cancelable_delayed_block.swift

typealias dispatch_cancelable_closure = (cancel : Bool) -> Void


/** 
 * Delay the execution of the block by time seconds
 *
 * With help from Waam at http://stackoverflow.com/questions/24034544/dispatch-after-gcd-in-swift/24318861#24318861
 */
func delay(time:NSTimeInterval, closure:()->Void) ->  dispatch_cancelable_closure? {

    func dispatch_later(clsr:()->Void) {
        dispatch_after(
            dispatch_time(
                DISPATCH_TIME_NOW,
                Int64(time * Double(NSEC_PER_SEC))
            ),
            dispatch_get_main_queue(), clsr)
    }

    var closure:dispatch_block_t? = closure
    var cancelableClosure:dispatch_cancelable_closure?

    let delayedClosure:dispatch_cancelable_closure = { cancel in
        if closure != nil {
            if (cancel == false) {
                dispatch_async(dispatch_get_main_queue(), closure!);
            }
        }
        closure = nil
        cancelableClosure = nil
    }

    cancelableClosure = delayedClosure

    dispatch_later {
        if let delayedClosure = cancelableClosure {
            delayedClosure(cancel: false)
        }
    }

    return cancelableClosure;
}

func cancel_delay(closure:dispatch_cancelable_closure?) {

    if closure != nil {
        closure!(cancel: true)
    }
}


// Usage
let retVal = delay(2.0) {
    println("Later")
}
delay(1.0) {
    cancel_delay(retVal)
}