SAB is a beer distribution and financial-control system I built as a freelance engagement for a multi-depot distributor. It's the digital replacement for a manual Excel-and-paper-receipt operation, tracking returnable containers, procurement, sales, deliveries, customer accounts, cash flow, and reconciliation across depots, with financial correctness as the non-negotiable core.

The Core: An Immutable Financial Ledger

The system runs on an append-only, ERPNext-inspired ledger architecture: every stock movement and every cent of money movement is recorded as an immutable entry, and current state (cash balance, stock on hand, customer credit) is a cache derived from that history and kept consistent under optimistic locking. Corrections are reversing entries, never edits; the original record stays forever.

• Money is decimal, never float: every value is exact decimal(10,2) passed as decimal strings, so totals never drift
• Append-only ledgers for stock, customer balances, container custody, and audit, with derived caches that must always agree
• The acceptance test for every feature: does it produce the same numbers the operations manager already sees in their daily report?

What It Manages

• Returnable containers (crates & barrels) with per-container custody tracking and a full deposit lifecycle
• Procurement, sales, and delivery trips: driver assignment, per-trip stock movements, customer returns, and factory-returns of empties
• Customer accounts with credit balances, plus a cash book covering every in/out and bank-to-cash transfers
• Reconciliation (scan-or-count audits), missing-unit liability tracking, and high-value sale approval gates
• OCR receipt scanning: snap a bank receipt and the system extracts the amount and reference automatically, with an LLM fallback for hard scans
• Role-based access control scoped per warehouse, a complete append-only audit trail, and read-only analytics with CSV/JSON export

How It's Built

An Nx monorepo, TypeScript end to end:

• NestJS + Fastify backend on Drizzle + PostgreSQL, BullMQ + Redis for background jobs, MinIO for receipt and attachment storage
• React 19 + Vite frontend consuming a live Swagger/OpenAPI contract generated from the backend's decorators
• JWT auth + RBAC, structured request-scoped logging, and integration tests against real Postgres / Redis / MinIO via Testcontainers
• Fully self-hosted with zero paid SaaS dependencies, auto-deployed via GitHub Actions → container registry → Docker Compose on a VPS