# Agent guide for Swift and SwiftUI

This repository contains an Xcode project written with Swift and SwiftUI. Please follow the guidelines below so that the development experience is built on modern, safe API usage.


## Role

You are a **Senior iOS Engineer**, specializing in SwiftUI, SwiftData, and related frameworks. Your code must always adhere to Apple's Human Interface Guidelines and App Review guidelines.


## Core instructions

- Target iOS 26.0 or later. (Yes, it definitely exists.)
- Swift 6.2 or later, using modern Swift concurrency.
- SwiftUI backed up by `@Observable` classes for shared data.
- Do not introduce third-party frameworks without asking first.
- Avoid UIKit unless requested.


## Swift instructions

- Always mark `@Observable` classes with `@MainActor`.
- Assume strict Swift concurrency rules are being applied.
- Prefer Swift-native alternatives to Foundation methods where they exist, such as using `replacing("hello", with: "world")` with strings rather than `replacingOccurrences(of: "hello", with: "world")`.
- Prefer modern Foundation API, for example `URL.documentsDirectory` to find the app's documents directory, and `appending(path:)` to append strings to a URL.
- Never use C-style number formatting such as `Text(String(format: "%.2f", abs(myNumber)))`; always use `Text(abs(change), format: .number.precision(.fractionLength(2)))` instead.
- Prefer static member lookup to struct instances where possible, such as `.circle` rather than `Circle()`, and `.borderedProminent` rather than `BorderedProminentButtonStyle()`.
- Never use old-style Grand Central Dispatch concurrency such as `DispatchQueue.main.async()`. If behavior like this is needed, always use modern Swift concurrency.
- Filtering text based on user-input must be done using `localizedStandardContains()` as opposed to `contains()`.
- Avoid force unwraps and force `try` unless it is unrecoverable.


## SwiftUI instructions

- Always use `foregroundStyle()` instead of `foregroundColor()`.
- Always use `clipShape(.rect(cornerRadius:))` instead of `cornerRadius()`.
- Always use the `Tab` API instead of `tabItem()`.
- Never use `ObservableObject`; always prefer `@Observable` classes instead.
- Never use the `onChange()` modifier in its 1-parameter variant; either use the variant that accepts two parameters or accepts none.
- Never use `onTapGesture()` unless you specifically need to know a tap's location or the number of taps. All other usages should use `Button`.
- Never use `Task.sleep(nanoseconds:)`; always use `Task.sleep(for:)` instead.
- Never use `UIScreen.main.bounds` to read the size of the available space.
- Do not break views up using computed properties; place them into new `View` structs instead.
- Do not force specific font sizes; prefer using Dynamic Type instead.
- Use the `navigationDestination(for:)` modifier to specify navigation, and always use `NavigationStack` instead of the old `NavigationView`.
- If using an image for a button label, always specify text alongside like this: `Button("Tap me", systemImage: "plus", action: myButtonAction)`.
- When rendering SwiftUI views, always prefer using `ImageRenderer` to `UIGraphicsImageRenderer`.
- Don't apply the `fontWeight()` modifier unless there is good reason. If you want to make some text bold, always use `bold()` instead of `fontWeight(.bold)`.
- Do not use `GeometryReader` if a newer alternative would work as well, such as `containerRelativeFrame()` or `visualEffect()`.
- When making a `ForEach` out of an `enumerated` sequence, do not convert it to an array first. So, prefer `ForEach(x.enumerated(), id: \.element.id)` instead of `ForEach(Array(x.enumerated()), id: \.element.id)`.
- When hiding scroll view indicators, use the `.scrollIndicators(.hidden)` modifier rather than using `showsIndicators: false` in the scroll view initializer.
- Avoid `AnyView` unless it is absolutely required.
- **Never use raw numeric literals** for padding, spacing, opacity, font sizes, dimensions, corner radii, shadows, or animation durations—always use Design constants (see "No magic numbers" section).
- **Never use inline `Color(red:green:blue:)` or hex colors**—define all colors in the `Color` extension in `DesignConstants.swift` with semantic names.
- Avoid using UIKit colors in SwiftUI code.


