Sesame-iOS/Sesame/ContentView.swift

import SwiftUI
import CryptoKit

let server = Client(server: URL(string: "https://christophhagen.de/sesame/")!)

struct ContentView: View {

    @AppStorage("counter")
    var nextMessageCounter: Int = 0
    
    @State
    var state: ClientState = .noKeyAvailable

    @State
    private var timer: Timer?

    @State
    private var hasActiveRequest = false

    @State
    private var responseTime: Date? = nil

    var isPerformingRequests: Bool {
        hasActiveRequest ||
        state == .waitingForResponse
    }

    var buttonBackground: Color {
        state.allowsAction ?
            .white.opacity(0.2) :
            .gray.opacity(0.2)
    }

    let buttonBorderWidth: CGFloat = 3

    var buttonColor: Color {
        state.allowsAction ? .white : .gray
    }

    private let buttonWidth: CGFloat = 250

    var body: some View {
        GeometryReader { geo in
            VStack(spacing: 20) {
                Spacer()
                if state.requiresDescription {
                    Text(state.description)
                        .padding()
                }
                Button(state.actionText, action: mainButtonPressed)
                    .frame(width: buttonWidth, height: buttonWidth, alignment: .center)
                    .background(buttonBackground)
                    .cornerRadius(buttonWidth / 2)
                    .overlay(RoundedRectangle(cornerRadius: buttonWidth / 2).stroke(lineWidth: buttonBorderWidth).foregroundColor(buttonColor))
                    .foregroundColor(buttonColor)
                    .font(.title)
                    .disabled(!state.allowsAction)
                    .padding(.bottom, (geo.size.width-buttonWidth) / 2)
            }
            .onAppear {
                if KeyManagement.hasKey {
                    state = .requestingStatus
                }
                startRegularStatusUpdates()
            }
            .onDisappear {
                endRegularStatusUpdates()
            }
            .frame(width: geo.size.width, height: geo.size.height)
            .background(state.color)
            .animation(.easeInOut, value: state.color)
        }
    }
    
    func mainButtonPressed() {
        guard let key = KeyManagement.key?.remote else {
            generateKey()
            return
        }
        sendMessage(using: key)
    }
    
    func sendMessage(using key: SymmetricKey) {
        let count = UInt32(nextMessageCounter)
        let now = Date()
        let content = Message.Content(
            time: now.timestamp,
            id: count)
        let message = content.authenticate(using: key)
        state = .waitingForResponse
        print("Sending message \(count)")
        Task {
            let (newState, message) = try await server.send(message)
            responseTime = now
            state = newState
            if let message = message {
                processResponse(message, sendTime: now)
            }
        }
    }

    private func processResponse(_ message: Message, sendTime: Date) {
        guard let key = KeyManagement.key?.device else {
            return
        }
        guard message.isValid(using: key) else {
            return
        }
        nextMessageCounter = Int(message.content.id)
        print("Next counter is \(message.content.id)")
        let now = Date()
        let total = now.timeIntervalSince(sendTime)
        print("Total time: \(Int(total * 1000)) ms")
        let deviceTime = Date(timestamp: message.content.time)
        let time1 = deviceTime.timeIntervalSince(sendTime)
        let time2 = now.timeIntervalSince(deviceTime)
        if time1 < 0 {
            print("Device time behind by at least \(Int(-time1 * 1000)) ms behind")
        } else if time2 < 0 {
            print("Device time behind by at least \(Int(-time2 * 1000)) ms ahead")
        } else {
            print("Device time synchronized")
        }
    }

    private func startRegularStatusUpdates() {
        guard timer == nil else {
            return
        }
        DispatchQueue.main.async {
            timer = Timer.scheduledTimer(withTimeInterval: 5, repeats: true, block: checkDeviceStatus)
            timer!.fire()
        }
    }

    private func endRegularStatusUpdates() {
        timer?.invalidate()
        timer = nil
    }
    
    func checkDeviceStatus(_ timer: Timer) {
        guard !hasActiveRequest else {
            return
        }
        hasActiveRequest = true
        print("Checking device status")
        Task {
            let newState = await server.deviceStatus()
            hasActiveRequest = false
            switch state {
            case .noKeyAvailable:
                return
            case .requestingStatus, .deviceNotAvailable, .ready:
                state = newState
            case .waitingForResponse:
                return
            case .messageRejected, .openSesame, .internalError:
                guard let time = responseTime else {
                    state = newState
                    return
                }
                responseTime = nil
                // Wait at least 5 seconds after these states have been reached before changing the
                let elapsed = Date.now.timeIntervalSince(time)
                guard elapsed < 5 else {
                    state = newState
                    return
                }
                let secondsToWait = Int(elapsed.rounded(.up))
                DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(secondsToWait)) {
                    state = newState
                }
            }
        }
    }
    
    func generateKey() {
        print("Regenerate key")
        KeyManagement.generateNewKeys()
        state = .requestingStatus
    }
    
    func shareKey() {
        
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
            .previewDevice("iPhone 8")
    }
}

extension Date {

    var timestamp: UInt32 {
        UInt32(timeIntervalSince1970.rounded())
    }

    init(timestamp: UInt32) {
        self.init(timeIntervalSince1970: TimeInterval(timestamp))
    }
}