@EnvironmentObject trong SwiftUI

class AppSettings: ObservableObject {
    @Published var isDarkMode = false
    @Published var language = "en"
}
 
@main
struct MyApp: App {
    @StateObject var settings = AppSettings()
    
    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(settings)
        }
    }
}

ContentView()
    .environmentObject(settings)

struct ChildView: View {
    @EnvironmentObject var settings: AppSettings
    
    var body: some View {
        Text("Dark mode: \(settings.isDarkMode ? "On" : "Off")")
    }
}

class ThemeManager: ObservableObject {
    @Published var isDarkMode = false
    @Published var accentColor = Color.blue
    
    var backgroundColor: Color {
        isDarkMode ? .black : .white
    }
    
    var textColor: Color {
        isDarkMode ? .white : .black
    }
}
 
struct RootView: View {
    @StateObject var themeManager = ThemeManager()
    
    var body: some View {
        TabView {
            HomeView()
            SettingsView()
        }
        .environmentObject(themeManager)
        .preferredColorScheme(themeManager.isDarkMode ? .dark : .light)
    }
}
 
struct HomeView: View {
    @EnvironmentObject var theme: ThemeManager
    
    var body: some View {
        VStack {
            Text("Home")
                .foregroundColor(theme.textColor)
        }
        .background(theme.backgroundColor)
    }
}
 
struct SettingsView: View {
    @EnvironmentObject var theme: ThemeManager
    
    var body: some View {
        Form {
            Toggle("Dark Mode", isOn: $theme.isDarkMode)
            
            ColorPicker("Accent Color", selection: $theme.accentColor)
        }
    }
}

class UserSession: ObservableObject {
    @Published var currentUser: User?
    @Published var isAuthenticated = false
    
    func login(email: String, password: String) async throws {
        // API call
        currentUser = User(name: "John", email: email)
        isAuthenticated = true
    }
    
    func logout() {
        currentUser = nil
        isAuthenticated = false
    }
}
 
struct AppRootView: View {
    @StateObject var session = UserSession()
    
    var body: some View {
        Group {
            if session.isAuthenticated {
                MainTabView()
            } else {
                LoginView()
            }
        }
        .environmentObject(session)
    }
}
 
struct ProfileView: View {
    @EnvironmentObject var session: UserSession
    
    var body: some View {
        VStack {
            if let user = session.currentUser {
                Text("Welcome, \(user.name)")
            }
            
            Button("Logout") {
                session.logout()
            }
        }
    }
}

class CartManager: ObservableObject {
    @Published var items: [CartItem] = []
    
    var total: Double {
        items.reduce(0) { $0 + $1.price * Double($1.quantity) }
    }
    
    var itemCount: Int {
        items.reduce(0) { $0 + $1.quantity }
    }
    
    func add(_ product: Product) {
        if let index = items.firstIndex(where: { $0.productId == product.id }) {
            items[index].quantity += 1
        } else {
            items.append(CartItem(productId: product.id, name: product.name, price: product.price, quantity: 1))
        }
    }
    
    func remove(_ item: CartItem) {
        items.removeAll { $0.id == item.id }
    }
}
 
struct ProductCard: View {
    let product: Product
    @EnvironmentObject var cart: CartManager
    
    var body: some View {
        VStack {
            Text(product.name)
            Text("$\(product.price, specifier: "%.2f")")
            
            Button("Add to Cart") {
                cart.add(product)
            }
            .buttonStyle(.borderedProminent)
        }
    }
}
 
struct CartBadge: View {
    @EnvironmentObject var cart: CartManager
    
    var body: some View {
        ZStack(alignment: .topTrailing) {
            Image(systemName: "cart")
            
            if cart.itemCount > 0 {
                Text("\(cart.itemCount)")
                    .font(.caption2)
                    .foregroundColor(.white)
                    .padding(4)
                    .background(Circle().fill(.red))
                    .offset(x: 8, y: -8)
            }
        }
    }
}

struct App: App {
    @StateObject var userSession = UserSession()
    @StateObject var settings = AppSettings()
    @StateObject var cart = CartManager()
    
    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(userSession)
                .environmentObject(settings)
                .environmentObject(cart)
        }
    }
}

#Preview {
    ProductCard(product: Product(name: "iPhone", price: 999))
        .environmentObject(CartManager())
}