architecture-spec

Generate technical architecture specification for iOS/macOS app.

Metadata

• Name: architecture-spec
• Version: 1.0.0
• Role: iOS/macOS Architect
• Author: ProductAgent Team

When This Skill Activates

This skill activates when the user says:

• "generate architecture"
• "create technical spec"
• "write architecture document"
• "generate architecture spec"
• "design technical architecture"
• "create ARCHITECTURE.md"

Description

You are an iOS/macOS Architect AI agent specializing in Apple platform app architecture. Your job is to design a comprehensive technical architecture based on the Product Requirements Document (PRD) and make opinionated technology stack decisions following Apple best practices.

Prerequisites

Before activating this skill, ensure:

1. PRD exists at docs/PRD.md
2. User has reviewed and approved the PRD
3. MVP scope is clear (from product-agent output or PRD)

Input Sources

Read and extract information from:

1. docs/PRD.md

   • Core features and their complexity
   • Non-functional requirements
   • Data model hints
   • Platform requirements
   • Technical considerations

2. Product development plan (if available)

   • MVP scope with technical requirements
   • Third-party dependencies mentioned
   • Platform and timeline constraints

3. User preferences (ask if needed):

   • SwiftUI vs UIKit preference
   • Third-party library preferences
   • Architecture pattern preference (if strong opinion)
   • Backend API availability (determines data strategy)

Output

Generate docs/ARCHITECTURE.md with the following structure:

# Technical Architecture: [App Name]

**Version**: 1.0.0
**Last Updated**: [Date]
**Status**: Draft / In Review / Approved
**Owner**: Technical Architect
**Platform**: iOS [version]+ / macOS [version]+

---

## 1. Architecture Overview

### 1.1 Architecture Pattern

**Selected Pattern**: MVVM (Model-View-ViewModel) with SwiftUI
*or* Clean Architecture *or* TCA (The Composable Architecture)

**Reasoning**:
[Explain why this pattern was chosen based on app complexity]

**Characteristics**:
- **Layers**: [Describe the architectural layers]
- **Data Flow**: [Unidirectional / Bidirectional]
- **State Management**: [@Observable, Combine, TCA Store, etc.]
- **Testability**: [How architecture supports testing]

### 1.2 High-Level Component Diagram

┌─────────────────────────────────────────────────┐ │ Presentation Layer │ │ ┌──────────┐ ┌──────────┐ ┌──────────┐ │ │ │ Views │ │ViewModels│ │ Models │ │ │ │ (SwiftUI)│←→│(@Observ.)│←→│ (Data) │ │ │ └──────────┘ └──────────┘ └──────────┘ │ └────────────────────┬────────────────────────────┘ │ ┌────────────────────┴────────────────────────────┐ │ Business Logic Layer │ │ ┌──────────┐ ┌──────────┐ ┌──────────┐ │ │ │ Services │ │ Use │ │Repository│ │ │ │ │ │ Cases │ │ Pattern │ │ │ └──────────┘ └──────────┘ └──────────┘ │ └────────────────────┬────────────────────────────┘ │ ┌────────────────────┴────────────────────────────┐ │ Data Layer │ │ ┌──────────┐ ┌──────────┐ ┌──────────┐ │ │ │SwiftData │ │ Network │ │ Keychain │ │ │ │ / Core │ │ Client │ │ Storage │ │ │ │ Data │ │ (URLSess)│ │ │ │ │ └──────────┘ └──────────┘ └──────────┘ │ └─────────────────────────────────────────────────┘

### 1.3 Key Architectural Decisions

| Decision | Choice | Alternative Considered | Rationale |
|----------|--------|----------------------|-----------|
| UI Framework | SwiftUI | UIKit | Modern, declarative, iOS 17+ target allows it |
| Data Persistence | SwiftData | Core Data | Simpler API, better SwiftUI integration |
| Architecture Pattern | MVVM | VIPER, TCA | Balanced complexity vs maintainability |
| Networking | URLSession | Alamofire | No third-party dependency needed |
| State Management | @Observable | Combine, TCA | iOS 17+ Observation framework |
| Navigation | NavigationStack | Coordinator | SwiftUI native, simpler for MVP |

---

## 2. Technology Stack

### 2.1 Apple Frameworks

**UI & Presentation**:
- **SwiftUI** (primary) - Declarative UI framework
  - Minimum iOS 17.0 for @Observable, ContentUnavailableView, etc.
  - Navigation: NavigationStack, NavigationPath
  - Data binding: @State, @Binding, @Environment

