alrahma_sunday_school/fix_financial.md

Financial Integrity and Production-Ready Refund Remediation Plan

1. Objective

The objective is to make invoice, discount, payment, refund, reimbursement, expense, and reporting calculations consistent, auditable, concurrency-safe, and suitable for production.

The completed system must guarantee that:

• The same financial inputs always produce the same balance.
• Historical invoices do not change because current configuration changes.
• A payment, refund, or reimbursement cannot be processed twice.
• Every financial write is atomic.
• Every financial event has an immutable audit trail.
• Reports use the same accounting rules as operational screens.
• Invalid or unauthorized financial operations are rejected before any data is changed.

2. Release Policy

The financial module must remain blocked from production until all Phase 0 requirements are complete.

No refund should be paid from the application until:

1. Refund accounting signs are corrected.
2. Refund eligibility is calculated from the canonical ledger.
3. Refund rows are locked during payout.
4. Duplicate submission protection exists.
5. Broken and unsecured refund routes are repaired.
6. Critical refund tests pass.

Manual operational review is not an acceptable substitute for these controls.

---

Phase 0: Stabilize and Prevent Further Damage

3. Freeze Risky Financial Operations

Temporarily disable or restrict the following operations in production:

• Refund payout
• Reimbursement payout
• Historical invoice recalculation
• Paid reimbursement editing
• Reimbursed expense editing
• Manual invoice status changes
• Repeated invoice generation

Permit these operations only for an authorized financial administrator until remediation is complete.

Add temporary logging around every financial write:

• User ID
• Request ID
• Record ID
• Old values
• New values
• Timestamp
• IP address
• Operation type

4. Back Up and Reconcile Existing Data

Before applying schema or calculation changes:

1. Create a full database backup.

2. Export all invoices, payments, refunds, discounts, expenses, reimbursements, and purchase orders.

3. Calculate current invoice balances using both:

   • Existing production formulas
   • Corrected canonical formulas

4. Produce a reconciliation report identifying:

   • Incorrect invoice balances
   • Negative balances
   • Duplicate refunds
   • Refunds exceeding available credit
   • Discounts exceeding eligible charges
   • Reimbursements not matching expenses
   • Paid expenses that were later edited
   • Duplicate invoices
   • Invalid status values

Do not automatically rewrite disputed historical values. Generate an exception list for financial review.

---

Phase 1: Establish One Canonical Financial Ledger

5. Define Canonical Accounting Rules

Use the following definitions throughout the application.

Gross charges

gross charges =
    frozen tuition lines
  + frozen event lines
  + signed additional adjustments

Applied discount

applied discount =
    minimum of:
    - valid requested discount
    - remaining eligible discount base

Net charges

net charges =
    gross charges - applied discount

Net cash received

net cash received =
    successful payments
  - completed cash refund payouts
  - completed payment reversals

Raw balance

raw balance =
    net charges - net cash received

Amount due

amount due =
    max(0, raw balance)

Customer credit

customer credit =
    max(0, -raw balance)

A completed cash refund must reduce customer credit. It must not increase it.

6. Separate Financial Concepts

Create explicit transaction types instead of using one refund concept for unrelated operations.

Required concepts:

• Payment
• Payment reversal
• Credit memo
• Discount
• Cash refund
• Refund payout
• Reimbursement
• Reimbursement reversal
• Invoice adjustment

Rules:

• A credit memo reduces charges.
• A cash refund reduces cash retained.
• A payment reversal reverses a payment.
• A reimbursement pays an expense and does not affect an invoice.
• A discount reduces only an eligible charge base.

7. Create a Single Ledger Service

Replace duplicated balance calculations with one service.

Suggested responsibilities:

FinancialLedgerService
- calculateInvoiceTotals(invoiceId)
- calculateRefundableCredit(parentId, invoiceId)
- calculatePaymentAllocation(invoiceId)
- calculateDiscountEligibility(invoiceId, voucherId)
- recalculateInvoiceProjection(invoiceId)
- validateLedgerConsistency(invoiceId)

Controllers must not calculate balances directly.

