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Backend

Central multi-application business API

One backend for the workshop, rentals, sales, invoicing and bank reconciliation

Key figures

lines of code
~37,000
automated tests
~280
data models
44
endpoints
~250

Context

The workshop, rentals, sales, invoicing, bank reconciliation and inventory all had to run on a single backend. That backend serves 7 internal applications, the showcase website and the online store.

My role

From design to operations, fully autonomously.

Solution

Routes are organised by consuming application: around 250 endpoints, backed by 44 Prisma models. The API generates quotes as PDFs and has them signed online through a single-use token link. It also issues payment requests with a bank transfer QR code, automatically reminded then cancelled.

Service invoices are pushed to the ERP without blocking the local action, and an idempotent invoicing gateway serves the online store. Bank reconciliation runs in a worker thread using fuzzy matching. On top of that: calendar, documents, transactional e-mails and cache revalidation for the public website.

Key features

  • PDF quotes signed online

    Customers sign their quote remotely through a single-use token link.

  • Bank transfer QR code payments

    Payment requests with an EPC QR code, plus automatic reminders and cancellations.

  • Idempotent invoicing gateway

    The online store can replay an invoicing request without ever creating a duplicate.

  • Background bank reconciliation

    Fuzzy matching runs in a worker thread, so request handling is never blocked.

Engineering challenges

  1. 1

    PostgreSQL transactional locks

    Advisory locks acquired in a consistent order rule out deadlocks.

  2. 2

    Strict data model and contracts

    44 Prisma models, 115 migrations and strict Zod contracts.

  3. 3

    Server-side OIDC SSO

    PKCE, HttpOnly sessions, tokens encrypted at rest and back-channel logout.

  4. 4

    CI-driven authentication switch

    Legacy, dual or OIDC modes, switchable from CI to migrate without anyone losing access.

Tech stack

Backend
Node.jsExpressTypeScriptZodWinstonnode-cron
Data
PrismaPostgreSQL 16
Security
jose
Integrations
@react-pdfsharpExcelJS
Infrastructure
DockerGHCR

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