Case — Mercearia R&V (Desktop Inventory and Sales Management System)

Type: In-house product for a real client (retail — grocery store) Role: Full Stack Developer — full authorship (product, installer and support) Status: In production (daily use in the grocery store's operation) Stack: Java 21 + Spring Boot 3.5, Angular 20 + Angular Material, Electron 27 + TypeScript, embedded PostgreSQL, Liquibase, JWT (Spring Security), OpenHTMLToPDF/PDFBox, Chart.js, electron-builder + NSIS

Context and problem

A neighborhood grocery store needed inventory, sales and cash-register management — but with no server, no SaaS subscription fee and no dependence on stable internet. Market systems were either too expensive for the business's size or required infrastructure the client didn't have.

Solution

An offline-first desktop application that embeds the entire enterprise stack in a single Windows installer:

Complete POS: cart, discounts, multiple payment methods (cash, card, PIX), exchanges and returns
Cash register management: opening/closing with movement control
Audited inventory: low-stock alerts, movement history, product image upload
Customers and loyalty: registration, purchase history, points system
Reports: Chart.js dashboards and server-side PDF generation (receipts and reports) with OpenHTMLToPDF

Architecture and technical decisions

Embedded PostgreSQL + bundled JDK in the NSIS installer: the client installs a single .exe and has an enterprise-grade relational database running locally — zero external dependency, zero subscription fee
Electron orchestrates the lifecycle: splash screen, Spring Boot backend startup as a child process, health check before releasing the UI, clean process shutdown
Liquibase for schema versioning: system updates migrate the client's database automatically, with no manual intervention
JWT even in a local app: user profiles (owner vs. employee) with real authorization, not just hiding a button
Structured logs persisted to file: viable remote support — the client sends the log, I diagnose without going on-site

Challenges and solutions

Non-technical user as operator: single installer, automatic startup of all services and a health check — if something doesn't come up, the UI warns instead of opening broken
Reliability without DevOps: local database backups and automatic schema migration on every update
Modest hardware: stack tuned to run on a typical counter machine

Results and impact

System in production running the grocery store's day-to-day operations (sales, cash register, inventory) [time in production / sales volume TO CONFIRM]
Zero recurring cost for the client — no server, no subscription
Complete product cycle: requirements gathering with the client → development → installer → operation and support