Controllers should:

1. Validate the request format.
2. Check authorization.
3. Call the domain service.
4. Return the service result.

Remove duplicate formulas from:

• Invoice controller
• Refund controller
• Discount controller
• Financial reporting controller
• Payment controller
• Manual payment controller

8. Use Integer Minor Units

Store and calculate money using integer cents.

Examples:

$10.25 = 1025 cents
$0.01 = 1 cent

Do not use floating-point arithmetic for:

• Invoice totals
• Discounts
• Payments
• Refunds
• Reimbursements
• Tax
• Purchase-order totals

Define one rounding policy for percentage calculations:

round half up to the nearest cent

Apply it exactly once per line or transaction according to documented rules.

---

Phase 2: Make Invoices Historically Immutable

9. Introduce Invoice Line Snapshots

Create an immutable invoice_lines table.

Suggested fields:

id
invoice_id
line_type
source_type
source_id
description
quantity
unit_amount_cents
line_amount_cents
discount_eligible
calculation_version
metadata_json
created_at

Possible line types:

• Tuition
• Event fee
• Additional charge
• Deduction
• Credit memo
• Manual adjustment

When an invoice is issued, copy the calculated values into invoice lines.

After issuance, invoice totals must be derived from invoice lines, not from:

• Current enrollments
• Current tuition settings
• Current event configuration
• Current student class assignment
• Current refund deadlines

10. Stop Rewriting Issued Invoices

Changes after invoice issuance must produce a new financial event:

• Debit adjustment
• Credit memo
• Replacement invoice
• Invoice cancellation and reissue

Do not silently rebuild the original invoice.

Define invoice lifecycle statuses:

draft
issued
partially_paid
paid
credited
voided

Only draft invoices may have their original line items edited directly.

11. Enforce Invoice Uniqueness

Choose and document the invoice identity rule:

one invoice per parent, school year, and semester

or another explicitly approved rule.

Enforce it with a database unique index.

Do not rely on:

SELECT existing invoice
then INSERT

That sequence is race-prone without a unique constraint.

---

Phase 3: Rebuild Refund Logic

12. Define Refund Eligibility

A refund request must reference a valid source.

Supported refund sources should be explicit:

• Invoice overpayment
• Specific payment
• Approved credit memo
• Duplicate payment
• Administrative correction

A refund cannot be created from a free-form amount without a verified credit source.

The maximum refundable amount must be:

minimum of:
- verified available customer credit
- remaining refundable amount from the source
- requested amount

13. Define Valid Payment Statuses

Only payments in a final successful state should contribute to refundable credit.

Suggested payment statuses:

pending
successful
failed
voided
reversed
partially_refunded
refunded
chargeback

Include only successful and the non-refunded portion of partially_refunded payments.

Exclude:

• Pending
• Failed
• Voided
• Reversed
• Refunded
• Chargeback

14. Create Immutable Refund Records

Use separate tables for refund intent and refund payouts.

Refund table

refunds
- id
- parent_id
- invoice_id
- source_type
- source_id
- approved_amount_cents
- status
- reason
- requested_by
- approved_by
- created_at
- approved_at

Refund payout table

refund_payouts
- id
- refund_id
- amount_cents
- payment_method
- external_reference
- idempotency_key
- status
- processed_by
- processed_at
- reversed_payout_id
- created_at

Do not repeatedly overwrite a single refund_paid_amount field as the source of truth.

Refund totals should be calculated from immutable payout rows.

15. Implement Transaction-Safe Refund Processing

Refund payout flow:

1. Begin database transaction.
2. Lock the refund row using FOR UPDATE.
3. Lock the relevant invoice or credit-source rows.
4. Reload completed refund payouts.
5. Recalculate the remaining refundable amount.
6. Reject the request if the remaining amount is insufficient.
7. Validate the payment method.
8. Insert the immutable refund payout.
9. Update the refund aggregate status if needed.
10. Recalculate the invoice ledger projection.
11. Write an audit event.
12. Commit.

