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Billing/invoicing/payments backend skeleton. Bun + Hono + bun:sqlite (zero network deps at runtime; TS runs natively, no build step).

⚡ START COMMAND (sticky)

bun run dev          # http://localhost:3000, hot reload

Other commands:

bun run start        # no watch
bun run db:reset     # wipe data.db and reseed
bunx tsc --noEmit    # typecheck

Layout

src/index.ts    Hono app + routes
src/ingest.ts   CSV parser/normalizer + transactional insert (shared by seed and POST /ingest)
src/db.ts       opens data.db, applies schema, seeds from invoices.csv if empty (runs on import)
src/schema.sql  customers / invoices / payments (idempotent)
invoices.csv    seed data — deliberately messy; DO NOT MODIFY

DB is data.db at repo root (WAL, FK on). Boot always re-applies schema, so adding a table = edit schema.sql + restart.

Routes

curl localhost:3000/health
curl localhost:3000/customers
curl localhost:3000/customers/<cus_id>/invoices
curl localhost:3000/invoice/INV-1011                          # by invoice_number or surrogate inv_ id
curl -X POST localhost:3000/ingest --data-binary @invoices.csv
curl -X POST localhost:3000/payment/INV-1011 \
  -H 'content-type: application/json' \
  -d "{\"idempotency_key\":\"$(uuidgen)\",\"amount\":1500000,\"currency\":\"USD\"}"

POST /ingest: CSV as raw request body. Rows failing validation (negative values, empty currency, missing/unparseable amount or dates) are still stored, with status corrupted. Returns { status, ingested, errors, rows }. No idempotency — re-posting the same file appends duplicates.
GET /invoice/:id: invoice (with status) + its payments (with PSP-owned status). Resolves surrogate id or invoice_number (newest wins on duplicate numbers).
POST /payment/:invoice_id: zod-validated {idempotency_key: uuid, amount, currency}; only open/partially_paid invoices are payable (409 otherwise — includes corrupted), repeated key replays the original payment (200), else inserts a pending payment (201).

Money is stored as integer minor units (cents): CSV 150 → 15000.

Seed data

Seeded by ingesting invoices.csv (25 rows → 22 open + 3 corrupted, 21 customers):

INV-1006 (line 7): empty currency code
INV-1010: negative quantity and amount
INV-1020: missing amount

Duplicate invoice numbers (INV-1001 ×2, INV-1006 reused) are ingested as-is — not a validation rule on the canvas. Customers dedupe by email case-insensitively (Acme Corp/ACME CORPORATION/acme corp → one customer); rows without email get a customer keyed by name.

Extension cheatsheet (interview)

New route: add to src/index.ts, db.query(...).all()/get(), db.run(sql, [params])
Multi-write: db.transaction(() => { ... })()
Validation: z.object({...}).safeParse(await c.req.json())
New table: append CREATE TABLE IF NOT EXISTS to schema.sql, restart (or db:reset if changing existing tables)

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