Assist_Design/docs/architecture/system-overview.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

Layered Type System Architecture

The codebase follows a strict layering pattern to ensure single source of truth for all types and prevent drift:

@customer-portal/contracts    (Pure TypeScript types)
         ↓
@customer-portal/schemas      (Runtime validation with Zod)
         ↓
@customer-portal/integrations (Mappers for external APIs)
         ↓
      Applications             (BFF, Portal)

1. Contracts Package (packages/contracts/)

• Purpose: Pure TypeScript interface definitions - single source of truth
• Contents: Cross-layer contracts for billing, subscriptions, payments, SIM, orders
• Exports: Organized by domain (e.g., @customer-portal/contracts/billing)
• Rule: ZERO runtime dependencies, only pure types

2. Schemas Package (packages/schemas/)

• Purpose: Runtime validation schemas using Zod
• Contents: Matching Zod validators for each contract + integration-specific payload schemas
• Exports: Organized by domain and integration provider
• Usage: Validate external API responses, request payloads, and user input

3. Integration Packages (packages/integrations/)

• Purpose: Transform raw provider data into shared contracts
• Structure:
  • packages/integrations/whmcs/ - WHMCS billing integration
  • packages/integrations/freebit/ - Freebit SIM provider integration
• Contents: Mappers, utilities, and helper functions
• Rule: Must use @customer-portal/schemas for validation at boundaries

4. Application Layers

• BFF (apps/bff/): Import from contracts/schemas, never define duplicate interfaces
• Portal (apps/portal/): Import from contracts/schemas, use shared types everywhere
• Rule: Applications only consume, never define domain types

Legacy: Domain Package (Deprecated)

• Status: Being phased out in favor of contracts + schemas
• Migration: Re-exports now point to contracts package for backward compatibility
• Rule: New code should import from @customer-portal/contracts or @customer-portal/schemas

Logging Package

• Purpose: Centralized structured logging
• Features: Pino-based logging with correlation IDs
• Security: Automatic PII redaction memory:6689308

🔗 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

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