ImageFetcher.swift

class ImageFetcher: Operation {
    
    var photo: PhotoRecord
    
    init(photo: PhotoRecord) {
        self.photo = photo
    }
    
    override func main() {
        
        if isCancelled {
            return
        }
        
        guard let imageData = try? Data(contentsOf: photo.imageUrl) else { return }
        
        if !imageData.isEmpty {
            
            photo.image = UIImage(data: imageData)
            photo.state = .downloaded
            
        } else {
            
            photo.image = UIImage(named: "Could not fetch image")
            photo.state = .failed
            print("Failed fetching image")
        }
    }
    
}


class PendingOperations {
    
    lazy var downloadInProgress: [IndexPath: Operation] = [:]
    
    lazy var downloadQueue: OperationQueue = {
        
        var queue = OperationQueue()
        queue.name = "Flickr fetching queue"
        
        return queue
    }()
    
    
}

ImageFetcherImplementation.swift

func startDownload(for photoRecord: PhotoRecord, indexPath: IndexPath) {
        
        guard pendingOperations.downloadInProgress[indexPath] == nil else { return }
        
        let imageFetching = ImageFetcher(photo: photoRecord)
        
        pendingOperations.downloadInProgress.updateValue(imageFetching, forKey: indexPath)
        pendingOperations.downloadQueue.addOperation(imageFetching)
        
        
        imageFetching.completionBlock = {
            
            if imageFetching.isCancelled {
                return
            }
            
            DispatchQueue.main.async {
                self.tableView.reloadRows(at: [indexPath], with: .fade)
                
            }
            self.pendingOperations.downloadInProgress.removeValue(forKey: indexPath)
        }
        
    }
    
     func suspendOperations() {
        
        pendingOperations.downloadQueue.isSuspended = true
    }
    
     func resumeOperations() {
        
        pendingOperations.downloadQueue.isSuspended = false
    }

PhotoRecord.swift

enum PhotoRecordState {
    
    case new
    case downloaded
    case failed
}

class PhotoRecord {
    
    let imageUrl: URL
    var latitude: Double?
    var longitude: Double?
    var image = UIImage(named: "Flickr image")
    var state = PhotoRecordState.new
    let name: String
    
    
    init(name: String, imageUrl: URL) {
        self.name = name
        self.imageUrl = imageUrl
        
    }
    
}