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Invoice Guard 💼🤖

AI-Powered Invoice Management & Automated Payment Reminders for Freelancers

A modern, full-stack invoice tracking application with AI-powered automated reminders. Track payments, manage due dates, and let AI handle payment follow-ups via email and SMS—so you can focus on your work.

License: MIT Node.js MongoDB

🌟 Key Features

💼 Core Invoice Management

  • Create, edit, and delete invoices with auto-generated invoice numbers
  • Real-time dashboard with financial insights
  • Track invoice status (pending, paid, overdue)
  • Multiple payment methods (UPI, Bank Transfer, PayPal, Cash)
  • Export/Import (CSV, JSON)
  • Search and filter functionality
  • Offline-first with localStorage

🤖 AI-Powered Automated Reminders

  • AI Message Generation: OpenAI/Anthropic integration for personalized, professional reminder messages
  • Smart Escalation: Automatic tone adjustment (gentle → firm → urgent) based on days overdue
  • Multi-Channel Delivery: Send reminders via Email (SendGrid/Resend/SMTP) and SMS (Twilio)
  • Automated Scheduling: Cron-based scheduler checks for overdue invoices every 6 hours
  • Manual Controls: Send immediate reminders, pause/resume automation per invoice
  • Business Hours: Respect business hours and exclude weekends

💰 Cost Management

  • Real-time cost tracking for AI, Email, and SMS services
  • Monthly spending dashboard with usage statistics
  • Budget limits with automatic enforcement
  • Cost warning notifications at 80% threshold
  • Service credit balance monitoring

🔐 Enterprise-Grade Security

  • Rate Limiting: 4-tier protection (general, strict, reminder, test)
  • JWT Authentication: Secure token-based authentication
  • Audit Logging: Complete audit trail with daily log rotation
  • Input Sanitization: XSS and NoSQL injection prevention
  • API Key Encryption: AES-256 encryption for all API keys
  • Security Headers: Helmet.js for HTTP security headers

📊 Analytics & Monitoring

  • Reminder history with delivery status tracking
  • Cost analysis and usage metrics
  • Reminder effectiveness tracking
  • Error logging and diagnostics
  • Audit log viewer with filtering

🚀 Quick Start

Prerequisites

  • Node.js 18+ and npm
  • MongoDB 6.0+ (local or cloud)
  • API keys for services (optional):
    • OpenAI or Anthropic (for AI reminders)
    • SendGrid/Resend (for email)
    • Twilio (for SMS)

Installation

  1. Clone the repository

    git clone https://github.com/yourusername/invoice-guard.git
cd invoice-guard

  2. Install dependencies

    # Install root dependencies
npm install

# Install backend dependencies
cd backend
npm install
cd ..

  3. Configure environment

    cd backend
cp .env.example .env
# Edit .env with your configuration

  4. Start the application

    # Start backend server
cd backend
npm start

# In another terminal, serve frontend
cd frontend
npx http-server -p 8000

  5. Access the application

    • Frontend: http://localhost:8000
    • Backend API: http://localhost:3000
    • Health Check: http://localhost:3000/api/health

