High-Performance Invoicing Engine & Automated Payment Recovery Platform

InvoiceFlow is a production-grade invoicing and payment infrastructure platform engineered for freelancers and boutique agencies. It streamlines client billing into a frictionless workflow with instant Stripe/Razorpay checkout links, automated PDF generation, background reminder queues via BullMQ, and real-time webhook telemetry.

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graph TD Client[Client / Browser UI] -->|HTTPS / WSS| CDN[Vercel Edge / Static Assets] Client -->|REST API Requests| API[Express API Server on Bun] subgraph Core Engine API --> Auth[JWT & Google OAuth2.0] API --> Validation[Zod Strict Schemas] API --> RateLimiter[Sliding Window Rate Limiter] API --> DB[(PostgreSQL Database via Prisma)] end subgraph Async Processing API -->|Enqueue Jobs| Redis[(Redis / Upstash)] Redis --> Worker[BullMQ Background Worker] Worker --> EmailService[Resend Delivery Engine] Worker --> PDFEngine[Headless PDF Generator] end subgraph Webhook Ingestion Stripe[Stripe / Razorpay Webhooks] -->|HMAC-Signed Events| Ingestion[Idempotent Webhook Handler] Ingestion -->|State Machine Update| DB Ingestion -->|Trigger Notification| Redis end

⚡ Sub-Millisecond Event Pipeline: Built on Bun and Express with strict Zod validation, ensuring sub-50ms API responses for invoice rendering and payment intent creation.

🔄 Idempotent Payment Ingestion: Webhook consumers verify cryptographic HMAC signatures (Stripe-Signature / Razorpay HMAC-SHA256) and enforce database transaction isolation to prevent double-crediting.

📬 Background Queue Worker: BullMQ + Redis handles async email dispatch, scheduled reminder escalations, and automated PDF document compilation without blocking the main event loop.

🛡️ Multi-Layered Security Core:

CSRF Double-Submit Cookie protection (csrf-csrf)

Argon2 / BCrypt 12-round salted password hashing with sentinel dummy compare to prevent username enumeration timing attacks

Strict tenant isolation on all Prisma queries via user-scoped foreign keys

Granular rate-limiting on sensitive auth and payment routes

🎨 Glassmorphic Interface: Built with React 19, Tailwind CSS 4, Framer Motion, and TanStack Query with optimistic UI mutations and dark/light system sync.

Subsystem

Stack / Tooling

Purpose

API Core

Bun / Node.js, Express 5, TypeScript

REST endpoints & business logic

Persistence

PostgreSQL (Neon / Supabase), Prisma ORM

ACID-compliant relational storage

Background Jobs

BullMQ, Redis (Upstash)

Scheduled payment reminders & retries

Frontend

React 19, Vite, Tailwind CSS 4, Framer Motion

High-converting client dashboard

Data Fetching

TanStack React Query v5

Cache invalidation, optimistic updates

Email Gateway

Resend API (Domain-verified DKIM/SPF)

Transactional invoice delivery

Payment Gateways

Stripe Checkout, Razorpay

Global USD ($) and local INR (₹) processing

Observability

Pino Structured Logging, Sentry

Request tracing and error profiling

Bun (v1.2+) or Node.js (v20+)

Redis instance (local or Upstash)

PostgreSQL database

git clone https://github.com/sidsri14/invoiceflow.git cd invoiceflow

cd backend bun install cp .env.example .env # Run database migrations bunx prisma migrate deploy # Start API server bun run dev # In a separate terminal, start background worker bun run worker

cd ../frontend npm install npm run dev

Navigate to http://localhost:5173 to explore the dashboard and interactive demo generator.

The test suite covers API response formatting, cryptographic auth workflows, schema validators, and webhook processors:

Results:

Backend: 38/38 Unit Tests Passing (2.36s execution time)

Frontend: 13/13 Vitest Tests Passing, 0 Type Errors across 3,000+ transformed modules

Public Demo Generator (No-Auth Sandbox)

Resend Automated Email Reminders & Delivery Telemetry

Multi-Gateway Ingestion (Stripe + Razorpay)

Dark / Light Adaptive Theme System

AI-Powered Invoice Extraction from Receipts (OCR + LLM)

Multi-Currency Real-time FX Auto-Conversion

Automated Webhook Dispatch to Custom Endpoints

Distributed under the MIT License. Crafted with precision by Siddharth Srivastava .

Full-stack invoicing product with payment workflows, client management, and a modern TypeScript interface.