Empty data set for ASDisplayNode

ASDisplayNode+BFREmptyView.m

//
//  ASDisplayNode+BFREmptyView.m
//  Buffer
//
//  Created by Jordan Morgan on 10/27/17.
//

#import "ASDisplayNode+BFREmptyView.h"
#import <objc/runtime.h>
#import <AsyncDisplayKit/AsyncDisplayKit.h>

static NSMutableDictionary *implementationLookupTable;
static BOOL experimentEnableGesture;

@interface ASDisplayNode ()

void swizzleInstanceUpdateMethods(id self);
void swizzledBatchUpdates(id self, SEL _cmd, void(^updates)(), void(^completion)(BOOL));
void swizzledReloadDataWithCompletion(id self, SEL _cmd, void(^completion)());

@property (strong, nonatomic, nullable, readonly) UIView *emptyView;
@property (strong, nonatomic, nullable, readonly) UIPanGestureRecognizer *pan;

@end

@implementation ASDisplayNode (BFREmptyView)

#pragma mark - Getters/Setters

static char const * BFREmptyDataViewDataSourcePropertyKey = "BFREmptyDataViewDataSourcePropertyKey";
static char const * BFREmptyDataViewPropertyKey = "BFREmptyDataViewPropertyKey";
static char const * BFREmptyDataViewPanPropertyKey = "BFREmptyDataViewPanPropertyKey";

- (id <BFREmptyDataViewDataSource>)emptyDataViewDataSourceDelegate {
    return objc_getAssociatedObject(self, BFREmptyDataViewDataSourcePropertyKey);
}

- (void)setEmptyDataViewDataSourceDelegate:(id <BFREmptyDataViewDataSource>)emptyDataSource {
    objc_setAssociatedObject(self, BFREmptyDataViewDataSourcePropertyKey, emptyDataSource, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    
    if ([self respondsToSelector:@selector(performBatchUpdates:completion:)]) {
        if ([self isKindOfClass:[ASCollectionNode class]]) {
            static dispatch_once_t onceCollectionNodeToken;
            dispatch_once(&onceCollectionNodeToken, ^{
                swizzleInstanceUpdateMethods(self);
            });
        } else if ([self isKindOfClass:[ASTableNode class]]) {
            static dispatch_once_t onceTableNodeToken;
            dispatch_once(&onceTableNodeToken, ^{
                swizzleInstanceUpdateMethods(self);
            });
        }
    }
        
    // Ensuring the empty view stays centered is a nightware with offsets. For that reason we add it to the view controller's view,
    // Not the collection node. This mimics the user scrollingn down on the collection node during pull to refresh.
    if (experimentEnableGesture) {
        // We will implement this later if we want it to scroll with the refresh
        self.pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
        self.pan.delegate = self;
        [self.view addGestureRecognizer:self.pan];
    }
}

- (UIView *)emptyView {
    return objc_getAssociatedObject(self, BFREmptyDataViewPropertyKey);
}

- (void)setEmptyView:(UIView *)view {
    objc_setAssociatedObject(self, BFREmptyDataViewPropertyKey, view, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (UIPanGestureRecognizer *)pan {
    return objc_getAssociatedObject(self, BFREmptyDataViewPanPropertyKey);
}

- (void)setPan:(UIPanGestureRecognizer *)pan {
    objc_setAssociatedObject(self, BFREmptyDataViewPanPropertyKey, pan, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

#pragma mark - Swizzle

void swizzleInstanceUpdateMethods(id self) {
    if (!implementationLookupTable) implementationLookupTable = [[NSMutableDictionary alloc] initWithCapacity:2];
    
    if ([self isKindOfClass:[ASCollectionNode class]]) {
        // Swizzle batchUpdates for collection node which is all we'll need
        Method methodBatchUpdates = class_getInstanceMethod([self class], @selector(performBatchUpdates:completion:));
        IMP performBatchUpdates_orig = method_setImplementation(methodBatchUpdates, (IMP)swizzledBatchUpdates);
        [implementationLookupTable setValue:[NSValue valueWithPointer:performBatchUpdates_orig] forKey:[self instanceLookupKeyForSelector:@selector(performBatchUpdates:completion:)]];
    } else if ([self isKindOfClass:[ASTableNode class]]) {
        // Swizzle batchUpdates and reloadData for table node since we'll need both
        Method methodBatchUpdates = class_getInstanceMethod([self class], @selector(performBatchUpdates:completion:));
        IMP performBatchUpdates_orig = method_setImplementation(methodBatchUpdates, (IMP)swizzledBatchUpdates);
        [implementationLookupTable setValue:[NSValue valueWithPointer:performBatchUpdates_orig] forKey:[self instanceLookupKeyForSelector:@selector(performBatchUpdates:completion:)]];
        
        Method methodReloadDataWithCompletion = class_getInstanceMethod([self class], @selector(reloadDataWithCompletion:));
        IMP performReloadDataWithCompletion_orig = method_setImplementation(methodReloadDataWithCompletion, (IMP)swizzledReloadDataWithCompletion);
        [implementationLookupTable setValue:[NSValue valueWithPointer:performReloadDataWithCompletion_orig] forKey:[self instanceLookupKeyForSelector:@selector(reloadDataWithCompletion:)]];
    }
}

void swizzledBatchUpdates(id self, SEL _cmd, void(^updates)(), void(^completion)(BOOL)) {
    // Get the original performBatchUpdates
    NSValue *impValue = [implementationLookupTable valueForKey:[self instanceLookupKeyForSelector:_cmd]];
    IMP performBatchUpdates_orig = [impValue pointerValue];
    
