# SecureStorageSample Watch App

A watchOS companion app demonstrating data synchronization with the iOS app using WatchConnectivity.

## Overview

This watch app receives `UserProfile` data and the syncable setting from the paired iPhone via WatchConnectivity. It does **not** use LocalData directly for storage—instead, it displays synced data in memory.

## Architecture

```
SecureStorageSample Watch App/
├── ContentView.swift           # Displays synced profile data
├── SecureStorageSampleApp.swift
├── Design/
│   └── WatchDesignConstants.swift
├── Protocols/
│   └── WatchDataHandling.swift # Protocol for payload handlers
├── State/
│   └── WatchProfileStore.swift # Holds synced profile in memory
└── Services/
    ├── WatchConnectivityService.swift
    └── Handlers/
        └── UserProfileWatchHandler.swift
        └── SyncableSettingWatchHandler.swift
```

## Data Flow

1. **Watch app** requests a sync when it launches or becomes reachable
2. **iOS app** replies with a snapshot of syncable keys and updates `applicationContext`
3. **Watch app** receives context in `WatchConnectivityService`
4. The service dispatches each payload key to its registered `WatchDataHandling` handler
5. Handlers decode values and update `WatchProfileStore`

## Launch-Order-Safe Sync

The watch app handles both cases:

- If the iPhone is reachable, it sends a `request_sync` message and applies the reply payload.
- If the iPhone is not reachable, it queues a request with `transferUserInfo` and shows a badge.

This ensures users do not need to launch the apps in a specific order.

## Adding New Sync Payloads

1. Create a new handler conforming to `WatchDataHandling`:

```swift
struct MyDataWatchHandler: WatchDataHandling {
    let key = "myData"
    
    func handle(data: Data) {
        // Decode and update state
    }
}
```

2. Register it in `WatchConnectivityService.registerDefaultHandlers()`

## Limitations

- **No persistent storage on watch**: Data is held in memory only
- **One-way sync**: Watch receives data from iPhone; it does not send data back
- **Simulator limitations**: WatchConnectivity may not work reliably in the simulator

## Requirements

- watchOS 10.0+
- Paired with iOS app via WatchConnectivity