throttle.swift

class Throttle<T>: NSObject {
    let timeout: Double
    let callback: T -> Void

    var timer: NSTimer? = nil
    var buffer: T? = nil

    init(timeout: Double, callback: T -> Void) {
        self.timeout = timeout
        self.callback = callback
    }

    deinit {
        timer?.invalidate()
    }

    func input(value: T) {
        cancel()
        buffer = value
        resetTimer()
    }

    func cancel() {
        if let timer = self.timer where timer.valid {
            timer.invalidate()
        }
        timer = nil
        buffer = nil
    }

    private func resetTimer() {
        timer = NSTimer(timeInterval: timeout, target: self, selector: #selector(fetchTimerDidFire(_:)), userInfo: nil, repeats: false)
    }

    func fetchTimerDidFire(sender: AnyObject) {
        guard let value = buffer else {
            return
        }
        callback(value)
    }
}