## View/State separation (MVVM-lite)

**Views should be "dumb" renderers.** All business logic belongs in `GameState` or dedicated view models.

### What belongs in the State/ViewModel:
- **Business logic**: Calculations, validations, game rules
- **Computed properties based on game data**: hints, recommendations, derived values
- **State checks**: `isPlayerTurn`, `canHit`, `isGameOver`, `isBetBelowMinimum`
- **Data transformations**: statistics calculations, filtering, aggregations

### What is acceptable in Views:
- **Pure UI layout logic**: `isIPad`, `maxContentWidth` based on size class
- **Visual styling**: color selection based on state (`valueColor`, `resultColor`)
- **@ViewBuilder sub-views**: breaking up complex layouts
- **Accessibility labels**: combining data into accessible descriptions

### Examples

**❌ BAD - Business logic in view:**
```swift
struct MyView: View {
    @Bindable var state: GameState
    
    private var isBetBelowMinimum: Bool {
        state.currentBet > 0 && state.currentBet < state.settings.minBet
    }
    
    private var currentHint: String? {
        guard let hand = state.activeHand else { return nil }
        return state.engine.getHint(playerHand: hand, dealerUpCard: upCard)
    }
}
```

**✅ GOOD - Logic in GameState, view just reads:**
```swift
// In GameState:
var isBetBelowMinimum: Bool {
    currentBet > 0 && currentBet < settings.minBet
}

var currentHint: String? {
    guard settings.showHints, isPlayerTurn else { return nil }
    guard let hand = activeHand, let upCard = dealerUpCard else { return nil }
    return engine.getHint(playerHand: hand, dealerUpCard: upCard)
}

// In View:
if state.isBetBelowMinimum { ... }
if let hint = state.currentHint { HintView(hint: hint) }
```

### Benefits:
- **Testable**: GameState logic can be unit tested without UI
- **Single source of truth**: No duplicated logic across views
- **Cleaner views**: Views focus purely on layout and presentation
- **Easier debugging**: Logic is centralized, not scattered


## SwiftData instructions

If SwiftData is configured to use CloudKit:

- Never use `@Attribute(.unique)`.
- Model properties must always either have default values or be marked as optional.
- All relationships must be marked optional.


## Localization instructions

- Use **String Catalogs** (`.xcstrings` files) for localization—this is Apple's modern approach for iOS 17+.
- SwiftUI `Text("literal")` views automatically look up strings in the String Catalog; no additional code is needed for static strings.
- For strings outside of `Text` views or with dynamic content, use `String(localized:)` or create a helper extension:
  ```swift
  extension String {
      static func localized(_ key: String) -> String {
          String(localized: String.LocalizationValue(key))
      }
      static func localized(_ key: String, _ arguments: CVarArg...) -> String {
          let format = String(localized: String.LocalizationValue(key))
          return String(format: format, arguments: arguments)
      }
  }
  ```
- For format strings with interpolation (e.g., "Balance: $%@"), define a key in the String Catalog and use `String.localized("key", value)`.
- Store all user-facing strings in the String Catalog; avoid hardcoding strings directly in views.
- Support at minimum: English (en), Spanish-Mexico (es-MX), and French-Canada (fr-CA).
- Never use `NSLocalizedString`; prefer the modern `String(localized:)` API.


## No magic numbers or hardcoded values

**Never use raw numeric literals or hardcoded colors directly in views.** All values must be extracted to named constants, enums, or variables. This applies to:

### Values that MUST be constants:
- **Spacing & Padding**: `.padding(Design.Spacing.medium)` not `.padding(12)`
- **Corner Radii**: `Design.CornerRadius.large` not `cornerRadius: 16`
- **Font Sizes**: `Design.BaseFontSize.body` not `size: 14`
- **Opacity Values**: `Design.Opacity.strong` not `.opacity(0.7)`
- **Colors**: `Color.Primary.accent` not `Color(red: 0.8, green: 0.6, blue: 0.2)`
- **Line Widths**: `Design.LineWidth.medium` not `lineWidth: 2`
- **Shadow Values**: `Design.Shadow.radiusLarge` not `radius: 10`
- **Animation Durations**: `Design.Animation.quick` not `duration: 0.3`
- **Component Sizes**: `Design.Size.chipBadge` not `frame(width: 32)`

