// The whole point of this experiment is to test various transition techniques.

import UIKit

enum PickWhichExperimentToRun {
    case regular    // call UIViewController.transition
    case brutal     // no animation
    case animated   // simple UIView.animate
    case transition // not UIViewController.transition but UIView's one
}

var yourChoice: PickWhichExperimentToRun = .animated

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

        window = UIWindow(frame: UIScreen.main.bounds)

        window?.rootViewController = Experiment()
        window?.rootViewController?.title = "parent"

        window?.makeKeyAndVisible()

        return true
    }
}

class ViewController: UIViewController {

    func log(_ message: String = #function, comment: String? = nil) {
        print("\(type(of: self))[\(title ?? "")].\(message)\( comment == nil ? "" : " :: \(comment!)")")
    }

    override func didMove(toParentViewController parent: UIViewController?) {
        super.didMove(toParentViewController: parent)
        log()
    }

    override func willMove(toParentViewController parent: UIViewController?) {
        super.willMove(toParentViewController: parent)
        log()
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        log()
    }

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

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

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

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

class Experiment : ViewController {

    let vc1 = ViewController()
    let vc2 = ViewController()

    var current: UIViewController? = nil

    override func viewDidLoad() {
        super.viewDidLoad()

        vc1.title = "vc1"
        vc2.title = "vc2"

        vc1.view.backgroundColor = .red
        vc2.view.backgroundColor = .blue

        addChildViewController(vc1)
        addChildViewController(vc2)

        view.addSubview(vc1.view)
        current = vc1

        // on tap, trigger transition
        let tapRecognizer = UITapGestureRecognizer(target: self, action: #selector(onTap(sender:)))
        view.addGestureRecognizer(tapRecognizer)
    }

    @objc func onTap(sender: UITapGestureRecognizer) {
        log(comment: "\(yourChoice)")

        guard let current = current else {
            // ignore the tap
            return
        }

        let nextVC: ViewController
        if current === vc1 {
            nextVC = vc2
        } else {
            nextVC = vc1
        }

        runExperiment(from:current, to:nextVC)
        self.current = nextVC
    }

    func runExperiment(from current: UIViewController, to nextVC: UIViewController) {
        switch yourChoice {
        case .regular:
            transition(from: current, to: nextVC, duration: 0.8, options: .transitionCrossDissolve, animations: nil)
        case .brutal:
            current.view.removeFromSuperview()
            view.addSubview(nextVC.view)
        case .animated:
            let inFrame = view.bounds
            let outLeftFrame = view.bounds.offsetBy(dx: -view.bounds.width, dy: 0)
            let outRightFrame = view.bounds.offsetBy(dx: view.bounds.width, dy: 0)

            nextVC.view.frame = outLeftFrame
            view.addSubview(nextVC.view)

            UIView.animate(withDuration: 0.8, animations: {
                current.view.frame = outRightFrame
                nextVC.view.frame = inFrame
            }, completion: {_ in
                current.view.removeFromSuperview()
            })
        case .transition:
            UIView.transition(from: current.view, to: nextVC.view, duration: 0.8, options: .transitionCrossDissolve, completion: nil)
        }
    }

}