An extension to Nuke for progressive image loading. [Required CocoaPods - RxNuke, RxSwift, FirebaseStorage]

Nuke+Firebase.swift

import RxNuke
import Nuke
import RxSwift
import Firebase
import RxCocoa

enum ImageVariants: String {
    case high = "_high"
    case med = "_med"
    case low = "_low"
}

extension Manager {
    func loadImage(with reference: String) -> Driver<Image> {
        let variantLoaders: [Observable<Image>] = [
            FirebaseStorageReference.base
                .child("\(reference)\(ImageVariants.low.rawValue)")
                .rx
                .downloadURL()
                .flatMap({ (url) -> Observable<Image> in
                    return Nuke.Manager.shared.loadImage(with: url).orEmpty
                }),
            FirebaseStorageReference.base
                .child("\(reference)\(ImageVariants.med.rawValue)")
                .rx
                .downloadURL()
                .flatMap({ (url) -> Observable<Image> in
                    return Nuke.Manager.shared.loadImage(with: url).orEmpty
                }),
            FirebaseStorageReference.base
                .child("\(reference)\(ImageVariants.high.rawValue)")
                .rx
                .downloadURL()
                .flatMap({ (url) -> Observable<Image> in
                    return Nuke.Manager.shared.loadImage(with: url).orEmpty
                }),
            FirebaseStorageReference.base
                .child(reference)
                .rx
                .downloadURL()
                .flatMap({ (url) -> Observable<Image> in
                    return Nuke.Manager.shared.loadImage(with: url).orEmpty
                })
        ]
        return Observable.concat(variantLoaders)
            .shareReplay(1)
            .asDriver(
                //Load original image if no variants found
                onErrorDriveWith: FirebaseStorageReference.base
                    .child(reference)
                    .rx
                    .downloadURL()
                    .flatMap({ (url) -> Observable<Image> in
                        return Nuke.Manager
                            .shared
                            .loadImage(with: url)
                            .orEmpty
                    })
                    .asDriver { error in
                        // Return a default error image instead
                        return .just(Image(asset: .imageViewControllerError))
                    }
            )
    }
}