📦 Project Structure

invoice-guard/
├── frontend/                    # Client-side application
│   ├── index.html              # Main application
│   ├── unsubscribe.html        # Opt-out page
│   ├── css/
│   │   ├── styles.css          # Main styles
│   │   ├── dark-premium.css    # Dark theme
│   │   └── premium-ui.css      # Premium components
│   └── js/
│       ├── app.js              # Main controller
│       ├── invoice.js          # Invoice logic
│       ├── reminder.js         # Reminder UI
│       ├── reminder-settings.js # Settings panel
│       ├── reminder-history.js  # History viewer
│       ├── service-config.js    # Service configuration
│       ├── cost-dashboard.js    # Cost monitoring
│       ├── test-preview.js      # Testing tools
│       └── ...                  # Other modules
├── backend/                     # Node.js/Express API
│   ├── server.js               # Express server
│   ├── models/                 # Mongoose models
│   │   ├── ClientContact.js
│   │   ├── ReminderLog.js
│   │   ├── ReminderConfig.js
│   │   └── ServiceConfig.js
│   ├── routes/                 # API routes
│   │   ├── reminders.js
│   │   ├── contacts.js
│   │   ├── serviceConfig.js
│   │   ├── costs.js
│   │   ├── auditLogs.js
│   │   └── ...
│   ├── services/               # Business logic
│   │   ├── aiService.js        # AI integration
│   │   ├── emailService.js     # Email delivery
│   │   ├── smsService.js       # SMS delivery
│   │   ├── schedulerService.js # Cron scheduler
│   │   └── notificationService.js
│   ├── middleware/             # Security & utilities
│   │   ├── rateLimiter.js      # Rate limiting
│   │   ├── auth.js             # JWT authentication
│   │   ├── auditLog.js         # Audit logging
│   │   └── sanitizer.js        # Input sanitization
│   └── config/
│       └── database.js         # MongoDB config
├── tests/                       # Property-based tests
│   ├── *.properties.test.js    # PBT tests
│   └── *.unit.test.js          # Unit tests
├── docs/                        # Documentation
│   ├── ARCHITECTURE.md
│   ├── DEPLOYMENT.md
│   └── SETUP.md
├── .kiro/                       # Spec documentation
│   └── specs/ai-automated-reminders/
│       ├── requirements.md
│       ├── design.md
│       └── tasks.md
├── SECURITY.md                  # Security guide
├── FEATURES.txt                 # Complete feature list
└── README.md                    # This file

⚙️ Configuration

Environment Variables

Create a .env file in the backend/ directory:

# Server
PORT=3000
NODE_ENV=development

# Database
DB_HOST=localhost
DB_PORT=3306
DB_NAME=invoice_guard

# Security
ENCRYPTION_KEY=your-32-character-encryption-key
JWT_SECRET=your-jwt-secret-key
JWT_EXPIRES_IN=7d

# AI Service (choose one)
AI_PROVIDER=openai
OPENAI_API_KEY=sk-your-key
# OR
ANTHROPIC_API_KEY=sk-ant-your-key

# Email Service (choose one)
EMAIL_PROVIDER=sendgrid
SENDGRID_API_KEY=SG.your-key
SENDER_EMAIL=noreply@yourdomain.com
# OR
RESEND_API_KEY=re_your-key
# OR use SMTP
SMTP_HOST=smtp.gmail.com
SMTP_PORT=587
SMTP_USER=your-email@gmail.com
SMTP_PASSWORD=your-app-password

# SMS Service
TWILIO_ACCOUNT_SID=ACyour-sid
TWILIO_AUTH_TOKEN=your-token
TWILIO_PHONE_NUMBER=+1234567890

# Scheduler
CRON_SCHEDULE=0 */6 * * *
ENABLE_SCHEDULER=true

# Rate Limiting
RATE_LIMIT_WINDOW_MS=900000
RATE_LIMIT_MAX_REQUESTS=100

🎯 Usage Guide

1. Basic Invoice Management

// Create an invoice
POST /api/invoices
{
  "clientName": "John Doe",
  "amount": 50000,
  "dueDate": "2024-02-15",
  "email": "john@example.com",
  "phone": "+919876543210"
}

2. Configure AI Reminders

  • Navigate to Settings → Service Configuration
  • Add your OpenAI/Anthropic API key
  • Configure email service (SendGrid/Resend/SMTP)
  • Configure SMS service (Twilio)
  • Test connections

3. Set Reminder Rules

  • Go to Settings → Reminder Settings
  • Enable automated reminders
  • Set interval (default: 3 days)
  • Choose channels (email, SMS, or both)
  • Configure business hours
  • Set maximum reminders per invoice

4. Monitor Costs

  • View Cost Dashboard for real-time spending
  • Set monthly budget limits
  • Receive warnings at 80% threshold
  • Track usage by service (AI, Email, SMS)