Do not calculate the remaining refund amount before acquiring the lock.

16. Add Idempotency

Every payout request must include or generate an idempotency key.

Create a unique database constraint on:

refund_payouts.idempotency_key

Repeated submission with the same key must return the original payout result instead of creating a new payout.

Recommended sources for the key:

• Payment gateway event ID
• Check-processing reference
• Application-generated operation UUID

Frontend button disabling is not idempotency. Humans double-click and networks retry because apparently distributed systems needed a sense of humor.

17. Validate Refund Payment Methods

Define an allowlist:

cash
check
bank_transfer
card_refund
account_credit

Validation examples:

• Check requires check number and issue date.
• Bank transfer requires a transaction reference.
• Card refund must reference the original card transaction.
• Cash payout may require acknowledgement or receipt.
• Account credit must not be treated as a cash payout.

Reject unknown payment methods.

18. Add Refund Authorization

Create explicit permissions:

refund.view
refund.request
refund.approve
refund.pay
refund.reverse
refund.report

Recommended segregation of duties:

• Requester cannot approve their own refund above a configured threshold.
• Approver cannot mark a refund paid without payout evidence.
• Refund reversal requires a separate permission.
• Large refunds require dual approval.

All refund routes must use explicit authentication and permission filters.

19. Repair Refund Routes

Audit every refund route against actual controller method signatures.

For each route:

• Verify the method exists.
• Verify URL arguments match method arguments.
• Verify POST body values are read from the request, not expected as PHP method arguments.
• Apply authentication.
• Apply authorization.
• Apply CSRF protection.
• Use POST for state changes.
• Remove obsolete routes.

Add a route test that fails when a configured controller method does not exist.

20. Implement Refund Reversals

Paid refund records should not be edited or deleted.

A correction must create a reversal payout referencing the original payout.

Required rules:

• Original payout remains unchanged.
• Reversal amount cannot exceed the original payout.
• Reversed amount is included in net cash calculations.
• Reversal requires reason, user, timestamp, and approval.

---

Phase 4: Repair Discounts

21. Centralize Discount Eligibility

The ledger service must determine:

• Eligible invoice lines
• Voucher validity
• Remaining voucher uses
• Maximum allowed discount
• Actual applied discount

Voucher validity must include:

• Active flag
• Start date
• End date
• School year
• Semester
• Parent eligibility
• Usage limits
• Minimum charge conditions

22. Store Requested and Applied Amounts Separately

Store:

requested_discount_cents
applied_discount_cents
eligible_base_cents

Reports must use the applied amount.

Never report the raw requested amount as though it reduced the invoice.

23. Lock Voucher Usage

Voucher application flow:

1. Begin transaction.
2. Lock voucher row.
3. Recheck validity.
4. Recheck remaining uses.
5. Lock invoice discount rows.
6. Calculate the eligible base.
7. Insert usage.
8. Update usage count.
9. Recalculate ledger.
10. Commit.

Add a unique constraint preventing the same voucher from being applied twice to the same invoice unless explicitly supported.

24. Define Multiple-Discount Ordering

Document the application order, for example:

1. Fixed credits
2. Fixed vouchers
3. Percentage discounts
4. Administrative adjustments

Apply each discount against the remaining eligible base.

Prevent total applied discounts from exceeding eligible charges.

---

Phase 5: Repair Additional Charges

25. Validate Invoice Ownership

When creating a charge, load the invoice first.

Derive from the invoice:

• Parent
• School year
• Semester

Do not trust redundant request fields.

Reject charges when the supplied parent or accounting period conflicts with the invoice.

26. Standardize Charge Sign Storage

Choose one representation.

Recommended model:

amount_cents is always positive
charge_type determines add or deduct

The ledger converts the type into a signed amount.

Add database validation:

amount_cents >= 0
charge_type IN ('add', 'deduct')

27. Complete the Pending-Charge Workflow

Define transitions:

pending
approved
applied
rejected
voided

Provide an explicit command to apply an approved charge to an invoice.