    // Call OG implementation for whichever instance we have
    if (performBatchUpdates_orig) {
        ((void(*)(id,SEL, void(^updates)(), void(^completion)(BOOL)))performBatchUpdates_orig)(self,_cmd, updates, completion);
    }
    
    // Now trigger empty view
    [self showEmptyViewIfNeeded];
}

void swizzledReloadDataWithCompletion(id self, SEL _cmd, void(^completion)()) {
    // Get the original reloadDataWithCompletion
    NSValue *impValue = [implementationLookupTable valueForKey:[self instanceLookupKeyForSelector:_cmd]];
    IMP performReloadDataWithCompletion_orig = [impValue pointerValue];
    
    // Call OG implementation for table node
    if (performReloadDataWithCompletion_orig) {
        ((void(*)(id,SEL, void(^completion)()))performReloadDataWithCompletion_orig)(self,_cmd, completion);
    }
    
    // Now trigger empty view
    [self showEmptyViewIfNeeded];
}

- (NSString *)instanceLookupKeyForSelector:(SEL)selector {
    return [NSString stringWithFormat:@"%@-%@", NSStringFromClass([self class]), NSStringFromSelector(selector)];
}

#pragma mark - Empty Data View Hide/Show

- (void)showEmptyViewIfNeeded {
    
    BOOL dataIsEmpty;
    
    NSInteger sections = 1;
    NSInteger totalItems = 0;
    
    if ([self isKindOfClass:[ASCollectionNode class]]) {
        id <ASCollectionDataSource> nodeDataSource = ((ASCollectionNode *)self).dataSource;
        
        if ([nodeDataSource respondsToSelector:@selector(numberOfSectionsInCollectionNode:)]) {
            sections = [nodeDataSource numberOfSectionsInCollectionNode:(ASCollectionNode *)self];
        }
        
        if ([nodeDataSource respondsToSelector:@selector(collectionNode:numberOfItemsInSection:)]) {
            for (NSInteger sectionIDX = 0; sectionIDX < sections; sectionIDX++) {
                totalItems += [nodeDataSource collectionNode:(ASCollectionNode *)self numberOfItemsInSection:sectionIDX];
            }
        }
        
    } else if ([self isKindOfClass:[ASTableNode class]]) {
        id <ASTableDataSource> nodeDataSource = ((ASTableNode *)self).dataSource;
        
        if ([nodeDataSource respondsToSelector:@selector(numberOfSectionsInTableNode:)]) {
            sections = [nodeDataSource numberOfSectionsInTableNode:(ASTableNode *)self];
        }
        
        if ([nodeDataSource respondsToSelector:@selector(tableNode:numberOfRowsInSection:)]) {
            for (NSInteger sectionIDX = 0; sectionIDX < sections; sectionIDX++) {
                totalItems += [nodeDataSource tableNode:(ASTableNode *)self numberOfRowsInSection:sectionIDX];
            }
        }
    }
    
    dataIsEmpty = totalItems <= 0;
    
    if (self.emptyDataViewDataSourceDelegate != nil && [NSThread currentThread].isMainThread) {
        if (dataIsEmpty) {
            if (self.emptyView.superview) [self.emptyView removeFromSuperview];
            self.emptyView = [self.emptyDataViewDataSourceDelegate viewForEmptyData];
            if (self.emptyView == nil) return;

            // Add empty view
            CGFloat offset = 0;
            if ([self.emptyDataViewDataSourceDelegate respondsToSelector:@selector(offsetForEmptyView)]) {
                offset = [self.emptyDataViewDataSourceDelegate offsetForEmptyView];
            }
            
            if (self.closestViewController == nil) {
                DDLogWarn(@"Closet view controller was nil when attempting to display empty data set.");
                return;
            }
            
            [self.closestViewController.view addSubview:self.emptyView];
            
            [self.emptyView  mas_makeConstraints:^(MASConstraintMaker *make) {
                if (@available(iOS 11.0, *)) {
                    make.width.equalTo(self.closestViewController.view.mas_safeAreaLayoutGuideWidth);
                    make.height.equalTo(self.closestViewController.view.mas_safeAreaLayoutGuideHeight);
                    make.centerX.equalTo(self.closestViewController.view.mas_safeAreaLayoutGuideCenterX);
                    make.centerY.equalTo(self.closestViewController.view.mas_safeAreaLayoutGuideCenterY).with.offset(offset);
                } else {
                    make.width.equalTo(self.closestViewController.view.mas_width);
                    make.height.equalTo(self.closestViewController.view.mas_height);
                    make.centerX.equalTo(self.closestViewController.view.mas_centerX);
                    make.centerY.equalTo(self.closestViewController.view.mas_centerY).with.offset(offset);
                }
            }];
            
        } else {
            [self.emptyView removeFromSuperview];
        }
    }
}

#pragma mark - UIGestureRecognizer Delegate

// Pans the empty view down, making it appear like it's part of the collectionnode's content view
- (void)handlePan:(UIPanGestureRecognizer *)pan {
    CGPoint pointsToMove = [pan translationInView:self.emptyView];
    [self.emptyView setCenter:CGPointMake(self.emptyView.center.x, self.emptyView.center.y + pointsToMove.y)];
    [pan setTranslation:CGPointZero inView:self.emptyView];
    
    if (pan.state == UIGestureRecognizerStateEnded) {
        [self.emptyView setCenter:self.closestViewController.view.center];
    }
}

// This allows users to still scroll the collection node to pull to refresh
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
    return YES;
}

@end