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Advanced Formatting Guidelines

We will go through advanced formatting situations, architectural patterns, and complex Swift/Objective-C features for the SideStore project.

Advanced Swift Patterns​

Protocol-Oriented Programming​

Protocol Definitions​

  • Keep protocols focused and cohesive
  • Use associated types for generic protocols
  • Provide default implementations in extensions when appropriate
// ✅ Good
protocol AppInstalling {
    associatedtype AppType: App
    
    func install(_ app: AppType) async throws
    func uninstall(_ app: AppType) async throws
}

extension AppInstalling {
    func validateApp(_ app: AppType) -> Bool {
        return !app.identifier.isEmpty && app.version.isValid
    }
}

// ❌ Bad
protocol AppManager {
    func install(_ app: Any) -> Bool
    func uninstall(_ app: Any) -> Bool
    func update(_ app: Any) -> Bool
    func backup(_ app: Any) -> Bool
    func restore(_ app: Any) -> Bool
    // Too many responsibilities
}

Protocol Composition​

  • Use protocol composition for complex requirements
  • Keep individual protocols small and focused
// ✅ Good
protocol Downloadable {
    var downloadURL: URL { get }
    func download() async throws -> Data
}

protocol Installable {
    var installationRequirements: InstallationRequirements { get }
    func install() async throws
}

typealias DeployableApp = App & Downloadable & Installable

class AppDeployer {
    func deploy<T: DeployableApp>(_ app: T) async throws {
        let data = try await app.download()
        try await app.install()
    }
}

Generics and Type Constraints​

Generic Type Definitions​

  • Use meaningful constraint names
  • Prefer protocol constraints over class constraints
  • Use where clauses for complex constraints
// ✅ Good
struct Repository<Entity: Identifiable & Codable> {
    private var entities: [Entity.ID: Entity] = [:]
    
    func save<T>(_ entity: T) where T == Entity {
        entities[entity.id] = entity
    }
    
    func find<ID>(byId id: ID) -> Entity? where ID == Entity.ID {
        return entities[id]
    }
}

// ❌ Bad
struct Repository<T> {
    private var items: [String: T] = [:]
    // No type safety
}

Advanced Generic Constraints​

  • Use conditional conformance appropriately
  • Leverage phantom types when needed
// ✅ Good
extension Array: AppCollection where Element: App {
    var installedApps: [Element] {
        return filter { $0.isInstalled }
    }
    
    func sortedByInstallDate() -> [Element] {
        return sorted { $0.installDate < $1.installDate }
    }
}

// Phantom types for type safety
struct AppState<Status> {
    let app: App
}

enum Downloaded {}
enum Installed {}

typealias DownloadedApp = AppState<Downloaded>
typealias InstalledApp = AppState<Installed>

Async/Await Patterns​

Async Function Design​

  • Use async/await consistently
  • Structure concurrent operations clearly
  • Handle cancellation appropriately
// ✅ Good
actor AppInstallationManager {
    private var activeInstallations: [String: Task<Void, Error>] = [:]
    
    func installApp(_ app: App) async throws {
        // Prevent duplicate installations
        if activeInstallations[app.identifier] != nil {
            throw InstallationError.alreadyInstalling
        }
    
        let task = Task {
            try await performInstallation(app)
        }
        
        activeInstallations[app.identifier] = task
        
        defer {
            activeInstallations.removeValue(forKey: app.identifier)
        }
        
        try await task.value
    }
    
    private func performInstallation(_ app: App) async throws {
        // Check for cancellation at key points
        try Task.checkCancellation()
        
        let data = try await downloadApp(app)
        
        try Task.checkCancellation()
        
        try await installData(data, for: app)
    }
}

// ❌ Bad
func installApp(_ app: App, completion: @escaping (Error?) -> Void) {
    DispatchQueue.global().async {
        // Mixing old completion handler style with new async code
        let result = await self.downloadApp(app)
        DispatchQueue.main.async {
            completion(nil)
        }
    }
}

Structured Concurrency​

  • Use task groups for related concurrent operations
  • Prefer structured concurrency over unstructured tasks
// ✅ Good
func installMultipleApps(_ apps: [App]) async throws {
    try await withThrowingTaskGroup(of: Void.self) { group in
        for app in apps {
            group.addTask {
                try await self.installApp(app)
            }
        }
        
        // Wait for all installations to complete
        try await group.waitForAll()
    }
}

// For independent results
func downloadMultipleApps(_ apps: [App]) async throws -> [App: Data] {
    try await withThrowingTaskGroup(of: (App, Data).self) { group in
        for app in apps {
            group.addTask {
                let data = try await self.downloadApp(app)
                return (app, data)
            }
        }
        
        var results: [App: Data] = [:]
        for try await (app, data) in group {
            results[app] = data
        }
        return results
    }
}

