Purchasing Module

The purchasing domain manages the full procurement lifecycle across three backend modules:

Module	Path	Purpose
Suppliers	apps/backend/src/suppliers/	Vendor/partner registry
Purchase Orders	apps/backend/src/purchase-orders/	Procurement documents before goods receipt
Purchases	apps/backend/src/purchases/	Goods received documents

Architecture

All three modules follow hexagonal architecture:

<module>/
├── <module>.module.ts                    # NestJS module definition
├── application/
│   ├── <module>.service.ts               # Business logic (use cases)
│   ├── <module>.listener.ts              # Event listeners (cross-module integration)
│   └── events/                           # Domain events
├── domain/
│   └── <module>-repository.domain.ts     # Repository interface (port)
├── infrastructure/
│   └── <module>.repository.ts            # Kysely DB implementation (adapter)
└── interfaces/
    ├── <module>.controller.ts            # HTTP routes (adapter)
    ├── dtos/                             # Request validation DTOs
    └── query/                            # Query parameter classes

Dependency flow: interfaces → application → domain ← infrastructure

Domain Concepts

Supplier

A vendor or partner from which goods are purchased. Contains tax information (taxId, taxName, taxAddress), contact details, and geographic location. All operations are scoped by businessId.

Purchase Order (PO)

A procurement document created before goods are received. Tracks:

• Order items with product/variant details, quantities, and pricing
• Receipt summary — ordered vs. received quantities per item (updated by GRN events)
• Goods received note status — pending → partial → received
• Document number — auto-generated unique identifier

Purchase

A goods-received document recording physical receipt of items from a supplier. Tracks:

• Purchase items with inventory detail (batch, serial, location allocation)
• Cost detail — WAC-based cost snapshot at document creation time
• Document number — auto-generated

Main Flows

1. Standard Procurement Flow

Create Supplier → Create PO → Create GRN → PO receipt summary auto-updated

2. GRN → PO Integration (Event-Driven)

When a Goods Received Note is created:

1. OnCreateGoodsReceivedNoteEvent is emitted
2. PurchaseOrdersListener handles the event, updates the PO's receiptSummary
3. If all items are fully received, goodsReceivedNoteStatus transitions to received

3. Cost Calculation

On document creation/update:

1. Items are extracted from purchaseDetail JSON
2. Grouped by location and product
3. Inventory records are ensured to exist
4. Current WAC costs are fetched from inventory
5. Cost detail is calculated and stored as costDetail JSON

API Endpoints

Suppliers — /suppliers

Method	Path	Description	Auth
POST	/suppliers	Create supplier	Create permission
GET	/suppliers	List suppliers (paginated)	Read permission
GET	/suppliers/:id	Get supplier by ID	Read permission
PATCH	/suppliers/:id	Update supplier	Update permission
DELETE	/suppliers/:id	Delete supplier	Delete permission

All endpoints require businessId for multi-tenancy scoping.

Purchase Orders — /purchase-orders

All endpoints are protected by RolesGuard with PolicyResource.Purchase and require appropriate PolicyAction permission (Create/Read/Update/Delete).

Method	Path	Description
POST	/purchase-orders	Create PO
GET	/purchase-orders	List POs (paginated, filtered)
GET	/purchase-orders/search	Search POs
GET	/purchase-orders/:id	Get PO by ID
GET	/purchase-orders/:id/pdf	Download PO as PDF
GET	/purchase-orders/:id/print	HTML print preview
PATCH	/purchase-orders/:id	Update PO
DELETE	/purchase-orders/:id	Delete PO (requires businessId query)

Filters: status, goodsReceivedNoteStatus, createdAt range, orderDate range.

Purchases — /purchases

Method	Path	Description
POST	/purchases	Create purchase
GET	/purchases	List purchases (paginated, filtered)
GET	/purchases/search	Search purchases
GET	/purchases/:id	Get purchase by ID
GET	/purchases/:id/pdf	Download purchase as PDF
GET	/purchases/:id/pdf/content	Get PDF as base64 + metadata
GET	/purchases/:id/print	HTML print preview
PATCH	/purchases/:id	Update purchase
DELETE	/purchases/:id	Delete purchase

Filters: status, documentNumber, createdAt range, purchaseDate range.

Database Tables

Table	Key columns
supplier	id, businessId, name, taxId, taxName, taxAddress, contact (JSON), supplierCode
purchaseOrder	id, businessId, supplierId, purchaseDetail (JSON), costDetail (JSON), receiptSummary (JSON), status, goodsReceivedNoteStatus, documentNumber
purchase	id, businessId, supplierId, purchaseDetail (JSON), costDetail (JSON), paymentDetail (JSON), status, documentNumber

Enums

• PurchaseStatus: draft, submitted, reviewed
• PurchaseOrderStatus: draft, submitted, reviewed, approved, canceled, completed
• ReceivedStatus: pending, partial, received
• PaymentStatus: pending, partial, completed

Key Design Decisions

1. Variant validation — PO creation validates that referenced product variants are active and belong to the correct product (done in repository layer).
2. Receipt tracking — POs maintain a receiptSummary JSON that is updated via events when GRNs are created, avoiding tight coupling.
3. Cost snapshot — costDetail captures WAC costs at document time, providing an audit trail independent of inventory cost changes.
4. PDF generation — Uses Puppeteer via a shared PdfModule. Supports configurable page size, margins, and template overrides.

Related Modules

• goods-received-notes/ — GRN documents that trigger PO receipt updates
• inventories/ — Inventory records and WAC cost data
• pdf/ — Shared PDF generation infrastructure