/*

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

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    A `UITableViewController` that, when subclassed, is used as the master view of `MenuSplitViewController` instances. Each subclass specifies a mapping of segue names to perform for each static cell in its storyboard instance.

*/

import UIKit

class MenuTableViewController: UITableViewController {

    // MARK: Properties

    /**

        A matrix of segue identifiers that should be performed when a cell

        becomes focused.

        Overridden by subclasses.

    */

    var segueIdentifierMap: [[String]] {

        return [[]]

    }

    private var lastPerformedSegueIdentifier: String?

    private let delayedSeguesOperationQueue = OperationQueue()

    private static let performSegueDelay: TimeInterval = 0.1

    // MARK: UIViewController

    override func viewDidLoad() {

        super.viewDidLoad()

        /*

            Set `remembersLastFocusedIndexPath` to `true` to ensure the same row

            becomes focused whenever focus is returned to the table view.

        */

        tableView.remembersLastFocusedIndexPath = true

        /*

            Adjust the layout margins of the `tableView` to add a horizontal inset

            to the cells. This will allow for overscan on older TVs and space for

            the focus effect.

        */

        tableView.layoutMargins.left = 90

        tableView.layoutMargins.right = 20

    }

    override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {

        // Check if the requested segue is a segue contained in our mapping.

        guard segueIdentifierMap.contains(where: { $0.contains(identifier) }) else { return true }

        // Don't perform the segue if it's the same as the last performed segue.

        return identifier != lastPerformedSegueIdentifier

    }

    // MARK: UITableViewDelegate

    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {

        guard let menuSplitViewController = splitViewController as? MenuSplitViewController else { return }

        /*

            Ask the containing `MenuSplitViewController` to move the focus to the

            current detail view controller.

        */

        menuSplitViewController.updateFocusToDetailViewController()

    }

    override func tableView(_ tableView: UITableView, didUpdateFocusIn context: UITableViewFocusUpdateContext, with coordinator: UIFocusAnimationCoordinator) {

        // Check that the next focus view is a child of the table view.

        guard let nextFocusedView = context.nextFocusedView, nextFocusedView.isDescendant(of: tableView) else { return }

        guard let indexPath = context.nextFocusedIndexPath else { return }

        // Cancel any previously queued segues.

        delayedSeguesOperationQueue.cancelAllOperations()

        // Create a `BlockOperation` to perform the detail segue after a delay.

        let performSegueOperation = BlockOperation()

        let segueIdentifier = segueIdentifierMap[indexPath.section][indexPath.row]

        performSegueOperation.addExecutionBlock { [weak self, unowned performSegueOperation] in

            // Pause the block so the segue isn't immediately performed.

            Thread.sleep(forTimeInterval: MenuTableViewController.performSegueDelay)

            /*

                Check that the operation wasn't cancelled and that the segue identifier

                is different to the last performed segue identifier.

            */

            guard !performSegueOperation.isCancelled && segueIdentifier != self?.lastPerformedSegueIdentifier else { return }

            OperationQueue.main.addOperation {

                // Perform the segue to show the detail view controller.

                self?.performSegue(withIdentifier: segueIdentifier, sender: nextFocusedView)

                // Record the last performed segue identifier.

                self?.lastPerformedSegueIdentifier = segueIdentifier

                /*

                    Select the focused cell so that the table view visibly reflects

                    which detail view is being shown.

                */

                self?.tableView.selectRow(at: indexPath, animated: true, scrollPosition: .none)

            }

        }

        delayedSeguesOperationQueue.addOperation(performSegueOperation)

    }

}