5. View Audit Logs

GET /api/audit-logs?userId=user123&startDate=2024-01-01

🧪 Testing

# Run all tests
npm test

# Run specific test suite
npm test -- invoice.properties.test.js

# Run tests in watch mode
npm run test:watch

# Run with coverage
npm run test:coverage

🔒 Security Features

  • Rate Limiting: Prevents API abuse with 4-tier protection
  • JWT Authentication: Secure token-based auth (ready for implementation)
  • Audit Logging: Complete audit trail stored in backend/logs/
  • Input Sanitization: XSS and injection attack prevention
  • API Key Encryption: AES-256 encryption for stored credentials
  • Security Headers: Helmet.js for HTTP security
  • CORS Configuration: Configurable cross-origin policies

See SECURITY.md for detailed security documentation.

📊 API Documentation

Core Endpoints

Invoices

  • GET /api/invoices - List all invoices
  • POST /api/invoices - Create invoice
  • PUT /api/invoices/:id - Update invoice
  • DELETE /api/invoices/:id - Delete invoice

Reminders

  • POST /api/reminders/send-now - Send immediate reminder
  • POST /api/reminders/pause - Pause automation
  • POST /api/reminders/resume - Resume automation
  • GET /api/reminders/status/:invoiceId - Check status

Service Configuration

  • POST /api/service-config - Add service config
  • GET /api/service-config - List configurations
  • PUT /api/service-config/:id - Update config
  • POST /api/service-config/test - Test connection

Cost Management

  • GET /api/costs/monthly - Monthly costs
  • GET /api/costs/usage - Usage statistics
  • POST /api/costs/budget - Set budget limit

Audit Logs

  • GET /api/audit-logs - View audit logs
  • GET /api/audit-logs/summary - Log summary

🚀 Deployment

Deploy to Heroku

# Login to Heroku
heroku login

# Create app
heroku create invoice-guard-app

# Add MongoDB addon
heroku addons:create mongolab:sandbox

# Set environment variables
heroku config:set OPENAI_API_KEY=sk-your-key
heroku config:set SENDGRID_API_KEY=SG-your-key

# Deploy
git push heroku main

Deploy to AWS

See docs/DEPLOYMENT.md for detailed AWS deployment guide.

Deploy Frontend to Netlify

# Install Netlify CLI
npm install -g netlify-cli

# Deploy
cd frontend
netlify deploy --prod

🛠️ Technology Stack

Frontend

  • Vanilla JavaScript (ES6+)
  • HTML5/CSS3
  • Tailwind CSS
  • Local Storage API

Backend

  • Node.js 18+
  • Express.js
  • MongoDB/Mongoose
  • JWT for authentication

AI & Communication

  • OpenAI GPT-4 / Anthropic Claude
  • SendGrid / Resend / Nodemailer
  • Twilio SMS

Security

  • Helmet.js
  • Express Rate Limit
  • Validator.js
  • Crypto (AES-256)

Testing

  • Vitest
  • Fast-check (property-based testing)

📈 Performance

  • Frontend Load Time: < 2 seconds
  • API Response Time: < 200ms (average)
  • Database Queries: Optimized with indexes
  • Caching: AI message caching for similar requests
  • Rate Limiting: Prevents abuse and ensures stability

🤝 Contributing

Contributions are welcome! Please follow these steps:

  1. Fork the repository
  2. Create a feature branch (git checkout -b feature/amazing-feature)
  3. Commit your changes (git commit -m 'Add amazing feature')
  4. Push to the branch (git push origin feature/amazing-feature)
  5. Open a Pull Request

📝 License

MIT License - see LICENSE file for details

🙏 Acknowledgments

  • OpenAI for GPT-4 API
  • Anthropic for Claude API
  • SendGrid for email delivery
  • Twilio for SMS services
  • All open-source contributors

📧 Support

🗺️ Roadmap

  • WhatsApp Business API integration
  • Multi-language support
  • Voice call reminders
  • Payment gateway integration
  • Mobile app (React Native)
  • Advanced analytics dashboard
  • Team collaboration features

Made with ❤️ for freelancers worldwide

⭐ Star this repo if you find it helpful!

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a powerful invoice manager for freelancers, small entreprenuers and all people who wants to manage thei invoices

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