Dependency Injection.swift

// A Playground that shows how to use protocol extensions to do Dependency Injection

import UIKit
import PlaygroundSupport

enum InjectorType: String {
    case mainType
    case mocType
}

protocol MyProtocol {
    var count: Int { get }
    var view: UIView { get set }
    func doSomething(withSring string: String)
}

protocol ManagerInjected { }

class MyClass: MyProtocol {
    
    static let shared = MyClass()
    public var view = UIView()
    private var internalCount: Int
    private var someString: String
    public var count: Int {
        self.internalCount += 1
        return self.internalCount
    }

    private init() {
        print("Main class initialized")
        someString = "here I am"
        internalCount = 0
        view.backgroundColor = .lightGray
    }

    public func doSomething(withSring string: String) {
        print("Look ma, no hands: \(string)")
    }
    
}

class MOCMyClass: MyProtocol {

    static let shared = MOCMyClass()
    
    public var view = UIView()
    private var internalCount: Int = 0
    public var count: Int {
        self.internalCount += 10
        return self.internalCount
    }
    public func doSomething(withSring string: String) {
        print("Look MOC, no hands and I'm MOC'ing you with \(string)")
    }
    
    private init() {
        print("MOC class initialized")
    }

}

struct ManagerInjector {
    static var manager: (InjectorType)->MyProtocol = {
        injectorType in
        switch injectorType {
        case .mainType: return MyClass.shared
        case .mocType: return MOCMyClass.shared
        }
    }
    private init() { }
}

extension ManagerInjected {
    var inject: (InjectorType) -> MyProtocol { get { return ManagerInjector.manager } }
}

extension ManagerInjected where Self: UIViewController {
    @discardableResult func setupMyView(managerType: InjectorType = .mainType) -> MyProtocol {
        let manager = inject(managerType)
        view.addSubview(manager.view)
        manager.view.backgroundColor = UIColor.blue.withAlphaComponent(0.75)
        manager.view.frame = CGRect(x: 10, y: view.frame.height, width: view.frame.width - 20, height: 100)

        return manager
    }
    
    func showView(managerType: InjectorType = .mainType) {
        let manager = inject(managerType)

        let deltaY = manager.view.frame.origin.y == view.frame.height ? -manager.view.frame.height : manager.view.frame.height
        
        UIView.animate(withDuration: 0.5, delay: 0.0, options: .curveEaseInOut, animations: {
            manager.view.frame.origin.y += deltaY
        }, completion: nil)
    }
}

// How to use this Dependency Inject in a class to conforms to the protocol

class SomeViewController: UIViewController, ManagerInjected {
    var myManager: MyProtocol?
    var bottomConstraint = NSLayoutConstraint()
    lazy var button: UIButton = {
        let button = UIButton(type: UIButtonType.infoLight)
        button.translatesAutoresizingMaskIntoConstraints = false
        button.addTarget(self, action: #selector(showInjectedView), for: .touchUpInside)
        
        return button
    }()

    init() {
        super.init(nibName: nil, bundle: nil)
        
        commonInit()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        
        commonInit()
    }
    
    override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
        super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
    
        commonInit()
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        showMeTheMoney()
    }

    func commonInit() {
        view.backgroundColor = .white
        view.addSubview(button)
        view.frame = CGRect(x: 20, y: 50, width: 375, height: 600)

        button.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -10).isActive = true
        button.topAnchor.constraint(equalTo: view.topAnchor, constant: 10).isActive = true

        myManager = setupMyView()
    }

    func showMeTheMoney() {
        guard let manager = myManager else { return }

        manager.doSomething(withSring: "some fun stuff")
        print("\(manager.count)")
        print("\(manager.count)")
        print("\(manager.count)")
    }
    
    func showInjectedView() {
        showView()
    }

}

let vc = SomeViewController()

PlaygroundPage.current.liveView = vc.view
PlaygroundPage.current.needsIndefiniteExecution = true