UIKeyCommand+Closure.swift

//
//  UIKeyCommand+Closure.swift
//
//  Created by Jonny Kuang.
//  Copyright © 2018 Jonny Kuang. All rights reserved.
//

import UIKit

protocol KeyCommandsProvider {
    func makeKeyCommands() -> [UIKeyCommand]
}

protocol KeyCommandInput {
    var keyCommandInput: String { get }
}

extension KeyCommandInput where Self : RawRepresentable, Self.RawValue == String {
    var keyCommandInput: String { return rawValue }
}


extension UIKeyCommand {
    
    typealias Handler = (UIKeyCommand) -> Void
    
    convenience init(input: String, modifiers: UIKeyModifierFlags = [], title: String = "", handler: @escaping Handler) {
        self.init(input: input, modifierFlags: modifiers, action: #selector(UIWindow.handleClosureBasedKeyCommand))
        self.title = title
        register(handler)
    }
    
    convenience init(input: Input, modifiers: UIKeyModifierFlags = [], title: String = "", handler: @escaping Handler) {
        self.init(input: input.keyCommandInput, modifiers: modifiers, title: title, handler: handler)
    }
    
    convenience init(input: KeyCommandInput, modifiers: UIKeyModifierFlags = [], title: String = "", handler: @escaping Handler) {
        self.init(input: input.keyCommandInput, modifiers: modifiers, title: title, handler: handler)
    }
    
    var modifiers: UIKeyModifierFlags {
        return modifierFlags
    }
    
    var title: String {
        get { return discoverabilityTitle ?? "" }
        set { discoverabilityTitle = newValue.isEmpty ? nil : newValue }
    }
    
    enum Input : String, KeyCommandInput {
        case upArrow
        case downArrow
        case leftArrow
        case rightArror
        case escape
        
        var rawValue: String {
            switch self {
            case .upArrow:    return UIKeyCommand.inputUpArrow
            case .downArrow:  return UIKeyCommand.inputDownArrow
            case .leftArrow:  return UIKeyCommand.inputLeftArrow
            case .rightArror: return UIKeyCommand.inputRightArrow
            case .escape:     return UIKeyCommand.inputEscape
            }
        }
        
        init?(rawValue: String) {
            fatalError("init(rawValue:) has not been implemented")
        }
    }
}


private extension UIWindow {
    
    @objc func handleClosureBasedKeyCommand(_ command: UIKeyCommand) {
        command.handle()
    }
}


private extension UIKeyCommand {
    
    typealias Identifier = String
    
    var identifier: Identifier {
        let input = self.input ?? ""
        let modifiers = "\(modifierFlags.rawValue)"
        return input + " " + modifiers
    }
    
    static var handlersByIdentifiers = [Identifier : Handler]()
    
    func register(_ handler: @escaping UIKeyCommand.Handler) {
        UIKeyCommand.handlersByIdentifiers[identifier] = handler
    }
    
    func handle() {
        UIKeyCommand.handlersByIdentifiers[identifier]?(self)
    }
}