# Secure Storage Implementation Guide for TimeSafari App

## Overview

This document outlines the implementation of secure storage for the TimeSafari app using a platform-agnostic approach with Capacitor and absurd-sql solutions. The implementation focuses on:

1. **Platform-Specific Storage Solutions**:
   - Web: absurd-sql with IndexedDB backend and Web Worker support
   - iOS/Android: Capacitor SQLite with native SQLite implementation
   - Electron: Node SQLite (planned, not implemented)

2. **Key Features**:
   - Platform-agnostic SQLite interface
   - Web Worker support for web platform
   - Consistent API across platforms
   - Performance optimizations (WAL, mmap)
   - Comprehensive error handling and logging
   - Type-safe database operations
   - Storage quota management
   - Platform-specific security features

## Architecture

The storage implementation follows a layered architecture:

1. **Platform Service Layer**
   - `PlatformService` interface defines platform capabilities
   - Platform-specific implementations:
     - `WebPlatformService`: Web platform with absurd-sql
     - `CapacitorPlatformService`: Mobile platforms with native SQLite
     - `ElectronPlatformService`: Desktop platform (planned)
   - Platform detection and capability reporting
   - Storage quota and feature detection

2. **SQLite Service Layer**
   - `SQLiteOperations` interface for database operations
   - Base implementation in `BaseSQLiteService`
   - Platform-specific implementations:
     - `AbsurdSQLService`: Web platform with Web Worker
     - `CapacitorSQLiteService`: Mobile platforms with native SQLite
     - `ElectronSQLiteService`: Desktop platform (planned)
   - Common features:
     - Transaction support
     - Prepared statements
     - Performance monitoring
     - Error handling
     - Database statistics

3. **Data Access Layer**
   - Type-safe database operations
   - Transaction support
   - Prepared statements
   - Performance monitoring
   - Error recovery
   - Data integrity verification

## Implementation Details

### Web Platform (absurd-sql)

The web implementation uses absurd-sql with the following features:

1. **Web Worker Support**
   - SQLite operations run in a dedicated worker thread
   - Main thread remains responsive
   - SharedArrayBuffer support when available
   - Worker initialization in `sqlite.worker.ts`

2. **IndexedDB Backend**
   - Persistent storage using IndexedDB
   - Automatic data synchronization
   - Storage quota management (1GB limit)
   - Virtual file system configuration

3. **Performance Optimizations**
   - WAL mode for better concurrency
   - Memory-mapped I/O (30GB when available)
   - Prepared statement caching
   - 2MB cache size
   - Configurable performance settings

Example configuration:
```typescript
const webConfig: SQLiteConfig = {
  name: 'timesafari',
  useWAL: true,
  useMMap: typeof SharedArrayBuffer !== 'undefined',
  mmapSize: 30000000000,
  usePreparedStatements: true,
  maxPreparedStatements: 100
};
```

### Mobile Platform (Capacitor SQLite)

The mobile implementation uses Capacitor SQLite with:

1. **Native SQLite**
   - Direct access to platform SQLite
   - Native performance
   - Platform-specific optimizations
   - 2GB storage limit

2. **Platform Integration**
   - iOS: Native SQLite with WAL support
   - Android: Native SQLite with WAL support
   - Platform-specific permissions handling
   - Storage quota management

Example configuration:
```typescript
const mobileConfig: SQLiteConfig = {
  name: 'timesafari',
  useWAL: true,
  useMMap: false, // Not supported on mobile
  usePreparedStatements: true
};
```

## Database Schema

The implementation uses the following schema:

```sql
-- Accounts table
CREATE TABLE accounts (
  did TEXT PRIMARY KEY,
  public_key_hex TEXT NOT NULL,
  created_at INTEGER NOT NULL,
  updated_at INTEGER NOT NULL
);

-- Settings table
CREATE TABLE settings (
  key TEXT PRIMARY KEY,
  value TEXT NOT NULL,
  updated_at INTEGER NOT NULL
);

-- Contacts table
CREATE TABLE contacts (
  id TEXT PRIMARY KEY,
  did TEXT NOT NULL,
  name TEXT,
  created_at INTEGER NOT NULL,
  updated_at INTEGER NOT NULL,
  FOREIGN KEY (did) REFERENCES accounts(did)
);

-- Performance indexes
CREATE INDEX idx_accounts_created_at ON accounts(created_at);
CREATE INDEX idx_contacts_did ON contacts(did);
CREATE INDEX idx_settings_updated_at ON settings(updated_at);
```

## Error Handling

The implementation includes comprehensive error handling:

1. **Error Types**
```typescript
export enum StorageErrorCodes {
  INITIALIZATION_FAILED = 'STORAGE_INIT_FAILED',
  QUERY_FAILED = 'STORAGE_QUERY_FAILED',
  TRANSACTION_FAILED = 'STORAGE_TRANSACTION_FAILED',
  PREPARED_STATEMENT_FAILED = 'STORAGE_PREPARED_STATEMENT_FAILED',
  DATABASE_CORRUPTED = 'STORAGE_DB_CORRUPTED',
  STORAGE_FULL = 'STORAGE_FULL',
  CONCURRENT_ACCESS = 'STORAGE_CONCURRENT_ACCESS'
}
```

2. **Error Recovery**
   - Automatic transaction rollback
   - Connection recovery
   - Data integrity verification
   - Platform-specific error handling
   - Comprehensive logging

## Performance Monitoring

The implementation includes built-in performance monitoring:

1. **Statistics**
```typescript
interface SQLiteStats {
  totalQueries: number;
  avgExecutionTime: number;
  preparedStatements: number;
  databaseSize: number;
  walMode: boolean;
  mmapActive: boolean;
}
```

2. **Monitoring Features**
   - Query execution time tracking
   - Database size monitoring
   - Prepared statement usage
   - WAL and mmap status
   - Platform-specific metrics

## Security Considerations

1. **Web Platform**
   - Worker thread isolation
   - Storage quota monitoring
   - Origin isolation
   - Cross-origin protection
   - SharedArrayBuffer availability check

2. **Mobile Platform**
   - Platform-specific permissions
   - Storage access control
   - File system security
   - Platform sandboxing

## Testing Strategy

1. **Unit Tests**
   - Platform service tests
   - SQLite service tests
   - Error handling tests
   - Performance tests

2. **Integration Tests**
   - Cross-platform tests
   - Migration tests
   - Transaction tests
   - Concurrency tests

3. **E2E Tests**
   - Platform-specific workflows
   - Error recovery scenarios
   - Performance benchmarks
   - Data integrity verification

## Success Criteria

1. **Performance**
   - Query response time < 100ms
   - Transaction completion < 500ms
   - Memory usage < 50MB
   - Database size < platform limits:
     - Web: 1GB
     - Mobile: 2GB

2. **Reliability**
   - 99.9% uptime
   - Zero data loss
   - Automatic recovery
   - Transaction atomicity

3. **Security**
   - Platform-specific security features
   - Storage access control
   - Data protection
   - Audit logging

4. **User Experience**
   - Smooth platform transitions
   - Clear error messages
   - Progress indicators
   - Recovery options

## Future Improvements

1. **Planned Features**
   - SQLCipher integration for mobile
   - Electron platform support
   - Advanced backup/restore
   - Cross-platform sync

2. **Security Enhancements**
   - Biometric authentication
   - Secure enclave usage
   - Advanced encryption
   - Key management

3. **Performance Optimizations**
   - Advanced caching
   - Query optimization
   - Memory management
   - Storage efficiency