**Data Persistence**:
- **SwiftData** (iOS 17+) - Data modeling and persistence
  - @Model macro for model classes
  - ModelContainer for database configuration
  - ModelContext for CRUD operations
  - @Query property wrapper for automatic observation

**Networking & Concurrency**:
- **URLSession** - HTTP networking
- **async/await** - Concurrency
- **Actors** - Thread-safe state management
- **Codable** - JSON serialization/deserialization

**Security**:
- **Keychain Services** - Secure credential storage
- **CryptoKit** - Encryption (if needed)
- **LocalAuthentication** - Biometric authentication (if needed)

**Other**:
- [List any other frameworks based on features]
  - MapKit (if maps needed)
  - Vision (if image recognition)
  - CoreML (if ML features)
  - StoreKit (if IAP)
  - CloudKit (if iCloud sync)

### 2.2 Third-Party Dependencies

**Via Swift Package Manager**:

1. **[Package Name]** (if needed)
   - **Repository**: https://github.com/[org]/[repo]
   - **Version**: ~> X.X.X
   - **Purpose**: [Why this is needed]
   - **Alternative Considered**: [Why not chosen]
   - **License**: [MIT, Apache, etc.]

*Note*: Keep dependencies minimal. Only add if:
- Provides significant value not available in Apple frameworks
- Well-maintained and trusted
- No suitable alternative

**Decision**: Start with zero third-party dependencies for MVP. Add only if needed.

### 2.3 Development Tools

- **Xcode**: [Latest stable version]
- **iOS Deployment Target**: iOS 26.0 (adjust lower for broader reach — iOS 17+ retains `@Observable` and SwiftData support)
- **Swift Version**: Swift 6+
- **Package Manager**: Swift Package Manager (SPM)
- **CI/CD**: Xcode Cloud / GitHub Actions (to be determined)

---

## 3. App Structure

### 3.1 Module Breakdown

[AppName]/ ├── App/ │ ├── [AppName]App.swift # App entry point (@main) │ ├── ContentView.swift # Root view │ └── AppState.swift # Global app state (if needed) │ ├── Features/ # Feature-based modules │ ├── Home/ │ │ ├── Views/ │ │ │ ├── HomeView.swift │ │ │ ├── HomeCardView.swift │ │ │ └── HomeEmptyStateView.swift │ │ ├── ViewModels/ │ │ │ └── HomeViewModel.swift │ │ └── Models/ │ │ └── HomeItem.swift (if feature-specific) │ │ │ ├── [Feature2]/ │ │ ├── Views/ │ │ ├── ViewModels/ │ │ └── Models/ │ │ │ └── [Feature3]/ │ └── ... │ ├── Core/ # Shared core functionality │ ├── Networking/ │ │ ├── APIClient.swift # HTTP client │ │ ├── APIEndpoint.swift # Endpoint definitions │ │ ├── APIError.swift # Error types │ │ └── RequestModels/ # API request DTOs │ │ └── ... │ │ │ ├── Storage/ │ │ ├── DataManager.swift # SwiftData container wrapper │ │ └── KeychainManager.swift # Keychain operations │ │ │ ├── Extensions/ │ │ ├── View+Extensions.swift # SwiftUI View extensions │ │ ├── Color+Extensions.swift # Color palette │ │ ├── Font+Extensions.swift # Typography │ │ └── Date+Extensions.swift # Date utilities │ │ │ └── Utilities/ │ ├── Logger.swift # Logging utility │ ├── Validator.swift # Input validation │ └── Constants.swift # App constants │ ├── Models/ # Domain models (shared) │ ├── User.swift # @Model classes │ ├── [Entity2].swift │ └── ResponseModels/ # API response DTOs │ └── ... │ ├── Services/ # Business logic services │ ├── AuthenticationService.swift │ ├── [Feature]Service.swift │ └── SyncService.swift (if background sync) │ ├── Resources/ │ ├── Assets.xcassets # Images, colors │ ├── Localizable.xcstrings # Translations │ └── PrivacyInfo.xcprivacy # Privacy manifest │ └── Tests/ ├── UnitTests/ │ ├── ViewModelTests/ │ ├── ServiceTests/ │ └── ModelTests/ └── UITests/ └── ...

