---
phase: 04-inventory-expenses-and-financial-reports
plan: 04
subsystem: reports, accounting
tags: [expense-reports, audit-trail, journal-entries, ACCT-08, prisma]

# Dependency graph
requires:
  - phase: 04-03
    provides: ExpenseService, VendorService, expense categories, vendor model
  - phase: 02-02
    provides: JournalEntryService, referenceType/referenceId on JEs
provides:
  - ExpenseReportService with category/vendor/summary aggregation
  - AuditTrailService with JE audit trail (ACCT-08 compliance)
  - Expense report API routes
  - JE audit trail API route
affects: []

# Tech tracking
tech-stack:
  added: []
  patterns:
    - "Expense aggregation in JS from Prisma findMany (same pattern as outstanding reports)"
    - "AuditTrailService works across all JE sources via referenceType/referenceId"

key-files:
  created:
    - src/lib/services/expense-report-service.ts
    - src/lib/services/audit-trail-service.ts
    - src/app/api/reports/expenses/route.ts
    - src/app/api/reports/expenses/by-vendor/route.ts
    - src/app/api/accounting/journal-entries/[id]/audit/route.ts
    - src/lib/__tests__/expense-report-service.test.ts
  modified: []

key-decisions:
  - "Expense aggregation done in JS after findMany (same pattern as outstanding reports, collector balances)"
  - "AuditTrailService queries JEs by referenceType+referenceId -- works for all sources (Invoice, Payment, Expense, Collection, etc.)"
  - "No Vendor bucket uses null vendorId key in grouping -- expenses without vendor are still reported"

patterns-established:
  - "AuditTrailService pattern: getJournalEntryAudit for single JE, getAuditTrailForEntity for all JEs related to a source record"

# Metrics
duration: 20min
completed: 2026-03-05
---

# Phase 4 Plan 4: Expense Reports and Audit Trail Summary

**ExpenseReportService aggregates spending by category/vendor with date filtering; AuditTrailService traces every JE to its creator and source transaction (ACCT-08)**

## Performance

- **Duration:** 20 min
- **Started:** 2026-03-05T06:35:27Z
- **Completed:** 2026-03-05T06:55:12Z
- **Tasks:** 2
- **Files created:** 6

## Accomplishments
- Expense reports by category and vendor with date range filtering (only POSTED expenses)
- Full JE audit trail showing creator, timestamp, source reference, and line details
- Audit trail works across ALL JE sources (proven with Payment JE test)
- 9 passing integration tests covering reports, filtering, and cross-source audit

## Task Commits

Each task was committed atomically:

1. **Task 1: ExpenseReportService and AuditTrailService** - `6bc24a3` (feat)
2. **Task 2: Tests for expense reports and audit trail** - `787b22e` (test)

## Files Created/Modified
- `src/lib/services/expense-report-service.ts` - Expense aggregation by category, vendor, and combined summary
- `src/lib/services/audit-trail-service.ts` - JE audit trail with creator, source reference, approval info
- `src/app/api/reports/expenses/route.ts` - GET expense summary by category (ADMIN)
- `src/app/api/reports/expenses/by-vendor/route.ts` - GET expense summary by vendor (ADMIN)
- `src/app/api/accounting/journal-entries/[id]/audit/route.ts` - GET JE audit trail (ADMIN, OFFICE_STAFF)
- `src/lib/__tests__/expense-report-service.test.ts` - 9 integration tests

## Decisions Made
- Expense aggregation done in JS after findMany -- same pattern as outstanding reports and collector balances (acceptable for ISP scale)
- AuditTrailService queries by referenceType+referenceId, works for all JE sources without source-specific logic
- "No Vendor" bucket included in vendor reports for expenses without vendorId
- Decimal amounts serialized as strings in API responses (consistent with other report endpoints)

## Deviations from Plan

None -- plan executed exactly as written.

## Issues Encountered
- Plan specified `npx jest` for test verification but project uses Vitest -- used `npx vitest run` instead (not a code deviation, just a verification command difference)

## User Setup Required

None -- no external service configuration required.

## Next Phase Readiness
- Phase 4 is now fully complete (all 5 plans: 04-01 through 04-05)
- All financial reporting capabilities built: trial balance, income statement, balance sheet, expense reports, and audit trail
- Ready for Phase 5 (Portal and Dashboard)

---
*Phase: 04-inventory-expenses-and-financial-reports*
*Completed: 2026-03-05*