IImageProvider.swift

import UIKit

protocol IImageProvider: AnyObject {
    func retrieve(_ completion: @escaping (UIImage?) -> Void)
    
    func preload()
}

protocol IImageProviderConsumer {
    var currentProvider: IImageProvider? { get set }
    
    func apply(_ provider: IImageProvider)
    
    func removeProvider()
}

var providerContext: UInt8 = 0

extension UIImageView: IImageProviderConsumer {
    var currentProvider: IImageProvider? {
        get {
            let currentProviderRawObject = objc_getAssociatedObject(self, &providerContext)
            
            guard let currentProviderRawObjectUnwrapped = currentProviderRawObject else {
                return nil
            }
            
            let currentProvider = currentProviderRawObjectUnwrapped as! IImageProvider
            return currentProvider
        }
        set {
            objc_setAssociatedObject(self, &providerContext, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
    
    func apply(_ provider: IImageProvider) {
        if provider !== currentProvider {
            image = nil
        }
        self.currentProvider = provider
        provider.retrieve { [weak self] image in
            guard let self = self else { return }
            guard self.currentProvider === provider else { return }
            
            self.image = image
        }
    }
    
    func removeProvider() {
        currentProvider = nil
        image = nil
    }
}