Operation.Swift

//
//  Operation.swift
//
//  Created by Jeremy Conkin on 1/29/16.
//

import Foundation

/**
 NSOperation with convenience for setting KVO states so that operations are
 marked complete by their queues
 */
class Operation: NSOperation {
    
    /**
     Internal state that has a corresponding KVO property in NSOperation
     
     - Ready:		NSOperation.ready
     - Executing:	NSOperation.executing
     - Finished:		NSOperation.finished
     */
    enum NSOperationState : String {
        case Ready = "isReady"
        case Executing = "isExecuting"
        case Finished = "isFinished"
    }
    
    /// Internal state that corresponds to the parent NSOperation state
    var state = NSOperationState.Ready {
        willSet {
            willChangeValueForKey(newValue.rawValue)
            willChangeValueForKey(state.rawValue)
        }
        didSet {
            didChangeValueForKey(oldValue.rawValue)
            didChangeValueForKey(state.rawValue)
        }
    }
    
    // MARK: NSOperation property overrides
    override var ready: Bool {
        return super.ready && state == .Ready
    }
    
    override var executing: Bool {
        return state == .Executing
    }
    
    override var finished: Bool {
        return state == .Finished
    }
    
    override var asynchronous: Bool {
        return true
    }
    
    // MARK: NSOperation method overrides
    override func start() {
        
        if cancelled {
            state = NSOperationState.Finished
            return
        }
        
        super.start()
    }
}