UIViewController+GetImage.swift

//
//  UIViewController+GetImage.swift
//
//  Created by Daniel Tartaglia on 4/25/16.
//  Copyright © 2016 MIT License
//

import UIKit
import PromiseKit


enum ImagePickerError: ErrorType {
	case UserCanceled
}

extension UIViewController {

	func getImage(focusView view: UIView) -> Promise<UIImage> {
		let proxy = ImagePickerProxy()
		let cameraAction: UIAlertAction? = !UIImagePickerController.isSourceTypeAvailable(.Camera) ? nil : UIAlertAction(title: "Camera", style: .Default) { _ in
			let controller = UIImagePickerController()
			controller.delegate = proxy
			controller.allowsEditing = true
			controller.sourceType = .Camera
			self.presentViewController(controller, animated: true, completion: nil)
		}
		let photobinAction: UIAlertAction? = !UIImagePickerController.isSourceTypeAvailable(.PhotoLibrary) ? nil : UIAlertAction(title: "Photos", style: .Default) { _ in
			let controller = UIImagePickerController()
			controller.delegate = proxy
			controller.allowsEditing = false
			controller.sourceType = .PhotoLibrary
			self.presentViewController(controller, animated: true, completion: nil)
		}
		let cancelAction = UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)

		let alert = UIAlertController(title: nil, message: nil, preferredStyle: .ActionSheet)
		if let cameraAction = cameraAction {
			alert.addAction(cameraAction)
		}
		if let photobinAction = photobinAction {
			alert.addAction(photobinAction)
		}
		alert.addAction(cancelAction)
		let popoverPresentationController = alert.popoverPresentationController
		popoverPresentationController?.sourceView = view
		popoverPresentationController?.sourceRect = view.bounds
		presentViewController(alert, animated: true, completion: nil)
		let promise = proxy.promise
		return promise.always {
			self.dismissViewControllerAnimated(true, completion: nil)
			proxy.retainCycle = nil
		}
	}
}


private final class ImagePickerProxy: NSObject, UIImagePickerControllerDelegate, UINavigationControllerDelegate {

	let (promise, fulfill, reject) = Promise<UIImage>.pendingPromise()
	var retainCycle: ImagePickerProxy?

	required override init() {
		super.init()
		retainCycle = self
	}

	@objc func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : AnyObject]) {
		let image = (info[UIImagePickerControllerEditedImage] as? UIImage) ?? (info[UIImagePickerControllerOriginalImage] as! UIImage)
		fulfill(image)
	}

	@objc func imagePickerControllerDidCancel(picker: UIImagePickerController) {
		reject(ImagePickerError.UserCanceled)
	}
}