/*

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

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    A subclass of `Operation` that manages the loading of a `ResourceLoadableType`'s resources.

*/

import Foundation

class LoadResourcesOperation: SceneOperation, ProgressReporting {

    // MARK: Properties

    /// A class that conforms to the `ResourceLoadableType` protocol.

    let loadableType: ResourceLoadableType.Type

    let progress: Progress

    // MARK: Initialization

    init(loadableType: ResourceLoadableType.Type) {

        self.loadableType = loadableType

        progress = Progress(totalUnitCount: 1)

        super.init()

    }

    // MARK: NSOperation

    override func start() {

        // If the operation is cancelled there's nothing to do.

        guard !isCancelled else { return }

        if progress.isCancelled {

            // Ensure the operation is marked as `cancelled`.

            cancel()

            return

        }

        // Avoid reloading the resources if they are already available.

        guard loadableType.resourcesNeedLoading else {

            finish()

            return

        }

        // Mark the operation as executing.

        state = .executing

        // Begin loading the resources.

        loadableType.loadResources() { [unowned self] in

            // Mark the operation as complete once the resources are loaded.

            self.finish()

        }

    }

    func finish() {

        progress.completedUnitCount = 1

        state = .finished

    }

}