# MercadoDeVida backend — modular monolith skeleton

TypeScript + Fastify modular monolith. Simple code, clear modules, small changes, no magic.

## Requirements

- Node.js >= 22
- npm

## Commands

```bash
npm install           # install dependencies
npm run build         # compile to dist/
npm start             # run compiled server (PORT, HOST env vars)
npm test              # vitest unit tests (no database needed)
npm run typecheck     # tsc --noEmit
npm run lint          # eslint + prettier check
npm run lint:boundaries  # module boundary check
```

## HTTP contract

- Every response carries an `x-request-id` header (propagated from a safe incoming
  `x-request-id`, or a fresh UUID). Every JSON log line for a request carries the same id.
- Errors always use one envelope:
  `{ "error": { "statusCode", "code", "message", "details?" }, "requestId" }`
  Codes: `NOT_FOUND`, `VALIDATION_ERROR`, `BAD_REQUEST`/Fastify 4xx codes, `INTERNAL_ERROR`.
  5xx messages are always generic; stack traces stay in server logs only.
- Input validation is explicit per route: `parseJson(schema, body)` (zod) in the handler.
- Log level via `LOG_LEVEL` env var (default `info`); logs are JSON only.

## Database (local dev)

```bash
cp .env.example .env  # once
npm run docker:up     # start PostgreSQL 16 + Redis 7
npm run db:up         # apply migrations
npm run db:status     # list applied migrations
npm run db:down       # revert last migration
npm run test:integration  # integration tests (need TEST_DATABASE_URL from .env)
npm run docker:down   # stop services (add -v to wipe volumes)
```

### Table naming convention

```text
<module>_<table>          e.g. catalog_products, inventory_stock, orders_orders
```

- Every table is prefixed with its owning module.
- A module never queries tables without its own prefix; data flows through module interfaces.
- Migrations are immutable once merged: fixes ship as new migrations.
- No schema change without migration.

## Layout

```text
src/
├── app/             # composition root (only place that wires modules)
├── infrastructure/  # http server entrypoint (later: db, redis, providers)
├── modules/         # business modules, one folder each
│   └── health/      # exemplar module: public API only via index.ts
└── shared/          # cross-cutting helpers (error envelope)
```

## Module rules

- A module exposes its public API only through its `index.ts`.
- Files inside a module may import: own subtree, `src/shared`, Node builtins, npm packages.
- Code outside modules (app/infrastructure) may import a module only via its `index.ts`.
- `npm run lint:boundaries` enforces these rules.