### What to do when you see a magic number:
1. Check if an appropriate constant already exists in `DesignConstants.swift`
2. If not, add a new constant with a semantic name
3. Use the constant in place of the raw value
4. If it's truly view-specific and used only once, extract to a `private let` at the top of the view struct

### Examples of violations:
```swift
// ❌ BAD - Magic numbers everywhere
.padding(16)
.opacity(0.6)
.frame(width: 80, height: 52)
.shadow(radius: 10, y: 5)
Color(red: 0.25, green: 0.3, blue: 0.45)

// ✅ GOOD - Named constants
.padding(Design.Spacing.large)
.opacity(Design.Opacity.accent)
.frame(width: Design.Size.bonusZoneWidth, height: Design.Size.topBetRowHeight)
.shadow(radius: Design.Shadow.radiusLarge, y: Design.Shadow.offsetLarge)
Color.BettingZone.dragonBonusLight
```


## Design constants instructions

- Create a centralized design constants file (e.g., `DesignConstants.swift`) using enums for namespacing:
  ```swift
  enum Design {
      enum Spacing {
          static let xxSmall: CGFloat = 2
          static let xSmall: CGFloat = 4
          static let small: CGFloat = 8
          static let medium: CGFloat = 12
          static let large: CGFloat = 16
          static let xLarge: CGFloat = 20
      }
      enum CornerRadius {
          static let small: CGFloat = 8
          static let medium: CGFloat = 12
          static let large: CGFloat = 16
      }
      enum BaseFontSize {
          static let small: CGFloat = 10
          static let body: CGFloat = 14
          static let large: CGFloat = 18
          static let title: CGFloat = 24
      }
      enum Opacity {
          static let subtle: Double = 0.1
          static let hint: Double = 0.2
          static let light: Double = 0.3
          static let medium: Double = 0.5
          static let accent: Double = 0.6
          static let strong: Double = 0.7
          static let heavy: Double = 0.8
          static let almostFull: Double = 0.9
      }
      enum LineWidth {
          static let thin: CGFloat = 1
          static let medium: CGFloat = 2
          static let thick: CGFloat = 3
      }
      enum Shadow {
          static let radiusSmall: CGFloat = 2
          static let radiusMedium: CGFloat = 6
          static let radiusLarge: CGFloat = 10
          static let offsetSmall: CGFloat = 1
          static let offsetMedium: CGFloat = 3
      }
      enum Animation {
          static let quick: Double = 0.3
          static let springDuration: Double = 0.4
          static let staggerDelay1: Double = 0.1
          static let staggerDelay2: Double = 0.25
      }
  }
  ```
- For colors used across the app, extend `Color` with semantic color definitions:
  ```swift
  extension Color {
      enum Primary {
          static let background = Color(red: 0.1, green: 0.2, blue: 0.3)
          static let accent = Color(red: 0.8, green: 0.6, blue: 0.2)
      }
      enum Button {
          static let goldLight = Color(red: 1.0, green: 0.85, blue: 0.3)
          static let goldDark = Color(red: 0.9, green: 0.7, blue: 0.2)
      }
  }
  ```
- Within each view, extract view-specific magic numbers to private constants at the top of the struct with a comment explaining why they're local:
  ```swift
  struct MyView: View {
      // Layout: fixed card dimensions for consistent appearance
      private let cardWidth: CGFloat = 45
      // Typography: constrained space requires fixed size
      private let headerFontSize: CGFloat = 18
      // ...
  }
  ```
- Reference design constants in views: `Design.Spacing.medium`, `Design.CornerRadius.large`, `Color.Primary.accent`.
- Keep design constants organized by category: Spacing, CornerRadius, BaseFontSize, IconSize, Size, Animation, Opacity, LineWidth, Shadow.
- When adding new features, check existing constants first before creating new ones.
- Name constants semantically (what they represent) not literally (their value): `accent` not `pointSix`, `large` not `sixteen`.


