IGListKit/Source/IGListUpdatingDelegate.h

/**
 * Copyright (c) 2016-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */

#import <UIKit/UIKit.h>

@protocol IGListDiffable;

NS_ASSUME_NONNULL_BEGIN

/**
 A completion block to execute when updates are finished.

 @param finished Specifies whether or not the update finished.
 */
NS_SWIFT_NAME(ListUpdatingCompletion)
typedef void (^IGListUpdatingCompletion)(BOOL finished);

/**
 A block to be called when the adapter applies changes to the collection view.

 @param toObjects The new objects in the collection.
 */
NS_SWIFT_NAME(ListObjectTransitionBlock)
typedef void (^IGListObjectTransitionBlock)(NSArray *toObjects);

/// A block that contains all of the updates.
NS_SWIFT_NAME(ListItemUpdateBlock)
typedef void (^IGListItemUpdateBlock)(void);

/// A block to be called when an adapter reloads the collection view.
NS_SWIFT_NAME(ListReloadUpdateBlock)
typedef void (^IGListReloadUpdateBlock)(void);

/**
 Implement this protocol in order to handle both section and row based update events. Implementation should forward or
 coalesce these events to a backing store or collection.
 */
NS_SWIFT_NAME(ListUpdatingDelegate)
@protocol IGListUpdatingDelegate <NSObject>

/**
 Asks the delegate for the pointer functions for looking up an object in a collection.

 @return Pointer functions for looking up an object in a collection.

 @note Since the updating delegate is responsible for transitioning between object sets, it becomes the "source of
 truth" for how objects and their corresponding section controllers are mapped. This allows the updater to control if
 objects are looked up by pointer, or more traditionally, with `-hash`/`-isEqual`.

 For behavior similar to `NSDictionary`, simply return
 `+[NSPointerFunctions pointerFunctionsWithOptions:NSPointerFunctionsObjectPersonality]`.
 */
- (NSPointerFunctions *)objectLookupPointerFunctions;

/**
 Tells the delegate to perform a section transition from an old array of objects to a new one.

 @param collectionView The collection view to perform the transition on.
 @param fromObjects The previous objects in the collection view. Objects must conform to `IGListDiffable`.
 @param toObjects The new objects in collection view. Objects must conform to `IGListDiffable`.
 @param animated A flag indicating if the transition should be animated.
 @param objectTransitionBlock A block that must be called when the adapter applies changes to the collection view.
 @param completion A completion block to execute when the update is finished.

 @note Implementations determine how to transition between objects. You can perform a diff on the objects, reload
 each section, or simply call `-reloadData` on the collection view. In the end, the collection view must be setup with a
 section for each object in the `toObjects` array.

 The `objectTransitionBlock` block should be called prior to making any `UICollectionView` updates, passing in the `toObjects`
 that the updater is applying.
 */
- (void)performUpdateWithCollectionView:(UICollectionView *)collectionView
                            fromObjects:(nullable NSArray<id <IGListDiffable>> *)fromObjects
                              toObjects:(nullable NSArray<id <IGListDiffable>> *)toObjects
                               animated:(BOOL)animated
                  objectTransitionBlock:(IGListObjectTransitionBlock)objectTransitionBlock
                             completion:(nullable IGListUpdatingCompletion)completion;

/**
 Tells the delegate to perform item inserts at the given index paths.

 @param collectionView The collection view on which to perform the transition.
 @param indexPaths The index paths to insert items into.
 */
- (void)insertItemsIntoCollectionView:(UICollectionView *)collectionView indexPaths:(NSArray <NSIndexPath *> *)indexPaths;

/**
 Tells the delegate to perform item deletes at the given index paths.

 @param collectionView The collection view on which to perform the transition.
 @param indexPaths The index paths to delete items from.
 */
- (void)deleteItemsFromCollectionView:(UICollectionView *)collectionView indexPaths:(NSArray <NSIndexPath *> *)indexPaths;

/**
 Tells the delegate to move an item from and to given index paths.

 @param collectionView The collection view on which to perform the transition.
 @param fromIndexPath The source index path of the item to move.
 @param toIndexPath The destination index path of the item to move.
 */
- (void)moveItemInCollectionView:(UICollectionView *)collectionView
                   fromIndexPath:(NSIndexPath *)fromIndexPath
                     toIndexPath:(NSIndexPath *)toIndexPath;

/**
 Tells the delegate to reload an item from and to given index paths.

 @param collectionView The collection view on which to perform the transition.
 @param fromIndexPath The source index path of the item to reload.
 @param toIndexPath The destination index path of the item to reload.

 @note Since UICollectionView is unable to handle calling -[UICollectionView reloadItemsAtIndexPaths:] safely while also
 executing insert and delete operations in the same batch updates, the updater must know about the origin and
 destination of the reload to perform a safe transition.
 */
- (void)reloadItemInCollectionView:(UICollectionView *)collectionView
                     fromIndexPath:(NSIndexPath *)fromIndexPath
                       toIndexPath:(NSIndexPath *)toIndexPath;

/**
 Tells the delegate to move a section from and to given indexes.
 
 @param collectionView The collection view on which to perform the transition.
 @param fromIndex The source index of the section to move.
 @param toIndex The destination index of the section to move.
 */
- (void)moveSectionInCollectionView:(UICollectionView *)collectionView
                          fromIndex:(NSInteger)fromIndex
                            toIndex:(NSInteger)toIndex;
    
/**
 Completely reload data in the collection.

 @param collectionView The collection view to reload.
 @param reloadUpdateBlock A block that must be called when the adapter reloads the collection view.
 @param completion A completion block to execute when the reload is finished.
 */
- (void)reloadDataWithCollectionView:(UICollectionView *)collectionView
                   reloadUpdateBlock:(IGListReloadUpdateBlock)reloadUpdateBlock
                          completion:(nullable IGListUpdatingCompletion)completion;

/**
 Completely reload each section in the collection view.

 @param collectionView The collection view to reload.
 @param sections The sections to reload.
 */
- (void)reloadCollectionView:(UICollectionView *)collectionView sections:(NSIndexSet *)sections;

/**
 Perform an item update block in the collection view.

 @param collectionView The collection view to update.
 @param animated A flag indicating if the transition should be animated.
 @param itemUpdates A block containing all of the updates.
 @param completion A completion block to execute when the update is finished.
 */
- (void)performUpdateWithCollectionView:(UICollectionView *)collectionView
                               animated:(BOOL)animated
                            itemUpdates:(IGListItemUpdateBlock)itemUpdates
                             completion:(nullable IGListUpdatingCompletion)completion;

@end

NS_ASSUME_NONNULL_END