import SwiftUI

@main
struct MyApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

struct ContentView: View {
    @State private var count = 0

    var body: some View {
        VStack(spacing: 20) {
            Text("Count: \(count)")
                .font(.largeTitle)

            Button("Increment") {
                count += 1
            }
            .buttonStyle(.borderedProminent)
        }
        .padding()
    }
}

// Local state
@State private var text = ""

// Binding (child components)
@Binding var isPresented: Bool

// Observable object
@StateObject private var viewModel = MyViewModel()
@ObservedObject var viewModel: MyViewModel

// Environment
@Environment(\.dismiss) private var dismiss
@Environment(\.colorScheme) private var colorScheme
@EnvironmentObject var appState: AppState

// App Storage (UserDefaults)
@AppStorage("username") private var username = ""

// Async/await
func fetchData() async throws -> [Item] {
    let url = URL(string: "https://api.example.com/items")!
    let (data, _) = try await URLSession.shared.data(from: url)
    return try JSONDecoder().decode([Item].self, from: data)
}

// In View
.task {
    do {
        items = try await fetchData()
    } catch {
        errorMessage = error.localizedDescription
    }
}

// Main actor for UI updates
@MainActor
class ViewModel: ObservableObject {
    @Published var items: [Item] = []

    func load() async {
        items = try? await fetchData()
    }
}

// NavigationStack with typed destinations
struct ContentView: View {
    @State private var path = NavigationPath()

    var body: some View {
        NavigationStack(path: $path) {
            List(items) { item in
                NavigationLink(value: item) {
                    Text(item.name)
                }
            }
            .navigationDestination(for: Item.self) { item in
                DetailView(item: item)
            }
        }
    }
}

// Modern List
List {
    ForEach(items) { item in
        ItemRow(item: item)
    }
    .onDelete(perform: delete)
    .onMove(perform: move)
}
.listStyle(.insetGrouped)
.searchable(text: $searchText)
.refreshable {
    await refresh()
}

// LazyVGrid
LazyVGrid(columns: [
    GridItem(.adaptive(minimum: 150))
]) {
    ForEach(items) { item in
        ItemCard(item: item)
    }
}

class MyViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        setupUI()
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        // About to appear
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        // Fully visible
    }
}

// Programmatic constraints
NSLayoutConstraint.activate([
    label.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20),
    label.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 16),
    label.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -16)
])

// Model
@objc(Item)
public class Item: NSManagedObject {
    @NSManaged public var id: UUID
    @NSManaged public var name: String
    @NSManaged public var createdAt: Date
}

// Fetch
@FetchRequest(
    sortDescriptors: [NSSortDescriptor(keyPath: \Item.createdAt, ascending: false)],
    animation: .default
)
private var items: FetchedResults<Item>

@Model
class Item {
    var id: UUID
    var name: String
    var createdAt: Date

    init(name: String) {
        self.id = UUID()
        self.name = name
        self.createdAt = Date()
    }
}

// In View
@Query(sort: \Item.createdAt, order: .reverse)
private var items: [Item]

@Environment(\.modelContext) private var modelContext

func addItem() {
    let item = Item(name: "New Item")
    modelContext.insert(item)
}

// Store sensitive data
import Security

func saveToKeychain(key: String, data: Data) throws {
    let query: [String: Any] = [
        kSecClass as String: kSecClassGenericPassword,
        kSecAttrAccount as String: key,
        kSecValueData as String: data
    ]
    SecItemDelete(query as CFDictionary)
    let status = SecItemAdd(query as CFDictionary, nil)
    guard status == errSecSuccess else {
        throw KeychainError.saveFailed
    }
}

actor NetworkService {
    func fetch<T: Decodable>(_ type: T.Type, from url: URL) async throws -> T {
        let (data, response) = try await URLSession.shared.data(from: url)

        guard let httpResponse = response as? HTTPURLResponse,
              (200...299).contains(httpResponse.statusCode) else {
            throw NetworkError.invalidResponse
        }

        return try JSONDecoder().decode(T.self, from: data)
    }
}

.safeAreaInset(edge: .bottom) {
    BottomBar()
}

// Ignore safe area
.ignoresSafeArea(.keyboard)
.ignoresSafeArea(.container, edges: .bottom)

// Split view
NavigationSplitView {
    Sidebar()
} content: {
    ContentList()
} detail: {
    DetailView()
}

// Keyboard shortcuts
.keyboardShortcut("n", modifiers: .command)

// Hover effects
.hoverEffect(.highlight)

// Focus management
@FocusState private var isFocused: Bool

Button("Action") { }
    .focused($isFocused)
    .focusable()

// Large text for 10-foot UI
.font(.system(size: 38))

<!-- Info.plist -->
<key>NSCameraUsageDescription</key>
<string>We need camera access to...</string>
<key>NSPhotoLibraryUsageDescription</key>
<string>We need photo access to...</string>

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSAllowsArbitraryLoads</key>
    <false/>
</dict>

import XCTest
@testable import MyApp

final class MyTests: XCTestCase {
    func testExample() async throws {
        let sut = MyViewModel()
        await sut.load()
        XCTAssertEqual(sut.items.count, 10)
    }
}

import XCTest

final class MyUITests: XCTestCase {
    let app = XCUIApplication()

    override func setUp() {
        continueAfterFailure = false
        app.launch()
    }

    func testNavigation() {
        app.buttons["Start"].tap()
        XCTAssertTrue(app.staticTexts["Welcome"].exists)
    }
}