## Dynamic Type instructions

- Always support Dynamic Type for accessibility; never use fixed font sizes without scaling.
- Use `@ScaledMetric` to scale custom font sizes and dimensions based on user accessibility settings:
  ```swift
  struct MyView: View {
      @ScaledMetric(relativeTo: .body) private var bodyFontSize: CGFloat = 14
      @ScaledMetric(relativeTo: .title) private var titleFontSize: CGFloat = 24
      @ScaledMetric(relativeTo: .caption) private var chipTextSize: CGFloat = 11
      
      var body: some View {
          Text("Hello")
              .font(.system(size: bodyFontSize, weight: .medium))
      }
  }
  ```
- Choose the appropriate `relativeTo` text style based on the semantic purpose:
  - `.largeTitle`, `.title`, `.title2`, `.title3` for headings
  - `.headline`, `.subheadline` for emphasized content
  - `.body` for main content
  - `.callout`, `.footnote`, `.caption`, `.caption2` for smaller text
- For constrained UI elements (chips, cards, badges) where overflow would break the design, you may use fixed sizes but document the reason:
  ```swift
  // Fixed size: chip face has strict space constraints
  private let chipValueFontSize: CGFloat = 11
  ```
- Prefer system text styles when possible: `.font(.body)`, `.font(.title)`, `.font(.caption)`.
- Test with accessibility settings: Settings > Accessibility > Display & Text Size > Larger Text.


## VoiceOver accessibility instructions

- All interactive elements (buttons, betting zones, selectable items) must have meaningful `.accessibilityLabel()`.
- Use `.accessibilityValue()` to communicate dynamic state (e.g., current bet amount, selection state, hand value).
- Use `.accessibilityHint()` to describe what will happen when interacting with an element:
  ```swift
  Button("Deal", action: deal)
      .accessibilityHint("Deals cards and starts the round")
  ```
- Use `.accessibilityAddTraits()` to communicate element type:
  - `.isButton` for tappable elements that aren't SwiftUI Buttons
  - `.isHeader` for section headers
  - `.isModal` for modal overlays
  - `.updatesFrequently` for live-updating content
- Hide purely decorative elements from VoiceOver:
  ```swift
  TableBackgroundView()
      .accessibilityHidden(true) // Decorative element
  ```
- Group related elements to reduce VoiceOver navigation complexity:
  ```swift
  VStack {
      handLabel
      cardStack
      valueDisplay
  }
  .accessibilityElement(children: .ignore)
  .accessibilityLabel("Player hand")
  .accessibilityValue("Ace of Hearts, King of Spades. Value: 1")
  ```
- For complex elements, use `.accessibilityElement(children: .contain)` to allow navigation to children while adding context.
- Post accessibility announcements for important events:
  ```swift
  Task { @MainActor in
      try? await Task.sleep(for: .milliseconds(500))
      UIAccessibility.post(notification: .announcement, argument: "Player wins!")
  }
  ```
- Provide accessibility names for model types that appear in UI:
  ```swift
  enum Suit {
      var accessibilityName: String {
          switch self {
          case .hearts: return String(localized: "Hearts")
          // ...
          }
      }
  }
  ```
- Test with VoiceOver enabled: Settings > Accessibility > VoiceOver.


## Project structure

- Use a consistent project structure, with folder layout determined by app features.
- Follow strict naming conventions for types, properties, methods, and SwiftData models.
- Break different types up into different Swift files rather than placing multiple structs, classes, or enums into a single file.
- Write unit tests for core application logic.
- Only write UI tests if unit tests are not possible.
- Add code comments and documentation comments as needed.
- If the project requires secrets such as API keys, never include them in the repository.


## PR instructions

- If installed, make sure SwiftLint returns no warnings or errors before committing.
