# LocalData Package Proposal

## Goal
Create a single, typed, discoverable namespace for persisted app data with consistent security guarantees and clear ownership. This makes it obvious what is stored, where it is stored, how it is secured, how it is serialized, who owns it, and which platforms it belongs to or should sync to.

## Package Placement
- localPackages/LocalData/
  - Sources/LocalData/
  - Tests/LocalDataTests/

## Dependencies
- Foundation
- Security (Keychain)
- CryptoKit (encryption)
- WatchConnectivity (sync helpers)

## Architecture

### Core Components
- **StorageKey** protocol - Defines storage configuration for each data type
- **StorageKey.migration** - Optional protocol-based migration attached to a key
- **StorageRouter** actor - Main entry point coordinating all storage operations
- **StorageProviding** protocol - Abstraction for storage operations
- **StorageKeyCatalog** protocol - Catalog of keys for auditing/validation
- **StorageMigration** protocol - Protocol-based migration workflows attached to keys

### Isolated Helper Classes (Actors)
Each helper is a dedicated actor providing thread-safe access to a specific storage domain:

- **KeychainHelper** - All keychain operations (set, get, delete, exists, deleteAll)
- **EncryptionHelper** - AES-256-GCM or ChaCha20-Poly1305 with PBKDF2/HKDF
- **FileStorageHelper** - File system operations (read, write, delete, list, size), including App Group containers
- **UserDefaultsHelper** - UserDefaults operations with suite and App Group support
- **SyncHelper** - WatchConnectivity sync operations

### Models
- **StorageDomain** - userDefaults, appGroupUserDefaults, keychain, fileSystem, encryptedFileSystem, appGroupFileSystem
- **SecurityPolicy** - none, keychain (with accessibility/accessControl), encrypted (AES-256 or ChaCha20-Poly1305)
- **Serializer** - JSON, property list, raw Data, or custom encode/decode with named serializer metadata
- **KeyMaterialSource** - Identifier for external key material providers
- **PlatformAvailability** - all, phoneOnly, watchOnly, phoneWithWatchSync
- **SyncPolicy** - never, manual, automaticSmall
- **KeychainAccessibility** - All 7 iOS options (whenUnlocked, afterFirstUnlock, etc.)
- **KeychainAccessControl** - All 6 options (userPresence, biometryAny, devicePasscode, etc.)
- **FileDirectory** - documents, caches, custom URL
- **StorageError** - Comprehensive error types
- **StorageKeyDescriptor** - Audit snapshot of a key’s storage metadata
- **AnyStorageKey** - Type-erased storage key for catalogs
- **AnyStorageMigration** - Type-erased migration for protocol-based workflows
- **AnyCodable** - Type-erased Codable for mixed-type payloads
- **MigrationContext** - Context for conditional migrations (app version, device, system info)
- **MigrationResult** - Migration outcome with errors and metadata
- **MigrationError** - Error types for migration failures
- **DeviceInfo / SystemInfo** - Device and system metrics used by migrations

## Usage Pattern
Apps extend StorageKeys with their own key types and use StorageRouter.shared. This follows the Notification.Name pattern for discoverable keys.

## Audit & Validation
Apps can register multiple `StorageKeyCatalog`s (e.g., one per module) to generate audit reports and enforce key registration. Registration is additive and validates:
- Duplicate key names (across all registered catalogs)
- Missing descriptions
- Unregistered keys at runtime (debug assertions)

The `StorageRouter` provides discovery APIs to retrieve all registered keys for global audit reporting.

## Sync Behavior
StorageRouter can call WCSession.updateApplicationContext for manual or automaticSmall sync policies when availability allows it. Session activation and receiving data are owned by the app.

### Bootstrapping and Watch Requests
LocalData exposes helper APIs to make watch sync reliable after relaunch or reconnection:

- `StorageRouter.syncRegisteredKeysIfNeeded()` re-sends stored values for eligible keys.
- `StorageRouter.syncSnapshot()` returns a payload snapshot for replying to watch requests.

Apps should call `syncRegisteredKeysIfNeeded()` on launch and on WatchConnectivity reachability changes, and reply to watch-initiated requests with `syncSnapshot()` to avoid launch-order issues.

## Platforms
- iOS 17+
- watchOS 10+

## Future Ideas (Not Implemented)
- Key rotation strategies for encrypted data
- Watch-optimized data representations
- Persistent storage for sync policy overrides

Any future changes should keep LocalData documentation in sync with code changes.