/*

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

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 The RootViewControllerDataSource manages a list of country codes and their flags and provides instances of `DataViewController` to the `RootViewController`'s `UIPageViewController`.

*/

import UIKit

import GameKit

class RootViewControllerDataSource: NSObject, UIPageViewControllerDataSource {

    // MARK: Properties

    private let regionCodes: [String]

    private let cachedDataViewControllers = NSCache<NSString, DataViewController>()

    private let storyboard: UIStoryboard

    var numberOfFlags: Int {

        return regionCodes.count

    }

    // MARK: Initialization

    init(storyboard: UIStoryboard) {

        self.storyboard = storyboard

        // Create a random array of region codes.

        regionCodes = GKRandomSource.sharedRandom().arrayByShufflingObjects(in: Locale.isoRegionCodes) as! [String]

        super.init()

    }

    // MARK: UIPageViewControllerDataSource

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

        guard let dataViewController = viewController as? DataViewController else { return nil }

        guard var index = indexOfViewController(dataViewController), index > 0 else { return nil }

        index -= 1

        return self.viewController(at: index)

    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {

        guard let dataViewController = viewController as? DataViewController else { return nil }

        guard var index = indexOfViewController(dataViewController), index < regionCodes.count - 1 else { return nil }

        index += 1

        return self.viewController(at: index)

    }

    // MARK: Convenience

    func viewController(at index: Int) -> DataViewController? {

        guard regionCodes.count > 0 && index < regionCodes.count else { return nil }

        let regionCode = regionCodes[index]

        // Return the data view controller for the given index.

        if let dataViewController = cachedDataViewControllers.object(forKey: regionCode as NSString) {

            return dataViewController

        }

        // Create a new view controller and pass suitable data.

        let dataViewController = storyboard.instantiateViewController(withIdentifier: "DataViewController") as! DataViewController

        dataViewController.regionCode = regionCodes[index]

        // Cache the view controller before returning it.

        cachedDataViewControllers.setObject(dataViewController, forKey: regionCode as NSString)

        return dataViewController

    }

    func indexOfViewController(_ viewController: DataViewController) -> Int? {

        guard let regionCode = viewController.regionCode else { return nil }

        return regionCodes.index(of: regionCode)

    }

}