fix(billing): stop duplicate credit overdraft invoices

[rohilsurana]

Summary

Fixes two bugs in GenerateForCredits that caused:

1. Duplicate invoices for the same customer every run
2. Other customers never receiving invoices after their first billing period

Bug 1: Duplicate invoices (inner loop break)

The break on finding a credit item only exited the inner items loop. The outer invoices loop (ordered newest-first) kept iterating, overwriting lastOverdraftInvoice with the oldest credit invoice. The alreadyInvoiced check then compared against the wrong invoice and never matched.

Fix: Break out of outer loop once the first (most recent) credit overdraft invoice is found.

Bug 2: Start range never advancing (strict Before comparison)

item.TimeRangeStart.Before(startRange) uses strict comparison — when the previous invoice's start exactly equals c.CreatedAt, startRange was never advanced to the previous invoice's end. This caused:

• New invoices to use overlapping date ranges
• CreateInProvider (Stripe) failures for the overlapping range
• Customers silently stuck after their first credit overdraft invoice

Fix: Use !item.TimeRangeStart.After(startRange) (equivalent to <=) so startRange correctly advances past previously invoiced periods.

Verified with production data

Customer	Old Behavior	After Fix
a5328c9a	20+ duplicate invoices for same range	Correctly skipped (already invoiced)
e2bcf44c	Stuck since Sep 2025, range never advanced	Will invoice for 2025-09-01 → 2026-04-01 (balance: -800)
847b93bb	Stuck since Feb 2026	Correctly skipped (range balance: +5000)
9be297b2	Stuck since Feb 2026	Correctly skipped (no transactions in new range)

Test plan

• go build ./billing/invoice/ passes
• Deploy → a5328c9a stops getting duplicates
• Deploy → e2bcf44c gets a new invoice for Sep 2025 – Apr 2026
• Customers with positive range balance are correctly skipped

[vercel]

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Project	Deployment	Actions	Updated (UTC)
frontier	Ready	Preview, Comment	Apr 1, 2026 6:59am

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 10a5ac60-0129-44d9-ae8e-28d2dc240b0d

📥 Commits

Reviewing files that changed from the base of the PR and between fd403b0 and f3acaf0.

📒 Files selected for processing (1)

• billing/invoice/service.go

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📝 Walkthrough

Summary by CodeRabbit

• Refactor
  • Improved invoice generation performance by optimizing how recent invoices are identified and processed during billing calculations.

Walkthrough

In billing/invoice/service.go, the GenerateForCredits function's inner loop now breaks immediately upon finding a lastOverdraftInvoice, rather than continuing to scan all invoices and items. This reduces the scope of invoices considered when selecting the most recent credit-overdraft invoice.

Changes

Cohort / File(s)	Summary
Invoice Service Logic billing/invoice/service.go	Added early loop break in GenerateForCredits when lastOverdraftInvoice is found, optimizing invoice scanning by limiting iteration depth.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

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[coveralls]

Pull Request Test Coverage Report for Build 23836203953

Details

• 0 of 2 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.003%) to 41.187%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
billing/invoice/service.go	0	2	0.0%

Totals
Change from base Build 23836031833:	-0.003%
Covered Lines:	14839
Relevant Lines:	36028

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💛 - Coveralls