## Core Components

### 1. MVVMEnvironment

The `MVVMEnvironment` provides FOSMVVM infrastructure to all views:

**Key configuration:**
- `appBundle` - Usually `Bundle.main` (the app bundle)
- `resourceBundles` - Array of localization bundles from your modules
- `deploymentURLs` - URLs for each deployment environment

**Resource Bundle Accessors:**

Each module that contains localization resources should provide a bundle accessor:

This pattern:
- Uses `Bundle.module` which SPM automatically provides for each module
- Provides a clean public API for accessing the module's resources
- Keeps bundle access centralized in one place per module

### 2. Environment Injection

The `MVVMEnvironment` is injected at the WindowGroup level:

This makes the environment available to all views in the hierarchy.

### 3. Test Infrastructure

The test infrastructure enables UI testing with specific configurations:

**`.testHost { }` modifier:**

**Key points:**
- **Apply to the top-level view** in WindowGroup (the outermost view in your hierarchy)
- This ensures the modifier wraps the entire view hierarchy to intercept test configurations
- Always include the `default:` case
- The default case detects test mode via process arguments
- Sets `@State private var underTest = false` flag
- Optional: Add specific test configurations for advanced scenarios

**`registerTestingViews()` function:**

**Key points:**
- Extension on the **App struct** (not MVVMEnvironment)
- Called from `init()`
- Registers every ViewModelView for isolated testing
- DEBUG only

## When to Use This Skill

- Starting a new FOSMVVM SwiftUI application
- Migrating an existing SwiftUI app to FOSMVVM
- Setting up the App struct with proper FOSMVVM infrastructure
- Configuring test infrastructure for UI testing

## What This Skill Generates

| Component | Location | Purpose |
|-----------|----------|---------|
| Main App struct | `Sources/App/{AppName}.swift` | Entry point with MVVMEnvironment setup |
| MVVMEnvironment configuration | Computed property in App struct | Bundles and deployment URLs |
| Test infrastructure | DEBUG blocks in App struct | UI testing support |

## Project Structure Configuration

| Placeholder | Description | Example |
|-------------|-------------|---------|
| `{AppName}` | Your app name | `MyApp`, `AccelApp` |
| `{AppTarget}` | Main app target | `App` |
| `{ResourceBundles}` | Module names with localization | `MyAppViewModels`, `SharedResources` |

## How to Use This Skill

**Invocation:**
/fosmvvm-swiftui-app-setup

**Prerequisites:**
- App name understood from conversation context
- Deployment URLs discussed or documented
- Resource bundles identified (modules with localization)
- Test support requirements clarified

**Workflow integration:**
This skill is used when setting up a new FOSMVVM SwiftUI application or adding FOSMVVM infrastructure to an existing app. The skill references conversation context automatically—no file paths or Q&A needed.

## Pattern Implementation

This skill references conversation context to determine App struct configuration:

### Configuration Detection

From conversation context, the skill identifies:
- **App name** (from project discussion or existing code)
- **Deployment environments** (production, staging, debug URLs)
- **Resource bundles** (modules containing localization YAML files)
- **Test infrastructure** (whether UI testing support needed)

### MVVMEnvironment Setup

Based on project structure:
- **App bundle** (typically Bundle.main)
- **Resource bundle accessors** (from identified modules)
- **Deployment URLs** (for each environment)
- **Current version** (from shared module)

### Test Infrastructure Planning

If test support needed:
- **Test detection** (process arguments check)
- **Test host modifier** (wrapping top-level view)
- **View registration** (all ViewModelViews for testing)

### File Generation

1. Main App struct with @main attribute
2. MVVMEnvironment computed property
3. WindowGroup with environment injection
4. Test infrastructure (if requested, DEBUG-only)
5. registerTestingViews() extension (if test support)

### Context Sources

Skill references information from:
- **Prior conversation**: App requirements, deployment environments discussed
- **Project structure**: From codebase analysis of module organization
- **Existing patterns**: From other FOSMVVM apps if context available

## Key Patterns

### MVVMEnvironment as Computed Property

The `MVVMEnvironment` is a computed property, not a stored property:

**Why computed?**
- Keeps initialization logic separate
- Can be customized in DEBUG vs RELEASE
- Clear dependency on bundles and URLs

### Test Detection Pattern

The default test detection uses process arguments:

**Why this approach?**
- Simple and reliable for DEBUG builds
- No additional dependencies
- Process arguments are set by test runner

### Register All ViewModelViews

Every ViewModelView should be registered for testing:

**Organization tips:**
- Group by feature/screen with comments
- Alphabetical order within groups
- One view per line for easy scanning

## Common Customizations

### Multiple Environment Values

You can inject multiple environment values:

### Conditional Test Registration

You can conditionally register views based on build configuration: