# SWP.Core - Technical Documentation

## Overview

SWP.Core is a modular .NET 9.0 enterprise application framework designed for multi-tenant SaaS applications. The system provides a comprehensive foundation for building scalable applications with advanced configuration management, security, telemetry, and database operations.

## Architecture

### High-Level Architecture

The system follows a layered architecture with clear separation of concerns:

```
┌─────────────────────────────────────────┐
│              Application Layer           │
├─────────────────────────────────────────┤
│               Core Library               │
│  ┌─────────────┬─────────────────────┐   │
│  │ Command/    │ Configuration       │   │
│  │ Query       │ Management          │   │
│  ├─────────────┼─────────────────────┤   │
│  │ Security &  │ Telemetry &         │   │
│  │ Encryption  │ Logging             │   │
│  ├─────────────┼─────────────────────┤   │
│  │ Database    │ Module Registry     │   │
│  │ Operations  │ (Autofac)           │   │
│  └─────────────┴─────────────────────┘   │
├─────────────────────────────────────────┤
│            Database Layer               │
│  ┌─────────────────────────────────────┐ │
│  │ PostgreSQL with Row Level Security  │ │
│  │ Multi-tenant Schema Management      │ │
│  └─────────────────────────────────────┘ │
└─────────────────────────────────────────┘
```

### Technology Stack

- **Framework**: .NET 9.0
- **Database**: PostgreSQL with Insight.Database
- **DI Container**: Autofac
- **Testing**: MSTest + Shouldly
- **Telemetry**: Application Insights + Seq
- **Security**: Sodium.Core for encryption
- **Configuration**: Custom multi-provider system

## Core Components

### 1. Configuration Management System

**Location**: `Core/Configurations/`

The system implements a sophisticated multi-provider configuration system that supports:

- **JSON Configuration Provider**: File-based configuration
- **Smart Configuration Provider**: Database-backed configuration with caching
- **Hierarchical Configuration**: Nested configuration with path-based access

**Key Classes**:
- [`ConfigurationBuilder`](Core/Configurations/ConfigurationBuilder.cs): Main builder for configuration providers
- [`SmartConfigProvider`](Core/Configurations/SmartConfigProvider/SmartConfigProvider.cs): Database-backed configuration
- [`PostgresConfigurationRepository`](Core/Configurations/SmartConfigProvider/Repositories/PostgresConfigurationRepository.cs): PostgreSQL storage

**Usage Example**:
```csharp
var config = new ConfigurationBuilder()
    .AddProvider(new JsonConfigProvider("appsettings.json"))
    .AddProvider(new SmartConfigProvider(connectionString))
    .Build();

var connectionString = config.GetConnectionString("DefaultConnection");
var feature = config.Get<FeatureConfig>("Feature");
```

### 2. Database Operations

**Location**: `Core/Database/`

Provides a robust database abstraction layer with:

- **Connection Factory Pattern**: [`IDbConnectionFactory`](Core/Database/ConnectionFactory/IDbConnectionFactory.cs)
- **Operation Scoping**: [`DatabaseScope`](Core/Database/DatabaseScope.cs) for transaction and telemetry management
- **Telemetry Integration**: Automatic performance tracking

**Key Classes**:
- [`SqlOperations`](Core/Database/SqlOperations.cs): Main database operations class
- [`PostgresConnectionFactory`](Core/Database/ConnectionFactory/PostgresConnectionFactory.cs): PostgreSQL connection management

**Usage Example**:
```csharp
var result = await _sqlOperations.ExecuteAsync(async conn => 
{
    return await conn.QueryAsync<User>("SELECT * FROM users WHERE id = @id", new { id });
}, "GetUserById");
```

### 3. Security & Encryption

**Location**: `Core/MultiKeyEncryption/`, `Core/ISecureTokenizer.cs`

Implements enterprise-grade security features:

- **Multi-Key Encryption**: [`MasterKey`](Core/MultiKeyEncryption/MasterKey.cs) for key management
- **Secure Connection Strings**: [`SecureConnectionString`](Core/MultiKeyEncryption/SecureConnectionString.cs)
- **Token Security**: [`SecureTokenizer`](Core/SecureTokenizer.cs) using Sodium.Core

**Features**:
- SHA-256 based token generation
- Secure password hashing
- Connection string encryption
- Key rotation support

### 4. Command/Query Pattern

**Location**: `Core/CommandQueries/`

Implements a lightweight command/query pattern without MediatR:

- **Base Command**: [`Command`](Core/CommandQueries/Command.cs) with correlation tracking
- **Command Interface**: [`ICommand`](Core/CommandQueries/ICommand.cs)
- **Response Handling**: [`CommandResponse`](Core/CommandQueries/CommandResponse.cs)
- **Problem Details**: [`ProblemDetails`](Core/CommandQueries/ProblemDetails.cs) for error handling

### 5. Telemetry & Logging

**Location**: `Core/Telemetry/`, `Core/SeqLogging/`

Comprehensive observability solution:

- **Application Insights Integration**: [`TelemetryExtensions`](Core/Telemetry/TelemetryExtensions.cs)
- **Seq Logging**: [`SeqLogger`](Core/SeqLogging/SeqLogger.cs) for structured logging
- **Custom Telemetry Channel**: [`SeqTelemetryChannel`](Core/Telemetry/SeqTelemetryChannel.cs)
- **Background Processing**: [`SeqBackgroundService`](Core/SeqLogging/SeqBackgroundService.cs)

**Features**:
- Structured logging with correlation IDs
- Performance metrics collection
- Exception tracking with full stack traces
- Custom enrichers for metadata

### 6. Module Registry (Dependency Injection)

**Location**: `Core/ModuleRegistry/`

Autofac-based modular dependency injection:

- **Security Module**: [`SecurityModule`](Core/ModuleRegistry/SecurityModule.cs)
- **Telemetry Module**: [`TelemetryModule`](Core/ModuleRegistry/TelemetryModule.cs)
- **Seq Logging Module**: [`SeqLoggingModule`](Core/ModuleRegistry/SeqLoggingModule.cs)
- **Database Module**: [`DbPostgreSqlModule`](Core/Database/ModuleRegistry/DbPostgreSqlModule.cs)

## Database Schema

### Multi-Tenant Architecture

The system implements a sophisticated multi-tenant architecture using PostgreSQL:

**Core Tables** (in identity schema):
- **users**: User authentication and profile data
- **organizations**: Tenant/organization management
- **user_organizations**: Many-to-many relationship with PIN codes

**Security Features**:
- **Row Level Security (RLS)**: Automatic tenant isolation
- **Schema-based Separation**: Each tenant can have dedicated schemas
- **Connection String Encryption**: Secure tenant database connections

**Example Schema Setup**:
```sql
-- From SetupIdentitySystem.cs
CREATE TABLE identity.users (
    id SERIAL PRIMARY KEY,
    email VARCHAR(256) NOT NULL UNIQUE,
    password_hash VARCHAR(256) NOT NULL,
    security_stamp VARCHAR(36) NOT NULL,
    email_confirmed BOOLEAN NOT NULL DEFAULT FALSE,
    created_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP
);

-- RLS Policy
CREATE POLICY organization_access ON identity.organizations
    USING (id IN (
        SELECT organization_id 
        FROM identity.user_organizations 
        WHERE user_id = current_setting('app.user_id', TRUE)::INTEGER
    ));
```

## Testing Strategy

**Location**: `Tests/`

Comprehensive testing approach using MSTest + Shouldly:

- **Unit Tests**: Component-level testing
- **Integration Tests**: Database and external service testing
- **Configuration Tests**: Multi-provider configuration validation

