fix(billing): exclude overdraft credits from credit overdraft balance

[rohilsurana]

Follows up on #1498.

When a customer pays an overdraft invoice, reconciliation adds a system.overdraft credit transaction. GenerateForCredits uses GetBalanceForRange to check if a customer has negative balance — but the reconciliation credit inflates the balance, masking new usage that should be billed.

Changes

• Add GetBalanceForRangeWithoutOverdraft to the transaction repository, credit service, and invoice service — excludes system.overdraft credits from the balance sum
• Switch GenerateForCredits to call GetBalanceForRangeWithoutOverdraft

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[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Invoice generation now uses corrected account balance calculations that exclude system overdraft transactions when evaluating balances over date ranges, improving overdraft detection, invoice line quantities, and resulting invoice creation so billed amounts reflect true account activity.

Walkthrough

Added a balance query that excludes overdraft-source credits and wired it into invoice generation; extended credit transaction interfaces and mocks; implemented a Postgres repository method that sums debits and credits while excluding overdraft-source credits for a time range.

Changes

Cohort / File(s)	Summary
Invoice service billing/invoice/service.go	GenerateForCredits now calls GetBalanceForRangeWithoutOverdraft and uses its returned balance for overdraft detection, invoice line quantity, and invoice create/upsert flow.
Credit service & mocks billing/credit/service.go, billing/credit/mocks/transaction_repository.go	Added GetBalanceForRangeWithoutOverdraft(ctx context.Context, accountID string, start time.Time, end time.Time) (int64, error) to TransactionRepository and Service; added corresponding mock method, expectation type, and call helpers (Run, Return, RunAndReturn).
Postgres repository implementation internal/store/postgres/billing_transactions_repository.go	Implemented GetBalanceForRangeWithoutOverdraft and helper getCreditBalanceExcludingSource: runs in a serializable tx, sums debits and credits while excluding credit.SourceSystemOverdraftEvent, normalizes NULL sums to zero, and returns excludedCredits - debits.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• fix(billing): stop duplicate credit overdraft invoices #1498: Also modifies billing/invoice/service.go GenerateForCredits logic; related to invoice scanning/time-range and overdraft invoicing behavior.

Suggested reviewers

• rsbh

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[coderabbitai]

Actionable comments posted: 1

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 09eb074a-1454-4a49-adb4-6b803cb518de

📥 Commits

Reviewing files that changed from the base of the PR and between 3660325 and 19dd037.

📒 Files selected for processing (1)

• billing/invoice/service.go

[coveralls]

Coverage Report for CI Build 24068983263

Coverage decreased (-0.06%) to 41.147%

Details

• Coverage decreased (-0.06%) from the base build.
• Patch coverage: 55 uncovered changes across 3 files (0 of 55 lines covered, 0.0%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
internal/store/postgres/billing_transactions_repository.go	51	0	0.0%
billing/credit/service.go	3	0	0.0%
billing/invoice/service.go	1	0	0.0%

Coverage Regressions

No coverage regressions found.

---

Coverage Stats

Relevant Lines:	36289
Covered Lines:	14932
Line Coverage:	41.15%
Coverage Strength:	11.89 hits per line

---

💛 - Coveralls

[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (2)

internal/store/postgres/billing_transactions_repository.go (2)

534-536: Mark the transaction as read-only for this balance query.

This method only reads; setting ReadOnly: true improves intent and can reduce lock pressure.

♻️ Proposed change

 	if err := r.dbc.WithTxn(ctx, sql.TxOptions{
 		Isolation: sql.LevelSerializable,
+		ReadOnly:  true,
 	}, func(tx *sqlx.Tx) error {

---

500-503: Consider an index strategy for the new filtered credit-sum path.

This path is used for invoice generation; add/verify a supporting index for (account_id, type, created_at, source) (or an equivalent partial index) to avoid full scans as transaction volume grows.

Also applies to: 531-557

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: a0d48227-bc12-483b-b696-3d57350eaf9a

📥 Commits

Reviewing files that changed from the base of the PR and between 19dd037 and b64c958.

📒 Files selected for processing (4)

• billing/credit/mocks/transaction_repository.go
• billing/credit/service.go
• billing/invoice/service.go
• internal/store/postgres/billing_transactions_repository.go

✅ Files skipped from review due to trivial changes (1)

• billing/credit/mocks/transaction_repository.go

🚧 Files skipped from review as they are similar to previous changes (1)

• billing/invoice/service.go

[coderabbitai]

Actionable comments posted: 1

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 57cb352f-5ea5-4cb4-b5a8-5128536835be

📥 Commits

Reviewing files that changed from the base of the PR and between b64c958 and 6a4e978.

📒 Files selected for processing (4)

• billing/credit/mocks/transaction_repository.go
• billing/credit/service.go
• billing/invoice/service.go
• internal/store/postgres/billing_transactions_repository.go

🚧 Files skipped from review as they are similar to previous changes (2)

• billing/invoice/service.go
• billing/credit/mocks/transaction_repository.go