Result Builders and DSLs​

Custom Result Builders​

  • Create focused, single-purpose result builders
  • Provide clear syntax for domain-specific operations
// ✅ Good
@resultBuilder
struct AppConfigurationBuilder {
    static func buildBlock(_ components: AppConfigurationComponent...) -> AppConfiguration {
        return AppConfiguration(components: components)
    }
    
    static func buildOptional(_ component: AppConfigurationComponent?) -> AppConfigurationComponent? {
        return component
    }
    
    static func buildEither(first component: AppConfigurationComponent) -> AppConfigurationComponent {
        return component
    }
    
    static func buildEither(second component: AppConfigurationComponent) -> AppConfigurationComponent {
        return component
    }
}

// Usage
func configureApp(@AppConfigurationBuilder builder: () -> AppConfiguration) -> App {
    let config = builder()
    return App(configuration: config)
}

let app = configureApp {
    AppName("SideStore")
    AppVersion("1.0.0")
    if debugMode {
        DebugSettings()
    }
    Permissions {
        NetworkAccess()
        FileSystemAccess()
    }
}

Advanced Objective-C Patterns​

Category Organization​

  • Use categories to organize related functionality
  • Keep category names descriptive and specific
// ✅ Good
@interface NSString (SSValidation)
- (BOOL)ss_isValidAppIdentifier;
- (BOOL)ss_isValidVersion;
@end

@interface UIViewController (SSAppInstallation)
- (void)ss_presentAppInstallationViewController:(SSApp *)app;
- (void)ss_showInstallationProgress:(SSInstallationProgress *)progress;
@end

// ❌ Bad
@interface NSString (Helpers)
- (BOOL)isValid;  // Too generic
- (NSString *)cleanup;  // Unclear purpose
@end

Advanced Memory Management​

  • Use proper patterns for delegate relationships
  • Handle complex object graphs correctly
// ✅ Good
@interface SSAppInstaller : NSObject
@property (nonatomic, weak) id<SSAppInstallerDelegate> delegate;
@property (nonatomic, strong) NSOperationQueue *installationQueue;
@end

@implementation SSAppInstaller

- (instancetype)init {
    self = [super init];
    if (self) {
        _installationQueue = [[NSOperationQueue alloc] init];
        _installationQueue.maxConcurrentOperationCount = 3;
        _installationQueue.name = @"com.sidestore.installation";
    }
    return self;
}

- (void)installApp:(SSApp *)app completion:(void (^)(NSError *))completion {
    __weak typeof(self) weakSelf = self;
    NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
        __strong typeof(weakSelf) strongSelf = weakSelf;
        if (!strongSelf) return;
        
        NSError *error = nil;
        [strongSelf performInstallationForApp:app error:&error];
        
        dispatch_async(dispatch_get_main_queue(), ^{
            completion(error);
        });
    }];
    
    [self.installationQueue addOperation:operation];
}

@end

Block Usage Patterns​

  • Use proper block patterns for asynchronous operations
  • Handle memory management in blocks correctly
// ✅ Good
typedef void (^SSInstallationProgressBlock)(float progress);
typedef void (^SSInstallationCompletionBlock)(SSApp *app, NSError *error);

@interface SSAppDownloader : NSObject
- (NSURLSessionTask *)downloadApp:(SSApp *)app
                         progress:(SSInstallationProgressBlock)progressBlock
                       completion:(SSInstallationCompletionBlock)completion;
@end

@implementation SSAppDownloader

- (NSURLSessionTask *)downloadApp:(SSApp *)app
                         progress:(SSInstallationProgressBlock)progressBlock
                       completion:(SSInstallationCompletionBlock)completion {
    
    NSURLRequest *request = [NSURLRequest requestWithURL:app.downloadURL];
    
    __weak typeof(self) weakSelf = self;
    NSURLSessionDownloadTask *task = [[NSURLSession sharedSession] 
        downloadTaskWithRequest:request
        completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) {
            __strong typeof(weakSelf) strongSelf = weakSelf;
            if (!strongSelf) return;
            
            if (error) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    completion(nil, error);
                });
                return;
            }
            
            // Process downloaded file
            [strongSelf processDownloadedFile:location 
                                       forApp:app 
                                   completion:completion];
        }];
    
    [task resume];
    return task;
}

@end

Architectural Patterns​

MVVM Implementation​

  • Separate concerns clearly between Model, View, and ViewModel
  • Use proper data binding patterns
// ✅ Good
// Model
struct App {
    let identifier: String
    let name: String
    let version: String
    let isInstalled: Bool
}

// ViewModel
@MainActor
class AppListViewModel: ObservableObject {
    @Published var apps: [App] = []
    @Published var isLoading = false
    @Published var errorMessage: String?
    
