Assist_Design/docs/ARCHITECTURE.md

# Customer Portal Architecture

## 🏗️ **System Overview**

The Customer Portal is a modern monorepo with clean separation between frontend (Next.js) and backend (NestJS), designed for maintainability and scalability.

### **High-Level Structure**

```
apps/
  portal/              # Next.js frontend
  bff/                 # NestJS Backend-for-Frontend
packages/
  domain/              # Pure domain/types/utils (isomorphic)
  logging/             # Centralized logging utilities
  validation/          # Shared validation schemas
```

## 🎯 **Architecture Principles**

### **1. Separation of Concerns**
- **Dev vs Prod**: Clear separation with appropriate tooling
- **Services vs Apps**: Development runs apps locally, production containerizes everything
- **Configuration vs Code**: Environment variables for configuration, code for logic

### **2. Single Source of Truth**
- **One environment template**: `.env.example`
- **One Docker Compose** per environment
- **One script** per operation type

### **3. Clean Dependencies**
- **Portal**: Uses `@/lib/*` for shared utilities and services
- **BFF**: Feature-aligned modules with shared concerns in `src/common/`
- **Domain**: Framework-agnostic types and utilities

## 🚀 **Portal (Next.js) Architecture**

```
src/
  app/                 # App Router routes
  components/          # Design system (atomic design)
    atoms/             # Basic UI elements
    molecules/         # Component combinations
    organisms/         # Complex UI sections
    templates/         # Page layouts
  features/            # Feature modules (auth, billing, etc.)
  lib/                 # Core utilities and services
    api/               # Zod-aware fetch client + helpers
    hooks/             # Shared React hooks
    utils/             # Utility functions
  providers/           # Context providers
  styles/              # Global styles
```

### **Conventions**
- Use `@/lib/*` for shared frontend utilities and services
- Feature modules own their `components/`, `hooks/`, `services/`, and `types/`
- Cross-feature UI belongs in `components/` (atomic design)
- Avoid duplicate layers - no `core/` or `shared/` inside apps

## 🔧 **BFF (NestJS) Architecture**

```
src/
  modules/             # Feature-aligned modules
    auth/              # Authentication
    billing/           # Invoice and payment management
    catalog/           # Product catalog
    orders/            # Order processing
    subscriptions/     # Service management
  core/                # Core services and utilities
  integrations/        # External service integrations
    salesforce/        # Salesforce CRM integration
    whmcs/             # WHMCS billing integration
  common/              # Nest providers/interceptors/guards
  main.ts              # Application entry point
```

### **Conventions**
- Prefer `modules/*` over flat directories per domain
- Keep DTOs and validators in-module
- Reuse `packages/domain` for domain types
- External integrations in dedicated modules

## 📦 **Shared Packages**

### **Domain Package**
- **Purpose**: Framework-agnostic domain models and types
- **Contents**: Status enums, validation helpers, business types
- **Rule**: No React/NestJS imports allowed

### **Logging Package**
- **Purpose**: Centralized structured logging
- **Features**: Pino-based logging with correlation IDs
- **Security**: Automatic PII redaction [[memory:6689308]]

### **Validation Package**
- **Purpose**: Shared Zod validation schemas
- **Usage**: Form validation, API request/response validation

## 🔗 **Integration Architecture**

### **API Client**
- **Implementation**: Fetch wrapper using shared Zod schemas from `@customer-portal/domain`
- **Features**: CSRF protection, auth handling, consistent `ApiResponse` helpers
- **Location**: `apps/portal/src/lib/api/`

### **External Services**
- **WHMCS**: Billing system integration
- **Salesforce**: CRM and order management
- **Redis**: Caching and session storage
- **PostgreSQL**: Primary data store

## 🔒 **Security Architecture**

### **Authentication Flow**
- Portal-native authentication with JWT tokens
- Optional MFA support
- Secure token rotation with Redis backing

### **Error Handling**
- Never leak sensitive details to end users [[memory:6689308]]
- Centralized error mapping to user-friendly messages
- Comprehensive audit trails

### **Data Protection**
- PII minimization with encryption at rest/in transit
- Row-level security (users can only access their data)
- Idempotency keys on all mutating operations

## 🚀 **Development Workflow**

### **Path Aliases**
- **Portal**: `@/*`, `@/lib/*`, `@/features/*`, `@/components/*`
- **BFF**: `@/*` mapped to `apps/bff/src`
- **Domain**: Import via `@customer-portal/domain`

### **Code Quality**
- Strict TypeScript rules enforced repository-wide
- ESLint and Prettier for consistent formatting
- Pre-commit hooks for quality gates

## 📈 **Performance & Scalability**

### **Caching Strategy**
- **Invoices**: 60-120s per page; bust on WHMCS webhook
- **Cases**: 30-60s; bust after create/update  
- **Catalog**: 5-15m; manual bust on changes
- **Keys include user_id** to prevent cross-user leakage

### **Database Optimization**
- Connection pooling with Prisma
- Proper indexing on frequently queried fields
- Optional mirrors for external system data

---

*This architecture supports clean, maintainable code with clear separation of concerns and production-ready security.*