Fallback URL handling in SDWebImage

UIImageView+RestaurantWebImage.h

//
//  UIImageView+RestaurantWebImage.h
//  DinerApp
//
//  Created by ALeszkiewicz on 6/21/16.
//  Copyright © 2016 GrubHub Inc. All rights reserved.
//

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface UIImageView (RestaurantWebImage)

- (void)beginImageDownloadWithURLs:(NSArray <NSURL *> *)imageURLs;

@end

NS_ASSUME_NONNULL_END

UIImageView+RestaurantWebImage.m

//
//  UIImageView+RestaurantWebImage.m
//  DinerApp
//
//  Created by ALeszkiewicz on 6/21/16.
//  Copyright © 2016 GrubHub Inc. All rights reserved.
//

#import "UIImageView+RestaurantWebImage.h"
#import "GKConstants.h"
#import <SDWebImage/UIImageView+WebCache.h>

@implementation UIImageView (RestaurantWebImage)

- (void)beginImageDownloadWithURL:(NSURL * _Nonnull)imageURL {
    UIImage *placeholderImageOnFailure;
    if (IS_IPAD) {
        placeholderImageOnFailure = [UIImage imageNamed:@"MenuHeaderRestaurantPlaceholder"];
    } else {
        placeholderImageOnFailure = [UIImage imageNamed:@"MenuHeaderRestaurantPlaceholder_iPhone"];
    }
    
    __weak __typeof(self)weakSelf = self;
    [self sd_setImageWithURL:imageURL
            placeholderImage:placeholderImageOnFailure
                     options:SDWebImageDelayPlaceholder
                    progress:nil
                   completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
                       [weakSelf didCompleteImageDownloadWithCacheType:cacheType];
                   }];
    
}

- (void)beginImageDownloadWithURLs:(NSArray <NSURL *> *)imageURLs {
    self.image = nil;
    NSURL *firstURL = [imageURLs firstObject];
    if (imageURLs.count > 1) {
        [self beginImageDownloadWithURL:firstURL fallbackURLsOnFailure:[imageURLs subarrayWithRange:NSMakeRange(1, imageURLs.count-1)]];
    } else {
        [self beginImageDownloadWithURL:firstURL];
    }
}

- (void)beginImageDownloadWithURL:(NSURL  * _Nonnull)imageURL fallbackURLsOnFailure:(NSArray <NSURL *> * _Nonnull)fallbackURLsOnFailure {
    NSURL *nextURLOnFailure = [fallbackURLsOnFailure firstObject];
    if (!nextURLOnFailure) {
        [self beginImageDownloadWithURL:imageURL];
    } else {
        __weak __typeof(self)weakSelf = self;
        [self sd_setImageWithURL:imageURL
                placeholderImage:nil
                         options:0
                        progress:nil
                       completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
                           __strong __typeof(self)strongSelf = weakSelf;
                           if (!strongSelf) {
                               return;
                           }
                           
                           if (!image) {
                               //Pop first fallbackURL item, we know it's present because 'nextURLOnFailure' is non-nil
                               NSMutableArray *fallbackURLsMutable = [fallbackURLsOnFailure mutableCopy];
                               [fallbackURLsMutable removeObjectAtIndex:0];
                               
                               [strongSelf beginImageDownloadWithURL:nextURLOnFailure
                                               fallbackURLsOnFailure:[fallbackURLsMutable copy]];
                           } else {
                               [strongSelf didCompleteImageDownloadWithCacheType:cacheType];
                           }
                       }];
        
    }
}

- (void)didCompleteImageDownloadWithCacheType:(SDImageCacheType)imageCacheType
{
    BOOL hasImage = self.image != nil;
    //Do not animate if the image was from cache, the user will not have time to see the animations
    if (hasImage && imageCacheType == SDImageCacheTypeNone) {
        [UIView transitionWithView:self
                          duration:0.2
                           options:UIViewAnimationOptionTransitionCrossDissolve
                        animations:nil
                        completion:nil];
    }
    self.accessibilityValue =
    hasImage ?
    GKAccessibilityString(@"Placeholder Image", @"Value", kSectionRestaurantHeader) :
    GKAccessibilityString(@"Restaurant Logo", @"Value", kSectionRestaurantHeader);
}



@end