/*

 Copyright (C) 2016 Apple Inc. All Rights Reserved.

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 The PhotoController manages the Photo object. All changes are pushed through the controller, allowing one or more subscribers to be alerted to changes.

*/

import Cocoa

class PhotoController: NSObject {

    private let subscribers = NSHashTable<AnyObject>.weakObjects()

    private(set) var photo: Photo

    init(photo: Photo) {

        self.photo = photo

    }

    // MARK: - Subscription

    func addSubscriber(_ subscriber: PhotoSubscriber) {

        subscribers.add(subscriber)

    }

    func removeSubscriber(_ subscriber: PhotoSubscriber) {

        subscribers.remove(subscriber)

    }

    private func forEachSubscriber(_ work: @noescape (PhotoSubscriber) -> Void) {

        for object in subscribers.objectEnumerator() {

            guard let subscriber = object as? PhotoSubscriber else { continue }

            work(subscriber)

        }

    }

    // MARK: - Actions

    func setPhotoImage(_ photoImage: NSImage?) {

        let oldImage = photo.image

        photo.image = photoImage

        forEachSubscriber { $0.photo(photo, didChangeImage: photo.image, from: oldImage) }

    }

    func setPhotoTitle(_ title: String) {

        photo.title = title

        forEachSubscriber { $0.photo(photo, didChangeTitle: title) }

    }   

}

protocol PhotoSubscriber: class {

    func photo(_ photo: Photo, didChangeImage image: NSImage?, from oldImage: NSImage?)

    func photo(_ photo: Photo, didChangeTitle title: String)

}

// Optionally provide a default empty implementation to make it "optional". Having it not be optional enforces you to implement the protocol, which can be desired in some cases.

/*

 extension PhotoSubscriber {

 func photo(_ photo: Photo, didChangeImage image: NSImage?, from oldImage: NSImage?) {

 }

 func photo(_ photo: Photo, didChangeTitle title: String) {

 }

 }

 */

// Any given view controller can implement the PhotoControllerConsumer to get assigned the current PhotoController

protocol PhotoControllerConsumer {

    var photoController: PhotoController? { get set }

}