# TANRAIL ONE — Phase 3.1 Implementation Report

## 1. Overview
Stage 3.1 — Core Data Foundation has been successfully implemented and tested. This stage provides the generic, business-agnostic foundation for Master Data and Cataloging required by the Shared Core architecture.

## 2. Implementations
The following domain entities were created within `App\Domains\Core`:

### Enums
- `CustomerType` (INDIVIDUAL, CORPORATE)
- `ItemType` (PHYSICAL, SERVICE, PACKAGE)
- `PaymentMethod` (CASH, BANK_TRANSFER, MOBILE_MONEY, CARD)

### Models & Migrations
- `Customer`: Scoped to `organization_id`. Tracks generic identity data.
- `Supplier`: Scoped to `organization_id`. Tracks procurement partners.
- `Unit`: Globally scoped. Base unit of measure (e.g., kg, hour).
- `TaxCategory`: Globally scoped. VAT and tax rates.
- `Item`: Scoped to `business_unit_id`. Represents the generic catalog item (product or service). Incorporates a unique compound index for `['business_unit_id', 'sku']` ensuring cross-BU catalog isolation.

## 3. Testing & Verification
The `Phase31DataFoundationTest` suite was authored and successfully executed.
- Verified that `Customer` and `Supplier` enforce Organizational constraints.
- Verified that `Item` correctly maps Enums and enforces Business Unit isolation.
- Verified that a duplicate SKU within the same Business Unit throws a database exception, while the identical SKU in a different Business Unit is permitted.

## 4. Architectural Decisions
- `PaymentMethod` was implemented as a native PHP Enum instead of a database lookup table to expedite development and reduce join complexity, adhering to the architecture review recommendation.
- Foreign Keys were set up with `cascadeOnDelete` for core parents (`organization_id`, `business_unit_id`) and `restrictOnDelete` or `nullOnDelete` for lookup tables (`unit_id`, `tax_category_id`) to prevent accidental destruction of historical data if a tax rate is removed.

## 5. Next Steps
Phase 3.1 is verified. The next approved step in the roadmap is Phase 3.2 — Inventory Foundation.