iOS Native Mobile Engineering & Apple Platform Architecture Masterclass

import SwiftUI

// 1. Immutable Domain Model
struct UserProfile: Identifiable, Codable {
    let id: UUID
    let name: String
    let email: String
}

// 2. Thread-Safe ViewModel Bound to Main Thread
@MainActor
final class UserProfileViewModel: ObservableObject {
    enum State {
        case idle
        case loading
        case loaded(UserProfile)
        case error(String)
    }

    @Published private(set) var state: State = .idle

    func fetchProfile() async {
        state = .loading
        do {
            let url = URL(string: "https://api.example.com/v1/user/me")!
            let (data, response) = try await URLSession.shared.data(from: url)

            guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200 else {
                state = .error("Invalid server response")
                return
            }

            let profile = try JSONDecoder().decode(UserProfile.self, from: data)
            state = .loaded(profile)
        } catch {
            if !Task.isCancelled {
                state = .error(error.localizedDescription)
            }
        }
    }
}

// 3. Declarative SwiftUI View
struct UserProfileView: View {
    @StateObject private var viewModel = UserProfileViewModel()

    var body: some View {
        NavigationStack {
            Group {
                switch viewModel.state {
                case .idle, .loading:
                    ProgressView("Loading profile...")
                case .loaded(let profile):
                    VStack(alignment: .leading, spacing: 12) {
                        Text(profile.name)
                            .font(.title2.bold())
                        Text(profile.email)
                            .font(.subheadline)
                            .foregroundStyle(.secondary)
                        Spacer()
                    }
                    .padding()
                case .error(let message):
                    ContentUnavailableView("Unable to Load", systemImage: "wifi.exclamationmark", description: Text(message))
                }
            }
            .navigationTitle("Account")
            .task {
                await viewModel.fetchProfile()
            }
        }
    }
}