Feat/usage metering

[tenbytecloud]

Fixes #

📝 Description

Please provide a clear and concise description of what this PR does.

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🔨 Changes Made

• Feature 1
• Bug Fix
• Refactor
• Documentation Update

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✅ Checklist

• My code follows the project's code style.
• I have added tests where applicable.
• All new and existing tests pass.
• I have updated documentation (if needed).

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📷 Screenshots / Demo (if applicable)

Add screenshots or demo links here.

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Disclaimer: This comment was generated by Greptile AI CTO

Greptile Overview

Greptile Summary

This PR delivers a comprehensive billing enhancement for Tenbyte's usage-metering requirements: SSLCommerz payment gateway integration for Bangladesh market, real-time overage billing with $5 threshold buckets, and unified webhook-driven upgrade flow across all payment methods.

Key Changes:

• SSLCommerz Integration: Full payment gateway with IPN webhook handling, MD5 validation, high-risk transaction detection. Clean separation follows existing Stripe/Razorpay patterns.
• Overage Billing: Bucket-based invoicing ($5 thresholds), idempotency-protected, allows unlimited negative wallet balances for post-paid usage. 766 lines of tests (21 test cases) demonstrate thorough validation.
• Unified Upgrade Flow: All payment methods (Stripe auto-charge, SSLCommerz, links) now execute upgrades via wallet.transaction.created webhook, eliminating inconsistent behavior.
• Security Fixes: CORS origin whitelisting (addresses P1 from previous review), credentials only with specific origins, removed debug logs leaking endpoints.
• Balance Tracking: Added balance_before/balance_after columns for audit trail (migration defaults to 0 for historical data).

Implementation Quality:
Solid production-ready code. The team kept it lean—no over-engineering, clear separation of concerns, proper error handling without failing event processing. Documentation (TENBYTE_CHANGES.md) is excellent for future maintenance.

Issues Found:

• Webhook spam risk in overage billing (line 209-212): sends duplicate wallet.balance.negative webhooks when balance stays negative across multiple bucket catches-up.

Confidence Score: 4/5

• Safe to merge with one minor webhook logic fix recommended
• Strong implementation with comprehensive test coverage (766 lines), proper error handling, security fixes applied. One webhook spam issue found but won't cause data corruption—just user experience degradation under specific scenarios. Team demonstrated discipline keeping changes focused and production-ready.
• internal/service/overage_billing.go (webhook logic at line 209-212)

Important Files Changed

Filename	Overview
internal/service/overage_billing.go	New overage billing service with bucket-based threshold invoicing ($5 buckets). Handles race conditions with idempotency, includes negative balance webhook, comprehensive test coverage (21 tests).
internal/integration/sslcommerz/webhook/handler.go	SSLCommerz IPN webhook handler. Validates via API, handles high-risk transactions, uses original payment amount (USD) not IPN amount (BDT). Never returns errors to ensure 200 OK.
internal/service/wallet.go	Added balance_before/balance_after tracking for audit trail. Refactored to return transaction object directly. No functional changes to core wallet logic.
internal/service/event_post_processing.go	Integrated overage billing after cost calculation. Added MAX aggregation support. Sentry error capture for monitoring. Clean integration point with proper error handling.
internal/rest/middleware/cors.go	Security fix: origin whitelisting, proper credentials handling (no credentials with wildcard), Vary header for cache safety. Addresses P1 CORS issue from previous review.
internal/api/v1/webhook.go	SSLCommerz webhook endpoint with goroutine processing. Responds immediately with 200 OK, processes in background with panic recovery. Context handling discussed in previous thread.
migrations/postgres/V5__wallet_transaction_balance_fields.up.sql	Adds balance_before/balance_after columns with default 0 for existing rows. Clean migration, backward compatible. Historical snapshots only accurate going forward (as noted in previous review).
internal/service/billing.go	Unified upgrade flow - all payment methods (Stripe auto-charge, SSLCommerz, payment links) now use webhook to execute upgrade. Ensures consistency across payment methods.

[greptile-apps]

_{8 files reviewed, 10 comments}

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[tenbytecloud]

@greptileai review

[greptile-apps]

_{5 files reviewed, 1 comment}

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[greptile-apps]

Additional Comments (1)

internal/service/event_post_processing.go
CRITICAL BUG: Logic is inverted. BILLING_MODEL_FLAT_FEE should NOT be used for usage-based billing. This returns true for FLAT_FEE and rejects all usage-based models.

All usage events will be skipped because they use usage-based billing models, not FLAT_FEE. This breaks the entire metering system.

	return billingModel != types.BILLING_MODEL_FLAT_FEE

Prompt To Fix With AI

This is a comment left during a code review.
Path: internal/service/event_post_processing.go
Line: 778:778

Comment:
CRITICAL BUG: Logic is inverted. `BILLING_MODEL_FLAT_FEE` should NOT be used for usage-based billing. This returns `true` for FLAT_FEE and rejects all usage-based models.

All usage events will be skipped because they use usage-based billing models, not FLAT_FEE. This breaks the entire metering system.

```suggestion
	return billingModel != types.BILLING_MODEL_FLAT_FEE
```

How can I resolve this? If you propose a fix, please make it concise.

[greptile-apps]

_{5 files reviewed, 4 comments}

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[greptile-apps]

Additional Comments (1)

internal/service/event_post_processing.go
[P0] Billing model support check is inverted

isSupportedBillingModel is documented as excluding FLAT_FEE (“not appropriate for usage-based billing”), but currently returns true only for BILLING_MODEL_FLAT_FEE (event_post_processing.go:774-778). This means usage line items with PACKAGE/TIERED billing models will be treated as unsupported and silently skipped at prepareProcessedEvents (via isSupportedAggregationForPostProcessing). That will break metering + overage billing for the models you likely care about.

Recommendation: flip the predicate to allow the actual usage billing models (and explicitly exclude FLAT_FEE). This is a small change with a big functional impact.

Prompt To Fix With AI

This is a comment left during a code review.
Path: internal/service/event_post_processing.go
Line: 774:778

Comment:
[P0] Billing model support check is inverted

`isSupportedBillingModel` is documented as *excluding* `FLAT_FEE` (“not appropriate for usage-based billing”), but currently returns `true` only for `BILLING_MODEL_FLAT_FEE` (`event_post_processing.go:774-778`). This means usage line items with PACKAGE/TIERED billing models will be treated as unsupported and silently skipped at `prepareProcessedEvents` (via `isSupportedAggregationForPostProcessing`). That will break metering + overage billing for the models you likely care about.

Recommendation: flip the predicate to allow the actual usage billing models (and explicitly exclude `FLAT_FEE`). This is a small change with a big functional impact.

How can I resolve this? If you propose a fix, please make it concise.

[tenbytecloud]

@greptileai review again

[greptile-apps]

_{5 files reviewed, 2 comments}

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[greptile-apps]

Additional Comments (1)

internal/config/config.go
Debug fmt.Printf still logging tenant webhook endpoints to stdout. Remove before production - bypasses structured logging and may leak sensitive URLs.

	// Debug logging removed - use structured logger if needed

Prompt To Fix With AI

This is a comment left during a code review.
Path: internal/config/config.go
Line: 322:326

Comment:
Debug `fmt.Printf` still logging tenant webhook endpoints to stdout. Remove before production - bypasses structured logging and may leak sensitive URLs.

```suggestion
	// Debug logging removed - use structured logger if needed
```

How can I resolve this? If you propose a fix, please make it concise.

[tenbytecloud]

@greptileai review all the files within this PR

[greptile-apps]

_{8 files reviewed, 1 comment}

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