//
//  Notification+Extension.swift
//
//
//  Created by Amit Kumar Swami on 20/08/17.
//  Copyright © 2017 aks.swami. All rights reserved.
//

import Foundation
import UIKit

class Token {
    let center: NotificationCenter
    let token: NSObjectProtocol

    init(token: NSObjectProtocol, center: NotificationCenter) {
        self.token = token
        self.center = center
    }

    deinit {
        center.removeObserver(token)
    }
}

struct NotificationDescriptor<A> {
    let name: Notification.Name
    let convert: (Notification) -> A
}

extension NotificationCenter {
    func addObserver<A>(forDescriptor d: NotificationDescriptor<A>, using block: @escaping (A) -> ()) -> Token {
        let t = addObserver(forName: d.name, object: nil, queue: nil, using: { note in
            block(d.convert(note))
        })
        return Token(token: t, center: self)
    }
}

struct KeyboardPayload {
    let size: CGSize
}

extension KeyboardPayload {
    init(note: Notification) {
        guard let userInfo = note.userInfo,
            let value = userInfo[UIKeyboardFrameBeginUserInfoKey] as? NSValue
            else {
            size = CGSize.zero

            return
        }
        size = value.cgRectValue.size
    }
}

let keyboardShowNotification = NotificationDescriptor<KeyboardPayload>(name: Notification.Name.UIKeyboardWillShow, convert: KeyboardPayload.init)
let keyboardHiderNotification = NotificationDescriptor<KeyboardPayload>(name: Notification.Name.UIKeyboardWillHide, convert: KeyboardPayload.init)