- Idempotency:
IdempotencyStore (DashMap, 24h TTL, method+path+key scoped) + Axum middleware + X-Idempotency-Replayed response header
- Spend Alerts: New
spend-alerts crate — SoftLimit/HardLimit alert types, SpendAlertService (create/check/reset), GET/POST /admin/v1/customers/:id/alerts + reset endpoint
- Usage Summary:
metering::summary::{UsageSummary, MeterSummary} + GET /v1/subscriptions/:id/usage + MeteringService in AppState
- Tax Engine:
TaxAdapter trait + PassThroughTaxAdapter + FlatRateTaxAdapter (bps, B2B exempt) + InvoiceLineItem.is_tax + InvoicingService::apply_tax() + POST /admin/v1/invoices/:id/calculate-tax
- Developer Docs: mdBook docs site deployed to
docs.bill.sh + OpenAPI 3.0 spec + Redoc UI at https://api.bill.sh/docs/api
- ClickHouse Metering: DDL, materialized views, aggregation query builder, batch/top/summary helpers (11 tests)
- Kafka Integration:
EventPublisher trait, StubEventPublisher, RdkafkaProducer (feature-gated)
- CockroachDB Schema: Multi-region
REGIONAL BY ROW schema in infra/crdb-schema/ (6 SQL files)
- Auth Middleware: JWT HS256 + constant-time API key validation (
auth.rs)
- Rate Limiting: Redis token bucket +
InMemoryRateLimiter + Lua script for atomic Redis operations
- Webhook Delivery: Retry engine + circuit breaker + HMAC-SHA256 signatures (
notifications/delivery.rs)
- Docker Compose: Full local dev environment (139 lines) — CockroachDB, ClickHouse, Kafka, Redis, TigerBeetle
- CI Pipeline: GitHub Actions clippy + test on every push
- Contracts: Full contract CRUD — Draft→Active→Amended/Expired/Terminated state machine
- Ramp Contracts:
ContractTerm phases with per-phase pricing, discounts, and committed amounts
- ContractSubscription: Join table with PLG/Coterm/Recontract adoption types
- Proration Engine: Pure functions —
prorate_days(), prorate_to_contract_end(), prorate_overlap_credit(), cancellation_credit()
- Commit Draw-Down:
apply_commit_drawdown() pure fn — priority-ordered, tag-scoped
- True-Up:
compute_true_up() + compute_phase_true_ups() pure fns
- Ledger Provisioning: TigerBeetle two-phase transfers — pending/post/void engine, customer account provisioning
- Audit Log:
billing-audit crate — 25+ action types, ActorRef/ActorRole, InMemoryAuditLog, idempotency
- Financial Reporting:
billing-reporting — AR aging, MRR report, MRR movements, deferred revenue schedule (ASC 606 compliant)
- Credit Notes:
CreditNoteService — partial/full credits, issue_wallet_credit() (TigerBeetle transfer, idempotent)
- PLG Adoption:
PlgAdoptionService — in-place contract linking for product-led growth companies
- Admin API: Customer 360, invoice void, credit note, pause/resume, catalog management endpoints
- Rating Engine:
PriceConfig, PriceSheet, TierOverride, RatedLineItem — flat/per_unit/graduated/volume/package/committed models
rate_all(): Pure rating function with contract discount (basis points) and tier override support- Invoice Calculation:
CalculateFeesService — converts RatedLineItem → InvoiceLineItem
- Invoice Finalization:
FinalizeService — finalize_auto() with Arc<AtomicU64> sequential counter (INV-XXXXXX)
- Progressive Billing:
ProgressiveBillingService — threshold-triggered finalize + new draft
- Period Advance:
advance_period() on subscriptions — moves charged_through_date
- Stripe Integration:
StripeClient — create_payment_intent(), capture(), refund(), webhook verification
- Dunning: 4-attempt retry schedule (+3d/+7d/+14d/+21d)
- Notifications:
OutboxEntry + OutboxRepository — transactional outbox pattern
- API Gateway: Axum router with subscriptions, invoices, events, webhooks routes
- Workspace Scaffold: 10 service crates in Cargo workspace
common crate: Money, NanoMoney, typed IDs (UUIDv7), domain enums, BillingEvent, BillingError (87 unit tests)- Metering:
MeterDefinition, MeterFilter, FilterOperator (7 operators), UsageEvent (CloudEvents-compatible), aggregation engine (COUNT/SUM/MAX/UNIQUE_COUNT/LATEST/WEIGHTED_SUM), InMemoryUsageEventStore
- Redis Accumulator: Real-time spend controls —
InMemoryAccumulator + Redis Lua script
- Subscriptions: CRUD with state machine enforcement,
InMemorySubscriptionRepository
- Invoicing:
Invoice + InvoiceLineItem + finalization state machine
- Ledger: TigerBeetle client wrapper —
InMemoryLedger (account create, transfer, balance query)
- API Gateway: Axum router scaffold with health check