How to Build a Posture Reminder App in SwiftUI

import SwiftData
import Foundation

@Model
final class PostureSchedule {
    var isEnabled: Bool
    var intervalMinutes: Int    // e.g. 20, 30, 45, 60
    var startHour: Int          // 0–23, e.g. 9 for 9 am
    var endHour: Int            // 0–23, e.g. 18 for 6 pm
    var reminderMessage: String

    init(
        isEnabled: Bool = true,
        intervalMinutes: Int = 30,
        startHour: Int = 9,
        endHour: Int = 18,
        reminderMessage: String = "Sit up straight and roll your shoulders back."
    ) {
        self.isEnabled = isEnabled
        self.intervalMinutes = intervalMinutes
        self.startHour = startHour
        self.endHour = endHour
        self.reminderMessage = reminderMessage
    }
}

struct ContentView: View {
    @Query private var schedules: [PostureSchedule]
    @Environment(\.modelContext) private var ctx

    private var s: PostureSchedule {
        schedules.first ?? { let n = PostureSchedule(); ctx.insert(n); return n }()
    }

    var body: some View {
        NavigationStack {
            Form {
                Section("Reminders") {
                    Toggle("Enabled", isOn: Bindable(s).isEnabled)
                    Picker("Interval", selection: Bindable(s).intervalMinutes) {
                        ForEach([10, 20, 30, 45, 60], id: \.self) { Text("Every \($0) min").tag($0) }
                    }
                }
                Section("Active hours") {
                    Picker("From", selection: Bindable(s).startHour) {
                        ForEach(6..<22) { Text("\($0):00").tag($0) }
                    }
                    Picker("Until", selection: Bindable(s).endHour) {
                        ForEach(7..<23) { Text("\($0):00").tag($0) }
                    }
                }
            }
            .navigationTitle("Posture Reminder")
            .onChange(of: s.intervalMinutes) { _, _ in
                Task { await NotificationScheduler.shared.scheduleRepeating(
                    every: s.intervalMinutes, from: s.startHour, to: s.endHour) }
            }
        }
    }
}

@MainActor
final class NotificationScheduler {
    static let shared = NotificationScheduler()
    private let center = UNUserNotificationCenter.current()

    func requestPermission() async -> Bool {
        (try? await center.requestAuthorization(options: [.alert, .sound])) ?? false
    }

    func scheduleRepeating(every minutes: Int, from start: Int, to end: Int) async {
        await center.removeAllPendingNotificationRequests()
        let content = UNMutableNotificationContent()
        content.title = "Posture check"
        content.body  = "Sit up straight and roll your shoulders back."
        content.sound = .default
        var count = 0
        for hour in start..