Invoice System

You are a backend developer building a production-ready invoice system. The user wants to create a complete invoice generation and management system with storage, PDF export, and payment tracking.

What to check first

• Verify you have a database set up (PostgreSQL recommended) with migration tools like Prisma or Sequelize
• Check that you have pdfkit or puppeteer available: npm list pdfkit puppeteer
• Confirm Node.js version is 16+ with node --version

Steps

1. Install required dependencies: npm install express prisma @prisma/client pdfkit uuid dotenv stripe for Stripe integration
2. Define your Prisma schema with Invoice, InvoiceItem, and Customer models including timestamps and status fields
3. Create a database migration with npx prisma migrate dev --name init_invoice_schema
4. Build the invoice controller with methods: createInvoice(), getInvoiceById(), listInvoices(), updateInvoiceStatus()
5. Implement PDF generation using pdfkit with invoice.generatePDF() that iterates through invoice items and calculates totals
6. Add invoice item calculations in the model: subtotal, tax amount (use tax_rate * subtotal), and total due
7. Create routes for POST /invoices, GET /invoices/:id, GET /invoices, PATCH /invoices/:id/status
8. Implement soft delete for invoices by adding deleted_at timestamp and filtering archived invoices in queries

Code

import express from 'express';
import { PrismaClient } from '@prisma/client';
import PDFDocument from 'pdfkit';
import { v4 as uuidv4 } from 'uuid';
import fs from 'fs';

const app = express();
const prisma = new PrismaClient();
app.use(express.json());

// Create invoice with items
app.post('/invoices', async (req, res) => {
  try {
    const { customerId, items, taxRate = 0.10, dueDate } = req.body;
    
    const subtotal = items.reduce((sum, item) => sum + (item.quantity * item.unitPrice), 0);
    const taxAmount = subtotal * taxRate;
    const totalAmount = subtotal + taxAmount;

    const invoice = await prisma.invoice.create({
      data: {
        invoiceNumber: `INV-${Date.now()}-${uuidv4().slice(0, 8)}`,
        customerId,
        subtotal,
        taxAmount,
        totalAmount,
        taxRate,
        status: 'DRAFT',
        dueDate: new Date(dueDate),
        items: {
          create: items.map(item => ({
            description: item.description,
            quantity: item.quantity,
            unitPrice: item.unitPrice,
            lineTotal

Note: this example was truncated in the source. See the GitHub repo for the latest full version.

Common Pitfalls

• Treating this skill as a one-shot solution — most workflows need iteration and verification
• Skipping the verification steps — you don't know it worked until you measure
• Applying this skill without understanding the underlying problem — read the related docs first

When NOT to Use This Skill

• When a simpler manual approach would take less than 10 minutes
• On critical production systems without testing in staging first
• When you don't have permission or authorization to make these changes

How to Verify It Worked

• Run the verification steps documented above
• Compare the output against your expected baseline
• Check logs for any warnings or errors — silent failures are the worst kind

Production Considerations

• Test in staging before deploying to production
• Have a rollback plan — every change should be reversible
• Monitor the affected systems for at least 24 hours after the change