Wrap PHPickerViewController with PromiseKit

PHPickerViewController+Promise.swift

//
//  PHPickerViewController+Promise.swift
//
//  Created by cleexiang on 2021/5/22.
//

import Foundation
import PhotosUI
import PromiseKit
import Photos

@available(iOS 14, *)
extension UIViewController {
    public func promise(_ vc: PHPickerViewController, completion: (() -> Void)? = nil) -> Promise<UIImage> {
        let proxy = PHPickerViewControllerProxy()
        vc.delegate = proxy
        present(vc, animated: true, completion: completion)
        return proxy.promise.ensure {
            vc.presentingViewController?.dismiss(animated: true, completion: nil)
        }
    }
}

@available(iOS 14, *)
extension PHPickerResult {
    public func fetchImage() -> Promise<UIImage> {
        return Promise { seal in
            self.itemProvider.loadObject(ofClass: UIImage.self, completionHandler: { (object, error) in
                if let err = error {
                    seal.reject(err)
                } else {
                    if let image = object as? UIImage {
                        seal.fulfill(image)
                    } else {
                        seal.reject(PMKError.emptySequence)
                    }
                }
            })
        }
    }
}

@available(iOS 14, *)
@objc private class PHPickerViewControllerProxy: NSObject, PHPickerViewControllerDelegate {
    let (promise, seal) = Promise<UIImage>.pending()
    var retainCycle: AnyObject?
    
    required override init() {
        super.init()
        retainCycle = self
    }
    func picker(_ picker: PHPickerViewController, didFinishPicking results: [PHPickerResult]) {
        guard let asset = results.first else {
            seal.reject(UIImagePickerController.PMKError.cancelled)
            retainCycle = nil
            return
        }
        let status = PHPhotoLibrary.authorizationStatus()
        if status == .notDetermined {
            PHPhotoLibrary.requestAuthorization({ _ in
                asset.itemProvider.loadObject(ofClass: UIImage.self, completionHandler: { (object, error) in
                    if let err = error {
                        self.seal.reject(err)
                        self.retainCycle = nil
                    } else {
                        if let image = object as? UIImage {
                            self.seal.fulfill(image)
                            self.retainCycle = nil
                        } else {
                            self.seal.reject(PMKError.emptySequence)
                            self.retainCycle = nil
                        }
                    }
                })
            })
        } else {
            asset.itemProvider.loadObject(ofClass: UIImage.self, completionHandler: { (object, error) in
                if let err = error {
                    self.seal.reject(err)
                    self.retainCycle = nil
                } else {
                    if let image = object as? UIImage {
                        self.seal.fulfill(image)
                        self.retainCycle = nil
                    } else {
                        self.seal.reject(PMKError.emptySequence)
                        self.retainCycle = nil
                    }
                }
            })
        }
    }
}