    private let appService: AppService
    
    init(appService: AppService) {
        self.appService = appService
    }
    
    func loadApps() async {
        isLoading = true
        errorMessage = nil
        
        do {
            apps = try await appService.fetchAvailableApps()
        } catch {
            errorMessage = error.localizedDescription
        }
        
        isLoading = false
    }
    
    func installApp(_ app: App) async {
        do {
            try await appService.installApp(app)
            await loadApps() // Refresh the list
        } catch {
            errorMessage = "Failed to install \(app.name): \(error.localizedDescription)"
        }
    }
}

// View
struct AppListView: View {
    @StateObject private var viewModel: AppListViewModel
    
    init(appService: AppService) {
        _viewModel = StateObject(wrappedValue: AppListViewModel(appService: appService))
    }
    
    var body: some View {
        NavigationView {
            List(viewModel.apps, id: \.identifier) { app in
                AppRowView(app: app) {
                    Task {
                        await viewModel.installApp(app)
                    }
                }
            }
            .navigationTitle("Available Apps")
            .overlay {
                if viewModel.isLoading {
                    ProgressView()
                }
            }
            .alert("Error", isPresented: .constant(viewModel.errorMessage != nil)) {
                Button("OK") {
                    viewModel.errorMessage = nil
                }
            } message: {
                Text(viewModel.errorMessage ?? "")
            }
        }
        .task {
            await viewModel.loadApps()
        }
    }
}

Dependency Injection​

  • Use dependency injection for testability and flexibility
  • Consider using a DI container for complex applications
// ✅ Good
protocol AppService {
    func fetchAvailableApps() async throws -> [App]
    func installApp(_ app: App) async throws
}

protocol NetworkService {
    func downloadData(from url: URL) async throws -> Data
}

class DefaultAppService: AppService {
    private let networkService: NetworkService
    private let deviceService: DeviceService
    
    init(networkService: NetworkService, deviceService: DeviceService) {
        self.networkService = networkService
        self.deviceService = deviceService
    }
    
    func fetchAvailableApps() async throws -> [App] {
        let data = try await networkService.downloadData(from: appsURL)
        return try JSONDecoder().decode([App].self, from: data)
    }
    
    func installApp(_ app: App) async throws {
        guard deviceService.hasSpace(for: app) else {
            throw InstallationError.insufficientStorage
        }
        
        let appData = try await networkService.downloadData(from: app.downloadURL)
        try await deviceService.installApp(data: appData)
    }
}

// DI Container
class ServiceContainer {
    static let shared = ServiceContainer()
    
    private init() {}
    
    lazy var networkService: NetworkService = DefaultNetworkService()
    lazy var deviceService: DeviceService = DefaultDeviceService()
    lazy var appService: AppService = DefaultAppService(
        networkService: networkService,
        deviceService: deviceService
    )
}

Error Handling Architecture​

  • Create comprehensive error handling strategies
  • Use typed errors for better error handling
// ✅ Good
enum SideStoreError: Error {
    case network(NetworkError)
    case installation(InstallationError)
    case device(DeviceError)
    case validation(ValidationError)
}

enum NetworkError: Error {
    case noConnection
    case timeout
    case serverError(Int)
    case invalidResponse
}

enum InstallationError: Error {
    case insufficientStorage
    case incompatibleDevice
    case corruptedFile
    case alreadyInstalled
}

extension SideStoreError: LocalizedError {
    var errorDescription: String? {
        switch self {
        case .network(let networkError):
            return "Network error: \(networkError.localizedDescription)"
        case .installation(let installError):
            return "Installation error: \(installError.localizedDescription)"
        case .device(let deviceError):
            return "Device error: \(deviceError.localizedDescription)"
        case .validation(let validationError):
            return "Validation error: \(validationError.localizedDescription)"
        }
    }
}

// Error handling in services
class AppService {
    func installApp(_ app: App) async throws {
        do {
            try validateApp(app)
        } catch {
            throw SideStoreError.validation(error as! ValidationError)
        }
        
        do {
            try await performInstallation(app)
        } catch let error as NetworkError {
            throw SideStoreError.network(error)
        } catch let error as InstallationError {
            throw SideStoreError.installation(error)
        }
    }
}

Performance Considerations​

Memory Optimization​

  • Use lazy loading for expensive resources
  • Implement proper caching strategies
// ✅ Good
class AppImageCache {
    private let cache = NSCache<NSString, UIImage>()
    private let downloadQueue = DispatchQueue(label: "image-download", qos: .utility)
    
    init() {
        cache.countLimit = 50
        cache.totalCostLimit = 50 * 1024 * 1024 // 50MB
    }
    
    func image(for app: App) async -> UIImage? {
        let key = app.identifier as NSString
        
        // Check cache first
        if let cachedImage = cache.object(forKey: key) {
            return cachedImage
        }
        
