//
//  ASElementMap.h
//  AsyncDisplayKit
//
//  Created by Adlai Holler on 2/22/17.
//  Copyright © 2017 Facebook. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <AsyncDisplayKit/ASBaseDefines.h>

NS_ASSUME_NONNULL_BEGIN

@class ASCollectionElement, ASSection, UICollectionViewLayoutAttributes;
@protocol ASSectionContext;

/**
 * An immutable representation of the state of a collection view's data.
 * All items and supplementary elements are represented by ASCollectionElement.
 * Fast enumeration is in terms of ASCollectionElement.
 */
AS_SUBCLASSING_RESTRICTED
@interface ASElementMap : NSObject <NSCopying, NSFastEnumeration>

/**
 * The number of sections (of items) in this map.
 */
@property (readonly) NSInteger numberOfSections;

/**
 * The kinds of supplementary elements present in this map. O(1)
 */
@property (copy, readonly) NSArray<NSString *> *supplementaryElementKinds;

/**
 * Returns number of items in the given section. O(1)
 */
- (NSInteger)numberOfItemsInSection:(NSInteger)section;

/**
 * Returns the context object for the given section, if any. O(1)
 */
- (nullable id<ASSectionContext>)contextForSection:(NSInteger)section;

/**
 * All the index paths for all the items in this map. O(N)
 *
 * This property may be removed in the future, since it doesn't account for supplementary nodes.
 */
@property (copy, readonly) NSArray<NSIndexPath *> *itemIndexPaths;

/**
 * Returns the index path that corresponds to the same element in @c map at the given @c indexPath. O(1)
 */
- (nullable NSIndexPath *)convertIndexPath:(NSIndexPath *)indexPath fromMap:(ASElementMap *)map;

/**
 * Returns the index path for the given element. O(1)
 */
- (nullable NSIndexPath *)indexPathForElement:(ASCollectionElement *)element;

/**
 * Returns the index path for the given element, if it represents a cell. O(1)
 */
- (nullable NSIndexPath *)indexPathForElementIfCell:(ASCollectionElement *)element;

/**
 * Returns the item-element at the given index path. O(1)
 */
- (nullable ASCollectionElement *)elementForItemAtIndexPath:(NSIndexPath *)indexPath;

/**
 * Returns the element for the supplementary element of the given kind at the given index path. O(1)
 */
- (nullable ASCollectionElement *)supplementaryElementOfKind:(NSString *)supplementaryElementKind atIndexPath:(NSIndexPath *)indexPath;

/**
 * Returns the element that corresponds to the given layout attributes, if any.
 *
 * NOTE: This method only regards the category, kind, and index path of the attributes object. Elements do not
 * have any concept of size/position.
 */
- (nullable ASCollectionElement *)elementForLayoutAttributes:(UICollectionViewLayoutAttributes *)layoutAttributes;

#pragma mark - Initialization -- Only Useful to ASDataController


// SectionIndex -> ItemIndex -> Element
typedef NSArray<NSArray<ASCollectionElement *> *> ASCollectionElementTwoDimensionalArray;

// ElementKind -> IndexPath -> Element
typedef NSDictionary<NSString *, NSDictionary<NSIndexPath *, ASCollectionElement *> *> ASSupplementaryElementDictionary;

/**
 * Create a new element map for this dataset. You probably don't need to use this – ASDataController is the only one who creates these.
 *
 * @param sections The array of ASSection objects.
 * @param items A 2D array of ASCollectionElements, for each item.
 * @param supplementaryElements A dictionary of gathered supplementary elements.
 */
- (instancetype)initWithSections:(NSArray<ASSection *> *)sections
                           items:(ASCollectionElementTwoDimensionalArray *)items
           supplementaryElements:(ASSupplementaryElementDictionary *)supplementaryElements;

@end

NS_ASSUME_NONNULL_END