**Testing Principles**:
- Clear variable names for debugging
- Shouldly assertions for readable test failures
- Isolated test environments
- Mock-based testing for external dependencies

**Example Test Structure**:
```csharp
[TestMethod]
public void SecureTokenizer_Should_Generate_Valid_Token()
{
    // Arrange
    var tokenizer = new SecureTokenizer();
    var inputText = "test-password";
    
    // Act
    var generatedToken = tokenizer.TokenizeText(inputText);
    
    // Assert
    generatedToken.ShouldNotBeNullOrEmpty();
    generatedToken.Length.ShouldBe(64); // SHA-256 hex length
}
```

## Configuration

### Multi-Provider Configuration System

The system supports multiple configuration sources with hierarchical merging:

1. **JSON Files**: Traditional appsettings.json
2. **Database**: Dynamic configuration stored in PostgreSQL
3. **Environment Variables**: Runtime configuration
4. **Azure App Configuration**: Cloud-based configuration (planned)

**Configuration Structure**:
```json
{
  "ConnectionStrings": {
    "DefaultConnection": "Host=localhost;Database=app;..."
  },
  "ApplicationInsights": {
    "ConnectionString": "InstrumentationKey=...",
    "UseSeqLoggingTelemetryChannel": true
  },
  "SeqConfiguration": {
    "IngestionEndpoint": "http://localhost:5341",
    "Environment": "Development"
  },
  "Feature": {
    "Enabled": true,
    "RolloutPercentage": 25,
    "AllowedUserGroups": ["beta"]
  }
}
```

## Deployment & Operations

### Prerequisites

- .NET 9.0 Runtime
- PostgreSQL 12+
- Seq (for logging)
- Application Insights (for telemetry)

### Environment Setup

1. **Database Setup**: Run DDL scripts from `Database/Core/DDL/`
2. **Configuration**: Set up appsettings.json with connection strings
3. **Logging**: Configure Seq endpoint
4. **Telemetry**: Set Application Insights connection string

### Performance Considerations

- **Connection Pooling**: Managed by Npgsql
- **Async Operations**: All database operations are async
- **Telemetry Overhead**: Minimal impact with background processing
- **Configuration Caching**: Smart config provider includes caching

## Security Considerations

### Authentication & Authorization

- **Password Security**: SHA-256 hashing with security stamps
- **Token Management**: Secure token generation and validation
- **Multi-Tenant Isolation**: RLS policies prevent cross-tenant data access

### Data Protection

- **Connection String Encryption**: Sensitive connection data encrypted
- **Audit Trails**: Comprehensive logging of all operations
- **Input Validation**: FluentValidation integration

### Compliance

- **GDPR Ready**: User data management and deletion capabilities
- **Audit Logging**: Complete operation tracking
- **Data Encryption**: At-rest and in-transit encryption

## Extension Points

### Adding New Modules

1. Create new Autofac module inheriting from `Module`
2. Register services in `Load()` method
3. Add module to container builder

### Custom Configuration Providers

1. Implement `IConfigurationProvider`
2. Add to `ConfigurationBuilder`
3. Handle configuration merging strategy

### Custom Telemetry

1. Extend `TelemetryExtensions`
2. Add custom enrichers
3. Configure Application Insights processors

## Troubleshooting

### Common Issues

1. **Database Connection**: Check PostgreSQL connection strings and user permissions
2. **Configuration Loading**: Verify JSON syntax and provider order
3. **Telemetry**: Ensure Application Insights and Seq endpoints are accessible
4. **Multi-Tenant**: Verify RLS policies and user context settings

### Debugging

- Enable detailed logging in Seq
- Use Application Insights for performance monitoring
- Check database query performance with PostgreSQL logs
- Validate configuration loading with debug output

## Future Roadmap

- Azure App Configuration integration
- Advanced caching strategies
- GraphQL API support
- Event sourcing capabilities
- Microservices decomposition support