A wrapper around Timer to make it pausable. Only `invalidate` has been exposed, but other functions and properties could be exposed if needed.

PausableTimer.swift

import Foundation

public class PausableTimer {
    public var isPaused: Bool { remainingTime != nil }
    private let timer: Timer
    private var remainingTime: TimeInterval?

    public static func scheduledTimer(withTimeInterval interval: TimeInterval,
                                      block: @escaping (Timer) -> Void) -> PausableTimer {
        PausableTimer(timer: .scheduledTimer(withTimeInterval: interval, 
                                             repeats: false,
                                             block: block))
    }

    private init(timer: Timer) {
        self.timer = timer
    }

    public func pause() {
        guard timer.fireDate > Date.now else { return }
        remainingTime = timer.fireDate.timeIntervalSince(Date.now)
        timer.fireDate = .distantFuture
    }

    public func resume() {
        guard let remainingTime else { return }
        timer.fireDate = Date(timeIntervalSinceNow: remainingTime)
        self.remainingTime = nil
    }

    public func invalidate() {
        timer.invalidate()
    }
}