**Organizational Principles**:
- **Feature-based organization**: Each major feature in its own folder
- **Vertical slicing**: Feature folder contains Views, ViewModels, and feature-specific Models
- **Core for shared**: Reusable components go in Core/
- **Models for domain**: Shared domain models (SwiftData @Model classes)
- **Services for business logic**: Business logic that spans features

### 3.2 Data Models

Based on PRD requirements, core entities are:

#### [Entity 1]: User

```swift
import Foundation
import SwiftData

@Model
final class User {
    // Identity
    @Attribute(.unique) var id: UUID
    var email: String
    var name: String
    var createdAt: Date
    var updatedAt: Date

    // Relationships
    @Relationship(deleteRule: .cascade)
    var [relatedEntities]: [RelatedEntity]

    // Computed Properties
    var displayName: String {
        name.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
            ? email
            : name
    }

    // Validation
    var isValid: Bool {
        !email.isEmpty && email.contains("@") && !name.isEmpty
    }

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

[Entity 2]: [Name]

@Model
final class [Entity2] {
    @Attribute(.unique) var id: UUID
    var [property1]: String
    var [property2]: Date

    // Relationships
    @Relationship(inverse: \User.[relatedEntities])
    var owner: User?

    init(...) {
        // Initialization
    }
}

Entity Relationships:

• User has many [Entity2] (one-to-many)
• [Entity2] belongs to User (many-to-one)
• [Add other relationships as per PRD]

SwiftData Considerations:

• Use @Attribute(.unique) for identifiers
• Define deleteRule for relationships (cascade, nullify, deny, noAction)
• Keep models simple - complex logic goes in ViewModels/Services
• Use @Transient for computed properties that shouldn't persist
• Consider privacy: Mark sensitive fields appropriately

3.3 Navigation Architecture

Pattern: NavigationStack (SwiftUI native)

Primary Navigation:

• TabView for main app sections (if 3-5 top-level sections)
• NavigationStack for drill-down navigation within tabs

Navigation State:

// In each feature's root view
@State private var navigationPath = NavigationPath()

NavigationStack(path: $navigationPath) {
    ListView()
        .navigationDestination(for: Item.self) { item in
            DetailView(item: item)
        }
        .navigationDestination(for: EditMode.self) { _ in
            EditView()
        }
}

Deep Linking:

• Handle URL schemes: [appname]://[route]/[id]
• Use .onOpenURL modifier at app root
• Parse URL and manipulate NavigationPath

Modal Presentation:

• Use .sheet for full-screen modal forms
• Use .alert for simple confirmations
• Use .confirmationDialog for action sheets

---

4. Data Flow

4.1 State Management

Pattern: @Observable (iOS 17+ Observation framework)

State Layers:

1. View State (@State)

   • Local to view
   • Examples: isLoading, showError, selectedItem
   • Transient, not persisted

2. ViewModel State (@Observable)

   • Shared across view hierarchy
   • Examples: Business logic, API state, validation
   • Passed as @Environment or direct reference

3. Persistent State (SwiftData @Query)

   • Automatically observed by SwiftUI
   • Database-backed
   • Examples: User data, items list

Example ViewModel:

import Foundation
import Observation

@Observable
final class HomeViewModel {
    // Published state
    var items: [Item] = []
    var isLoading = false
    var errorMessage: String?
    var showError = false

    // Dependencies (injected)
    private let apiClient: APIClient
    private let dataManager: DataManager

    init(apiClient: APIClient = .shared,
         dataManager: DataManager = .shared) {
        self.apiClient = apiClient
        self.dataManager = dataManager
    }

    // Actions
    @MainActor
    func loadItems() async {
        isLoading = true
        defer { isLoading = false }

        do {
            let fetchedItems = try await apiClient.fetchItems()
            items = fetchedItems
            // Persist to SwiftData
            try dataManager.saveItems(fetchedItems)
        } catch {
            errorMessage = error.localizedDescription
            showError = true
        }
    }
}

Data Flow Diagram:

User Action (Tap Button)
    ↓
View calls ViewModel method
    ↓
ViewModel calls Service/APIClient
    ↓
Service makes API call
    ↓
Response updates ViewModel @Observable properties
    ↓
SwiftUI automatically updates View
    ↓
(Optional) Persist to SwiftData

4.2 Data Persistence

Strategy: Local-first with optional sync

Local Storage:

• SwiftData for structured data (models)
• UserDefaults for simple preferences
• Keychain for sensitive data (tokens, passwords)
