# Phase 4.3 Implementation Report — Three-Way Matching Engine

**Phase:** 4.3 Three-Way Matching Engine  
**Status:** PASS & VERIFIED  
**Date:** September 4, 2026  
**Role:** Senior Enterprise Architect, Financial Systems Architect, Lead Laravel Engineer  

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## Executive Summary

Phase 4.3 implements the **Three-Way Matching Engine** (`ThreeWayMatchingEngine`) within TANRAIL ONE's commercial domain layer (`app/Domains/Core/Services/`). The engine performs automated, multi-tenant 3-way commercial cross-validation between **Purchase Orders**, **Purchase Receipts**, and **Supplier Invoices (Vendor Bills)**.

The implementation detects unit price variances, quantity overages/underages, and line item mismatches, updating `SupplierInvoice.match_status` to either `MATCHED` or `DISCREPANCY`. It records structured discrepancy logs and line-by-line comparison details, while supporting managerial overrides (`overrideDiscrepancy`) that preserve historical audit trails without erasing discrepancy history.

Zero General Ledger posting logic was added (GL postings remain strictly deferred to Phase 4.7). All 187 baseline tests continue passing, alongside 18 new Phase 4.3 feature verification tests (totaling 205 tests, 368 assertions, 0 failures, 0 errors).

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## 1. Scope & Architectural Scope Reconciliation

During initial architecture planning, Stage 4.3 was listed as "SupplierInvoice & SupplierInvoiceLine Models & Service". However, during execution, Phase 4.1 implemented all commercial schemas and Phase 4.2 implemented all commercial document lifecycle services (`InvoiceService`, `SupplierInvoiceService`, `CreditNoteService`, `PaymentAllocationService`).

Under explicit human authorization, Phase 4.3 was formally redefined as the **Three-Way Matching Engine**, completing the commercial verification layer prior to GL ledger integration.

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## 2. Files Created & Modified

### New Database Migration
- `database/migrations/2026_09_04_180001_add_matching_audit_fields_to_supplier_invoices_table.php`
  - Adds nullable audit fields: `discrepancy_reason` (`text`), `match_details` (`json`), `overridden_by` (`foreignId`), `overridden_at` (`timestamp`), `override_reason` (`text`).

### New Data Transfer Object (DTO)
- `app/Domains/Core/DTOs/MatchResult.php`
  - Encapsulates `status`, `isMatched`, `discrepancies` (string array), `lineDetails` (structured array), and `summary`.

### New Domain Service
- `app/Domains/Core/Services/ThreeWayMatchingEngine.php`
  - `evaluateMatch(SupplierInvoice $supplierInvoice): MatchResult`
  - `overrideDiscrepancy(SupplierInvoice $supplierInvoice, User $manager, string $reason): SupplierInvoice`

### New Feature Test Suite
- `tests/Feature/Core/Phase43ThreeWayMatchingTest.php`
  - 18 comprehensive feature test cases covering 3-way matching, unit price variances, quantity mismatches, missing receipts, cross-organization/BU rejections, discrepancy persistence, manager overrides, transaction rollbacks, decimal precision, and tenant isolation.

### Modified Models & Docs
- `app/Domains/Core/Models/SupplierInvoice.php` (Added audit fillables, casts, `overriddenBy()` relationship).
- `docs/CHANGELOG.md` (Updated with Phase 4.3 completion).
- `docs/phase-4.3-implementation-report.md` (This document).
- `docs/phase-4.3-verification-gate.md` (Verification gate checklist).

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## 3. Matching Rules & Variance Calculation

1. **Purchase Order Relationship**:
   - Every 3-way match requires a valid `purchase_order_id` on the `SupplierInvoice`.
   - If missing, status becomes `DISCREPANCY` ("No Purchase Order attached").
2. **Unit Price Verification**:
   - `invoiced_unit_price` vs `po_unit_price`.
   - Measured using 4-decimal precision (`bccomp`). If prices differ, a price discrepancy is recorded.
3. **Quantity Verification**:
   - Sums received quantities across all `PurchaseReceiptLine` records linked to the PO line (`bcadd`).
   - If `invoiced_quantity > received_quantity`, a quantity overage discrepancy is recorded.
   - If `invoiced_quantity < received_quantity`, a quantity underage discrepancy is recorded.
   - If no goods receipt exists, an unreceived item discrepancy is recorded.
4. **Line Item Verification**:
   - Matches invoice lines to PO lines via `purchase_receipt_line_id` or `item_id`.
   - If an invoiced item does not exist on the PO, an unmatched line discrepancy is recorded.

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## 4. Discrepancy & Managerial Override Auditability

- When discrepancies are detected, `SupplierInvoice.match_status` is updated to `DISCREPANCY`.
- The human-readable reason list is saved to `discrepancy_reason`, and structured comparison details are saved to `match_details` (JSON).
- **Managerial Override (`overrideDiscrepancy`)**:
  - Requires an explicit non-empty `override_reason`.
  - Enforces manager tenant context (`ContextManager`).
  - Sets `match_status = SupplierInvoiceMatchStatus::MATCHED`, `overridden_by = $manager->id`, `overridden_at = now()`, `override_reason = $reason`.
  - **Audit Invariant**: The original `discrepancy_reason` and `match_details` are preserved for audit historical integrity and are NEVER erased.

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## 5. Security Boundaries & Multi-Tenant Isolation

- Every 3-way match validates that `SupplierInvoice.organization_id == PurchaseOrder.organization_id` and `SupplierInvoice.business_unit_id == PurchaseOrder.business_unit_id`.
- Attempts to match documents across Organizations or Business Units throw `CrossOrganizationException`.
- Overrides performed under an active `ContextManager` context belonging to a different tenant throw `CrossOrganizationException`.

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## 6. Verification Results

### Test Execution Command
`php artisan test --compact`

### Test Output Summary
- **Total Tests:** 205
- **Passed:** 205
- **Assertions:** 368
- **Failures:** 0
- **Errors:** 0
- **Skipped:** 0
- **Code Style (Laravel Pint):** `{"tool":"pint","result":"passed"}`

All 187 baseline tests (Phases 1–4.2) remained 100% green without regression.

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## 7. Known Limitations & Deferred Work

- **GL Posting Deferred**: Zero General Ledger journal entries were added (reserved for Phase 4.7).
- **Tolerance Percentage Configuration**: Matching currently enforces exact unit price and quantity alignment. Configurable percentage tolerance thresholds remain a future enhancement.