Record:

• Applied invoice
• Applied user
• Applied time
• Generated invoice line

---

Phase 6: Repair Expenses and Reimbursements

28. Make Paid Records Immutable

Once an expense is reimbursed:

• Amount cannot be edited.
• Category cannot be edited.
• Purchaser cannot be edited.
• Accounting period cannot be edited.
• Receipt cannot be replaced silently.

Corrections require:

1. Reimbursement reversal
2. Expense correction record
3. New reimbursement

The same rule applies to paid reimbursement records.

29. Validate Reimbursement Eligibility

Before reimbursement:

• Expense must exist.
• Expense must be approved.
• Expense must not be a donation.
• Expense must not already be reimbursed.
• Expense amount must be positive.
• Recipient must match the approved purchaser unless an exception is authorized.
• Accounting period must match.
• Requested amount must not exceed the remaining reimbursable amount.

30. Make Reimbursement Creation Atomic

Transaction flow:

1. Begin transaction.
2. Lock expense row.
3. Confirm eligibility.
4. Confirm no active reimbursement exists.
5. Insert reimbursement.
6. Link expense to reimbursement.
7. Write audit record.
8. Commit.

Add a database unique constraint preventing multiple active reimbursements for one expense.

31. Repair Reimbursement Batches

Batch processing must be all-or-nothing.

Before closing a batch:

• Validate every active item.
• Lock the batch.
• Lock every expense.
• Confirm all items were processed.
• Reject the entire batch if any item is invalid.
• Confirm every batch item has a reimbursement record.
• Close the batch only after successful completion.

Never silently skip invalid items.

---

Phase 7: Repair Purchase Orders and Inventory

32. Validate Purchase-Order Values

Add constraints:

quantity > 0
unit_cost_cents >= 0
received_quantity >= 0
received_quantity <= ordered_quantity

33. Recalculate Receipt Completion from All Lines

After receiving items:

1. Lock the purchase order.
2. Lock all purchase-order lines.
3. Apply receipt quantities.
4. Update inventory atomically.
5. Query every line.
6. Mark the order received only when every line is complete.

Do not derive order completion only from posted rows.

34. Make Inventory Updates Atomic

Inventory receipt must occur in one transaction.

For each item:

• Confirm the supply record exists before updating received quantity.
• Lock the supply row.
• Increment inventory atomically.
• Insert inventory transaction log.
• Fail the entire transaction if any step fails.

---

Phase 8: Normalize Statuses and Database Constraints

35. Define Canonical Status Enums

Standardize lowercase machine values.

Examples:

Invoice

draft
issued
unpaid
partially_paid
paid
credited
voided

Refund

requested
approved
partially_paid
paid
rejected
cancelled
reversed

Reimbursement

pending
approved
paid
rejected
reversed

Do not store display labels such as Partially Paid as database values.

36. Add Database Constraints

Recommended constraints:

• Unique invoice identity
• Unique refund payout idempotency key
• Unique active reimbursement per expense
• Nonnegative money columns where applicable
• Valid enum or check-constrained statuses
• Foreign keys for invoice, payment, refund, expense, and reimbursement references
• Unique batch sequence per year
• Unique voucher application where applicable

Application validation is useful. Database constraints are the part that still works when application code has a difficult afternoon.

---

Phase 9: Secure Financial Endpoints

37. Apply Explicit Route Protection

Every financial route must require:

• Authentication
• Role or permission authorization
• CSRF validation for browser writes
• Correct HTTP method
• Input validation
• Audit logging

State changes must not use GET.

38. Add Ownership and Scope Checks

Every operation must verify the relationship between records.

Examples:

• Invoice belongs to parent.
• Payment belongs to invoice.
• Refund source belongs to parent and invoice.
• Expense belongs to the correct accounting period.
• Reimbursement belongs to the expense.
• Additional charge belongs to the invoice.
• Voucher is valid for the invoice period.

---

Phase 10: Repair Reporting

39. Use Canonical Ledger Projections

Reports must not independently reconstruct totals.

