//
//  UIImagePickerController+RxCreate.swift
//  RxExample
//
//  Created by Krunoslav Zaher on 1/10/16.
//  Copyright © 2016 Krunoslav Zaher. All rights reserved.
//

import UIKit
import RxSwift
import RxCocoa

//取消指定视图控制器函数
func dismissViewController(_ viewController: UIViewController, animated: Bool) {
    if viewController.isBeingDismissed || viewController.isBeingPresented {
        DispatchQueue.main.async {
            dismissViewController(viewController, animated: animated)
        }
        return
    }
    
    if viewController.presentingViewController != nil {
        viewController.dismiss(animated: animated, completion: nil)
    }
}

//对UIImagePickerController进行Rx扩展
extension Reactive where Base: UIImagePickerController {
    //用于创建并自动显示图片选择控制器的静态方法
    static func createWithParent(_ parent: UIViewController?,
                                 animated: Bool = true,
                                 configureImagePicker: @escaping (UIImagePickerController) throws -> () = { x in })
        -> Observable<UIImagePickerController> {
            
            //返回可观察序列
            return Observable.create { [weak parent] observer in
                
                //初始化一个图片选择控制器
                let imagePicker = UIImagePickerController()
                
                //不管图片选择完毕还是取消选择，都会发出.completed事件
                let dismissDisposable = Observable.merge(
                    imagePicker.rx.didFinishPickingMediaWithInfo.map{_ in ()},
                    imagePicker.rx.didCancel
                    )
                    .subscribe(onNext: {  _ in
                        observer.on(.completed)
                    })
                
                //设置图片选择控制器初始参数，参数不正确则发出.error事件
                do {
                    try configureImagePicker(imagePicker)
                }
                catch let error {
                    observer.on(.error(error))
                    return Disposables.create()
                }
                
                //判断parent是否存在，不存在则发出.completed事件
                guard let parent = parent else {
                    observer.on(.completed)
                    return Disposables.create()
                }
                // 处理IOS11下偏移问题
                if #available(iOS 11.0, *) {
                    UIScrollView.appearance().contentInsetAdjustmentBehavior = .automatic
                }
                //弹出控制器，显示界面
                parent.present(imagePicker, animated: animated, completion: nil)
                //发出.next事件（携带的是控制器对象）
                observer.on(.next(imagePicker))
                
                //销毁时自动退出图片控制器
                return Disposables.create(dismissDisposable, Disposables.create {
                    dismissViewController(imagePicker, animated: animated)
                    if #available(iOS 11.0, *) {
                        UIScrollView.appearance().contentInsetAdjustmentBehavior = .never
                    }
                })
            }
    }
}