AsynchronousOperation.swift

//
//  AsynchronousOperation.swift
//  Primer
//
//  Created by Alex Usbergo on 18/10/15.
//  Copyright © 2015 Alex Usbergo. All rights reserved.
//

import Foundation

@objc public class AsynchronousOperationContext: NSObject {
    
    ///The user info for the operation
    @objc public var userInfo = [String: AnyObject]()
    @objc public var error: NSError?
}

///Base class for a asynchronous operation.
///Subclasses are expected to override the 'execute' function and call
///the function 'finish' when they're done with their task
@objc public class AsynchronousOperation: NSOperation {

    ///The operation context
     public typealias Context = AsynchronousOperationContext
        
    //property overrides
    override public var asynchronous: Bool { return true }
    override public var concurrent: Bool { return true }
    override public var executing: Bool { return __executing }
    override public var finished: Bool { return __finished }
    
    ///The context for this operation.
    ///Useful to pass data from/to dependant operations
    @objc public let context: Context?
    
    init(withContext context: Context? = nil) {
        self.context = context
    }
    
    //__ to avoid name clash with the superclass
    private var __executing = false {
        willSet { willChangeValueForKey("isExecuting") }
        didSet  { didChangeValueForKey("isExecuting") }
    }
    
    private var __finished = false {
        willSet { willChangeValueForKey("isFinished") }
        didSet  { didChangeValueForKey("isFinished") }
    }
    
    override public func start() {
        __executing = true
        execute()
    }
    
    ///Subclasses are expected to override the 'execute' function and call
    ///the function 'finish' when they're done with their task
    @objc public func execute() {
        fatalError("Your subclass must override this")
    }
    
    ///This function should be called inside 'execute' when the task for this 
    ///operation is completed
    @objc public func finish() {
        __executing = false
        __finished = true
    }
}

///Shorthand for creating an asynchronous operation with a given block
///Remember to call the 'finish' function on the operation within the block passed as argument
@objc public class AsynchronousBlockOperation: AsynchronousOperation {
    
    ///The operation execution block
    public typealias ExecutionBlock = ((operation: AsynchronousBlockOperation, context: Context?) -> Void)
    
    @objc public let block: ExecutionBlock
    
    init(withContext context: Context?, block: ExecutionBlock) {
        self.block = block
        super.init(withContext: context)
    }
    
    public override func execute() {
        self.block(operation: self, context: self.context)
    }
    
}