• FileManager for large files (images, documents)

SwiftData Setup:

// In App struct
@main
struct [AppName]App: App {
    let container: ModelContainer

    init() {
        do {
            let schema = Schema([User.self, Item.self, ...])
            let config = ModelConfiguration(
                schema: schema,
                isStoredInMemoryOnly: false
            )
            container = try ModelContainer(
                for: schema,
                configurations: config
            )
        } catch {
            fatalError("Failed to create ModelContainer: \(error)")
        }
    }

    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        .modelContainer(container)
    }
}

Data Migration:

• SwiftData handles migrations automatically for simple changes
• For complex migrations, use VersionedSchema and MigrationPlan
• Test migrations thoroughly before releases

Backup & Sync (if needed):

• iCloud CloudKit: For user data sync across devices
• File-based: For documents (UIDocument + iCloud Drive)
• Implementation: Phase 2 (post-MVP unless critical)

4.3 Networking Layer

Architecture: Protocol-oriented with async/await

APIClient Design:

actor APIClient {
    static let shared = APIClient()

    private let baseURL = URL(string: "https://api.example.com/v1")!
    private let session: URLSession
    private var authToken: String?

    init() {
        let config = URLSessionConfiguration.default
        config.timeoutIntervalForRequest = 30
        config.waitsForConnectivity = true
        self.session = URLSession(configuration: config)
    }

    // Generic request method
    func request<T: Decodable>(
        _ endpoint: APIEndpoint,
        responseType: T.Type
    ) async throws -> T {
        var request = URLRequest(url: baseURL.appendingPathComponent(endpoint.path))
        request.httpMethod = endpoint.method.rawValue
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")

        // Add auth token if available
        if let token = authToken {
            request.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
        }

        // Add body for POST/PUT
        if let body = endpoint.body {
            request.httpBody = try JSONEncoder().encode(body)
        }

        // Perform request
        let (data, response) = try await session.data(for: request)

        // Validate response
        guard let httpResponse = response as? HTTPURLResponse else {
            throw APIError.invalidResponse
        }

        guard (200...299).contains(httpResponse.statusCode) else {
            throw APIError.httpError(statusCode: httpResponse.statusCode, data: data)
        }

        // Decode
        let decoder = JSONDecoder()
        decoder.keyDecodingStrategy = .convertFromSnakeCase
        decoder.dateDecodingStrategy = .iso8601

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

// Endpoint definition
struct APIEndpoint {
    let path: String
    let method: HTTPMethod
    let body: (any Encodable)?

    enum HTTPMethod: String {
        case get = "GET"
        case post = "POST"
        case put = "PUT"
        case delete = "DELETE"
        case patch = "PATCH"
    }
}

// Error handling
enum APIError: LocalizedError {
    case invalidResponse
    case httpError(statusCode: Int, data: Data?)
    case decodingError(Error)
    case networkError(Error)

    var errorDescription: String? {
        switch self {
        case .invalidResponse:
            return "Invalid response from server"
        case .httpError(let code, _):
            return "Server error: \(code)"
        case .decodingError:
            return "Failed to parse response"
        case .networkError:
            return "Network connection failed"
        }
    }
}

Request/Response Models:

• Separate DTOs (Data Transfer Objects) from domain models
• Keep in Core/Networking/RequestModels/ and ResponseModels/
• Map from DTO to domain model in service layer

Error Handling Strategy:

• Use typed errors (APIError enum)
• Provide user-friendly messages
• Log technical details for debugging
• Implement retry with exponential backoff for transient failures
• Cache responses when appropriate

Caching:

• Use URLCache for HTTP caching (images, static content)
• Implement custom cache for API responses (if needed)
• Cache strategy: Cache-Control headers + custom logic

---

5. Security & Privacy

5.1 Data Security

Sensitive Data Storage:

// KeychainManager for secure storage
final class KeychainManager {
    static let shared = KeychainManager()

    func save(key: String, data: Data) throws {
        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrAccount as String: key,
            kSecValueData as String: data
        ]

        let status = SecItemAdd(query as CFDictionary, nil)
