/*

 Copyright (C) 2016 Apple Inc. All Rights Reserved.

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 The `RootViewController` manages an embedded `UIPageViewController` to display a randomized list of flags provided by a `RootViewControllerDataSource`.

*/

import UIKit

class RootViewController: UIViewController, UIPageViewControllerDelegate {

    // MARK: Properties

    private var pageViewController: UIPageViewController?

    private var currentIndex = 0

    private lazy var dataSource: RootViewControllerDataSource = {

        let controller = RootViewControllerDataSource(storyboard: self.storyboard!)

        return controller

    }()

    // MARK: UIViewController

    override func viewDidLoad() {

        super.viewDidLoad()

        pageViewController = childViewControllers[0] as? UIPageViewController

        guard let pageViewController = pageViewController else { return }

        guard let startingViewController = dataSource.viewController(at: 0) else { return }

        let viewControllers = [startingViewController]

        pageViewController.setViewControllers(viewControllers, direction: .forward, animated: false, completion: nil)

        pageViewController.dataSource = dataSource

        pageViewController.didMove(toParentViewController: self)

    }

    // MARK: Interface Builder actions

    @IBAction func forwardButtonPressed(_ sender: UIButton) {

        currentIndex += 1

        currentIndex = currentIndex % dataSource.numberOfFlags

        let viewController = dataSource.viewController(at: currentIndex)!

        pageViewController?.setViewControllers([viewController], direction: .forward, animated: true, completion: nil)

    }

    @IBAction func backButtonPressed(_ sender: UIButton) {

        currentIndex -= 1

        if currentIndex < 0 {

            currentIndex = dataSource.numberOfFlags - 1

        }

        let viewController = dataSource.viewController(at: currentIndex)!

        pageViewController?.setViewControllers([viewController], direction: .reverse, animated: true, completion: nil)

    }

}