MyApp/
├── App/
│   └── MyApp.swift
├── Features/
│   ├── Home/
│   │   ├── HomeView.swift
│   │   └── HomeViewModel.swift
│   └── Settings/
│       └── SettingsView.swift
├── Core/
│   ├── Models/
│   ├── Services/
│   └── Extensions/
├── Resources/
│   ├── Assets.xcassets
│   └── Localizable.strings
└── Tests/

import Observation

// New pattern: @Observable macro (replaces ObservableObject + @Published)
@Observable
class UserViewModel {
    var user: User?
    var isLoading = false
    var errorMessage: String?

    func load() async {
        isLoading = true
        defer { isLoading = false }
        do {
            user = try await fetchUser()
        } catch {
            errorMessage = error.localizedDescription
        }
    }
}

// In View: no @StateObject/@ObservedObject wrappers needed
struct UserView: View {
    @State private var viewModel = UserViewModel()

    var body: some View {
        Group {
            if viewModel.isLoading {
                ProgressView()
            } else if let user = viewModel.user {
                Text(user.name)
            }
        }
        .task { await viewModel.load() }
    }
}

// @Bindable for two-way bindings
struct EditView: View {
    @Bindable var viewModel: EditViewModel

    var body: some View {
        TextField("Name", text: $viewModel.name)
    }
}

// Mesh gradient (iOS 18+)
MeshGradient(
    width: 3, height: 3,
    points: [
        .init(0, 0), .init(0.5, 0), .init(1, 0),
        .init(0, 0.5), .init(0.5, 0.5), .init(1, 0.5),
        .init(0, 1), .init(0.5, 1), .init(1, 1)
    ],
    colors: [
        .red, .purple, .indigo,
        .orange, .cyan, .blue,
        .yellow, .green, .mint
    ]
)

// Zoom navigation transition
NavigationLink {
    DetailView(item: item)
} label: {
    ItemCard(item: item)
}
.matchedTransitionSource(id: item.id, in: namespace)

// ScrollView enhancements
ScrollView {
    LazyVStack {
        ForEach(items) { item in
            ItemRow(item: item)
        }
    }
}
.scrollPosition(id: $scrolledID)
.defaultScrollAnchor(.bottom)

// Custom containers
@Entry macro for EnvironmentValues
@Environment(\.myCustomValue) var value

// Complete data race safety (strict concurrency checking)
// Enable in Xcode: SWIFT_STRICT_CONCURRENCY = complete

// Sendable conformance required for data crossing isolation boundaries
struct UserData: Sendable {
    let id: UUID
    let name: String
}

// Actor isolation
actor DatabaseManager {
    private var cache: [String: Data] = [:]

    func get(_ key: String) -> Data? { cache[key] }
    func set(_ key: String, value: Data) { cache[key] = value }
}

// Global actors
@MainActor
class ViewModel {
    var items: [Item] = []

    func load() async {
        let data = await fetchFromNetwork() // Runs off main actor
        items = data // Back on main actor automatically
    }
}

// Typed throws (Swift 6)
enum DataError: Error {
    case notFound, corrupted
}

func loadData() throws(DataError) -> Data {
    guard let data = cache.get("key") else {
        throw .notFound
    }
    return data
}

// visionOS app structure
@main
struct MyVisionApp: App {
    var body: some Scene {
        // 2D window
        WindowGroup {
            ContentView()
        }

        // Immersive space
        ImmersiveSpace(id: "immersiveScene") {
            ImmersiveView()
        }

        // 3D volume
        WindowGroup(id: "3dContent") {
            Model3D(named: "Globe") { model in
                model.resizable()
                    .aspectRatio(contentMode: .fit)
            } placeholder: {
                ProgressView()
            }
        }
        .windowStyle(.volumetric)
    }
}

// RealityKit integration
import RealityKit

struct ImmersiveView: View {
    var body: some View {
        RealityView { content in
            let sphere = MeshResource.generateSphere(radius: 0.5)
            let material = SimpleMaterial(color: .blue, isMetallic: true)
            let entity = ModelEntity(mesh: sphere, materials: [material])
            content.add(entity)
        }
        .gesture(TapGesture().targetedToAnyEntity().onEnded { value in
            // Handle spatial tap
        })
    }
}

// watchOS app with SwiftUI
@main
struct MyWatchApp: App {
    var body: some Scene {
        WindowGroup {
            NavigationStack {
                ContentView()
            }
        }
    }
}

// Complications / Widgets
struct MyWidget: Widget {
    var body: some WidgetConfiguration {
        StaticConfiguration(kind: "myWidget", provider: Provider()) { entry in
            MyWidgetView(entry: entry)
        }
        .configurationDisplayName("My Widget")
        .supportedFamilies([
            .accessoryCircular,
            .accessoryRectangular,
            .accessoryInline,
        ])
    }
}

// Watch Connectivity for iPhone <-> Watch communication
import WatchConnectivity

class ConnectivityManager: NSObject, WCSessionDelegate {
    func session(_ session: WCSession, didReceiveMessage message: [String: Any]) {
        // Handle message from paired device
    }
}