UIViewController+AddBehaviors.swift

//
//  UIViewController+addBehaviors.swift
//  ExampleMVVM
//
//  Created by Oleh Kudinov on 03/04/2020.
//
// View controller lifecycle behaviors https://irace.me/lifecycle-behaviors
// Behaviors are very useful to reuse logic for cases like Keyboard Behaviour.
// Where ViewController on didLoad adds behaviour which observes keyboard frame
// and scrollView content inset changes based on keyboard frame.

import UIKit

protocol ViewControllerLifecycleBehavior {
    func viewDidLoad(viewController: UIViewController)
    func viewWillAppear(viewController: UIViewController)
    func viewDidAppear(viewController: UIViewController)
    func viewWillDisappear(viewController: UIViewController)
    func viewDidDisappear(viewController: UIViewController)
    func viewWillLayoutSubviews(viewController: UIViewController)
    func viewDidLayoutSubviews(viewController: UIViewController)
}
// Default implementations
extension ViewControllerLifecycleBehavior {
    func viewDidLoad(viewController: UIViewController) {}
    func viewWillAppear(viewController: UIViewController) {}
    func viewDidAppear(viewController: UIViewController) {}
    func viewWillDisappear(viewController: UIViewController) {}
    func viewDidDisappear(viewController: UIViewController) {}
    func viewWillLayoutSubviews(viewController: UIViewController) {}
    func viewDidLayoutSubviews(viewController: UIViewController) {}
}

extension UIViewController {
    /*
     Add behaviors to be hooked into this view controller’s lifecycle.

     This method requires the view controller’s view to be loaded, so it’s best to call
     in `viewDidLoad` to avoid it being loaded prematurely.

     - parameter behaviors: Behaviors to be added.
     */
    func addBehaviors(_ behaviors: [ViewControllerLifecycleBehavior]) {
        let behaviorViewController = LifecycleBehaviorViewController(behaviors: behaviors)

        addChild(behaviorViewController)
        view.addSubview(behaviorViewController.view)
        behaviorViewController.didMove(toParent: self)
    }

    private final class LifecycleBehaviorViewController: UIViewController, UIGestureRecognizerDelegate {
        private let behaviors: [ViewControllerLifecycleBehavior]

        // MARK: - Lifecicle

        init(behaviors: [ViewControllerLifecycleBehavior]) {
            self.behaviors = behaviors

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

        required init?(coder aDecoder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }

        override func viewDidLoad() {
            super.viewDidLoad()

            view.isHidden = true

            applyBehaviors { behavior, viewController in
                behavior.viewDidLoad(viewController: viewController)
            }
        }

        override func viewWillAppear(_ animated: Bool) {
            super.viewWillAppear(animated)

            applyBehaviors { behavior, viewController in
                behavior.viewWillAppear(viewController: viewController)
            }
        }

        override func viewDidAppear(_ animated: Bool) {
            super.viewDidAppear(animated)

            applyBehaviors { behavior, viewController in
                behavior.viewDidAppear(viewController: viewController)
            }
        }

        override func viewWillDisappear(_ animated: Bool) {
            super.viewWillDisappear(animated)

            applyBehaviors { behavior, viewController in
                behavior.viewWillDisappear(viewController: viewController)
            }
        }

        override func viewDidDisappear(_ animated: Bool) {
            super.viewDidDisappear(animated)

            applyBehaviors { behavior, viewController in
                behavior.viewDidDisappear(viewController: viewController)
            }
        }

        override func viewWillLayoutSubviews() {
            super.viewWillLayoutSubviews()

            applyBehaviors { behavior, viewController in
                behavior.viewWillLayoutSubviews(viewController: viewController)
            }
        }

        override func viewDidLayoutSubviews() {
            super.viewDidLayoutSubviews()

            applyBehaviors { behavior, viewController in
                behavior.viewDidLayoutSubviews(viewController: viewController)
            }
        }

        // MARK: - Private

        private func applyBehaviors(body: (_ behavior: ViewControllerLifecycleBehavior, _ viewController: UIViewController) -> Void) {
            guard let parent = parent else { return }

            for behavior in behaviors {
                body(behavior, parent)
            }
        }
    }
}