SwiftUI Schedule Countdown Timer - Pause & Start - timer

Question

I'm trying to make Clock(actual time) / Timer (CountDown) to my app.. I know my solution is kind of rough, but everything works kind of ok BUT. When I pause my Countdown and then start it again - In the first time Counter adds time (for like a second) that passed since i press Pause button and afterwards loads my timeCounter value that i saved and continues counting down.. Why? Also if you have better smoother solution I will be very pleased.. THANKS!
import SwiftUI
struct Clock : View {
#State private var nowDate: Date = Date()
#State private var referenceDate: Date = Date()
#State private var display: Bool = true
#State private var updateTimer: Timer?
#State private var timeCounter: Double = 0
#State private var timerRunning: Bool = false
var body: some View {
VStack {
Button(action: {
self.display.toggle()
}) {
Text(display ? "COUNTDOWN" : "TIME")
}
Text(display ? "\(timeString(date: nowDate))" : "\(countDownString(for: referenceDate))")
HStack {
Button(action: {
self.display = false
self.timeCounter = 10
self.referenceDate = Date(timeIntervalSinceNow: self.timeCounter)
}) {
Text("10")
}
}
Button(action: {
if self.timerRunning {
self.referenceDate = Date(timeIntervalSinceNow: self.timeCounter)
self.startTimer()
self.timerRunning.toggle()
} else {
self.updateTimer?.invalidate()
self.timerRunning.toggle()
}
}) {
Text(timerRunning ? "START" : "PAUSE")
}
}
.onAppear {
self.startTimer()
}
}
//MARK: Timer
func startTimer() {
self.updateTimer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { _ in
self.nowDate = Date()
if self.referenceDate.distance(to: self.nowDate) >= 0 {
self.referenceDate = Date(timeIntervalSinceNow: 0)
self.display = true
}
self.timeCounter -= 1
}
}
//MARK: - CountDown Timer
func countDownString(for date: Date) -> String {
let calendar = Calendar(identifier: .gregorian)
let components = calendar
.dateComponents([.hour, .minute, .second],
from: nowDate,
to: referenceDate)
return String(format: "%02d:%02d:%02d",
components.hour ?? 00,
components.minute ?? 00,
components.second ?? 00)
}
//MARK: - Clock Timer
var timeFormat: DateFormatter {
let formatter = DateFormatter()
formatter.dateFormat = "HH:mm:ss"
return formatter
}
func timeString(date: Date) -> String {
let time = timeFormat.string(from: date)
return time
}
}

Answer 1

Ive seen lots of complicated ways to do this on the net.
New in iOS 14:
let closeDate = Date(timeIntervalSinceNow: 60.0)
Text(closeDate, style: .relative)

Answer 2

maybe you need Timer publisher
https://www.hackingwithswift.com/quick-start/swiftui/how-to-use-a-timer-with-swiftui