Library Management System

Event-Driven Library Management System built with TypeScript
following SOLID principles and Event-Driven Design.

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🎯 Architecture Overview

This project implements a complete library management system using an event-driven methodology where each business event maps directly to a public method, providing clear API contracts and maintainable code structure.

Core Principles

• Event-Driven Design: 140+ catalogued events drive the API design
• SOLID Principles: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion
• Type Safety: Full TypeScript with strict mode
• Test Coverage: Comprehensive Jest test suites for all components

📦 Project Structure

src/
├── enums/           # 11 enumerations (BookCategory, BorrowingStatus, etc.)
├── interfaces/      # 4 core interfaces (IUser, INotifiable, ISearchable, IBorrowable)
├── types/           # Type definitions and DTOs
├── models/          # 4 data models (Book, BorrowingRecord, Comment, Notification)
├── domains/         # 3 domain classes (Borrower, Library, Librarian)
└── policies/        # Business rules and validation policies (100+ constants)

tests/
├── domains/         # Domain class tests
├── models/          # Model tests
└── policies/        # Business rules tests

🏗️ Domain Classes

Borrower (27 public methods + 2 private)

Represents library users who borrow books.

• Implements: IUser, INotifiable, ISearchable
• Key Features: Book borrowing, comments/reviews, claims management, notifications

Library (12 methods)

Central system orchestrator managing all library operations.

• Key Features: Book catalog management, user registration, borrowing transactions, overdue tracking

Librarian (33 methods)

Library staff with administrative capabilities.

• Implements: IUser, INotifiable
• Key Features: Book/user management, comment moderation, claims processing, analytics

🎨 Business Policies

8 policy categories with 100+ configurable constants:

• BORROWING_POLICIES: Max books per user (3), extension limits
• TIME_POLICIES: Borrowing period (14 days), reminder schedule
• FEE_POLICIES: Late fees (€0.50/day), damage fees
• ACCESS_POLICIES: Age restrictions, role permissions
• VALIDATION_POLICIES: Input validation rules
• ANALYTICS_POLICIES: Reporting thresholds
• WORKFLOW_POLICIES: Automation rules
• CATEGORIZATION_POLICIES: Content organization

🚀 Getting Started

Prerequisites

• Node.js 16+
• npm or yarn

Installation

# Install dependencies
npm install

# Build the project
npm run build

# Run tests
npm test

# Run tests with coverage
npm run test:coverage

# Lint code
npm run lint

🧪 Testing

Comprehensive test suites covering:

• Domain Logic: Borrower, Library, Librarian workflows
• Models: Book, BorrowingRecord, Comment, Notification
• Policies: Business rules validation
• Integration: Complete borrowing workflows

# Run all tests
npm test

# Run specific test suite
npm test -- Borrower.test.ts

# Watch mode
npm test -- --watch

📝 Event-Driven Methodology

Each public method corresponds to a business event from the original specification:

/**
 * Borrow a book from the library
 * Event: "le USER emprunte un livre"
 */
borrowBook(bookId: UUID): BorrowingRecord {
  // Validation using policies
  if (!bookId) throw new Error('Book ID is required.');
  if (this.borrowedBooks.length >= BORROWING_POLICIES.MAX_BOOKS_PER_USER) {
    throw new Error('Maximum books limit reached.');
  }
  // Business logic...
}

🛠️ Development

Code Style

• TypeScript: Strict mode enabled
• ESLint: Configured for TypeScript
• Prettier: Code formatting
• Path Aliases: @models, @interfaces, @enums, etc.

Adding New Features

1. Define the event in your catalog
2. Create the corresponding public method
3. Add validation using business policies
4. Write comprehensive tests
5. Update documentation

📊 Code Quality

• Type Safety: 100% TypeScript with strict checks
• Linting: ESLint with TypeScript rules
• Testing: Jest with ts-jest
• Coverage: Comprehensive test coverage across all layers

🔄 Future Enhancements

• Implement concrete service integrations (NotificationService, EmailService, SearchService)
• Add database persistence layer
• Create REST API with Express/Fastify
• Build admin dashboard
• Add real-time notifications (WebSocket)
• Implement Python/FastAPI version

📄 License

MIT

👥 Contributing

Contributions welcome! Please follow the event-driven methodology and ensure:

• All new features have corresponding events
• Comprehensive tests are included
• SOLID principles are respected
• TypeScript strict mode passes

🙏 Acknowledgments

Built with a "civilized" approach to software design - like writing a sonnet, where discipline within structure creates elegant, maintainable code.