WWDCCountdownContentView.swift

import SwiftUI

struct ContentView: View {
    @State var days = 0
    @State var hours = 0
    @State var minutes = 0
    @State var seconds = 0
    static let wwdc = Date(timeIntervalSince1970: 1654534800)
    let timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()
    
    var body: some View {
        VStack {
            Text("\(days) days")
                .font(.largeTitle.monospacedDigit())
            Text("\(hours) hours")
                .font(.title.monospacedDigit())
            Text("\(minutes) minutes")
                .font(.title2.monospacedDigit())
            Text("\(seconds) seconds")
                .font(.title3.monospacedDigit())
        }
            .onReceive(timer) { input in
                
                let difference = Self.wwdc.timeIntervalSince1970 - input.timeIntervalSince1970
                let doubleDays = difference / 86400
                let truncatedDays = Int(doubleDays)
                days = truncatedDays
                let doubleHours = Double((doubleDays - Double(truncatedDays)) * 24)
                let truncatedHours = Int(doubleHours)
                hours = Int(doubleHours)
                let doubleMinutes = Double((doubleHours - Double(truncatedHours)) * 60)
                let truncatedMinutes = Int(doubleMinutes)
                minutes = truncatedMinutes
                let doubleSeconds = Double((doubleMinutes - Double(truncatedMinutes)) * 60)
                let truncatedSeconds = Int(doubleSeconds)
                seconds = truncatedSeconds
        }
    }
}