PGG ERP

Pune Global Group operates as a general trading and retail business in India. The core operational need was a local-first invoicing system that handles Indian GST compliance correctly — CGST/SGST for intra-state transactions and IGST for inter-state ones — while also managing suppliers, purchase tracking, and payment receivables/payables.

Off-the-shelf tools like Tally or Zoho are either too heavyweight, too expensive for the volume, or lack the customisation needed for a lean manufacturing operation. The requirement was a fast, server-rendered tool that a single operator can use without training, deployed to the cloud but functional even on a local network.

The ERP is organised into six tightly integrated modules, each handling a distinct part of the business workflow. All modules share a common product catalog and GST engine.

Module A — Customers & Suppliers

Full CRUD for buyers and vendors. Stores GSTIN, state code, business name, phone, and address. State is used to auto-determine GST type (intra vs inter-state).

Module B — Products

Shared catalog used in both sales and purchases. Each product stores name, HSN code, unit, GST rate, and base price — single source of truth across all transactions.

Module C — Sales (Invoicing)

Create outgoing invoices with dynamic line items. Auto-numbering (INV-2526-001), automatic GST calculation, customer dropdown, and notes field. PDF download on detail page.

Module D — Purchases

Record incoming invoices from suppliers (PUR-2526-001). Tracks vendor's own invoice reference. Same dynamic line items and GST engine as sales, but on the payables side.

Module E — Payments (Receivables)

Track money owed by customers. Lists all sales with outstanding balances. Record partial or full payments against specific invoices with method and notes.

Module F — Payments Out (Payables)

Track money owed to suppliers. Lists all purchases with outstanding balances. Record payments to vendors with method tracking (cash, NEFT, UPI).

The GST calculation logic is the heart of the system. A single shared service (src/services/gst.js) handles tax computation for both sales and purchases, ensuring consistent behaviour across the application.

Tax Determination Logic

determineGstType(businessState, counterpartyState) // If business state === customer/supplier state → "CGST_SGST" (split rate equally into CGST + SGST) // If business state !== customer/supplier state → "IGST" (full rate goes to IGST column)

Line Item Computation

computeLineItem(qty, unitPrice, gstRate, gstType) taxableAmount = qty * unitPrice // If CGST_SGST: cgst = taxableAmount * (gstRate / 2) / 100 sgst = taxableAmount * (gstRate / 2) / 100 igst = 0 // If IGST: cgst = 0 sgst = 0 igst = taxableAmount * gstRate / 100 lineTotal = taxableAmount + cgst + sgst + igst

Every sales invoice can be downloaded as a pixel-perfect A4 PDF, generated server-side using Puppeteer (headless Chromium). The PDF template is a dedicated EJS file (views/invoice-pdf.ejs) with no navigation chrome — purely formatted for print.

The system uses 9 Prisma models backed by PostgreSQL 15. The schema enforces referential integrity through foreign keys and supports auto-incrementing invoice numbers per financial year via atomic DB transactions.

Invoice Number Generation

Sales: INV-YYXX-NNN (e.g. INV-2526-001) Purchases: PUR-YYXX-NNN (e.g. PUR-2526-001)

// YY = FY start year (25 for 2025-26) // XX = FY end year (26 for 2025-26) // NNN = zero-padded sequential, resets each April 1 // Both sequences are independent — atomic DB transaction

The system is intentionally simple: a pure server-rendered architecture with no SPA framework, no build step, and no client-side routing. This makes it fast to develop, easy to debug, and trivial to deploy.

Authentication

Single master password stored as a bcrypt hash in environment variables. Session-based authentication using express-session with connect-pg-simple for session storage in PostgreSQL. No multi-user, no roles — this is an internal tool for one operator.

Design Decisions

NO SPA — Pure server-rendered HTML via EJS. No React, no Vue, no build step. Pages load instantly, forms work without JavaScript (progressive enhancement for dynamic line items only).

STORED TOTALS — All GST amounts and grand totals are computed on POST and stored in the database. Views never recompute — they display what was stored. This prevents drift and ensures PDF accuracy.

ATOMIC INVOICE NUMBERS — Invoice and purchase numbers are generated inside a DB transaction to prevent duplicates under concurrent access. The sequence resets each financial year (April 1).

LOCAL-FIRST DEPLOY — Designed to run on localhost for daily use. Cloud Run deployment is the target for remote access, but the app functions perfectly without internet connectivity.

Route Structure

SALES & INVOICING GET /sales — List all invoices GET /sales/new — Invoice form (dynamic line items) POST /sales — Create invoice + compute GST GET /sales/:id — Detail view + payment history GET /sales/:id/pdf — Download PDF (Puppeteer)

PURCHASES GET /purchases — List all purchases GET /purchases/new — Purchase form (supplier dropdown) POST /purchases — Create purchase + compute GST GET /purchases/:id — Purchase detail view

PAYMENTS GET /payments — Receivables — outstanding from customers POST /payments — Record payment received GET /payments-out — Payables — outstanding to suppliers POST /payments-out — Record payment made

Project Layout

invoicer/ server.js — Express entry point prisma/schema.prisma — 9 models, migrations src/routes/ — customers, suppliers, products, sales, purchases, payments, paymentsOut src/services/gst.js — GST calculation (shared sales + purchases) src/services/pdf.js — Puppeteer PDF generation src/services/invoiceNo.js — Auto-numbering (FY-aware) src/middleware/auth.js — Master password session check views/ — EJS templates (layout, dashboard, CRUD forms) views/invoice-pdf.ejs — PDF-only template (no nav) public/style.css — Single CSS file, no build