# Infra Adapters

## Summary

All external systems are reached through adapters in `infra/`. Prefer an
existing internal library over writing a new adapter.

---

## Database (MongoDB)

- A single connection manager owns the client lifecycle.
  `setup_database(uri, db_name)` / `shutdown_database()`.
- A repository **factory** selects the repository flavour:

  ```python
  repo_factory(collection, document, engine=None,
               populate_rules=None, cache=None)
  ```

  - base repository — plain CRUD;
  - populating repository — resolves referenced documents (foreign keys);
  - cached repository — an LRU/TTL cache in front of reads.

- Referenced documents are described declaratively:

  ```python
  PopulateRule(field="owner", collection="users",
               nested_rules=[], max_depth=2, projection=None)
  ```

- Transactions use a session context manager provided by the library.

**Library:** the Mongo operations library (see registry). Do not write raw
Motor calls in the domain.

## HTTP response cache

A generic GET cache sits behind a decorator.

```python
@cache_response(ttl=60)
async def list_items(request): ...
```

- Keyed on path + query + user.
- No-op when no store is wired.
- `invalidate(*resources)` bumps a generation counter for write-triggered
  invalidation.

## Event / progress bus

A port with an in-memory default adapter (`publish`, `get_events`). Swap for a
durable broker in production (see Worker & Progress).

## External clients (ingestion)

External fetchers (files, mail, HTTP) are adapters that wrap ingestion
libraries. Construct them in the composition root and inject into
orchestrators.

**Libraries:** the ingestion library (formats) and the mail library (email).

## LLM clients

When a pipeline calls a model provider, route through a pool adaptor that
handles provider selection, retries, and client lifecycle:

```python
pool = setup_async_pool(provider=settings.llm_provider)
result = await pool.complete(model="...", messages=[...])
```

Providers are selected by `LLM_PROVIDER` and configured by environment.

## Key-value store

For report/snapshot storage, provide a pluggable store port with a Redis
adapter and an in-memory fallback.

## Rule

If a capability already exists as a library (DB, DI, ingestion, mail, auth,
docs), **use it**. Writing a private copy of a library is a defect.