::mac::ObjCCastStrict<GridCell>(placeholderCell);
+    gridCell.theme = self.theme;
+  };
+  placeholder.previewParametersProvider =
+      ^UIDragPreviewParameters*(UICollectionViewCell* placeholderCell) {
+    GridCell* gridCell = base::mac::ObjCCastStrict<GridCell>(placeholderCell);
+    return gridCell.dragPreviewParameters;
+  };
+
+  id<UICollectionViewDropPlaceholderContext> context =
+      [coordinator dropItem:item.dragItem toPlaceholder:placeholder];
+  [self.dragDropHandler dropItemFromProvider:item.dragItem.itemProvider
+                                     toIndex:destinationIndex
+                          placeholderContext:context];
 }
 
 #pragma mark - UIScrollViewDelegate

ios/chrome/browser/ui/tab_grid/tab_grid_mediator.mm

@@ -465,11 +465,17 @@ web::WebState* GetWebStateWithId(WebStateList* web_state_list,
                        withURL:net::GURLWithNSURL(droppedURL)];
     return;
   }
+}
+
+- (void)dropItemFromProvider:(NSItemProvider*)itemProvider
+                     toIndex:(NSUInteger)destinationIndex
+          placeholderContext:
+              (id<UICollectionViewDropPlaceholderContext>)placeholderContext {
+  if (![itemProvider canLoadObjectOfClass:[NSURL class]]) {
+    [placeholderContext deletePlaceholder];
+    return;
+  }
 
-  // Handle URLs from other apps asynchronously, as synchronous is not possible
-  // with NSItemProvider.
-  NSItemProvider* itemProvider = dragItem.itemProvider;
-  if ([itemProvider canLoadObjectOfClass:[NSURL class]]) {
   // The parameter type has changed with Xcode 12 SDK.
   // TODO(crbug.com/1098318): Remove this once Xcode 11 support is dropped.
 #if defined(__IPHONE_14_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_14_0
@@ -480,16 +486,13 @@ web::WebState* GetWebStateWithId(WebStateList* web_state_list,
 
   auto loadHandler = ^(providerType providedItem, NSError* error) {
     dispatch_async(dispatch_get_main_queue(), ^{
+      [placeholderContext deletePlaceholder];
       NSURL* droppedURL = static_cast<NSURL*>(providedItem);
       [self insertNewItemAtIndex:destinationIndex
                          withURL:net::GURLWithNSURL(droppedURL)];
     });
   };
-
-    [itemProvider loadObjectOfClass:[NSURL class]
-                  completionHandler:loadHandler];
-    return;
-  }
+  [itemProvider loadObjectOfClass:[NSURL class] completionHandler:loadHandler];
 }
 
 #pragma mark - GridImageDataSource