Counter.swift

import Foundation

struct Counter {

    private var start: Double?
    private var totalCount: Double = 0
    private var incrementBy: Double

    var isCounterRunning: Bool {
        return start != nil
    }

    var incrementedCount: Double {
        return totalCount + (start.map{ _ in incrementBy} ?? 0)
    }

    mutating func startCounter() {
        start = 1
    }

    mutating func pauseCounter() {
        totalCount = incrementedCount
        start = nil
    }

    mutating func resetCounter() {
        start = nil
        totalCount = 0
    }
}