A loader for asset images

PHImageAssetLoader.swift

import Photos
import RxSwift

final class PHAssetImageLoader: ImageLoader {
    func loadImage(with url: URL) -> Single<UIImage> {
        return Single<UIImage>.create { observer in
            let imageManager = PHImageManager.default()
            var requestIdentifier: PHImageRequestID?

            DispatchQueue.global(qos: .userInitiated).async {
                let fetchResult = PHAsset.fetchAssets(withALAssetURLs: [url], options: nil)

                guard let asset = fetchResult.firstObject else {
                    observer(.error(PHAssetImageLoaderError.assetNotFound))
                    return
                }

                let request = PHImageRequestOptions()
                request.isSynchronous = true
                request.deliveryMode = .highQualityFormat
                request.resizeMode = .exact

                let size = CGSize(width: asset.pixelWidth, height: asset.pixelHeight)

                requestIdentifier = imageManager.requestImage(
                    for: asset,
                    targetSize: size,
                    contentMode: .aspectFill,
                    options: request) { image, info in
                        if let image = image {
                            observer(.success(image))
                        } else if let info = info, let isCancelled = info[PHImageCancelledKey] as? NSNumber, isCancelled == 1 {
                            observer(.error(PHAssetImageLoaderError.requestCancelled))
                        } else if let info = info, let error = info[PHImageErrorKey] as? Error {
                            observer(.error(error))
                        } else {
                            observer(.error(PHAssetImageLoaderError.unknownFailure))
                        }
                }
            }

            return Disposables.create {
                if let requestIdentifier = requestIdentifier {
                    imageManager.cancelImageRequest(requestIdentifier)
                }
            }
        }
    }
}

enum PHAssetImageLoaderError: Error {
    case assetNotFound
    case requestCancelled
    case unknownFailure
}