Simple TapTempo class for Swift

gistfile1.swift

class DTTapTempo {
    private let timeOutInterval: NSTimeInterval
    private let minTaps: Int
    private var taps: [NSDate] = []
    
    init(timeOut: NSTimeInterval, minimumTaps: Int) {
        timeOutInterval = timeOut
        minTaps = minimumTaps
    }
    
    func addTap() -> Double? {
        let thisTap = NSDate()
        
        if let lastTap = taps.last {
            if thisTap.timeIntervalSinceDate(lastTap) > timeOutInterval {
                taps.removeAll()
            }
        }
        
        taps.append(thisTap)
        guard taps.count >= minTaps else { return nil }
        guard let firstTap = taps.first else { return nil }
        
        let avgIntervals = thisTap.timeIntervalSinceDate(firstTap) / Double(taps.count - 1)
        return 60.0 / avgIntervals
    }
}