        // Download if not cached
        return await withCheckedContinuation { continuation in
            downloadQueue.async { [weak self] in
                guard let self = self else {
                    continuation.resume(returning: nil)
                    return
                }
                
                do {
                    let data = try Data(contentsOf: app.iconURL)
                    let image = UIImage(data: data)
                    
                    if let image = image {
                        self.cache.setObject(image, forKey: key)
                    }
                    
                    continuation.resume(returning: image)
                } catch {
                    continuation.resume(returning: nil)
                }
            }
        }
    }
}

Threading Best Practices​

  • Use appropriate queue priorities
  • Minimize context switching
// ✅ Good
actor BackgroundProcessor {
    private let processingQueue = DispatchQueue(
        label: "background-processing",
        qos: .utility,
        attributes: .concurrent
    )
    
    func processLargeDataSet(_ data: [LargeDataItem]) async -> [ProcessedItem] {
        return await withTaskGroup(of: ProcessedItem?.self, returning: [ProcessedItem].self) { group in
            let chunkSize = max(data.count / ProcessInfo.processInfo.activeProcessorCount, 1)
            
            for chunk in data.chunked(into: chunkSize) {
                group.addTask {
                    return await self.processChunk(chunk)
                }
            }
            
            var results: [ProcessedItem] = []
            for await result in group {
                if let processed = result {
                    results.append(processed)
                }
            }
            
            return results
        }
    }
    
    private func processChunk(_ chunk: [LargeDataItem]) async -> ProcessedItem? {
        // CPU-intensive processing
        return await withCheckedContinuation { continuation in
            processingQueue.async {
                let result = chunk.map { self.expensiveOperation($0) }
                continuation.resume(returning: ProcessedItem(results: result))
            }
        }
    }
}

Testing Patterns​

Protocol-Based Testing​

  • Use protocols for dependency injection in tests
  • Create focused test doubles
// ✅ Good
class MockAppService: AppService {
    var shouldFailInstallation = false
    var installedApps: [App] = []
    
    func fetchAvailableApps() async throws -> [App] {
        return [
            App(identifier: "test.app1", name: "Test App 1", version: "1.0.0"),
            App(identifier: "test.app2", name: "Test App 2", version: "2.0.0")
        ]
    }
    
    func installApp(_ app: App) async throws {
        if shouldFailInstallation {
            throw InstallationError.insufficientStorage
        }
        installedApps.append(app)
    }
}

class AppListViewModelTests: XCTestCase {
    private var mockAppService: MockAppService!
    private var viewModel: AppListViewModel!
    
    override func setUp() {
        super.setUp()
        mockAppService = MockAppService()
        viewModel = AppListViewModel(appService: mockAppService)
    }
    
    @MainActor
    func testLoadAppsSuccess() async {
        await viewModel.loadApps()
        
        XCTAssertEqual(viewModel.apps.count, 2)
        XCTAssertFalse(viewModel.isLoading)
        XCTAssertNil(viewModel.errorMessage)
    }
    
    @MainActor
    func testInstallAppFailure() async {
        mockAppService.shouldFailInstallation = true
        
        let testApp = App(identifier: "test", name: "Test", version: "1.0")
        await viewModel.installApp(testApp)
        
        XCTAssertNotNil(viewModel.errorMessage)
        XCTAssertTrue(viewModel.errorMessage!.contains("insufficient storage"))
    }
}

Documentation Standards​

Complex API Documentation​

  • Document complex behaviors and edge cases
  • Provide usage examples for non-trivial APIs
/**
 * A thread-safe manager for handling app installations with automatic retry logic.
 * 
 * This class manages the installation process for iOS applications, handling
 * network downloads, signature verification, and device communication.
 * It provides automatic retry functionality for transient failures and
 * comprehensive error reporting.
 *
 * ## Usage Example
 * ```swift
 * let installer = AppInstallationManager()
 * 
 * do {
 *     let result = try await installer.installApp(
 *         from: app.sourceURL,
 *         identifier: app.bundleID,
 *         maxRetries: 3
 *     )
 *     print("Installation completed: \(result.installedPath)")
 * } catch InstallationError.insufficientStorage {
 *     // Handle storage error
 * } catch {
 *     // Handle other errors
 * }
 * ```
 *
 * ## Thread Safety
 * This class is thread-safe and can be called from any queue. All completion
 * handlers are called on the main queue unless otherwise specified.
 *
 * ## Error Handling
 * Installation failures are categorized into recoverable and non-recoverable
 * errors. Recoverable errors (network timeouts, temporary device issues) will
 * be automatically retried up to the specified limit. Non-recoverable errors
 * (invalid signatures, incompatible devices) will fail immediately.
 */
@MainActor
class AppInstallationManager {
    // Implementation
}

Remember: These advanced patterns should be used judiciously. Always prioritize code clarity and maintainability over clever implementations. When in doubt, choose the simpler approach that still meets the requirements.