/*

    Copyright (C) 2017 Apple Inc. All Rights Reserved.

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    A `UICollectionViewController` who's cells each contain a `UICollectionView`. This class demonstrates how to ensure focus behaves correctly in this situation.

*/

import UIKit

class CollectionViewContainerViewController: UICollectionViewController {

    // MARK: Properties

    private static let minimumEdgePadding = CGFloat(90.0)

    private let dataItemsByGroup: [[DataItem]] = {

        return DataItem.Group.allGroups.map { group in

            return DataItem.sampleItems.filter { $0.group == group }

        }

    }()

    // MARK: UIViewController

    override func viewDidLoad() {

        super.viewDidLoad()

        // Make sure their is sufficient padding above and below the content.

        guard let collectionView = collectionView, let layout = collectionView.collectionViewLayout as? UICollectionViewFlowLayout else { return }

        collectionView.contentInset.top = CollectionViewContainerViewController.minimumEdgePadding - layout.sectionInset.top

        collectionView.contentInset.bottom = CollectionViewContainerViewController.minimumEdgePadding - layout.sectionInset.bottom

    }

    // MARK: UICollectionViewDataSource

    override func numberOfSections(in collectionView: UICollectionView) -> Int {

        // Our collection view displays 1 section per group of items.

        return dataItemsByGroup.count

    }

    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {

        // Each section contains a single `CollectionViewContainerCell`.

        return 1

    }

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

        // Dequeue a cell from the collection view.

        return collectionView.dequeueReusableCell(withReuseIdentifier: CollectionViewContainerCell.reuseIdentifier, for: indexPath)

    }

    // MARK: UICollectionViewDelegate

    override func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {

        guard let cell = cell as? CollectionViewContainerCell else { fatalError("Expected to display a `CollectionViewContainerCell`.") }

        // Configure the cell.

        let sectionDataItems = dataItemsByGroup[indexPath.section]

        cell.configure(with: sectionDataItems)

    }

    override func collectionView(_ collectionView: UICollectionView, canFocusItemAt indexPath: IndexPath) -> Bool {

        /*

            Return `false` because we don't want this `collectionView`'s cells to

            become focused. Instead the `UICollectionView` contained in the cell

            should become focused.

        */

        return false

    }

}