/*

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

See LICENSE.txt for this sample’s licensing information

Abstract:

A subclass of `NSOperation` that maps the different states of an `NSOperation`

        to an explicit `state` enum.

*/

import Foundation

class SceneOperation: Operation {

    // MARK: Types

    /**

        Using the `@objc` prefix exposes this enum to the ObjC runtime,

        allowing the use of `dynamic` on the `state` property.

    */

    @objc enum State: Int {

        /// The `Operation` is ready to begin execution.

        case ready

        /// The `Operation` is executing.

        case executing

        /// The `Operation` has finished executing.

        case finished

        /// The `Operation` has been cancelled.

        case cancelled

    }

    // MARK: Properties

    /// Marking `state` as dynamic allows this property to be key-value observed.

    dynamic var state = State.ready

    // MARK: NSOperation

    override var isExecuting: Bool {

        return state == .executing

    }

    override var isFinished: Bool {

        return state == .finished

    }

    override var isCancelled: Bool {

        return state == .cancelled

    }

    /**

        Add the "state" key to the key value observable properties of `NSOperation`.

    */

    class func keyPathsForValuesAffectingIsReady() -> Set<String> {

        return ["state"]

    }

    class func keyPathsForValuesAffectingIsExecuting() -> Set<String> {

        return ["state"]

    }

    class func keyPathsForValuesAffectingIsFinished() -> Set<String> {

        return ["state"]

    }

    class func keyPathsForValuesAffectingIsCancelled() -> Set<String> {

        return ["state"]

    }

}