UITabBarController inside Master View of UISplitViewController

SplitViewController.swift

//
//  SplitViewController.swift
//  Gist
//
//  Created by Maxim Potapov on 17/12/2017.
//  Copyright © 2017 Maxim Potapov. All rights reserved.
//

import UIKit

protocol MasterViewController {
    var collapseDetailViewController: Bool { get set }
}

protocol DetailViewController {}

final class SplitViewController: UISplitViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        delegate = self
        detail.topViewController!.navigationItem.leftBarButtonItem = displayModeButtonItem
        preferredDisplayMode = UIDevice.current.userInterfaceIdiom == .pad ? .allVisible : .automatic
    }

}

extension SplitViewController: UISplitViewControllerDelegate {

    private var master: UITabBarController {
        return viewControllers.first as! UITabBarController
    }

    private var detail: UINavigationController {
        return viewControllers.last as! UINavigationController
    }

    func splitViewController(_ splitViewController: UISplitViewController, showDetail vc: UIViewController, sender: Any?) -> Bool {
        guard splitViewController.isCollapsed else { return false }
        guard let selected = master.selectedViewController as? UINavigationController else { return false }
        let controller: UIViewController
        if let navigation = vc as? UINavigationController {
            controller = navigation.topViewController!
        } else {
            controller = vc
        }
        controller.hidesBottomBarWhenPushed = true
        selected.pushViewController(controller, animated: true)
        return true
    }

    func splitViewController(_ splitViewController: UISplitViewController, collapseSecondary secondaryViewController: UIViewController, onto primaryViewController: UIViewController) -> Bool {
        guard let secondaryAsNavController = secondaryViewController as? UINavigationController else { return false }
        guard let topAsDetailController = secondaryAsNavController.topViewController, topAsDetailController is DetailViewController else { return false }
        guard let tabBar = primaryViewController as? UITabBarController else { return false }
        for controller in tabBar.viewControllers! {
            guard let navigation = controller as? UINavigationController else { continue }
            guard let master = navigation.topViewController as? MasterViewController, master.collapseDetailViewController == false else { continue }
            topAsDetailController.hidesBottomBarWhenPushed = true
            navigation.pushViewController(topAsDetailController, animated: false)
            return true
        }
        return false
    }

    func splitViewController(_ splitViewController: UISplitViewController, separateSecondaryFrom primaryViewController: UIViewController) -> UIViewController? {
        guard let selected = master.selectedViewController as? UINavigationController else { return nil }
        guard selected.topViewController is DetailViewController else { return nil }
        guard let details = selected.popViewController(animated: false) else { return nil }
        return UINavigationController(rootViewController: details)
    }

}