Create reporting views or projections for:

• Invoice gross charges
• Applied discounts
• Net charges
• Successful payments
• Completed refunds
• Amount due
• Customer credit
• Reimbursed expenses
• Outstanding reimbursements

All operational screens and reports must call the same ledger logic or use the same persisted ledger projection.

40. Add Reconciliation Reports

Create administrative reports for:

• Ledger total versus stored invoice total
• Payment total versus payment allocation total
• Refund payouts versus approved refund amount
• Expense amount versus reimbursement amount
• Invoice credit versus outstanding refund amount
• Duplicate external transaction references
• Invalid or unknown statuses
• Historical record modifications

---

Phase 11: Automated Testing

41. Unit Tests

Test every canonical formula:

• Exact payment
• Partial payment
• Multiple payments
• Overpayment
• Zero balance
• Partial refund
• Full refund
• Multiple refund payouts
• Reversed refund
• Payment reversal
• Fixed discount
• Percentage discount
• Discount cap
• Multiple discount ordering
• Additional charge
• Deduction
• Rounding boundaries

42. Integration Tests

Test database workflows:

• Payment creates correct invoice projection.
• Refund reduces customer credit.
• Refund cannot exceed available credit.
• Failed payments do not contribute to refundable credit.
• Issued invoice does not change when tuition settings change.
• Issued invoice does not change when enrollment changes.
• Extra charge cannot target another parent’s invoice.
• Reimbursement and expense update commit together.
• Failed second write rolls back the first write.
• Reports match invoice ledger totals.

43. Concurrency Tests

Run two simultaneous requests for:

• Invoice generation
• Voucher application
• Refund payout
• Reimbursement creation
• Reimbursement batch closing
• Purchase-order receipt
• Inventory increment

Expected result:

• Only one operation succeeds when the resource is exclusive.
• No duplicated payout occurs.
• No balance becomes inconsistent.
• Database constraints reject duplicate operations safely.

44. Route and Authorization Tests

Verify:

• Every configured route points to an existing method.
• Method argument counts match the route.
• Unauthorized users receive rejection.
• Users cannot modify another parent’s financial records.
• State-changing GET requests do not exist.
• Invalid statuses are rejected.
• Invalid payment methods are rejected.

45. Property-Based Financial Tests

Generate random combinations of:

• Charges
• Discounts
• Payments
• Refunds
• Reversals

Assert invariants:

amount due >= 0
customer credit >= 0
amount due and customer credit cannot both be positive
completed refund payouts cannot exceed approved refundable credit
applied discounts cannot exceed eligible charge base

---

Phase 12: Data Migration

46. Prepare Migration Scripts

Migrations should:

1. Add integer-cent columns.
2. Backfill cents from legacy decimal fields.
3. Add invoice line snapshots.
4. Normalize status values.
5. Create refund payout records from existing paid-refund totals.
6. Create ledger projection fields or tables.
7. Add constraints only after invalid data is reconciled.
8. Preserve legacy values for audit purposes.

47. Reconcile Existing Refunds

For every existing refund:

• Identify its source.
• Confirm approved amount.
• Confirm actual payout amount.
• Confirm payout method and reference.
• Compare it with customer credit at the payout time.
• Mark exceptions for manual review.

Do not invent missing transaction references.

48. Recalculate Existing Invoices Carefully

Use frozen historical source data where available.

When source data is incomplete:

• Preserve the existing issued total.
• Record a reconciliation warning.
• Do not rebuild the invoice from current configuration.

---

Phase 13: Observability and Operational Controls

49. Add Structured Financial Logging

Every financial command should log:

• Request ID
• Idempotency key
• Actor
• Action
• Entity type
• Entity ID
• Amount
• Currency
• Previous status
• New status
• External reference
• Transaction outcome

Never log full card data or sensitive bank information.

