/*

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

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    A state used by `SceneLoader` to indicate that the loader is currently downloading on demand resources.

*/

import GameplayKit

class SceneLoaderDownloadingResourcesState: GKState {

    // MARK: Properties

    unowned let sceneLoader: SceneLoader

    /// Optionally progress directly to preparing state when download completes.

    var enterPreparingStateWhenFinished = false

    // MARK: Initialization

    init(sceneLoader: SceneLoader) {

        self.sceneLoader = sceneLoader

    }

    // MARK: GKState Life Cycle

    override func didEnter(from previousState: GKState?) {

        super.didEnter(from: previousState)

        // Clear any previous errors, and begin downloading the scene's resources. 

        sceneLoader.error = nil

        beginDownloadingScene()

    }

    override func isValidNextState(_ stateClass: AnyClass) -> Bool {

        switch stateClass {

            case is SceneLoaderDownloadFailedState.Type, is SceneLoaderResourcesAvailableState.Type, is SceneLoaderPreparingResourcesState.Type:

                return true

            default:

                return false

        }

    }

    // MARK: Downloading Actions

    /// Downloads the scene into local storage.

    private func beginDownloadingScene() {

        /*

            Create a new bundle request every time downloading needs to begin 

            because `NSBundleResourceRequest`s are single use objects.

        */

        let bundleResourceRequest = NSBundleResourceRequest(tags: sceneLoader.sceneMetadata.onDemandResourcesTags)

        // Hold onto the new resource request. 

        sceneLoader.bundleResourceRequest = bundleResourceRequest

        // Begin downloading the on demand resources.

        bundleResourceRequest.beginAccessingResources { error in

            // Progress to the next appropriate state from the main queue.

            DispatchQueue.main.async {

                if let error = error {

                    // Release the resources because we'll need to start a new request.

                    bundleResourceRequest.endAccessingResources()

                    // Set the error on the sceneLoader. 

                    self.sceneLoader.error = error

                    self.stateMachine!.enter(SceneLoaderDownloadFailedState.self)

                }

                else if self.enterPreparingStateWhenFinished {

                    // If requested, proceed to the preparing state immediately.

                    self.stateMachine!.enter(SceneLoaderPreparingResourcesState.self)

                }

                else {

                    self.stateMachine!.enter(SceneLoaderResourcesAvailableState.self)

                }

            }

        }

    }

}