        guard status == errSecSuccess else {
            throw KeychainError.saveFailed(status)
        }
    }

    func retrieve(key: String) throws -> Data {
        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrAccount as String: key,
            kSecReturnData as String: true
        ]

        var result: AnyObject?
        let status = SecItemCopyMatching(query as CFDictionary, &result)

        guard status == errSecSuccess, let data = result as? Data else {
            throw KeychainError.retrieveFailed(status)
        }

        return data
    }
}

Encryption:

• API tokens: Stored in Keychain
• User passwords: Never stored locally (use tokens)
• Sensitive files: Encrypt with CryptoKit before saving
• Database: SwiftData encryption enabled (if available)

Communication Security:

• All API calls over HTTPS
• TLS 1.2+ required
• Certificate pinning: Consider for Phase 2 if high security needed
• No hardcoded secrets in code (use environment config)

5.2 Privacy

Privacy Manifest (PrivacyInfo.xcprivacy):

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>NSPrivacyTracking</key>
    <false/>
    <key>NSPrivacyTrackingDomains</key>
    <array/>
    <key>NSPrivacyCollectedDataTypes</key>
    <array>
        <dict>
            <key>NSPrivacyCollectedDataType</key>
            <string>NSPrivacyCollectedDataTypeEmailAddress</string>
            <key>NSPrivacyCollectedDataTypeLinked</key>
            <true/>
            <key>NSPrivacyCollectedDataTypeTracking</key>
            <false/>
            <key>NSPrivacyCollectedDataTypePurposes</key>
            <array>
                <string>NSPrivacyCollectedDataTypePurposeAppFunctionality</string>
            </array>
        </dict>
    </array>
    <key>NSPrivacyAccessedAPITypes</key>
    <array>
        <!-- List any required reason APIs used -->
    </array>
</dict>
</plist>

Data Collection Policy:

• Collect minimum data necessary
• Document what data is collected and why
• Provide clear privacy policy
• Allow users to delete their data
• No tracking without explicit consent

App Tracking Transparency:

• Only if analytics/ads used
• Request permission with clear explanation
• App must work if denied

---

6. Performance Considerations

6.1 App Launch Optimization

Cold Launch (< 1.5s target):

• Defer non-critical initialization
• Use lazy loading for heavy components
• Optimize image assets (compress, use asset catalogs)
• Profile with Instruments (Time Profiler)

Warm Launch (< 0.5s target):

• Keep memory footprint low
• Proper state restoration

6.2 Memory Management

Best Practices:

• Use value types (structs) where possible
• Avoid retain cycles with [weak self] in closures
• Use @MainActor for UI updates
• Profile with Instruments (Leaks, Allocations)
• Implement proper deinitialization

Image Handling:

• Lazy loading with AsyncImage
• Downsample large images
• Cache thumbnail versions
• Use proper image formats (HEIC for photos)

6.3 Background Task Handling

Background Refresh:

// If needed for data sync
func scheduleBackgroundRefresh() {
    BGTaskScheduler.shared.register(
        forTaskWithIdentifier: "com.app.refresh",
        using: nil
    ) { task in
        self.handleBackgroundRefresh(task: task as! BGAppRefreshTask)
    }
}

Background URLSession:

• For large downloads/uploads
• Continues even if app terminated
• Implement URLSessionDelegate

6.4 Launch Time Optimization

Strategies:

• Minimize work in app launch path
• Defer heavy operations to background
• Use lazy initialization
• Optimize image assets
• Remove unused frameworks

---

7. Testing Strategy

7.1 Unit Testing

Coverage Target: 70%+ for business logic

What to Test:

• ViewModels: All business logic methods
• Services: API calls, data transformations
• Models: Validation logic, computed properties
• Utilities: Pure functions

Testing Framework: XCTest

Example:

import XCTest
@testable import [AppName]

final class HomeViewModelTests: XCTestCase {
    var sut: HomeViewModel!
    var mockAPIClient: MockAPIClient!
    var mockDataManager: MockDataManager!

    override func setUp() {
        super.setUp()
        mockAPIClient = MockAPIClient()
        mockDataManager = MockDataManager()
        sut = HomeViewModel(
            apiClient: mockAPIClient,
            dataManager: mockDataManager
        )
    }

    override func tearDown() {
        sut = nil
        mockAPIClient = nil
        mockDataManager = nil
        super.tearDown()
    }

    func testLoadItems_Success() async throws {
        // Given
        let expectedItems = [Item(id: UUID(), name: "Test")]
        mockAPIClient.itemsToReturn = expectedItems

        // When
        awai

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