50. Add Alerts

Alert on:

• Refund greater than configured threshold
• Multiple refund attempts using the same source
• Failed ledger recalculation
• Negative stored amount where prohibited
• Duplicate invoice attempt
• Refund payout without reference
• Reimbursement exceeding expense
• Report-to-ledger mismatch
• Database transaction rollback

51. Add Daily Reconciliation

Run a scheduled reconciliation job that verifies:

• Invoice projection equals ledger activity.
• Payment totals equal allocated payment totals.
• Refund payouts do not exceed approved refunds.
• Reimbursements do not exceed approved expenses.
• No paid record was modified in place.
• No unknown status exists.

The job should report exceptions, not silently modify financial records.

---

Phase 14: Deployment Strategy

52. Deploy Behind Feature Flags

Use separate flags for:

• New invoice ledger
• New refund processing
• New discount calculation
• New reimbursement processing
• New financial reports

53. Shadow Calculation

Before switching production writes:

1. Continue using the current calculation for operational output.
2. Run the new ledger calculation in parallel.
3. Log differences.
4. Investigate every unexplained difference.
5. Require a zero-unexplained-difference period before cutover.

54. Staged Rollout

Recommended order:

1. Internal test environment
2. Staging with production-like data
3. Finance-administrator pilot
4. Limited production cohort
5. Full production rollout

55. Rollback Plan

Rollback must disable new writes without deleting new immutable records.

Do not design rollback around reversing database migrations that contain financial transactions.

Keep:

• Compatibility reads
• Feature flags
• Migration checkpoints
• Database backups
• Reconciliation exports

---

Phase 15: Production Acceptance Criteria

The refund workflow is production-ready only when all of the following are true:

• A completed refund reduces customer credit correctly.
• A refund cannot create additional overpayment.
• A refund cannot exceed verified refundable credit.
• Two concurrent payout requests cannot pay twice.
• Repeated requests with the same idempotency key return the same result.
• Only successful payment amounts are refundable.
• Issued invoice totals remain unchanged when live configuration changes.
• Every payout has an immutable record.
• Paid refunds cannot be edited or deleted.
• Refund reversals preserve the original record.
• All refund routes are valid and protected.
• All database writes are checked.
• Partial failures roll back completely.
• Reports match ledger values.
• Unit, integration, concurrency, route, and authorization tests pass.
• Existing financial data has been reconciled.
• Finance staff have approved the reconciliation report.
• Monitoring and daily reconciliation are active.

---

Recommended Implementation Order

Sprint 1: Critical accounting and security

• Fix refund sign.
• Introduce raw balance and customer credit.
• Secure all financial routes.
• Repair broken refund routes.
• Normalize payment status filtering.
• Add immediate refund amount validation.
• Block editing paid financial records.

Sprint 2: Canonical ledger and invoice snapshots

• Build the ledger service.
• Create invoice line snapshots.
• Stop recalculation from live data.
• Remove duplicate controller formulas.
• Normalize invoice statuses.

Sprint 3: Refund transaction model

• Add refund payout table.
• Add row locking.
• Add idempotency.
• Add approval workflow.
• Add payout-method validation.
• Add refund reversal support.

Sprint 4: Discounts and additional charges

• Centralize eligibility.
• Lock vouchers.
• Store applied discount amounts.
• Define multiple-discount ordering.
• Validate additional-charge ownership.
• Repair charge sign handling.

Sprint 5: Reimbursements, expenses, and purchase orders

• Add reimbursement locking and uniqueness.
• Make paid records immutable.
• Repair batch processing.
• Repair PO receiving and inventory transactions.

Sprint 6: Reporting, migration, and rollout

• Rebuild reports from the ledger.
• Reconcile historical data.
• Add monitoring and alerts.
• Run shadow calculations.
• Perform staged rollout.

---

Definition of Done

A financial feature is not complete merely because the controller returns success.

It is complete only when:

• Accounting behavior is documented.
• Calculation occurs in the canonical service.
• Money uses integer minor units.
• Authorization is enforced.
• Writes are transactional.
• Concurrent execution is safe.
• Idempotency is implemented where needed.
• Database constraints defend invariants.
• Audit records are immutable.
• Reports use the same ledger.
• Automated tests cover success, failure, retry, and concurrency.
• Existing data has a defined migration and reconciliation path.