Invoice API

A robust backend service built to streamline the invoicing process for freelancers, businesses, and finance platforms using JavaScript, Express, and MongoDB.

Core Features

For Businesses & Freelancers

• Client Management: Create and manage client profiles
• Invoice Generation: Generate and send professional invoices
• Payment Tracking: Monitor payment statuses and due dates
• Recurring Invoices: Automate invoicing for repeat services
• PDF Export: Download invoices in PDF format

For Admins

• Revenue Reports: Generate financial summaries
• Overdue Alerts: Notifications for overdue invoices
• Currency Support: Handle multiple currencies
• Activity Logs: Track invoice and payment activity

Technical Architecture

Built on a scalable stack tailored for financial data integrity and performance:

• Node.js & Express: Lightweight RESTful API
• MongoDB: NoSQL storage for invoices, clients, and payments
• PDFKit: Generate downloadable invoice documents
• JWT Authentication: Secure access control
• Cron Jobs: Automate recurring billing and overdue reminders

Implementation Highlights

Automated Recurring Invoicing

// Example of recurring invoice generation
const generateRecurringInvoices = async () => {
  const recurringInvoices = await Invoice.find({
    isRecurring: true,
    nextBillingDate: { $lte: new Date() }
  });

  for (const invoice of recurringInvoices) {
    const newInvoice = new Invoice({
      ...invoice.toObject(),
      issueDate: new Date(),
      dueDate: new Date(Date.now() + 7 * 24 * 60 * 60 * 1000),
      paid: false,
      _id: undefined,
      createdAt: undefined,
      updatedAt: undefined
    });

    await newInvoice.save();

    // Update next billing date
    invoice.nextBillingDate = new Date(Date.now() + invoice.billingCycleDays * 24 * 60 * 60 * 1000);
    await invoice.save();
  }
};